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

The M_BH-M_star relation of obscured AGNs at high redshift

We report the detection of broad Halpha emission in three X-ray selected obscured AGNs at z=1-2. By exploiting the Halpha width and the intrinsic X-ray luminosity, we estimate their black hole masses, which are in the range 0.1-3x10^9 Msun. By means of multi-band photometric data, we measure the stellar mass of their host galaxy and, therefore, infer their M_BH/M_star ratio. These are the first obscured AGNs at high-z, selected based on their black hole accretion (i.e. on the basis of their X-ray luminosity), that can be located on the M_BH-M_star relation at high-z. All of these obscured high-z AGNs are fully consistent with the local M_BH-M_star relation. This result conflicts with those for other samples of AGNs in the same redshift range, whose M_BH/M_star ratio departs significantly from the value observed in local galaxies. We suggest that the obscured AGNs in our sample are in an advanced evolutionary stage, have already settled onto the local M_BH-M_star relation, and whose nuclear activity has been temporarily revived by recent galaxy interactions.Comment: 4 pages, 2 figures, accepted for publication in A&A Letters, slightly revised discussion on SMG

The obscured X-ray source population in the HELLAS2XMM survey: the Spitzer view

Recent X-ray surveys have provided a large number of high-luminosity, obscured Active Galactic Nuclei (AGN), the so-called Type 2 quasars. Despite the large amount of multi-wavelength supporting data, the main parameters related to the black holes harbored in such AGN are still poorly known. Here we present the results obtained for a sample of eight Type 2 quasars in the redshift range 0.9-2.1 selected from the HELLAS2XMM survey, for which we used Ks-band, Spitzer IRAC and MIPS data at 24 micron to estimate bolometric corrections, black hole masses, and Eddington ratios.Comment: 6 pages, to appear in "The Multicoloured Landscape of Compact Objects and their Explosive Progenitors: Theory vs Observations" (Cefalu, Sicily, June 2006). Eds. L. Burderi et al. (New York: AIP

ISO observations of a sample of Compact Steep Spectrum and GHz Peaked Spectrum Radio Galaxies

We present results from observations obtained with ISOPHOT, on board the ISO satellite, of a representative sample of seventeen CSS/GPS radio galaxies and of a control sample of sixteen extended radio galaxies spanning similar ranges in redshift (0.2 = 10^26 W/Hz). The observations have been performed at lambda = 60, 90, 174 and 200 microns. Seven of the CSS/GPS sources have detections >= 3 sigma at one or more wavelengths, one of which is detected at >= 5 sigma. By co-adding the data we have obtained average flux densities at the four wavelengths. We found no evidence that the FIR luminosities of the CSS/GPS sources are significantly different from those of the extended objects and therefore there is not any support for CSS/GPS sources being objects "frustrated" by an abnormally dense ambient medium. The two samples were then combined, providing FIR information on a new sample of radio galaxies at intermediate redshifts. We compare this information with what previously known from IRAS and discuss the average properties of radio galaxies in the redshift range 0.2 - 0.8. The FIR emission cannot be accounted for by extrapolation of the synchrotron radio spectrum and we attribute it to thermal dust emission. The average FIR luminosity is >= 6*10^11 L_sun. Over the observed frequency range the infrared spectrum can be described by a power law with spectral index alpha >~1.0 +/- 0.2. Assuming the emission to be due to dust, a range of temperatures is required, from >=80 K to \~25 K. The dust masses required to explain the FIR emission range from 5*10^5 M_sun for the hotter component up to 2*10^8 M_sun for the colder one. (abridged)Comment: Astronomy & Astrophysics, in press, 16 pages, 2 Figure

The dust-to-stellar mass ratio as a valuable tool to probe the evolution of local and distant star forming galaxies

The survival of dust grains in galaxies depends on various processes. Dust can be produced in stars, it can grow in the interstellar medium and be destroyed by astration and interstellar shocks. In this paper, we assemble a few data samples of local and distant star-forming galaxies to analyse various dust-related quantities in low- and high-redshift galaxies, and to study how the relations linking the dust mass to the stellar mass and star formation rate evolve with redshift. We interpret the available data by means of chemical evolution models for discs and proto-spheroid (PSPH) starburst galaxies. In particular, we focus on the dust-to-stellar mass (DTS) ratio, as this quantity represents a true measure of how much dust per unit stellar mass survives the various destruction processes in galaxies and is observable. The theoretical models outline the strong dependence of this quantity on the underlying star formation history. Spiral galaxies are characterized by a nearly constant DTS as a function of the stellar mass and cosmic time, whereas PSPHs present an early steep increase of the DTS, which stops at a maximal value and decreases in the latest stages. In their late starburst phase, these models show a decrease of the DTS with their mass, which allows us to explain the observed anti-correlation between the DTS and the stellar mass. The observed redshift evolution of the DTS ratio shows an increase from z ∼ 0 to z ∼ 1, followed by a roughly constant behaviour at 1 ≲ z ≲ 2.5. Our models indicate a steep decrease of the global DTS at early times, which implies an expected decrease of the DTS at larger redshift.PS acknowledges financial support from the European Union's Seventh Framework Programme ASTRODEEP (FP7/2007- 2013), grant agreement no. 312725

