The stellar mass assembly of galaxies from z=0 to z=4. Analysis of a sample selected in the rest-frame near-infrared with Spitzer

Using a sample of ~28,000 sources selected at 3.6-4.5 microns with Spitzer observations of the HDF-N, the CDF-S, and the Lockman Hole (surveyed area: ~664 arcmin^2), we study the evolution of the stellar mass content of the Universe at 0<z<4. We calculate stellar masses and photometric redshifts, based on ~2,000 templates built with stellar and dust emission models fitting the UV-to-MIR SEDs of galaxies with spectroscopic redshifts. We estimate stellar mass functions for different redshift intervals. We find that 50% of the local stellar mass density was assembled at 0<z<1 (average SFR:0.048 M_sun/yr/Mpc^3), and at least another 40% at 1<z<4 (average SFR: 0.074 M_sun/yr/Mpc^3). Our results confirm and quantify the ``downsizing'' scenario of galaxy formation. The most massive galaxies (M>10^12.0 M_sun) assembled the bulk of their stellar content rapidly (in 1-2 Gyr) beyond z~3 in very intense star formation events (producing high specific SFRs). Galaxies with 10^11.5<M/M_sun<10^12.0 assembled half of their stellar mass before z~1.5, and more than 90% of their mass was already in place at z~0.6. Galaxies with M<10^11.5 M_sun evolved more slowly (presenting smaller specific SFRs), assembling half of their stellar mass below z~1. About 40% of the local stellar mass density of 10^9.0<M/M_sun<10^11.0 galaxies was assembled below z~0.4, most probably through accretion of small satellites producing little star formation. The cosmic stellar mass density at z>2.5 is dominated by optically faint (R>25) red galaxies (Distant Red Galaxies or BzK sources) which account for ~30% of the global population of galaxies, but contribute at least 60% to the cosmic stellar mass density. Bluer galaxies (e.g., Lyman Break Galaxies) are more numerous but less massive, contributing less than 50% to the global stellar mass density at high redshift.Comment: Published in ApJ. 38 pages, 10 figures, 5 tables, 2 appendices. Some changes to match the final published versio

Physical properties of Lyman-alpha emitters at z∼0.3z\sim 0.3 from UV-to-FIR measurements

The analysis of the physical properties of low-redshift Ly$\alpha$ emitters (LAEs) can provide clues in the study of their high-redshift analogues. At $z \sim 0.3$, LAEs are bright enough to be detected over almost the entire electromagnetic spectrum and it is possible to carry out a more precise and complete study than at higher redshifts. In this study, we examine the UV and IR emission, dust attenuation, SFR and morphology of a sample of 23 GALEX-discovered star-forming (SF) LAEs at $z \sim 0.3$ with direct UV (GALEX), optical (ACS) and FIR (PACS and MIPS) data. Using the same UV and IR limiting luminosities, we find that LAEs at $z\sim 0.3$ tend to be less dusty, have slightly higher total SFRs, have bluer UV continuum slopes, and are much smaller than other galaxies that do not exhibit Ly$\alpha$ emission in their spectrum (non-LAEs). These results suggest that at $z \sim 0.3$ Ly$\alpha$ photons tend to escape from small galaxies with low dust attenuation. Regarding their morphology, LAEs belong to Irr/merger classes, unlike non-LAEs. Size and morphology represent the most noticeable difference between LAEs and non-LAEs at $z \sim 0.3$. Furthermore, the comparison of our results with those obtained at higher redshifts indicates that either the Ly$\alpha$ technique picks up different kind of galaxies at different redshifts or that the physical properties of LAEs are evolving with redshift.Comment: Accepted for publication in Ap

MEGADES: MEGARA Galaxy Discs Evolution Survey. Data Release I: central fields

The main interest of the Science Team for the exploitation of the MEGARA instrument at the 10.4m Gran Telescopio Canarias (GTC hereafter) is devoted to the study of nearby galaxies, with focus on the research of the history of star formation, and chemical and kinematical properties of disc systems. We refer to this project as MEGADES: MEGARA Galaxy Discs Evolution Survey. The initial goal of MEGADES is to provide a detailed study of the inner regions of nearby disc galaxies, both in terms of their spectrophotometric and chemical evolution, and their dynamical characterisation, by disentangling the contribution of in-situ and ex-situ processes to the history of star formation and effective chemical enrichment of these regions. In addition, the dynamical analysis of these inner regions naturally includes the identification and characterization of galactic winds potentially present in these regions. At a later stage, we will extend this study further out in galactocentric distance. The first stage of this project encompasses the analysis of the central regions of a total of 43 nearby galaxies observed with the MEGARA Integral Field Unit for 114 hours, including both Guaranteed Time and Open Time observations. In this paper we provide a set of all the processed data products available to the community and early results from the analysis of these data regarding stellar continuum, ionized and neutral gas features.Comment: Accepted for publication in Astronomy & Astrophysic

