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
31 results
Search Results
Now showing 1 - 10 of 31
Item Empirical calibration of the near-infrared CaII triplet - I. The stellar library and index definition(Monthly notices of the Royal Astronomical Society, 2001) Cenarro, A. J.; Cardiel López, Nicolás; Gorgas García, Francisco Javier; Peletier, R. F.; Vazdekis, A.; Prada, F.A new stellar library at the near-IR spectral region developed for the empirical calibration of the Ca II triplet and stellar population synthesis modelling is presented. The library covers the range lambda lambda 8348-9020 at 1.5-Angstrom (FWHM) spectral resolution, and consists of 706 stars spanning a wide range in atmospheric parameters. We have defined a new set of near-IR indices, CaT*, CaT and PaT, which mostly overcome the limitations of previous definitions, the former being specially suited for the measurement of the Ca II triplet strength corrected for the contamination from Paschen lines. We also present a comparative study of the new and the previous Ca indices, as well as the corresponding transformations between the different systems. A thorough analysis of the sources of index errors and the procedure to calculate them is given. Finally, index and error measurements for the whole stellar library are provided together with the final spectra.Item Early-type galaxies in the Coma Cluster: A new piece in the calcium puzzle(Astrophysical journal, 2004) Cenarro, A. J.; Sánchez Blázquez, Patricia; Cardiel López, Nicolás; Gorgas García, Francisco JavierWe present measurements of the Ca II triplet and the Ca4227 Lick index for a sample of early-type galaxies in the Coma Cluster, deriving, for the first time, their corresponding relationships with velocity dispersion. Compared with a similar subsample of elliptical galaxies in the field, Coma galaxies with velocity dispersions in the range approximate to180-270 km s(-1) exhibit significant differences in the strengths of the Ca features, suggesting an influence of the environment on the star formation histories of these galaxies. We argue that the main scenarios previously proposed to explain the relatively low Ca II triplet of galaxies are not able by themselves to simultaneously reconcile the strengths of the two Ca indices in both environments.Item Evidence for intermediate-age stellar populations in early-type galaxies from K-band spectroscopy(Astrophysical Journal Letters, 2009) Mármol Queraltó, E.; Cardiel López, Nicolás; Sánchez Blázquez, Patricia; Trager, S. C.; Peletier, R. F.; Kuntschner, H.; Silva, D. R.; Cenarro, A. J.; Vazdekis, A.; Gorgas García, Francisco JavierThe study of stellar populations in early-type galaxies in different environments is a powerful tool for constraining their star formation histories. This study has been traditionally restricted to the optical range, where dwarfs around the turn-off and stars at the base of the red giant branch dominate the integrated light at all ages. The near-infrared spectral range is especially interesting since in the presence of an intermediate-age population, asymptotic giant branch stars are the main contributors. In this Letter, we measure the near-infrared indices Na I and D(CO) for a sample of 12 early-type galaxies in low-density environments and compare them with the Fornax galaxy sample presented by Silva et al.. The analysis of these indices in combination with Lick/IDS indices in the optical range reveals that (1) the Na I index is a metallicity indicator as good as C4668 in the optical range, and (2) D(CO) is a tracer of intermediate-age stellar populations. We find that low-mass galaxies in low-density environments show higher Na I and D(CO) than those located in the Fornax cluster, which points toward a late stage of star formation for the galaxies in less dense environments, in agreement with results from other studies using independent methods.Item Stellar populations of early-type galaxies in different environments - I. Line-strength indices. Relations of line-strengths with sigma(Astronomy & Astrophysics, 2006) Sánchez Blázquez, Patricia; Gorgas García, Francisco Javier; Cardiel López, Nicolás; González, J. J.This paper commences 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. In this paper we describe the details of the galaxy sample, the observations, and the data reduction. Line-strength indices and velocity dispersions (sigma) are measured in 98 early-type galaxies drawn from different environments, and the relation of the indices with the velocity dispersion analysed in detail. Results. The present sample indicates that some of the index-sigma relations depend on galaxy environment. In particular, the slope of the relation between Balmer lines and s is steeper for galaxies in the Virgo cluster, small groups, and in the field than for galaxies in the Coma cluster. In several indices there is also a significant sigma. set in the zero point between the relations defined by the different subsamples. The slopes of the index-sigma relation for the Virgo and low-density environment galaxies are explained by a variation of both age and metallicity, with velocity dispersion, as previously noted in other studies. For the galaxies in the Coma cluster, however, the relation of the indices with s only requires a variation of the abundance along the s sequence. In agreement with other studies, we find that the models that better reproduce the slopes are those in which the a elements vary more than the Fe-peak elements along the s sequence, while, at a given s, older galaxies show an higher sigma/Fe ratio. Conclusions. The results can be explained assuming that galaxies in the Coma cluster have experienced a truncated star formation and chemical enrichment history compared to a more continuous time-extended history for their counterparts in lower density environments.Item Medium-resolution Isaac Newton Telescope library of empirical spectra - II. The stellar atmospheric parameters(Monthly notices of the Royal Astronomical Society, 2007) Cenarro, A. J.; Peletier, R. F.; Sánchez Blázquez, Patricia; Selam, S. O.; Toloba, E.; Cardiel López, Nicolás; Falcón Barroso, J.; Gorgas García, Francisco Javier; Jiménez Vicente, J.; Vazdekis, A.We present a homogeneous set of stellar atmospheric parameters (T-eff, log g, [Fe/H]) for MILES, a new spectral stellar library covering the range lambda lambda 3525-7500 angstrom at 2.3 angstrom (FWHM) spectral resolution. The library consists of 985 stars spanning a large range in atmospheric parameters, from super-metal-rich, cool stars to hot, metal-poor stars. The spectral resolution, spectral type coverage and number of stars represent a substantial improvement over previous libraries used in population synthesis models. The atmospheric parameters that we present here are the result of a previous, extensive compilation from the literature. In order to construct a homogeneous data set of atmospheric parameters we have taken the sample of stars of Soubiran, Katz & Cayrel, which has very well determined fundamental parameters, as the standard reference system for our field stars, and have calibrated and bootstrapped the data from other papers against it. The atmospheric parameters for our cluster stars have also been revised and updated according to recent metallicity scales, colour-temperature relations and improved set of isochrones.Item Kinematic properties and stellar populations of faint early-type galaxies. II. Line-strength measurements of central coma galaxies(Astrophysical journal, 2009) Matkovic, A.; Guzmán, R.; Sánchez Blázquez, Patricia; Gorgas García, Francisco Javier; Cardiel López, Nicolás; Gruel, N.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(-1). The index-sigma relations for our sample, including galaxies with sigma < 100 km s(-1) (low-sigma), differ in shape depending on which index is used. We note two types of relations for the metallic indices: one showing a break in the slope around similar to 100 km s(-1) and another group with strong linear relations between an index and log s. 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 microturbulent 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 with E/S0s. Our data show that these trends derived for high-sigma galaxies extend down to dE/dS0s. This is a factor of similar to 2 lower in sigma than previously published work. We confirm that the observed anticorrelation 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.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 5175 Å and the 4000 Å 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 onto cooling- flow 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 (1987). 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 ow (5-17%) 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 ow galaxies flatten in the internal regions ( r <̃ 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 ow 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 ow attain extremely low values, suggesting that they could be hosting star formation with an origin not related to the cooling flows.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 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, PatriciaThe 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 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.