Evolution of the anti-truncated stellar profiles of S0 galaxies since z=0.6 in the SHARDS survey I. Sample and methods
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2017
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Abstract
Context. The controversy about the origin of the structure of early-type S0-E/S0 galaxies may be due to the difficulty of comparing surface brightness profiles with different depths, photometric corrections and point spread function (PSF) effects (which are almost always ignored). Aims. We aim to quantify the properties of Type-III (anti-truncated) discs in a sample of S0 galaxies at 0.2 < z < 0.6. In this paper, we present the sample selection and describe in detail the methods to robustly trace the structure in their outskirts and correct for PSF effects. Methods. We have selected and classified a sample of 150 quiescent galaxies at 0.2 < z < 0.6 in the GOODS-N field. We performed a quantitative structural analysis of 44 S0-E/S0 galaxies. We have corrected their surface brightness profiles for PSF distortions and analysed the biases in the structural and photometric parameters when the PSF correction is not applied. Additionally, we have developed Elbow, an automatic statistical method to determine whether a possible break is significant - or not - and its type. We have made this method publicly available. Results. We find 14 anti-truncated S0-E/S0 galaxies in the range 0.2 < z < 0.6 (similar to 30% of the final sample). This fraction is similar to the those reported in the local Universe. In our sample, similar to 25% of the Type-III breaks observed in PSF-uncorrected profiles are artifacts, and their profiles turn into a Type I after PSF correction. PSF effects also soften Type-II profiles. We find that the profiles of Type-I S0 and E/S0 galaxies of our sample are compatible with the inner profiles of the Type-III, in contrast with the outer profiles. Conclusions. We have obtained the first robust and reliable sample of 14 anti-truncated S0-E/S0 galaxies beyond the local Universe, in the range 0.2 < z < 0.6. PSF effects significantly affect the shape of the surface brightness profiles in galaxy discs even in the case of the narrow PSF of HST/ACS images, so future studies on the subject should make an effort to correct them.
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© ESO, 2017. We thank the referee very much for comments that have significantly improved the quality of this work. Supported by the Ministerio de Economía y Competitividad del Gobierno de España (MINECO) under project AYA2012-31277 and project P3/86 of the Instituto de Astrofísica de Canarias. PGP-G acknowledges support from MINECO grants AYA2015-70815-ERC and AYA2015-63650-P. This work has made use of the Rainbow Cosmological Surveys Database, which is operated by the Universidad Complutense de Madrid (UCM) partnered with the University of California Observatories at Santa Cruz (UCO/Lick, UCSC). We are deeply grateful to the SHARDS team, since this work would not have been possible without their efforts. Based on observations made with the Gran Telescopio Canarias (GTC) installed at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, in the island of La Palma. We thank all the GTC Staff for their support and enthusiasm with the SHARDS project. This work is based on observations taken by the 3D-HST Treasury Program (GO 12177 and 12328) with the NASA/ESA HST, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. We acknowledge Dr. Pilar Esquej for describing us the usual procedure followed to identify AGN hosts in our S0 sample. The authors thank David Velilla for his kind technical support, and Ignacio Trujillo for his advice with the PSF correction procedures.