arXiv subjects

P. Popesso

Publications and source records attributed to P. Popesso.

At least 109 records · Page 6Linked to original sources

arXiv2010

The Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory

The Photodetector Array Camera and Spectrometer (PACS) is one of the three science instruments on ESA's far infrared and submillimetre observatory. It employs two Ge:Ga photoconductor arrays (stressed and unstressed) with 16x25 pixels, each, and two filled silicon bolometer arrays with 16x32 and 32x64 pixels, respectively, to perform integral-field spectroscopy and imaging photometry in the 60-210μ m wavelength regime. In photometry mode, it simultaneously images two bands, 60-85μ m or 85-125μ\m and 125-210μ m, over a field of view of ~1.75'x3.5', with close to Nyquist beam sampling in each band. In spectroscopy mode, it images a field of 47"x47", resolved into 5x5 pixels, with an instantaneous spectral coverage of ~1500km/s and a spectral resolution of ~175km/s. We summarise the design of the instrument, describe observing modes, calibration, and data analysis methods, and present our current assessment of the in-orbit performance of the instrument based on the Performance Verification tests. PACS is fully operational, and the achieved performance is close to or better than the pre-launch predictions.

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arXiv2010

Herschel PEP: The star-formation rates of 1.5<z<2.5 massive galaxies

The star formation rate (SFR) is a key parameter in the study of galaxy evolution. The accuracy of SFR measurements at z~2 has been questioned following a disagreement between observations and theoretical models. The latter predict SFRs at this redshift that are typically a factor 4 or more lower than the measurements. We present star-formation rates based on calorimetric measurements of the far-infrared (FIR) luminosities for massive 1.5 12.2 L_sun. The SFGs and AGNs tend to exhibit the same 24 micron excess. The UV SFRs are in closer agreement with the FIR-based SFRs. Using a Calzetti UV extinction correction results in a mean excess of up to 0.3 dex and a scatter of 0.35 dex from the FIR SFRs. The previous UV SFRs are thus confirmed and the mean excess, while narrowing the gap, is insufficient to explain the discrepancy between the observed SFRs and simulation predictions.

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arXiv2010

Herschel unveils a puzzling uniformity of distant dusty galaxies

The Herschel Space Observatory enables us to accurately measure the bolometric output of starburst galaxies and active galactic nuclei (AGN) by directly sampling the peak of their far-infrared (IR) emission. Here we examine whether the spectral energy distribution (SED) and dust temperature of galaxies have strongly evolved since z~2.5. We use Herschel deep extragalactic surveys from 100 to 500um to compute total IR luminosities in galaxies down to the faintest levels, using PACS and SPIRE in the GOODS-North field (PEP and HerMES key programs). We show that measurements in the SPIRE bands can be used below the statistical confusion limit if information at higher spatial resolution is used to identify isolated galaxies whose flux is not boosted by bright neighbors. Below z~1.5, mid-IR extrapolations are correct for star-forming galaxies with a dispersion of only 40% (0.15dex), therefore similar to z~0 galaxies. This narrow distribution is puzzling when considering the range of physical processes that could have affected the SED of these galaxies. Extrapolations from only one of the 160um, 250um or 350um bands alone tend to overestimate the total IR luminosity. This may be explained by the lack of far-IR constraints around and above ~150um (rest-frame) on local templates. We also note that the dust temperature of luminous IR galaxies around z~1 is mildly colder by 10-15% than their local analogs and up to 20% for ULIRGs at z~1.6. Above z=1.5, distant galaxies are found to exhibit a substantially larger mid- over far-IR ratio, which could either result from stronger broad emission lines or warm dust continuum heated by a hidden AGN. Two thirds of the AGNs identified in the field with a measured redshift exhibit the same behavior as purely star-forming galaxies. Hence a large fraction of AGNs harbor star formation at very high SFR and in conditions similar to purely star-forming galaxies.

