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IR mergers and IR QSOs with galactic winds. III. Mrk 231: composite outflow with multiple expanding bubbles and BALs (an exploding young QSO?)

A study of outflow (OF) and BAL systems in Mrk 231 (and in similar IR QSOs) is presented. This study is based mainly on 1D and 2D spectroscopy (obtained at La Palma/WHT, HST, IUE, ESO/NTT, KPNO, APO and CASLEO observatories) plus HST images. For Mrk 231 we report evidence that the extreme nuclear OF process has at least 3 main components, which are probably associated with: (i) the radio jet, at pc scale, and (ii(the extreme starburst at pc and kpc scale. This OF has generate 4 or more concentric expanding bubbles and the BAL systems. The variability of the short lived BAL-III system was studied. Finally, the IR colour diagram and the UV BAL system of IR+OF+FeII QSOs are analysed. We propose that the phase of young QSO is associated with:accretion of large amount of gas (by the SMBH)+extreme starburst+extreme composite OFs/BALs.


INTRODUCTION
An important issue in astrophysics and cosmology is the study of extreme star formation and galactic winds/out flows, in mergers and QSOs and their relation to the early phases of the formation of galaxies and AGNs (see for references Lipari et al. 2004a,b,c,d).

Luminous IR galaxies, mergers and AGNs
Luminous and ultraluminous IR galaxies (LIRGs: LIR ≥ 10 11 L⊙ and ULIRGs: LIR ≥ 10 12 L⊙, respectively) are dusty, strong IR emitters where frequently a strong enhancement of star formation is taking place (for references see Lípari et al. 2004a,b,c,d). Imaging surveys of LIRGs and ULIRGs show that a very high proportion ( ∼70-95%) are mergers or interacting systems (Joseph & Wright 1985;Rieke et al. 1985;Sanders et al. 1988a;Clements et al. 1996). In luminous IR galaxies there is a clear increase of the nuclear activity with the increase of the IR luminosity (Sanders et al. 1988a,b;Veilleux et al. 1999.
Strong evidence indicates that virtually all luminous IRAS galaxies are rich in interstellar gas, which is highly concentrated in their nuclei (Sanders et al. 1987(Sanders et al. , 1988a. Specifically, there are observational evidence and theoretical works suggesting that in IR mergers and IR QSOs tidal torque and loss of angular momentum drive large amount of interstellar gas into the central regions, leading to extreme starburst processes and probably fuelling a supermassive black hole (see for references Lipari et al. 2004a,d) An important, common phenomenon associated with the IR galaxies is the galactic wind: we found observational evidence for galactic wind (GW) features from starbursts and/or AGNs in luminous IR systems (Lípari et al. 2004a(Lípari et al. ,b,c,d, 2003(Lípari et al. , 2000a(Lípari et al. ,b, 1994.
There are clear evidence of galactic -and local-winds, shells, arcs and bubbles generated by multiple SN explosion and massive star winds in starbursts. Our understanding of the main phases of galactic winds associated with starbursts was improved significantly by the use of theoretical and numerical models (see Strickland & Stevens 2000;Suchkov et al. 1994;Mac Low, McCray & Norman 1989;Tomisaka & Ikeuchi 1988). In general, good agreement has been found between these models and the observations.
On the other hand, for galactic winds associated with AGN the situation is more complex, and very different models are proposed in order to explain the observed data. In these models the OF could be generated by jets driven thermal winds, accretion discs winds, X-ray heated torus winds, etc. (see Veilleux et al. 2002a;Cecil et al. 2002;Capetti 2002;Morganti et al. 2003). However, there are increase evidence that nuclear galactic jets are one of the main sources of out flows in QSOs/AGNs (Cecil et al. 2002;Veilleux et al. 2002a;Capetti 2002). In particular, there are clear detection and evidences of the interaction of jets with various phases of the ISM, including the narrow line region (NLR).

IR Mergers with galactic winds
IR mergers often show strong starbursts with powerful out flow (OF) and galactic winds (GW; Lípari et al. 2003Lípari et al. , 2004a. Comparing our OF data base of IR mergers/QSOs (Lipari et al. 2004a, their Table 1) with two samples of nearby IR mergers we found in both samples a high proportion of mergers with galactic winds: ∼75%. These results suggest (or confirm) that: (i) GWs are "frequent events" in IR mergers, and (ii) extreme starbursts + GW and extreme IR emission could be simultaneous processes, induced by merger events. This last conclusion is also supported by a clear trend found in the plot of OF velocity vs. log LIR (see their Fig. 13), in the sense that extreme OF velocities are detected only in extreme IR emitters (ULIRGs). We note that the reported trend is observed mainly for IR mergers (Lipari et al. 2004a). An explanation for this observed trend is that high values of OF velocity and LIR are both associated mainly with the same process: "starburst + QSO" events, probably induced by mergers (already suggested by Lípari et al. 2003; see also Genzel et al. 1998;Veilleux et al. 1999;Sanders et al. 1988a;Rieke et al. 1985).
The low velocity OF process (LVOF, VLVOF < 700 km s −1 ; see Lípari et al. 2004a,b, 2003, 2000a,b) observed in NGC 3256, 2623 spectroscopy-is consistent with those found previously in Arp 220, Mrk 266, NGC 1614, NGC 3690, and other IR mergers with massive starbursts. In addition, we found an interesting fact: starbursts and LINERs are the main sources of ionization in "low velocity OF" IR mergers (Lípari et al. 2000b(Lípari et al. , 2004a.

IR QSOs with galactic winds
The discovery and study of IR QSOs (see for references Lípari et al. 2004dLípari et al. , 2003Zheng et al. 2002) raises several interesting questions, in particular whether they are a special class of QSOs. We found, or confirm, that a high percentage of IR QSOs show extreme out flows with giant galactic arcs, merger features, BAL systems, and extreme Fe ii emission, and are radio quiet (Lípari et al. 2004b(Lípari et al. , 2004aLípari, Terlevich & Macchetto 1993;Lípari, Macchetto & Golombek 1991a). We suggested that these objects could be young IR−active galaxies at the end phase of a strong starburst: i.e., composite and transition QSOs (Lípari 1994).
Recently, using our data base of GW/OF in IR mergers/QSOs we found that in all the IR QSO candidates the Hβ broad line component is blushifted in relation to the narrow one, which is clearly consistent with the result obtained from the study of strong Fe ii + BAL emitters, by Boroson & Meyer (1992). They proposed that blueshifted offset/asymmetry detected in the Hα broad components-of IR QSOs with strong Fe ii + BAL systems-is probably due to the emission of the out flowing material, associated with the BAL process. Furthermore, our measurements are also consistent with the results of the study of multiple emission line components, in some starburst nucleus of galaxies (Taniguchi 1987). Thus, a possible explanation for "at least part" of these blushifted broad line systems in IR QSOs is the high speed OF/GW generated in a burst of SN event near the nuclear region (Heckman et al. 1990;Terlevich et al. 1992;Lipari et al. 2003Lipari et al. , 1994Lipari et al. , 2003Lipari et al. , 2004aTaniguchi et al. 1994;Scoville & Norman 1996;Lawrence et al. 1997;Collin & Joly 2000; and others).

BALs in IR mergers/QSOs
Some of the results obtained for nearby BAL QSOs, such as strong IR and Fe ii emission, strong blue asymmetry/OF in Hα, radio quietness, and very weak [O iii]λ5007 emission Boroson & Meyers 1992;Lípari et al. 1993Lípari et al. , 1994Lípari et al. , 2003Lipari 1994;Turnshek et al. 1997), can be explained in the framework of the starburst+AGN scenario. In our study of Mrk 231 and IRAS 0759+6559 (the nearest extreme IR + GW/OF + Fe ii + BAL systems), we detected typical characteristics of young-starburst QSOs. In our evolutive model for young and composite IR QSOs (see for ref- erences Lípari 1994) suggested that BAL systems could be linked to violent supermassive starburst+AGN which can lead to a large-scale expanding shells, often obscured by dust. Several articles suggested that this evolutive model shows a good agreement with the observations (see Canalizo & Stockton 1997;Lawrence et al. 1997;Canalizo et al. 1998).

Possible links between IR mergers and IR QSOs
The luminosities and space densities of ULIRGs in the local Universe are similar to those of quasistellar objects (QSOs; Soifer, Houck & Neugebauer 1987). In addition, at the highest IR luminosities, the presence of AGNs (and mergers) in LIRGs becomes important. Thus LIRGs probably represent an important stage in the formation of QSOs and elliptical galaxies. These results strongly suggest that it is important to perform detailed studies of possible links among mergers, ULIRGs, QSOs and elliptical galaxies (Toomre & Toomre 1972;Larson 1974;Toomre 1977;Schweizer 1982;Joseph & Wright 1985;Sanders et al. 1988a,b;Lípari et al. 1993Lípari et al. , 1994Lípari et al. , 2003Sanders & Mirabel 1996;Colina et al. 2001).
Furthermore, the important detection of a correlation between the mass of galactic bulges and the mass of supermasive black hole is a confirmation that the formation and evolution of galaxies (bulges/ellipticals, mergers) and supermassive black hole (AGNs and QSOs) are physically related to one another (Magorrian et al. 1998;Ferrarese & Merrit 2000;Gebhardt et al. 2000;Kormendy 2000;Merrit & Ferrarese 2001;Kormendy & Richstone 1995).
Recently, several studies have confirmed the composite nuclear nature and the presence of merger and galactic wind features in several IR QSOs (Canalizo & Stockton 2001). In particular, Lipari et al. (2003Lipari et al. ( , 2004a found kinematical and morphological evidence of galactic winds in nearby "IR + Fe ii + BAL QSOs". Thus, the study nearby "IR + Fe ii + BAL composite/transition QSOs" is one observational way to analyse the possible relation between IR mergers and IR QSOs. We have started detailed morphological, spectroscopic and kinematics studies of this kind of objects (since 1987: see Lípari et al. 1991aLípari et al. , 1993Lípari et al. , 1994Lípari et al. , 2003Lípari et al. , 2004dLipari 1994).

