D. Pierini

Stellar and Total Baryon Mass Fractions in Groups and Clusters Since Redshift 1

We investigate if the discrepancy between estimates of the total baryon mass fraction obtained from observations of the cosmic microwave background (CMB) and of galaxy groups/clusters persists when a large sample of groups is considered. To this purpose, 91 candidate X-ray groups/poor clusters at redshift 0.1 ≤ z ≤ 1 are selected from the COSMOS 2 deg^2 survey, based only on their X-ray luminosity and extent. This sample is complemented by 27 nearby clusters with a robust, analogous determination of the total and stellar mass inside R_(500). The total sample of 118 groups and clusters with z ≤ 1 spans a range in M_(500) of ~10^(13)-10^(15) M_☉. We find that the stellar mass fraction associated with galaxies at R_(500) decreases with increasing total mass as M^(–0.37 ± 0.04)_(500), independent of redshift. Estimating the total gas mass fraction from a recently derived, high-quality scaling relation, the total baryon mass fraction (f^(stars+gas)_(500) = f^(stars)_(500) + f^(gas)_(500)) is found to increase by ~25%, when M_(500) increases from = 5 × 10^(13) M_☉ to = 7 × 10^(14) M_☉. After consideration of a plausible contribution due to intracluster light (11%-22% of the total stellar mass) and gas depletion through the hierarchical assembly process (10% of the gas mass), the estimated values of the total baryon mass fraction are still lower than the latest CMB measure of the same quantity (WMAP5), at a significance level of 3.3σ for groups of = 5 × 10^(13) M_☉. The discrepancy decreases toward higher total masses, such that it is 1σ at = 7 × 10^(14) M_☉. We discuss this result in terms of nongravitational processes such as feedback and filamentary heating.

The 3D structure of the Virgo cluster from H-band Fundamental Plane and Tully—Fisher distance determinations

We undertook a surface photometry survey of 200 galaxies in the Virgo cluster (complete to B<14.0 mag) carried out in the near-infrared (NIR) H band. Combining velocity dispersion measurements from the literature with new spectroscopic data for 11 galaxies, we derive distances of 59 early-type galaxies using the Fundamental Plane (FP) method. The distances of another 75 late-type galaxies are determined using the Tully--Fisher (TF) method. For this purpose we use the maximum rotational velocity, as derived from H I spectra from the literature, complemented with new Hα rotation curves of eight highly H I-deficient galaxies. The zero-points of the FP and TF template relations are calibrated assuming the distance modulus of Virgo μ0=31.0, as determined with the Cepheids method. Using these 134 distance determinations (with individual uncertainties of 0.35 mag (TF) and 0.45 mag (FP)) we find that the distance of cluster A, associated with M87, is μ0=30.84 ± 0.06. Cluster B, offset to the south, is found at μ0=31.84 ± 0.10. This subcluster is falling on to A at about 750 km s-1. Clouds W and M are at twice the distance of A. Galaxies on the north-west and south-east of the main cluster A belong to two clouds composed almost exclusively of spiral galaxies with distances consistent with A, but with significantly different velocity distributions, suggesting that they are falling on to cluster A at approximately 770 km s-1 from the far side and at 200 km s-1 from the near side respectively. The mass of Virgo inferred from the peculiar motions induced on its vicinity is consistent with the virial expectation.

The Representative XMM-Newton Cluster Structure Survey (REXCESS) of an X-ray Luminosity Selected Galaxy Cluster Sample

Context.The largest uncertainty for cosmological studies using clusters of galaxies is introduced by our limited knowledge of the statistics of galaxy cluster structure, and of the scaling relations between observables and cluster mass.

