ALBERT

Description: The Herschel Extragalactic Legacy Project (HELP) brings together a vast range of data from many astronomical observatories. Its main focus is on the Herschel data, which maps dust-obscured star formation over 1300 deg 2 . With this unprecedented combination of data sets, it is possible to investigate how the star formation versus stellar mass relation (main sequence) of star-forming galaxies depends on environment. In this pilot study, we explore this question within 0.1 〈 z 〈 3.2 using data in the COSMOS field. We estimate the local environment from a smoothed galaxy density field using the full photometric redshift probability distribution. We estimate star formation rates by stacking the SPIRE data from the Herschel Multi-tiered Extragalactic Survey. Our analysis rules out the hypothesis that the main sequence for star-forming systems is independent of environment at 1.5 〈 z 〈 2, while a simple model in which the mean specific star formation rate declines with increasing environmental density gives a better description. However, we cannot exclude a simple hypothesis in which the main sequence for star-forming systems is independent of environment at z 〈 1.5 and z 〉 2. We also estimate the evolution of the star formation rate density in the COSMOS field, and our results are consistent with previous measurements at z 〈 1.5 and z 〉 2 but we find a $1.4^{+0.3}_{-0.2}$ times higher peak value of the star formation rate density at z ~ 1.9.

Description: We present the first cross-correlation measurement between Sloan Digital Sky Survey type 1 quasars and the cosmic infrared background (CIB) measured by Herschel . The quasars cover the redshift range 0.15 〈 z 〈 3.5 where most of the CIB originates. We detect the sub-millimetre emission of the quasars, which dominates on small scales, and correlated emission from dusty star-forming galaxies (DSFGs) dominant on larger scales. The mean flux of the Data Release 7 (DR7) quasars (median redshift 〈 z 〉 = 1.4) is 11.1, 7.1 and 3.6 mJy at 250, 350 and 500 μm, respectively, while the mean flux of the DR9 quasars (〈 z 〉 = 2.5) is 5.7, 5.0 and 1.8 mJy at 250, 350 and 500 μm, respectively. Assuming a modified blackbody spectral energy distribution with a power law in the mid-infrared, we infer that the mean infrared luminosity of the DR7 and DR9 quasars is 10 12.4 and 10 12.8 L , respectively. The correlated emission arises from DSFGs in the same halo as the quasar (the one-halo term) and DSFGs in separate haloes correlated with the quasar-hosting halo (the two-halo term). Using a simple halo model, we find that most quasars are hosted by central galaxies. The host halo mass scale of the DR7 central and satellite quasars is 10 12.4 ± 0.9 and 10 13.6 ± 0.4 M , respectively. The host halo mass scale of the DR9 central and satellite quasars is 10 12.3 ± 0.6 and 10 12.8 ± 0.4 M , respectively. Thus, the halo environment of the central quasars is similar to that of the most actively star-forming galaxies, which supports the view that dusty starburst and quasar activity are evolutionarily linked.

