Luminosity Evolution Of Early-type Galaxies Research Articles

The Tolman Surface Brightness Test for the Reality of the Expansion. IV. A Measurement of the Tolman Signal and the Luminosity Evolution of Early-Type Galaxies

We review a sample of the early literature in which the reality of the expansion is discussed. Hubble's reluctance, even as late as 1953, to accept the expansion as real is explained as due to his use of equations for distances and absolute magnitudes of redshifted galaxies that do not conform to the modern Mattig equations of the standard model. The Tolman surface brightness test, once the only known test for the reality of the expansion, is contrasted with three other modern tests. These are (1) the time dilation in Type Ia supernovae light curves, (2) the temperature of the relic radiation as a function of redshift, and (3) the surface brightness normalization of the Planckian shape of the relic radiation. We search for the Tolman surface brightness depression with redshift using the Hubble Space Telescope (HST) data from Paper III for 34 early-type galaxies from the three clusters Cl 1324+3011 (z = 0.76), Cl 1604+4304 (z = 0.90), and Cl 1604+4321 (z = 0.92). Depressions of the surface brightness relative to the zero-redshift fiducial lines in the mean surface brightness–logarithm of the linear radius diagrams of Paper I are found for all three clusters. Expressed as the exponent, n, in 2.5 log (1 + z)n mag, the value of n averaged over Petrosian radii of η = 1.7 and η = 2.0 for all three clusters is n = 2.59 ± 0.17 in the R band and 3.37 ± 0.13 in the I band for a q0 = 1/2 model. The sensitivity of the result to the assumed value of q0 is shown to be less than 23% between q = 0 and +1. The conclusion is that the exponent on (1 + z) varies from 2.28 to 2.81 (± 0.17) in the R band and 3.06 to 3.55 (± 0.13) in the I band, depending on the value of q0. For a true Tolman signal with n = 4, the luminosity evolution in the look-back time, expressed as the exponent in 2.5 log (1 + z)4-n mag, must then be between 1.72 to 1.19 (± 0.17) in the R band and 0.94 to 0.45 (± 0.13) in the I band. We show that this is precisely the range expected from the evolutionary models of Bruzual and Charlot and other measurements of the luminosity evolution of early-type galaxies. We conclude that the Tolman surface brightness test is consistent with the reality of the expansion to within the combined errors of the observed ⟨SB⟩ depression and the theoretical correction for luminosity evolution. We have also used the high-redshift HST data to test the "tired light" speculation for a nonexpansion model for the redshift. The HST data rule out the tired light model at a significance level of better than 10 σ.

Morphological Evolution and the Ages of Early‐Type Galaxies in Clusters

Morphological and spectroscopic studies of high-redshift clusters indicate that a significant fraction of present-day, early-type galaxies was transformed from star-forming galaxies at z < 1. On the other hand, the slow luminosity evolution of early-type galaxies and the low scatter in their color-magnitude relation indicate a high formation redshift of their stars. In this paper we construct models that reconcile these apparently contradictory lines of evidence, and we quantify the effects of morphological evolution on the observed photometric properties of early-type galaxies in distant clusters. We show that in the case of strong morphological evolution the apparent luminosity and color evolution of early-type galaxies are similar to those of a single-age stellar population formed at z = ∞, irrespective of the true star formation history of the galaxies. Furthermore, the scatter in age, and hence the scatter in color and luminosity, is approximately constant with redshift. These results are consequences of the bias: the progenitors of the youngest low-redshift, early-type galaxies drop out of the sample at high redshift. We construct models that reproduce the observed evolution of the number fraction of early-type galaxies in rich clusters and their color and luminosity evolution simultaneously. Our modeling indicates that ~50% of early-type galaxies were transformed from other galaxy types at z < 1, and their progenitor galaxies may have had roughly constant star formation rates prior to morphological transformation. The effect of the progenitor bias on the evolution of the mean M/L ratio and color can be estimated. The progenitor bias is a linear function of the scatter in the color-magnitude relation produced by age variations and is maximal if the observed scatter is entirely due to age differences. After correcting the observed evolution of the mean M/LB ratio for the maximum progenitor bias, we find that the mean luminosity-weighted formation redshift of stars in early-type galaxies z* = 3.0 for Ωm = 0.3 and ΩΛ = 0 and z* = 2.0 for Ωm = 0.3 and ΩΛ = 0.7. Our analysis places the star formation epoch of early-type galaxies later than previous studies, which ignored the effects of progenitor bias. The results are consistent with the idea that (some) Lyman break galaxies are star-forming building blocks of massive early-type galaxies in clusters.

Luminosity Evolution of Early-Type Galaxies to [CLC][ITAL]z[/ITAL][/CLC] = 0.83: Constraints on Formation Epoch and Ω

We present deep spectroscopy with the Keck telescope of eight galaxies in the luminous X-ray cluster MS1054-03 at z=0.83. The data are combined with imaging observations from the Hubble Space Telescope (HST). The spectroscopic data are used to measure the internal kinematics of the galaxies, and the HST data to measure their structural parameters. Six galaxies have early-type spectra, and two have E+A spectra. The galaxies with early-type spectra define a tight Fundamental Plane (FP) relation. The evolution of the mass-to-light ratio is derived from the FP. The M/L ratio evolves as \Delta log M/L_B \propto -0.40 z (Omega_m=0.3, Omega_Lambda=0). The observed evolution of the M/L ratio provides a combined constraint on the formation redshift of the stars, the IMF, and cosmological parameters. For a Salpeter IMF (x=2.35) we find that z_form>2.8 and Omega_m 0: z_form>1.7 if Omega_m=0.3 and Omega_Lambda=0.7. At present the limiting factor in constraining z_form and Omega from the observed luminosity evolution of early-type galaxies is the poor understanding of the IMF. We find that if Omega_m=1 the IMF must be significantly steeper than the Salpeter IMF (x>2.6).

Modelling the number counts of early-type galaxies by pure luminosity evolution

In this paper, we explore the plausible luminosity evolution of early-type galaxies in different cosmological models by constructing a set of pure luminosity evolution (PLE) models via the choices of the star formation rate (SFR) parameters and formation redshift $z_f$ of galaxies, with the observational constraints derived from the Hubble Space Telescope (HST) morphological number counts for elliptical and S0 galaxies of the Medium Deep Survey (MDS) and the Hubble Deep Field (HDF). We find that the number counts of early-type galaxies can be explained by the pure luminosity evolution models, without invoking exotic scenarios such as merging or introducing an additional population. But the evolution should be nearly passive, with a high $z_f$ assumed. The conclusion is valid in all of the three cosmological models we adopted in this paper. We also present the redshift distributions for three bins of observed magnitudes in F814w pass-band, to show at which redshift are the objects that dominate the counts at a given magnitude. The predictions of the redshift distribution of $22.5<b_j<24.0$ are also presented for comparison with future data.