The SEDs and Host Galaxies of the dustiest GRB afterglows

Context. The afterglows and host galaxies of long gamma-ray bursts (GRBs) offer unique opportunities to study star-forming galaxies in the high-z Universe. Until recently, however, the information inferred from GRB follow-up observations was mostly limited to optically bright afterglows, biasing all demographic studies against sight-lines that contain large amounts of dust. Aims. Here we present afterglow and host observations for a sample of bursts that are exemplary of previously missed ones because of high visual extinction (A GRB 1 mag) along the sight-line. This facilitates an investigation of the properties, geometry, and location of the absorbing dust of these poorly-explored host galaxies, and a comparison to hosts from optically-selected samples. Methods. This work is based on GROND optical/NIR and Swift/XRT X-ray observations of the afterglows, and multi-color imaging for eight GRB hosts. The afterglow and galaxy spectral energy distributions yield detailed insight into physical properties such as the dust and metal content along the GRB sight-line and galaxy-integrated characteristics such as the host’s stellar mass, luminosity, color-excess, and star-formation rate. Results. For the eight afterglows considered in this study, we report for the first time the redshift of GRB 081109 (z = 0.9787±0.0005), and the visual extinction towards GRBs 081109 (A GRB = 3.4 +0.4 −0.3 mag) and 100621A (A GRB V = 3.8 ± 0.2 mag), which are among the largest ever derived for GRB afterglows. Combined with non-extinguished GRBs, there is a strong anti-correlation between the afterglow’s metal-to-dust ratio and visual extinction. The hosts of the dustiest afterglows are diverse in their properties, but on average redder (� (R − K)AB �∼ 1.6 mag), more luminous (� L �∼ 0.9L ∗ ), and massive (� log M∗[M� ] �∼ 9.8) than the hosts of optically-bright events. Hence, we probe a different galaxy population, suggesting that previous host samples miss most of the massive and metal-rich members. This also indicates that the dust along the sight-line is often related to host properties, and thus probably located in the diffuse ISM or interstellar clouds and not in the immediate GRB environment. Some of the hosts in our sample, are blue, young, or of low stellar mass illustrating that even apparently non-extinguished galaxies possess very dusty sight-lines owing to a patchy dust distribution. Conclusions. The afterglows and host galaxies of the dustiest GRBs provide evidence of a complex dust geometry in star-forming galaxies. In addition, they establish a population of luminous, massive, and correspondingly chemically evolved GRB hosts. This suggests that GRBs trace the global star-formation rate better than studies based on optically selected host samples indicate, and that the previously claimed deficiency of high-mass hosts was at least partially a selection effect.

The dust scaling relations of the Herschel Reference Survey

We combine new Herschel/SPIRE sub-millimeter observations with existing multiwavelength data to investigate the dust scaling relations of the Herschel Reference Survey, a magnitude-, volume-limited sample of similar to 300 nearby galaxies in different environments. We show that the dust-to-stellar mass ratio anti-correlates with stellar mass, stellar mass surface density and NUV - r colour across the whole range of parameters covered by our sample. Moreover, the dust-to-stellar mass ratio decreases significantly when moving from late-to early-type galaxies. These scaling relations are similar to those observed for the Hi gas-fraction, supporting the idea that the cold dust is tightly coupled to the cold atomic gas component in the interstellar medium. We also find a weak increase of the dust-to-Hi mass ratio with stellar mass and colour but no trend is seen with stellar mass surface density. By comparing galaxies in different environments we show that, although these scaling relations are followed by both cluster and field galaxies, Hi-deficient systems have, at fixed stellar mass, stellar mass surface density and morphological type systematically lower dust-to-stellar mass and higher dust-to-Hi mass ratios than Hi-normal/field galaxies. This provides clear evidence that dust is removed from the star-forming disk of cluster galaxies but the effect of the environment is less strong than what is observed in the case of the Hi disk. Such effects naturally arise if the dust disk is less extended than the Hi and follows more closely the distribution of the molecular gas phase, i.e., if the dust-to-atomic gas ratio monotonically decreases with distance from the galactic center.

Cold dust in late-type Virgo cluster galaxies

We have statistically analyzed the spatially integrated far-infrared (FIR) emissions of the complete volume- and luminosity-limited sample of late-type (later than S0) Virgo Cluster galaxies measured using the Infrared Space Observatory by Tuffs and coworkers in bands centered on 60, 100, and 170 μm. Thirty of 38 galaxies detected at all three wavelengths contain a cold dust emission component, present within all morphological types of late-type systems ranging from early giant spiral galaxies to blue compact dwarfs (BCDs) and which could not have been recognized by IRAS. We fitted the data with a superposition of two modified blackbody functions, physically identified with a localized warm dust emission component associated with H II regions (whose temperature was constrained to be 47 K), and a diffuse emission component of cold dust. The cold dust temperatures were found to be broadly distributed, with a median of 18 K, some 8-10 K lower than would have been predicted from IRAS. The derived total dust mass is correspondingly increased by factors of typically 6-13. A good linear correlation is found between the warm FIR luminosities and the Hα equivalent widths (EWs), supporting the assumptions of our constrained spectral energy distribution fit procedure. We also found a good nonlinear correlation between the cold FIR luminosities and the Hα EWs, consistent with the prediction of Popescu and coworkers that the FIR-submillimeter emission should mainly be due to diffuse nonionizing UV photons. Both the warm and the cold FIR luminosity components are nonlinearly correlated with the (predominantly nonthermal) radio luminosities. There is a tendency for the temperatures of the cold dust component to become colder and for the cold dust surface densities (normalized to optical area) to increase for later morphological types. A particularly significant result concerns the low dust temperatures (ranging down to less than 10 K) and large dust masses associated with the Im and BCD galaxies in our sample. We propose two scenarios to account for the FIR characteristics of these systems.