IR mergers/QSOs with galactic winds (the main programme)
A current key issue in astrophysics is to explore the evolution of the star formation process, especially at high redshift, when the galaxies/QSOs formed, and where it is expected that the star formation rate is very high. With these aims in mind we began a project to study nearby star forming + GW galaxies and distant Lyα emitters (see Lipari et al. 2004a,b,c,d). The first step in this project is to understand the star formation process in nearby galaxies because we can obtain more detailed and unambiguous information. Thus, our groups started a study of nearby IR mergers/QSOs, which are an excellent laboratory-at low redshift-for the analysis of extreme star formation and GW processes (Lipari et al. 2004a(Lipari et al. , 2003(Lipari et al. , 2000a(Lipari et al. ,b, 1994. This study is based mainly on integral field spectroscopy, obtained at the European Northern Observatory (ENO, La Palma-Spain), the European Southern Observatory (ESO, Chile), the Complejo Astronomico El Leoncito (CASLEO, Argentina), and Bosque Alegre (BALEGRE, Argentina) observatories, with the 4.2 m, 3.6 m, 2.15 m and 1.5 m telescopes, respectively. The characteristics and goals of the programme have been described in detail by Lípari et al. (2004a). In particular, the main goals of this programme (at low redshift) is to analyse in detail the properties of the different stages of extreme starbursts, galactic winds, mergers, QSOs, and elliptical galaxies (and their interrelation).
In the present paper we present new results from our programme of study of "nearby" IR mergers/QSOs with galactic winds (EVOF): for Mrk 231.

BALs in IR + GW + Fe ii mergers/QSOs
A study and search of UV (and optical) BAL systems in extreme IR + GW/OF + Fe ii QSOs have been started since 1993 (see Lipari 1994;Zheng et al. in preparation), using mainly IUE and HST UV-spectra, plus ESO NTT, KPNO, APO and CASLEO optical data. In general, the role of BALs in IR+GW/OF+Feii QSOs/mergers must be carefully considered, since: (i) Low et al. (1989) and Boroson & Meyers (1992) found that IR selected QSOs show a 27% low-ionization BAL QSO fraction compared with 1.4% for the optically selected high-redshift QSOs sample (Weymann et al. 1991); (ii) extreme IR galaxies (ULIRGs) are mainly mergers (Section 1); (iii) very recently Maiolino et al. (2003) reported also a high fraction of BAL QSOs at very high redshift (z ∼6). The high percent of occurrence of broad absorption in extreme IR + GW/OF + Feii QSOs/mergers may be signals a fundamental relation (rather than merely a coincidence), and deserves detailed studies. Lípari et al. (1993Lípari et al. ( , 1994Lípari et al. ( , 2003Lípari et al. ( , 2004a; Scoville & Norman (1996);Egami et al. (1996); Lawrence et al. (1997) and others proposed that the extreme IR + GW/OF + Fe ii + BAL phenomena are related -at least in part-to the end phase of an "extreme starburst+AGN" and the associated "powerful bubble/galactic-wind". At the final stage of a strong starburst, i.e., type II SN phase ([8-60] ×10 6 yr from the initial burst; Terlevich et al. 1992;Norman & Ikeuchi 1989;Suchkov et al. 1994) giant galactic arcs and extreme Fe ii+BAL systems can appear.
Specifically, the search of UV broad absorption line was focused mainly in the IR objects of our data base of IR + GW/OF + Feii QSOs/mergers (see Table 4), and studying the redshifted lines: Lyα, Si IV, C IV, and Mg II. Lipari (1994) reported a first study of the UV BAL systems in IRAS 0759+651, with projected ejection velocity of about 10000 kms −1 . Previously, it was also reported UV BAL systems in Mrk 231 (IRAS 12540+5708), IRAS 17002+5153, and IRAS 14026+4341.
It is important to note that in Table 4 several examples clearly show the consistency of the OF data presented. In particular, for IRAS F05024-1941, our study of EVOF in the ULIRG 1 Jy Sample (using "emission" lines), we found that this object is a candidate to EVOF, with a velocity close to 1500 km s −1 (Lipari et al. 2000b). From a study of narrow "absorption" lines Rupke et al. (2002) obtained for this object an OF value of 1600 km s −1 . We have verified that for Mrk 231 the results using the offset method (by Zheng et al. 2002) gave the same value of OF: -1000 km s −1 , to that already obtained from the detection of two emission line systems in [O ii]λ3727 (by Lipari et al. 1994). A similar agreement between the values of the OF obtained from multiple emission lines (Lipari et al. 2000b) and the offset method (Zheng et al. 2002) was found, for the cases of IRAS 11119+3257 and IRAS 15462-0450 (see Table 4).
In this paper we report new results from this programme. In particular, the detection of a new IR + GW/OF + Fe ii QSO with BAL system. Since Markarian 231 was discovered (by its strong ultraviolet continuum; Markarian 1979) it has been extensively studied and has been recognised as a remarkable galaxy: it is the most luminous galaxy in the local universe (z < 0.1), the nuclear spectrum shows extreme broad emission lines and strong BAL systems, the morphology is associated with a merger, etc (Arakelian et al. 1991;Adams 1972;Adams & Weedman 1972;Rieke & Low 1972, 1975Boksemberg et al. 1977;and others). In particular, it is important to remark that Sanders et al. (1987); Bryant & Scoville (1996) and Downes & Solomon (1998) found a very high concentration of CO molecular gas in the nuclear region (3 × 10 9 M⊙, within a diameter of 1. ′′ 0, 814 pc). Before the IRAS was lunched, Mrk 231 was known to have an extreme IR luminosity with MK = -24.7 (Rieke & Low 1972, 1975Cutri, Rieke & Lebofsky 1984). Even after IRAS expand the known population of ULIRG, Mrk 231 remain one of the most luminous object in the local universe, with L IR[8−1000µm] = 3.56 × 10 12 L⊙, and LIR/LB = 32. Consequently, the bolometric luminosity (dominated by the continuum IR emission) places the nucleus of this IR merger among the QSOs. Weedman (1973) already proposed that this extreme IR luminosity is associated with ultraviolet (UV) emission re-radiate thermally -in the IR-by dust.
Mrk 231 also shows very interesting spectral characteristics, dominated in the optical by extremely strong Fe ii and broad Balmer emission lines at Zem = 0.042 (Arakelian et al. 1971;Adam & Weedman 1972;Boksemberg et al. 1977).
In addition, it shows remarkable absorption line systems: a clear stellar absorption at Z abs = 0.042 plus at least three strong broad absorption line (BAL) systems. These strong BAL systems show the following velocity of ejection: Veject of BAL I, II and III ∼4700, ∼6000, and ∼8000 km s −1 . The last BAL-III system sudden appear sometime between 1984 December and 1988 May  The extreme IR luminosity of Mrk 231 is associated with two main sources of energy: (i) an AGN detected clearly at radio and X-ray wavelengths (see for references Condon et al. 1991;Ulvestad et al. 1999;Turner 1999;Gallagher et al. 2002), and (ii) an extreme nuclear + circumnuclear starburst observed almost at all wavelengths (see Downes & Solomon 1998;Taylor et al. 1999;Gallagher et al. 2002). In addition, Lipari et al. (1994) reported kinematics, morphological and physical evidence of a powerful nuclear outflow process: i.e. a "galactic superwind with a broken shell, in the blowout phase". Even Lipari et al. (1994Lipari et al. ( , 1993 suggested that Mrk 231 is an evolving "young and composite IR QSO". Thus, Mrk 231 is the nearest extreme IR + GW/OF + BAL + Fe ii QSOs. In this paper, new results of the OF process in Mrk 231 are reported. Throughout the paper, a Hubble constant of H0 = 75 km s −1 Mpc −1 will be assumed. For Mrk 231 we adopted the distance of ∼168 Mpc (cz = 12465 ±10 km s −1 ), and thus, the angular scale is 1 ′′ ≈814 pc.  (Arribas et al. 1998) and the WYFFOS spectrograph (Bingham et al. 1994). The seeing was approximately 1. ′′ 0.