Implications of the differing roles of the beta 1 and beta 3 transmembrane and cytosplasmic domains for integrin function

Integrins are transmembrane receptors composed of alpha and beta subunits. Although most integrins contain beta 1, canonical activation mechanisms are based on studies of the platelet integrin, allb beta 3. Its inactive conformation is characterized by the association of the alpha llb transmembrane and cytosolic domain (TM/CT) with a tilted beta 3 TM/CT that leads to activation when disrupted. We show significant structural differences between beta 1 and beta 3 TM/CT in bicelles. Moreover, the 'snorkeling' lysine at the TM/CT interface of beta subunits, previously proposed to regulate alpha llb beta 3 activation by ion pairing with nearby lipids, plays opposite roles in beta 1 and beta 3 integrin function and in neither case is responsible for TM tilt. A range of affinities from almost no interaction to the relatively high avidity that characterizes alpha llb beta 3 is seen between various alpha subunits and beta 1 TM/CTs. The alpha llb beta 3-based canonical model for the roles of the TM/CT in integrin activation and function clearly does not extend to all mammalian integrins

A motivational approach to support healthy habits in long-term child–robot interaction

We examine the use of role-switching as an intrinsic motivational mechanism to increase engagement in long-term child–robot interaction. The present study describes a learning framework where children between 9 and 11-years-old interact with a robot to improve their knowledge and habits with regards to healthy life-styles. Experiments were carried out in Italy where 41 children were divided in three groups interacting with: (i) a robot with a role-switching mechanism, (ii) a robot without a role-switching mechanism and (iii) an interactive video. Additionally, a control group composed of 43 more children, who were not exposed to any interactive approach, was used as a baseline of the study. During the intervention period, the three groups were exposed to three interactive sessions once a week. The aim of the study was to find any difference in healthy-habits acquisition based on alternative interactive systems, and to evaluate the effectiveness of the role-switch approach as a trigger for engagement and motivation while interacting with a robot. The results provide evidence that the rate of children adopting healthy habits during the intervention period was higher for those interacting with a robot. Moreover, alignment with the robot behaviour and achievement of higher engagement levels were also observed for those children interacting with the robot that used the role-switching mechanism. This supports the notion that role-switching facilitates sustained long-interactions between a child and a robot

ALMA reveals a warm and compact starburst around a heavily obscured supermassive black hole at z=4.75

We report ALMA Cycle 0 observations at 1.3mm of LESS J033229.4-275619 (XID403), an Ultraluminous Infrared Galaxy at $z=4.75$ in the Chandra Deep Field South hosting a Compton-thick QSO. The source is not resolved in our data at a resolution of $\sim$0.75 arcsec, placing an upper-limit of 2.5 kpc to the half-light radius of the continuum emission from heated-dust. After deconvolving for the beam size, however, we found a $\sim3\sigma$ indication of an intrinsic source size of $0.27\pm0.08$ arcsec (Gaussian FWHM), which would correspond to $r_{half}\sim0.9\pm0.3$ kpc. We build the far-IR SED of XID403 by combining datapoints from both ALMA and Herschel and fit it with a modified blackbody spectrum. For the first time, we measure the dust temperature $T_d=58.5\pm5.3$ K in this system, which is comparable to what has been observed in other high-z submillimeter galaxies. The measured star formation rate is SFR=$1020\pm150$ $M_{\odot}$ yr$^{-1}$, in agreement with previous estimates at lower S/N. Based on the measured SFR and source size, we constrain the SFR surface density to be $\Sigma_{SFR}>26\;M_{\odot}$yr$^{-1}$kpc$^{-2}$ ($\sim200\;M_{\odot}$yr$^{-1}$kpc$^{-2}$ for $r_{half}\sim0.9$ kpc). The compactness of this starburst is comparable to what has been observed in other local and high-z starburst galaxies. If the gas mass measured from previous [CII] and CO(2-1) observations at low resolution is confined within the same dust region, assuming $r_{half}\sim0.9\pm0.3$ kpc, this would produce a column density of $N_H\sim0.3-1.1\times10^{24}$cm$^{-2}$ towards the central SMBH, similar to the column density of $\approx1.4\times10^{24}$cm$^{-2}$ measured from the X-rays. Then, in principle, if both gas and dust were confined on sub-kpc scales, this would be sufficient to produce the observed X-ray column density without any need of a pc-scale absorber [abridged].Comment: 11 pages, 5 figures. Accepted for publication in A&