arXiv subjects

Patricia Sanchez-Blazquez

Publications and source records attributed to Patricia Sanchez-Blazquez.

46 records · Page 3Linked to original sources

arXiv2009

The Chemical Evolution of Globular Clusters I. Reactive Elements and Non-Metals

We propose a new chemical evolution model aimed at explaining the chemical properties of globular clusters (GC) stars. Our model depends upon the existence of (i) a peculiar pre-enrichment phase in the GC's parent galaxy associated with very low-metallicity Type II supernovae (SNeII), and (ii) localized inhomogeneous enrichment from a single Type Ia supernova (SNeIa) and intermediate-mass (4 7Msun) asymptotic giant branch (AGB) field stars. GC formation is then assumed to take place within this chemically-peculiar region. Thus, in our model the first low-mass GC stars to form are those with peculiar abundances (i.e., O-depleted and Na-enhanced) while ``normal'' stars (i.e., O-rich and Na depleted) are formed in a second stage when self-pollution from SNeII occurs and the peculiar pollution from the previous phase is dispersed. In this study, we focus on three different GCs: NGC6752, NGC6205 (M13) and NGC2808. We demonstrate that, within this framework, a model can be constructed which is consistent with (i) the elemental abundance anti-correlations, (ii) isotopic abundance patterns, and (iii) the extreme [O/Fe] values observed in NGC2808 and M13, without violating the global constraints of approximately unimodal [Fe/H] and C+N+O.

astro-ph.GA↗

arXiv2008

Carbon and Nitrogen Abundances in Early-type Galaxies

For the first time, we undertake a systematic examination of the nitrogen abundances for a sample of 35 early-type galaxies spanning a range of masses and local environment. The nitrogen-sensitive molecular feature at 3360Åhas been employed in conjunction with a suite of atomic- and molecular-sensitive indices to provide unique and definitive constraints on the chemical content of these systems. By employing NH3360, we are now able to break the carbon, nitrogen, and oxygen degeneracies inherent to the use of the CN-index. We demonstrate that the NH3360 feature shows little dependency upon the velocity dispersion (our proxy for mass) of the galaxies, contrary to what is seen for carbon- and magnesium-sensitive indices. At face value, these results are at odds with conclusions drawn previously using indices sensitive to both carbon and nitrogen, such as cyanogen (CN). With the aid of stellar population models, we find that the N/Fe ratios in these galaxies are consistent with being mildly-enhanced with respect to the solar ratio. We also explore the dependence of these findings upon environment, by analyzing the co-added spectra of galaxies in the field and the Coma cluster. We confirm the previously found differences in carbon abundances between galaxies in low- and high-density environments, while showing that these differences do not seem to exist for nitrogen. We discuss the implications of these findings for the derivation of the star formation histories in early-type galaxies, and for the origin of carbon and nitrogen, themselves.

astro-ph↗

arXiv2008

Kinematic Properties and Stellar Populations of Faint Early-Type Galaxies: II. Line-Strength Measurements of Central Coma Galaxies

We present line-strength measurements for 74 early-type galaxies in the core of the Coma cluster reaching down to velocity dispersions, sigma, of 30 km/s. The index-sigma relations for our sample, including galaxies with sigma<100 km/s (low-sigma), differ in shape depending on which index is used. We notice two types of relations for the metallic indices: one showing a break in the slope around ~100 km/s, and another group with strong linear relations between an index and log sigma. We find no connection between the behavior of index-sigma relations with either alpha- or Fe-peak elements. However, we find indications that the relations are tighter for indices which do not depend on the micro-turbulent velocities of stellar atmospheres. We confirm previous results that low-sigma galaxies including dE/dS0s are on average younger, less metal rich, and have lower [alpha/Fe] in comparison to E/S0s. Our data show that these trends derived for high-sigma galaxies extend down to dE/dS0s. This is a factor of ~2 lower in sigma than previously published work. We confirm that the observed anti-correlation between age and metallicity for high-sigma galaxies is consistent with the effects of correlated errors. Low-sigma galaxies also show a similar relation between age and metallicity as a result of correlated errors. However, they are offset from this relationship so that, on average, they are less metal rich and younger than their high-sigma counterparts.

astro-ph↗

arXiv2008

Hydrodynamical Adaptive Mesh Refinement Simulations of Disk Galaxies

To date, fully cosmological hydrodynamic disk simulations to redshift zero have only been undertaken with particle-based codes, such as GADGET, Gasoline, or GCD+. In light of the (supposed) limitations of traditional implementations of smoothed particle hydrodynamics (SPH), or at the very least, their respective idiosyncrasies, it is important to explore complementary approaches to the SPH paradigm to galaxy formation. We present the first high-resolution cosmological disk simulations to redshift zero using an adaptive mesh refinement (AMR)-based hydrodynamical code, in this case, RAMSES. We analyse the temporal and spatial evolution of the simulated stellar disks' vertical heating, velocity ellipsoids, stellar populations, vertical and radial abundance gradients (gas and stars), assembly/infall histories, warps/lopsideness, disk edges/truncations (gas and stars), ISM physics implementations, and compare and contrast these properties with our sample of cosmological SPH disks, generated with GCD+. These preliminary results are the first in our long-term Galactic Archaeology Simulation program.

astro-ph↗

arXiv2006

Chemical Evolution of the Galactic Bulge

Adopting a single-zone framework, with accretion of primordial gas on a free-fall timescale, the chemical evolution of the Galactic bulge is calculated, assuming (i) a corresponding rapid timescale for star formation, and (ii) an initial mass function biased towards massive stars. We emphasise here the uncertainties associated with the underlying physics (specifically, stellar nucleosynthesis) and how those uncertainties are manifest in the predicted abundance ratio patterns in the resulting present-day Galactic bulge stellar populations.

astro-ph↗

arXiv2006

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.

astro-ph↗

arXiv2006

MILES: A Medium resolution INT Library of Empirical Spectra

A new stellar library developed for stellar population synthesis modeling is presented. The library consist of 985 stars spanning a large range in atmospheric parameters. The spectra were obtained at the 2.5m INT telescope and cover the range 3525-7500A at 2.3A (FWHM) spectral resolution. The spectral resolution, spectral type coverage, flux calibration accuracy and number of stars represent a substantial improvement over previous libraries used in population synthesis models.

astro-ph↗

arXiv2006

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.

astro-ph↗

arXiv2005

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.

astro-ph↗

arXiv2005

The Correlation of Metallicity Gradient with Galaxy Mass

A number of previous studies have searched for a correlation between radial metallicity gradients and early-type galaxy mass -- no convincing trends have been found. Here we re-examine this issue with several key enhancements: using total metallicity from studies that have broken the age-metallicity degeneracy, excluding galaxies with young stellar ages (i.e. tho se that have experienced a recent central starburst) and using the K-band to derive galaxy luminosities. We find that Coma cluster galaxies have metallicity gradients which correlate with galaxy mass. Furthermore, gradients have values similar to those of monolithic collapse models. The combination of dissipative formation and energy injection from supernova provides a mechanism for the trends with galaxy mass, however other explanations are possible. Additional high quality observational data is needed to further constrain the gas physics involved in galaxy formation.

astro-ph↗