Aims. The goal of this work is to infer the star formation properties and the mass assembly process of high redshift ($0.3 \leq z < 2.5$) galaxies from their IR emission using the 24 μm band of ...MIPS-Spitzer. Methods. We used an updated version of the GOODS-MUSIC catalog, which has multiwavelength coverage from 0.3 to 24 μm and either spectroscopic or accurate photometric redshifts. We describe how the catalog has been extended by the addition of mid-IR fluxes derived from the MIPS 24 μm image. We compared two different estimators of the star formation rate (SFR hereafter). One is the total infrared emission derived from 24 μm, estimated using both synthetic and empirical IR templates. The other one is a multiwavelength fit to the full galaxy SED, which automatically accounts for dust reddening and age-star formation activity degeneracies. For both estimates, we computed the SFR density and the specific SFR. Results. We show that the two SFR indicators are roughly consistent, once the uncertainties involved are taken into account. However, they show a systematic trend, IR-based estimates exceeding the fit-based ones as the star formation rate increases. With this new catalog, we show that: a) at $z>0.3$, the star formation rate is correlated well with stellar mass, and this relationship seems to steepen with redshift if one relies on IR-based estimates of the SFR; b) the contribution to the global SFRD by massive galaxies increases with redshift up to $\simeq $2.5, more rapidly than for galaxies of lower mass, but appears to flatten at higher z; c) despite this increase, the most important contributors to the SFRD at any z are galaxies of about, or immediately lower than, the characteristic stellar mass; d) at $z\simeq 2$, massive galaxies are actively star-forming, with a median ${\it SFR} \simeq 300~ M_\odot$ yr-1. During this epoch, our targeted galaxies assemble a substantial part of their final stellar mass; e) the specific SFR (SSFR) shows a clear bimodal distribution. Conclusions. The analysis of the SFR density and the SSFR seems to support the downsizing scenario, according to which high mass galaxies have formed their stars earlier and more rapidly than their low mass counterparts. A comparison with renditions of theoretical simulations of galaxy formation and evolution indicates that these models follow the global increase in the SSFR with redshift and predict the existence of quiescent galaxies even at $z>1.5$. However, the average SSFR is systematically underpredicted by all models considered.
We report the spectroscopic confirmation of two Lyman break galaxies at redshift >7. The galaxies were observed as part of an ultra-deep spectroscopic campaign with FORS2 at the ESO/VLT for the ...confirmation of z 7 'z-band dropout' candidates selected from our VLT/Hawk-I imaging survey. Both galaxies show a prominent emission line at 9735 A and 9858 A, respectively: the lines have fluxes of ~(1.6-1.2) X 10--17 erg s--1 cm--2 and exhibit a sharp decline on the blue side and a tail on the red side. The asymmetry is quantitatively comparable to the observed asymmetry in z ~ 6 Ly Delta *a lines, where absorption by neutral hydrogen in the intergalactic medium (IGM) truncates the blue side of the emission-line profile. We carefully evaluate the possibility that the galaxies are instead at lower redshift and we are observing either O II, O III, or H Delta *a emission: however from the spectroscopic and the photometric data we conclude that there are no other plausible identifications, except for Ly Delta *a at redshift >7, implying that these are two of the most robust redshift determination for galaxies in the reionization epoch. Based on their redshifts and broadband photometry, we derive limits on the star formation rate and on the ultraviolet spectral slopes of the two galaxies. We argue that these two galaxies alone are unlikely to have ionized the IGM in their surroundings.
We used Early Release Science (ERS) observations taken with the Wide Field Camera 3 (WFC3) in the GOODS-S field to study the galaxy stellar mass function (GSMF) at 0.6 ≤ z < 4.5. Deep WFC3 near-IR ...data (for Y as faint as 27.3, J and H as faint as 27.4 AB mag at 5σ), as well as deep KS (as faint as 25.5 at 5σ) Hawk-I band data, provide an exquisite data set with which determine in an unprecedented way the low-mass end of the GSMF, allowing an accurate probe of masses as low as M∗ ≃ 7.6 × 109 M⊙ at z ~ 3. Although the area used is relatively small (~33 arcmin2), we found generally good agreement with previous studies on the entire mass range. Our results show that the slope of the faint-end increases with redshift, from α = −1.44 ± 0.03 at z ~ 0.8 to α = −1.86 ± 0.16 at z ~ 3, although indications exist that it does not steepen further between z ~ 3 and z ~ 4. This result is insensitive to any uncertainty in the M∗ parameter. The steepness of the GSMF faint-end solves the well-known disagreement between the stellar mass density (SMD) and the integrated star-formation history at z > 2. However, we confirm that there appears to be an excess of integrated star formation with respect to the SMD at z < 2, by a factor of ~2−3. Our comparison of the observations with theoretical predictions shows that the models forecast a greater abundance of low mass galaxies, at least up to z ~ 3, as well as a dearth of massive galaxies at z ~ 4 with respect to the data, and that the predicted SMD is generally overestimated at z ≲ 2.
