199 research outputs found
Formation and evolution of dwarf early-type galaxies in the Virgo cluster II. Kinematic Scaling Relations
We place our sample of 18 Virgo dwarf early-type galaxies (dEs) on the V-K -
velocity dispersion, Faber-Jackson, and Fundamental Plane (FP) scaling
relations for massive early-type galaxies (Es). We use a generalized velocity
dispersion, which includes rotation, to be able to compare the location of both
rotationally and pressure supported dEs with those of early and late-type
galaxies. We find that dEs seem to bend the Faber-Jackson relation of Es to
lower velocity dispersions, being the link between Es and dwarf spheroidal
galaxies (dSphs). Regarding the FP relation, we find that dEs are significantly
offset with respect to massive hot stellar systems, and re-casting the FP into
the so-called kappa-space suggests that this offset is related to dEs having a
total mass-to-light ratio higher than Es but still significantly lower than
dSph galaxies. Given a stellar mass-to-light ratio based on the measured line
indices of dEs, the FP offset allows us to infer that the dark matter fraction
within the half light radii of dEs is on average >~ 42% (uncertainties of 17%
in the K band and 20% in the V band), fully consistent with an independent
estimate in an earlier paper in this series. We also find that dEs in the
size-luminosity relation in the near-infrared, like in the optical, are offset
from early-type galaxies, but seem to be consistent with late-type galaxies. We
thus conclude that the scaling relations show that dEs are different from Es,
and that they further strengthen our previous findings that dEs are closer to
and likely formed from late-type galaxies.Comment: 14 pages, 9 figures, 2 appendixes. Accepted for publication in A&
Stellar Populations in Bulges of Spiral Galaxies
We have conducted a spectroscopic analysis of the bulges of a sample of 31
spiral galaxies, spanning the Hubble sequence from S0 to Scd type, in order to
study the radial distribution of their stellar population properties.Comment: To be published in "The Evolution of Galaxies. II. Basic Building
Blocks", ed. M. Sauvage et al., Kluwe
Spatially resolved spectroscopy of Coma cluster early-type galaxies IV. Completing the dataset
The long-slit spectra obtained along the minor axis, offset major axis and
diagonal axis are presented for 12 E and S0 galaxies of the Coma cluster drawn
from a magnitude-limited sample studied before. The rotation curves, velocity
dispersion profiles and the H_3 and H_4 coefficients of the Hermite
decomposition of the line of sight velocity distribution are derived. The
radial profiles of the Hbeta, Mg, and Fe line strength indices are measured
too. In addition, the surface photometry of the central regions of a subsample
of 4 galaxies recently obtained with Hubble Space Telescope is presented. The
data will be used to construct dynamical models of the galaxies and study their
stellar populations.Comment: 40 pages, 7 figures, 6 tables. Accepted for publication in ApJ
Stellar population gradients in Fornax Cluster S0 galaxies: connecting bulge and disk evolution
We present absorption-line index gradients for a sample of S0 galaxies in the
Fornax Cluster. The sample has been selected to span a wide range in galaxy
mass, and the deep VLT-FORS2 spectroscopy allows us to explore the stellar
populations all the way to the outer disk-dominated regions of these galaxies.
We find that globally, in both bulges and disks, star formation ceased earliest
in the most massive systems, as a further manifestation of downsizing. However,
within many galaxies, we find an age gradient which indicates that star
formation ended first in the outermost regions. Metallicity gradients, when
detected, are always negative such that the galaxy centres are more metal-rich.
This finding fits with a picture in which star formation continued in the
central regions, with enriched material, after it had stopped in the outskirts.
Age and metallicity gradients are correlated, suggesting that large differences
in star formation history between the inner and outer parts of S0 galaxies
yield large differences in their chemical enrichment. In agreement with
previous results, we conclude that the radial variations in the stellar
populations of S0 galaxies are compatible with the hypothesis that these
galaxies are the descendants of spiral galaxies whose star formation has
ceased. With the addition of radial gradient information, we are able to show
that this shutdown of star formation occurred from the outside inward, with the
later star formation in the central regions offering a plausible mechanism for
enhancing the bulge light in these systems, as the transformation to more
bulge-dominated S0 galaxies requires.Comment: 9 pages, 4 figures and Appendix, accepted for publication in MNRA
Stellar Population Diagnostics of Elliptical Galaxy Formation
Major progress has been achieved in recent years in mapping the properties of
passively-evolving, early-type galaxies (ETG) from the local universe all the
way to redshift ~2. Here, age and metallicity estimates for local cluster and
field ETGs are reviewed as based on color-magnitude, color-sigma, and
fundamental plane relations, as well as on spectral-line indices diagnostics.
