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