HI Observations of SA 68-6597: the faintest Blue Compact Dwarf Galaxy
  Blue compact dwarf galaxies (BCDs) are faint (M(B) < -17 mag) compact (R <1 kpc), at least qualitatively very blue galaxies due to active star formation, and have low metallicities. Found serendipitously as part of a redshift survey of faint galaxies with the Keck Telescope (DEEP), SA 68-6597 is at a distance of 80 Mpc, and is one of the faintest, -12.4 mag, lowest metallicity, ~0.05 Z(sun), BCDs known. Its H-beta linewidth of sigma =27 km/s and small size, R(eff) ~ 190 pc, suggest that it is an extremely low mass galaxy. We have used the Arecibo telescope to measure the HI properties of SA 68-6597 in order to better constrain its total mass and its potential for future star formation. SA 68-6597 has a M(HI) = (1.4+-0.4)x10^7 M(sun) and an HI FWHM linewidth of 33$\pm^{60}_{12}$. Combining the HI linewidth with an estimate of the size of the HI disk, we derive a M(dyn)>~3x10^7 M(sun). The M(HI)/L(B)=1.0+-0.3 M(sun)/L(sun), M(dyn)/L(B) >= 2 M(sun)/L(sun) and M(HI)/M(dyn) <~ 0.47 values are typical for BCDs. Combining the measured star formation rate of 0.003 M(sun)/yr with the HI mass, we derive a gas depletion timescale of 5+-2 Gyr. While SA 68-6597 is a fainter, lower-mass, higher metallicity counterpart to other BCDs like I Zw 18 and SBS 0335-052, its HI properties suggest it will not evolve dramatically in the near future. Given the limits on its gaseous and dynamical masses, SA 68-6597 may be able to evolve into a moderately massive dwarf spheroidal galaxy. 
D.J. Pisano (NRL), David C. Koo, Christopher N.A. Willmer, Kai Gerhard   Noeske, A.C. Phillips (UCO/Lick Observatory)