Dust spectral energy distributions of nearby galaxies: an insight from the Herschel Reference Survey

Although it accounts only for a small fraction of the baryonic mass, dust has a profound impact on the physical processes at play in galaxies. Thus, to understand the evolution of galaxies, it is essential not only to characterize dust properties per se, but also in relation to global galaxy properties. To do so, we derive the dust properties of galaxies in a volume limited, K-band selected sample, the Herschel Reference Survey (HRS). We gather infrared photometric data from 8 μm to 500 μm from Spitzer, WISE, IRAS, and Herschel for all of the HRS galaxies. Draine & Li (2007, ApJ, 663, 866) models are fit to the data from which the stellar contribution has been carefully removed. We find that our photometric coverage is sufficient to constrain all of the parameters of the Draine & Li models and that a strong constraint on the 20−60 μm range is mandatory to estimate the relative contribution of the photo-dissociation regions to the infrared spectral energy distribution (SED). The SED models tend to systematically underestimate the observed 500 μm flux densities, especially for low-mass systems. We provide the output parameters for all of the galaxies, i.e., the minimum intensity of the interstellar radiation field, the fraction of polycyclic aromatic hydrocarbon (PAH), the relative contribution of PDR and evolved stellar population to the dust heating, the dust mass, and the infrared luminosity. For a subsample of gas-rich galaxies, we analyze the relations between these parameters and the main integrated properties of galaxies, such as stellar mass, star formation rate, infraredluminosity, metallicity, Hα and H-band surface brightness, and the far-ultraviolet attenuation. A good correlation between the fraction of PAH and the metallicity is found, implying a weakening of the PAH emission in galaxies with low metallicities and, thus, low stellar masses. The intensity of the diffuse interstellar radiation field and the H-band and Hα surface brightnesses are correlated, suggesting that the diffuse dust component is heated by both the young stars in star-forming regions and the diffuse evolved population. We use these results to provide a new set of infrared templates calibrated with Herschel observations on nearby galaxies and a mean SED template to provide the z = 0 reference for cosmological studies. For the same purpose, we place our sample on the SFR − M∗ diagram. The templates are compared to the most popular infrared SED libraries, enlightening a large discrepancy between all of them in the 20−100 μm range.

The Herschel Virgo Cluster Survey - II. Truncated dust disks in H I-deficient spirals

By combining Herschel-SPIRE observations obtained as part of the Herschel Virgo Cluster Survey with 21 cm Hi data from the literature, we investigate the role of the cluster environment on the dust content of Virgo spiral galaxies. We show for the first time that the extent of the dust disk is significantly reduced in Hi-deficient galaxies, following remarkably well the observed “truncation” of the Hi disk. The ratio of the submillimetre-to-optical diameter correlates with the Hi-deficiency, suggesting that the cluster environment is able to strip dust as well as gas. These results provide important insights not only into the evolution of cluster galaxies but also into the metal enrichment of the intra-cluster medium.

Dust Attenuation in Late-Type Galaxies. I. Effects on Bulge and Disk Components

We present results of new Monte Carlo calculations made with the DIRTY code of radiative transfer of stellar and scattered radiation for a dusty giant late-type galaxy like the Milky Way, which illustrate the effect of the attenuation of stellar light by internal dust on the integrated photometry of the individual bulge and disk components. Here we focus on the behavior of the attenuation function, the color excess, and the fraction of light scattered or directly transmitted toward the outside observer as a function of the total amount of dust and the inclination of the galaxy, and the structure of the dusty interstellar medium (ISM) of the disk. We confirm that dust attenuation produces qualitatively and quantitatively different effects on the integrated photometry of bulge and disk, whatever the wavelength. In addition, we find that the structure of the dusty ISM affects more sensitively the observed magnitudes than the observed colors of both bulge and disk. Finally, we show that the contribution of the scattered radiation to the total monochromatic light received by the outside observer is significant, particularly at UV wavelengths, even for a two-phase, clumpy, dusty ISM. Thus, understanding dust scattering properties is fundamental for the interpretation of extragalactic observations in the rest-frame UV.

Discovery of a massive X-ray luminous galaxy cluster at z = 1.579

We report on the discovery of a very distant galaxy cluster serendipitously detected in the archive of the XMM-Newton mission, within the scope of the XMM-Newton Distant Cluster Project (XDCP). XMMUJ0044.0-2033 was detected at a high significance level (5σ) as a compact, but significantly extended source in the X-ray data, with a soft-band flux f (r 1.6.