Person:
Gorgas García, Francisco Javier

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First Name
Francisco Javier
Last Name
Gorgas García
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Department
Física de la Tierra y Astrofísica
Area
Astronomía y Astrofísica
Identifiers
UCM identifierORCIDScopus Author IDWeb of Science ResearcherIDDialnet ID

Search Results

Now showing 1 - 10 of 25
  • Publication
    Stellar population study in early-type galaxies: an approach from the K band
    (Cambridge Univ. Press, 2009-08) Mármol Queraltó, Esther; Cardiel López, Nicolás; Sánchez Blázquez, P.; Trager, S.C.; Peletier, R. F.; Kuntschner, H.; Silva, D. R.; Cenarro, A. J.; Vazdekis, A.; Gorgas García, Francisco Javier
    A full understanding of the physical properties of integrated stellar systems demands a multiwavelength approach since each spectral window shows us the contribution of different types of stars. However, most of the observational effort in stellar population studies has been focused on the optical range. Now, the new generation of instruments allow us to explore the K band, where RGB and AGB stars dominate the light of the integrated spectra. Here we present a K-band spectroscopic analysis of early-type galaxies in different environments. Our sample comprises 12 field early-type galaxies observed with ISAAC at VLT with medium resolution, and they are compared with 11 Fornax cluster galaxies previously reported by Silva et al. (2008). The clear differences found in the infrared DCO and NaI indices between field and Fornax galaxies are discussed, trying to solve the puzzle formed by the near-infrared and optical measurements.
  • Publication
    Differences in carbon and nitrogen abundances between field and cluster early-type galaxies
    (IOP Publishing, 2003-06-20) Sánchez Blázquez, Patricia; Gorgas García, Francisco Javier; Cardiel López, Nicolás; Cenarro, J.; González, J. J.
    Central line-strength indices were measured in the blue spectral region for a sample of 98 early-type galaxies in different environments. For most indices (Mg b and [Fe] in particular), elliptical galaxies in rich clusters and in low-density regions follow the same index-sigma relations. However, striking spectral differences between field elliptical galaxies and their counterparts in the central region of the Coma Cluster are found for the first time, with galaxies in the denser environment showing significantly lower C4668 and CN2 absorption strengths. The most convincing interpretation of these results is that they represent a difference in abundance ratios arising from distinct star formation and chemical-enrichment histories of galaxies in different environments. A scenario in which elliptical galaxies in clusters are fully assembled at earlier stages than their low-density counterparts is discussed.
  • Publication
    Empirical calibration of the near-infrared CaII triplet - II. The stellar atmospheric parameters
    (Wiley, 2001-09-21) Cenarro, A. J.; Gorgas García, Francisco Javier; Cardiel López, Nicolás; Pedraz, S.; Peletier, R. F.; Vazdekis, A.
    We present a homogeneous set of stellar atmospheric parameters (T-eff, log g, [Fe/H]) for a sample of about 700 field and cluster stars which constitute a new stellar library in the near-IR developed for stellar population synthesis in this spectral region (lambda 8350-9020). Having compiled the available atmospheric data in the literature for field stars, we have found systematic deviations between the atmospheric parameters from different bibliographic references. The Soubiran, Katz & Cayrel sample of stars with very well determined fundamental parameters has been taken as our standard reference system, and other papers have been calibrated and bootstrapped against it. The obtained transformations are provided in this paper. Once most of the data sets were on the same system, final parameters were derived by performing error weighted means. Atmospheric parameters for cluster stars have also been revised and updated according to recent metallicity scales and colour-temperature relations.
  • Publication
    Effect of Environment on the Underlying Stellar Populations of Dwarf Elliptical Galaxies in the Coma Cluster
    (American Institute of Physics, 2009) Matkovic, A.; Guzmán, R.; Sánchez Blázquez, P.; Cardiel López, Nicolás; Gorgas García, Francisco Javier
    We derive ages, metallicities and [alpha/Fe] ratios for dwarf early-type galaxies (dE/dS0) in the center and a region believed to be infalling into the Coma cluster. We find that a set of metallic indices cannot be described by linear relations with velocity dispersion (sigma), while another group of indices exhibits linear index-sigma relations. dE/dS0 galaxies in the core of the cluster are on average younger, and have lower metallicities and lower alpha-ratios (solar to sub-solar) than the more luminous elliptical galaxies. On the other hand, dEs/dSos in the infall region of Coma form a less homogeneous population. We find an unusually high fraction of dE/dS0s with high [alpha/Fe] ratios, suggesting short time scales for the star formation histories for these galaxies. Furthermore, the dE/dS0s with high alpha-ratios have a range of ages and metallicities implying multiple formation scenarios where some galaxies have experienced their short star formation bursts at more recent epochs.
