4,864 research outputs found
Extragalactic Source Counts in the Spitzer 24-micron Band: What Do We Expect From ISOCAM 15-micron Data and Models?
The comparison between the new Spitzer data at 24 micron and the previous
ISOCAM data at 15 micron is a key tool to understand galaxy properties and
evolution in the infrared and to interpret the observed number counts, since
the combination of Spitzer with the ISO cosmological surveys provides for the
first time the direct view of the Universe in the Infrared up to z~2. We
present the prediction in the Spitzer 24-micron band of a phenomenological
model for galaxy evolution derived from the 15-micron data. Without any ``a
posteriori'' update, the model predictions seem to agree well with the recently
published 24-micron extragalactic source counts, suggesting that the peak in
the 24-micron counts is dominated by ``starburst'' galaxies like those detected
by ISOCAM at 15 micron, but at higher redshifts (1 < z < 2 instead of 0.5 < z <
1.5).Comment: 8 pages: 4 pages of main text + 5 postscript figures, use aastex.
Accepted for publication in ApJL. Replaced with the proof version (added
missing references and corrected a few sentences
Broad-band X-ray analysis of local mid-infrared selected Compton-thick AGN candidates
The estimate of the number and space density of obscured AGN over cosmic time
still represents an open issue. While the obscured AGN population is a key
ingredient of the X-ray background synthesis models and is needed to reproduce
its shape, a complete census of obscured AGN is still missing. Here we test the
selection of obscured sources among the local 12-micron sample of Seyfert
galaxies. Our selection is based on a difference up to three orders of
magnitude in the ratio between the AGN bolometric luminosity, derived from the
spectral energy distribution (SED) decomposition, and the same quantity
obtained by the published XMM-Newton 2-10 keV luminosity.
The selected sources are UGC05101, NGC1194 and NGC3079 for which the
available X-ray wide bandpass, from Chandra and XMM-Newton plus NuSTAR data,
extending to energies up to ~30-45 keV, allows us an accurate determination of
the column density, and hence of the true intrinsic power.
The newly derived NH values clearly indicate heavy obscuration (about 1.2,
2.1 and 2.4 x10^{24} cm-2 for UGC05101, NGC1194 and NGC3079, respectively) and
are consistent with the prominent silicate absorption feature observed in the
Spitzer-IRS spectra of these sources (at 9.7 micron rest frame). We finally
checked that the resulting X-ray luminosities in the 2-10 keV band are in good
agreement with those derived from the mid-IR band through empirical L_MIR-L_X
relations.Comment: 14 pages, 6 figures, accepted for publication in MNRA
World Equity Premium Based Risk Aversion Estimates
The equity premium puzzle holds that the coefficient of relative risk aversion estimated from the consumption based CAPM under power utility is excessively high. Moreover, estimates in the literature vary considerably across countries. We gauge the uncertainty pertaining to the country risk aversion estimates by means of jackknife resampling and pooling. The confidence band for the world risk aversion estimate from the pooled country data is much tighter and the pooled point estimate presents less of a puzzle than the individual country estimates.equity premium puzzle, jackknife, pooling
The dust content of QSO hosts at high redshift
Infrared observations of high-z quasar (QSO) hosts indicate the presence of
large masses of dust in the early universe. When combined with other
observables, such as neutral gas masses and star formation rates, the dust
content of z~6 QSO hosts may help constraining their star formation history. We
have collected a database of 58 sources from the literature discovered by
various surveys and observed in the FIR. We have interpreted the available data
by means of chemical evolution models for forming proto-spheroids,
investigating the role of the major parameters regulating star formation and
dust production. For a few systems, given the derived small dynamical masses,
the observed dust content can be explained only assuming a top-heavy initial
mass function, an enhanced star formation efficiency and an increased rate of
dust accretion. However, the possibility that, for some systems, the dynamical
mass has been underestimated cannot be excluded. If this were the case, the
dust mass can be accounted for by standard model assumptions. We provide
predictions regarding the abundance of the descendants of QSO hosts; albeit
rare, such systems should be present and detectable by future deep surveys such
as Euclid already at z>4.Comment: 22 pages, 8 figures, MNRAS, accepte
CO excitation in the Seyfert galaxy NGC7130
