290 research outputs found
BAYES-LOSVD: a bayesian framework for non-parametric extraction of the line-of-sight velocity distribution of galaxies
We introduce BAYES-LOSVD, a novel implementation of the non-parametric
extraction of line-of-sight velocity distributions (LOSVDs) in galaxies. We
employ bayesian inference to obtain robust LOSVDs and associated uncertainties.
Our method relies on principal component analysis to reduce the dimensionality
of the base of templates required for the extraction and thus increase the
performance of the code. In addition, we implement several options to
regularise the output solutions. Our tests, conducted on mock spectra, confirm
the ability of our approach to model a wide range of LOSVD shapes, overcoming
limitations of the most widely used parametric methods (e.g. Gauss-Hermite
expansion). We present examples of LOSVD extractions for real galaxies with
known peculiar LOSVD shapes, i.e. NGC4371, IC0719 and NGC4550, using MUSE and
SAURON integral-field unit (IFU) data. Our implementation can also handle data
from other popular IFU surveys (e.g. ATLAS3D, CALIFA, MaNGA, SAMI). Details of
the code and relevant documentation are freely available to the community in
the dedicated repositories.Comment: 13 pages, 7 figures. Accepted for publication in Astronomy &
Astrophysics. Public repository with the code can be found at:
https://github.com/jfalconbarroso/BAYES-LOSV
Kinematics & stellar populations of nearby bulges
In this thesis, we investigate the internal kinematics and stellar populations of a subsample of the bulges of nearby galaxies defined by Balcells & Peletier (1994). To do that we have analysed minor axis spectroscopic data of the sample together with Integral Field observations of one the most interesting galaxies in it (NGC7332).
We introduce, for the first time, the use of single-burst stellar population models to obtain stellar velocities, velocity dispersions and higher order Gauss-Hermite moments (h_3, h_4) from galaxy spectra in the near-infrared Ca II triplet region. We detect small-amplitude minor-axis rotation, generally due to inner isophotal twists as a result of slightly triaxial bulges or misaligned inner disks. Velocity dispersion profiles, which extend well into the disk region, show a wide range of slopes. Flattened bulges tend to have shallower velocity dispersion profiles. The inferred similarity of radial velocity dispersion profiles of bulge and disk supports the interpretation of these bulges as thickened disks.
We also investigate the position of our sample on the fundamental plane of early-type galaxies. We find that bulges, both in the B and K band, lie close to but slightly below the relation defined by ellipticals and S0s. The most deviant point is NGC7332, whose offset w.r.t the FP cannot be explained by measurement errors. Besides, there are hints that bulges of later morphological type are situated below the other bulges in our sample. The fact that bulges lie so close to the FP of ellipticals and S0s implies that their formation epoch must have been similar to that of cluster Es and S0s.
We then proceed to present measurements of near-IR Ca triplet (CaT, CaT*), Paschen (PaT) and Magnesium (MgI) indices for the same sample. We find that CaT* decreases with central velocity dispersion (sigma) with small scatter, unlike other metal indices that generally increase. Our result shows that the CaT* - sigma relation is independent of galaxy type from ellipticals to intermediate-type spirals.
Finally we have made use of SAURON observations to unravel the origin of peculiar features in the S0 galaxy NGC7332. We have discovered a Kinematically Decoupled Core, found kinematic evidence for a central disk and mapped a rather disturbed gas distribution counter-rotating w.r.t the stellar body of the galaxy. 2D stellar populations maps reveal that NGC7332 is young everywhere. The fact that we see gas inflow now, together with many features indicates that there must have been gas infall for Gyrs in a row, leading to a continuum formation of this galaxy
MILES extended: Stellar population synthesis models from the optical to the infrared
We present the first single-burst stellar population models which covers the
optical and the infrared wavelength range between 3500 and 50000 Angstrom and
which are exclusively based on empirical stellar spectra. To obtain these joint
models, we combined the extended MILES models in the optical with our new
infrared models that are based on the IRTF (Infrared Telescope Facility)
library. The latter are available only for a limited range in terms of both age
and metallicity. Our combined single-burst stellar population models were
calculated for ages larger than 1 Gyr, for metallicities between [Fe/H] = -0.40
and 0.26, for initial mass functions of various types and slopes, and on the
basis of two different sets of isochrones. They are available to the scientific
community on the MILES web page. We checked the internal consistency of our
models and compared their colour predictions to those of other models that are
available in the literature. Optical and near infrared colours that are
measured from our models are found to reproduce the colours well that were
observed for various samples of early-type galaxies. Our models will enable a
detailed analysis of the stellar populations of observed galaxies.Comment: 9 pages, 10 figures, published in A&
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&
Kinematics & stellar populations of nearby bulges
In this thesis, we investigate the internal kinematics and stellar populations of a subsample of the bulges of nearby galaxies defined by Balcells & Peletier (1994). To do that we have analysed minor axis spectroscopic data of the sample together with Integral Field observations of one the most interesting galaxies in it (NGC7332).
