The Possible z=0.83 Precursors of z=0 M* Early-type Cluster Galaxies

We examine the distribution of stellar masses of galaxies in MS 1054-03 and RX J0152.7-1357, two X-ray selected clusters of galaxies at z=0.83. Our stellar mass estimates, from spectral energy distribution fitting, reproduce the dynamical masses as measured from velocity dispersions and half-light radii with a scatter of 0.2 dex in the mass for early-type galaxies. When we restrict our sample of members to high stellar masses, > 1e11.1 Msun (M* in the Schechter mass function for cluster galaxies), we find that the fraction of early-type galaxies is 79 +/- 6% at z=0.83 and 87 +/- 6% at z=0.023 for the Coma cluster, consistent with no evolution. Previous work with luminosity-selected samples finds that the early-type fraction in rich clusters declines from =~80% at z=0 to =~60% at z=0.8. The observed evolution in the early-type fraction from luminosity-selected samples must predominately occur among sub-M* galaxies. As M* for field and group galaxies, especially late-types, is below M* for clusters galaxies, infall could explain most of the recent early-type fraction growth. Future surveys could determine the morphological distributions of lower mass systems which will confirm or refute this explanation.Comment: 5 pages in emulate ApJ format with three color figures. Accepted for publication in ApJ Letters, v642n2. Updated to correct grammatical and typographic errors found by the journa

Mass-Selection and the Evolution of the Morphology-Density Relation from z=0.8 to z=0

We examined the morphology-density relations for galaxy samples selected by luminosity and by mass in each of five massive X-ray clusters from z=0.023 to 0.83 for 674 spectroscopically-confirmed members. Rest-frame optical colors and visual morphologies were obtained primarily from Hubble Space Telescope images. Morphology-density relations (MDR) are derived in each cluster from a complete, luminosity-selected sample of 452 galaxies with a magnitude limit M_V < M^{*}_{V} + 1. The change in the early-type fraction with redshift matches previous work for massive clusters of galaxies. We performed a similar analysis, deriving MDRs for complete, mass-selected samples of 441 galaxies with a mass-limit of 10^{10.6} M_{\sun}. Our mass limit includes faint objects, the equivalent of =~1 mag below L^{*} for the red cluster galaxies, and encompasses =~70% of the stellar mass in cluster galaxies. The MDRs in the mass-selected sample at densities of Sigma > 50 galaxies Mpc^{-2} are similar to those in the luminosity-selected sample but show larger early-type fractions. However, the trend with redshift in the fraction of elliptical and S0 galaxies with masses > 10^{10.6} M_{\sun} differs significantly between the mass- and luminosity-selected samples. The clear trend seen in the early-type fraction from z=0 to z=~ 0.8 is not found in mass-selected samples. The early-type galaxy fraction changes much less, and is consistent with being constant at 92% +/- 4% at \Sigma> 500 galaxies Mpc^{-2} and 83 +/- 3% at 50 < \Sigma < 500 galaxies Mpc^{-2}. This suggests that galaxies of mass lower than > 10^{10.6} M_{\sun} play a significant role in the evolution of the early-type fraction in luminosity-selected samples. (Abstract abridged)Comment: 18 pages in emulate ApJ format, with 10 color figures, Accepted to ApJ. Version updated to reflect published version, includes new references and a correction to table

Harmonic analysis of iterated function systems with overlap

In this paper we extend previous work on IFSs without overlap. Our method involves systems of operators generalizing the more familiar Cuntz relations from operator algebra theory, and from subband filter operators in signal processing.Comment: 37 page

Cluster vs. Field Elliptical Galaxies and Clues on their Formation

Using new observations for a sample of 931 early-type galaxies we investigate whether the \mg2--\so relation shows any dependence on the local environment. The galaxies have been assigned to three different environments depending on the local overdensity: clusters, groups, and field, having used our completeredshift database to guide the assignment of galaxies. It is found that cluster, group and field early-type galaxies follow almost identical \mg2--\so\ relations, with the largest \mg2 zero-point difference (clusters minus field) being only $0.007\pm 0.002$ mag. No correlation of the residuals is found with the morphological type or the bulge to disk ratio. Using stellar population models in a differential fashion, this small zero-point difference implies a luminosity-weighted age difference of only $\sim 1$ Gyr between the corresponding stellar populations, with field galaxies being younger. The mass-weighted age difference could be significantly smaller, if minor events of late star formation took place preferentially in field galaxies. We combine these results with the existing evidence for the bulk of stars in cluster early-type galaxies having formed at very high redshift, and conclude that the bulk of stars in galactic spheroids had to form at high redshifts (z\gsim 3), no matter whether such spheroids now reside in low or high density regions. The cosmological implications of these findings are briefly discussed.Comment: 16 pages, 2 figures, accepted for publication in the ApJ.

