J/ApJ/453/48 J/ApJ/453/48 VI photometry of HST faint field galaxies S P Driver R A Windhorst R E Griffiths Astrophys. J. 453 48 1995 1995ApJ...453...48D Galaxies, photometry Morphology galaxies: evolution galaxies: fundamental parameters galaxies: irregular galaxies: luminosity function, mass function galaxies: starburst surveys We present a complete morphologically classified sample of 144 faint field galaxies from the HST Medium Deep Survey with 20.0=<Imag<22.0mag. We compare the global properties of the ellipticals and early- and late-type spirals and find a non-negligible fraction (13/144) of compact blue [(V-I)<1.0mag] systems with r^1/4^ profiles. We give the differential galaxy number counts for ellipticals and early-type spirals independently and find that the data are consistent with no-evolution predictions based on conventional flat Schechter luminosity functions (LFs) and a standard cosmology. Conversely, late-type/irregulars show a steeply rising differential number count with slope ({delta}logN/{delta}m)=0.64+/-0.1. No-evolution models based on the Loveday et al. (1992ApJ...390..338L) and Marzke et al. (1994AJ....108..437M & 1994ApJ...428...43M) local luminosity functions underpredict the late-type/irregular counts by 1.0 and 0.5dex, respectively, at Imag=21.75mag. Examination of the irregulars alone shows that ~50% appear inert and the remainder have multiple cores. If the inert galaxies represent a non-evolving late-type population, then a Loveday-like LF ({alpha}=~-1.0) is ruled out for these types, and an LF with a steep faint end ({alpha}=~-1.5) is suggested. If multiple core structure indicates recent star formation, then the observed excess of faint blue field galaxies is likely a result of et evolutionary processes acting on a steep field LF for late-type/irregulars. The evolutionary mechanism is unclear, but 60% of the multiple-core irregulars show close companions. To reconcile a Marzke-like LF with the faint redshift surveys, this evolution must be preferentially occurring in the brightest late-type galaxies with z>=0.5 at m_I_=21.75mag.

HST

ID Object identification number --- MDS MDS field name --- WFPC2 WFPC2 CCD number (1=PC, 2, 3, 4=WFC) --- Xpos Original X pixel position on the WFPC2 CCD pix Ypos Original Y pixel position on the WFPC2 CCD pix RAh Right ascension (J2000.0) h RAm Right ascension (J2000.0) min RAs Right ascension (J2000.0) number=1 Relative RAs and DEs should be accurate to within 0.1". Absolute WFPC2 astrometry is only accurate to ~0.5"-1." s DE- Declination sign --- DEd Declination (J2000.0) deg DEm Declination (J2000.0) arcmin DEs Declination (J2000.0) number=1 Relative RAs and DEs should be accurate to within 0.1". Absolute WFPC2 astrometry is only accurate to ~0.5"-1." arcsec Imag Total I_814_ magnitude mag V-I Total (V-I) color mag SuBr Central I-band surface brightness within a radius of 0.2" mag/arcsec2 (V-I)c Central (V-I) color within a radius of 0.2" mag eps Image ellipticity e=1-a/b, computed from the outermost isophote --- Mtype Galaxy type number=2 0 = E, 1 = 5a, 2 = 5b, 3 = 5c, 4 = 5d, 5 = Irr, 6 = peculiar --- Radius Aperture radius used to determine the I-band magnitude pix James Marcout, Patricia Bauer CDS 1997Feb14 UNKNOWN UNKNOWN Prepared via OCR at CDS. J_ApJ_453_48.xml