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arXiv2010

Star formation in AGN hosts in GOODS-N

Sensitive Herschel far-infrared observations can break degeneracies that were inherent to previous studies of star formation in high-z AGN hosts. Combining PACS 100 and 160um observations of the GOODS-N field with 2Msec Chandra data, we detect ~20% of X-ray AGN individually at >3sig. The host far-infrared luminosity of AGN with L2-10~10^43erg/s increases with redshift by an order of magnitude from z=0 to z~1. In contrast, there is little dependence of far-infrared luminosity on AGN luminosity, for L2-10<~10^44erg/s AGN at z>~1. We do not find a dependence of far-infrared luminosity on X-ray obscuring column, for our sample which is dominated by L2-10<10^44erg/s AGN. In conjunction with properties of local and luminous high-z AGN, we interpret these results as reflecting the interplay between two paths of AGN/host coevolution. A correlation of AGN luminosity and host star formation is traced locally over a wide range of luminosities and also extends to luminous high z AGN. This correlation reflects an evolutionary connection, likely via merging. For lower AGN luminosities, star formation is similar to that in non-active massive galaxies and shows little dependence on AGN luminosity. The level of this secular, non-merger driven star formation increasingly dominates over the correlation at increasing redshift.

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arXiv2010

Herschel observations of FIR emission lines in brightest cluster galaxies

The question of how much gas cools in the cores of clusters of galaxies has been the focus of many, multiwavelength studies in the past 30 years. In this letter we present the first detections of the strongest atomic cooling lines, [C II], [O I] and [N I] in two strong cooling flow clusters, A1068 and A2597, using Herschel PACS. These spectra indicate that the substantial mass of cold molecular gas (>10^9 Mo) known to be present in these systems is being irradiated by intense UV radiation, most probably from young stars. The line widths of these FIR lines indicate that they share dynamics similar but not identical to other ionised and molecular gas traced by optical, near-infrared and CO lines. The relative brightness of the FIR lines compared to CO and FIR luminosity is consistent with other star-forming galaxies indicating that the properties of the molecular gas clouds in cluster cores and the stars they form are not unusual. These results provide additional evidence for a reservoir of cold gas that is fed by the cooling of gas in the cores of the most compact clusters and provide important diagnostics of the temperature and density of the dense clouds this gas resides in.

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arXiv2010

Herschel photometry of brightest cluster galaxies in cooling flow clusters

The dust destruction timescales in the cores of clusters of galaxies are relatively short given their high central gas densities. However, substantial mid-infrared and sub-mm emission has been detected in many brightest cluster galaxies. In this letter we present Herschel PACS and SPIRE photometry of the brightest cluster galaxy in three strong cooling flow clusters, A1068, A2597 and Zw3146. This photometry indicates that a substantial mass of cold dust is present (>3 x 10^7 Mo) at temperatures significantly lower (20-28K) than previously thought based on limited MIR and/or sub-mm results. The mass and temperature of the dust appear to match those of the cold gas traced by CO with a gas-to-dust ratio of 80-120.

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arXiv2010

PEP: first Herschel probe of dusty galaxy evolution up to z~3

We exploit the deepest existing far-infrared (FIR) data obtained so far by Herschel at 100 and 160 um in the GOODS-N, as part of the PACS Evolutionary Probe (PEP) survey, to derive for the first time the evolution of the rest-frame 60-um, 90-um, and total IR luminosity functions (LFs) of galaxies and AGNs from z=0 to unprecedented high redshifts (z~2-3). The PEP LFs were computed using the 1/Vmax method. The FIR sources were classified by means of a detailed broad- band SED-fitting analysis and spectral characterisation. Based on the best-fit model results, k-correction and total IR (8-1000 um) luminosity were obtained for each source. LFs (monochromatic and total) were then derived for various IR populations separately in different redshift bins and compared to backward evolution model predictions. We detect strong evolution in the LF to at least z~2. Objects with SEDs similar to local spiral galaxies are the major contributors to the star formation density (SFD) at z< 0.3, then, as redshift increases, moderate SF galaxies - most likely containing a low-luminosity AGN - start dominating up to z ~= 1.5. At >1.5 the SFD is dominated by the contributions of starburst galaxies. In agreement with previous findings, the comoving IR LD derived from our data evolves approximately as (1 + z)^(3.8+/-0.3) up to z~1, there being some evidence of flattening up to z~2.

