A. Cooray

Publications (215)237.02 Total impact

• Article: An Overview of the Dwarf Galaxy Survey

  S. C. Madden, A. Remy Ruyer, M. Galametz, D. Cormier, V. Lebouteiller, F. Galliano, S. Hony, G. J. Bendo, M. W. L. Smith, M. Pohlen, [......], J. A. MacHattie, B. O Halloran, T. J. Parkin, N. Rangwala, M. R. P. Schirm, B. Schulz, L. Spinoglio, M. Vaccari, C. D. Wilson, H. Wozniak
  [show abstract] [hide abstract]
  ABSTRACT: The Dwarf Galaxy Survey (DGS) program is studying low-metallicity galaxies using 230h of far-infrared (FIR) and submillimetre (submm) photometric and spectroscopic observations of the Herschel Space Observatory and draws to this a rich database of a wide range of wavelengths tracing the dust, gas and stars. This sample of 50 galaxies includes the largest metallicity range achievable in the local Universe including the lowest metallicity (Z) galaxies, 1/50 Zsun, and spans 4 orders of magnitude in star formation rates. The survey is designed to get a handle on the physics of the interstellar medium (ISM) of low metallicity dwarf galaxies, especially on their dust and gas properties and the ISM heating and cooling processes. The DGS produces PACS and SPIRE maps of low-metallicity galaxies observed at 70, 100, 160, 250, 350, and 500 mic with the highest sensitivity achievable to date in the FIR and submm. The FIR fine-structure lines, [CII] 158 mic, [OI] 63 mic, [OI] 145 mic, [OIII] 88 mic, [NIII] 57 mic and [NII] 122 and 205 mic have also been observed with the aim of studying the gas cooling in the neutral and ionized phases. The SPIRE FTS observations include many CO lines (J=4-3 to J=13-12), [NII] 205 mic and [CI] lines at 370 and 609 mic. This paper describes the sample selection and global properties of the galaxies, the observing strategy as well as the vast ancillary database available to complement the Herschel observations. The scientific potential of the full DGS survey is described with some example results included.
  05/2013;
• Article: {\em Herschel}-ATLAS/GAMA: The Environmental Density of Far-Infrared Bright Galaxies at $z \leq 0.5$

  C. S. Burton, Matt J. Jarvis, D. J. B. Smith, D. G. Bonfield, M. J. Hardcastle, J. A. Stevens, N. Bourne, M. Baes, S. Brough, A. Cava, [......], S. Eales, R. Hopwood, E. Ibar, R. J. Ivison, J. Liske, J. Loveday, S. J. Maddox, M. Negrello, M. W. L. Smith, E. Valiante
  [show abstract] [hide abstract]
  ABSTRACT: We compare the environmental and star formation properties of far-infrared detected and non--far-infrared detected galaxies out to $z \sim0.5$. Using optical spectroscopy and photometry from the Galaxy And Mass Assembly (GAMA) and Sloan Digital Sky Survey (SDSS), with far-infrared observations from the {\em Herschel}-ATLAS Science Demonstration Phase (SDP), we apply the technique of Voronoi Tessellations to analyse the environmental densities of individual galaxies. Applying statistical analyses to colour, $r-$band magnitude and redshift-matched samples, we show there to be a significant difference at the 3.5$\sigma$ level between the normalized environmental densities of these two populations. This is such that infrared emission (a tracer of star formation activity) favours underdense regions compared to those inhabited by exclusively optically observed galaxies selected to be of the same $r-$band magnitude, colour and redshift. Thus more highly star-forming galaxies are found to reside in the most underdense environments, confirming previous studies that have proposed such a correlation. However, the degeneracy between redshift and far-infrared luminosity in our flux-density limited sample means that we are unable to make a stronger statement in this respect. We then apply our method to synthetic light cones generated from semi-analytic models, finding that over the whole redshift distribution the same correlations between star-formation rate and environmental density are found.
  05/2013;
• Article: On the redshift evolution (0 < z < 4) of dust attenuation and of the total (UV+IR) star formation rate density

  D. Burgarella, V. Buat, C. Gruppioni, O. Cucciati, S. Heinis, S. Berta, M. Bethermin, J. Bock, A. Cooray, J. S. Dunlop, [......], D. Lutz, B. Magnelli, R. Nordon, S. J. Oliver, M. J. Page, P. Popesso, F. Pozzi, L. Riguccini, M. Vaccari, M. Viero
  [show abstract] [hide abstract]
  ABSTRACT: Using new homogeneous LFs in the FUV and in the FIR Herschel/PEP and Herschel/HerMES, we study the evolution of the dust attenuation with redshift. With this information in hand, we are able to estimate the redshift evolution of the total (FUV + FIR) star formation rate density SFRD_TOT. By integrating SFRD_TOT, we follow the mass building and analyze the redshift evolution of the stellar mass density (SMD). This letter aims at providing a complete view of star formation from the local universe to z = 4 and, using assumptions on earlier star formation history, compares this evolution to what was known before in an attempt to draw a homogeneous picture of the global evolution of star formation in galaxies. The main conclusions of this letter are: 1) the dust attenuation A_FUV is found to increase from z = 0 to z \sim 1.2 and then starts to decrease up to our last data point at z = 3.6; 2) the estimated SFRD confirms published results up to z = 2. At z > 2, we observe either a plateau or a small increase up to z = 3 and then a likely decrease up to z = 3.6; 3) the peak of A_FUV is delayed with respect to the plateau of SFRD_TOT and a likely origin might be found in the evolution of the bright ends of the FUV and FIR LFs; 4) using assumptions (namely exponential rise and linear rise with time) for the evolution of the star formation density from z = 3.6 to z_form = 10, we integrate SFRD_TOT and find a good agreement with the published SMDs.
  04/2013;
• Source