  • Publication
    Stellar populations of early-type galaxies in different environments - III. Line-strength gradients
    (EDP Sciencies, 2006-10) Sánchez Blázquez, Patricia; Gorgas García, Francisco Javier; Cardiel López, Nicolás
    Aims. This is the third paper of a series devoted to the study of the stellar content of early-type galaxies. The goal of the series is to set constraints on the evolutionary status of these objects. Methods. We present line-strength gradients for 22 spectral indices measured in a sample of 82 early-type galaxies in different environments, including the high-density cores of the Coma cluster, the Virgo cluster, poor groups, and isolated field galaxies. Using new evolutionary population synthesis models, we derive age and metallicity gradients, and compare the mean values with the predictions of different galaxy formation models. We explore the behaviour of individual chemical species by deriving the metallicity gradient with different indicators. Results. We find that the strength of the metallicity gradient inferred from stellar population models depends on the specific Lick index employed. In particular, metallicity gradients obtained with CN2 and C4668 combined with H beta are steeper than those measured using Ca4227 or Fe4383. The correlation of the metallicity gradients with other parameters also depends on the specific index employed. If the metallicity gradient is obtained using CN2 and Mgb, then it correlates with the central age of the galaxies. On the contrary, if Fe4383 or Ca4227 is used, the metallicity gradient correlates with the velocity dispersion gradient. Conclusions. This may suggest that several mechanisms have helped to set the age and metallicity gradients in early-type galaxies. While we do not find any correlation between the metallicity gradient and the central velocity dispersion for galaxies in low-density environments, we find a marginal correlation between the metallicity gradient and the mass for galaxies in the centre of the Coma cluster. We also find a trend for which galaxies in denser environments show a steeper metallicity gradient than galaxies in less dense environments. We interpret these results in light of the different mechanisms proposed to explain the observed changes between galaxies as a function of environment.
  • Publication
    Stellar populations of early-type galaxies in different environments - II. Ages and metallicities
    (EDP Sciencies, 2006-10) Sánchez Blázquez, P.; Gorgas García, Francisco Javier; Cardiel López, Nicolás; González, J. J.
    This is the second paper of a series devoted to the study of the stellar content of early-type galaxies. The goal of the series is to set constraints on the evolutionary status of these objects Methods. We use a new set of models that include an improved stellar library (MILES) to derive simple stellar population (SSP)-equivalent parameters in a sample of 98 early-type galaxies. The sample contains galaxies in the field, poor groups, and galaxies in the Virgo and Coma clusters. Results. We find that low-density environment galaxies span a larger range in SSP age and metallicity than their counterparts in high density environments, with a tendency for lower sigma galaxies to be younger. Early-type galaxies in low-density environments appear on average similar to 1.5 Gyr younger and more metal rich than their counterparts in high density environments. The sample of low-density environment galaxies shows an age-metallicity relation in which younger galaxies are found to be more metal rich, but only when metallicity is measured with a Fe-sensitive index. Conversely, there is no age-metallicity relation when the metallicity is measured with a Mg sensitive index. The mass-metallicity relation is only appreciable for the low-density environment galaxies when the metallicity is measured with a Mg-sensitive index, and not when the metallicity is measured with other indicators. On the contrary, this relation exists for the high-density environment galaxies independent of the indicator used to measure the metallicity. Conclusions. This suggests a dependence of the mass-metallicity relation on the environment of the galaxies. Our data favour a scenario in which galaxies in low density environments have suffered a more extended star formation history than the galaxies in the Coma cluster, which appear to host more homogenous stellar populations.
