672 research outputs found
How young are early-type cluster galaxies ? Quantifying the young stellar component in a rich cluster at z=0.41
We present a new method of quantifying the mass fraction of young stars in
galaxies by analyzing near-ultraviolet (NUV)-optical colors. We focus our
attention on early-type cluster galaxies, whose star formation history is at
present undetermined. Rest-frame NUV (F300W) and optical (F702W) images of
cluster Abell 851 (z=0.41) using HST/WFPC2 allow us to determine a NUV-optical
color-magnitude relation, whose slope is incompatible with a monolithic
scenario for star formation at high redshift. A degeneracy between a young
stellar component and its fractional mass contribution to the galaxy is found,
and a photometric analysis comparing the data with the predictions for a simple
two-stage star formation history is presented. The analysis shows that some of
the early-type galaxies may have fractions higher than 10% of the total mass
content in stars formed at z~0.5. An increased scatter is found in the
color-magnitude relation at the faint end, resulting in a significant fraction
of faint blue early-type systems. This would imply that less massive galaxies
undergo more recent episodes of star formation, and this can be explained in
terms of a positive correlation between star formation efficiency and
luminosity.Comment: Accepted for publication in ApJ Letters. Uses emulateapj.sty. 5 pages
with 3 embedded EPS figure
The necessity of dark matter in MOND within galactic scales
To further test MOdified Newtonian Dynamics (MOND) on galactic scales --
originally proposed to explain the rotation curves of disk galaxies without
dark matter -- we study a sample of six strong gravitational lensing early-type
galaxies from the CASTLES database. To determine whether dark matter is present
in these galaxies, we compare the total mass (from lensing) with the stellar
mass content (from a comparison of photometry and stellar population
synthesis). We find that strong gravitational lensing on galactic scales
requires a significant amount of dark matter, even within MOND. On such scales
a 2 eV neutrino cannot explain this excess matter -- in contrast with recent
claims to explain the lensing data of the bullet cluster. The presence of dark
matter is detected in regions with a higher acceleration than the
characteristic MONDian scale of m/s. This is a serious
challenge to MOND unless the proper treatment of lensing is qualitatively
different (possibly to be developed within a consistent theory such as TeVeS).Comment: 5 pages, 3 figures, 1 table Amended version to match publication in
Phys. Rev. let
Mapping the distribution of luminous and dark matter in strong lensing galaxies
We present the distribution of luminous and dark matter in a set of strong
lensing (early-type) galaxies. By combining two independent techniques -
stellar population synthesis and gravitational lensing - we can compare the
baryonic and dark matter content in these galaxies within the regions that can
be probed using the images of the lensed background source. Two samples were
studied, extracted from the CASTLES and SLACS surveys. The former probes a
wider range of redshifts and allows us to explore the mass distribution out to
~5Re. The high resolution optical images of the latter (using HST/ACS) are used
to show a pixellated map of the ratio between total and baryonic matter. We
find dark matter to be absent in the cores of these galaxies, with an
increasing contribution at projected radii R>Re. The slopes are roughly
compatible with an isothermal slope (better interpreted as an adiabatically
contracted NFW profile), but a large scatter in the slope exists among
galaxies. There is a trend suggesting most massive galaxies have a higher
content of dark matter in the regions probed by this analysis.Comment: 10 pages, 6 figures. To appear in "Dark Galaxies and Lost Baryons",
IAU244 conference proceeding
SPIDER X - Environmental effects in central and satellite early-type galaxies through the stellar fossil record
A detailed analysis of how environment affects the star formation history of
early-type galaxies (ETGs) is undertaken via high signal to noise ratio stacked
spectra obtained from a sample of 20,977 ETGs (morphologically selected) from
the SDSS-based SPIDER survey. Two major parameters are considered for the
study: the central velocity dispersion (sigma), which relates to local drivers
of star formation, and the mass of the host halo, which relates to
environment-related effects. In addition, we separate the sample between
centrals (the most massive galaxy in a halo) and satellites. We derive trends
of age, metallicity, and [alpha/Fe] enhancement, with sigma. We confirm that
the major driver of stellar population properties in ETGs is velocity
dispersion, with a second-order effect associated to the central/satellite
nature of the galaxy. No environmental dependence is detected for satellite
ETGs, except at low sigma - where satellites in groups or in the outskirts of
clusters tend to be younger than those in the central regions of clusters. In
contrast, the trends for centrals show a significant dependence on halo mass.