La Palma/WHT + INTEGRAL 2D spectroscopy
INTEGRAL links the f/11 Naysmith focus of WHT with the slit of WYFFOS via three optical fibre bundles. A detailed technical description of INTEGRAL is provide by Arribas et al. (1998); here we only recall its main characteristics. The three bundles have different spatial configuration on the focal plane and can be interchanged depending the scientific programme or the seeing conditions. At the focal plane the fibres of each bundles are arranged in two groups, one forming a rectangle and the other an outer ring (for collecting background light, in the case of small-sized objects). The data analysed in this paper were obtained with the standard bundle 2: which consistent of 219 fibres, each of 0. ′′ 9 in diameter in the sky. The central rectangle is formed by 189 fibres, covering a field of view of 16. ′′ 4 × 12. ′′ 3; and the other 30 fibres form a ring 90 ′′ in diameter.
The WYFOS spectrograph was equipped with a 1200 lines mm −1 grating, covering the λλ6200-7600Årange. A Tex CCD array of 1124 × 1124 pixels of 24 µm size was used, giving a linear dispersion of about ∼1.45Å pixel −1 (∼2.5Å effective resolution, ∼ 70 km s −1 ). With this configuration and pointing to the central region of Mrk 231, we took three exposure of 1800 s.

HST ACS, WFPC2 and NICMOS broad band images
Near-UV HST Advanced Camera for Surveys (ACS) archival images of Mrk 231 were analysed, obtained with the High Resolution Channel (HRC). They include images with the filter F330W (3354Å, ∆λ 588Å). The scale is 0. ′′ 027 pixel −1 .
For details of the HST observations see also Table 1.

HST UV-FOS and UV-STIS 1D Spectroscopy
HST FOS aperture spectroscopy of the main optical nucleus of Mrk 231 was obtained, from the HST archive (at ESO Garching). The spectra were taken with the G190L (λλ1150-2300), G190H (λλ1575-2320) and G270H (λλ2225-3290) gratings and the blue detector. The G190H and G270H observations were made with the effective aperture of 4. ′′ 3 × 1. ′′ 4; and these spectra have a resolution of ∼3 and 4Å, FWHM respectively. The G160L observations were made with the aperture of 1. ′′ 0, and the spectra have a resolution of ∼8, FWHM. In addition, HST FOS spectra of extreme IR + Fe ii QSOs with GW were analysed. These data were used in our study/search of UV-BAL systems (for details see Table 1).
HST STIS long slit spectra of IR + GW/OF + Fe ii QSOs were obtained (mainly from the HST archive). The spectra were taken with the G750M grating, with the slit 0. ′′ 1 × 52. ′′ 0, giving a resolution of 50 km s −1 . The STIS CCD has a scale of 0. ′′ 05 pixel −1 .

La Palma/NOT optical broad band images
Optical V broad band optical image of Mrk 231 was obtained during a photometric night in 1991 May at the 2.5 m Nordic Optical Telescope (NOT) at Observatorio Roque de los Muchachos on the Canary island of La Palma. A TEX CCD chip with scale 0. ′′ 197 per pixel was used. The observations were carried out in excellent seeing conditions, with a values of 0. ′′ 7 (FWHM).

KPNO long-slit 1D spectroscopy
Optical long slit spectra of Mrk 231 and IR + GW/OF + Fe ii QSOs were obtained on the KPNO 2.15 m telescope with the Gold Cam Spectrograph, by using two grating of 300 grooves mm −1 (7Å ∼300 km s −1 resolution) covering the wavelength ranges 3350-5200 and 5100-7100Å. The observations were taken during one photometric night in February 1991 (Table 1). The spectra were obtained with a slit width of 1.5 arcsec. The seeing was in the range 1.0-1.5 arcsec (FWHM).
The data of the IRAS 1 Jy ULIRGs sample were obtained with the Gold Cam Spectrograph on the KPNO 2.15 m telescope by using a grating of 300 grooves mm −1 (8Å resolution); and covering the wavelength range 4500-9000Å.

IUE UV 1D spectroscopy
UV International Ultraviolet Explorer (IUE) spectra were obtained for our programme of search of UV-BAL systems in extreme IR + GW/OF + Fe ii QSOs (Table 1). In addition, data from the IUE archival -of this type of objectswere analysed. The IUE LWP and SWP spectra cover the wavelength ranges 1150-1980 and 1900-3290Å,; with a resolution of ∼8Å (∼300 km s −1 ).

ESO NTT and 3.6 m telescope spectra
The ESO Faint Object Spectrograph and Camera II (EFOSC II) on the 3.5 m new technology telescope (NTT) at La Silla was used, to obtain long slit spectra of IR + GW/OF + Fe ii QSOs. These long-slit observations were taken during 1 photometric night in July 1993 (see Table  1). The spectra cover the wavelength ranges ∼3560-5200Å, with a resolution of ∼7Å (∼300 km s −1 ) The ESO Faint Object Spectrograph and Camera (EFOSC) on the 3.6 m telescope at La Silla was used to obtain long-slit spectra and high resolution images. Mediumresolution spectra were obtained with the B150, O150, and R150 grisms, which provide a resolution of ∼ 7Å in the wavelength range 3600-9800Å (during 3 photometric nights in 1995 January and 1991 July; see Table 1).

Apache Point Observatory (APO) 1D spectroscopy
The APO spectra of IR GW/OF + Fe ii QSOs were taken with the 3.5 m telescope. Optical long-slit observations were obtained during 1 photometric night in September 2004 (see Table 1). The medium resolution spectra give an effective resolution of ∼6Å (∼290 km s −1 ), covering the wavelength ranges λλ3500-5600 and 5300-10000Å. The seeing was ∼1. ′′ 5 (FWHM).

CASLEO 1D spectroscopy
Spectrophotometric observations of IR + GW/OF + Fe ii QSOs were taken at CASLEO (San Juan, Argentina) with the 2.15 m Ritchey-Chrétien telescope. Optical long-slit and aperture spectroscopy observations were obtained during 3 photometric nights in June 1989, July 1993, March 1997 (see Table 1). Long-slit spectroscopic observations with medium resolution were obtained with the University of Columbia spectrograph (UCS; e.g. Lípari et al. 1997). The medium resolution spectra were made using a 600 line mm −1 grating, a slit width of 2. ′′ 5, which gives an effective resolution of ∼6Å (∼290 km s −1 ) and a dispersion of 120Å mm −1 , covering the wavelength range λλ4000-7500Å. Aperture spectroscopic data were obtained with the 'Z-machine' (e.g. Lípari et al. 1991a,b). These aperture spectra were made using a 600 line mm −1 grating, giving a dispersion of 130Å mm −1 and an effective resolution of ∼8Å (∼300 km s −1 ) covering the wavelength range λλ4700-7200. The seeing was in the range 1. ′′ 5-2. ′′ 5 (FWHM).

Reduction
The IRAF ⋆ software package was used to reduce and analyse the data. The reduction of the 2D spectroscopic observations consist of two main steps: (1) reduction of the spectra (for each 219 fibres), and (2) generation of 2D maps by interpolated the selected parameter (e.g., emission-line intensity, continuum intensity, radial velocity, etc) from the grid values defined by the fibre bundle. The step (1) was basically done in the same way as for long-slit spectroscopy, including bias subtraction, aperture definition and trace, straylight subtraction, the extraction of the spectra, wavelength calibration, throughput correction and cosmic-ray rejection. We obtained typical wavelength calibration errors of 0.1Å, which give velocity uncertainties of 5 km s−1. For step (2) we used the software package Integral † , with 2D interpolation routines. In particular we transformed ASCII files with the positions of the fibres and the corresponding spectral features, into regularly spaced standard FITS files. Maps generated in this way are presented in the next sections. The IRAF and STSDAS ‡ software packages were used to analyse the HST , ESO, IUE, ESO, KPNO, NOT, APO, CASLEO imaging and spectrophotometric data.
The HST data were reduced at the Space Telescope Science Institute (STScI), using the standard process. All the bands were calibrated according to the procedures detailed in Lipari et al. (2004a). Specifically, photometric calibration of the HST data was performed using published photometric solution (Lipari et al. 2004a).
For the study of the kinematics data we used the software ADHOC § ⋆ IRAF is the imaging analysis software facility developed by NOAO † Integral is the imaging and spectroscopic analysis software facility developed by the Instituto de Astrofisica de Canarias (IAC) ‡ STSDAS is the reduction and analysis software facility devel- This section focuses on presenting (for Mrk 231): (i) high resolution HST near-UV, optical and near-IR images of the main body; (ii) 2D spectroscopy mainly for the central regions; (iii) 1D spectroscopy for the nuclear region; (iv) a study of variability of the Na ID BAL-III system (based in 1D spectroscopy). In particular, we study the extreme nuclear OF with multiple expanding concentric shells, giant shocks and BAL systems. In addition, new observations of UV-BAL systems in IR+GW/OF+Fe ii QSOs are analysed.