  Available from: Roxana E. Lupu

  Article: A dust-obscured massive maximum-starburst galaxy at a redshift of 6.34.

  Dominik A Riechers, C M Bradford, D L Clements, C D Dowell, I Pérez-Fournon, R J Ivison, C Bridge, A Conley, Hai Fu, J D Vieira, [......], D Scott, A J Smith, J G Staguhn, A Streblyanska, A P Thomson, I Valtchanov, M Viero, L Wang, M Zemcov, J Zmuidzinas
  [show abstract] [hide abstract]
  ABSTRACT: Massive present-day early-type (elliptical and lenticular) galaxies probably gained the bulk of their stellar mass and heavy elements through intense, dust-enshrouded starbursts-that is, increased rates of star formation-in the most massive dark-matter haloes at early epochs. However, it remains unknown how soon after the Big Bang massive starburst progenitors exist. The measured redshift (z) distribution of dusty, massive starbursts has long been suspected to be biased low in z owing to selection effects, as confirmed by recent findings of systems with redshifts as high as ∼5 (refs 2-4). Here we report the identification of a massive starburst galaxy at z = 6.34 through a submillimetre colour-selection technique. We unambiguously determined the redshift from a suite of molecular and atomic fine-structure cooling lines. These measurements reveal a hundred billion solar masses of highly excited, chemically evolved interstellar medium in this galaxy, which constitutes at least 40 per cent of the baryonic mass. A 'maximum starburst' converts the gas into stars at a rate more than 2,000 times that of the Milky Way, a rate among the highest observed at any epoch. Despite the overall downturn in cosmic star formation towards the highest redshifts, it seems that environments mature enough to form the most massive, intense starbursts existed at least as early as 880 million years after the Big Bang.
  Nature 04/2013; 496(7445):329-333. · 36.28 Impact Factor
• Article: Far-IR Emission From Dust-Obscured Galaxies

  J. A. Calanog, J. Wardlow, Hai Fu, A. Cooray, R. J. Assef, J. Bock, C. M. Casey, A. Conley, D. Farrah, E. Ibar, [......], I. Perez-Fournon, D. Riechers, D. Rigopoulou, I. G. Roseboom, B. Schulz, Douglas Scott, M. Symeonidis, M. Vaccari, M. Viero, M. Zemcov
  [show abstract] [hide abstract]
  ABSTRACT: Dust-obscured galaxies (DOGs) are a UV-faint, IR-bright galaxy population that reside at z~2 and are believed to be in a phase of dusty star-forming and AGN activity. We present far-IR observations of a complete sample of DOGs in the 2 deg^2 of COSMOS. The 3077 DOGs have =1.9+/-0.3 and are selected from 24 um and r+ observations using a color cut of r+ - [24] >= 7.5 (AB mag) and S24 >= 100 uJy. Based on the mid-IR SEDs, 47% are star-formation dominated and 10% are AGN-dominated. We use SPIRE far-IR photometry from HerMES to calculate the IR luminosity and characteristic dust temperature for the 1572 (51%) DOGs that are detected at 250 um (>=3sigma). For the remaining 1505 (49%) that are undetected, we perform a median stacking analysis to probe fainter luminosities. Detected and undetected DOGs have average IR luminosities of (2.8+/-0.4) x 10^12 L_Sun and (0.77+/-0.08) x 10^12L_Sun, and dust temperatures of 34+/-7 K and 31+/-3 K, respectively. Using far-IR observations, DOGs contribute 30% to the 24 um-selected galaxies' IR luminosity. If the IR luminosity is extrapolated using the 24 um flux density alone, it is overestimated by a factor of 2 on average. DOGs contribute 10-30% to the total star formation rate density of the Universe at z=1.5-2.5, dominated by 250{\mu}m detected and bump DOGs, compared to around 40% for all 24 um galaxies above our flux limit. DOGs have a large scatter about the star-formation main sequence and their specific star-formation rates show that the observed phase of star-formation could be responsible for their observed stellar mass at z~2.
  04/2013;
• Source

  Available from: Bogdan Adrian Pastrav

  Article: GAMA/H-ATLAS: The Dust Opacity - Stellar Mass Surface Density Relationfor Spiral Galaxies

