70 research outputs found
The cosmic evolution of the spatially-resolved star formation rate and stellar mass of the CALIFA survey
We investigate the cosmic evolution of the absolute and specific star
formation rate (SFR, sSFR) of galaxies as derived from a spatially-resolved
study of the stellar populations in a set of 366 nearby galaxies from the
CALIFA survey. The analysis combines GALEX and SDSS images with the 4000 break,
H_beta, and [MgFe] indices measured from the datacubes, to constrain parametric
models for the SFH, which are then used to study the cosmic evolution of the
star formation rate density (SFRD), the sSFR, the main sequence of star
formation (MSSF), and the stellar mass density (SMD). A delayed-tau model,
provides the best results, in good agreement with those obtained from
cosmological surveys. Our main results from this model are: a) The time since
the onset of the star formation is larger in the inner regions than in the
outer ones, while tau is similar or smaller in the inner than in the outer
regions. b) The sSFR declines rapidly as the Universe evolves, and faster for
early than for late type galaxies, and for the inner than for the outer regions
of galaxies. c) SFRD and SMD agree well with results from cosmological surveys.
At z< 0.5, most star formation takes place in the outer regions of late spiral
galaxies, while at z>2 the inner regions of the progenitors of the current E
and S0 are the major contributors to SFRD. d) The inner regions of galaxies are
the major contributor to SMD at z> 0.5, growing their mass faster than the
outer regions, with a lookback time at 50% SMD of 9 and 6 Gyr for the inner and
outer regions. e) The MSSF follows a power-law at high redshift, with the slope
evolving with time, but always being sub-linear. f) In agreement with galaxy
surveys at different redshifts, the average SFH of CALIFA galaxies indicates
that galaxies grow their mass mainly in a mode that is well represented by a
delayed-tau model, with the peak at z~2 and an e-folding time of 3.9 Gyr.Comment: 23 pages, 16 figures, 6 tables, accepted for publication in Astronomy
& Astrophysics. *Abridged abstract
Uncovering the chemical enrichment and mass-assembly histories of star-forming galaxies
We explore the mass-assembly and chemical enrichment histories of star
forming galaxies by applying a population synthesis method to a sample of 84828
galaxies from the Sloan Digital Sky Survey Data Release 5. Our method
decomposes the entire observed spectrum in terms of a sum of simple stellar
populations spanning a wide range of ages and metallicities, thus allowing the
reconstruction of galaxy histories. A comparative study of galaxy evolution is
presented, where galaxies are grouped onto bins of nebular abundances or mass.
We find that galaxies whose warm interstellar medium is poor in heavy elements
are slow in forming stars. Their stellar metallicities also rise slowly with
time, reaching their current values () in the last
Myr of evolution. Systems with metal rich nebulae, on the other
hand, assembled most of their mass and completed their chemical evolution long
ago, reaching already at lookback times of several Gyr.
These same trends, which are ultimately a consequence of galaxy downsizing,
appear when galaxies are grouped according to their stellar mass. The
reconstruction of galaxy histories to this level of detail out of integrated
spectra offers promising prospects in the field of galaxy evolution theories.Comment: Accepted for publication in MNRA
The ALHAMBRA survey: Bayesian photometric redshifts with 23 bands for 3 deg2
The Advance Large Homogeneous Area Medium-Band Redshift Astronomical (ALHAMBRA) survey has observed eight different regions of the sky, including sections of the Cosmic Evolution Survey (COSMOS), DEEP2, European Large-Area Infrared Space Observatory Survey (ELAIS), Great Observatories Origins Deep Survey North (GOODS-N), Sloan Digital Sky Survey (SDSS) and Groth fields using a new photometric system with 20 optical, contiguous ~300-Å filters plus the JHKs bands. The filter system is designed to optimize the effective photometric redshift depth of the survey, while having enough wavelength resolution for the identification of faint emission lines. The observations, carried out with the Calar Alto 3.5-m telescope using the wide-field optical camera Large Area Imager for Calar Alto (LAICA) and the near-infrared (NIR) instrument Omega-2000, represent a total of ~700 h of on-target science images. Here we present multicolour point-spread function (PSF) corrected photometry and photometric redshifts for ~438 000 galaxies, detected in synthetic F814W images. The catalogues are complete down to a magnitude I~24.5AB and cover an effective area of 2.79 deg2. Photometric zero-points were calibrated using stellar transformation equations and refined internally, using a new technique based on the highly robust photometric redshifts measured for emission-line galaxies. We calculate Bayesian photometric redshifts with the Bayesian Photometric Redshift (BPZ)2.0 code, obtaining a precision of δz/(1+zs)=1 per cent for I<22.5 and δz/(1+zs)=1.4 per cent for 22.5<I<24.5. The global n(z) distribution shows a mean redshift 〈z〉=0.56 for I<22.5 AB and 〈z〉=0.86 for I<24.5 AB. Given its depth and small cosmic variance, ALHAMBRA is a unique data set for galaxy evolution studies
Structure and large scale environment of galaxy pairs in the S-PLUS DR4
In this paper, we use photometric data from the S-PLUS DR4 survey to identify
isolated galaxy pairs and analyse their characteristics and properties. Our
results align with previous spectroscopic studies, particularly in luminosity
function parameters, suggesting a consistent trait among galaxy systems. Our
findings reveal a high fraction of red galaxies across all samples,
irrespective of projected distance, velocity difference, or luminosity ratio.
We found that the proximity of a neighbour to its central galaxy influences its
colour due to environmental effects. We also found that central and neighbour
have different behaviours: central galaxies maintain a stable red colour
regardless of luminosity, while neighbour colours vary based on luminosity
ratios. When the central is significantly brighter, the neighbour tends to be
less red. According to our division in red, blue and mixed pairs, we found
evidence of galactic conformity. Red pair fractions increase in closer pairs
and in pairs of similar luminosity, indicating shared environments promoting
red galaxy formation. Analysing local density, the expected colour-density
relation is of course recovered, but it is strongly determined by the stellar
mass of the pair. In denser environments, the red pair fractions increase, blue
pairs decrease and for mixed pairs it depends on their stellar mass: more
massive mixed pairs decrease their fraction whereas the lower massive ones
increase it. These results shed light on the intricate relationship between
galaxy pairs, their characteristics, and environmental influences on colour,
providing insights into their evolutionary histories.Comment: 15 pages, 12 figures, accepted for publication in MNRA
Characterisation of high velocity stars in the S-PLUS internal fourth data release
In general, the atypical high velocity of some stars in the Galaxy can only
be explained by invoking acceleration mechanisms related to extreme
astrophysical events in the Milky Way. Using astrometric data from Gaia and the
photometric information in 12 filters of the S-PLUS, we performed a kinematic,
dynamical, and chemical analysis of 64 stars with galactocentric velocities
higher than 400 . All the stars are gravitationally bound
to the Galaxy and exhibit halo kinematics. Some of the stars could be remnants
of structures such as the Sequoia and the Gaia-Sausage/Enceladus. Supported by
orbital and chemical analysis, we identified Gaia DR3 5401875170994688896 as a
star likely to be originated at the centre of the Galaxy. Application of a
machine learning technique to the S-PLUS photometric data allows us to obtain
very good estimates of magnesium abundances for this sample of high velocity
stars
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