107 research outputs found
Medium-resolution Isaac Newton Telescope library of empirical spectra
A new stellar library developed for stellar population synthesis modelling is presented. The library consists of 985 stars spanning a large range in atmospheric parameters. The spectra were obtained at the 2.5-m Isaac Newton Telescope and cover the range λλ 3525-7500 Å at 2.3 Å (full width at half-maximum) spectral resolution. The spectral resolution, spectral-type coverage, flux-calibration accuracy and number of stars represent a substantial improvement over previous libraries used in population-synthesis model
Evidence for intermediate-age stellar populations in early-type galaxies from K-band spectroscopy
The study of stellar populations in early-type galaxies in different
environments is a powerful tool for constraining their star formation
histories. This study has been traditionally restricted to the optical range,
where dwarfs around the turn-off and stars at the base of the RGB dominate the
integrated light at all ages. The near-infrared spectral range is especially
interesting since in the presence of an intermediate-age population, AGB stars
are the main contributors. In this letter, we measure the near-infrared indices
NaI and D for a sample of 12 early-type galaxies in low density
environments and compare them with the Fornax galaxy sample presented by Silva
et al. (2008). The analysis of these indices in combination with Lick/IDS
indices in the optical range reveals i) the NaI index is a metallicity
indicator as good as C4668 in the optical range, and ii) D is a
tracer of intermediate-age stellar populations. We find that low-mass galaxies
in low density environments show higher NaI and D than those located
in Fornax cluster, which points towards a late stage of star formation for the
galaxies in less dense environments, in agreement with results from other
studies using independent methods.Comment: 7 pages, 3 figures, accepted for publication in ApJ
Medium-resolution Isaac Newton Telescope library of empirical spectra - II. The stellar atmospheric parameters
We present a homogeneous set of stellar atmospheric parameters (T-eff, log g, [Fe/H]) for MILES, a new spectral stellar library covering the range lambda lambda 3525-7500 angstrom at 2.3 angstrom (FWHM) spectral resolution. The library consists of 985 stars spanning a large range in atmospheric parameters, from super-metal-rich, cool stars to hot, metal-poor stars. The spectral resolution, spectral type coverage and number of stars represent a substantial improvement over previous libraries used in population synthesis models. The atmospheric parameters that we present here are the result of a previous, extensive compilation from the literature. In order to construct a homogeneous data set of atmospheric parameters we have taken the sample of stars of Soubiran, Katz & Cayrel, which has very well determined fundamental parameters, as the standard reference system for our field stars, and have calibrated and bootstrapped the data from other papers against it. The atmospheric parameters for our cluster stars have also been revised and updated according to recent metallicity scales, colour-temperature relations and improved set of isochrones
Near-Infrared Imaging of Early-Type Galaxies IV. The Physical Origins of the Fundamental Plane Scaling Relations
The physical origins of the Fundamental Plane (FP) scaling relations are
investigated for early-type galaxies observed at optical and near-infrared
wavelengths. The slope for the FP is shown to increase systematically with
wavelength from the U-band through the K-band. A distance-independent
construction of the observables is described which provides an accurate
measurement of the change in the FP slope between any pair of bandpasses. The
variation of the FP slope with wavelength is strong evidence of systematic
variations in stellar content along the elliptical galaxy sequence. The
intercept of the diagnostic relationship between log(D_K/D_V) and log(sigma_0)
shows no significant dependence on environment within the uncertainties of the
Galactic extinction corrections, demonstrating the universality of the stellar
populations contributions at the level of Delta(V-K)=0.03 mag to the zero-point
of the global scaling relations.
Several other constraints on the properties of early-type galaxies --- the
slope of the Mg_2-sigma_0 relation, the effects of stellar populations
gradients, and deviations of early-type galaxies from a dynamically homologous
family --- are included to construct an empirical, self-consistent model which
provides a complete picture of the underlying physical properties which are
varying along the early-type galaxy sequence. This empirical approach
demonstrates that there are significant systematic variations in both age and
metallicity along the elliptical galaxy sequence, and that a small, but
systematic, breaking of dynamical homology (or a similar, wavelength
independent effect) is required. Predictions for the evolution of the slope of
the FP with redshift are described. [abriged]Comment: to appear in The Astronomical Journal; 40 pages, including 10
Postscript figures and 3 tables; uses AAS LaTeX style file
Gradients of absorption-line strengths in elliptical galaxies
© 1999. The American Astronomical Society. All rights reserved. This is the final published version of the work, which was originally published at https://doi.org/10.1086/308092We have restudied line-strength gradients of 80 elliptical galaxies. Typical metallicity gradients of elliptical galaxies are Delta[Fe/H]/Delta log r similar or equal to -0.3, which is flatter than the gradients predicted by monolithic collapse simulations. The metallicity gradients do not correlate with any physical properties of galaxies, including central and mean metallicities, central velocity dispersions sigma(0), absolute B magnitudes M-B, absolute effective radii R-e, and dynamical masses of galaxies. By using the metallicity gradients, we have calculated mean stellar metallicities for individual ellipticals. Typical mean stellar metallicities are [[Fe/H]] similar or equal to -0.3 and range from [[Fe/H]] similar or equal to -0.8 to +0.3, which is contrary to what Gonzalez & Gorgas claimed; the mean metallicities of ellipticals are not universal. The mean metallicities correlate well with sigma(0) and dynamical masses, though relations for M-B and R-e include significant scatters. We find fundamental planes defined by surface brightnesses SBe, [[Fe/H]], and R-e (or M-B), the scatters of which are much smaller than those of the [[Fe/H]]-R-e (or [[Fe/H]]-M-B) relations. The [[Fe/H]]-log sigma(0) relation is nearly