  M. W. Grootes, R. J. Tuffs, C. C. Popescu, B. Pastrav, E. Andrae, M. Gunawardhana, L. S. Kelvin, J. Liske, M. Seibert, E. N. Taylor, [......], S. Maddox, B. F. Madore, M. J. Michałowski, P. Norberg, H. R. Parkinson, M. Prescott, A. S. G. Robotham, D. J. B. Smith, D. Thomas, E. Valiante
  [show abstract] [hide abstract]
  ABSTRACT: We report the discovery of a well-defined correlation between B-band face-on central optical depth due to dust, \tau^f_B, and the stellar mass surface density, \mu_{*}, of nearby (z < 0.13) spiral galaxies: log(\tau^f_B) = 1.12(+-0.11)log(\mu_{*}/M_sol kpc^2)-8.6(+-0.8). This relation was derived from a sample of spiral galaxies taken from the Galaxy and Mass Assembly (GAMA) survey and detected in the FIR/submm in the Herschel-ATLAS survey. Using a quantitative analysis of the NUV attenuation-inclination relation for complete samples of GAMA spirals categorized according to \mu_{*} we demonstrate that this correlation can be used to statistically correct for dust attenuation purely on the basis of optical photometry and S'ersic-profile morphological fits. Considered together with previously established empirical relationships between stellar mass, metallicity and gas mass, the near linearity and high constant of proportionality of the \tau^f_B-\mu_{*} relation disfavors a stellar origin for the bulk of refractory grains in spiral galaxies, instead being consistent with the existence of a ubiquitous and very rapid mechanism for the growth of dust in the ISM. We use the \tau^f_B-\mu_{*} relation in conjunction with the radiation transfer model for spiral galaxies of Popescu & Tuffs (2011) to derive intrinsic scaling relations between specific star formation rate (sSFR), stellar mass, and \mu_{*}, in which the attenuation of the UV light used to measure the SFR is corrected on an object-to-object basis. A marked reduction in scatter in these relations is achieved which is demonstrably due to correction of both the inclination-dependent and face-on components of attenuation. Our results are consistent with a picture of spiral galaxies in which most of the submm emission originates from grains residing in translucent structures, exposed to UV in the diffuse interstellar radiation field.
  The Astrophysical Journal 03/2013; 766:59. · 6.02 Impact Factor
• Article: Towards understanding the relation between the gas and the attenuation in galaxies at kpc scales

  M. Boquien, A. Boselli, V. Buat, M. Baes, G. Bendo, S. Boissier, L. Ciesla, A. Cooray, L. Cortese, S. Eales, J. Koda, V. Lebouteiller, I. de Looze, M. W. L. Smith, L. Spinoglio, C. D. Wilson
  [show abstract] [hide abstract]
  ABSTRACT: [abridged] Aims. The aim of the present paper is to provide new and more detailed relations at the kpc scale between the gas surface density and the face-on optical depth directly calibrated on galaxies, in order to compute the attenuation not only for semi-analytic models but also observationally as new and upcoming radio observatories are able to trace gas ever farther in the Universe. Methods. We have selected a sample of 4 nearby resolved galaxies and a sample of 27 unresolved galaxies from the Herschel Reference Survey and the Very Nearby Galaxies Survey, for which we have a large set of multi-wavelength data from the FUV to the FIR including metallicity gradients for resolved galaxies, along with radio HI and CO observations. For each pixel in resolved galaxies and for each galaxy in the unresolved sample, we compute the face-on optical depth from the attenuation determined with the CIGALE SED fitting code and an assumed geometry. We determine the gas surface density from HI and CO observations with a metallicity-dependent XCO factor. Results. We provide new, simple to use, relations to determine the face-on optical depth from the gas surface density, taking the metallicity into account, which proves to be crucial for a proper estimate. The method used to determine the gas surface density or the face-on optical depth has little impact on the relations except for galaxies that have an inclination over 50d. Finally, we provide detailed instructions on how to compute the attenuation practically from the gas surface density taking into account possible information on the metallicity. Conclusions. Examination of the influence of these new relations on simulated FUV and IR luminosity functions shows a clear impact compared to older oft-used relations, which in turn could affect the conclusions drawn from studies based on large scale cosmological simulations.
  03/2013;
• Article: The Herschel PEP/HerMES Luminosity Function. I: Probing the Evolution of PACS selected Galaxies to z~4