Finding cool subdwarfs using a V-J reduced proper-motion diagram: Stellar parameters for 91 candidates

We present the results of a search for cool subdwarfs for which our candidates were drawn from a V-J reduced proper-motion diagram constructed by Salim & Gould (2002). Kinematic (U, V, and W) and self-consistent stellar parameters (Teff, log g, [Fe/H], and V_t) are derived for 91 candidate subdwarfs based on high resolution spectra. The observed stars span 3900K < Teff < 6200K and -2.63 < [Fe/H] < 0.25 including only 3 giants (log g < 4.0). Of the sample, 77 stars have MgH lines present in their spectra. With more than 56% of our candidate subdwarfs having [Fe/H] < -1.5, we show that the V-J reduced proper-motion diagram readily identifies metal-poor stars.Comment: PASP (in press

Galaxy Evolution, Deep Galaxy Counts and the Near-IR Cosmic Infrared Background

Accurate synthetic models of stellar populations are constructed and used in evolutionary models of stellar populations in forming galaxies. Following their formation, the late type galaxies are assumed to follow the Schmidt law for star formation, while early type galaxies are normalized to the present-day fundamental plane relations assumed to mimic the metallicity variations along their luminosity sequence. We then compute predictions of these models for the observational data at early epochs for various cosmological parameters $\Omega, \Omega_\Lambda$ and $H_0$. We find good match to the metallicity data from the damped $L_\alpha$ systems and the evolution of the luminosity density out to $z\simeq 1$. Likewise, our models provide good fits for low values of $\Omega$ to the deep number counts of galaxies in all bands where data is available; this is done without assuming existence of extra populations of galaxies at high $z$. Our models also match the data on the redshift distribution of galaxy counts in $B$ and $K$ bands. We compute the predicted mean levels and angular distribution of the cosmic infrared background produced from the early evolution of galaxies. The predicted fluxes and fluctuations are still below the current observational limits, but not by a large factor. Finally, we find that the recent detection of the diffuse extragalactic light in the visible bands requires for our models high redshift of galaxy formation, $z_f \geq$(3-4); otherwise the produced flux of the extragalactic light at optical bands exceeds the current observational limits.Comment: Accepted to Ap

The Fundamental Plane of Gravitational Lens Galaxies and The Evolution of Early-Type Galaxies in Low Density Environments

Most gravitational lenses are early-type galaxies in relatively low density environments -- a ``field'' rather than a ``cluster'' population. We show that field early-type galaxies with 0 < z < 1, as represented by the lens galaxies, lie on the same fundamental plane as those in rich clusters at similar redshifts. We then use the fundamental plane to measure the combined evolutionary and K-corrections for early-type galaxies in the V, I and H bands. Only for passively evolving stellar populations formed at z > 2 (H_0=65 km/s Mpc, Omega_0=0.3, Lambda_0=0.7) can the lens galaxies be matched to the local fundamental plane. The high formation epoch and the lack of significant differences between the field and cluster populations contradict many current models of the formation history of early-type galaxies. Lens galaxy colors and the fundamental plane provide good photometric redshift estimates with an empirical accuracy of -0.03 +/- 0.11 for the 17 lenses with known redshifts. A mass model dominated by dark matter is more consistent with the data than either an isotropic or radially anisotropic constant M/L mass model, and a radially anisotropic model is better than an isotropic model.Comment: 36 pages, 9 figures, 6 tables. ApJ in press. Final version contains more observational dat

The Stellar Population Histories of Early-Type Galaxies. II. Controlling Parameters of the Stellar Populations

