Showing papers by "S. Berta published in 2011"

PACS Evolutionary Probe (PEP) – a Herschel key program

Abstract: Deep far-infrared photometric surveys studying galaxy evolution and the nature of the cosmic infrared background are a key strength of the Herschel mission. We describe the scientific motivation for the PACS Evolutionary Probe (PEP) guaranteed time key program and its role within the entire set of Herschel surveys, and the field selection that includes popular multiwavelength fields such as GOODS, COSMOS, Lockman Hole, ECDFS, and EGS. We provide an account of the observing strategies and data reduction methods used. An overview of first science results illustrates the potential of PEP in providing calorimetric star formation rates for high-redshift galaxy populations, thus testing and superseding previous extrapolations from other wavelengths, and enabling a wide range of galaxy evolution studies.

Building the cosmic infrared background brick by brick with Herschel/PEP. ⋆

Abstract: The cosmic infrared background (CIB) includes roughly half of the energy radiated by all galaxies at all wavelengths across cosmic time, as observed at the present epoch The PACS Evolutionary Probe (PEP) survey is exploited here to study the CIB and its redshift differential, at 70, 100 and 160 μ m, where the background peaks Combining PACS observations of the GOODS-S, GOODS-N, Lockman Hole and COSMOS areas, we define number counts spanning over more than two orders of magnitude in flux: from ~1 mJy to few hundreds mJy Stacking of 24 μ m sources and P (D ) statistics extend the analysis down to ~02 mJy Taking advantage of the wealth of ancillary data in PEP fields, differential number counts d 2 N /dS /dz and CIB are studied up to z = 5 Based on these counts, we discuss the effects of confusion on PACS blank field observations and provide confusion limits for the three bands considered While most of the available backward evolution models predict the total PACS number counts with reasonable success, the consistency to redshift distributions and CIB derivatives can still be significantly improved The new high-quality PEP data highlight the need to include redshift-dependent constraints in future modeling The total CIB surface brightness emitted above PEP 3σ flux limits is ν I ν = 452 ± 118, 835 ± 095 and 949 ± 059 [nW m-2 sr-1 ] at 70, 100, and 160 μ m, respectively These values correspond to 58 ± 7% and 74 ± 5% of the COBE/DIRBE CIB direct measurements at 100 and 160 μ m Employing the P (D ) analysis, these fractions increase to ~65% and ~89% More than half of the resolved CIB was emitted at redshift z ≤ 1 The 50%-light redshifts lie at z = 058, 067 and 073 at the three PACS wavelengths The distribution moves towards earlier epochs at longer wavelengths: while the 70 μ m CIB is mainly produced by z ≤ 10 objects, the contribution of z > 10 sources reaches 50% at 160 μ m Most of the CIB resolved in the three PACS bands was emitted by galaxies with infrared luminosities in the range 1011 − 1012 L ⊙

The Redshift and Nature of AzTEC/COSMOS 1: A Starburst Galaxy at z = 4.6

Abstract: Based on broadband/narrowband photometry and Keck DEIMOS spectroscopy, we report a redshift of z = 4.64^(+0.06)_(–0.08) for AzTEC/COSMOS 1, the brightest submillimeter galaxy (SMG) in the AzTEC/COSMOS field. In addition to the COSMOS-survey X-ray to radio data, we report observations of the source with Herschel/PACS (100, 160 μm), CSO/SHARC II (350 μm), and CARMA and PdBI (3 mm). We do not detect CO(5 → 4) line emission in the covered redshift ranges, 4.56-4.76 (PdBI/CARMA) and 4.94-5.02 (CARMA). If the line is within this bandwidth, this sets 3σ upper limits on the gas mass to ≲8 × 10^9 M_☉ and ≲5 × 10^(10) M_☉, respectively (assuming similar conditions as observed in z ~ 2 SMGs). This could be explained by a low CO-excitation in the source. Our analysis of the UV-IR spectral energy distribution of AzTEC 1 shows that it is an extremely young (≲50 Myr), massive (M * ~ 10^(11) M_☉), but compact (≲2 kpc) galaxy, forming stars at a rate of ~1300 M_☉ yr^(–1). Our results imply that AzTEC 1 is forming stars in a "gravitationally bound" regime in which gravity prohibits the formation of a superwind, leading to matter accumulation within the galaxy and further generations of star formation.

Disk, merger, or outflow ? Molecular gas kinematics in two powerful obscured QSOs at z>3.4

Abstract: We report on the detection of bright CO(4-3) line emission in two powerful, obscured quasars discovered in the SWIRE survey, SW022513 and SW022550 at z≥3.4. We analyze the line strength and profile to determine the gas mass, dynamical mass and the gas dynamics for both galaxies. In SW022513 we may have found the first evidence for a molecular, AGN-driven wind in the ear ly Universe. The line profile in SW022513 is broad (FWHM = 1000 km s −1 ) and blueshifted by−200 km s −1 relative to systemic (where the systemic velocity is estimated from the narrow components of ionized gas lines, as is commonly done for AGN at low and high redshifts). SW022550 has a more regular, double-peaked profile, which is marginally spatially resolved in our data, con sistent with either a merger or an extended disk. The molecular gas masses, 4×10 10 M⊙, are large and account for<30% of the stellar mass, making these obscured QSOs as gas rich as other powerful CO emitting galaxies at high redshift, i.e., submillimeter galaxies. Our sources exhibit relatively lo wer star-formation effi ciencies compared to other dusty, powerful starburst galax ies at high redshift. We speculate that this could be a consequence of the AGN perturbing the molecular gas.