Near-UV, optical and near-IR HST and NOT
images: multiple concentric nuclear bubbles (and knots) Here, a multiwavelength morphological study (using mainly high resolution HST near-UV, optical and near-IR broad band images) of the nuclear and circumnuclear structures of Mrk 231 is presented. The NOT V image ( Fig. 1) shows almost the whole merger. This galaxy consist of a nearly elliptical main body (R ∼ 10 kpc) with a compact nucleus, plus two faint tidal tails (see also Lipari et al. 1994;Hamilton & Keel 1987;Neff & Ulvestad 1988). These are typical features observed in advanced mergers.
It is important to note, that previously, in the circumnuclear region of Mrk 231 Lípari et al. (1994) found clear evidence of a powerful nuclear galactic-wind and they proposed that this OF process (in part associated with a starburst) has generated the circumnuclear blue arc/shell (at r ∼ 3 kpc, and to the south of the nucleus). However, Armus et al. (1994) suggested that this arc is associated with an obscured second nucleus (they also suggested that in this blue region or "shell" there is no evidence of star-formation process). HST-WFPC2 observations of Mrk 231 confirmed that this blue arc is a "dense shell of star-forming knots" (see Surace et al. 1998;Lipari et al. 2003). In the next sections we will expand these previous studies. We note that Figs. 3a,b,c,d were obtained from the subtraction of a smooth image (for each filter) of the main body of Mrk 231, in order to study the morphological residuals.

The multiple concentric nuclear bubbles/shells
These figures show intereting structures, in particular: (i) Bubble or Shell-S1: This is the more external and well defined shell detected in Mrk 231, with a radius RS1 = 3. ′′ 5 = 2.9 kpc. Lipari et al. (1994) already noted that this shell shows a clear elongation to the south (of the nucleus). At the border of this elongation there is a blue arc with several knots. They associated this arc with typical structures generated in the blowout phase of a nuclear galactic wind (with giant shocks). These shocks probably generated a new extranuclear star formation process, with knotty structure. Fig. 2 shows interesting details of this bubble + arc in the HST ACS, WFPC2 and NICMOS images. In particular, the HST WFPC2/B image depicts clearly the complete shell S1. However the HST ACS/U image shows remarkable details of the blue compact knots located at the border of the southern arc.
(ii) Bubble-S2: The next internal bubble, at RS2 = 1. ′′ 8 = 1.5 kpc, shows also a well defined circular shape. However, this more internal bubble is clearly obscured in the southeast region by reddening, associated with the presence of dust. Again, the HST WFPC2/B image depicts more clearly the partial shell S2. It is important to remark that this shell shows a very interesting knot-2 in the south-west direction (see Table 2 and the next sections for details about the properties of this knot).
(iii) Shell-S3: The next bubble, with a radius RS3 = 1. ′′ 2 = 1.0 kpc, depicts also a circular shape, and their emission is strong mainly in the south area. This structure is well defined in the HST ACS/U image, which shows also a knotty structure. This shell depicts a bright knot-3, to the south-east.
(iv) Shell-S4: This shell is clearly observed mainly in the HST ACS/U image ( Fig. 2a; we note that this ACS image has the best spatial resolution) and also in the ACS/U, WFPC2/B residual images (Figs. 3a,b). The radius of this shell S4 is RS4 = 0. ′′ 7 = 0.6 kpc.
(v) Possible shell-S5: This possible shell is only observed in the HST optical (I-B) colour image (Fig. 4) and very close to the nucleus, with a radius RS5 = 0. ′′ 3 = 0.2 kpc.
(vi) Close to the nucleus, the HST images show radial filaments. These structures are more clear in the near-IR image since at these wavelengths the dust absorption is significantly smaller. In particular, it was found that these filaments are more larger and clear in the direction north-south (PA ∼00 • ) and at the position angle of the radio jet (PA ∼65 • ; see sections 4.2 and 4.3 for details about this jet). We note that these PAs are coincident with the directions of the two main OF processes in Mrk 231 (see the next sections). In our programme of study of galactic winds in IR mergers/QSOs, similar filaments were detected associated with the OF processes of NGC 3256, NGC 2623 and NGC 5514.
This type of circular and concentric "bubbles or shells" could be associated mainly with symmetric explosive events. In sections 3.2 and 4.3 the kinematics, age, energy and possible origin of these structures will be discussed. Table 2 presents the location and properties of the main knots, in the nuclear and circumnuclear areas of Mrk 231. In addition, the positions of these knots are labeled in Fig.  3b. Surace et al. (1998) already studied in detail these knots using HST photometry, in the B and I bands. In this paper, we will study mainly their properties in relation to the process of OFs and their location in the shells.

The circumnuclear knots
From the data of Table 2, it is clear that in the southern part of the shell S1, the knots 5, 6, 11 and 12 show blue colours, probably associated with new star formation events. In particular, these knots emit a strong UV continuum, due to the presence of a large number of massive O and B stars. These massive stars are usually responsible for the rupture phase of the galactic bubble and also are the progenitors of core-collapse SNe. In the supergiant bubble of NGC 5514 we also detected the presence of several knots with massive WR stars (inside the areas of rupture of the external shell). The radius of this bubble in NGC 5514 -just detected in the rupture phase-is also of ∼3 kpc, i.e. the same value of the shell S1 in Mrk 231. We already noted that the results of hydrodynamical models for galactic winds (associated mainly with extreme starbursts) suggest that 3 kpc is the typical value of radius for the beginning of the blowout phase (after ∼8 Myr, from the initial starburst; Suchkov et al. 1994).
The remaining knots show different colours (see Table  2). Some of the knots depict red colours, which could be explained -in part-by the presence of dust in star formation areas. In particular, the HST NICMOS image shows that the knot 14 is bright at the H-band, suggesting that the red colour in this knot (located in the southern arc of the shell S1) is due mainly to reddening by dust. However, for another two knots with very red colours, the 2D spectroscopy suggest another origin for the red colours. For the knot 2 (located in the shell S2) the spectrum shows properties typical of bow shocks, similar to those found in radio jets (see for details the next section). In addition, the knot 29 (positioned at the north-west area of the shell S1) also shows very red colour, and it is located in another OF region. Where the [S ii]/Hα and [N ii]/Hα maps depict extended radial filament, probably emerging from the bubble (see section 3.4). For this area also Krabbe et al. (1997) reported OF ejection (of ∼1400 km s −1 in Paα; from a study of 2D near-IR spectroscopy).
In the next section, the kinematics and physical properties of the multiple concentric shells and the circumnuclear knots will be analysed (using mainly WHT 2D spectroscopy). First, the OF at small scale will be analysed, in the region close to the nucleus (R < 1-2 kpc). In particular, it is important to remark the following main results: (i) In the fibre 101 (adjacent to the fibre of the nucleus) the 2D spectrum shows the presence of an strong OF emission bump in the blend Hα+[N ii], with the peak corresponding to the same velocity of the main BAL-I system (VEjectionBAL−I ∼ -4700 km s −1 ).
This bump was detected in the area covered by this fibre, at 0. ′′ 6-1. ′′ 5 (490-1220 pc), to the south-west of the nucleus core at PA ∼60 • , showing a strong and broad peak (see Fig.  6b).
It is important to note that the direction/PA of fibre 101 (from the main nucleus) is the same that the PA of the small scale radio jet (PAjet ∼60-70 • ).
Therefore, these results are consistent with the interesting fact that the blue OF Hα bump plus the BAL-I system could be related with OF clouds associated with the small scale jet. A discussion of this point will be presented in section 4.3. Now, the OF kinematics of the multiple shells will be analysed, for the central region (R < 6 kpc). In the 3 external bubbles S1, S2 and S3 the 2D WHT spectra show multiple emission line components (see Fig. 6), specially in the bright knots. Where the following OF velocities values were measured: (i) For the shell S1, These values are consistent with expanding bubbles, and their properties and origin will be discussed in section 4.3

