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
41 results
Search Results
Now showing 1 - 10 of 41
Item A new stellar library in the region of the CO index at 2.3 mu m - New index definition and empirical fitting functions(Astronomy & Astrophysics, 2008) Mármol Queraltó, E.; Cardiel López, Nicolás; Cenarro, A. J.; Vazdekis, A.; Gorgas García, Francisco Javier; Pedraz, S.; Peletier, R. F.; Sánchez Blázquez, P.The analysis of unresolved stellar populations demands evolutionary synthesis models with realistic physical ingredients and extended wavelength coverage. Aims. We quantitatively describe the first CO bandhead at 2.3 mu m to allow stellar population models to provide improved predictions in this wavelength range. Methods. We observed a new stellar library with a better coverage of the stellar atmospheric parameter space than in earlier works. We performed a detailed analysis of the robustness of previous CO index definitions with spectral resolution, wavelength calibration, signal-to-noise ratio, and flux calibration. Results. We define a new line-strength index for the first CO bandhead at 2.3 mu m, DCO, better suited for stellar population studies than previous index definitions. We derive empirical fitting functions for the CO feature as a function of the stellar parameters (T(eff), log g and [Fe/H]), showing a detailed quantitative metallicity dependence.Item Stellar populations in bulges of spiral galaxies(Astrophysics and space science, 2002) Jablonka, Pascale; Gorgas García, Francisco Javier; Goudfrooij, PaulWe present a few results of a work in progress tackling the radial spectroscopic properties of bulges of spiral galaxies.Item Spectral gradients in central cluster galaxies: further evidence of star formation in cooling flows(Monthly notices of the Royal Astronomical Society, 1998) Cardiel López, Nicolás; Gorgas García, Francisco Javier; Aragón Salamanca, A.We have obtained radial gradients in the spectral features of the lambda 4000-Angstrom break (D(4000)) and Mg(2) for a sample of 11 central cluster galaxies (CCGs): eight in clusters with cooling flows and three in clusters without. After careful removal of the emission lines found within the D(4000) and Mg(2) bandpasses for some objects, the new data strongly confirm the correlations between line-strength indices and the cooling flow phenomenon found in our earlier study. We find that such correlations depend on the presence and characteristics of emission lines in the inner regions of the CCGs. The nuclear indices are correlated with the mass deposition rate ((M) over dot) only when emission lines are found in the central regions of the galaxies. The central D(4000) and Mg(2) indices in cooling flow galaxies without emission lines are completely consistent with the indices measured in CCGs in clusters without cooling flows. CCGs in cooling flow clusters exhibit a clear sequence in the D(4000)-Mg(2) plane, with a neat segregation depending on emission-line type and blue morphology. This sequence can be modelled, using stellar population models with a normal initial mass function (IMF), by a recent (similar to 0.1 Gyr old) burst of star formation, although model uncertainties do not allow us to completely discard continuous star formation or a series of bursts over the last few Gyr. In CCGs with emission lines, the gradients in the spectral indices are flat or positive inside the emission-line regions, suggesting the presence of young stars. Outside the emission-line regions, and in cooling flow galaxies without emission lines, gradients are negative and consistent with those measured in CCGs in clusters without cooling hows and giant elliptical galaxies. Index gradients measured exclusively in the emission-line region correlate with hi. Using the same population models we have estimated the radial profiles of the mass transformed into new stars. The derived profiles are remarkably parallel to the expected radial behaviour of the mass deposition rate derived from X-ray observations. Moreover, a large fraction (probably most) of the cooling flow gas accreted into the emission-line region is converted into stars. In the Light of these new data, we discuss the evolutionary sequence suggested by McNamara, in which radio-triggered star formation bursts take place several times during the lifetime of the cooling flow. We conclude that this scenario is consistent with the available observations.Item Empirical calibration of the near-infrared CaII triplet - II. The stellar atmospheric parameters(Monthly notices of the Royal Astronomical Society, 2001) 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.Item Differences in carbon and nitrogen abundances between field and cluster early-type galaxies(Astrophysical journal, 2003) 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.Item Old stellar populations .4. Empirical fitting functions for features in the Spectra of G and K stars(Astrophysical journal supplement series, 1993) Gorgas García, Francisco Javier; Faber, S. M.; Burstein, David; González, J. Jesús; Courteau, Stéphane; Prosser, CharlesEmpirical fitting functions are presented that model the behavior of 11 strong atomic and molecular features in the spectra of Galactic G and K stars. The functions express the strength of spectral features as a function of V - K, surface gravity, and metallicity. The gravity calibration rests on stars in Galactic globular and open clusters, for which gravities have been derived by fitting to stellar evolutionary isochrones. The range of application of the fitting functions is set by the calibrating stars. There is good metallicity coverage from [Fe/H] = -0.75 to +0.50 dex, and cluster ages span 3.15 x 10^9 yr. However, the range in age is large only near solar metallicity, and the gravity partial derivatives may therefore be uncertain at metallicities much higher or lower than this value. In addition, the fitting functions build in whatever abundance ratio trajectories of elements relative to iron are present in local Galactic stars; these might differ from the element ratios present in external galaxies. In general, the behavior of the fitting