Aims. We present a high quality multiwavelength (from 0.3 to 8.0 km) catalog of the large and deep area in the GOODS Southern Field covered by the deep near-IR observations obtained with the ESO VLT. ...Methods. The catalog is entirely based on public data: in our analysis, we have included the F435W, F606W, F115W and F850LP ACS images, the JHKs VLT data, the Spitzer data provided by IRAC instrument (3.6, 4.5, 5.8 and 8.0 km), and publicly available U-band data from the 2.2ESO and VLT-VIMOS. We describe in detail the procedures adopted to obtain this multiwavelength catalog. In particular, we developed a specific software for the accurate "PSF-matching" of space and ground-based images of different resolution and depth (ConvPhot), of which we analyse performances and limitations. We have included both z-selected, as well as Ks-selected objects, yielding a unique, self-consistent catalog. The largest fraction of the sample is 90% complete at z 26 or Ks 23.8 (AB scale). Finally, we cross-correlated our data with all the spectroscopic catalogs available to date, assigning a spectroscopic redshift to more than 1000 sources. Results. The final catalog is made up of 14 847 objects, at least 72 of which are known stars, 68 are AGNs, and 928 galaxies with spectroscopic redshift (668 galaxies with reliable redshift determination). We applied our photometric redshift code to this data set, and the comparison with the spectroscopic sample shows that the quality of the resulting photometric redshifts is excellent, with an average scatter of only 0.06. The full catalog, which we named GOODS-MUSIC (MUltiwavelength Southern Infrared Catalog), including the spectroscopic information, is made publicly available, together with the software specifically designed to this end.
Context. Study of the dust extinction in high-redshift galaxies is fundamental to obtaining an estimate of the corrected star formation rate density (SFRD) and to put constraints on galaxy evolution ...models. Aims. We plan to analyse dust extinction in Lyman break galaxies (LBGs) by introducing a new and more reliable approach to their selection and to the characterization of their distribution of UV slopes β, using deep IR images from HST. We fully discuss the methodology and the results, focusing on a robust sample of z ~ 4 LBGs. Methods. We exploit deep WFC3 IR observations of the ERS and HUDF fields over GOODS-South, combined with HST-ACS optical data, to select z ~ 4 LBGs through a new (B − V) vs. (V − H) colour diagram. The UV slope of the selected galaxies is robustly determined by a linear fit over their observed I,Z,Y,J magnitudes, coherently with the original definition of β. The same fit is used to determine their rest-frame UV magnitudes M1600 through a simple interpolation. We estimate the effect of observational uncertainties with detailed simulations that we also exploit, under a parametric maximum-likelihood approach, to constrain the probability density function of UV slopes PDF(β) as a function of rest-frame magnitude. Results. We find 142 robust LBGs in the ERS and 25 in the HUDF field, limiting our sample to S/N(H) > 10 objects. Our newly defined criteria improve the selection of z ~ 4 LBGs and allow us to exclude red interlopers at lower redshifts, especially z ~ 3–3.5 objects. We show that using a linear fit to estimate β and accurately characterizing observational effects are required in this kind of analysis of flux-limited samples. We find that z ~ 4 LBGs are characterized by blue UV slopes, suggesting a low dust extinction: all L < L∗ galaxies have an average UV slope ⟨β⟩ ≃ −2.1, while brighter objects are only slightly redder (⟨β⟩ ≃ −1.9). We find an intrinsic dispersion ≃0.3 for PDF(β) at all magnitudes. The SFRD at z ~ 4 corrected according to these estimates turns out to be lower than previously found: log(SFRD) ≃ −1.09 M⊙/yr/Mpc3. Finally, we discuss how the UV slope of z ~ 4 galaxies changes as a function of the dust-corrected UV magnitude (i.e. SFR). We show that most galaxies with high SFR (≳80 M⊙/yr) are highly extincted objects. Among galaxies with lower SFR, we detect many with a much lower amount of reddening, although current observational limits prevent us from detecting those with high extinction, if they exist.