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arXiv2010

Far-infrared properties of submillimeter and optically faint radio galaxies

We use deep observations obtained with the Photodetector Array Camera and Spectrometer (PACS) onboard the Herschel space observatory to study the far-infrared (FIR) properties of submm and optically faint radio galaxies (SMGs and OFRGs). From literature we compiled a sample of 35 securely identified SMGs and nine OFRGs located in the GOODS-N and the A2218 fields. This sample is cross-matched with our PACS 100 um and 160 um multi-wavelength catalogs. About half of the galaxies in our sample are detected with PACS. The dust temperatures and the infrared luminosities of our galaxies are derived by fitting their PACS and SCUBA 850 um (only the upper limits for the OFRGs) flux densities with a single modified (beta=1.5) black body function. The median dust temperature of our SMG sample is T=36+/-8K while for our OFRG sample it is T=47+/-3K. For both samples, median dust temperatures derived from Herschel data agree well with previous estimates. In particular, Chapman et al. (2005) found a dust temperature of T=36+/-7K for a large sample of SMGs assuming the validity of the FIR/radio correlation. The agreement between our studies confirms that the local FIR/radio correlation effectively holds at high redshift even though we find =2.17+/-0.19, a slightly lower value than that observed in local systems. The median IR luminosities of SMGs and OFRGs are 4.6*10^12 Lsun and 2.6*10^12 Lsun, respectively. We note that for both samples the IR luminosity estimates from the radio part of the spectral energy distribution are accurate, while estimates from the mid-IR are considerably (x3) more uncertain. Our observations confirm the remarkably high luminosities of SMGs and thus imply median star-formation rates of 960Msun yr^-1 for SMGs with S(850um)>5mJy and 460Msun yr^-1 for SMGs with S(850um)>2mJy, assuming a Chabrier IMF and no dominant AGN contribution to the far-infrared luminosity.

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arXiv2010

The far-infrared/radio correlation as probed by Herschel

We set out to determine the ratio, q(IR), of rest-frame 8-1000um flux, S(IR), to monochromatic radio flux, S(1.4GHz), for galaxies selected at far-IR and radio wavelengths, to search for signs that the ratio evolves with redshift, luminosity or dust temperature, and to identify any far-IR-bright outliers - useful laboratories for exploring why the far-IR/radio correlation is generally so tight when the prevailing theory suggests variations are almost inevitable. We use flux-limited 250-um and 1.4-GHz samples, obtained in GOODS-N using Herschel (HerMES; PEP) and the VLA. We determine bolometric IR output using ten bands spanning 24-1250um, exploiting data from PACS and SPIRE, as well as Spitzer, SCUBA, AzTEC and MAMBO. We also explore the properties of an L(IR)-matched sample, designed to reveal evolution of q(IR) with z, spanning log L(IR) = 11-12 L(sun) and z=0-2, by stacking into the radio and far-IR images. For 1.4-GHz-selected galaxies, we see tentative evidence of a break in the flux ratio, q(IR), at L(1.4GHz) ~ 10^22.7 W/Hz, where AGN are starting to dominate the radio power density, and of weaker correlations with z and T(d). From our 250-um-selected sample we identify a small number of far-IR-bright outliers, and see trends of q(IR) with L(1.4GHz), L(IR), T(d) and z, noting that some of these are inter-related. For our L(IR)-matched sample, there is no evidence that q(IR) changes significantly as we move back into the epoch of galaxy formation: we find q(IR) goes as (1+z)^gamma, where gamma = -0.04 +/- 0.03 at z=0-2; however, discounting the least reliable data at z<0.5 we find gamma = -0.26 +/- 0.07, modest evolution which may be related to the radio background seen by ARCADE2, perhaps driven by <10uJy radio activity amongst ordinary star-forming galaxies at z>1.

