45 research outputs found
Study of stellar populations in the bulges of barred galaxies
We have obtained long-slit spectroscopy for a sample of 20 early-type barred
galaxies to study the influence of bars in the building of galaxy bulges. Line
strength indices were measured and used to derive age and metallicity gradients
in the bulge region by comparing with stellar population models. The same
analysis was also carried out with similar data of unbarred galaxies taken from
the literature. The bulges of barred galaxies seem to be more metal rich, at a
given velocity dispersion (sigma), than the bulges of unbarred galaxies, as
measured by some metallicity sensitive indices. There are indications that the
ratio of relative abundance of alpha-elements with respect to iron, [E/Fe],
derived for the bulges of barred galaxies tend to lie above the values of the
unbarred galaxies at a given sigma. The metallicity gradients for the majority
of the bulges are negative, less metal rich towards the end of the bulge. The
gradient values show a large scatter for galaxies with sigma below 150 km/s.
The age distribution is related to the presence of bulge substructure such as a
nuclear ring or an inner disk. The metallicity of both the bulge and the bar
are very well correlated indicating a close link between the enrichment
histories of both components. Bulges of barred early type galaxies might have
suffered a different chemical enrichment compared to the bulges of unbarred
galaxies of the same morphological type, same central velocity dispersion and
low inclination angles. The hinted stellar populations differences separating
the bulges of barred and unbarred galaxies and the strong link existing between
the metallicity of the bulge and the presence of a bar points to scenarios were
they both form simultaneously in processes leading to rapid and massive
episodes of star formation, possibly linked to the bar formation.Comment: Accepted for publication in Astronomy and Astrophysic
Two semi-automated computational approaches for spectroscopic analysis of stellar photospheres: detailed characterization at high resolution and abundance determination at medium resolution
We report on two distinct computational approaches to self-consistently
measure photospheric properties of large samples of stars. Both procedures
consist of a set of several semi-integrated tasks based on shell and Python
scripts, which efficiently run either our own codes or open source software
commonly adopted by the astronomical community. One approach aims to derive the
main stellar photospheric parameters and abundances of a few elements by
analysing high-resolution spectra from a given public library homogeneously
constructed. The other one is applied to recover the abundance of a single
element in stars with known photospheric parameters by using mid-resolution
spectra from another open homogeneous database and calibrating derived
abundances. Both semi-automated computational approaches provide homogeneity
and objectivity to every step of the process and represent a fast way to reach
partial and final results as well as to estimate measurement errors, making
possible to systematically evaluate and improve the distinct steps.Comment: 7 pages, 4 figures, conference paper (I Workshop of Computacao
Cientifica em Astronomia, Brazil, 2011) to appear in the Journal of
Computational Interdisciplinary Sciences - JCI
Chemodynamical Simulations of Elliptical Galaxies
We review recent developments in the field of chemodynamical simulations of
elliptical galaxies, highlighting (in an admittedly biased fashion) the work
conducted with our cosmological N-body/SPH code GCD+. We have demonstrated
previously the recovery of several primary integrated early-type system scaling
relations (e.g. colour-magnitude relation, L_X-T_X-[Fe/H]_X) when employing a
phenomenological AGN heating scheme in conjunction with a self-consistent
treatment of star formation, supernovae feedback, radiative cooling, chemical
enrichment, and stellar/X-ray population synthesis. Here we emphasise
characteristics derived from the full spatial information contained within the
simulated dataset, including stellar and coronal morphologies, metallicity
distribution functions, and abundance gradients.Comment: to appear in the proceedings of Chemodynamics: from first stars to
local galaxies, Lyon, Franc
NGC1277: a massive compact relic galaxy in the nearby Universe
As early as 10 Gyr ago, galaxies with more than 10^11 Msun in stars already
existed. While most of these massive galaxies must have subsequently
transformed through on-going star formation and mergers with other galaxies, a
small fraction (<0.1%) may have survived untouched till today. Searches for
such relic galaxies, useful windows to explore the early Universe, have been
inconclusive to date: galaxies with masses and sizes like those observed at
high redshift (M*>10^11 Msun; Re<1.5 kpc) have been found in the local
Universe, but their stars are far too young for the galaxy to be a relic
galaxy. This paper explores the first case of a nearby galaxy, NGC1277 (in the
Perseus cluster at a distance of 73 Mpc), which fulfills all the criteria to be
considered a relic galaxy. Using deep optical spectroscopy, we derive the star
formation history along the structure of the galaxy: the stellar populations
are uniformly old (>10 Gyr) with no evidence for more recent star formation
episodes. The metallicity of their stars is super-solar ([Fe/H]=0.20+-0.04) and
alpha enriched ([alpha/Fe]=0.4+-0.1). This suggests a very short formation time
scale for the bulk of stars of this galaxy. This object also rotates very fast
(Vrot~300 km/s) and has a large velocity dispersion (sigma>300 km/s). NGC1277
will allow future explorations in full detail of properties such as the
structure, internal dynamics, metallicity, dust content and initial mass
function at around 10-12 Gyr back in time when the first massive galaxies were
built.Comment: 4 figures; Accepted for publication at ApJ Letter
Are Red Tidal Features Unequivocal Signatures of Major Dry Mergers?
