Person: Cardiel López, Nicolás
Universidad Complutense de Madrid
Faculty / Institute
Física de la Tierra y Astrofísica
Astronomía y Astrofísica
Now showing 1 - 10 of 114
PublicationStellar 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 JavierA 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. PublicationMEGARA, the R=6000-20000 IFU and MOS of GTC(SPIE-Int Soc Optical Engineering, 2018) Gil de Paz, Armando; Gallego Maestro, Jesús; Bouquin, A.; Carbajo, J.; Cardiel López, Nicolás; Castillo Morales, África; Esteban San Román, Segundo; López Orozco, José Antonio; Pascual, S.; Picazo, P.; Sánchez Penim, Ainhoa; Velázquez, M.; Zamorano Calvo, Jaime; Catalán Torrecilla, Cristina; Dullo, Bililign; Pérez González, P.G.; Roca Fábrega, SantiMEGARA is the new generation IFU and MOS optical spectrograph built for the 10.4m Gran Telescopio CANARIAS (GTC). The project was developed by a consortium led by UCM (Spain) that also includes INAOE (Mexico), IAA-CSIC (Spain) and UPM (Spain). The instrument arrived to GTC on March 28th 2017 and was successfully integrated and commissioned at the telescope from May to August 2017. During the on-sky commissioning we demonstrated that MEGARA is a powerful and robust instrument that provides on-sky intermediate-to-high spectral resolutions R_(FWHM) ~ 6,000, 12,000 and 20,000 at an unprecedented efficiency for these resolving powers in both its IFU and MOS modes. The IFU covers 12.5 x 11.3 arcsec2 while the MOS mode allows observing up to 92 objects in a region of 3.5 x 3.5 arcmin^(2) . In this paper we describe the instrument main subsystems, including the Folded-Cassegrain unit, the fiber link, the spectrograph, the cryostat, the detector and the control subsystems, and its performance numbers obtained during commissioning where the fulfillment of the instrument requirements is demonstrated. PublicationDifferences 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. PublicationEmpirical 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. PublicationThe very faint K-band afterglow of GRB 020819 and the dust extinction hypothesis of the dark bursts(IOP Publishing, 2003-08-01) Klose, S.; Henden, A. A.; Greiner, J.; Hartmann, D. H.; Cardiel López, Nicolás; Castro Tirado, A. J.; Cerón, J. M. C.; Gallego Maestro, Jesús; Gorosabel, J.; Stecklum, B.; Tanvir, N.; Thiele, U.; Vrba, F. J.; Zeh, A.We report rapid follow-up K'-band observations of the error box of the bright High Energy Transient Explorer burst GRB 020819. We find that any afterglow was fainter than K' = 19 only 9 hr after the burst. Because no optical afterglow was found, GRB 020819 represents a typical "dark burst.'' At first, we discuss if extinction by cosmic dust in the GRB host galaxy could explain the faintness of the afterglow of GRB 020819. We then turn to the entire ensemble of K-band dark afterglows. We find that extinction by cosmic dust in the GRB host galaxies is still a possible explanation for the faintness of many afterglows. In all investigated cases a combination of only a modest extinction with a modest redshift can explain the observations. However, the required extinction is very high if these bursts occurred at redshifts smaller than unity, perhaps arguing for alternative models to explain the nature of the dark bursts. PublicationData boundary fitting using a generalized least-squares method(Wiley, 2009-06-21) Cardiel López, NicolásIn many astronomical problems one often needs to determine the upper and/or lower boundary of a given data set. An automatic and objective approach consists in fitting the data using a generalized least-squares method, where the function to be minimized is defined to handle asymmetrically the data at both sides of the boundary. In order to minimize the cost function, a numerical approach, based on the popular DOWNHILL simplex method, is employed. The procedure is valid for any numerically computable function. Simple polynomials provide good boundaries in common situations. For data exhibiting a complex behaviour, the use of adaptive splines gives excellent results. Since the described method is sensitive to extreme data points, the simultaneous introduction of error weighting and the flexibility of allowing some points to fall outside of the fitted frontier, supplies the parameters that help to tune the boundary fitting depending on the nature of the considered problem. Two simple examples are presented, namely the estimation of spectra pseudo-continuum and the segregation of scattered data into ranges. The normalization of the data ranges prior to the fitting computation typically reduces both the numerical errors and the number of iterations required during the iterative minimization procedure. PublicationSpectral indexes in cooling flow galaxies: evidence of star