32 research outputs found
What makes a galaxy radio-loud?
We compare the Spectral Energy Distribution (SED) of radio-loud and
radio-quiet AGNs in three different samples observed with SDSS: radio-loud AGNs
(RLAGNs), Low Luminosity AGNs (LLAGNs) and AGNs in isolated galaxies (IG-AGNs).
All these galaxies have similar optical spectral characteristics. The median
SED of the RLAGNs is consistent with the characteristic SED of quasars, while
that of the LLAGNs and IG-AGNs are consistent with the SED of LINERs, with a
lower luminosity in the IG-AGNs than in the LLAGNs. We infer the masses of the
black holes (BHs) from the bulge masses. These increase from the IG-AGNs to the
LLAGNs and are highest for the RLAGNs. All these AGNs show accretion rates near
or slightly below 10% of the Eddington limit, the differences in luminosity
being solely due to different BH masses. Our results suggests there are two
types of AGNs, radio quiet and radio loud, differing only by the mass of their
bulges or BHs.Comment: 3 pages, 3 figures; to appear in Proceedings of IAU Symposium No.
284, The Spectral Energy Distribution of Galaxies (SED2011), Preston, UK, 5-9
sep. 201
SSDSS IV MaNGA - Properties of AGN host galaxies
We present here the characterization of the main properties of a sample of 98
AGN host galaxies, both type-II and type-I, in comparison with those of about
2700 non-active galaxies observed by the MaNGA survey. We found that AGN hosts
are morphologically early-type or early-spirals. For a given morphology AGN
hosts are, in average, more massive, more compact, more central peaked and
rather pressurethan rotational-supported systems. We confirm previous results
indicating that AGN hosts are located in the intermediate/transition region
between star-forming and non-star-forming galaxies (i.e., the so-called green
valley), both in the ColorMagnitude and the star formation main sequence
diagrams. Taking into account their relative distribution in terms of the
stellar metallicity and oxygen gas abundance and a rough estimation of their
molecular gas content, we consider that these galaxies are in the process of
halting/quenching the star formation, in an actual transition between both
groups. The analysis of the radial distributions of the starformation rate,
specific star-formation rate, and molecular gas density shows that the
quenching happens from inside-out involving both a decrease of the efficiency
of the star formation and a deficit of molecular gas. All the intermediate
data-products used to derive the results of our analysis are distributed in a
database including the spatial distribution and average properties of the
stellar populations and ionized gas, published as a Sloan Digital Sky Survey
Value Added Catalog being part of the 14th Data Release:
http://www.sdss.org/dr14/manga/manga-data/manga-pipe3d-value-added-catalog/Comment: 48 pages, 14 figures, in press in RMxA
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