5,538 research outputs found
On the nature of the near-UV extended light in Seyfert galaxies
We study the nature of the extended near-UV emission in the inner kiloparsec
of a sample of 15 Seyfert galaxies which have both near-UV (F330W) and narrow
band [OIII] high resolution Hubble images. For the majority of the objects we
find a very similar morphology in both bands. From the [OIII] images we
construct synthetic images of the nebular continuum plus the emission line
contribution expected through the F330W filter, which can be subtracted from
the F330W images. We find that the emission of the ionised gas dominates the
near-UV extended emission in half of the objects. A further broad band
photometric study, in the bands F330W (U), F547M (V) and F160W (H), shows that
the remaining emission is dominated by the underlying galactic bulge
contribution. We also find a blue component whose nature is not clear in 4 out
of 15 objects. This component may be attributed to scattered light from the
AGN, to a young stellar population in unresolved star clusters, or to
early-disrupted clusters. Star forming regions and/or bright off-nuclear star
clusters are observed in 4/15 galaxies of the sample.Comment: 23 pages, 6 figures, 3 tables; accepted for publication in MNRA
Comparación de los hábitos de consumo de carne de conejo entre consumidores jóvenes y compradores tradicionales de Sevilla
Se estudiaron los hábitos de consumo de carne de conejo de 499 estudiantes universitarios y de 399 compradores en mercados tradicionales de Sevilla (España). Los estudiantes universitarios afirmaron haber probado
(67,9%) y consumir actualmente (38,6%) la carne de conejo en menor proporción que los compradores tradicionales (prueban: 84,5%; consumen:
46,6%). Ambos grupos afirman que les gusta esta carne en la misma proporción (78%).Las mujeres, sobre todo jóvenes, afirmaron haber probado y que les gusta en menor proporción esta carne que en el caso de los hombres. Se reveló además un mayor hábito de consumo y preferencia por la carne de conejo de monte en comparación con la del de granja, siendo la carne de conejo de monte preferida a la del de granja por un 88,2% de los consumidores sin distinción de grupo. Se dedujo una disminución del consumo de la carne de conejo entre los jóvenes en comparación con los compradores en mercados tradicionales
VLT observations of metal-rich extra galactic HII regions. I. Massive star populations and the upper end of the IMF
We have obtained high quality FORS1/VLT optical spectra of 85 disk HII regions several nearby spiral galaxies. Our sample of metal-rich HII regions with metallicities close to solar and higher reveal the presence of Wolf-Rayet (WR) stars in 27 objects from the blue WR bump and 15 additional candidate WR regions. This provides for the first time a large set of metal-rich WR regions. Approximately half of the WR regions also show broad CIV emission attributed to WR stars of the WC subtype (...). The WR regions show quite clear trends between their observed WR features and the Hbeta emission line. Detailed synthesis models are presented to understand/interpret these observations. (...) The availability of a fairly large sample of metal-rich WR regions allows us to improve existing estimates of the upper mass cut-off of the IMF in a robust way and independently of detailed modeling: from the observed maximum Hbeta equivalent width of the WR regions we derive a LOWER LIMIT for M_up of 60-90 Msun in the case of a Salpeter slope and larger values for steeper IMF slopes. From our direct probe of the massive star content we conclude that there is at present no evidence for systematic variations of the upper mass cut-off of the IMF in metal-rich environments, in contrast to some claims based on indirect nebular diagnostics. (abridged abstract
The CaT strength in Seyfert nuclei revisited: analyzing young stars and non-stellar light contributions to the spectra
In a former paper (Garcia-Rissmann et al. 2005; hereafter Paper I), we have
presented spectra of 64 active, 9 normal and 5 Starburst galaxies in the region
around the near-IR Calcium triplet absorption lines and the [SIII]9069 line. In
the present paper we analyze the CaT strength (WCaT), and kinematical products
derived in that study, namely stellar and ionized gas velocity dispersions. Our
main results may be summarized as follows: (1) Seyfert 2s show no sign of
dilution in WCaT with respect to the values spanned by normal galaxies, even
when optical absorption lines such as the CaII K band at 3933 A are much weaker
than in old, bulge-like stellar populations. (2) The location of Seyfert 2s in
the WCaT-WCaK plane is consistent with evolutionary synthesis models. The
implication is that the source responsible for the dilution of optical lines in
these AGN is a young stellar population, rather than an AGN featureless
continuum, confirming the conclusion of the pioneer study of Terlevich, Diaz &
Terlevich. (3) In Seyfert 1s, both W[SIII] and WCaT tend to be diluted due to
the presence of a non-stellar component, in agreement with the unification
paradigm. (4) A comparison of stellar and gas velocity dispersions confirms the
existence of a correlation between the typical velocities of stars and clouds
of the Narrow Line Region. The strength and scatter around this correlation are
similar to those previously obtained from the [OIII]5007 line width.Comment: 14 pages, 15 figures. Paper accepted for publication in MNRA
Synthesis models in a probabilistic framework: metrics of fitting
In general, synthesis models provide the mean value of the distribution of
possible integrated luminosities, this distribution (and not only its mean
value) being the actual description of the integrated luminosity. Therefore, to
obtain the closest model to an observation only provides confi- dence about the
precision of such a fit, but not information about the accuracy of the result.
