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$_{\rm{1-100\,keV}} \simeq 4.0\times10^{42}$ erg s$^{-1}$. ALMA high resolution data ($\theta \simeq 0.2''$) allows us to scan the nuclear region down to a spatial scale of $\approx 100$ 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 ${\rm log}(n/{\rm cm^{-3}})=2.5$ and temperature $T=30$ K, reproduces the low-J CO line luminosities. The XDR is instead characterised by a denser and warmer gas (${\rm log}(n/{\rm cm^{-3}})=4.5$, $T =65$ 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