  C. Gruppioni, F. Pozzi, G. Rodighiero, I. Delvecchio, S. Berta, L. Pozzetti, G. Zamorani, P. Andreani, A. Cimatti, O. Ilbert, [......], M. Zemcov, S. Bardelli, M. Carollo, T. Contini, O. Le Fevre, S. Lilly, V. Mainieri, A. Renzini, M. Scodeggio, E. Zucca
  [show abstract] [hide abstract]
  ABSTRACT: We exploit the deep and extended far infrared data sets (at 70, 100 and 160 um) of the Herschel GTO PACS Evolutionary Probe (PEP) Survey, in combination with the HERschel Multi tiered Extragalactic Survey (HerMES) data at 250, 350 and 500 um, to derive the evolution of the restframe 35 um, 60 um, 90 um, and total infrared (IR) luminosity functions (LFs) up to z~4. We detect very strong luminosity evolution for the total IR LF combined with a density evolution. In agreement with previous findings, the IR luminosity density increases steeply to z~1, then flattens between z~1 and z~3 to decrease at z greater than 3. Galaxies with different SEDs, masses and sSFRs evolve in very different ways and this large and deep statistical sample is the first one allowing us to separately study the different evolutionary behaviours of the individual IR populations contributing to the IR luminosity density. Galaxies occupying the well established SFR/stellar mass main sequence (MS) are found to dominate both the total IR LF and luminosity density at all redshifts, with the contribution from off MS sources (0.6 dex above MS) being nearly constant (~20% of the total IR luminosity density) and showing no significant signs of increase with increasing z over the whole 0.8<z<2.2 range. Sources with mass in the 10< log(M/Msun) <11 range are found to dominate the total IR LF, with more massive galaxies prevailing at the bright end of the high-z LF. A two-fold evolutionary scheme for IR galaxies is envisaged: on the one hand, a starburst-dominated phase in which the SMBH grows and is obscured by dust, is followed by an AGN dominated phase, then evolving toward a local elliptical. On the other hand, moderately starforming galaxies containing a low-luminosity AGN have various properties suggesting they are good candidates for systems in a transition phase preceding the formation of steady spiral galaxies.
  02/2013;
• Article: A multiwavelength study of the Magellanic-type galaxy NGC 4449 - I. Modelling the spectral energy distribution, the ionization structure and the star formation history

  O. Ł. Karczewski, M. J. Barlow, M. J. Page, N. P. M. Kuin, I. Ferreras, M. Baes, G. J. Bendo, A. Boselli, A. Cooray, D. Cormier, I. De Looze, M. Galametz, F. Galliano, V. Lebouteiller, S. C. Madden, M. Pohlen, A. Rémy-Ruyer, M. W. L. Smith, L. Spinoglio
  [show abstract] [hide abstract]
  ABSTRACT: [Abridged] We present an integrated photometric spectral energy distribution (SED) of the Magellanic-type galaxy NGC 4449 from the far-ultraviolet (UV) to the submillimetre, including new observations acquired by the Herschel Space Observatory. We include integrated UV photometry from the Swift Ultraviolet and Optical Telescope using a measurement technique which is appropriate for extended sources with coincidence loss. In this paper, we examine the available multiwavelength data to infer a range of ages, metallicities and star formation rates for the underlying stellar populations, as well as the composition and the total mass of dust in NGC 4449. We present an iterative scheme, which allows us to build an in-depth and multicomponent representation of NGC 4449 `bottom-up', taking advantage of the broad capabilities of the photoionization and radiative transfer code MOCASSIN (MOnte CArlo SimulationS of Ionized Nebulae). We fit the observed SED, the global ionization structure and the emission line intensities, and infer a recent SFR of 0.4 Msolar/yr and a total stellar mass of approximately 1e9 Msolar emitting with a bolometric luminosity of 5.7e9 Lsolar. Our fits yield a total dust mass of 2.9e6 Msolar including 2 per cent attributed to polycyclic aromatic hydrocarbons. We deduce a dust to gas mass ratio of 1/190 within the modelled region. While we do not consider possible additional contributions from even colder dust, we note that including the extended HI envelope and the molecular gas is likely to bring the ratio down to as low as ~ 1/800.
  02/2013;
• Article: The Herschel census of infrared SEDs through cosmic time

  Myrto Symeonidis, M. Vaccari, S. Berta, M. J. Page, D. Lutz, V. Arumugam, H. Aussel, J. Bock, A. Boselli, V. Buat, [......], B. Schulz, Douglas Scott, N. Seymour, D. L. Shupe, A. J. Smith, I. Valtchanov, L. Wang, C. K. Xu, M. Zemcov, S. Wuyts
  [show abstract] [hide abstract]
  ABSTRACT: Using Herschel data from the deepest SPIRE and PACS surveys (HerMES and PEP) in COSMOS and GOODS (N+S), we examine the dust properties of IR-luminous (L_IR>10^10 L_sun) galaxies at 0.1<z<2 and determine how these evolve with cosmic time. The unique angle of this work is the rigorous analysis of survey selection effects, making this the first study of the star-formation-dominated, IR-luminous population within a framework almost entirely free of selection biases. We find that IR-luminous galaxies have SEDs with broad far-IR peaks characterised by cool/extended dust emission and average dust temperatures in the 25-45K range. Hot (T>45K) SEDs and cold (T<25K), cirrus-dominated SEDs are rare, with most sources being within the range occupied by warm starbursts such as M82 and cool spirals such as M51. We observe a luminosity-temperature (L-T) relation, where the average dust temperature of log[L_IR/L_sun]=12.5 galaxies is about 10K higher than that of their log[L_IR/L_sun]=10.5 counterparts. However, although the increased dust heating in more luminous systems is the driving factor behind the L-T relation, the increase in dust mass and/or starburst size with luminosity plays a dominant role in shaping it. Our results show that the dust conditions in IR-luminous sources evolve with cosmic time: at high redshift, dust temperatures are on average up to 10K lower than what is measured locally. This is manifested as a flattening of the L-T relation, suggesting that (U)LIRGs in the early Universe are typically characterised by a more extended dust distribution and/or higher dust masses than local equivalent sources. Interestingly, the evolution in dust temperature is luminosity dependent, with the fraction of LIRGs with T<35K showing a 2-fold increase from z~0 to z~2, whereas that of ULIRGs with T<35K shows a 6-fold increase.
  02/2013;
• Article: Herschel-ATLAS: a binary HyLIRG pinpointing a cluster of starbursting proto-ellipticals

