1,142 research outputs found
The mass and environmental dependence on the secular processes of AGN in terms of morphology, colour, and specific star-formation rate
Galaxy mass and environment play a major role in the evolution of galaxies.
In the transition from star-forming to quenched galaxies, Active galactic
nuclei (AGN) have also a principal action. However, the connections between
these three actors are still uncertain. In this work we investigate the effects
of stellar mass and the large-scale environment (LSS), on the fraction of
optical nuclear activity in a population of isolated galaxies, where AGN would
not be triggered by recent galaxy interactions or mergers. As a continuation of
a previous work, we focus on isolated galaxies to study the effect of stellar
mass and the LSS in terms of morphology (early- and late-type), colour (red and
blue), and specific star formation rate (quenched and star-forming). To explore
where AGN activity is affected by the LSS we fix the stellar mass into low- and
high-mass galaxies. We use the tidal strength parameter to quantify their
effects. We found that AGN is strongly affected by stellar mass in 'active'
galaxies (namely late-type, blue, and star-forming), however it has no
influence for 'quiescent' galaxies (namely early-type, red, and quenched), at
least for masses down to . In relation to the LSS, we
found an increment on the fraction of SFN with denser LSS in low-mass star
forming and red isolated galaxies. Regarding AGN, we find a clear increment of
the fraction of AGN with denser environment in quenched and red isolated
galaxies, independently of the stellar mass. AGN activity would be 'mass
triggered' in 'active' isolated galaxies. This means that AGN is independent of
the intrinsic property of the galaxies, but on its stellar mass. On the other
hand, AGN would be 'environment triggered' in 'quiescent' isolated galaxies,
where the fraction of AGN in terms of sSFR and colour increases from void
regions to denser LSS, independently of its stellar mass.Comment: 14 pages, 9 figures (11 pages and 6 figures without appendix),
accepted for publication in Astronomy & Astrophysic
Steady-state signatures of radiation trapping by cold multilevel atoms
In this paper, we use steady-state measurements to obtain evidence of
radiation trapping in an optically thick a cloud of cold rubidium atoms. We
investigate the fluorescence properties of our sample, pumped on opened
transitions. The intensity of fluorescence exhibits a non trivial dependence on
the optical thickness of the media. A simplified model, based on rate equations
self-consistently coupled to a diffusive model of light transport, is used to
explain the experimental observations in terms of incoherent radiation trapping
on one spectral line. Measurements of atomic populations and fluorescence
spectrum qualitatively agree with this interpretation.Comment: 8 pages, 5 figure
Caracterización de nitratos alcalinos y alcalinoterreos por espectroscopia vibracional Characterization of alkali-metal and alkaline-earth nitrates by vibrational spectroscopy
[EN] Infrared spectra of sodium and potassium alkaline-metal
nitrates and magnesium and calcium alkali-earth nitrates in
solid phase had been recorded in order to assign the
fundamental bands. The influence of the dispersal médium
(alkaline halide), employed in the solid sample preparation
have been discussed. The quantitative measurements of
the band in ten sities at 1.387 cm~^ (present in the I.R.
spectra of the four nitrates in KBr médium) allowed us to
determine the Lambert-Beer law slopes for each compound.
These valúes are differents (bearing in mind experimental
random errors), so we have could to affirm the nonexistence
of solid solution between the nitrate and the
alkaline halide médium. The L-B law obtained by us can be
used for the Identification differentiation and quantitative
analysis of these nitrates in solid phase, even if they are
present in a very low concentration.[ES] Se ha realizado la asignación de los espectros infrarrojo
(IR) de los nitratos alcalinos, sódico y potásico, y de los
alcalinoterreos, magnésico y calcico, en estado sólido.
Se ha visto la influencia del medio dispersante (haluro
alcalino), utilizado en la preparación de la muestra sólida.
El estudio cuantitativo de la absorbancia de la banda a
1.387 cm~^ (presente en los espectros IR de los cuatro
nitratos en medio KBr) permite determinar las pendientes
de la Ley de Lambert-Beer Se comprueba que dichas
pendientes son diferentes lo que conduce a poder afirmar
que no se produce disolución sólida entre el KBr y el nitrato
alcalino o alcalinotérreo. La determinación de la ley de
Lambert-Beer permite la identificación y el análisis
cualitativo y cuantitativo por espectroscopia IR de estos
nitratos cuando están presentes en bajas concentraciones
en muestras sólidas.Peer reviewe
Aperture-free star formation rate of SDSS star-forming galaxies
Large area surveys with a high number of galaxies observed have undoubtedly
marked a milestone in the understanding of several properties of galaxies, such
as star-formation history, morphology, and metallicity. However, in many cases,
these surveys provide fluxes from fixed small apertures (e.g. fibre), which
cover a scant fraction of the galaxy, compelling us to use aperture corrections
to study the global properties of galaxies. In this work, we derive the current
total star formation rate (SFR) of Sloan Digital Sky Survey (SDSS) star-forming
galaxies, using an empirically based aperture correction of the measured flux for the first time, thus minimising the uncertainties associated
with reduced apertures. All the fluxes have been
extinction-corrected using the ratio free from aperture
effects. The total SFR for 210,000 SDSS star-forming galaxies has been
derived applying pure empirical and aperture
corrections based on the Calar Alto Legacy Integral Field Area (CALIFA) survey.
We find that, on average, the aperture-corrected SFR is 0.65dex higher
than the SDSS fibre-based SFR. The relation between the SFR and stellar mass
for SDSS star-forming galaxies (SFR--) has been obtained, together
with its dependence on extinction and equivalent width. We
compare our results with those obtained in previous works and examine the
behaviour of the derived SFR in six redshift bins, over the redshift range . The SFR-- sequence derived here is in
agreement with selected observational studies based on integral field
spectroscopy of individual galaxies as well as with the predictions of recent
theoretical models of disc galaxies
The less significant role of large-scale environment than optical AGN in nearby, isolated elliptical galaxies
The formation and evolution of elliptical galaxies in low-density
environments are less understood than classical elliptical galaxies in
high-density environments. Isolated galaxies are defined as galaxies without
massive neighbors within scales of galaxy groups. The effect of the environment
at several Mpc scales on their properties has been barely explored. Here we
study the role of large-scale environment in some physical properties of 573
isolated elliptical galaxies out to z=0.08. We use three environmental
estimators of the large-scale structure within a projected radius of 5 Mpc
around isolated galaxies: the tidal strength parameter, the projected density
eta_k, and the distance to the fifth nearest neighbor galaxy. We find 80% of
galaxies at lower densities correspond to 'red and dead' elliptical galaxies.
Blue and red galaxies do not tend to be located in different environments
according to eta_k. Almost all the isolated ellipticals in the densest
large-scale environments are red or quenched, where a third of them are
low-mass galaxies. The percentage of isolated elliptical galaxies located in
the AGN region of the BPT diagram is 64%. We have identified 33 blue,
star-forming isolated ellipticals using both color and sSFR. Half of them are
star-forming nuclei in the BPT diagram, which is 5% of the galaxies in this
diagram. The large-scale environment is not playing the primary role to
determine the color or sSFR of isolated elliptical galaxies. The large-scale
environment seems to be negligible from a stellar mass scale around 10^10.6
Msun, probably because of the dominant presence of AGN at higher masses. For
lower masses, the processes of cooling and infall of gas from large scales are
very inefficient in ellipticals. AGN might also be an essential ingredient to
keep most of the low-mass isolated elliptical galaxies quenched.Comment: 15 pages, 6 figures (10 pages and 4 figures without appendices).
Accepted for publication in A&
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