J. P. Torres-Papaqui

THE BRIGHTEST CLUSTER GALAXY IN A85: THE LARGEST CORE KNOWN SO FAR

We have found that the brightest cluster galaxy (BCG) in Abell 85, Holm 15A, displays the largest core so far known. Its cusp radius, r = 4.57 ± 0.06 kpc (4. ′′ 26±0.

THE STAR FORMATION HISTORY AND CHEMICAL EVOLUTION OF STAR-FORMING GALAXIES IN THE NEARBY UNIVERSE

We have determined the metallicity (O/H) and nitrogen abundance (N/O) of a sample of 122,751 star-forming galaxies (SFGs) from the Data Release 7 of the Sloan Digital Sky Survey. For all these galaxies we have also determined their morphology and obtained a comprehensive picture of their star formation history (SFH) using the spectral synthesis code STARLIGHT. The comparison of the chemical abundance with the SFH allows us to describe the chemical evolution of the SFGs in the nearby universe (z ≤ 0.25) in a manner consistent with the formation of their stellar populations and morphologies. A high fraction (45%) of the SFGs in our sample show an excess abundance of nitrogen relative to their metallicity. We also find this excess to be accompanied by a deficiency of oxygen, which suggests that this could be the result of effective starburst winds. However, we find no difference in the mode of star formation of the nitrogen-rich and nitrogen-poor SFGs. Our analysis suggests that they all form their stars through a succession of bursts of star formation extended over a period of few Gyr. What produces the chemical differences between these galaxies seems therefore to be the intensity of the bursts: the galaxies with an excess of nitrogen are those that are presently experiencing more intense bursts or have experienced more intense bursts in their past. We also find evidence relating the chemical evolution process to the formation of the galaxies: the galaxies with an excess of nitrogen are more massive, and have more massive bulges and earlier morphologies than those showing no excess. Contrary to expectation, we find no evidence that the starburst wind efficiency decreases with the mass of the galaxies. As a possible explanation we propose that the loss of metals consistent with starburst winds took place during the formation of the galaxies, when their potential wells were still building up, and consequently were weaker than today, making starburst winds more efficient and independent of the final mass of the galaxies. In good agreement with this interpretation, we also find evidence consistent with downsizing, according to which the more massive SFGs formed before the less massive ones.

On the nature of the brightest globular cluster in M81

We analyse the photometric, chemical, star formation history and structural properties of the brightest globular cluster (GC) in M81, referred to as GC1 in this work, with the intention of establishing its nature and origin. We find that it is a metal-rich ([Fe/H] =− 0.60 ± 0.10), alpha-enhanced ([α/Fe] ∼ 0.20 ± 0.05), core-collapsed (core radius rc = 1.2 pc, tidal radius rt = 76rc), old (>13 Gyr) cluster. It has an ultraviolet excess equivalent of ∼2500 blue horizontal branch stars. It is detected in X-rays indicative of the presence of low-mass binaries. With a mass of 1.0 × 10 7 M� , the cluster is comparable in mass to M31-G1 and is four times more massive than ω Cen. The values of rc, absolute magnitude and mean surface brightness of GC1 suggest that it could be, like massive GCs in other giant galaxies, the left-over nucleus of a dissolved dwarf galaxy.

What sparks the radio-loud phase of nearby quasars?

To better constrain the hypotheses proposed to explain why only a few quasars are radio loud (RL), we compare the characteristics of 1958 nearby

A Search for Giant Radio Galaxy Candidates and Their Radio-Optical Follow-up

(z\le 0.3)

Statistical assessment of the relation between the inferred morphological type and the emission-line activity type of a large sample of galaxies

SDSS quasars, covered by the FIRST and NVSS radio surveys. Only 22\% are RL with

Narrow-Line AGNs: confirming the relationship between metallicity and accretion rate

\log(L_{1.4{\rm GHz}}) \ge 22.5

THE NATURE AND ORIGIN OF NARROW LINE AGN ACTIVITY IN A SAMPLE OF ISOLATED SDSS GALAXIES

W Hz

A MID INFRARED STUDY OF LOW-LUMINOSITY AGNS WITH WISE

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The Chemical Evolution of Narrow Emission Line Galaxies: the Key to their Formation Processes

, the majority being compact (C), weak radio sources (WRS), with