We present a coherent multi-band modelling of the CO Spectral Energy
Distribution of the local Seyfert Galaxy NGC7130 to assess the impact of the
AGN activity on the molecular gas. We take advantage of all the available data
from X-ray to the sub-mm, including ALMA data. The high-resolution (~0.2") ALMA
CO(6-5) data constrain the spatial extension of the CO emission down to ~70 pc
scale. From the analysis of the archival CHANDRA and NuSTAR data, we infer the
presence of a buried, Compton-thick AGN of moderate luminosity, L_2-10keV ~
1.6x10^{43} ergs-1. We explore photodissociation and X-ray-dominated regions
(PDRs and XDRs) models to reproduce the CO emission. We find that PDRs can
reproduce the CO lines up to J~6, however, the higher rotational ladder
requires the presence of a separate source of excitation. We consider X-ray
heating by the AGN as a source of excitation, and find that it can reproduce
the observed CO Spectral Energy Distribution. By adopting a composite PDR+XDR
model, we derive molecular cloud properties. Our study clearly indicates the
capabilities offered by current-generation of instruments to shed light on the
properties of nearby galaxies adopting state-of-the art physical modelling.Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letter
The star formation rate cookbook at 1 < z < 3: Extinction-corrected relations for UV & [OII]{\lambda}3727 luminosities
We use a spectroscopic sample of 286 star-forming galaxies (SFGs) at 1<z<3
from the GMASS survey to study different star formation rate (SFR) estimators.
Infrared (IR) data are used to derive empirical calibrations to correct
ultraviolet (UV) and [OII]{\lambda}3727 luminosities for dust extinction and
dust-corrected estimates of SFR. In the selection procedure we fully exploit
the available spectroscopic information. On the basis of three continuum
indices, we are able to identify and exclude from the sample galaxies in which
old stellar populations might bring a non-negligible contribution to IR
luminosity (LIR) and continuum reddening. Using Spitzer-MIPS and Herschel-PACS
data we derive LIR for two-thirds of our sample. The LIR/LUV ratio is used as a
probe of effective attenuation (AIRX) to search for correlations with continuum
and spectroscopic features. The relation between AIRX and UV continuum slope
({\beta}) was tested for our sample and found to be broadly consistent with the
literature results at the same redshift, though with a larger dispersion with
respect to UV-selected samples. We find a correlation between the rest-frame
equivalent width (EW) of the [OII]{\lambda}3727 line and {\beta}, which is the
main result of this work. We therefore propose the [OII]{\lambda}3727 line EW
as a dust attenuation probe and calibrate it through AIRX, though the
assumption of a reddening curve is still needed to derive the actual
attenuation towards the [OII]{\lambda}3727 line. We tested the issue of
differential attenuation towards stellar continuum and nebular emission: our
results are in line with the traditional prescription of extra attenuation
towards nebular lines. A set of relations is provided that allows the recovery
of the total unattenuated SFR from UV and [OII]{\lambda}3727 luminosities.
(Abridged)Comment: Accepted for publication in A&A; 20 pages, 19 figures, 5 table
CO excitation in the Seyfert galaxy NGC 34: stars, shock or AGN driven?
We present a detailed analysis of the X-ray and molecular gas emission in the
nearby galaxy NGC 34, to constrain the properties of molecular gas, and assess
whether, and to what extent, the radiation produced by the accretion onto the
central black hole affects the CO line emission. We analyse the CO Spectral
Line Energy Distribution (SLED) as resulting mainly from Herschel and ALMA
data, along with X-ray data from NuSTAR and XMM-Newton. The X-ray data analysis
suggests the presence of a heavily obscured AGN with an intrinsic luminosity of
L erg s. ALMA high
resolution data () allows us to scan the nuclear region
down to a spatial scale of pc for the CO(6-5) transition. We
model the observed SLED using Photo-Dissociation Region (PDR), X-ray-Dominated
Region (XDR), and shock models, finding that a combination of a PDR and an XDR
provides the best fit to the observations. The PDR component, characterized by
gas density and temperature K,
reproduces the low-J CO line luminosities. The XDR is instead characterised by
a denser and warmer gas (, K), and is
necessary to fit the high-J transitions. The addition of a third component to
account for the presence of shocks has been also tested but does not improve
the fit of the CO SLED. We conclude that the AGN contribution is significant in
heating the molecular gas in NGC 34.Comment: Accepted for publication in MNRAS. 10 pages, 6 figure
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