Velocity field of the ionized gas, in the nuclear and central regions (2D Spectra)
In order to study the kinematics of the ionized gas, in the central region of Mrk 231, we measured the velocities from the centroids of the stronger emission lines Hα, [N ii]λ6584 and [S ii]λλ6717-6731, fitting gaussians (with the software SPLOT and SPECFIT; for details see section 2). In Mrk 231, first we study the main emission line component; which is strong in all the central region. In the shells the presence of multiple OF components required a detailed study. Fig. 7 shows -for the ionized gas-the Hα velocity field for the central region ∼16 ′′ ×12 ′′ ∼13 kpc×10 kpc, with a spatial resolution/sampling of 0. ′′ 9. This map was constructed using the techniques described in section 2, and for the main component of the Hα emission lines. The errors vary from approximately ±10 km s −1 in the nuclear and central regions (where the emission lines are strong), to ∼20 km s −1 for the weakest lines away from the nuclear areas. Using the 2D Hα velocity field (VF) we have obtained a mean value of the systemic velocity VSyst = 12645±10 km s −1 , this value was defined as the zero of the VF.
The Hα isovelocity colour map (Fig. 7) shows interesting structures: (i) Coincident with almost the border of the more extended bubble or shell (S1), parts of a ring with blueshifted values of velocities and circular shape was detected. We note, that this structure reach the south border of the field, and probably part of this ring (to the south) is located outside of our INTEGRAL field. The radius of this structure/ring is r ∼ 5. ′′ 0 ∼ 4 kpc.
(ii) Close to the centre of this ring (which it is located near to the nucleus) there is a small and circular lobe with blueshifted velocities.
In addition, inside of the ring 4 symmetric redshifted lobes were also detected.
(iii) To the north-west, part of an elongated blueshifted lobe was found. In this structure we have measured high values of velocities of ∆ V ∼-200 km s −1 .
These results are clearly consistent with those found in section 3.2. In particular, the detection of a blueshifted ring coincident with the position of the shell S1 confirm the OF/expansion of this shell ( (i) For the area where we measured the narrow emission line components, i.e. in almost all the circumnuclear region (1. ′′ 8 < r < 5 ′′ ; i.e. including the 2 more external shells/bubbles S1 and S2), the [N ii]/Hα emission line ratios show high values (> 0.8). This result, obtained from the 2D map (Fig. 8a) was verified using the individual spectrum of each fibre (Fig. 8c).
(iii) Specially, to the north-west the [S ii] λ6717 + 31/Hα and [N ii]/Hα maps show filaments, which are probably associated with ejection from the bubble. Lipari et al. (2004d) already discussed in detail the fact that the [S ii]/Hα map is one of the best tracer of filaments associated with OF and shock processes.
Thus, in almost all the circumnuclear and central regions of Mrk 231 (including the shells) these INTEGRAL emission line ratio maps show high values (> 0.8), which are consistent with an ionization process produced mainly by shock-heating in a in the outflowing gas of the expanding shells (Lipari et al. 2004a,d;Dopita & Sutherland 1995;Heckman 1980Heckman , 1996Heckman et al. 1987Heckman et al. , 1990Dopita 1994). Furthermore, these ratios (for the main emission line components) are located in the area of fast shock velocities of ∼400-500 km s −1 in the upper part of the [N ii] λ6583/Hα vs. [S ii] λ6717 + 31/Hα diagram (published by Dopita & Sutherland 1995, their Fig. 3a).
Similar results were obtained in the 2D studies of the bubble NGC 3079 (Veilleux et al. 1994) and the OF nebula and bubble of NGC 2623 and NGC 5514 (Lípari et al. 2004a,d). They found that the ratios [N ii]λ6583/Hα and [S ii]λ 6717 + 31/Hα are > 1, in almost all the bubbles and the OF regions. They associated these results to the presence of large scale OF + shocks.
3.5 The optical BAL systems and the nuclear spectrum of Mrk 231 (1D-spectra)

Optical BAL systems: the variability of the Na ID BAL III systems
It is important to study in detail the optical absorption and emission features of this IR QSOs, in order to detect similarities and differences between this object and similar extreme IR + GW/OF + Fe ii emitters. The optical and UV spectrum of Mrk 231 (see Fig. 9a) presents the features that are typical of extremely strong optical Fe ii emitters with BALs: i.e., strong Na I Dλλ5889-5895 absorption, strong unresolved blends of optical Fe ii lines, and very weak highexcitation forbidden emission lines. It is important to remark the strong fall in the continuum flux at the UV wavelengths (this is also a typical feature of dusty luminous infrared galaxies; see section 3.6). Boksemberg et al. (1977) detected two nonstellar absorption lines systems (I and II) with velocities of 6250 and 8000 km s −1 , respectively. This correspond to ejection velocities of -6650 and -4950 km s −1 , with respect to the systemic velocity of 12900 km s −1 . Boroson et al. (1991) detected a new absorption system III in the Na ID Ca H,K and He I, in their optical spectra of 1988. This system was not present in the spectra of Boksemberg et al. (1977), taken in 1975. With an observed radial velocity of 4660 km s −1 , this new system has the highest ejection velocity -8240 km s −1 . The origin of these absorption-line systems have been discussed by Boroson et al. (1991) It is interesting to recall about the detection of another absorption system (IV), which correspond to the systemic velocity and has the narrower absorption width. This system was already associated by Boksemberg et al. (1977) with hot stars in the nucleus of Mrk 231. Fig. 9b shows the BAL systems at the line Na ID. The corresponding width of these absorptions systems are: FWHM of BAL system I, II and III = 700, 130, 80 km s −1 , respectively. These are in general low values for BAL systems. Thus, these values are more consistent with those of mini-BALs or associated absorption lines (AAL; de Kool et al. 2001Kool et al. , 2002. Now, we will expand the previous study of variability of the Na ID BAL III system (covering almost all the period in which this system appeared). In order to study the behaviour of the variability of this absorption system, the measured values of the equivalent width ratio of BAL III/(BAL I + II) were included in Table 3. These data were obtained from our observation and also derived from published spectra (together with data previously published by Kollatschny et al. 1992;. We note that the previous study of variability cover the period 1980-1992 (with only few point after the maximum). The observation of Table 3 cover the period between ∼1980-2000. Figs. 10a,b show the shape of the BAL-III light curve (LC), which is clearly asymmetric with: a steep increase, a clear maximum and an exponential fall. In particular Fig. 10b shows a very good fit of the LC fall, using an exponential function. In general, the shape of the BAL III system LC is similar to those LC of SNe flux, emission line, etc.
The probable origin of this BAL III system will be discussed in section 4.3. Specifically, we will discuss 4 possible scenarios. One of this scenario is an explosive event associated with explosions of giant SNe/hypernova (with very massive progenitors and located close to the AGN and/or in accretion disks of AGNs).
It is important to note that previously it was assumed that this light curve (of BAL III) is symmetric. This type of variability was associated mainly with absorbing clouds crossing the central continuum light source (Kollatschny et al. 1992). It is interesting to note that Schmidt & Miller (1985) from a spectropolarimetry study detected an OF velocity (for the dust) of 700 km s −1 . Which is a value very close -within the errors-to our OF1 velocity.

Out flow from the nuclear optical emission line
A discussion of the extreme optical Fe ii emission of this IR QSO, was reported by Boksemberg et al. (1978) and Lipari et al. (1994). A ratio of Fe IIOP T /Hβ ∼8, [O III5007/Hβ ∼0.01, Na ID/Hα ∼ 0.03 and Hα/Hβ ∼5 were measured. These results are in agreement with the typical values obtained for extreme Fe IIOP T emitters, like IRAS 07598+6508, PG 1700+518, IRAS 18508-7815 (Lipari 1994).

UV spectrum and BALs in Mrk 231
Significant reddening in luminous infrared sources hampers the study of their UV properties. For Mrk 231, Figs. 11a,b and 9a show -at UV wavelengths-a strong reddening, with weak Mg ii, C iv and Lyα emission lines. UV absorption associated with the BAL system I are present in the Mg ii and C iv lines (Figs. 11a,b). In particular, The low-ionization emission line Mg II is observed superposed to the BAL system I (Fig. 11a). We measured for this absorption line a width (FWHM) of ∼ 700 km s −1 . This value is equal to the that measured -in this system-in the Na ID optical line. In addition, in the region between λλ2000-2800 there are weak absorption due to UV Fe II.
It is important to study in detail the UV (plus optical) continuum of extreme IR-Fe ii emitters and specifically BAL-QSOs because they show a clear deficit in the UV flux as compared to the non-BAL QSOs (see Weymann et al. 1991;Sprayberry & Foltz 1992). Fig. 9a shows a clear drop in the level of the UV (and even in the B) continuum of Mrk 231, for λ shorter than 4500Å. We found that an SMC-like reddening of E(B-V) ∼ 0.13 accounts for the differences between the UV spectrum of Mrk 231 and the non-BAL QSO composite/mean spectrum (Reichard et al. 2003).