Description: We study the 850-μm emission in X-ray-selected active galactic nuclei (AGN) in the ~2 deg 2 COSMOS field using new data from the SCUBA-2 Cosmology Legacy Survey. We find 19 850-μm bright X-ray AGN in a ‘high-sensitivity’ region covering 0.89 deg 2 with flux densities of S 850 = 4–10 mJy. The 19 AGN span the full range in redshift and hard X-ray luminosity covered by the sample – 0.7   z   3.5 and 43.2  log 10 ( L X )  45. We report a highly significant stacked 850-μm detection of a hard X-ray flux-limited population of 699 z  〉 1 X-ray AGN – S 850  = 0.71 ± 0.08 mJy. We explore trends in the stacked 850-μm flux densities with redshift, finding no evolution in the average cold dust emission over the redshift range probed. For type 1 AGN, there is no significant correlation between the stacked 850-μm flux and hard X-ray luminosity. However, in type 2 AGN the stacked submillimeter flux is a factor of 2 higher at high luminosities. When averaging over all X-ray luminosities, no significant differences are found in the stacked submillimeter fluxes of type 1 and type 2 AGN as well as AGN separated on the basis of X-ray hardness ratios and optical-to-infrared colours. However, at log 10 ( L 2 – 10 /erg s –1 ) 〉 44.4, dependences in average submillimeter flux on the optical-to-infrared colours become more pronounced. We argue that these high-luminosity AGN represent a transition from a secular to a merger-driven evolutionary phase where the star formation rates and accretion luminosities are more tightly coupled. Stacked AGN 850-μm fluxes are compared to the stacked fluxes of a mass-matched sample of K -band-selected non-AGN galaxies. We find that at 10.5 〈log 10 ( M * /M )〈11.5, the non-AGN 850-μm fluxes are 1.5–2 times higher than in type 2 AGN of equivalent mass. We suggest these differences are due to the presence of massive dusty, red starburst galaxies in the K -band-selected non-AGN sample, which are not present in optically selected catalogues covering a smaller area.

Description: We investigate the multiwavelength properties of a sample of 450-μm-selected sources from the SCUBA-2 Cosmology Legacy Survey. A total of 69 sources were identified above 4 in deep SCUBA-2 450-μm observations overlapping the UDS and COSMOS fields and covering 210 arcmin 2 to a typical depth of 450  = 1.5 mJy. Reliable cross-identifications are found for 58 sources (84 per cent) in Spitzer and Hubble Space Telescope WFC3/IR data. The photometric redshift distribution (d N /d z ) of 450-μm-selected sources is presented, showing a broad peak in the redshift range 1 〈  z  〈 3 and a median of z  = 1.4. Combining the SCUBA-2 photometry with Herschel SPIRE data from HerMES, the submm spectral energy distribution (SED) is examined via the use of modified blackbody fits, yielding aggregate values for the IR luminosity, dust temperature and emissivity of 〈 L IR 〉 = 10 12 ± 0.8 L , 〈 T D 〉 = 42 ± 11 K and 〈β D 〉 = 1.6 ± 0.5, respectively. The relationship between these SED parameters and the physical properties of galaxies is investigated, revealing correlations between T D and L IR and between β D and both stellar mass and effective radius. The connection between the star formation rate (SFR) and stellar mass is explored, with 24 per cent of 450-μm sources found to be ‘starbursts’, i.e. displaying anomalously high specific SFRs. However, both the number density and observed properties of these ‘starburst’ galaxies are found to be consistent with the population of normal star-forming galaxies.

Description: The dynamic range of photon counting micro-channel-plate (MCP) intensified charged-coupled device (CCD) instruments such as the Swift Ultraviolet/Optical Telescope (UVOT) and the XMM–Newton Optical Monitor (XMM-OM) is limited at the bright end by coincidence loss, the superposition of multiple photons in the individual frames recorded by the CCD. Photons which arrive during the brief period in which the image frame is transferred for read out of the CCD are displaced in the transfer direction in the recorded images. For sufficiently bright sources, these displaced counts form read-out streaks. Using UVOT observations of Tycho-2 stars, we investigate the use of these read-out streaks to obtain photometry for sources which are too bright (and hence have too much coincidence loss) for normal aperture photometry to be reliable. For read-out-streak photometry, the bright-source limiting factor is coincidence loss within the MCPs rather than the CCD. We find that photometric measurements can be obtained for stars up to 2.4 mag brighter than the usual full-frame coincidence-loss limit by using the read-out streaks. The resulting bright-limit Vega magnitudes in the UVOT passbands are UVW2 = 8.80, UVM2 = 8.27, UVW1 = 8.86, u  = 9.76, b  = 10.53, v  = 9.31 and White = 11.71; these limits are independent of the windowing mode of the camera. We find that a photometric precision of 0.1 mag can be achieved through read-out streak measurements. A suitable method for the measurement of read-out streaks is described and all necessary calibration factors are given.

