Paola Andreani

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 ESAs far infrared and submil- limetre observatory. It employs two Ge:Ga photoconductor arrays (stressed and unstressed) with 16 × 25 pixels, each, and two filled silicon bolometer arrays with 16 × 32 and 32 × 64 pixels, respectively, to perform integral-field spectroscopy and imaging photom- etry in the 60−210 μm wavelength regime. In photometry mode, it simultaneously images two bands, 60−85 μ mo r 85−125 μ ma nd 125−210 μm, over a field of view of ∼1.75 � × 3.5 � , with close to Nyquist beam sampling in each band. In spectroscopy mode, it images afi eld of 47 �� × 47 �� , resolved into 5 × 5 pixels, with an instantaneous spectral coverage of ∼ 1500 km s −1 and a spectral resolution of ∼175 km s −1 . 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.

The Lesser Role of Starbursts in Star Formation at z = 2

Two main modes of star formation are know to control the growth of galaxies: a relatively steady one in disk-like galaxies, defining a tight star formation rate (SFR)-stellar mass sequence, and a starburst mode in outliers to such a sequence which is generally interpreted as driven by merging. Such starburst galaxies are rare but have much higher SFRs, and it is of interest to establish the relative importance of these two modes. PACS/Herschel observations over the whole COSMOS and GOODS-South fields, in conjunction with previous optical/near-IR data, have allowed us to accurately quantify for the first time the relative contribution of the two modes to the global SFR density in the redshift interval 1.5 1000 M ☉ yr-1, off-sequence sources significantly contribute to the SFR density (46% ± 20%). We conclude that merger-driven starbursts play a relatively minor role in the formation of stars in galaxies, whereas they may represent a critical phase toward the quenching of star formation and morphological transformation in galaxies.

The Herschel ATLAS

The Herschel ATLAS is the largest open-time key project that will be carried out on the Herschel Space Observatory. It will survey 570 deg2 of the extragalactic sky, 4 times larger than all the other Herschel extragalactic surveys combined, in five far-infrared and submillimeter bands. We describe the survey, the complementary multiwavelength data sets that will be combined with the Herschel data, and the six major science programs we are undertaking. Using new models based on a previous submillimeter survey of galaxies, we present predictions of the properties of the ATLAS sources in other wave bands.

PACS Evolutionary Probe (PEP) - A Herschel Key Program

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.

THE 2014 ALMA LONG BASELINE CAMPAIGN: FIRST RESULTS FROM HIGH ANGULAR RESOLUTION OBSERVATIONS TOWARD THE HL TAU REGION

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations from the 2014 Long Baseline Campaign in dust continuum and spectral line emission from the HL Tau region. The continuum images at wavelengths of 2.9, 1.3, and 0.87 mm have unprecedented angular resolutions of 0. ′′ 075 (10 AU) to 0. ′′ 025 (3.5 AU), revealing an astonishing level of detail in the cir cumstellar disk surrounding the young solar analogue HL Tau, with a pattern of bright and dark rings observed at all wavelengths. By fitting ellipses to the most distinct rings, we measure precise values for the disk inclination (46.72 ◦ ± 0.05 ◦ ) and position angle (+138.02 ◦ ± 0.07 ◦ ). We obtain a high-fidelity image of the 1.0 mm spectral index (�), which ranges from � � 2.0 in the optically-thick central peak and two brightest ring s, increasing to 2.3-3.0 in the dark rings. The dark rings are not devoid of emission, and we estimate a grain emissivity index of 0.8 for the innermost dark ring and lower for subsequent dark rings, consistent with some degree of grain growth and evolution. Additional clues that the rings arise from planet formation incl ude an increase in their central offsets with radius and the presence of numerous orbital resonances. At a resolution of 35 AU, we resolve the molecular component of the disk in HCO + (1-0) which exhibits a pattern over LSR velocities from 2-12 km s -1 consistent with Keplerian motion around a �1.3M⊙ star, although complicated by absorption at low blue-shifted velocities. We also serendipitously detect and resolve the nearby protost ars XZ Tau (A/B) and LkH�358 at 2.9 mm. Subject headings: stars: individual (HL Tau, XZ Tau, LkH�358) — protoplanetary disks — stars: formation — submillimeter: planetary systems — techniques: interferometric