UV-BALs in IR + GW/OF + Fe ii QSOs
From our programme of study and search of UV and optical BAL systems in extreme IR + GW/OF + Feii QSOs we already found interesting results in relation with the UV low ionization BAL system detected in IRAS 07598+6508 (Lipari 1994).
We recall that the standard definition of BAL QSO (Weymann et al. 1991) is based in the measurement of the equivalent width of the C iv resonance absorption line system (called balcity index: BI). The QSOs with BI > 0 km s −1 are considered BAL QSO. In part by this reason we observed the BAL candidates at UV (for C iv and Mg ii lines) and optical (for Na ID absorption) wavelengths.
From this programme, the following main results were found: (i) The UV-IUE spectrum of IRAS 21219-1757 (Figs. 12a,b) clearly shows a blend of emission and absorption features -at low S/N-in the C iv line. In these two figures the UV spectrum of IRAS 21219-1757 is superposed with the spectra of standard low ionization BAL and non-BALs QSO, respectively (obtained from Reichard et al. 2003). From these figures it is clear that the profile of the line C iv is very similar to the spectrum of low-ionization BAL QSO (and different to the spectra of non-BAL QSOs).
In the IUE UV spectrum of IRAS 21219-1757 the following features were also observed: • The absorption feature in the C ivλ1549 line extends from ∼1719 to ∼1665Å, implying outflow/ejection velocities of ∼1500 to ∼10400 km s −1 .
The emission line of C ivλ1549 is also weak, as has been observed in BAL- QSO (Weymann et al. 1991).
• Figs. 12a,b also show the presence of weak low-and high-ionization "emission" lines. In particular, Lyα and N Vλ1240 are weak.
• There are also weak emissions from O Iλ1303 and Si IV+O IV λ1400.
We note that the archive HST STIS spectra of IRAS 21219-1757 does not cover the region where we detected the BAL in this IR QSO (the line C ivλ1549).
(ii) In order to compare this BAL IR QSO, with the previous observed BAL IR QSOs, we have also included in Fig. 13 the UV spectra of IRAS 07598+6508, PG 1700+518, IRAS 14026+4341.
Furthermore, it is important to note that the UV-BAL features observed in these IR + GW/OF + Fe ii QSOs are very similar to those observed at high redshift in lowionization BAL-QSOs (at z > 6.0; see Maiolino et al. 2003).
(iii) In Fig. 13d the IUE spectrum of IRAS 18508-7815 is presented. In this extreme IR + GW/OF + Fe ii QSO there is only evidence of a possible narrow absorption system in the line C iv (and close to the systemic velocity).
(iv) For PHL 1092 (another extreme IR + GW/OF + Fe ii QSO) we have studied mainly the region of the Mg ii+UV-Fe ii. Fig. 13e does not show evidence of Mg II BAL systems, in PHL 1092. However, the fit of the emission line in this area required to include an UV Fe ii template (we used the UV Fe II emission of I Zw 1, from the HST spectra) and also a blue OF component. For this blue component a OF value of -8565 km s −1 was measured.
At the optical/red wavelengths, this OF (with very high velocity) was not detected at the line Hα. However, we found 3 blue OF componets with relativelly low velocities. For these blue components the following OF values were measured, OF1 = -1500, OF2 = -2500 and OF3 = -3100 km s −1 (see Fig. 13f). These velocities are almost the same to those obtained for the OFs detected in Hβ (using the offset method; Lipari et al. 2004d: their Table 8).
It is important to note that Dietrich et al. (2002) and Barth et al. (2003) already discussed that in order to obtain a good fit of the UV lines Mg ii + Fe ii in very high redshift QSOs, they need to include a strong blushifted component (they explain that this component was used without a physical explanation). In particular, Barth et al. (2003) in their Fig. 2 show this strong blue OF component in the line Mg ii, for the Fe ii-QSO SDSS J114816.64+525150.3. This object is one of the younger QSO known, with a redshift z = 6.4. They measured for the Mg ii OF component -of this distant/young QSO-a value of ∼ -5700 km s −1 (Barth et al. 2003: their Fig. 2), which is almost 1/3 smaller than the value obtained for PHL 1092.
Therefore, we strongly suggest that this type of blue component observed in the Mg ii emission line -in very high redshift QSOs-is associated with extreme OF processes. Again, the results obtained from QSOs at very high redshift (by Dietrich et al. 2002 andBarth et al. 2003 and Mg ii emission lines). However, these OF emissions are probably associated with very different OF processes, similar to those found in this paper for Mrk 231.

DISCUSSION
In this section we discuss the properties of Mrk 231 as: (i) an evolving elliptical galaxy; (ii) a merger with composite nuclear energy; (iii) an EVOF QSO, with also a composite nature; (iv) as an exploding QSO. In addition, we analyse the IR colours diagram for a large sample of IR mergers/QSOs with galactic winds (including BAL QSOs and Mrk 231).

The merger Mrk 231 as an evolving elliptical
galaxy with galactic wind Hamilton & Kell (1987) already found that the optical R broad band surface brightness profiles of Mrk 231 follow the r 1/4 law (in the range 1.0 kpc ≤ r ≤ 10 kpc). Lipari et al. (1994) from high resolution NOT V broad band images found that the nucleus is compact at scales of 0. ′′ 7 (∼500 pc). Soifer et al. (2000) using Keck mid-IR 7.9 to 19.7 µm broad band images found that the nucleus is compact and unresolved at 0. ′′ 13 (100 pc). At radio wavelengths, Condon et al. (1991) also detected an unresolved radio core, smaller than 0. ′′ 25 (at 8.44 GHz), in Mrk 231. HST ACS/U, WFPC2/I and NICMOS/H broad band images (see section 3 and Quillen et al. 2001) confirmed that at scales better than 0. ′′ 1 (∼80 pc, FWHM), the bright compact nuclear peak is unresolved. These results suggest that the nuclei of the original colliding galaxies have coalesced into a common nucleus with an AGN, and that the merger is in a very advanced phase (a relaxed system), probably evolving to an elliptical galaxy. Therefore Mrk 231 is another candidates for a protoelliptical galaxy. It is important to note that from the theoretical point of view there is a wealth of literature proposing a relevant role for galactic wind and OF in the formation and evolution of elliptical galaxies. We can highlight that: (i) Mathews & Baker (1971) suggested that a galactic wind can explain the deficiency of observed gas as compared to that returned by stars in ellipticals; (ii) Larson (1974), Vader (1986 and Kauffmann & Charlot (1998) proposed for ellipticals a galactic wind associated with the early star formation episode to explain their colour-magnitude and mass-metallicity relation; (iii) Larson (1974), Vader (1987 and Dekel & Silk (1986) proposed that dwarf ellipticals evolved from initially more massive elliptical galaxies that suffered substantial gas loss through supernova-driven galactic winds.
The results obtained for Mrk 231 (and previous studies of mergers with OF) suggest that extreme starbursts plus AGN with galactic winds play an important role in galaxy evolution, e.g. giant expanding shells in composite galactic winds could produce BAL systems, massive starbursts could generate AGNs/QSOs, successive extreme starburst processes could transform the observed high gas-density (in the ISM of mergers) to high stellar-density, etc. Furthermore, these extreme starburst+AGN with galactic winds -induced by mergers-could be a nearby analogy for processes that occurred at high redshift, when the galaxies and QSOs formed, i.e. similar to the first massive star formation episodes (population III stars) in hierarchical mergers and/or primordial collapses (Larson 2003(Larson , 1999(Larson , 1998Bromm & Loeb 2003;Bromm, Coppi, & Larson 1999;Scannapieco & Broadhurst 2001).

The composite nucleus of Mrk 231: an AGN/QSO embedded in an extreme starburst
In order to study the nature and origin of the complex nuclear outflow process detected in Mrk 231, it is important to analyse -previously-the composite nature of the nuclear energy.

The AGN/QSO
There is clear and interesting evidence of the presence of an AGN/QSO in the nucleus of Mrk 231. Specifically, at radio wavelength Preuss & Fosbury (1983) already detected a very compact nuclear radio source, at scale <1 pc (using VLBI interferometric observations). Recently, using the Very Long Baseline Array (VLBA) Ulvestad et al. (1999a,b) found a parsec scale radio jet, with an extension of ∼2.5 pc. At X-ray wavelength, using ASCSA data Turner (1999) found that the optical-to-X ray spectrum of Mrk 231 is typical of a QSO. In addition, using Chandra observations Gallagher et al. (2002) detected that the bulk of the X-ray luminosity is emitted from an unresolved nuclear point source and the spectrum is remarkably hard.
In section 3, we found clear evidence that -at least-the Na ID BAL system I is associated with the presence of the AGN+jet.

The extreme starburst
Recently, the star formation in the nucleus of Mrk 231 was studied at very high resolution by Bryant & Scoville (1996) and Downes & Solomon (1998), observing the CO gas. In particular, Bryant & Scoville (1996) found that the CO distribution is elongated with kinematics properties consistent with a disk oriented in the east-west direction, and containing a mass of 3 × 10 9 M⊙ of molecular gas (within a diameter of 1. ′′ 0, 814 pc). Downes & Solomon (1998) using CO interferometer data also detected a 1. ′′ 2 diameter inner disk plus a 3. ′′ 0 diameter outer disk. They found extreme star formation processes in the nuclear CO disks or rings of Mrk 231. Confirming previous results that suggested the presence of a strong nuclear starburst in this IR merger (Hamilton & Keel 1987;Hutching & Neff 1987, and others). In particular Lipari et al. (1994) also suggested the presence of an extreme nuclear starburst, as the main source of the strong galactic wind, detected in Mrk 231. These works suggested that at least 1/3 of the total source of the nuclear energy in Mrk 231 is generated by the extreme starburst.
On the other hand, continuum observations at 21 cm with VLBA (Carrilli, Wrobel & Ulvestad 1998) show emission from an extended disk of 370 pc, that exhibits absorption against the radio emission from the inner disk (r < 160 pc). Further radio continuum observations reported by Taylor et al. (1999) trace this emission out to 1. ′′ 0. They interpret this disk radio emission also as due to strong star formation activity with a SFR of 60-200 M⊙ yr −1 . At near-IR wavelengths, the nuclear spectrum of this galaxy shows an anomalously large Paα/Brγ ratio (Cutri et al. 1984), which imply that the electron density in the broad line clouds of Mrk 231 is higher than the standard values of the BLR in AGNs/QSOs. In section 3.4, it was found that extended shocks (associated with multiple expanding bubbles) are also an important source of energy and ionization, in the nuclear and circumnuclear regions. In addition, we found evidence of a multiple explosive event in Mrk 231, which is in part associated with the extreme starburst, probably generated during the merger process.
At least two strong starbursts were generated in the merger process of Mrk 231: one associated with the origin of an extended post-starburst population (associated with the underlain hot stellar population in the optical spectrum), plus a young and dusty nuclear extreme starburst.