We analyze single-stellar-population (SSP) equivalent parameters for 50 local elliptical galaxies as a function of their structural parameters. These galaxies fill a two-dimensional plane in the four-dimensional space of [Z/H], log t, log $\sigma$, and [E/Fe]. SSP age and velocity dispersion can be taken as the two independent parameters that specify a galaxy's location in this ``hyperplane.'' The hyperplane can be decomposed into two sub-relations: (1) a ``Z-plane,'' in which [Z/H] is a linear function of log $\sigma$ and log t; and (2) a relation between [E/Fe] and $\sigma$ in which [E/Fe] is larger in high-$\sigma$ galaxies. Cluster and field ellipticals follow the same hyperplane, but their ($\sigma$,t) distributions within it differ. Nearly all cluster galaxies are old; the field ellipticals span a large range in SSP age. The tight Mg--$\sigma$ relations of these ellipticals can be understood as two-dimensional projections of the metallicity hyperplane showing it edge-on; the tightness of these relations does not necessarily imply a narrow range of ages at fixed $\sigma$. The relation between [E/Fe] and $\sigma$ is consistent with a higher effective yield of Type II SNe elements at higher $\sigma$. The Z-plane is harder to explain and may be a powerful clue to star formation in elliptical galaxies if it proves to be general. Present data favor a ``frosting'' model in which low apparent SSP ages are produced by adding a small frosting of younger stars to an older base population. If the frosting abundances are close to or slightly greater than the base population, simple two-component models run along lines of constant $\sigma$ in the Z-plane, as required. This favors star formation from well-mixed pre-enriched gas rather than unmixed low-metallicity gas from an accreted object. (Abridged)Comment: To be published in the June 2000 issue of the Astronomical Journal. 28 pages, 13 figures, uses emulateap

On the relation between circular velocity and central velocity dispersion in high and low surface brightness galaxies

In order to investigate the correlation between the circular velocity Vc and the central velocity dispersion of the spheroidal component sigma_c, we analyzed these quantities for a sample of 40 high surface brightness disc galaxies (hereafter HSB), 8 giant low surface brightness spiral galaxies (hereafter LSB), and 24 elliptical galaxies characterized by flat rotation curves. We find that the Vc-sigma_c relation is descri ed by a linear law out to velocity dispersions as low as sigma_c~50km/s, while in previous works a power law was adopted for galaxies with sigma_c>80k/ms. Elliptical galaxies with Vc based on dynamical models or directly derived from the HI rotation curves follow the same relation as the HSB galaxies in the Vc-sigma_c plane. On the contrary, the LSB galaxies follow a different relation, since most of them show either higher Vc (or lower sigma_c) with respect to the HSB galaxies. This argues against the relevance of baryon collapse in the radial density profile of the dark matter haloes of LSB galaxies. (abridged)Comment: 18 pages, 4 figures, ApJ in pres

Dzyaloshinsky-Moriya Spin Canting in the LTT Phase of La2-x-yEuySrxCuO4

The Cu spin magnetism in La2-x-yEuySrxCuO4 (x<=0.17; y<=0.2) has been studied by means of magnetization measurements up to 14 T. Our results clearly show that in the antiferromagnetic phase Dzyaloshinsky-Moriya (DM)superexchange causes Cu spin canting not only in the LTO phase but also in the LTLO and LTT phases. In La1.8Eu0.2CuO4 the canted DM-moment is about 50% larger than in pure La2CuO4 which we attribute to the larger octahedral tilt angle. We also find clear evidence that the size of the DM-moment does not change significantly at the structural transition at T_LT from LTO to LTLO and LTT. The most important change induced by the transition is a significant reduction of the magnetic coupling between the CuO2 planes. As a consequence, the spin-flip transition of the canted Cu spins which is observed in the LTO phase for magnetic field perpendicular to the CuO2 planes disappears in the LTT phase. The shape of the magnetization curves changes from the well known spin-flip type to a weak-ferromagnet type. However, no spontaneous weak ferromagnetism is observed even at very low temperatures, which seems to indicate that the interlayer decoupling in our samples is not perfect. Nonetheless, a small fraction (<15%) of the DM-moments can be remanently magnetized throughout the entire antiferromagnetically ordered LTT/LTLO phase, i.e. for T<T_LT and x<0.02. It appears that the remanent DM-moment is perpendicular to the CuO2 planes. For magnetic field parallel to the CuO2 planes we find that the critical field of the spin-flop transition decreases in the LTLO phase, which might indicate a competition between different in-plane anisotropies. To study the Cu spin magnetism in La2-x-yEuySrxCuO4, a careful analysis of the Van Vleck paramagnetism of the Eu3+ ions was performed.Comment: 22 pages, 27 figure