  R. J. Ivison, A. M. Swinbank, Ian Smail, A. I. Harris, R. S. Bussmann, A. Cooray, P. Cox, Hai Fu, A. Kovacs, M. Krips, [......], S. Maddox, A. Omont, D. Scott, S. Serjeant, M. W. L. Smith, M. A. Thompson, E. Valiante, I. Valtchanov, J. Vieira, P. van der Werf
  [show abstract] [hide abstract]
  ABSTRACT: Exploiting the relationship between CO luminosity and line width determined for fainter starbursts, we identify and remove lensed sources from the widest Herschel extragalactic imaging survey to yield a sample of intrinsically luminous galaxies. Panchromatic observations of the best candidate HyLIRG then led to the discovery of at least four luminous galaxies across a ~100-kpc region at z=2.41. Our technique separates HyLIRGs from the more numerous, strongly lensed population, and can also pinpoint clusters of starbursting proto-ellipticals. Via sub-arcsecond interferometric imaging we have measured accurate gas and star-formation surface densities. The two brightest galaxies span ~3 kpc FWHM in submm/radio continuum and CO J=4-3, and double that in CO J=1-0. The broad CO line is due partly to the multitude of constituent galaxies and partly to large rotational velocities in two counter-rotating gas disks -- a scenario predicted to lead to the most intense starbursts, which will therefore come in pairs. The disks have M(dyn) of several x 10^11 Msun, and gas fractions of ~40%. Velocity dispersions are modest so the disks are unstable, potentially on scales commensurate with their radii: these galaxies are undergoing extreme bursts of star formation, not confined to their nuclei, at close to the Eddington limit. Their specific star-formation rates place them ~>5x above the main sequence, which supposedly comprises large gas disks like these. Their high star-formation efficiencies are difficult to reconcile with a simple volumetric star-formation law. N-body and dark matter simulations suggest this system is the progenitor of a B(inary)-type ~10^14.6-Msun cluster.
  02/2013;
• Article: GAMA/H-ATLAS: Linking the Properties of Sub-mm Detected and Undetected Early-Type Galaxies: I. z$\le$0.06 Sample

  N. K. Agius, A. E. Sansom, C. C. Popescu, E. Andrae, M. Baes, I. Baldry, N. Bourne, S. Brough, C. J. R. Clark, C. Conselice, [......], S. Maddox, B. Madore, S. Phillipps, A. Robotham, K. Rowlands, M. Seibert, M. W. L. Smith, P. Temi, R. Tuffs, E. Valiante
  [show abstract] [hide abstract]
  ABSTRACT: We present two large, nearby (0.013$\le$z$\le$0.06) samples of Early-Type Galaxies (ETGs): a visually classified sample of 220 ETGs, created using source-matched data from the Galaxy and Mass Assembly (GAMA) database with FIR/sub-mm detections from $Herschel$-ATLAS; and a visually classified sample of 551 ETGs which are undetected with $Herschel$-ATLAS. Active galactic nuclei (AGN) are removed from our samples using optical emission line diagnostics. These samples are scrutinised to determine characteristics of sub-mm detected versus undetected ETGs. We find similarities in the stellar mass distributions of the two ETG samples but testing other properties uncovers significant differences. The sub-mm detected sample is shown to have lower concentration and S\'ersic indices than those in the undetected sample - a result which may be linked to the presence of dust in the former. Optical and UV-optical colours are also shown to be much bluer, indicating that the dust is linked with recent star formation. The intrinsic effective radii are on average 1.5 times larger for the sub-mm detected ETGs. Surface densities and groups data from the GAMA database are examined for the two samples, leading to the conclusion that dusty ETGs inhabit sparser environments than non-dusty ETGs in the nearby universe, although environments of the brightest ETGs are shown to differ the least. Modified Planck functions are fit to the H-ATLAS detected PACS and SPIRE fluxes for ETGs with sub-mm flux densities of at least 3$\sigma$ in the 350$\mu$m SPIRE band, giving a resultant mean cold dust temperature of T$_{d}$=22.1K, with a range of 9-30K. The corresponding mean dust mass is 1.8$\times10^{7}$M$_{\odot}$, with a range of (0.08-35.0)$\times10^{7}$M$_{\odot}$. The dust masses calculated from these fits, normalised by stellar mass, are shown to increase with decreasing stellar mass and bluer colours.
  02/2013;
• Article: H2O emission in high-z ultra-luminous infrared galaxies

