arXiv subjects

Abilio Mateus

Publications and source records attributed to Abilio Mateus.

4 recordsLinked to original sources

arXiv2009

Emission line taxonomy and the nature of AGN-looking galaxies in the SDSS

Massive spectroscopic surveys like the SDSS have revolutionized the way we study AGN and their relations to the galaxies they live in. A first step in any such study is to define samples of different types of AGN on the basis of emission line ratios. This deceivingly simple step involves decisions on which classification scheme to use and data quality censorship. Galaxies with weak emission lines are often left aside or dealt with separately because one cannot fully classify them onto the standard Star-Forming, Seyfert of LINER categories. This contribution summarizes alternative classification schemes which include this very numerous population. We then study how star-formation histories and physical properties of the hosts vary from class to class, and present compelling evidence that the emission lines in the majority of LINER-like systems in the SDSS are not powered by black-hole accretion. The data are fully consistent with them being galaxies whose old stars provide all the ionizing power needed to explain their line ratios and luminosities. Such retired galaxies deserve a place in the emission line taxonomy.

astro-ph.CO↗

arXiv2008

The scale dependence of mass assembly in galaxies

We compare the results of the mark correlation analysis of galaxies in a sample from the Sloan Digital Sky Survey and from two galaxy catalogs obtained by semi-analytical galaxy formation models implemented on the Millennium Simulation. We use the MOPED method to retrieve the star formation history of observed galaxies and use star formation parameters as weights to the mark correlations. We find an excellent match between models and observations when the mark correlations use stellar mass and luminosity as weights. The most remarkable result is related to the mark correlations associated to the evolution of mass assembly through star formation in galaxies, where we find that semi-analytical models are able to reproduce the main trends seen in the observational data. In addition, we find a good agreement between the redshift evolution of the mean total mass formed by star formation predicted by the models and that measured by MOPED. Our results show that close galaxy pairs today formed more stellar mass ~10 Gyr ago than the average, while more recently this trend is the opposite, with close pairs showing low levels of star formation activity. We also show a strong correlation in simulations between the shape and time evolution of the star formation marks and the number of major mergers experienced by galaxies, which drive the environmental dependence in galaxy formation by regulating the star formation process.

astro-ph↗

arXiv2008

Evolution of the galaxy merger rate in model universes

We investigate the evolution of the galaxy merger rate predicted by two semi-analytical galaxy formation models implemented on the Millennium Simulation of dark matter structure growth. The fraction of merging galaxy pairs at each time-step of the simulation is derived from the galaxy catalogues obtained by the models and the results are compared with various observational estimates of merger fractions taken from the literature. We find a good match between the pair fractions derived from the simulation and the observed counting of galaxy pairs obtained by different sources in the redshift range 0 < z < 1.2. The predicted evolution of the number of galaxy mergers per Gyr grows with redshift as an exponential rate proportional to (1+z)^m, with m ranging from 0.6 to 0.8 for 0 < z < 2, depending on the luminosity and mass ratios of the merging galaxies. Our results are in agreement with recent observational results that argue for a flat evolution in the fraction of galaxy mergers since z ~ 1.2. The weak evolution predicted for the galaxy merger rate in an hierarchical model universe shows that the mass assembly evolution of galaxies through mergers does not follow the rapid evolution of the halo merger rate obtained in previous studies.

astro-ph↗

arXiv2006

Semi-empirical analysis of Sloan Digital Sky Survey galaxies: II. The bimodality of the galaxy population revisited

We revisit the bimodal distribution of the galaxy population commonly seen in the local universe. Here we address the bimodality observed in galaxy properties in terms of spectral synthesis products, such as mean stellar ages and stellar masses, derived from the application of this powerful method to a volume-limited sample, with magnitude limit cutoff M_r = -20.5, containing about 50 thousand luminous galaxies from the SDSS Data Release 2. In addition, galaxies are classified according to their emission line properties in three distinct spectral classes: star-forming galaxies, with young stellar populations; passive galaxies, dominated by old stellar populations; and, hosts of active nuclei, which comprise a mix of young and old stellar populations. We show that the extremes of the distribution of some galaxy properties, essentially galaxy colours, 4000 A break index, and mean stellar ages, are associated to star-forming galaxies at one side, and passive galaxies at another. We find that the mean light-weighted stellar age of galaxies is the direct responsible for the bimodality seen in the galaxy population. The stellar mass, in this view, has an additional role since most of the star-forming galaxies present in the local universe are low-mass galaxies. Our results also give support to the existence of a 'downsizing' in galaxy formation, where massive galaxies seen nowadays have stellar populations formed at early times.

astro-ph↗