In this contribution we show how to overcome this drawback and we propose the
use of the theoretical mean-averaged dispersion that can be produced by
synthesis models as a metric of fitting to infer accurate physical parameters
of observed systems.Comment: Invited talk in "New Quests in stellar astrophysics II. Ultraviolet
properties of evolved stellar populations" in press. 8 pages, 5 figures.
(Part II on metric of fitting for population synthesis
The cosmic evolution of the spatially-resolved star formation rate and stellar mass of the CALIFA survey
We investigate the cosmic evolution of the absolute and specific star
formation rate (SFR, sSFR) of galaxies as derived from a spatially-resolved
study of the stellar populations in a set of 366 nearby galaxies from the
CALIFA survey. The analysis combines GALEX and SDSS images with the 4000 break,
H_beta, and [MgFe] indices measured from the datacubes, to constrain parametric
models for the SFH, which are then used to study the cosmic evolution of the
star formation rate density (SFRD), the sSFR, the main sequence of star
formation (MSSF), and the stellar mass density (SMD). A delayed-tau model,
provides the best results, in good agreement with those obtained from
cosmological surveys. Our main results from this model are: a) The time since
the onset of the star formation is larger in the inner regions than in the
outer ones, while tau is similar or smaller in the inner than in the outer
regions. b) The sSFR declines rapidly as the Universe evolves, and faster for
early than for late type galaxies, and for the inner than for the outer regions
of galaxies. c) SFRD and SMD agree well with results from cosmological surveys.
At z< 0.5, most star formation takes place in the outer regions of late spiral
galaxies, while at z>2 the inner regions of the progenitors of the current E
and S0 are the major contributors to SFRD. d) The inner regions of galaxies are
the major contributor to SMD at z> 0.5, growing their mass faster than the
outer regions, with a lookback time at 50% SMD of 9 and 6 Gyr for the inner and
outer regions. e) The MSSF follows a power-law at high redshift, with the slope
evolving with time, but always being sub-linear. f) In agreement with galaxy
surveys at different redshifts, the average SFH of CALIFA galaxies indicates
that galaxies grow their mass mainly in a mode that is well represented by a
delayed-tau model, with the peak at z~2 and an e-folding time of 3.9 Gyr.Comment: 23 pages, 16 figures, 6 tables, accepted for publication in Astronomy
& Astrophysics. *Abridged abstract
The spatially resolved star formation history of CALIFA galaxies: Cosmic time scales
This paper presents the mass assembly time scales of nearby galaxies observed
by CALIFA at the 3.5m telescope in Calar Alto. We apply the fossil record
method of the stellar populations to the complete sample of the 3rd CALIFA data
release, with a total of 661 galaxies, covering stellar masses from 10
to 10 M and a wide range of Hubble types. We apply spectral
synthesis techniques to the datacubes and process the results to produce the
mass growth time scales and mass weighted ages, from which we obtain temporal
and spatially resolved information in seven bins of galaxy morphology and six
bins of stellar mass (M) and stellar mass surface density
(). We use three different tracers of the spatially resolved
star formation history (mass assembly curves, ratio of half mass to half light
radii, and mass-weighted age gradients) to test if galaxies grow inside-out,
and its dependence with galaxy stellar mass, , and morphology.
Our main results are as follows: (a) The innermost regions of galaxies assemble
their mass at an earlier time than regions located in the outer parts; this
happens at any given M, , or Hubble type, including
the lowest mass systems. (b) Galaxies present a significant diversity in their
characteristic formation epochs for lower-mass systems. This diversity shows a
strong dependence of the mass assembly time scales on and
Hubble type in the lower-mass range (10 to 10), but a very
mild dependence in higher-mass bins. (c) All galaxies show negative
log age gradients in the inner 1 HLR. The profile
flattens with increasing values of . There is no significant
dependence on M within a particular bin, except for
the lowest bin, where the gradients becomes steeper.Comment: 15 pages, 13 figures, 3 tables, accepted for publication in Astronomy
& Astrophysics. *Abridged abstract
The Starburst-AGN connection: The role of stellar clusters in AGNs
Nuclear stellar clusters are a common phenomenon in spirals and in starbursts
galaxies, and they may be a natural consequence of the star formation processes
in the central regions of galaxies. HST UV imaging of a few Seyfert 2 galaxies
have resolved nuclear starbursts in Seyfert 2 revealing stellar clusters as the
main building blocks of the extended emission. However, we do not know whether
stellar clusters are always associated with all types of nuclear activity. We
present NUV and optical images provided by HST to find out the role that
stellar clusters play in different types of AGNs (Seyferts and LLAGNs). Also
with these images, we study the circumnuclear dust morphology as a probe of the
circumnuclear environment of AGNs. Here we present a summary of the the first
results obtained for the sample of Seyferts and LLAGN galaxies.Comment: Contribution to the conference proceedings "Space Astronomy: The UV
window to the Universe", El Escorial (Spain), May 28-June 1 2007, submitted
to Ap&SS, invited ed. Gomes de Castro, A.I. Further explanations are in
Mu\~noz Marin, et al (2007) and Gonzalez Delgado et al (2007); and the full
collection of figures are at the ULR:
http://www.iaa.es/~rosa/research/LLAGNs2007/LLAGNs-HSTIma1.html
http://www.iaa.es/~manuel/publications/paper01.htm
- …