Description: The extragalactic background light at far-infrared wavelengths comes from optically faint, dusty, star-forming galaxies in the Universe with star formation rates of a few hundred solar masses per year. These faint, submillimetre galaxies are challenging to study individually because of the relatively poor spatial resolution of far-infrared telescopes. Instead, their average properties can be studied using statistics such as the angular power spectrum of the background intensity variations. A previous attempt at measuring this power spectrum resulted in the suggestion that the clustering amplitude is below the level computed with a simple ansatz based on a halo model. Here we report excess clustering over the linear prediction at arcminute angular scales in the power spectrum of brightness fluctuations at 250, 350 and 500 mum. From this excess, we find that submillimetre galaxies are located in dark matter haloes with a minimum mass, M(min), such that log(10)[M(min)/M(middle dot in circle)] = 11.5(+0.7)(-0.2) at 350 mum, where M(middle dot in circle) is the solar mass. This minimum dark matter halo mass corresponds to the most efficient mass scale for star formation in the Universe, and is lower than that predicted by semi-analytical models for galaxy formation.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Amblard, Alexandre -- Cooray, Asantha -- Serra, Paolo -- Altieri, B -- Arumugam, V -- Aussel, H -- Blain, A -- Bock, J -- Boselli, A -- Buat, V -- Castro-Rodriguez, N -- Cava, A -- Chanial, P -- Chapin, E -- Clements, D L -- Conley, A -- Conversi, L -- Dowell, C D -- Dwek, E -- Eales, S -- Elbaz, D -- Farrah, D -- Franceschini, A -- Gear, W -- Glenn, J -- Griffin, M -- Halpern, M -- Hatziminaoglou, E -- Ibar, E -- Isaak, K -- Ivison, R J -- Khostovan, A A -- Lagache, G -- Levenson, L -- Lu, N -- Madden, S -- Maffei, B -- Mainetti, G -- Marchetti, L -- Marsden, G -- Mitchell-Wynne, K -- Nguyen, H T -- O'Halloran, B -- Oliver, S J -- Omont, A -- Page, M J -- Panuzzo, P -- Papageorgiou, A -- Pearson, C P -- Perez-Fournon, I -- Pohlen, M -- Rangwala, N -- Roseboom, I G -- Rowan-Robinson, M -- Portal, M Sanchez -- Schulz, B -- Scott, Douglas -- Seymour, N -- Shupe, D L -- Smith, A J -- Stevens, J A -- Symeonidis, M -- Trichas, M -- Tugwell, K -- Vaccari, M -- Valiante, E -- Valtchanov, I -- Vieira, J D -- Vigroux, L -- Wang, L -- Ward, R -- Wright, G -- Xu, C K -- Zemcov, M -- England -- Nature. 2011 Feb 24;470(7335):510-2. doi: 10.1038/nature09771. Epub 2011 Feb 16.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Physics & Astronomy, University of California, Irvine, California 92697, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21326201" target="_blank"〉PubMed〈/a〉