  A. Omont, Chentao Yang, P. Cox, R. Neri, A. Beelen, S. Bussmann, R. Gavazzi, P. van der Werf, D. Riechers, D. Downes, [......], R. Hopwood, C. Hoyos, E. Ibar, S. Maddox, M. W. L. Smith, E. Valiante, J. Bock, C. M. Bradford, J. Glenn, K. S. Scott
  [show abstract] [hide abstract]
  ABSTRACT: Using IRAM PdBI we report the detection of H2O in six new lensed ultra-luminous starburst galaxies at high redshift, discovered in the Herschel H-ATLAS survey. The sources are detected either in the 2_{02}-1_{11} or 2_{11}-2_{02} H_2O emission lines with integrated line fluxes ranging from 1.8 to 14 Jy.km/s. The corresponding apparent luminosities are mu x L_H2O ~ 3-12 x 10^8 Lo, where mu is the lensing magnification factor (3 < mu < 12). These results confirm that H2O lines are among the strongest molecular lines in such galaxies, with intensities almost comparable to those of the high-J CO lines, and same profiles and line widths (200-900 km/s) as the latter. With the current sensitivity of PdBI, H2O can therefore easily be detected in high-z lensed galaxies (with F(500um) > 100 mJy) discovered in the Herschel surveys. Correcting the luminosities for lensing amplification, L_H2O is found to have a strong dependence on the IR luminosity, varying as ~L_IR^{1.2}. This relation which needs to be confirmed with better statistics, may indicate a role of radiative (IR) excitation of the H2O lines, and implies that high-z galaxies with L_IR >~ 10^13 Lo tend to be very strong emitters in H2O, that have no equivalent in the local universe.
  01/2013;
• Article: Panchromatic spectral energy distributions of Herschel sources

  S. Berta, D. Lutz, P. Santini, S. Wuyts, D. Rosario, D. Brisbin, A. Cooray, A. Franceschini, C. Gruppioni, E. Hatziminaoglou, [......], L. Pozzetti, F. Pozzi, L. Riguccini, G. Rodighiero, I. Roseboom, Douglas Scott, M. Symeonidis, I. Valtchanov, M. Viero, L. Wang
  [show abstract] [hide abstract]
  ABSTRACT: (abridged) Far-infrared Herschel photometry from the PEP and HerMES programs is combined with ancillary datasets in the GOODS-N, GOODS-S, and COSMOS fields. Based on this rich dataset, we reproduce the restframe UV to FIR ten-colors distribution of galaxies using a superposition of multi-variate Gaussian modes. The median SED of each mode is then fitted with a modified version of the MAGPHYS code that combines stellar light, emission from dust heated by stars and a possible warm dust contribution heated by an AGN. The defined Gaussian grouping is also used to identify rare sources. The zoology of outliers includes Herschel-detected ellipticals, very blue z~1 Ly-break galaxies, quiescent spirals, and torus-dominated AGN with star formation. Out of these groups and outliers, a new template library is assembled, consisting of 32 SEDs describing the intrinsic scatter in the restframe UV-to-submm colors of infrared galaxies. This library is tested against L(IR) estimates with and without Herschel data included, and compared to eight other popular methods often adopted in the literature. When implementing Herschel photometry, these approaches produce L(IR) values consistent with each other within a median absolute deviation of 10-20%, the scatter being dominated more by fine tuning of the codes, rather than by the choice of SED templates. Finally, the library is used to classify 24 micron detected sources in PEP GOODS fields. AGN appear to be distributed in the stellar mass (M*) vs. star formation rate (SFR) space along with all other galaxies, regardless of the amount of infrared luminosity they are powering, with the tendency to lie on the high SFR side of the "main sequence". The incidence of warmer star-forming sources grows for objects with higher specific star formation rates (sSFR), and they tend to populate the "off-sequence" region of the M*-SFR-z space.
  01/2013;
• Article: Mid-J CO Emission in Nearby Seyfert Galaxies

  M. Pereira-Santaella, L. Spinoglio, G. Busquet, J. Glenn, K. Isaak, J. Kamenetzky, N. Rangwala, M. R. P. Schirm, M. Baes, M. J. Barlow, A. Boselli, A. Cooray, D. Cormier
  [show abstract] [hide abstract]
  ABSTRACT: We study for the first time the complete sub-millimeter spectra (450 GHz to 1550 GHz) of a sample of nearby active galaxies observed with the SPIRE Fourier Transform Spectrometer (SPIRE/FTS) onboard Herschel. The CO ladder (from Jup = 4 to 12) is the most prominent spectral feature in this range. These CO lines probe warm molecular gas that can be heated by ultraviolet photons, shocks, or X-rays originated in the active galactic nucleus or in young star-forming regions. In these proceedings we investigate the physical origin of the CO emission using the averaged CO spectral line energy distribution (SLED) of six Seyfert galaxies. We use a radiative transfer model assuming an isothermal homogeneous medium to estimate the molecular gas conditions. We also compare this CO SLED with the predictions of photon and X-ray dominated region (PDR and XDR) models.
  01/2013;
• Article: Inferring the mass of sub-millimetre galaxies by exploiting their gravitational magnification of background galaxies

