112 research outputs found
Age and metallicity gradients in early-type galaxies: A dwarf to giant sequence
We studied the stellar populations of 40 early-type galaxies using medium
resolution long-slit spectroscopy along their major axes (and along the minor
axis for two of them), from 10^7 Msol to 10^12 Msol (-9.2 > M_B > -22.4 mag).
All the studied galaxies lie on the mass-metallicity and age-mass relations.
The transition type dwarfs deviate from the latter relation having younger mean
age, and the low-mass dwarf spheroidals have older ages, marking a
discontinuity in the relation, possibly due to selection effects.
In all mass regimes, the mean metallicity gradients are approximately -0.2
and the mean age gradients +0.1 dex per decade of radius. The individual
gradients are widely spread: and . We do not find evidence for a correlation
between the metallicity gradient and luminosity, velocity dispersion, central
age or age gradient. Likewise, we do not find a correlation between the age
gradient and any other parameter in bright early-type galaxies. In faint
early-types with mag, on the other hand, we find a
correlation between the age gradient and luminosity: the age gradient becomes
more positive for fainter galaxies.
We conclude that various physical mechanisms can lead to similar gradients
and that these gradients are robust against the environmental effects. In
particular, the gradients observed in dwarfs galaxies certainly survived the
transformation of the progenitors through tidal harassment or/and ram-pressure
stripping. The diversity of metallicity gradients amongst dwarf elliptical
galaxies may reflect a plurality of progenitors' morphologies. The dwarfs with
steep metallicity gradients could have originated from blue compact dwarfs and
those with flat profiles from dwarf irregulars and late type spirals.
(Abridged)Comment: 31 pages, 16 figures. Accepted for publications in MNRA
Abundance gradient slopes versus mass in spheroids: predictions by monolithic models
We investigate whether it is possible to explain the wide range of observed
gradients in early type galaxies in the framework of monolithic models. To do
so, we extend the set of hydrodynamical simulations by Pipino et al. (2008a) by
including low-mass ellipticals and spiral (true) bulges. These models satisfy
the mass-metallicity and the mass-[alpha/Fe] relations. The typical metallicity
gradients predicted by our models have a slope of -0.3 dex per decade variation
in radius, consistent with the mean values of several observational samples.
However, we also find a few quite massive galaxies in which this slope is -0.5
dex per decade, in agreement with some recent data. In particular, we find a
mild dependence from the mass tracers when we transform the stellar abundance
gradients into radial variations of the Mg_2 line-strength index, but not in
the Mg_b. We conclude that, rather than a mass- slope relation, is more
appropriate to speak of an increase in the scatter of the gradient slope with
the galactic mass. We can explain such a behaviour with different efficiencies
of star formation in the framework of the revised monolithic formation
scenario, hence the scatter in the observed gradients should not be used as an
evidence of the need of mergers. Indeed, model galaxies that exhibit the
steepest gradient slopes are preferentially those with the highest star
formation efficiency at that given mass.Comment: Accepted for publication by MNRAS, the paper contains 7 figures and 2
table
Color and stellar population gradients in galaxies. Correlation with mass
We analyze the color gradients (CGs) of ~50000 nearby SDSS galaxies. From
synthetic spectral models based on a simplified star formation recipe, we
derive the mean spectral properties, and explain the observed radial trends of
the color as gradients of the stellar population age and metallicity (Z). The
most massive ETGs (M_* > 10^{11} Msun) have shallow CGs in correspondence of
shallow (negative) Z gradients. In the stellar mass range 10^(10.3-10.5) < M_*
< 10^(11) Msun, the Z gradients reach their minimum of ~ -0.5 dex^{-1}. At M_*
~ 10^{10.3-10.5} Msun, color and Z gradient slopes suddenly change. They turn
out to anti-correlate with the mass, becoming highly positive at the very low
masses. We have also found that age gradients anti-correlate with Z gradients,
as predicted by hierarchical cosmological simulations for ETGs. On the other
side, LTGs have gradients which systematically decrease with mass (and are
always more negative than in ETGs), consistently with the expectation from gas
infall and SN feedback scenarios. Z is found to be the main driver of the trend
of color gradients, especially for LTGs, but age gradients are not negligible
and seem to play a significant role too. We have been able to highlight that
older galaxies have systematically shallower age and Z gradients than younger
ones. Our results for high-mass galaxies are in perfect agreement with
predictions based on the merging scenario, while the evolution of LTGs and
younger and less massive ETGs seems to be mainly driven by infall and SN
feedback. (Abridged)Comment: 20 pages, 16 figures, accepted for publication on MNRAS. This version
includes revisions after the referee's report
Coronary microvascular dysfunction in Takotsubo syndrome: an analysis using angiography-derived index of microcirculatory resistance
BACKGROUND
Coronary microvascular dysfunction (CMD) has been proposed as a crucial factor in the pathophysiology of Takotsubo syndrome (TTS). The angiography-derived index of microcirculatory resistance (caIMR) offers an alternative to conventional hyperemic wire-based IMR to assess CMD. We aimed to evaluate CMD's prevalence, transience, and impact on in-hospital outcomes in TTS.