We use a cosmological numerical simulation to study the tidal features
produced by a minor merger with an elliptical galaxy. We find that the
simulated tidal features are quantitatively similar to the red tidal features,
i.e., dry tidal features, recently found in deep images of elliptical galaxies
at intermediate redshifts. The minor merger in our simulation does not trigger
star formation due to active galactic nuclei heating. Therefore, both the tidal
features and the host galaxy are red, i.e. a dry minor merger. The stellar mass
of the infalling satellite galaxy is about 10^10 Msun, and the tidal debris
reach the surface brightness of mu_R~27 mag arcsec^-2. Thus, we conclude that
tidal debris from minor mergers can explain the observed dry tidal features in
ellipticals at intermediate redshifts, although other mechanisms (such as major
dry mergers) may also be important.Comment: 7 pages, 7 figures, accepted for publication in Ap
An Imaging Study of the Globular Cluster Systems of NGC 1407 and NGC 1400
We present wide-field Keck telescope imaging of the globular cluster (GC)
systems around NGC 1407 and NGC 1400 in the Eridanus galaxy cloud. This is
complemented by Hubble Space Telescope images from the Advanced Camera for
Surveys of NGC 1407 and Wide Field and Planetary Camera 2 images of NGC 1400.
We clearly detect bimodality in the GC colour distribution of NGC 1407. The
blue GC subpopulation has a mean colour of B-I = 1.61 and a relative
contribution of around 40%, whereas the red subpopulation with B-I = 2.06
contributes 60% to the overall GC system. Assuming old ages, this corresponds
to [Fe/H] = -1.45 and -0.19. Both subpopulations are intrinsically broad in
colour (indicating a range in ages and/or metallicities), with the red
subpopulation being broader than the blue. The GC colour distribution for NGC
1400 is less clear cut than for NGC 1407, however, we also find evidence for a
bimodal distribution. We find the NGC 1407 red GCs to be 20% smaller in size
than the blue ones. We find both GC systems to possess a GC surface density
distribution which is largely constant in these inner galaxy regions. We fit
isothermal-like profiles and derive GC system core radii of 9.4 kpc for NGC
1407 and 5.8 kpc for NGC 1400. For NGC 1407 we are able to separate the surface
density distribution into blue and red subpopulations, giving 17.8 and 7.6 kpc
respectively. Outside this central region, the radial profile of the GC surface
density is similar to that of the galaxy light for NGC 1407 but it is flatter
for NGC 1400. A fit to the GC luminosity function gives a distance modulus of
31.6, which is in good agreement with distances based on the Faber-Jackson
relation and the Virgo infall corrected velocity.Comment: 13 pages, 20 figures, 1 table, 4 tables in the appendix (available
from first author). Accepted for publication in MNRAS. Updated SBF distance
valu
Constraining stellar population parameters from narrow band photometric surveys using convolutional neural networks
Upcoming large-area narrow band photometric surveys, such as J-PAS, will
enable us to observe a large number of galaxies simultaneously and efficiently.
However, it will be challenging to analyse the spatially-resolved stellar
populations of galaxies from such big data to investigate galaxy formation and
evolutionary history. We have applied a convolutional neural network (CNN)
technique, which is known to be computationally inexpensive once it is trained,
to retrieve the metallicity and age from J-PAS-like narrow band images. The CNN
was trained using mock J-PAS data created from the CALIFA IFU survey and the
age and metallicity at each data point, which are derived using full spectral
fitting to the CALIFA spectra. We demonstrate that our CNN model can
consistently recover age and metallicity from each J-PAS-like spectral energy
distribution. The radial gradients of the age and metallicity for galaxies are
also recovered accurately, irrespective of their morphology. However, it is
demonstrated that the diversity of the dataset used to train the neural
networks has a dramatic effect on the recovery of galactic stellar population
parameters. Hence, future applications of CNNs to constrain stellar populations
will rely on the availability of quality spectroscopic data from samples
covering a wide range of population parameters.Comment: 9 pages, 10 figures, 2 tables. Accepted by MNRA
Velocity Dispersions and Stellar Populations of the Most Compact and Msssive early-Type Galaxies at Redshift similar to 1
We present Gran-Telescopio-Canarias/OSIRIS optical spectra of four of the most compact and massive early-type galaxies (ETGs) in the Groth Strip Survey at redshift z similar to 1, with effective radii R-e = 0.5-2.4 kpc and photometric stellarmasses M-star = (1.2-4) x 10(11)M(circle dot). We find that these galaxies have velocity dispersions sigma = 156-236 km s(-1). The spectra are well fitted by single stellar population models with approximately 1 Gyr of age and solar metallicity. We find that (1) the dynamical masses of these galaxies are systematically smaller by a factor of similar to 6 than the published stellarmasses using BRIJK photometry, and (2) when estimating stellarmasses as 0.7xM(dyn), a combination of passive luminosity fading with mass/size growth due to minor mergers can plausibly evolve our objects to match the properties of the local population of ETGs