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arXiv2010

Dissecting the cosmic infra-red background with Herschel/PEP

The constituents of the cosmic IR background (CIB) are studied at its peak wavelengths (100 and 160 um) by exploiting Herschel/PACS observations of the GOODS-N, Lockman Hole, and COSMOS fields in the PACS Evolutionary Probe (PEP) guaranteed-time survey. The GOODS-N data reach 3 sigma depths of ~3.0 mJy at 100 um and ~5.7 mJy at 160 um. At these levels, source densities are 40 and 18 beams/source, respectively, thus hitting the confusion limit at 160 um. Differential number counts extend from a few mJy up to 100-200 mJy, and are approximated as a double power law, with the break lying between 5 and 10 mJy. The available ancillary information allows us to split number counts into redshift bins. At z<=0.5 we isolate a class of luminous sources (L(IR)~1e11 Lsun), whose SEDs resemble late-spiral galaxies, peaking at ~130 um restframe and significantly colder than what is expected on the basis of pre-Herschel models. By integrating number counts over the whole covered flux range, we obtain a surface brightness of 6.36 +/- 1.67 and 6.58 +/-1.62 [nW m^-2 sr^-1] at 100 and 160 um, resolving ~45% and ~52% of the CIB, respectively. When stacking 24 um sources, the inferred CIB lies within 1.1 sigma and 0.5 sigma from direct measurements in the two bands, and fractions increase to 50% and 75%.Most of this resolved CIB fraction was radiated at z<=1.0, with 160 um sources found at higher redshift than 100 um ones.

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arXiv2010

The first Herschel view of the mass-SFR link in high-z galaxies

We exploit deep observations of the GOODS-N field taken with PACS, on board of Herschel, as part of the PEP guaranteed time, to study the link between star formation and stellar mass in galaxies to z~2. Starting from a stellar mass-selected sample of ~4500 galaxies with mag[4.5mu]<23 (AB), we identify ~350 objects with a PACS detection at 100 or 160mu and ~1500 with only Spitzer 24 mu counterpart. Stellar masses and total IR luminosities (LIR) are estimated by fitting the SEDs. Consistently with other Herschel results, we find that LIR based only on 24 mu data is overestimated by a median factor ~1.8 at z~2, whereas it is underestimated (with our approach) up to a factor ~1.6 at 0.5 10^(11) (M_sun) galaxies from z=0 to z=2, and seems to flatten at z>1.5 in this mass range. Moreover, the most massive galaxies have the lowest SSFR at any z, implying that they have formed their stars earlier and more rapidly than their low mass counterparts.

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arXiv2010

The LABOCA survey of the Extended Chandra Deep Field South: Two modes of star formation in AGN hosts?

We study the co-existence of star formation and AGN activity in X-ray selected AGN by analyzing stacked 870um submm emission from a deep and wide map of the Extended Chandra Deep Field South, obtained with LABOCA at the APEX telescope. The total X-ray sample of 895 sources with median redshift z~1 is detected at a mean submm flux of 0.49+-0.04mJy, corresponding to a typical star formation rate around 30Msun/yr for a T=35K, beta=1.5 greybody far-infrared SED. The good S/N permits stacking analyses for subgroups. We observe a trend of star formation rate increasing with redshift. An increase of star formation rate with AGN luminosity is indicated at the highest L_2-10>~1E44erg/s luminosities only. Increasing trends with X-ray obscuration as expected in some AGN evolutionary scenarios are not observed for the bulk of the X-ray AGN sample but may be present for the highest intrinsic luminosity objects. This suggests a transition between two modes in the coexistence of AGN activity and star formation. For the bulk of the sample, the X-ray luminosity and obscuration of the AGN are not intimately linked to the global star formation rate of their hosts. The hosts are likely massive and forming stars secularly, at rates similar to the pervasive star formation seen in massive galaxies without an AGN at similar redshifts. The change indicated towards more intense star formation, and a more pronounced increase in star formation rates between unobscured and obscured AGN at highest luminosities suggests that luminous AGN follow an evolutionary path on which obscured AGN activity and intense star formation are linked, possibly via merging. Comparison to local hard X-ray selected AGN supports this interpretation. [Abridged]

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arXiv2010

The Great Observatories Origins Deep Survey - VLT/VIMOS Spectroscopy in the GOODS-South Field: Part II