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

Aims. We exploit deep observations of the GOODS-N field taken with PACS, the Photodetector Array Camera and Spectrometer, onboard of Herschel, as part of the PACS evolutionary probe guaranteed time (PEP), to study the link between star formation and stellar mass in galaxies to z ∼ 2. Methods. Starting from a stellar mass – selected sample of ∼4500 galaxies with mag4.5 μm < 23.0 (AB), we identify ∼350 objects with a PACS detection at 100 or 160 μ ma nd∼ 1500 with only Spitzer 24 μm counterpart. Stellar masses and total IR luminosities (LIR) are estimated by fitting the spectral energy distributions (SEDs). Results. Consistently with other Herschel results, we find that LIR based only on 24 μm data is overestimated by a median factor ∼ 1. 8a tz ∼ 2, whereas it is underestimated (with our approach) up to a factor ∼ 1. 6a t 0.5 < z < 1.0. We then exploit this calibration to correct LIR based on the MIPS/Spitzer fluxes. These results clearly show how Herschel is fundamental to constrain LIR, and hence the star formation rate (SFR), of high redshift galaxies. Using the galaxies detected with PACS (and/or MIPS), we investigate the existence and evolution of the relations between the SFR, the specific star formation rate (SSFR=SFR/mass) and the stellar mass. Moreover, in order to avoid selection effects, we also repeat this study through a stacking analysis on the PACS images to fully exploit the far-IR information also for the Herschel and Spitzer undetected subsamples. We find that the SSFR-mass relation steepens with redshift, being almost flat at z < 1.0 and reaching a slope of α = −0.50 +0.13 −0.16 at z ∼ 2, at odds with recent works based on radio-stacking analysis at the same redshift. The mean SSFR of galaxies increases with redshift, by a factor ∼15 for

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 160 μm observations of the GOODS-N field with 2 Ms Chandra data, we detect ∼20% of X-ray AGN individually at >3σ. The host far-infrared luminosity of AGN with L2−10 keV ≈ 10 43 erg s −1 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 keV 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 keV < 10 44 erg s −1 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.

Dust emission from quasars and quasar host galaxies

We test emission models of circum-nuclear dust torii around quasars, at low and high redshifts, by using a large collection of photometric data for an unbiased sample of 120 optically-selected objects with millimetric and sub-millimetric fluxes, including new unpublished data. Under the assumption that the dust is heated by a point-like source with a power-law primary spectrum, as defined by the observed optical-UV continuum, we infer the basic model parameters, such as dust masses, temperature distributions and torus sizes, by numerically solving the radiative transfer equation in the dust distribution. In addition to the substantiated statistics, an essential improvement over previous analyses comes from the use of optical-UV data to constrain the primary illuminating continuum, which is needed to estimate dust temperatures and sizes. Dependences of the best-fit parameters on luminosity and redshift are studied and the contribution of dust in the host galaxy to the observed fluxes is briefly mentioned. This analysis constrains the properties of the enriched interstellar medium in the galaxies hosting the quasars. The dust abundance does not display appreciable trends as a function of redshift, from z ≃ 1 to almost 5, and shows that dust and metals are at least as, and often more, abundant at these early epochs than they are in local galactic counterparts. This evolutionary pattern is remarkably at variance with respect to what is expected for disk galaxies, like the Milky Way, slowly building metals during the whole Hubble time. It rather points in favour of a much more active phase of star-formation at early epochs, probably related to the formation of massive spheroidal galaxies.

PAH emission and star formation in the host of the z ~ 2.56 Cloverleaf QSO

We report the first detection of the 6.2 and 7.7 μm infrared polycyclic aromatic hydrocarbon (PAH) emission features in the spectrum of a high-redshift QSO, from the Spitzer IRS spectrum of the Cloverleaf lensed QSO (H1413+117, z ~ 2.56). The ratio of PAH features and rest-frame far-infrared emission is the same as in lower luminosity star-forming ULIRGs and in local PG QSOs, supporting a predominantly starburst nature of the Cloverleafs huge far-infrared luminosity (5.4 × 1012 L☉, corrected for lensing). The Cloverleafs period of dominant QSO activity (LBol ~ 7 × 1013 L☉) is coincident with an intense (star formation rate ~1000 M☉ yr-1) and short (gas exhaustion time ~3 × 107 yr) star-forming event.

Star formation properties of sub-mJy radio sources

We investigate the star formation properties of � 800 sources detected in one of the deepest radio surveys at 1.4 GHz. Our sample spans a wide redshift range (� 0.1 4) and about four orders of magnitude in star formation rate (SFR). It includes both star forming galaxies (SFGs) and active galactic nuclei (AGNs), further divided into radio-quiet and radio-loud objects. We compare the SFR derived from the far infrared luminosity, as traced by Herschel, with the SFR computed from their radio emission. We find that the radio power is a good SFR tracer not only for pure SFGs but also in the host galaxies of RQ AGNs, with no significant deviation with redshift or specific SFR. Moreover, we quantify the contribution of the starburst activity in the SFGs population and the occurrence of AGNs in sources with different level of star formation. Finally we discuss the possibility of using deep radio survey as a tool to study the cosmic star formation history.