Central ETGs in groups (i.e. with a halo mass >10^12.5 M_Sun) have younger
ages, lower [alpha/Fe], and higher internal reddening, than "isolated" systems
(i.e. centrals residing in low-mass, <10^12.5 M_Sun, halos). Our findings imply
that central ETGs in groups formed their stellar component over longer time
scales than "isolated" centrals, mainly because of gas-rich interactions with
their companion galaxies.Comment: 22 pages, 19 figures, accepted for publication in MNRA
The Origin of Color Gradients in Early-Type Systems and Their Compactness at High-z
In this Letter, we present mean optical+NIR color gradient estimates for 5080
early-type galaxies (ETGs) in the grizYJHK wavebands of the Sloan Digital Sky
Survey (SDSS) plus UKIRT Infrared Deep Sky Survey (UKIDSS). The color gradient
is estimated as the logarithmic slope of the radial color profile in ETGs. With
such a large sample size, we study the variation of the mean color gradient as
a function of waveband with unprecedented accuracy. We find that (i) color
gradients are mainly due, on average, to a metallicity variation of about
-0.4dex per decade in galaxy radius; and (ii) a small, but significant,
positive age gradient is present, on average, in ETGs, with the inner stellar
population being slightly younger, by ~0.1dex per radial decade, than the outer
one. Also, we show that the presence of a positive mean age gradient in ETGs,
as found in the present study, implies their effective radius to be smaller at
high z, consistent with observations.Comment: 4 pages, 2 color figures, accepted for publication in the
Astrophysical Journal Letter
Effect of Sunflower and Marine Oils on Ruminal Microbiota, In vitro Fermentation and Digesta Fatty Acid Profile
Funding This work has been funded by Consejería de Educación, Junta de Castilla y León (research project LE007A07). Acknowledgments We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI). Support received from CICYT project AGL2005-04760-C02-02 is gratefully acknowledged.Peer reviewedPublisher PD
IMF and [Na/Fe] abundance ratios from optical and NIR Spectral Features in Early-type Galaxies
We present a joint analysis of the four most prominent sodium-sensitive
features (NaD, NaI8190, NaI1.14, and NaI2.21), in the optical and Near-Infrared
spectral range, of two nearby, massive (sigma~300km/s), early-type galaxies
(named XSG1 and XSG2). Our analysis relies on deep VLT/X-Shooter long-slit
spectra, along with newly developed stellar population models, allowing for
[Na/Fe] variations, up to 1.2dex, over a wide range of age, total metallicity,
and IMF slope. The new models show that the response of the Na-dependent
spectral indices to [Na/Fe] is stronger when the IMF is bottom heavier. For the
first time, we are able to match all four Na features in the central regions of
massive early-type galaxies, finding an overabundance of [Na/Fe], in the range
0.5-0.7dex, and a bottom-heavy IMF. Therefore, individual abundance variations
cannot be fully responsible for the trends of gravity-sensitive indices,
strengthening the case towards a non-universal IMF. Given current limitations
of theoretical atmosphere models, our [Na/Fe] estimates should be taken as
upper limits. For XSG1, where line strengths are measured out to 0.8Re, the
radial trend of [Na/Fe] is similar to [Mg/Fe] and [C/Fe], being constant out to
0.5Re, and decreasing by 0.2-0.3dex at 0.8Re, without any clear correlation
with local metallicity. Such a result seems to be in contrast with the
predicted increase of Na nucleosynthetic yields from AGB stars and TypeII SNe.
For XSG1, the Na-inferred IMF radial profile is consistent, within the errors,
with that derived from TiO features and the Wing-Ford band, presented in a
recent paper.Comment: 22 pages, 8 figure, accepted for publication in MNRAS. The new
Na-enhanced models will be available soon at http://miles.iac.es
Mapping the Distribution of Luminous and Dark Matter in Strong Lensing Galaxies
We present the distribution of luminous and dark matter in a set of strong lensing (early-type) galaxies. By combining two independent techniques - stellar population synthesis and gravitational lensing - we can compare the baryonic and dark matter content in these galaxies within the regions that can be probed using the images of the lensed background source. Two samples were studied, extracted from the CASTLES and SLACS surveys. The former probes a wider range of redshifts and allows us to explore the mass distribution out to ~ 5Re. The high resolution optical images of the latter (using HST/ACS) are used to show a pixellated map of the ratio between total and baryonic matter. We find dark matter to be absent in the cores of these galaxies, with an increasing contribution at projected radii R Re. The slopes are roughly compatible with an isothermal slope (better interpreted as an adiabatically contracted NFW profile), but a large scatter in the slope exists among galaxies. There is a trend suggesting most massive galaxies have a higher content of dark matter in the regions probed by this analysi
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