We have evaluated the diffuse intracluster light (ICL) in the central core of the galaxy cluster CL0024+17 at z ~ 0.4 observed with the prime focus camera (Large Binocular Camera) at the Large ...Binocular Telescope. The latter shows an approximate exponential decline as expected from theoretical cold dark matter models where the ICL is due to the integrated contribution of light from stars that are tidally stripped from the halo of their host galaxies due to encounters with other galaxies in the cluster cold dark matter (CDM) potential. It is possible to show that the latter quantity is almost independent of the properties of the individual host galaxies but mainly depends on the average cluster properties. The present analysis shows that the measure of the ICL fraction in clusters can quantitatively account for the stellar stripping activity in their cores and can be used to probe their CDM distribution and evolutionary status.
Aims. We present the characteristics and some early scientific results of the first instrument at the Large Binocular Telescope (LBT), the Large Binocular Camera (LBC). Each LBT telescope unit will ...be equipped with similar prime focus cameras. The blue channel is optimized for imaging in the $UV-B$ bands and the red channel for imaging in the VRIz bands. The corrected field-of-view of each camera is approximately 30 arcmin in diameter, and the chip area is equivalent to a 23$\times$23 arcmin2 field. In this paper we also present the commissioning results of the blue channel. Methods. The scientific and technical performance of the blue channel was assessed by measurement of the astrometric distortion, flat fielding, ghosts, and photometric calibrations. These measurements were then used as input to a data reduction pipeline applied to science commissioning data. Results. The measurements completed during commissioning show that the technical performance of the blue channel is in agreement with original expectations. Since the red camera is very similar to the blue one we expect similar performance from the commissioning that will be performed in the following months in binocular configuration. Using deep UV image, acquired during the commissioning of the blue camera, we derived faint UV galaxy-counts in a ~ 500 sq. arcmin sky area to U(Vega) = 26.5. These galaxy counts imply that the blue camera is the most powerful UV imager presently available and in the near future in terms of depth and extent of the field-of-view. We emphasize the potential of the blue camera to increase the robustness of the UGR multicolour selection of Lyman break galaxies at redshift z ~ 3.
Aims. With an observed and rest-frame duration of <2 s and <0.5 s, respectively, GRB 090426 could be classified as a short GRB. The prompt detection, both from space and ground-based telescopes, of a ...bright optical counterpart to this GRB offered a unique opportunity to complete a detailed study. Methods. Based on an extensive ground-based observational campaign, we obtained the spectrum of the optical afterglow of GRB 090426, measuring its redshift and obtaining information about the medium in which the event took place. We completed follow-up observations of the afterglow optical light curve down to the brightness level of the host galaxy that we firmly identified and studied. We also retrieved and analyzed all the available high-energy data of this event, and compared the results with our findings in the optical. This represents one of the most detailed studies of a short-duration event presented so far. Results. The time properties qualify GRB 090426 as a short burst. In this case, its redshift of $z = 2.61$ would be the highest yet found for a GRB of this class. On the other hand, the spectral and energy properties are more similar to those of long bursts. LBT late-time deep imaging identifies a star-forming galaxy at a redshift consistent with that of the GRB. The afterglow lies within the light of its host and shows evidence of local absorption.
This paper describes the achievements of the H2020 project INDIGO-DataCloud. The project has provided e-infrastructures with tools, applications and cloud framework enhancements to manage the ...demanding requirements of scientific communities, either locally or through enhanced interfaces. The middleware developed allows to federate hybrid resources, to easily write, port and run scientific applications to the cloud. In particular, we have extended existing PaaS (Platform as a Service) solutions, allowing public and private e-infrastructures, including those provided by EGI, EUDAT, and Helix Nebula, to integrate their existing services and make them available through AAI services compliant with GEANT interfederation policies, thus guaranteeing transparency and trust in the provisioning of such services. Our middleware facilitates the execution of applications using containers on Cloud and Grid based infrastructures, as well as on HPC clusters. Our developments are freely downloadable as open source components, and are already being integrated into many scientific applications.
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