  H. Hildebrandt, L. van Waerbeke, D. Scott, M. Bethermin, J. Bock, D. Clements, A. Conley, A. Cooray, J. S. Dunlop, S. Eales, [......], S. J. Oliver, M. J. Page, I. Perez-Fournon, A. J. Smith, M. Rowan-Robinson, I. Valtchanov, R. F. J. van der Burg, J. D. Vieira, M. Viero, L. Wang
  [show abstract] [hide abstract]
  ABSTRACT: Dust emission at sub-millimetre wavelengths allows us to trace the early phases of star formation in the Universe. In order to understand the physical processes involved in this mode of star formation, it is essential to gain knowledge about the dark matter structures - most importantly their masses - that sub-millimetre galaxies live in. Here we use the magnification effect of gravitational lensing to determine the average mass and dust content of sub-millimetre galaxies with 250mu flux densities of S_250>15mJy selected using data from the Herschel Multi-tiered Extragalactic Survey. The positions of hundreds of sub-millimetre foreground lenses are cross-correlated with the positions of background Lyman-break galaxies at z~3-5 selected using optical data from the Canada-France Hawaii Telescope Legacy Survey. We detect a cross-correlation signal at the 7-sigma level over a sky area of one square degree, with ~80% of this signal being due to magnification, whereas the remaining ~20% comes from dust extinction. Adopting some simple assumptions for the dark matter and dust profiles and the redshift distribution enables us to estimate the average mass of the halos hosting the sub-millimetre galaxies to be log(M_200/M_sun)=13.17+0.05-0.08(stat.) and their average dust mass fraction (at radii of >10kpc) to be M_dust/M_200~6x10^-5. This supports the picture that sub-millimetre galaxies are dusty, forming stars at a high rate, reside in massive group-sized halos, and are a crucial phase in the assembly and evolution of structure in the Universe.
  12/2012;
• Article: Herschel-ATLAS/GAMA: a difference between star-formation rates in strong-line and weak-line radio galaxies

  M. J. Hardcastle, J. H. Y. Ching, J. S. Virdee, M. J. Jarvis, S. M. Croom, E. M. Sadler, T. Mauch, D. J. B. Smith, J. A. Stevens, M. Baes, [......], S. Eales, R. Hopwood, J. Liske, S. Maddox, M. J. Michalowski, E. E. Rigby, A. S. G. Robotham, O. Steele, D. Thomas, E. Valiante
  [show abstract] [hide abstract]
  ABSTRACT: We have constructed a sample of radio-loud objects with optical spectroscopy from the Galaxy and Mass Assembly (GAMA) project over the Herschel-ATLAS Phase 1 fields. Classifying the radio sources in terms of their optical spectra, we find that strong-emission-line sources (`high-excitation radio galaxies') have, on average, a factor ~4 higher 250-micron Herschel luminosity than weak-line (`low-excitation') radio galaxies and are also more luminous than magnitude-matched radio-quiet galaxies at the same redshift. Using all five H-ATLAS bands, we show that this difference in luminosity between the emission-line classes arises mostly from a difference in the average dust temperature; strong-emission-line sources tend to have comparable dust masses to, but higher dust temperatures than, radio galaxies with weak emission lines. We interpret this as showing that radio galaxies with strong nuclear emission lines are much more likely to be associated with star formation in their host galaxy, although there is certainly not a one-to-one relationship between star formation and strong-line AGN activity. The strong-line sources are estimated to have star-formation rates at least a factor 3-4 higher than those in the weak-line objects. Our conclusion is consistent with earlier work, generally carried out using much smaller samples, and reinforces the general picture of high-excitation radio galaxies as being located in lower-mass, less evolved host galaxies than their low-excitation counterparts.
  11/2012;
• Article: The complex physics of dusty star-forming galaxies at high redshifts as revealed by Herschel and Spitzer