  • Publication
    The fundamental properties of dwarf elliptical galaxies in clusters
    (Astronomical Soc Pacific, 2003) Guzmán, R.; Graham, A. W.; Matkovic, A.; Vass, I.; Gorgas García, Francisco Javier; Cardiel López, Nicolás
    We present preliminary results of an extensive study of the fundamental properties of dwarf elliptical galaxies (dEs) in the Coma cluster. Our study will combine HST surface photometry with ground-based UBRIJK photometry and optical spectroscopy. The combined data set will be used to investigate the intrinsic correlations among global parameters in cluster dEs, including the Fundamental Plane, color-magnitude, Faber-Jackson's, Kormendy's, and velocity dispersion vs line strength indices. These empirical correlations have provided important constraints to theoretical models of galaxy formation and evolution for "normal" ellipticals. Although dEs are the most abundant galaxy population in clusters their properties remain, however, largely unknown. Our study aims to provide an essential reference for testing current theories on the formation and evolution of dEs in clusters, and understanding their relation to more massive ellipticals.
  • Publication
    Mg and TiO spectral features at the near-IR: spectrophotometric index definitions and empirical calibrations
    (Wiley, 2009-07-11) Cenarro, A. J.; Cardiel López, Nicolás; Vazdekis, A.; Gorgas García, Francisco Javier
    Using the near-infrared spectral stellar library of Cenarro et al., the behaviour of the Mg i line at 8807 A and nearby TiO bands is analyzed in terms of the effective temperature, surface gravity and metallicity of the library stars. New spectroscopic indices for both spectral features - namely MgI and sTiO - are defined, and their sensitivities to different signal-to-noise ratios, spectral resolutions, flux calibrations and sky emission-line residuals are characterized. The two new indices exhibit interesting properties. In particular, MgI is a good indicator of the Mg abundance, whereas sTiO is a powerful dwarf-to-giant discriminator for cold spectral types. Empirical fitting polynomials that reproduce the strength of the new indices as a function of the stellar atmospheric parameters are computed, and a fortran routine with the fitting function predictions is made available. A thorough study of several error sources, non-solar [Mg/Fe] ratios and their influence on the fitting function residuals is also presented. From this analysis, an [Mg/Fe] underabundance of similar to -0.04 is derived for the Galactic open cluster M67.
  • Publication
    Using spectroscopic data to disentangle stellar population properties
    (EDP Sciencies, 2003-10) Cardiel López, Nicolás; Gorgas García, Francisco Javier; Sánchez Blázquez, P.; Cenarro, A. J.; Pedraz, S.; Bruzual, G.; Klement, J.
    It is well known that, when analyzed in the light of current synthesis model predictions, variations in the physical properties of single stellar populations (e.g. age, metallicity, initial mass function, element abundance ratios) may have a similar effect in their integrated spectral energy distributions. The confusion is even worsened when more realistic scenarios, i.e. composite star formation histories, are considered. This is, in fact, one of the major problems when facing the study of stellar populations in star clusters and galaxies. Typically, the observational efforts have aimed to find the most appropriate spectroscopic indicators in order to avoid, as far as possible, degeneracies in the parameter space. However, from a practical point of view, the most suited observables are not, necessarily, those that provide more orthogonality in that parameter space, but those that give the best balance between parameter degeneracy and sensitivity to signal-to-noise ratio per Angstrom, S/N(Angstrom). In order to achieve the minimum combined total error in the derived physical parameters, this work discusses how the functional dependence of typical line-strength indices and colors on S/N(Angstrom) allows to define a suitability parameter which helps to obtain more realistic combinations of spectroscopic data. As an example, we discuss in more detail the problem of breaking the well known age-metallicity degeneracy in relatively old stellar populations, comparing the suitability of different spectroscopic diagrams for a simple stellar population of solar metallicity and of 12 Gyr in age.
  • Publication
    A K band survey in the Groth Strip Flanking Fields
    (Instituto de Astronomía. Universidad Nacional Autónoma de México, 2003) Serrano, A.; Cardiel López, Nicolás; Gallego Maestro, Jesús; Balcells, M.; Prieto, M.; Cristóbal, D.; Guzmán, R.; Pelló, R.; Gorgas García, Francisco Javier; Zamorano Calvo, Jaime
    As a part of our collaboration in the COSMOS Project, devoted to the characterization of galaxies during the ep o c h of maximum star formation in the history of the Universe, we have carried out a deep photometric survey covering about 380 arcmin^(2) in the so-called Groth Strip Flanking Fields. The observations were obtained in the K´ band with the OMEGA-PRIME infrared camera at the 3.5 m telescope at the Hispano–German Calar Alto Observatory . Galaxy counts and photometric redshifts will be computed in order to prepare future observations with EMIR.