Gorgas García, Francisco Javier

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

Search Results

Now showing 1 - 10 of 22
  • 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
    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
    Formation and evolution of dwarf early-type galaxies in the Virgo cluster II. Kinematic scaling relations (Corrigendum) (vol 548, pg A76, 2012)
    (EDP Sciencies, 2013-09) Toloba, E.; Boselli, A.; Peletier, R. F.; Falcón Barroso, J.; van de Ven, G.; Gorgas García, Francisco Javier
  • Publication
    The origin of dwarf early-type galaxies in the Virgo cluster
    (EDP Sciencies, 2011) Toloba, E.; Boselli, A.; Peletier, R. F.; Gorgas García, Francisco Javier
    We present new medium resolution kinematic data for a sample of 21 dwarf early-type galaxies (dEs) mainly in the Virgo cluster. These data are used to study the origin of the dE population inhabiting rich clusters. Within them we detect two different subpopulations: half of the sample (52%) are rotationally supported and the other half are pressure supported. We also find that the rotationally supported dEs are located in the outer parts of the cluster, present disky morphological shapes and are younger than those pressure supported that are concentrated in the core of the cluster without any underlying structures. Our analysis reveals that the rotationally supported objects have rotation curves similarly shaped to those of star forming galaxies of similar luminosities and follow the Tully-Fisher relation. This is expected if dE galaxies are the descendant of low luminosity star forming systems which recently entered the cluster and lost their gas due to a ram pressure stripping event, quenching their star formation activity and transforming them into quiescent systems, but conserving their angular momentum.
  • Publication
    Kinematic properties as probes of the evolution of dwarf galaxies in the Virgo cluster
    (IOP Publishing, 2009-12-10) Toloba, E.; Boselli, A.; Gorgas García, Francisco Javier; Peletier, R. F.; Cenarro, A. J.; Gadotti, D. A.; Gil de Paz, Armando; Pedraz, S.; Yildiz, U.
    We present new observational results on the kinematical, morphological, and stellar population properties of a sample of 21 dEs located both in the Virgo Cluster and in the field, which show that 52% of the dEs (1) are rotationally supported, (2) exhibit structural signs of typical rotating systems such as disks, bars, or spiral arms, (3) are younger (~3 Gyr) than non-rotating dEs, and (4) are preferentially located either in the outskirts of Virgo or in the field. This evidence is consistent with the idea that rotationally supported dwarfs are late-type spirals or irregulars that recently entered the cluster and lost their gas through a ram pressure stripping event, quenching their star formation and becoming dEs through passive evolution. We also find that all, but one, galaxies without photometric hints for hosting disks are pressure supported and are all situated in the inner regions of the cluster. This suggests a different evolution from the rotationally supported systems. Three different scenarios for these non-rotating galaxies are discussed (in situ formation, harassment, and ram pressure stripping).
  • Publication
    Stellar kinematics and structural properties of virgo cluster dwarf early-type galaxies from the smakced project. II. The survey and a systematic analysis of kinematic anomalies and asymmetries
    (University Chicago Press, 2014-12) Toloba, E.; Guhathakurta, P.; Peletier, R. F.; Boselli, A.; Lisker, T.; Falcón Barroso, J.; Simón, J. D.; van de Ven, G.; Paudel, S.; Emsellem, E.; Janz, J.; den Brok, M.; Gorgas García, Francisco Javier; Hensler, G.; Laurikainen, E.; Niemi, S. M.; Rys, A.; Salo, H.
    We present spatially resolved kinematics and global stellar populations and mass-to-light ratios for a sample of 39 dwarf early-type (dE) galaxies in the Virgo cluster studied as part of the SMAKCED stellar absorption-line spectroscopy and imaging survey. This sample is representative of the early-type population in the Virgo cluster in the absolute magnitude range -19.0 < M-r < -16.0 and of all morphological subclasses found in this galaxy population. For each dE, we measure the rotation curve and velocity dispersion profile and fit an analytic function to the rotation curve. We study the significance of the departure of the rotation curve from the best-fit analytic function (poorly fit) and of the difference between the approaching and receding sides of the rotation curve (asymmetry). Our sample includes two dEs with kinematically decoupled cores that have been previously reported. We find that 62 +/- 8% (23 out of the 39) of the dEs have a significant anomaly in their rotation curve. Analysis of the images reveals photometric anomalies for most galaxies. However, there is no clear correlation between the significance of the photometric and kinematic anomalies. We measure age-sensitive (H-beta and H-gamma A) and metallicity sensitive (Fe4668 and Mgb) Lick spectral indices in the LIS-5 angstrom system. This population of galaxies exhibits a wide range of ages and metallicities; we also find that 4 dEs show clear evidence of emission partially filling in the Balmer absorption lines. Finally, we estimate the total masses and dark matter fractions of the dEs and plot them in the mass-size, themass-velocity dispersion, and the fundamental plane scaling relations. The dEs seem to be the bridge between massive early-type galaxies and dSphs, and have a median total mass within the R-e of logM(e) = 9.1 +/- 0.2 and a median dark matter fraction within the R-e of f(DM) = 46 +/- 18%. Any formation model for the dE galaxy class must account for this diversity of kinematic and photometric anomalies and stellar populations.
  • Publication
    Stellar kinematics and structural properties of virgo cluster dwarf early-type galaxies from the smakced project. III. Angular momentum and constraints on formation scenarios