The results of applying the same tools at high redshifts are then discussed,
and their consistency with the low-redshift results is assessed. Most low- as
well as high-redshift (z~1) observations consistently indicate 1) a formation
redshift z>~3 for the bulk of stars in cluster ETGs, with their counterparts in
low-density environments being on average ~1-2 Gyr younger, i.e., formed at
z>~1.5-2, 2) the duration of the major star formation phase anticorrelates with
galaxy mass, and the oldest stellar populations are found in the most massive
galaxies. With increasing redshift there is evidence for a decrease in the
number density of ETGs, especially of the less massive ones, whereas existing
data appear to suggest that most of the most-massive ETGs were already fully
assembled at z~1. Beyond this redshift, the space density of ETGs starts
dropping significantly, and as ETGs disappear, a population of massive,
strongly clustered, starburst galaxies progressively becomes more and more
prominent, which makes them the likely progenitors to ETGs.Comment: To appear on Annual Review of Astronomy & Astrophysics, Vol. 44
(2006). 46 pages with 16 figures. Replaced version includes updated
references, few typos less, and replaces Fig. 11 and Fig. 16 which had been
skrewed u
Using spectroscopic data to disentangle stellar population properties
It is well known that, when analyzed in the light of current synthesis model predictions, variations in the physical properties of single stellar populations (e.g. age, metallicity, initial mass function, element abundance ratios) may have a similar effect in their integrated spectral energy distributions. The confusion is even worsened when more realistic scenarios, i.e. composite star formation histories, are considered. This is, in fact, one of the major problems when facing the study of stellar populations in star clusters and galaxies. Typically, the observational efforts have aimed to find the most appropriate spectroscopic indicators in order to avoid, as far as possible, degeneracies in the parameter space. However, from a practical point of view, the most suited observables are not, necessarily, those that provide more orthogonality in that parameter space, but those that give the best balance between parameter degeneracy and sensitivity to signal-to-noise ratio per Angstrom, S/N(Angstrom). In order to achieve the minimum combined total error in the derived physical parameters, this work discusses how the functional dependence of typical line-strength indices and colors on S/N(Angstrom) allows to define a suitability parameter which helps to obtain more realistic combinations of spectroscopic data. As an example, we discuss in more detail the problem of breaking the well known age-metallicity degeneracy in relatively old stellar populations, comparing the suitability of different spectroscopic diagrams for a simple stellar population of solar metallicity and of 12 Gyr in age
Formation and evolution of dwarf early-type galaxies in the Virgo cluster II. Kinematic scaling relations (Corrigendum) (vol 548, pg A76, 2012)
© ESO, 2013Depto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasTRUEpu
Spatially resolved spectroscopy of Coma cluster early-type galaxies - II:the minor axis dataset
We present minor axis, off set major axis and one diagonal long slit spectra for 10 E and S0 galaxies of the Coma cluster drawn from a magnitude-limited sample studied before. We derive rotation curves, velocity dispersion profiles and the H-3 and H-4 coefficients of the Hermite decomposition of the line of sight velocity distribution. Moreover, we derive the line index profiles of Mg, Fe and Hbeta line indices and assess their errors. The data will be used to construct dynamical models of the galaxies and study their stellar populations
Line-strengths in early-type galaxies
We have analysed Mg, Hβ and Fe line-strengths in a sample of elliptical, SO and brightest cluster galaxies. For 15 galaxies, our spectra extend to approximately the half-light radius(r_e), and we are able to measure radial line-strength gradients. The metallic line-strength gradients vary markedly from object to object, and do not correlate strongly with parameters such as total luminosity and rotation, though we find sorne evidence that gradients in the Mg_2 index correlate with central velocity dispersion and central line-strength. The highly variable line-strength gradients in early-type galaxies shows that they have experienced different star formation histories. We suggest that this may be explained if they formed by the mergers of subunits in which star formation had proceeded to varying degrees of completion. We find that the line-strengths at r~r_e in elliptical galaxies are slightly larger than those of metal rich galactic globulars, suggesting that typical elliptical galaxies have roughly solar abundance at r~r_e and therefore that most ellipticals have relatively weak abundance gradients. The relative line-strengths in the outer parts of ellipticals differ from those in the nuclei of low-luminosity ellipticals, indicating that these stellar populations do not represent a simple one-parameter family governed by mean metal abundance. We find no significant differences in the central Mg and Fe line-strengths of the brightest cluster galaxies and normal ellipticals with the same central velocity dispersion. How ever, we find that two cD galaxies show Hβ in emission and are also at the centres of the prodigious cooling flows with mass-deposition rates of ≥ 100 M_⨀ yr^-1. Galaxies with cooling flows have identical Mg and Fe line-strengths to galaxies without cooling flows. We show that this implies that only a small fraction of the total luminosity of cooling flow galaxies could come from ongoing star formation with a normal stellar initial mass function
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
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