The DEEP Groth Strip Survey. X. Number Density and Luminosity Function of Field E/S0 Galaxies atz< 1

Abstract

We present the luminosity function and color-redshift relation of a magnitude-limited sample of 145 mostly red field E/S0 galaxies at zd1 from the DEEP Groth Strip Survey (GSS). Using nearby galaxy images as a training set, we develop a quantitative method to classify E/S0 galaxies based on smoothness, symmetry, and bulge-to-total light ratio. Using this method, we identify 145 E/S0's at 16:5 < I < 22 within the GSS, for which 44 spectroscopic redshifts (z spec ) are available. Most of the galaxies with spectroscopic redshifts (86%) form a '' red envelope '' in the redshift-color diagram, consistent with predictions of spectral synthesis models in which the dominant stellar population is formed at redshifts ze1:5. We use the tight correlation between VÀI and z spec for this red subset to estimate redshifts of the remaining E/S0's to an accuracy of $10%, with the exception of a small number (16%) of blue interlopers at low redshift that are quantitatively classified as E/S0's but are not contained within the red envelope. Constructing a luminosity function of the full sample of 145 E/S0's, we find that there is about 1.1-1.9 mag brightening in rest-frame B-band luminosity back to z ' 0:8 from z ¼ 0, consistent with other studies. Together with the red colors, this brightening is consistent with models in which the bulk of stars in red field E/S0's formed before z for e1:5 and have been evolving rather quiescently, with few large starbursts since then. Evolution in the number density of field E/ S0 galaxies is more difficult to measure, and uncertainties in the raw counts and their ratio to local samples might amount to as much as a factor of 2. Within that uncertainty, the number density of red E/S0's to z ' 0:8 seems relatively static, being comparable to or perhaps moderately less than that of local E/S0's, depending on the assumed cosmology. A doubling of E/S0 number density since z ¼ 1 can be ruled out with high confidence (97%) if m ¼ 1. Taken together, our results are consistent with the hypothesis that the majority of luminous field E/S0's were already in place by z $ 1, that the bulk of their stars were already fairly old, and that their number density has not changed by large amounts since then.

Improved Cosmological Constraints from Gravitational Lens Statistics

“…This noevolution assumption is usually justified by appealing to results from galaxy number counts ( Im et al 2002;Schade et al 1999) and the redshift distribution of lens galaxies (Ofek et al 2003), which are consistent with the hypothesis that the early-type population evolves only through passive luminosity evolution. However, the observational status of early-type evolution has been controversial (Lin et al 1999;Kauffmann et al 1996;Totani & Yoshii 1998;Fried et al 2001), and the observational uncertainties are large enough that dynamical number or mass evolution in the early-type galaxy population cannot be ruled out.…”

“…This is equivalent to saying that massive early-type 7 galaxies have not undergone significant mergers since z $ 1. Although galaxy counts appear to be consistent with this ''no-evolution'' model in the concordance cosmology (Schade et al 1999;Im et al 2002), the observational uncertainties are still large, and other possibilities cannot be ruled out. The problem for lens statistics is that evolution is degenerate with cosmology.…”

The DEEP Groth Strip Survey. IX. Evolution of the Fundamental Plane of Field Galaxies

“…Since we require absorption lines, the sample consists of predominantly early-type galaxies. Im et al (2002) identify early-type galaxies from the DEEP sample based on structural parameters; 21 galaxies (58%) from our sample are classified as early-type galaxies in that paper. Im et al (2002) provide a detailed description of the separation into early-and late-type galaxies.…”

“…Im et al (2002) identify early-type galaxies from the DEEP sample based on structural parameters; 21 galaxies (58%) from our sample are classified as early-type galaxies in that paper. Im et al (2002) provide a detailed description of the separation into early-and late-type galaxies. This separation relies primarily on bulge fraction (> 0.4), smoothness, and symmetry, but not color.…”

“…The colors represent a logarithmic stretch using the V and I images only. If the text on the bottom of an image is red, then that galaxy is an early-type (from Im et al 2002); otherwise the text is blue.…”