The composite nuclear outflow + BAL systems in Mrk 231: an exploding QSO?
In section 3 very interesting results, about the OF and BAL systems in Mrk 231 were found. Specifically, it was detected: (i) multiple concentric expanding bubbles, (ii) a blue Hαemission bump at the ejection velocity of the BAL I, and (iii) a light curve for the BAL-III system showing a steep increase and exponential fall (very similar to the shape of a SN light curve).
In order to analyse these new results, it is important to remark previous studies at radio wavelengths, which are relevant for the discussion of the OF in Mrk 231. In particular: (i) VLBI images at 1.7 Ghz (Neff & Ulvestad 1988) and VLBA images at 2.3 Ghz (Ulvestad et al. 1999a) show a north-south triple structure with a central unresolved core and two symmetric resolved lobes; with a total extension of ∼40 pc. This radio structure is elongated (at PA ∼00 • ) in the direction perpendicular to a 350 pc HI + CO starburst disk/ring.
(ii) VLA images at 4.9 Ghz (Baum et al. 1993) and at 1.5 Ghz (Ulvestad et al. 1999a) show a very large structure of ∼35-50 kpc, also elongated in the direction north-south.
(iii) Using the VLBA at 15.3 GHz, Ulvestad et al. (1999a,b) found a parsec scale radio jet, with an extension of ∼2.5 pc, low apparent speed, and at the position angle PA ∼65 • .

Multiple expanding shells
The presence of multiple concentric expanding bubbles/shells, with centre in the nucleus and with highly symmetric circular shape could be associated mainly with giant symmetric explosive events. These giant explosive events could be explained in a composite scenario: where mainly the interaction between the starburst and the AGN could generate giant explosive events. In particular, Artymowicz, Lin, & Wampler (1993) and Collin & Zahan (1999) already analysed the evolution of the star formation (SF) close to super massive black hole (SMBH) and inside of accretion disks. They suggested that the condition of the SF close to the AGNs could be similar to those of the early/first SF events, where it is expected giant explosive process generated by hyper-novae (with very massive progenitors: M ∼100-200 M⊙).
For the shell S1, Lipari et al. (1994) already proposed that the morphology and kinematics of the blue arc (located to the south of the nucleus) are in agreement with the results of glactic winds hydrodynamic models. Specifically, the starburst GW models of Suchkov et al. (1994) predict after 8 Myr in the blowout phase: blue arcs with radius r ∼ 3 kpc. We noted that after 8 Myr the starburst is in the type II SN phase.
It is important to remark that exactly in the direction of this arc (north-south from the nucleus, PA ∼00 • ) Neff & Ulvestad (1988) and Ulvestad et al. (1999a) found a elongate structure of ∼40 pc, which is perpendicular to the CO starburst disk/ring. Furthermore, Baum et al. (1993) and Ulvestad et al. (1999a) detected a large structure (of ∼35-50 kpc), also elongated in the direction north-south. These results are all clearly consistent with the blowout or rupture phase of the bubble S1.
Following our study of the superbubble in NGC 5514 (Lipari et al. 2004d) the dynamical timescale of the more extended shells S1 and S2 in Mrk 231 were derived, using the relation: where R bubble,kpc and V −1 bubble,1000 are the linear dimension of the bubble and the velocity of the entrained material (in units of kpc and 1000 km s −1 , respectively). The following values were obtained for the shells S1 and S2: • t dyn−S1 ∼ 4.8 × 10 6 yr; • t dyn−S2 ∼ 3.0 × 10 6 yr.
Then a period of ∼1.8 × 10 6 yr is the separation between the two explosive events that probably generate the shells S1 and S2.
From the 2D spectra a mean value of Hα flux of 0.5 × 10 −13 erg cm −2 s −1 was obtained, for the OF associated with the shell S1. Using the relations given by Mendes de Olivera et al. (1998) and Colina et al. (1991) a value for the ionized-gas mass, in the OF associated with the shell S1, of 2.0 × 10 6 M⊙ was found. Using this value of ionizedgas mass, we derived for the kinetic energy of the OF-S1, EKINOF−S1 ∼ 0.5 × MOF−IG × VOF−S1 2 = 2.0 × 10 54 erg. This high level of energy, obviously required the presence of multiple SNe events, or an unusual type of "giant SN" or hypernovae. Heiles (1979) already suggested that this last alternative need to be considered seriously, in order to explain supershells with enegy > 3.0 ×10 52 erg (even if these energies of supershells are hundred of times larger than that available from a single and "standard" SNe).
In section 4.3.4 the origin of this multiple shells will be discussed in detail.

The blue Hα-emission bump at velocity of BAL I system
In section 3 another interesting results was found: a blue Hα-emission bump at the ejection velocity of the BAL I (and in a area located very close to the nucleus and at the same PA of the radio jet). Furthermore, in the same direction where we detected this bump (at PA ∼60-70 • ) at 1. ′′ 3-2. ′′ 2, we also found multiple narrow emission line components, with "greatly" enhanced [N ii]/Hα ratio (very similar to the spectra of jets bow shocks). These results are consis-tent with a scenario where the BAL-I system is generated in OF clouds associated with the parsec scale jet. It is important to note, that de Kool et al. (2001Kool et al. ( , 2002 found a very interesting result -and physically similar to those found for Mrk 231-in their Keck high resolution spectroscopic study of AAL and BAL, in the QSOs FIRST J104459.6+365605 and FBQS 0840+3633. The absorption lines of these QSOs cover a ranges of velocities of -200 to -1200, -3400 to -5200 km s −1 ; and the width of the individual absorption lines ranges from 50 to 1000 km s −1 (these are values similar to those measured in Mrk 231). They found that the distances between the AGN and the region where the OF gas generate the AAL and BAL line are ∼700 and ∼230 pc, respectively. Therefore, for Mrk 231 (BAL system-I), J104459.6+365605 and FBQS 0840+3633 the distances found between BAL or AAL forming regions and the continuum source (AGN) are large, of: ∼ 200-1000 pc (BALs and AALs are generally thought to be formed in OF at a much smaller distance from the nucleus; de Kool et al. 2001). Boroson et al. (1991) and Kollatschny et al. (1992) already explained some physical mechanism that could explain variations in the absorption line strengths. Here we re-analyse these and new mechanisms, according to the results obtained in section 3.

The origin of the variability of the BAL III system
The principal mechanisms that can explain the variability of the NA ID BAL III system, can be enumerate as follow: (i) Changes in the intensity of the continuum source (and the ionizing parameter in the absorbing region). Since the continuum flux remained constant in the period in which the system III varied, the first possible explanation can be excluded.
(ii) Changes in the ionizing parameters and density in the absorbing clouds when they move away from the centre. This second possibility have been excluded by Boroson et al. (1991), since the relative change in distance can not explain the strong change and the systematic increasing and decreasing epochs.
(iii) Motion of absorption clouds with traverse velocity occulting the continuum source. This was in the past the best explanation for part of the light curve of BAL III, observed between 1980 and 1992. However, the new observation -presented in section 3.5-exclude this explanation, sincethe LC fall is clearly asymmetric/exponential.
(iv) An explosive scenario for the origin of the BAL III system could explain: the shape of the light curve variability, and also the presence of multiple concentric expanding bubbles/shells (with circular shape). In the next section we will discuss in detail this explosive scenario and the probable origin.

