213 research outputs found
Mass dependent Evolution of Field Early-Type Galaxies Since z=1
We present the Fundamental Plane (FP) of field early-type galaxies at
0.5<z<1.0. Our project is a continuation of our efforts to understand the
formation and evolution of early-type galaxies in different environments. The
target galaxies were selected from the comprehensive and homogeneous data set
of the Gemini/HST Galaxy Cluster Project. The distant field early-type galaxies
follow a steeper FP relation compared to the local FP. The change in the slope
of the FP can be interpreted as a mass-dependent evolution. Similar results
have been found for cluster early-type galaxies in high redshift galaxy
clusters at 0.8<z<1. Therefore, the slope change of the FP appears to be
independent of the environment of the galaxies.Comment: 2 pages, 1 figure, to appear in the proceedings of the IAU Symposium
no. 262, "Stellar Populations - Planning for the Next Decade", eds. G. R.
Bruzual and S. Charlo
Star Clusters in M 31. IV. A Comparative Analysis of Absorption Line Indices in Old M 31 and Milky Way Clusters
We present absorption line indices measured in the integrated spectra of
globular clusters both from the Galaxy and from M 31. Our samples include 41
Galactic globular clusters, and more than 300 clusters in M 31. The conversion
of instrumental equivalent widths into the Lick system is described, and
zero-point uncertainties are provided. Comparison of line indices of old M 31
clusters and Galactic globular clusters suggests an absence of important
differences in chemical composition between the two cluster systems. In
particular, CN indices in the spectra of M 31 and Galactic clusters are
essentially consistent with each other, in disagreement with several previous
works. We reanalyze some of the previous data, and conclude that reported CN
differences between M 31 and Galactic clusters were mostly due to data
calibration uncertainties. Our data support the conclusion that the chemical
compositions of Milky Way and M 31 globular clusters are not substantially
different, and that there is no need to resort to enhanced nitrogen abundances
to account for the optical spectra of M 31 globular clusters.Comment: 72 pages, including 15 figures and 14 tables. Published by the
Astronomical Journa
RXJ0848.6+4453: The Evolution of Galaxy Sizes and Stellar Populations in a z=1.27 Cluster
RXJ0848.6+4453 (Lynx W) at redshift 1.27 is part of the Lynx Supercluster of
galaxies. Our analysis of stellar populations and star formation history in the
cluster covers 24 members and is based on deep optical spectroscopy from Gemini
North and imaging data from HST. Focusing on the 13 bulge-dominated galaxies
for which we can determine central velocity dispersions, we find that these
show a smaller evolution of sizes and velocity dispersions than reported for
field galaxies and galaxies in poorer clusters. The galaxies in RXJ0848.6+4453
populate the Fundamental Plane similar to that found for lower redshift
clusters with a zero point offset corresponding to an epoch of last star
formation at z_form= 1.95+-0.2. The spectra of the galaxies in RXJ0848.6+4453
are dominated by young stellar populations at all galaxy masses and in many
cases show emission indicating low level on-going star formation. The average
age of the young stellar populations (estimated from H-zeta) is consistent with
a major star formation episode 1-2 Gyr prior, which in turn agrees with
z_form=1.95. Galaxies dominated by young stellar populations are distributed
throughout the cluster. We speculate that low level star formation has not yet
been fully quenched in the center of this cluster may be because the cluster is
significantly poorer than other clusters previously studied at similar
redshifts, which appear to have very little on-going star formation in their
centers.Comment: Accepted for publication in Astronomical Journal. High-resolution
figures available from the first author by reques
The Integrated Spectrum of M67 and the Spectroscopic Age of M32
We construct an integrated spectrum of the intermediate-age, solar-metallicity Galactic cluster M67, from individual spectroscopic observations of bona fide cluster members. The spectrum so obtained is used as a template to test our stellar population synthesis models, in an age and metallicity regime where such models remain largely untested. As a result, we demonstrate that our models predict a spectroscopic age of 3.5 ± 0.5 Gyr for M67, which is the same age we obtain from fitting isochrones to the color-magnitude diagram of the cluster. Full consistency is reached when using either Hβ, Hγ, or Hδ as the age indicator. We also check if the models, when applied to the cluster integrated spectrum, predict elemental abundances in agreement with the known detailed abundance pattern of the cluster. The models also pass the latter test, by predicting the abundances of iron, magnesium, carbon, and nitrogen in agreement with detailed abundance analyses of cluster stars to within 0.1 dex. Encouraged by the high degree of consistency of our models, we apply them to the study of the integrated spectrum of the central 3'' of the compact elliptical galaxy M32. The resulting luminosity-weighted age of the galaxy ranges between 2 and 3.5 Gyr, depending on the age indicator adopted. According to our models, the center of M32 seems to have a supersolar iron abundance, ranging between [Fe/H] ~ +0.1 and +0.3, depending on the spectral index adopted. The light element magnesium seems to be underabundant in the center of M32 relative to iron by about ~0.1–0.2 dex, whereas the data are consistent with nearly solar carbon and nitrogen abundances relative to iron. We find that single-age, single-metallicity stellar population models with solar-scaled abundance patterns cannot fit all the Balmer and metal lines in the integrated spectrum of M32. In particular, there is a systematic trend in the sense that bluer absorption lines indicate a younger age and a higher metallicity. This slight inconsistency can be due either to (unaccounted for) abundance ratio effects on blue iron and Balmer line indices or to a spread of the ages of the stellar populations in M32. Current stellar population models cannot break this degeneracy at the level of accuracy required to address this problem
Population Synthesis in the Blue. I. Synthesis of the Integrated Spectrum of 47 Tucanae from Its Color‐Magnitude Diagram
We perform an empirical synthesis of the blue integrated spectrum of the metal-rich globular cluster 47 Tucanae, based directly on the color-magnitude diagram of the cluster coupled to a moderately high resolution spectral library. Freed from any significant dependence on theory, we are able to perform a fundamental test of the adequacy of the spectral library and its associated stellar parameters. Excellent fits are achieved for almost all absorption-line indices studied, provided the computations are corrected for two limitations of the spectral library, namely, the lack of a representative set of metal-poor giants and the absence of CN-strong stars. The latter effect is corrected by means of spectrum synthesis from model photospheres, considering the abundance pattern of CN-strong and CN-normal stars. We also need to perform a slight correction of the metallicity of the cluster (by -0.05 dex in relation to the standard value [Fe/H] = -0.7) in order to match the metal line index measurements in the cluster spectrum. After these relatively small adjustments, the overall spectral agreement is good. Good fits are achieved for Hβ, Hγ, Mg b, , Ca λ4227, and Fe λ4383, and only HδF is overpredicted. Thus, ages inferred from HδF are slightly older than the ages based on the other Balmer lines, by ~3 Gyr. The success of this exercise suggests that previous failures to synthesize the spectrum of 47 Tuc must have arisen from inadequacies in the theoretical evolutionary isochrones and/or luminosity functions. Such a possibility is considered in a companion paper
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