    (IOP Publishing, 2015-02-01) Toloba, E.; Guhathakurta, P.; Boselli, A.; Peletier, R. F.; Emsellem, E.; Lisker, T.; van de Ven, G.; Simon, J. D.; Falcón Barroso, J.; Adams, J. J.; Benson, A. J.; Boissier, S.; den Brok, M.; Gorgas García, Francisco Javier; Hensler, G.; Janz, J.; Laurikainen, E.; Paudel, S.; Rys, A.; Salo, H.
    We analyze the stellar kinematics of 39 dwarf early-type galaxies (dEs) in the Virgo Cluster. Based on the specific stellar angular momentum lambda(Re) and the ellipticity, we find 11 slow rotators and 28 fast rotators. The fast rotators in the outer parts of the Virgo Cluster rotate significantly faster than fast rotators in the inner parts of the cluster. Moreover, 10 out of the 11 slow rotators are located in the inner 3 degrees (D < 1 Mpc) of the cluster. The fast rotators contain subtle disk-like structures that are visible in high-pass filtered optical images, while the slow rotators do not exhibit these structures. In addition, two of the dEs have kinematically decoupled cores and four more have emission partially filling in the Balmer absorption lines. These properties suggest that Virgo Cluster dEs may have originated from late-type star-forming galaxies that were transformed by the environment after their infall into the cluster. The correlation between lambda(Re) and the clustercentric distance can be explained by a scenario where low luminosity star-forming galaxies fall into the cluster, their gas is rapidly removed by ram-pressure stripping, although some of it can be retained in their core, their star formation is quenched but their stellar kinematics are preserved. After a long time in the cluster and several passes through its center, the galaxies are heated up and transformed into slow rotating dEs.
  • Publication
    Formation and evolution of dwarf early-type galaxies in the Virgo cluster II. Kinematic scaling relations
    (EDP Sciencies, 2012-12) Toloba, E.; Boselli, A.; Peletier, R. F.; Falcón Barroso, J.; van de Ven, G.; Gorgas García, Francisco Javier
    We place our sample of 18 Virgo dwarf early-type galaxies (dEs) on the (V - K)_e-velocity dispersion, Faber-Jackson, and fundamental plane (FP) scaling relations for massive early-type galaxies (Es). We use a generalized velocity dispersion, which includes rotation, to be able to compare the location of both rotationally and pressure supported dEs with those of early and late-type galaxies. We find that dEs seem to bend the Faber-Jackson relation of Es to lower velocity dispersions, being the link between Es and dwarf spheroidal galaxies (dSphs). Regarding the FP relation, we find that dEs are significantly offset with respect to massive hot stellar systems, and re-casting the FP into the so-called.-space suggests that this offset is related to dEs having a total mass-to-light ratio higher than Es but still significantly lower than dSph galaxies. Given a stellar mass-to-light ratio based on the measured line indices of dEs, the FP offset allows us to infer that the dark matter fraction within the half light radii of dEs is on average ≳42% (uncertainties of 17% in the K band and 20% in the V band), fully consistent with an independent estimate in an earlier paper in this series. We also find that dEs in the size-luminosity relation in the near-infrared, like in the optical, are offset from early-type galaxies, but seem to be consistent with late-type galaxies. We thus conclude that the scaling relations show that dEs are different from Es, and that they further strengthen our previous findings that dEs are closer to and likely formed from late-type galaxies.
  • Publication
    Empirical calibration of the near-infrared CaII triplet - IV. The stellar population synthesis models
    (Wiley, 2003-04-21) Vazdekis, A.; Cenarro, A. J.; Gorgas García, Francisco Javier; Cardiel López, Nicolás; Peletier, R. F.
    We present a new evolutionary stellar population synthesis model, which predicts spectral energy distributions for single-age single-metallicity stellar populations (SSPs) at resolution 1.5 Angstrom (FWHM) in the spectral region of the near-infrared Ca II triplet feature. The main ingredient of the model is a new extensive empirical stellar spectral library that has been recently presented by Cenarro et al., which is composed of more than 600 stars with an unprecedented coverage of the stellar atmospheric parameters. Two main products of interest for stellar population analysis are presented. The first is a spectral library for SSPs with metallicities -1.7<[Fe/H]<+0.2, a large range of ages (0.1-18 Gyr) and initial mass function (IMF) types. They are well suited to modelling galaxy data, since the SSP spectra, with flux-calibrated response curves, can be smoothed to the resolution of the observational data, taking into account the internal velocity dispersion of the galaxy, allowing the user to analyse the observed spectrum in its own system. We also produce integrated absorption-line indices (namely CaT*, CaT and PaT) for the same SSPs in the form of equivalent widths. We find the following behaviour for the Ca II triplet feature in old-aged SSPs: (i) the strength of the CaT* index does not change much with time for all metallicities for ages larger than similar to3 Gyr; (ii) this index shows a strong dependence on metallicity for values below [M/H]similar to-0.5; and (iii) for larger metallicities this feature does not show a significant dependence either on age or on the metallicity, being more sensitive to changes in the slope of power-like IMF shapes. The SSP spectra have been calibrated with measurements for globular clusters by Armandroff & Zinn, which are well reproduced, probing the validity of using the integrated Ca II triplet feature for determining the metallicities of these systems. Fitting the models to two early-type galaxies of different luminosities (NGC 4478 and 4365), we find that the Ca II triplet measurements cannot be fitted unless a very dwarf-dominated IMF is imposed, or if the Ca abundance is even lower than the Fe abundance. More details can be found in work by Cenarro et al.
  • Publication
    A new stellar library in the region of the CO index at 2.3 mu m - New index definition and empirical fitting functions
    (EDP Sciencies, 2008-10) 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.