234 research outputs found
The Brightest Cluster Galaxy in Abell 85: 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, kpc (), is more than 18 times
larger than the mean for BCGs, and kpc larger than A2261-BCG, hitherto
the largest-cored BCG (Postman, Lauer, Donahue, et al. 2012) Holm 15A hosts the
luminous amorphous radio source 0039-095B and has the optical signature of a
LINER. Scaling laws indicate that this core could host a supermassive black
hole (SMBH) of mass . We
suggest that cores this large represent a relatively short phase in the
evolution of BCGs, whereas the masses of their associated SBMH might be set by
initial conditions.Comment: 14 pages, 3 figure, 2 tables, accepted for publication in ApJ Letters
on October 6th, 2014, replacement of previous manuscript submitted on May
30th, 2014 to astro-p
The star formation history and chemical evolution of star forming galaxies in the nearby universe
We have determined the O/H and N/O of a sample of 122751 SFGs from the DR7 of
the SDSS. For all these galaxies we have also determined their morphology and
their SFH using the code STARLIGHT. The comparison of the chemical abundance
with the SFH allows us to describe the chemical evolution in the nearby
universe (z < 0.25) in a manner which is consistent with the formation of their
stellar populations and morphologies. A 45% of the SFGs in our sample show an
excess of abundance in 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 they all form their stars through a succession of
bursts of star formation extended over a few Gyr period. 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, have more massive bulges and earlier morphologies
than those showing no excess. As a possible explanation we propose that the
lost 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.Comment: 69 pages, 27 figures, accepted for publication in Ap
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