  B. Lo Faro, A. Franceschini, M. Vaccari, L. Silva, G. Rodighiero, S. Berta, J. Bock, D. Burgarella, V. Buat, A. Cava, [......], P. Popesso, F. Pozzi, D. Rigopoulou, M. Rowan-Robinson, I. G. Roseboom, Douglas Scott, A. J. Smith, M. Symeonidis, L. Wang, S. Wuyts
  [show abstract] [hide abstract]
  ABSTRACT: We combine far-infrared photometry from Herschel (PEP/HERMES) with deep mid-infrared spectroscopy from Spitzer to investigate the nature and the mass assembly history of a sample of 31 Luminous and Ultraluminous Infrared Galaxies at z~1 and 2 selected in GOODS-S with 24 $\mu$m fluxes between 0.2 and 0.5 mJy. We model the data with a self-consistent physical model (GRASIL) which includes a state-of-the-art treatment of dust extinction and reprocessing. We find that all of our galaxies appear to require massive populations of old (>1 Gyr) stars and, at the same time, to host a moderate ongoing activity of SF (SFR < 100 M$_{\odot}$/yr). The bulk of the stars appear to have been formed a few Gyr before the observation in essentially all cases. Only five galaxies of the sample require a recent starburst superimposed on a quiescent star formation history (SFH). We also find discrepancies between our results and those based on optical-only SED fitting for the same objects; by fitting their observed Spectral Energy Distributions with our physical model we find higher extinctions (by $\Delta$A_{V} ~ 0.81 and 1.14) and higher stellar masses (by $\Delta$Log(M*) ~ 0.16 and 0.36 dex) for z~1 and z~2 (U)LIRGs, respectively. The stellar mass difference is larger for the most dust obscured objects. We also find lower SFRs than those computed from L_{IR} using the Kennicutt relation due to the significant contribution to the dust heating by intermediate-age stellar populations through 'cirrus' emission (~73% and ~66% of total L_{IR} for z~1 and z~2 (U)LIRGs, respectively).
  11/2012;
• Article: HerMES: Unveiling obscured star formation - the far infrared luminosity function of ultraviolet-selected galaxies at z~1.5

  S. Heinis, V. Buat, M. Béthermin, H. Aussel, J. Bock, A. Boselli, D. Burgarella, A. Conley, A. Cooray, D. Farrah, [......], S. J. Oliver, M. J. Page, G. Rodighiero, Y. Roehlly, B. Schulz, Douglas Scott, A. J. Smith, M. Viero, L. Wang, M. Zemcov
  [show abstract] [hide abstract]
  ABSTRACT: We study the far-infrared (IR) and sub-millimeter properties of a sample of ultraviolet (UV) selected galaxies at z\sim1.5. Using stacking at 250, 350 and 500 um from Herschel Space Observatory SPIRE imaging of the COSMOS field obtained within the HerMES key program, we derive the mean IR luminosity as a function of both UV luminosity and slope of the UV continuum beta. The IR to UV luminosity ratio is roughly constant over most of the UV luminosity range we explore. We also find that the IR to UV luminosity ratio is correlated with beta. We observe a correlation that underestimates the correlation derived from low-redshift starburst galaxies, but is in good agreement with the correlation derived from local normal star-forming galaxies. Using these results we reconstruct the IR luminosity function of our UV-selected sample. This luminosity function recovers the IR luminosity functions measured from IR selected samples at the faintest luminosities (Lir ~ 10^{11} L_sun), but might underestimate them at the bright-end (Lir > 5.10^{11} L_sun). For galaxies with 10^{11}<Lir/L_sun<10^{13}, the IR luminosity function of a UV selection recovers (given the differences in IR-based estimates) 52-65 to 89-112 per cent of the star-formation rate density derived from an IR selection. The cosmic star-formation rate density derived from this IR luminosity function is 61-76 to 100-133 per cent of the density derived from IR selections at the same epoch. Assuming the latest Herschel results and conservative stacking measurements, we use a toy model to fully reproduce the far IR luminosity function from our UV selection at z\sim 1.5. This suggests that a sample around 4 magnitudes deeper (i.e. reaching u \sim 30 mag) and a large dispersion of the IR to UV luminosity ratio are required.
  11/2012;
• Article: A Redshift Survey of Herschel Far-Infrared Selected Starbursts and Implications for Obscured Star Formation

  C. M. Casey, S. Berta, M. Béthermin, J. Bock, C. Bridge, J. Budynkiewicz, D. Burgarella, E. Chapin, S. C. Chapman, D. L. Clements, [......], D. Rigopoulou, L. Riguccini, I. G. Roseboom, D. B. Sanders, D. Scott, N. Seymour, I. Valtchanov, J. D. Vieira, M. Viero, J. Wardlow
  [show abstract] [hide abstract]
  ABSTRACT: We present Keck spectroscopic observations and redshifts for a sample of 767 Herschel-SPIRE selected galaxies (HSGs) at 250, 350, and 500um, taken with the Keck I Low Resolution Imaging Spectrometer (LRIS) and the Keck II DEep Imaging Multi-Object Spectrograph (DEIMOS). The redshift distribution of these SPIRE sources from the Herschel Multitiered Extragalactic Survey (HerMES) peaks at z=0.85, with 731 sources at z<2 and a tail of sources out to z~5. We measure more significant disagreement between photometric and spectroscopic redshifts ( /(1+z)>=0.29) than is seen in non-infrared selected samples, likely due to enhanced star formation rates and dust obscuration in infrared-selected galaxies. We estimate that the vast majority (72-83%) of z<2 Herschel-selected galaxies would drop out of traditional submillimeter surveys at 0.85-1mm. We estimate the luminosity function and implied star-formation rate density contribution of HSGs at z<1.6 and find overall agreement with work based on 24um extrapolations of the LIRG, ULIRG and total infrared contributions. This work significantly increased the number of spectroscopically confirmed infrared-luminous galaxies at z>>0 and demonstrates the growing importance of dusty starbursts for galaxy evolution studies and the build-up of stellar mass throughout cosmic time. [abridged]
  10/2012;