We present the full data set of the VIMOS spectroscopic campaign of the ESO/GOODS program in the CDFS, which complements the FORS2 ESO/GOODS spectroscopic campaign. The GOODS/VIMOS spectroscopic campaign is structured in two separate surveys using two different VIMOS grisms. The VIMOS Low Resolution Blue (LR-Blue) and Medium Resolution (MR) orange grisms have been used to cover different redshift ranges. The LR-Blue campaign is aimed at observing galaxies mainly at 1.8 3.5. The full GOODS/VIMOS spectroscopic campaign consists of 20 VIMOS masks. This release adds 8 new masks to the previous release (12 masks, Popesso et al. 2009). In total we obtained 5052 spectra, 3634 from the 10 LR-Blue masks and 1418 from the 10 MR masks. A significant fraction of the extracted spectra comes from serendipitously observed sources: ~21% in the LR-Blue and ~16% in the MR masks. We obtained 2242 redshifts in the LR-Blue campaign and 976 in the MR campaign for a total success rate of 62% and 69% respectively, which increases to 66% and 73% if only primary targets are considered. The typical redshift uncertainty is estimated to be ~0.0012 (~255 km/s) for the LR-Blue grism and ~0.00040 (~120 km/s) for the MR grism. By complementing our VIMOS spectroscopic catalog with all existing spectroscopic redshifts publicly available in the CDFS, we compiled a redshift master catalog with 7332 entries, which we used to investigate large scale structures out to z~3.7. We produced stacked spectra of LBGs in a few bins of equivalent width (EW) of the Ly-alpha and found evidence for a lack of bright LBGs with high EW of the Ly-alpha. Finally, we obtained new redshifts for 12 X-ray sources of the CDFS and extended-CDFS.

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arXiv2009

Weak lensing observations of potentially X-ray underluminous galaxy clusters

Optically selected clusters of galaxies display a relation between their optical mass estimates and their X-ray luminosities Lx that has a large scatter. A substantial fraction of optically selected clusters have Lx estimates or upper limits significantly below the values expected from the Lx-mass relation established for X-ray selected clusters, i.e., these clusters are X-ray underluminous for their mass. We attempt to confirm or falsify the X-ray underluminous nature of two clusters, Abell 315 and Abell 1456, by using weak gravitational lensing as a third and independent measure of the clusters' masses. We obtained optical wide-field imaging data and selected background galaxies using their colors and measured the shear exerted by the tidal field of the foreground galaxy clusters. We then fitted parametrized models to our shear catalogs. After accounting for projections of large-scale structure and halo triaxiality, we find that A 315 is significantly X-ray underluminous for its mass, while no significant lensing signal was detected for A 1456. We re-evaluate earlier kinematic and X-ray analyses of these two clusters and discuss the nature of the X-ray underluminous cluster A 315 and why A 1456 was probably erroneously identified as being X-ray underluminous.

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arXiv2009

Spectroscopic Observations of Lyman-Break Galaxies at Redshift ~ 4, 5 and 6 in the GOODS-South Field

We report on observations of Lyman-break galaxies (LBGs) selected from the Great Observatories Origins Deep Survey at mean redshift z~4, 5 and 6, obtained with FORS2 spectrograph at the ESO-VLT.This program has yielded spectroscopic identifications for 114 galaxies of which 51 are at z~4, 31 at z~5, and 32 at z~6. The adopted selection criteria are effective, identifying galaxies at the expected redshift with minimal foreground contamination. Once selection effects are properly accounted for, the rest-frame UV spectra of the higher-redshift LBGs appear to be similar to their counterparts at z~3. As at z~3, LBGs at z~4 and z~5 show Lya both in emission and in absorption; when in absorption, strong interstellar lines and red UV spectra are observed, a fact also measured at z~2 and 3. At z~6, sensitivity issues bias our sample towards galaxies with Lya in emission; nevertheless, these spectra appear to be similar to their lower-redshift counterparts. As in other studies at similar redshifts, we find clear evidence that brighter LBGs tend to have weaker Lya emission lines. At fixed rest-frame UV luminosity, the equivalent width of the Lya emission line is larger at higher redshifts. At all redshifts where the measurements can be reliably made, the redshift of the Lya emission line turns out to be larger than that of the interstellar absorption lines,with a median velocity difference DeltaV~400 km/s at z~4 and 5, consistent with results at lower redshifts. This shows that powerful, large-scale winds are common at high redshift.In general,there is no strong correlation between the morphology of the UV light and the spectroscopic properties. However, galaxies with deep interstellar absorption lines and strong Lya absorption appear to be more diffuse than galaxies with Lya in emission.(abridged)

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arXiv2008

The VLA Survey of the Chandra Deep Field South. II. Identification and host galaxy properties of submillijansky sources

