Resurrection of Traditional Luminosity Evolution Models to Explain Faint Field Galaxies

We explore the nature of the evolution of faint field galaxies by assuming that the local luminosity function is not well defined. We use a non-negative least squares technique to derive a near optimal set of local luminosity functions for different spectral types of galaxies by fitting to the observed optical and near-infrared counts, B-R colors, and redshift distributions for galaxies with 15 < B < 27. We report here the results of using only traditional luminosity evolution (ie. the photometric evolution of stars in a galaxy over time given reasonable assumptions of the form of the star formation history for various galaxy types), and simple galaxy reddening and find excellent fits to the observed data to B = 27. We conclude that models more exotic than traditional luminosity evolution are not yet required to explain existing faint field galaxy data and thus the need for contributions by mergers or new populations of galaxies is at least 5x less than previously estimated.Comment: 9 pages + 1 table + 4 figures; uuencoded tar compressed postscript; to be published in The Astrohysical Journal Letter

A deep redshift survey of field galaxies. Comments on the reality of the Butcher-Oemler effect

A spectroscopic survey of over 400 field galaxies has been completed in three fields for which we have deep UBVI photographic photometry. The galaxies typically range from B=20 to 22 and possess redshifts z from 0.1 to 0.5 that are often quite spiky in distribution. Little, if any, luminosity evolution is observed up to redshifts z approx 0.5. By such redshifts, however, an unexpectedly large fraction of luminous galaxies has very blue intrinsic colors that suggest extensive star formation; in contrast, the reddest galaxies still have colors that match those of present-day ellipticals

Two Conditions for Galaxy Quenching: Compact Centres and Massive Haloes

We investigate the roles of two classes of quenching mechanisms for central and satellite galaxies in the SDSS ($z<0.075$): those involving the halo and those involving the formation of a compact centre. For central galaxies with inner compactness $\Sigma_{\rm 1kpc} \sim 10^{9-9.4}M_{\odot} {\rm kpc}^{-2}$, the quenched fraction $f_{q}$ is strongly correlated with $\Sigma_{\rm 1kpc}$ with only weak halo mass $M_{\rm h}$ dependence. However, at higher and lower $\Sigma_{\rm 1kpc}$, sSFR is a strong function of $M_{\rm h}$ and mostly independent of $\Sigma_{\rm 1kpc}$. In other words, $\Sigma_{\rm 1kpc} \sim 10^{9-9.4} M_{\odot} {\rm kpc}^{-2}$ divides galaxies into those with high sSFR below and low sSFR above this range. In both the upper and lower regimes, increasing $M_{\rm h}$ shifts the entire sSFR distribtuion to lower sSFR without a qualitative change in shape. This is true even at fixed $M_{*}$, but varying $M_{*}$ at fixed $M_{\rm h}$ adds no quenching information. Most of the quenched centrals with $M_{\rm h} > 10^{11.8}M_{\odot}$ are dense ($\Sigma_{\rm 1kpc} > 10^{9}~ M_{\odot} {\rm kpc}^{-2}$), suggesting compaction-related quenching maintained by halo-related quenching. However, 21% are diffuse, indicating only halo quenching. For satellite galaxies in the outskirts of halos, quenching is a strong function of compactness and a weak function of host $M_{\rm h}$. In the inner halo, $M_{\rm h}$ dominates quenching, with $\sim 90\%$ of the satellites being quenched once $M_{\rm h} > 10^{13}M_{\odot}$. This regional effect is greatest for the least massive satellites. As demonstrated via semi-analytic modelling with simple prescriptions for quenching, the observed correlations can be explained if quenching due to central compactness is rapid while quenching due to halo mass is slow.Comment: 16 pages, 11 figures, MNRAS accepte

Spatially Resolved Stellar Populations of Eight GOODS-South Active Galactic Nuclei at z ~ 1

We present a pilot study of the stellar populations of eight active galactic nucleus (AGN) hosts at z ~ 1 and compare with (1) lower redshift samples and (2) a sample of nonactive galaxies of similar redshift. We utilize K' images in the Great Observatories Origins Deep Survey South field obtained with the laser guide star adaptive optics system at Keck Observatory. We combine these K' data with B, V, i, and z imaging from the Advanced Camera for Surveys on Hubble Space Telescope to give multicolor photometry at a matched spatial resolution better than 100 mas in all bands. The hosts harbor AGNs as inferred from their high X-ray luminosities (LX > 10^42 erg s^–1) or mid-IR colors. We find a correlation between the presence of younger stellar populations and the strength of the AGN, as measured with [O III] line luminosity or X-ray (2-10 keV) luminosity. This finding is consistent with similar studies at lower redshift. Of the three Type II galaxies, two are disk galaxies and one is of irregular type, while in the Type I sample there are only one disk-like source and four sources with smooth, elliptical/spheroidal morphologies. In addition, the mid-IR spectral energy distributions of the strong Type II AGNs indicate that they are excited to Luminous InfraRed Galaxy (LIRG) status via galactic starbursting, while the strong Type I AGNs are excited to LIRG status via hot dust surrounding the central AGN. This supports the notion that the obscured nature of Type II AGNs at z ~ 1 is connected with global starbursting and that they may be extincted by kpc-scale dusty features that are by-products of this starbursting