functions matches expectations as to how these spectral features should behave as a function of basic stellar atmospheric parameters. The exception is CN (4150 Å), for which we find strong evidence for rapid onset of giant-branch mixing of CNO products to the stellar surface, setting in at V - K = 2.10. This confirms other recent studies of this index. The paper also presents new Lick line strength data on 112 field dwarfs and 92 cluster stars, plus colors, metallicities, and surface gravities for all Lick G and K stars published previously. The fitting functions are inverted to produce new output gravity and metallicity estimates for these stars and new average metallicities for all clusters, with errors of ±0.15 dex in [Fe/H] and ±0.23 dex in log g per star.Item The relation between stellar populations, structure and environment for dwarf elliptical galaxies from the MAGPOP-ITP(Monthly notices of the Royal Astronomical Society, 2008) Michielsen, D.; Boselli, A.; Conselice, C. J.; Toloba, E.; Whiley, I. M.; Aragón Salamanca, A.; Balcells, M.; Cardiel López, Nicolás; Cenarro, A. J.; Gorgas García, Francisco Javier; Peletier, R. F.; Vazdekis, A.Dwarf galaxies, as the most numerous type of galaxy, offer the potential to study galaxy formation and evolution in detail in the nearby universe. Although they seem to be simple systems at first view, they remain poorly understood. In an attempt to alleviate this situation, the MAGPOP EU Research and Training Network embarked on a study of dwarf galaxies named MAGPOP-ITP. In this paper, we present the analysis of a sample of 24 dwarf elliptical galaxies (dEs) in the Virgo cluster and in the field, using optical long-slit spectroscopy. We examine their stellar populations in combination with their light distribution and environment. We confirm and strengthen previous results that dEs are, on average, younger and more metal-poor than normal elliptical galaxies, and that their [alpha/Fe] abundance ratios scatter around solar. This is in accordance with the downsizing picture of galaxy formation where mass is the main driver for the star formation history. We also find new correlations between the luminosity-weighted mean age, the large-scale asymmetry, and the projected Virgocentric distance. We find that environment plays an important role in the termination of the star formation activity by ram-pressure stripping of the gas in short time-scales, and in the transformation of discy dwarfs to more spheroidal objects by harassment over longer time-scales. This points towards a continuing infalling scenario for the evolution of dEs.Item Line strengths and line strength gradients in bulges along the Hubble sequence(Astrophysics and space science, 1999) Goudfrooij, Paul; Gorgas García, Francisco Javier; Jablonka, PascaleWe present first results of a comprehensive survey of deep long-slit spectra along the minor axis of bulges of edge-on spiral galaxies. Our results indicate that stellar populations in bulges are fairly old and encompass a range of metallicities. The luminosity-weighted ages of bulges range from those found for cluster ellipticals to slightly 'younger' (by up to only a few Gyr, however). Their alpha/Fe element ratio is typically supersolar, consistent with those found in giant ellipticals. The radial line-strength gradients in bulges correlate with bulge luminosity. Generally, these findings are more compatible with predictions of the 'dissipative collapse' model than with those of the 'secular evolution' model.Item Spectral indexes in cooling flow galaxies: evidence of star formation(Monthly notices of the Royal Astronomical Society, 1995) Cardiel López, Nicolás; Gorgas García, Francisco Javier; Aragón Salamanca, A.Spectroscopic observations of central dominant cluster galaxies, with and without cooling flows, are presented. Through the analysis of absorption spectral features, namely the strength of the magnesium absorption at lambda 5175 Angstrom and the lambda 4000-Angstrom break, both in the galaxy centres and as a function of radius, we have been able to estimate the ongoing star formation induced by the large amounts of gas accreted on to cooling now galaxies. A correlation between the central spectral indices and the mass accretion rate is found in the sense that galaxies located in clusters with large cooling flows exhibit lower Mg-2 and D-4000 indices. A similar correlation with D-4000 was previously reported by Johnstone, Fabian & Nulsen. Our work, with the inclusion of the correlation in Mg-2, adds further weight to the conclusion that these spectral anomalies are caused by recent star formation. The application of simple stellar population models reveals that the measured indices are explained if a relatively small fraction of the total mass now (5-17 per cent) is forming new stars with a normal initial mass function. However, we argue that this is only a lower limit, and conclude that a large fraction of the gas accreted inside the galaxy could be forming stars. We find that spectral gradients in some cooling now galaxies flatten in the internal regions (r less than or similar to r(e)), where emission lines are usually detected. Gradients measured in the inner galaxy regions are, in the mean, lower than those of normal ellipticals, and exhibit a hint of a correlation with M. Application of the same population models to the observed spectral gradients allows us to conclude that the ongoing star formation is concentrated towards the inner parts of the cooling now galaxies and, therefore, the star formation does not follow the X-ray derived mass accretion profiles. Simultaneously, the spectral indices in the outer regions of some galaxies with and without cooling flow attain extremely low values, suggesting that they could be hosting star formation with an origin that is not related to the cooling flows.Item Effect of Environment on the Underlying Stellar Populations of Dwarf Elliptical Galaxies in the Coma Cluster(AIP Conference Proceedings, 2009) Matkovic, A.; Guzmán, R.; Sánchez Blázquez, P.; Cardiel López, Nicolás; Gorgas García, Francisco JavierWe 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.