We present the optical and infrared identifications of the 266 radio sources detected at 20 cm with the Very Large Array in the Chandra Deep Field South (Kellermann et al. 2008). Using deep i-band Advanced Camera for Surveys, R-band Wide Field Imager, K-band SOFI/NTT, K-band ISAAC/VLT and Spitzer imaging data, we are able to find reliable counterparts for 254 (~95%) VLA sources. Twelve radio sources remain unidentified and three of them are ``empty fields''. Using literature and our own data we are able to assign redshifts to 186 (~70%) radio sources: 108 are spectroscopic redshifts and 78 reliable photometric redshifts. Based on the rest frame colors and morphological distributions of the host galaxies we find evidences for a change in the submillijansky radio source population: a) above ~ 0.08 mJy early-type galaxies are dominating; b) at flux densities below ~0.08 mJy, starburst galaxies become dominant.

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arXiv2008

The Evolution of AGN Host Galaxies: From Blue to Red and the Influence of Large-Scale Structures

We present an analysis of 109 moderate-luminosity (41.9 < Log L{0.5-8.0 keV} < 43.7) AGN in the Extended Chandra Deep Field-South survey, which is drawn from 5,549 galaxies from the COMBO-17 and GEMS surveys having 0.4 < z < 1.1. These obscured or optically-weak AGN facilitate the study of their host galaxies since the AGN provide an insubstantial amount of contamination to the galaxy light. We find that the color distribution of AGN host galaxies is highly dependent upon (1) the strong color-evolution of luminous (M_V < -20.7) galaxies, and (2) the influence of ~10 Mpc scale structures. When excluding galaxies within the redshift range 0.63 < z < 0.76, a regime dominated by sources in large-scale structures at z=0.67 and z=0.73, we observe a bimodality in the host galaxy colors. Galaxies hosting AGN at z > 0.8 preferentially have bluer (rest-frame U-V < 0.7) colors than their z <~ 0.6 counterparts (many of which fall along the red sequence). The fraction of galaxies hosting AGN peaks in the ``green valley'' (0.5 < U-V < 1.0); this is primarily due to enhanced AGN activity in the redshift interval 0.63 < z < 0.76. The AGN fraction in this redshift and color interval is 12.8% (compared to its `field' value of 7.8%) and reaches a maximum of 14.8% at U-V~0.8. We further find that blue, bulge-dominated (Sersic index n>2.5) galaxies have the highest fraction of AGN (21%) in our sample. We explore the scenario that the evolution of AGN hosts is driven by galaxy mergers and illustrate that an accurate assessment requires a larger area survey since only three hosts may be undergoing a merger with timescales <1 Gyr following a starburst phase.

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arXiv2008

The Great Observatories Origins Deep Survey. VLT/VIMOS Spectroscopy in the GOODS-South Field

We present the first results of the VIsible Multiobject Spectrograph (VIMOS) ESO/GOODS program of spectroscopy of faint galaxies in the Chandra Deep Field South (CDF-S). The program complements the FORS2 ESO/GOODS campaign. 3312 spectra have been obtained in service mode with VIMOS at the ESO/VLT UT3. The VIMOS LR-Blue and MR grisms have been used to cover different redshift ranges. Galaxies at 1.8 < z < 3.5 have been observed in the GOODS VIMOS-LR-Blue campaign. Galaxies at z < 1 and Lyman Break Galaxies at z > 3.5 have been observed in the VIMOS MR survey. Here we report results for the first 6 masks (out of 10 total) that have been analyzed from each of the LR-Blue and MR grisms. Spectra of 2344 spectra have been extracted from these 6 LR-Blue masks and 968 from 6 MR masks. 33% of the LR-Blue and 18% of the MR spectra are serendipitous observations. We obtained 1481 redshifts in the LR-Blue campaign and 656 in the MR campaign for a total success rate of 63% and 68%, respectively, which increase to 70% and 75% when only the primary targets are considered. By complementing our VIMOS spectroscopic catalog with all existing spectroscopic redshifts publicly available in the CDF-S, we created a redshift master catalog. By comparing this redshift compilation with different photometric redshift catalogs we estimate the completeness level of the CDF-S spectroscopic coverage in several redshift bins. The completeness level is very high, > 60%, at z < 3.5, and it is very uncertain at higher redshift. The master catalog has been used also to estimate completeness and contamination levels of different galaxy photometric selection techniques, such as the BzK, the so called 'sub'-U-dropout and the drop-out methods and to identify large scale structures in the field.

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