The exploding scenario for Mrk 231 and BAL systems
In section 3 strong evidence for a composite origin of the OF in the nuclear region of Mrk 231 were detected. Furthermore, for IR mergers/QSOs with EVOF a similar result was found (see for details section 1 and Lipari et al. 2004a,d). Thus it is probably that also very energetic explosive events are originated in the interaction between extreme starbursts and AGNs. We already explained that Artymowicz et al. (1993) and Collin & Zahan (1999) suggested that the conditions of the SF close to the AGNs+accretion disks could be similar to those of the early/first SF events, where it is expected giant explosive processes generated by giant SNe. On the other hand, different works also proposed that the BLR could be associated with OF processes in accretion disks, extended stellar envelopes, etc (see for references/review Sulentic, Marziani, & Dultzin-Hacyan 2000;Scoville & Norman 1996;Terlevich et al. 1992). Thus an interesting questions is: could an explosive event generate a very unusual spectrum similar to that detected in the nuclear region of Mrk 231?. Figure 14 shows the superposition of the spectrum of the unusual radio SN of type II 1979c(observed in 1979Branch et al. 1981). Only using colours we can distinguish each spectrum, since they are almost identical. Thus, an more constant OF (than a single/standard SN) could explain even the spectrum of the BLR in Mrk 231.
In the composite (starburst+AGN) scenarios, two main theoretical models for the origin of BAL systems were proposed: (i) for IR dusty QSOs/galaxies, in the outflowing gas+dust material the presence of discrete trails of debris (shed by individual mass-loss stars) produce the BAL features (Scoville & Norman 1996); and (ii) in SN ejecta, which are shock heated when a fast forward shock moves out into the ISM (with a velocity roughly equal to the ejecta) and a reverse shock accelerates back and moves towards the explosion centre; the suppression of red-shifted absorption lines arise since SN debris moving toward the central source are slowed down much more rapidly -by the wind-than is material moving away Perry 1992). The presence of large galactic-scale OF, shells or rings in IR QSOs could be a third explanation -in a composite scenariofor the origin of BAL systems, in these objects.
It is interesting to recall that in their study of PG 1700+518, Hazard et al. (1984) already suggested that: high redshift low-ionization BAL-QSOs could be explained by a violent ejection during the first onset of the QSO activity, similar to a "giant SN explosion". This approach is very similar to that proposed in this paper for Mrk 231 (where "giant expandig superbubbles" were foundd). Therefore, it is important to study in detail the contribution of extended outflow associated with superwind/superbubble regions in order to explain the origin of some BAL systems and even the BLR of Mrk 231 (see Lipari 1994;Lipari et al. 1994;Terlevich et al. 1992;Dyson, Perry & Williams 1992;Voit, Weymann & Korista 1993). In general, the results and conclusions presented in Section 3 appear to be in good agreement with this unusual explosive scenario proposed in this paper for Mrk 231: where the strong IR+Fe II emission and BAL system could be linked -in part-to a violent extreme-starburst+AGN.
Finally, the serendipitous finding that a high number of QSOs show BAL systems at low redshift (in IR + Fe ii emitters) and at very high redshift (in Fe ii emitters; Maiolino et al. 2003Maiolino et al. , 2004) is very interesting. On the other hand, the relation between BAL, IR, GW and Fe II emission is not well understood. Fe II emission (with low ionization level) could be originate in warm regions, and thus obscured from the direct ionizing UV photons. In the case of strong Fe ii emitters, the obscuring material may be in the form of an expanding shell. If so, BAL+Fe ii+IR objects are not ordinary AGN, rather, they may be associated with early starburst activities. If some absorptions are the result of outbursts, the mass involved should be much larger than a typical supernova, since the Fe II emission and"some" BAL systems do not fall in years. However, in order to understand this type of giant outbursts (i.e., from hypernova, SN explosion from population III stars, SN in accretion discks of AGNs, etc) it is required more detailed theoretical studies. The results found in this paper for Mrk 231 (and similar IR QSOs) support the reality of these giant explosive processes.

Mrk 231 and extreme IR + GW/OF + Fe ii + BAL QSOs as transition/young QSOs
In this section, we will analyse the properties of Mrk 231 together with the other members of the interesting group of IR + GW/OF + Fe ii + BAL transition/young QSOs.

The IR colours diagram for a small sample of IR + GW/OF + Fe ii + BAL QSOs
In general, the IRAS colour-colour diagrams have been used as an important tool to detect and discriminate different types of activity in the nuclear/circumnuclear regions of galaxies (e.g., Seyfert and starburst activity; see de Gripj et al. 1985Gripj et al. , 1987Sekiguchi 1987;Rowan-Robinson & Crawford 1989). Lipari (1994) Canalizo & Stocton (2001) confirmed that the host galaxies of both QSOs have strong starburst populations (using Keck spectroscopy). In general, the extreme Fe II + IR emitters show weaker "Seyfert/AGN" components than the low Fe II QSOs.
Furthermore, we found that the IR properties/colours of narrow-line Seyfert 1 IR AGN with extreme Fe II emission (like Mrk 507 and Mrk 957), lie also in the transition area between the BB and PL regions, and close to standard disk galaxies (Rowan-Robinson & Crawford 1989) and starburst objects (Sekiguchi 1987).
It is important to remark that of a total of ∼10 IR transition objects of this original sample, the first 4 systems are BAL IR QSOs. Therefore, we already suggested that BALs IR QSOs (like Mrk 231, IRAS 07598+6508, IRAS 17002+5153 and IRAS 14026+4341) could be associated with the young phase of the QSO activity.

The IR colours diagram for a large sample of IR mergers and IR QSOs with galactic winds
In this paper, using our data base of more than 50 IR Mergers and QSOs with galactic winds and using for comparison the large sample of standard PG QSO (from Boroson & Green 1992) we will expand our previous study. Figure 15 and Table 4  IR fluxes-densities, in the bands of 12, 25, 60 and 100 µm, were obtained from the IRAS and ISO Archival Catalogue (using NED). Only objects with a good detection in the three required bands have been included. Also, the localisation of the three main regions in this colour-colour diagram (i.e., the QSOs/Seyferts, Starbursts, and powerful IR galaxies areas) have been plotted. An inspection of this diagram clearly shows the following: (i) All the IR mergers with LVOF are located very close to the BB and starburst area.
(ii) Almost all the IR QSOs with EVOF are located in the transition region.
The only object, NGC 3079, not following this trend is the only spiral galaxy in this sample.
(iii) The standard QSOs and radio QSOs are located around the PL region.
(iv) All the BAL IR QSOs are located in the transition region, in almost a clear sequence: from Mrk 231 (close to the BB area) → IRAS 07598+6508 → IRAS 21219-1757 → IRAS/PG 17072+5153 and IRAS 14026+4341 (close to the PL area) → standard QSOs. Therefore, these results confirm our previous finding (obtained from a small sample of IR galaxies): in the sense that IR QSOs are probably "transition" objects, between IR mergers and standard QSOs. However, it is important to remark that it is required more detailed studies of individual IR systems (like Mrk 231) in order to determine the different paths of possible evolution (see Farrah et al. 2001;Rigopoulow et al. 1999).

The possible relation between IR + GW/OF + Fe ii + BAL transition/young QSOs and very high redshift BAL QSOs
It has been proposed that extreme starburst + galactic wind processes associated with IR mergers could play a relevant role in the formation and evolution of galaxies and QSOs/AGNs, i.e. in their structure, kinematics, metallicity, etc. (see sections 1 for references). Furthermore, recent detailed observations and theoretical studies have confirmed that OF, galactic winds, BAL, large amount of gas+dust and strong Fe ii emission are important components and processes at high redshift (z ∼ 4-6), when the galaxies and QSOs formed (Frye, Broadhurst, & Benitez 2002;Ajiki et al. 2002;Pettini et al. 2001;Dawson et al. 2002;Carilli et al. 2004a Bertoldi et al. 2003a,b;Omont et al. 2001;Maiolino et al. 2004a,b). Specifically, cm and mm observations of thermal molecular line emission from high redshift QSOs reveal massive gas reservoirs (10 10 to 10 11 M⊙) required to fuel extreme star formation (Carilli et al. 2004a,b;Solomon et al. 2003;Carilli & Blain 2002;Carilli, Menten & Yung 1999). In addition, cm and mm observations also reveal in high redshift QSOs very large amount of dust of 10 8 M⊙. The presence of this large mass of dust is associated mainly with massive starbursts concurrent with AGNs, which implied star formation rates greater than 10 3 M⊙ yr −1 (Carilli et al. 2000;Bertoldi et al. 2003a,b;Omont et al. 2001;Cox et al. 2002).
On the other hand, Maiolino et al. (2004aMaiolino et al. ( ,b, 2003 presented near-IR spectra of eight of the more distant QSO (at 4.9 < z < 6.4). Half of these QSOs are characterised by strong UV BAL systems (at C IV, Mg II, Si IV, Al III lines). Although the sample is small, the large fraction of BAL QSOs suggest that the accretion of gas, the amount of dust and the presence of OF process are more larger (in these objects) than in standard QSO at z < 4.0. They also suggested that the very high amount of dust was generated by early explosions of SNe (Maiolino et al. 2004b).
Finally, it is important to remark the similar properties found in IR + GW/OF + Fe ii + BAL QSOs at low redshift (like Mrk 231) and very high redshift BAL QSOs (at z ∼ 6.0; Maiolino et al. 2003Maiolino et al. , 2004aCarilli et al. 2004a,b). According to these similarities, we propose that the phase of young QSO could be associated with the following main processes: (i) In young QSOs with extremely large amount of gas (concentrate in their nuclear region), the accretion rate of gas -by the SMBH-could be extremely high (see Maiolino et al. 2004a).
(ii) In addition this extremely large amount of molecular gas could generate extreme starbursts; and the presence of AGNs could increase the SF close to the nucleus. Specially in the accretion disks, with properties -of the SF-similar to the population III of stars. In these extreme starbursts -close associated with QSOs/AGNs-it is expected giant SN explosions.
(iii) In young and distant QSOs the very high number of BAL detections suggest that composite OFs (or EVOFs) play a main role in their evolution.
Furthermore, this scenario is in close agreement with the results of the study of proto-QSO evolution and black hole growth (using hydrodynamic models). In particular, Kawakatu et al. (2003) found that a ULIRG phase (where the host galaxy is the dominant source of luminosity: i.e. IR galaxies/mergers with starbursts) precedes a galactic wind epoch: i.e., composite young IR+OF/GW+BAL mergers/QSOs. Which would be a transition state to the AGNdominated phase: i.e., the standard QSO phase. This evolutive path is almost identical to the sequence found for BAL IR+Fe ii QSOs, in Figure 15.