Aperture effects on the oxygen abundance determinations from CALIFA data

This paper aims at providing aperture corrections for emission lines in a sample of spiral galaxies from the Calar Alto Legacy Integral Field Area Survey (CALIFA) database. In particular, we explore the behavior of the log([OIII]5007/Hbeta)/([NII]6583/Halpha) (O3N2) and log[NII]6583/Halpha (N2) flux ratios since they are closely connected to different empirical calibrations of the oxygen abundances in star forming galaxies. We compute median growth curves of Halpha, Halpha/Hbeta, O3N2 and N2 up to 2.5R_50 and 1.5 disk R_eff. The growth curves simulate the effect of observing galaxies through apertures of varying radii. The median growth curve of the Halpha/Hbeta ratio monotonically decreases from the center towards larger radii, showing for small apertures a maximum value of ~10% larger than the integrated one. The median growth curve of N2 shows a similar behavior, decreasing from the center towards larger radii. No strong dependence is seen with the inclination, morphological type and stellar mass for these growth curves. Finally, the median growth curve of O3N2 increases monotonically with radius. However, at small radii it shows systematically higher values for galaxies of earlier morphological types and for high stellar mass galaxies. Applying our aperture corrections to a sample of galaxies from the SDSS survey at 0.02<=z<=0.3 shows that the average difference between fiber-based and aperture corrected oxygen abundances, for different galaxy stellar mass and redshift ranges, reaches typically to ~11%, depending on the abundance calibration used. This average difference is found to be systematically biased, though still within the typical uncertainties of oxygen abundances derived from empirical calibrations. Caution must be exercised when using observations of galaxies for small radii (e.g. below 0.5R_eff) given the high dispersion shown around the median growth curves.Comment: Accepted for publication in Ap

The O3N2 and N2 abundance indicators revisited: improved calibrations based on CALIFA and Te-based literature data

The use of IFS is since recently allowing to measure the emission line fluxes of an increasingly large number of star-forming galaxies both locally and at high redshift. The main goal of this study is to review the most widely used empirical oxygen calibrations, O3N2 and N2, by using new direct abundance measurements. We pay special attention to the expected uncertainty of these calibrations as a function of the index value or abundance derived and the presence of possible systematic offsets. This is possible thanks to the analysis of the most ambitious compilation of Te-based HII regions to date. This new dataset compiles the Te-based abundances of 603 HII regions extracted from the literature but also includes new measurements from the CALIFA survey. Besides providing new and improved empirical calibrations for the gas abundance, we also present here a comparison between our revisited calibrations with a total of 3423 additional CALIFA HII complexes with abundances derived using the ONS calibration by Pilyugin et al. (2010). The combined analysis of Te-based and ONS abundances allows us to derive their most accurate calibration to date for both the O3N2 and N2 single-ratio indicators, in terms of all statistical significance, quality and coverage of the space of parameters. In particular, we infer that these indicators show shallower abundance dependencies and statistically-significant offsets compared to those of Pettini and Pagel (2004), Nagao et al. (2006) and P\'erez-Montero and Contini (2009). The O3N2 and N2 indicators can be empirically applied to derive oxygen abundances calibrations from either direct abundance determinations with random errors of 0.18 and 0.16, respectively, or from indirect ones (but based on a large amount of data) reaching an average precision of 0.08 and 0.09 dex (random) and 0.02 and 0.08 dex (systematic; compared to the direct estimations),respectively.Comment: 12 pages, 5 figures, accepted for publication in A&

MEGARA-GTC stellar spectral library: I

MEGARA (Multi Espectrografo en GTC de Alta Resolucion para Astronomia) is an optical (3650-9750 Å), fibre-fed, medium-high spectral resolution (R = 6000, 12 000 and 20 000) instrument for the Gran Telescopio CANARIAS (GTC) 10.4-m telescope, commissioned in the summer of 2017, and currently in operation. The scientific exploitation of MEGARA requires a stellar spectra library to interpret galaxy data and to estimate the contribution of the stellar populations. In this paper, we introduce the MEGARA-GTC spectral library, detailing the rationale behind the building of this catalogue. We present the spectra of 97 stars (21 individual stars and 56 members of the globular cluster M15, which are both subsamples taken during the commissioning runs, and 20 stars from our ongoing GTC Open-Time programme). The spectra have R = 20 000 in the HR-R and HR-I set-ups, centred at 6563 and 8633 Å, respectively. We describe the procedures to reduce and analyse the data. Then, we determine the best-fitting theoretical models to each spectrum through a χ^(2) minimization technique, to derive the stellar physical parameters, and we discuss the results. We have also measured some absorption lines and indices. Finally, we introduce our project to complete the library and the data base in order to make the spectra available to the community