parallel to the [Fe/H](0)-log sigma(0) relation but systematically lower by 0.3 dex; thus the mean metallicities are about one-half of the central values. The metallicity-mass relation or, equivalently, the color-magnitude relation of ellipticals holds not only for the central parts of galaxies but also for entire galaxies. Assuming that Mg-2 and Fe-1 give [Mg/H] and [Fe/H], respectively, we find [[Mg/Fe]] similar or equal to +0.2 in most of elliptical galaxies. [[Mg/Fe]] shows no correlation with galaxy mass tracers such as sigma(0), in contrast to what was claimed for the central [Mg/Fe]. This can be most naturally explained if the star formation had stopped in elliptical galaxies before the bulk of Type Ia supernovae began to occur. Elliptical galaxies can have significantly different metallicity gradients and [[Fe/H]], even if they have the same galaxy mass. This may result from galaxy mergers, but no evidence is found from presently available data to support the same origin for metallicity gradients, the scatters around the metallicity-mass relation, and dynamical disturbances. This may suggest that the scatters have their origin at the formation epoch of galaxies.Peer reviewe
The Iron Discrepancy in Elliptical Galaxies after ASCA
We present estimates for the iron content of the stellar and diffused
components of elliptical galaxies, as derived respectively from integrated
optical spectra and from ASCA X-ray observations. A macroscopic discrepancy
emerges between the expected iron abundances in the hot interstellar medium
(ISM) and what is indicated by the X-ray observations, especially when
allowance is made for the current iron enrichment by Type Ia supernovae. This
strong discrepancy, that in some extreme instances may be as large as a factor
of , calls into question our current understanding of supernova
enrichment and chemical evolution of galaxies. We discuss several astrophysical
implications of the inferred low iron abundances in the ISM, including the
chemical evolution of galaxies and cluster of galaxies, the evolution of gas
flows in ellipticals, and the heating of the intracluster medium. Some of the
consequences appear hard to accept, and in the attempt to avoid some of these
difficulties we explore ways of hiding or diluting iron in the ISM of
ellipticals. None of these possibilities appears astrophysically plausible, and
we alternatively rise the question of the reliability of iron-L line
diagonostic tools. Various thin plasma emission models are shown to give iron
abundances that may differ significantly, especially at low temperatures (kT
\lsim 1 keV). From a collection of ASCA and other X-ray observatory data, it
is shown that current thin plasma codes tend to give very low iron abundances
when the temperature of the objects is below keV. We conclude that --
besides rethinking the chemical evolution of galaxies -- one should also
consider the possibility that existing thin plasma models may incorporate
inaccurate atomic physics for the ions responsible for the iron-L complex.Comment: 39 pages, TeX file, 5 figures, Accepted for publication in the Ap
The relation between stellar populations, structure and environment for dwarf elliptical galaxies from the MAGPOP-ITP
Dwarf galaxies, as the most numerous type of galaxy, offer the potential to
study galaxy formation and evolution in detail in the nearby Universe. Although
they seem to be simple systems at first view, they remain poorly understood. In
an attempt to alleviate this situation, the MAGPOP EU Research and Training
Network embarked on a study of dwarf galaxies named MAGPOP-ITP (Peletier et
al., 2007). In this paper, we present the analysis of a sample of 24 dwarf
elliptical galaxies (dEs) in the Virgo Cluster and in the field, using optical
long-slit spectroscopy. We examine their stellar populations in combination
with their light distribution and environment. We confirm and strengthen
previous results that dEs are, on average, younger and more metal-poor than
normal elliptical galaxies, and that their [alpha/Fe] abundance ratios scatter
around solar. This is in accordance with the downsizing picture of galaxy
formation where mass is the main driver for the star formation history. We also
find new correlations between the luminosity-weighted mean age, the large-scale
asymmetry, and the projected Virgocentric distance. We find that environment
plays an important role in the termination of the star formation activity by
ram pressure stripping of the gas in short timescales, and in the
transformation of disky dwarfs to more spheroidal objects by harassment over
longer timescales. This points towards a continuing infall scenario for the
evolution of dEs.Comment: Accepted for publication in MNRAS: 22 pages, 13 figures and 9 table
Stellar populations of bulges at low redshift
This chapter summarizes our current understanding of the stellar population
properties of bulges and outlines important future research directions.Comment: Review article to appear in "Galactic Bulges", Editors: Laurikainen
E., Peletier R., Gadotti D., Springer Publishing. 34 pages, 12 figure
Do observed metallicity gradients of early-type galaxies support a hybrid formation scenario?
We measure radial gradients of the Mg2 index in 15 E-E/S0 and 14 S0 galaxies.
Our homogeneous data set covers a large range of internal stellar velocity
dispersions (2.0<logsigma<2.5) and Mg2 gradients (dMg2/dlogr/re* up to
-0.14mag/dex). We find for the first time, a noticeable lower boundary in the
relation between Mg2 gradient and sigma along the full range of sigma, which
may be populated by galaxies predominantly formed by monolithic collapse. At
high sigma, galaxies showing flatter gradients could represent objects which
suffered either important merging episodes or later gas accretion. These
processes contribute to the flattening of the metallicity gradients and their
increasing importance could define the distribution of the objects above the
boundary expected by the ``classical'' monolithic process. This result is in
marked contrast with previous works which found a correlation between
dMg2/dlogr/re* and sigma confined to the low mass galaxies, suggesting that
only galaxies below some limiting sigma were formed by collapse whereas the
massive ones by mergers. We show observational evidence that a hybrid scenario
could arise also among massive galaxies. Finally, we estimated d[Z/H] from Mg2
and Hbeta measurements and single stellar population models. The conclusions
remain the same, indicating that the results cannot be ascribed to age effects
on Mg2.Comment: 11 pages, 2 figures, to appear in ApJLetter
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