formation(Wiley, 1995-11-15) 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. PublicationConstraints on the evolutionary mechanisms of massive galaxies since z ∼ 1 from their velocity dispersions(Wiley, 2015-10-11) Peralta de Arriba, L.; Balcells, M.; Trujillo, I.; Falcón Barroso, J.; Tapia, T.; Cardiel López, Nicolás; Gallego Maestro, Jesús; Guzmán, R.; Hempel, A.; Martín Navarro, I.; Pérez González, Pablo Guillermo; Sánchez Blázquez, P.Several authors have reported that the dynamical masses of massive compact galaxies (M_⋆ ≳ 10^11 M_⊙, r_e ∼ 1 kpc), computed as M_dyn=5.0 σ_e^2r_e/GMdyn=5.0 σe2re/G, are lower than their stellar masses M_⋆. In a previous study from our group, the discrepancy is interpreted as a breakdown of the assumption of homology that underlie the M_dyn determinations. Here, we present new spectroscopy of six redshift z ≈ 1.0 massive compact ellipticals from the Extended Groth Strip, obtained with the 10.4 m Gran Telescopio Canarias. We obtain velocity dispersions in the range 161–340 km s^−1. As found by previous studies of massive compact galaxies, our velocity dispersions are lower than the virial expectation, and all of our galaxies show M_dyn < M_⋆ (assuming a Salpeter initial mass function). Adding data from the literature, we build a sample covering a range of stellar masses and compactness in a narrow redshift range z ≈ 1.0. This allows us to exclude systematic effects on the data and evolutionary effects on the galaxy population, which could have affected previous studies. We confirm that mass discrepancy scales with galaxy compactness. We use the stellar mass plane (M_⋆, σ_e, r_e) populated by our sample to constrain a generic evolution mechanism. We find that the simulations of the growth of massive ellipticals due to mergers agree with our constraints and discard the assumption of homology. PublicationPulse processing in TES detectors: comparative of different short filter methods based on optimal filtering. Case study for Athena X-IFU(SPI-Int Soc. Optical Engineering, 2021-12-28) Coboa, Beatriz; Cardiel López, Nicolás; Ceballosa, María Teresa; Peillec, PhilippeIn the framework of the ESA Athena mission, the X-ray Integral Field Unit (X-IFU) instrument to be on board the X-ray Athena Observatory is a cryogenic micro-calorimeter array of Transition Edge Sensor (TES) detectors aimed at providing spatially resolved high-resolution spectroscopy. As a part of the on-board Event Processor (EP), the reconstruction software will provide the energy, spatial location and arrival time of the incoming X-ray photons hitting the detector and inducing current pulses on it. Being the standard optimal filtering technique the chosen baseline reconstruction algorithm, different modifications have been analyzed to process pulses shorter than those considered of high resolution (those where the full length is not available due to a close pulse after them) in order to select the best option based on energy resolution and computing performance results. It can be concluded that the best approach to optimize the energy resolution for short filters is the 0-padding filtering technique, benefiting also from a reduction in the computational resources. However, it’s high sensitivity to offset fluctuations currently prevents its use as the baseline treatment for the X-IFU application for lack of consolidated information on the actual stability it will get in flight. PublicationLine-strength indices in bright spheroidal galaxies: Evidence for a stellar population dichotomy between spheroidal and elliptical galaxies(IOP Publishing, 1997-05-20) Gorgas García, Francisco Javier; Pedraz, Santos; Guzmán, Rafael; Cardiel López, Nicolás; González, J. J.We present new measurements of central line-strength indices (namely, Mg-2, (Fe), and H beta) and gradients for a sample of six bright spheroidal (Sph) galaxies in the Virgo Cluster. Comparison with similar measurements for elliptical (E) galaxies, galactic globular clusters (GGCs), and stellar population models yield the following results: (1) in contrast with bright E galaxies, bright Sph galaxies are consistent with solar abundance [Mg/Fe] ratios; (2) bright Sph galaxies exhibit metallicities ranging from values typical for metal-rich GGCs to those for E galaxies; (3) although absolute mean ages are quite model dependent, we find evidence that the stellar populations of some (if not all) Sph galaxies look significantly younger than GCCs; and (4) Mg-2 gradients of bright Sph galaxies are significantly shallower than those of E galaxies. We conclude that the dichotomy found in the structural properties of Sph and E galaxies is also observed in their stellar populations. A tentative interpretation in terms of differences in star formation histories is suggested.