The Evolution of Ellipticals, Spirals and Irregulars: Overcoming Selection Bias

The Hubble Deep Fields represent our best opportunity for probing galaxy evolution over a substantive look-back time. However as with any dataset the HDFs are prone to selection biases. These biases are extremely severe beyond z \~1.25 such that a meaningful interpretation of generic galaxy evolution is not possible. We can however extract well defined volume-limited samples at z < 1. The data are entirely consistent with passive/null-evolution for ellipticals, spirals and irregulars however this concluion is tempered by small number statistics. Alas stringent constraints on galaxy evolution await an order of magnitude increase in the number of HDFs.Comment: To appear in Proc. of the ESO/ECF/STSCI workshop on Deep Fields, Garching Oct 2000, (Publ: Springer

The decade of galaxy formation: pitfalls in the path ahead

At the turn of the decade we arguably move from the era of precision cosmology to the era of galaxy formation. One approach to this problem will be via the construction of comprehensive galaxy samples. In this review I take the opportunity to highlight a number of challenges which must be overcome before we can use such data to construct a robust empirical blueprint of galaxy evolution. The issues briefly highlighted here are: the Hubble tuning fork versus galaxy components, the hierarchy of structure, the accuracy of structural decompositions, galaxy photometry, incompleteness, cosmic variance, photometric versus spectroscopic redshifts, wavelength bias, dust attenuation, and the disconnect with theory. These concerns essentially form one of the key motivations of the GAMA survey which, as one of its goals, will establish a complete comprehensive kpc-resolution 3D multi-wavelength (UV-Opt-IR-Radio) database of 250k galaxy systems to z <0.5.Comment: Review paper (12 pages, 11 figures) in "Hunting for the Dark: The Hidden Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P.Debattista & C.C.Popescu, AIP Conf. Ser., in pres

The Ccontribution of normal, dim and dwarf galaxies to the local luminosity density

From the Hubble Deep Field catalog presented in Driver et al. (1998) we derive the local (0.3 < z < 0.5) Bivariate Brightness Distribution (BBD) of field galaxies within a 326 Mpc**3 Volume-Limited sample. The sample contains 47 galaxies which uniformally sample the underlying galaxy population within the specified redshift, magnitude and surface brightness limits (0.3 < z < 0.5, -21.3 < M_{B} < -13.7 mags, 18.0 < mu_{B} < 24.55 mags/sq arcsec). We conclude: (i) A luminosity-surface brightness relation exists for both the field and cluster galaxy populations, M_{B} ~ 1.5 mu_{e} - 50, (ii) Luminous low surface brightness galaxies account for <10% of the L* population, (iii) Low luminosity low surface brightness galaxies outnumber Hubble types by a factor of ~ 1.4, however their space density is NOT sufficient to explain the faint blue excess either by themselves or as faded remnants. In terms of the local luminosity density and galaxy dynamical mass budget, normal galaxies (i.e. Hubble tuning fork) contribute 88% and 72% respectively. This compares to 7% and 12% for dim galaxies and 5% and 16% for dwarf galaxies (within the above specified limits).Comment: Accepted for publication in Astrophysical Journal Letters. Nine pages and two figure

Are disappearing dwarfs just lying low ?

Recent redshift surveys have shown that the excess galaxies seen in faint galaxy number counts (above those expected given the local galaxy luminosity function) are not evolved giants at high redshifts, but low to moderate luminosity objects at more modest redshifts. This has led to the suggestion that there was once an additional population of dwarf galaxies which has since disappeared, ie. there is non-conservation of galaxy number. Here we investigate the possibility that these disappearing dwarfs have actually evolved to become the population of very low surface brightness galaxies which is now being detected in nearby clusters.Comment: 12 pages, 7 figures. Figures available from http://www.phys.unsw.edu.au/~spd/bib.htm