We introduce, for the first time, the use of single-burst stellar population models to obtain stellar velocities, velocity dispersions and higher order Gauss-Hermite moments (h_3, h_4) from galaxy spectra in the near-infrared Ca II triplet region. We detect small-amplitude minor-axis rotation, generally due to inner isophotal twists as a result of slightly triaxial bulges or misaligned inner disks. Velocity dispersion profiles, which extend well into the disk region, show a wide range of slopes. Flattened bulges tend to have shallower velocity dispersion profiles. The inferred similarity of radial velocity dispersion profiles of bulge and disk supports the interpretation of these bulges as thickened disks.
We also investigate the position of our sample on the fundamental plane of early-type galaxies. We find that bulges, both in the B and K band, lie close to but slightly below the relation defined by ellipticals and S0s. The most deviant point is NGC7332, whose offset w.r.t the FP cannot be explained by measurement errors. Besides, there are hints that bulges of later morphological type are situated below the other bulges in our sample. The fact that bulges lie so close to the FP of ellipticals and S0s implies that their formation epoch must have been similar to that of cluster Es and S0s.
We then proceed to present measurements of near-IR Ca triplet (CaT, CaT*), Paschen (PaT) and Magnesium (MgI) indices for the same sample. We find that CaT* decreases with central velocity dispersion (sigma) with small scatter, unlike other metal indices that generally increase. Our result shows that the CaT* - sigma relation is independent of galaxy type from ellipticals to intermediate-type spirals.
Finally we have made use of SAURON observations to unravel the origin of peculiar features in the S0 galaxy NGC7332. We have discovered a Kinematically Decoupled Core, found kinematic evidence for a central disk and mapped a rather disturbed gas distribution counter-rotating w.r.t the stellar body of the galaxy. 2D stellar populations maps reveal that NGC7332 is young everywhere. The fact that we see gas inflow now, together with many features indicates that there must have been gas infall for Gyrs in a row, leading to a continuum formation of this galaxy
Single Stellar Populations in the Near-Infrared - I. Preparation of the IRTF spectral stellar library
We present a detailed study of the stars of the IRTF spectral library to
understand its full extent and reliability for use with Stellar Population (SP)
modeling. The library consist of 210 stars, with a total of 292 spectra,
covering the wavelength range of 0.94 to 2.41 micron at a resolution R = 2000.
For every star we infer the effective temperature (Teff), gravity (logg) and
metallicity ([Z/Zsun]) using a full-spectrum fitting approach in a section of
the K band (2.19 to 2.34 micron) and temperature-NIR colour relations. We test
the flux calibration of these stars by calculating their integrated colours and
comparing them with the Pickles library colour-temperature relations. We also
investigate the NIR colours as a function of the calculated effective
temperature and compared them in colour-colour diagrams with the Pickles
library. This latter test shows a good broad-band flux calibration, important
for the SP models. Finally, we measure the resolution R as a function of
wavelength. We find that the resolution increases as a function of lambda from
about 6 angstrom in J to 10 angstrom in the red part of the K-band. With these
tests we establish that the IRTF library, the largest currently available
general library of stars at intermediate resolution in the NIR, is an excellent
candidate to be used in stellar population models. We present these models in
the next paper of this series.Comment: 17 pages, 19 figures. Accepted for publication in Astronomy and
Astrophysic
Timing the formation and assembly of early-type galaxies via spatially resolved stellar populations analysis
To investigate star formation and assembly processes of massive galaxies, we
present here a spatially-resolved stellar populations analysis of a sample of
45 elliptical galaxies (Es) selected from the CALIFA survey. We find rather
flat age and [Mg/Fe] radial gradients, weakly dependent on the effective
velocity dispersion of the galaxy within half-light radius. However, our
analysis shows that metallicity gradients become steeper with increasing galaxy
velocity dispersion. In addition, we have homogeneously compared the stellar
populations gradients of our sample of Es to a sample of nearby relic galaxies,
i.e., local remnants of the high-z population of red nuggets. This comparison
indicates that, first, the cores of present-day massive galaxies were likely
formed in gas-rich, rapid star formation events at high redshift (z>2). This
led to radial metallicity variations steeper than observed in the local
Universe, and positive [Mg/Fe] gradients. Second, our analysis also suggests
that a later sequence of minor dry mergers, populating the outskirts of
early-type galaxies (ETGs), flattened the pristine [Mg/Fe] and metallicity
gradients. Finally, we find a tight age-[Mg/Fe] relation, supporting that the
duration of the star formation is the main driver of the [Mg/Fe] enhancement in
massive ETGs. However, the star formation time-scale alone is not able to fully
explain our [Mg/Fe] measurements. Interestingly, our results match the expected
effect that a variable stellar initial mass function would have on the [Mg/Fe]
ratio.Comment: Accepted for publication in MNRA
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