METHODS
All three coronary arteries of 96 patients with TTS were assessed for their coronary angiography derived Index of microcirculatory Resistance (caIMR) and compared to non-obstructed vessels of matched patients with ST-elevation myocardial infarction. Further, the association between caIMR and the TTS-specific combined in-hospital endpoint of death, cardiac arrest, ventricular arrhythmogenic events and cardiogenic shock was investigated.
RESULTS
Elevated IMR was present in all TTS patients, with significantly elevated caIMR values in all coronary arteries compared to controls. CaIMR did not differ between apical and midventricular TTS types. CaIMR normalized in TTS patients with follow-up angiographies performed at a median of 28 months (median caIMR at event vs follow-up: LAD 34.8 [29.9-41.1] vs 20.3 [16.0-25.3], p < 0.001; LCX: 38.7 [32.9-50.1] vs 23.7 [19.4-30.5], p < 0.001; RCA: 31.7 [25.0-39.1] vs 19.6 [17.1-24.0], p < 0.001). The extent of caIMR elevation significantly correlated with the combined in-hospital endpoint (p = 0.036).
CONCLUSION
TTS patients had evidence of elevated caIMR in at least one coronary artery with a trend towards higher LAD caIMR in apical type TTS and normalization after recovery. Furthermore, extent of caIMR elevation was associated with increased risk of in-hospital MACE of TTS patients
Nature vs. nurture in the low-density environment: structure and evolution of early-type dwarf galaxies in poor groups
We present the stellar population properties of 13 dwarf galaxies residing in
poor groups (low-density environment, LDE) observed with VIMOS@VLT. Ages,
metallicities, and [alpha/Fe] ratios were derived from the Lick indices Hbeta,
Mgb, Fe5270 and Fe5335 through comparison with our simple stellar population
(SSP) models accounting for variable [alpha/Fe] ratios. For a fiducial
subsample of 10 early-type dwarfs we derive median values and scatters around
the medians of 5.7 \pm 4.4 Gyr, -0.26 \pm 0.28, and -0.04 \pm 0.33 for age, log
Z/Zsun, and [alpha/Fe], respectively. For a selection of bright early-type
galaxies (ETGs) from the Annibali et al.2007 sample residing in comparable
environment we derive median values of 9.8 \pm 4.1 Gyr, 0.06 \pm 0.16, and 0.18
\pm 0.13 for the same stellar population parameters. It follows that dwarfs are
on average younger, less metal rich, and less enhanced in the alpha-elements
than giants, in agreement with the extrapolation to the low mass regime of the
scaling relations derived for giant ETGs. From the total (dwarf + giant) sample
we derive that age \propto sigma^{0.39 \pm 0.22}, Z \propto sigma^{0.80 \pm
0.16}, and alpha/Fe \propto sigma^{0.42 \pm 0.22}. We also find correlations
with morphology, in the sense that the metallicity and the [alpha/Fe] ratio
increase with the Sersic index n or with the bulge-to-total light fraction B/T.
The presence of a strong morphology-[alpha/Fe] relation appears to be in
contradiction to the possible evolution along the Hubble sequence from low B/T
(low n) to high B/T (high n) galaxies. We also investigate the role played by
environment comparing the properties of our LDE dwarfs with those of Coma red
passive dwarfs from the literature. We find possible evidence that LDE dwarfs
experienced more prolonged star formations than Coma dwarfs, however larger
data samples are needed to draw more firm conclusions.Comment: Accepted for publication on A&
The Formation and Evolution of Virgo Cluster Galaxies - II. Stellar Populations
We use a combination of deep optical and near-infrared light profiles for a
morphologically diverse sample of Virgo cluster galaxies to study the
radially-resolved stellar populations of cluster galaxies over a wide range of
galaxy structure. We find that, in the median, the age gradients of Virgo
galaxies are either flat (lenticulars and Sa-Sb spirals) or positive
(ellipticals, Sbc+Sc spirals, gas-rich dwarfs, and irregulars), while all
galaxy types have a negative median metallicity gradient. Comparison of the
galaxy stellar population diagnostics (age, metallicity, and gradients thereof)
against structural and environmental parameters also reveals that the ages of
gas-rich systems depend mainly on their atomic gas deficiencies. Conversely,
the metallicities of Virgo gas-poor galaxies depend on their concentrations,
luminosities, and surface brightnesses. The stellar population gradients of all
Virgo galaxies exhibit no dependence on either their structure or environment.
