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Narrow-line Seyfert Galaxies. Connection between abundance and the large-scale structure

In this work the correlations between spatial concentrations of active nuclei (NLS and BLS) and concentration of galaxies of full uniform sample were obtained. Methods, developed by the author in earlier paper were used. Galaxies of this uniform sample trace the large-scale structure. We used SDSS DR 7 data. The correlations obtained are linear and the NLS/BLS ratio is constant. That leads to conclusion that amounts NLS and BLS are some fixed fraction of all galaxies independent on the density of large-scale environment. In order to check validity of our results were also confirmed the well known result that fraction of red galaxies increases with density of environment. Also it was confirmed that this trend is more prominent for less massive galaxies.


INTODUCTION
According to the current classification the population of Seyfert galaxies is divided into two main types. Objects with broad permitted lines are classified as Sy1, objects without broad permitted lines as Sy2. This difference might be caused by the lack of BLR (Broad Line Region) or by obscuration of BLR by dusty torus. In former case such objects are called "true Sy2". Intermediate types (Sy 1.2 -Sy 1.8) in this classification are defined according to prominence of the broad components of permitted lines.
It is very important to pay some attention to the existing confusion in terminology about NLS. Seyfert galaxies often have very broad permitted lines, their widths can reach even 10 000 km/s and more. When we speak about Narrow Line Seyfert galaxies we imply that their broad permitted lines are merely slightly wider than forbidden lines. But broad permitted lines in Narrow Line Seyfert galaxies are present! Various authors define the threshold between NLS and BLS (Broad Line Seyfert Galaxies) differently, convenient value is in range 2000 -2200 km/s.
There is a growing interest in this type of AGN in the recent years. Their host galaxies have on average later Hubble types, HT = 3.0 and HT = 1.0 for NLS and BLS respectively [2]. Numerical coding of Hubble types is according to the RC3 (Third Reference catalog), [3]. I.e. T = 1 means Sa, T = 2 Sab, T = 3 Sb etc. Bulges in host galaxies of NLS are always pseudobulges [4], their nuclear spirals show regular two-arm morphology, in contrast to BLS.
In recent years more and more authors had confirmed that NLS accrete with high Eddington ratios close to the Eddington limit and that their black holes are less massive than such of BLS [5,6]. Black holes in NLS also seem to have high angular momenta [4,[7][8][9]. It is curious that NLS can produce relativistic jets in many ways similar to jets in blasars.
Let us briefly discuss the evolutionary status of host galaxies of this type of AGN. Many authors believe that NLS evolve through so-called secular processes in contrast with BLS.
See, for example, [4]. Secular evolution implies slow evolution of the host galaxy via internal instabilities (internal secular evolution) or tidal interactions or minor mergings with small satellite galaxies (external secular evolution). For details see [10].
Relatively small attention was paid to the surroundings of NLS galaxies in the literature.
In [11] the connection between environment and properties of host galaxies of LINERs 1 and TO 2 was studied. As a result, no connection was found. On the other hand, in [12] it was found that there is a significant difference between environments of Sy1 and Sy2. Sy2 have more close companions. Authors had also compared environments of control samples of galaxies of same morphological types as hosts of Sy1 and Sy2. No difference between host galaxies of AGN and normal galaxies of same morphological types was found. That led to conclusion that differences in environmental density of Sy1 and Sy2 are due to differences in morphological types of their host galaxies and not due to the presence of an active nuclei.
In [13] correlation between infrared luminosity and environmental density was discovered for a sample of bright IRAS galaxies. Paper [14] was dedicated directly to the problem of environment of NLS. Authors came to conclusion that NLS tend to have close companions less frequently. Nevertheless, it should be noted that this paper is relatively old (year 2001) and all conclusions are based on a sample of 27 galaxies.
In our previous work [1] we have obtained the luminosity function of NLS in [OIII]λ5007Å. This forbidden line is emitted at large distance from the active nuclei in NLR, which has conical geometry, thus this line does not suffer from orientation effects and obscuration.
Modified V /V max method was used. For a complete magnitude limited sample it is very easy to calculate V max , but the situation is quite difficult for spectral lines. In order to solve this problem we calculated the function of probability of observation of object for every luminosity bin p(d c ), where d c comoving distance.
We also took into account variations of the density of the Universe due to the largescale structure. The idea was as following. If we know the luminosity function of inactive galaxies with good accuracy, then having a uniform sample it is possible to calculate for considered volume N obs N calc , where N obs -the observed amount of galaxies, N calc calculated amount of galaxies from luminosity function. This approach allows us to normalize sample of considered objects to uniform complete sample of galaxies which traces variations of density We have also selected a magnitude limited sample of galaxies in r band taking extinction into account. This sample was used for normalization.
In our work we used the following cosmological parameters: At first for every defined interval of redshift we calculated the normalization ρ gal ρ gal , where ρ gal is the density of galaxies in the considered volume element, ρ gal average density of galaxies. Then for every luminosity bin we found amount of AGN objects N AGN . The amount of AGN normalized to the average density of the Local Universe is: The ratio ρ gal ρ gal was calculated the following way. Luminosity function is usually fitted with the Schechter function: For absolute magnitudes this formula takes the following form: We took parameters for local luminosity function of galaxies from [16], where they are as following: Φ * = 0.0090 ± 0.0007, M * − 5 lg 10 h = −20.73 ± 0.04, α = −1.23 ± 0.02 in r band of SDSS survey. Knowing this parameters one can obtain total luminosity of galaxies per unit of volume: where L 1 and L 2 are the limits of integration.
Now we can obtain ρ gal ρ gal = L sch V L obs , where L obs total observed luminosity of galaxies in considered volume element, V considered volume. Luminosity of each galaxy is in range It is crucial to stress that transition from luminosities to spatial densities is possible only if parameters of Schechter function α and L * are constant. For the redshift interval considered this is correct. For details see [1]. Hence, normalized amount of AGN is Having normalized sample of AGN, we can now calculate the probability function of observation of objects in considered luminosity bin p(d c ), where d c comoving volume.
This function has a following form: . Details see in [1]. Then we have split the considered volume of the Universe into elements limited by redshift (z i < z < z i+1 ), ascension and declination (α min,j < α < α max,j ; δ min,j < δ < δ max,j ). Total count of NLS and BLS was obtained for the considered luminosity interval. It was then corrected using the probability function p(d c ). Making the same calculations for each volume bin we obtained the dependence of N N LS , N BLS and and N BLS spatial densities of NLS and BLS respectively.
Errors were estimated the following way. The amount of objects corrected using the probability function of observation of object in considered volume in luminosity interval The total error is contributed by Poisson errors and error in determining the p(d c ) function. Hence, we obtain: According to the fact that function p(d c ) has the following form: we can obtain the equation for errors:

SPATIAL DENSITY OF AGN AND THE LARGE-SCALE STRUCTURE
Firstly, it is necessary to define volume bins of the SDSS survey. If we use too large elements we will lose information about small-scale variations of density. But in the case of too small volume elements there will be insufficient galaxies for calculating the ρ gal ρ gal ratio in volume bins with rather low density. I.e. in such a case it is possible to study the ρ N LS ρ BLS ratio in small areas of increased density.
We have only considered volume elements with amount of inactive galaxies for normalization N ≥ 100 so that Poisson error is ≤ 10%. In order to check our results the same calculations were performed also for N ≥ 50. The results obtained are identical except that errors are lower (there are more objects for each density bin) and uncertainties in ρ are Nevertheless, statistical significance is too small for any conclusions.
It seems that for all considered luminosity intervals the correlations between N N LS , N BLS and ρ gal ρ gal are linear. All the above said implies that NLS and BLS are some fraction of all galaxies which depends on nuclear luminosity but not on density of large-scale environment.

DEPENDENCE OF THE RED FRACTION OF GALAXIES ON LUMINOSITY AND DENSITY OF ENVIRONMENT
The fact that the fraction of early-type galaxies is higher in more dense regions is wellknown. See, e.g., [17]. Also with increasing density of environment increases the fraction of red galaxies.
Paper [17] is dedicated to analysis of data provided by the Galaxy Zoo project. For today it is the largest catalog of visually classified galaxies. Right panel of fig. 12 in [17] shows the correlation of the fraction of red galaxies with lg 10 (Σ[Mpc In order to classify galaxies we used u − r colors. Galaxy was considered red if u − r > 2.2 according to [18].
The obtained correlations between red fraction N red N all and ρ gal ρ gal are shown in figure 5a-f.
Let us compare our result with the one from [17] shown on fig. 5g. We confirm not only that there is a tendency of increasing of fraction of red galaxies with density of environment, but also the fact that this trend is more prominent for less massive galaxies. This effect can be explained in the following way. In order to form a giant galaxy mergings are required.
They in turn will lead to depletion of gas reservoir and redder color of galaxy. I.e. there definitely should be few giant galaxies in voids, but significant fraction of them will be red. For less massive galaxies the situation is drastically different. In voids such galaxies will evolve on their own via secular processes and to present epoch they will still have gas and significant star formation rates. In dense regions gas reservoirs of such galaxies will be depleted by different processes (ram pressure stripping, mergings, nuclear activity etc.) which will result in redder colors.
Hence, confirmation of this result means that our approach is correct and results obtained about NLS and BLS are trustworthy.

CONCLUSION
Using our method discussed in detail in [1] relations between spatial concentrations of NLS, BLS and ρ gal ρ gal were obtained. Here ρ gal ρ gal is a ratio of concentration of galaxies in considered volume to the average concentration of galaxies in the Universe. Also the relation was obtained for the ratio N N LS N BLS .
Correlations of N N LS and N BLS are linear. The value N N LS N BLS is constant within errors.
Deviations are small and statistically insignificant.
NLS and BLS are a fixed fraction of all galaxies in wide range independent from density of the Universe.
All this argue for the idea that NLS activity is launched through internal processes, not by interactions. It should be noted, however, that our approach allows to analyze connection of nuclear activity with variations of concentration of galaxies on scales of large-scale structure cells (i.e. with the position of AGN in large-scale structure), but it does not account at all for the presence or absence of close companions. Some authors state that interactions with close companions lead to formation of classical bulges in BLS (see, e.g., [4]) In order to check validity of our approach we have obtained the relation between fraction of red galaxies and ρ gal ρ gal . The results from [17] were confirmed. Fraction of red galaxies is higher in more dense regions and this trend is more prominent for less massive galaxies.   limited by redshift z i < z < z i+1 and coordinates (α min,j < α < α max,j ; δ min,j < δ < δ max,j ).       Table 2. Results of fitting of the correlations obtained using the second grid (see fig. 2b). Structure of the table is the same as such of table 1.