PACS Evolutionary Probe (PEP) - A Herschel Key Program

Abstract: Deep far-infrared photometric surveys studying galaxy evolution and the nature of the cosmic infrared background are a key strength of the Herschel mission. We describe the scientific motivation for the PACS Evolutionary Probe (PEP) guaranteed time key program and its role in the complement of Herschel surveys, and the field selection which includes popular multiwavelength fields such as GOODS, COSMOS, Lockman Hole, ECDFS, EGS. We provide an account of the observing strategies and data reduction methods used. An overview of first science results illustrates the potential of PEP in providing calorimetric star formation rates for high redshift galaxy populations, thus testing and superseeding previous extrapolations from other wavelengths, and enabling a wide range of galaxy evolution studies.

Building the cosmic infrared background brick by brick with Herschel/PEP

Abstract: The cosmic infrared background (CIB) includes roughly half of the energy radiated by all galaxies at all wavelengths across cosmic time, as observed at the present epoch. The PACS Evolutionary Probe (PEP) survey is exploited here to study the CIB and its redshift differential, at 70, 100 and 160 micron, where the background peaks. Combining PACS observations of the GOODS-S, GOODS-N, Lockman Hole and COSMOS areas, we define number counts spanning over more than two orders of magnitude in flux: from ~1 mJy to few hundreds mJy. Stacking of 24 micron sources and P(D) statistics extend the analysis down to ~0.2 mJy. Taking advantage of the wealth of ancillary data in PEP fields, differential number counts and CIB are studied up to z=5. Based on these counts, we discuss the effects of confusion on PACS blank field observations and provide confusion limits for the three bands considered. The total CIB surface brightness emitted above PEP 3 sigma flux limits is 4.52 +/- 1.18, 8.35 +/- 0.95 and 9.49 +/- 0.59 [nW/m2/sr] at 70, 100, and 160 micron, respectively. These values correspond to 58 +/- 7% and 74 +/- 5% of the COBE/DIRBE CIB direct measurements at 100 and 160 micron. Employing the P(D) analysis, these fractions increase to ~65% and ~89%. More than half of the resolved CIB was emitted at redshift z 1.0 sources reaches 50% at 160 micron. Most of the CIB resolved in the three PACS bands was emitted by galaxies with infrared luminosities in the range 1e11-1e12 L(sun).

The impact of evolving infrared spectral energy distributions of galaxies on star formation rate estimates

Abstract: We combine Herschel-PACS data from the PEP program with Spitzer 24 um and 16 um photometry and ultra deep IRS mid-infrared spectra, to measure the mid- to far-infrared spectral energy distribution (SED) of 0.7

The evolution of the star formation activity per halo mass up to redshift ~ 1.6 as seen by Herschel

Abstract: Star formation in massive galaxies is quenched at some point during hierarchical mass assembly. To understand where and when the quenching processes takes place, we study the evolution of the total star formation rate per unit total halo mass (\Sigma(SFR/M)) in three different mass scales: low mass halos (field galaxies), groups, and clusters, up to a redshift ~1.6. We use deep far-infrared PACS data at 100 and 160 um to accurately estimate the total star formation rate of the Luminous Infrared Galaxy population of 9 clusters with mass ~10^{15} M_{\odot}, and 9 groups/poor clusters with mass ~ 5 x 10^{13} M_{\odot}. Estimates of the field \Sigma(SFR/M) are derived from the literature, by dividing the star formation rate density by the mean comoving matter density of the universe. The field \Sigma(SFR/M) increases with redshift up to z~1 and it is constant thereafter. The evolution of the \Sigma(SFR/M)-z relation in galaxy systems is much faster than in the field. Up to redshift z~0.2, the field has a higher \Sigma(SFR/M) than galaxy groups and galaxy clusters. At higher redshifts, galaxy groups and the field have similar \Sigma(SFR/M), while massive clusters have significantly lower \Sigma(SFR/M) than both groups and the field. There is a hint of a reversal of the SFR activity vs. environment at z~1.6, where the group \Sigma(SFR/M) lies above the field \Sigma(SFR/M)-z relation. We discuss possible interpretations of our results in terms of the processes of downsizing, and star-formation quenching.

Disk, merger, or outflow ? Molecular gas kinematics in two powerful obscured QSOs at z>3.4

Abstract: We report on the detection of bright CO(4-3) line emission in two powerful, obscured quasars discovered in the SWIRE survey, SW022513 and SW022550 at z>3.4. We analyze the line strength and profile to determine the gas mass, dynamical mass and the gas dynamics for both galaxies. In SW022513 we may have found the first evidence for a molecular, AGN-driven wind in the early Universe. The line profile in SW022513 is broad (FWHM = 1000 km/s) and blueshifted by -200 km/s relative to systemic (where the systemic velocity is estimated from the narrow components of ionized gas lines, as is commonly done for AGN at low and high redshifts). SW022550 has a more regular, double-peaked profile, which is marginally spatially resolved in our data, consistent with either a merger or an extended disk. The molecular gas masses, 4x10^10 Msun, are large and account for <30% of the stellar mass, making these obscured QSOs as gas rich as other powerful CO emitting galaxies at high redshift, i.e., submillimeter galaxies. Our sources exhibit relatively lower star-formation efficiencies compared to other dusty, powerful starburst galaxies at high redshift. We speculate that this could be a consequence of the AGN perturbing the molecular gas.