A new insight of AGC 198691 (Leoncino) galaxy with MEGARA at the GTC

We describe the observations of the low metallicity nearby galaxy AGC 198691 (Leoncino Dwarf) obtained with the Integral Field Unit of the instrument MEGARA at the Gran Telescopio Canarias. The observations cover the wavelength ranges 4304–5198 Å and 6098–7306 Å with a resolving power R ≈ 6000. We present 2D maps of the ionized gas, deriving the extension of the H II region and gas kinematics from the observed emission lines. We have not found any evidence of recent gas infall or loss of metals by means of outflows. This result is supported by the closed-box model predictions, consistent with the oxygen abundance found by other authors in this galaxy and points towards Leoncino being a genuine XMD galaxy. We present for the first time spatially resolved spectroscopy allowing the detailed study of a star-forming region. We use POPSTAR + CLOUDY models to simulate the emission-line spectrum. We find that the central emission-line spectrum can be explained by a single young ionizing cluster with an age of ≈ 3.5 ± 0.5 Myr and a stellar mass of ≈ 2 ×103 M⊙. However, the radial profiles of [OIII] λ 5007Å and the Balmer lines in emission demand photoionization by clusters of different ages between 3.5 and 6.5 Myr that might respond either to the evolution of a single cluster evolving along the cooling time of the nebula (≈ 3 Myr at the metallicity of Leoncino, Z≈ 0.0004) or to mass segregation of the cluster, being both scenarios consistent with the observed equivalent widths of the Balmer lines. © 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.This work is based on observations made with the Gran Telescopio Canarias (GTC), installed in the Spanish Observatorio del Roque de los Muchachos, on the island of La Palma. The work is based on data obtained with the MEGARA instrument, funded by European Regional Development Funds (ERDF), through the Programa Operativo Canarias FEDER 2014-2020. The authors thank the support given by Dr. Antonio Cabrera and Dr. Daniel Reverté, GTC Operations Group staff, during the preparation and execution of the observations at the GTC. This work has been supported by DGICYT grant RTI2018- 096188-B-I00, which is partly funded by the European Regional Development Fund (ERDF). Jorge Iglesias acknowledges financial support from the following projects: Estallidos6 AYA2016-79724-C4 (Spanish Ministerio de Economía y Competitividad), Estallidos7 PID2019-107408GB-C44 (Spanish Ministerio de Ciencia e Innovación), grant P18-FR-2664 (Junta de Andalucía), and grantSEV-2017-0709 ‘Centro de Excelencia Severo Ochoa Program’ (Spanish Science Ministry). This research is based on observations made with the NASA/ESA Hubble Space Telescope obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5–26555. These observations are associated with program 15243. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555.Peer reviewe

A new insight of AGC 198691 (Leoncino) galaxy with MEGARA at the GTC

We describe the observations of the low metallicity nearby galaxy AGC 198691 (Leoncino Dwarf) obtained with the Integral Field Unit of the instrument MEGARA at the Gran Telescopio Canarias. The observations cover the wavelength ranges 4304-5198 Aand 6098-7306 Awith a resolving power R approximate to 6000. We present 2D maps of the ionized gas, deriving the extension of the H II region and gas kinematics from the observed emission lines. We have not found any evidence of recent gas infall or loss of metals by means of outflows. This result is supported by the closed-box model predictions, consistent with the oxygen abundance found by other authors in this galaxy and points towards Leoncino being a genuine XMD galaxy. We present for the first time spatially resolved spectroscopy allowing the detailed study of a star-forming region. We use POPSTAR + CLOUDY models to simulate the emission-line spectrum. We find that the central emission-line spectrum can be explained by a single young ionizing cluster with an age of approximate to 3.5 +/- 0.5 Myr and a stellar mass of approximate to 2 x10(3) M-circle dot. However, the radial profiles of [O III].5007Aand the Balmer lines in emission demand photoionization by clusters of different ages between 3.5 and 6.5 Myr that might respond either to the evolution of a single cluster evolving along the cooling time of the nebula (approximate to 3 Myr at the metallicity of Leoncino, Z approximate to 0.0004) or to mass segregation of the cluster, being both scenarios consistent with the observed equivalent widths of the Balmer lines

Mapa de series, geoseries y geopermaseries de vegetación de España (Memoria del mapa de vegetación potencial de España). Parte II

Peer Reviewe