We interpret these stellar population data for Virgo galaxies in the context of
popular formation and evolution scenarios, and suggest that gas-poor giants
grew hierarchically (through dissipative starbursts), gas-poor dwarfs have
descended from at least two different production channels (e.g., environmental
transformation and merging), while spirals formed inside-out, but with star
formation in the outskirts of a significant fraction of the population having
been quenched due to ram pressure stripping. (Abridged)Comment: 54 pages, 16 figures, 3 tables, re-submitted to MNRAS (edited to
reflect the referee's suggestions
Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
We review HB stars in a broad astrophysical context, including both variable
and non-variable stars. A reassessment of the Oosterhoff dichotomy is
presented, which provides unprecedented detail regarding its origin and
systematics. We show that the Oosterhoff dichotomy and the distribution of
globular clusters (GCs) in the HB morphology-metallicity plane both exclude,
with high statistical significance, the possibility that the Galactic halo may
have formed from the accretion of dwarf galaxies resembling present-day Milky
Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the
second-parameter problem is presented. A technique is proposed to estimate the
HB types of extragalactic GCs on the basis of integrated far-UV photometry. The
relationship between the absolute V magnitude of the HB at the RR Lyrae level
and metallicity, as obtained on the basis of trigonometric parallax
measurements for the star RR Lyrae, is also revisited, giving a distance
modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are
studied. Finally, the conductive opacities used in evolutionary calculations of
low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and
Space Scienc
Observed versus modelled u,g,r,i,z-band photometry of local galaxies - Evaluation of model performance
We test how well available stellar population models can reproduce observed
u,g,r,i,z-band photometry of the local galaxy population (0.02<=z<=0.03) as
probed by the SDSS. Our study is conducted from the perspective of a user of
the models, who has observational data in hand and seeks to convert them into
physical quantities. Stellar population models for galaxies are created by
synthesizing star formations histories and chemical enrichments using single
stellar populations from several groups (Starburst99, GALAXEV, Maraston2005,
GALEV). The role of dust is addressed through a simplistic, but observationally
motivated, dust model that couples the amplitude of the extinction to the star
formation history, metallicity and the viewing angle. Moreover, the influence
of emission lines is considered (for the subset of models for which this
component is included). The performance of the models is investigated by: 1)
comparing their prediction with the observed galaxy population in the SDSS
using the (u-g)-(r-i) and (g-r)-(i-z) color planes, 2) comparing predicted
stellar mass and luminosity weighted ages and metallicities, specific star
formation rates, mass to light ratios and total extinctions with literature
values from studies based on spectroscopy. Strong differences between the
various models are seen, with several models occupying regions in the
color-color diagrams where no galaxies are observed. We would therefore like to
emphasize the importance of the choice of model. Using our preferred model we
find that the star formation history, metallicity and also dust content can be
constrained over a large part of the parameter space through the use of
u,g,r,i,z-band photometry. However, strong local degeneracies are present due
to overlap of models with high and low extinction in certain parts of color
space.Comment: MNRAS accepted. 18 pages, incl. 15 figure
In and out star formation in z~1.5 quiescent galaxies from rest-frame UV spectroscopy and the far-infrared
We present a sample of 34 spectroscopically confirmed BzK-selected ~1e11 Msun quiescent galaxies (pBzK) in the COSMOS field. The targets were initially observed with VIMOS on the VLT to facilitate the calibration of the photometric redshifts of massive galaxies at z >~ 1.5. Here we describe the reduction and analysis of the data, and the spectrophotometric properties of these pBzK galaxies. In particular, using a spatially resolved median 2D spectrum, we find that the fraction of stellar populations with ages <1 Gyr is at least 3 times higher in the outer regions of the pBzK galaxies than in their cores. This results in a mild age gradient of ~<0.4 Gyr over ~6 kpc and suggests either the occurrence of widespread rejuvenation episodes or that inside-out quenching played a role in the passivization of this galaxy population. We also report on low-level star formation rates derived from the [OII]3727A emission line, with SFR_OII = 3.7-4.5 Msun/yr. This estimate is confirmed by an independent measurement on a separate sample of similarly-selected quiescent galaxies in the COSMOS field, using stacked far-infrared data (SFR_FIR = 2-4 Msun/yr). This second, photometric sample also displays significant excess at 1.4 GHz, suggestive of the presence of radio-mode AGN activity
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