Description: The old, red stars that constitute the bulges of galaxies, and the massive black holes at their centres, are the relics of a period in cosmic history when galaxies formed stars at remarkable rates and active galactic nuclei (AGN) shone brightly as a result of accretion onto black holes. It is widely suspected, but unproved, that the tight correlation between the mass of the black hole and the mass of the stellar bulge results from the AGN quenching the surrounding star formation as it approaches its peak luminosity. X-rays trace emission from AGN unambiguously, whereas powerful star-forming galaxies are usually dust-obscured and are brightest at infrared and submillimetre wavelengths. Here we report submillimetre and X-ray observations that show that rapid star formation was common in the host galaxies of AGN when the Universe was 2-6 billion years old, but that the most vigorous star formation is not observed around black holes above an X-ray luminosity of 10(44) ergs per second. This suppression of star formation in the host galaxy of a powerful AGN is a key prediction of models in which the AGN drives an outflow, expelling the interstellar medium of its host and transforming the galaxy's properties in a brief period of cosmic time.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Page, M J -- Symeonidis, M -- Vieira, J D -- Altieri, B -- Amblard, A -- Arumugam, V -- Aussel, H -- Babbedge, T -- Blain, A -- Bock, J -- Boselli, A -- Buat, V -- Castro-Rodriguez, N -- Cava, A -- Chanial, P -- Clements, D L -- Conley, A -- Conversi, L -- Cooray, A -- Dowell, C D -- Dubois, E N -- Dunlop, J S -- Dwek, E -- Dye, S -- Eales, S -- Elbaz, D -- Farrah, D -- Fox, M -- Franceschini, A -- Gear, W -- Glenn, J -- Griffin, M -- Halpern, M -- Hatziminaoglou, E -- Ibar, E -- Isaak, K -- Ivison, R J -- Lagache, G -- Levenson, L -- Lu, N -- Madden, S -- Maffei, B -- Mainetti, G -- Marchetti, L -- Nguyen, H T -- O'Halloran, B -- Oliver, S J -- Omont, A -- Panuzzo, P -- Papageorgiou, A -- Pearson, C P -- Perez-Fournon, I -- Pohlen, M -- Rawlings, J I -- Rigopoulou, D -- Riguccini, L -- Rizzo, D -- Rodighiero, G -- Roseboom, I G -- Rowan-Robinson, M -- Sanchez Portal, M -- Schulz, B -- Scott, D -- Seymour, N -- Shupe, D L -- Smith, A J -- Stevens, J A -- Trichas, M -- Tugwell, K E -- Vaccari, M -- Valtchanov, I -- Viero, M -- Vigroux, L -- Wang, L -- Ward, R -- Wright, G -- Xu, C K -- Zemcov, M -- England -- Nature. 2012 May 9;485(7397):213-6. doi: 10.1038/nature11096.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK. mjp@mssl.ucl.ac.uk〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22575961" target="_blank"〉PubMed〈/a〉

Description: We separate the extragalactic radio source population above ~50 μJy into active galactic nuclei (AGN) and star-forming sources. The primary method of our approach is to fit the infrared spectral energy distributions (SEDs), constructed using Spitzer /IRAC (Infrared Array Camera) and Multiband Imaging Photometer for Spitzer (MIPS) and Herschel /SPIRE photometry, of 380 radio sources in the Extended Chandra Deep Field -South. From the fitted SEDs, we determine the relative AGN and star-forming contributions to their infrared emission. With the inclusion of other AGN diagnostics such as X-ray luminosity, Spitzer /IRAC colours, radio spectral index and the ratio of star-forming total infrared flux to k -corrected 1.4 GHz flux density, q IR , we determine whether the radio emission in these sources is powered by star formation or by an AGN. The majority of these radio sources (60 per cent) show the signature of an AGN at some wavelength. Of the sources with AGN signatures, 58 per cent are hybrid systems for which the radio emission is being powered by star formation. This implies that radio sources which have likely been selected on their star formation have a high AGN fraction. Below a 1.4 GHz flux density of 1 mJy, along with finding a strong contribution to the source counts from pure star-forming sources, we find that hybrid sources constitute 20–65 per cent of the sources. This result suggests that hybrid sources have a significant contribution, along with sources that do not host a detectable AGN, to the observed flattening of the source counts at ~1 mJy for the extragalactic radio source population.

Description: We used wide-area surveys over 39 deg 2 by the HerMES ( Herschel Multi-tiered Extragalactic Survey) collaboration, performed with the Herschel Observatory SPIRE multiwavelength camera, to estimate the low-redshift, 0.02 〈  z  〈 0.5, monochromatic luminosity functions (LFs) of galaxies at 250, 350 and 500 μm. Within this redshift interval, we detected 7087 sources in five independent sky areas, ~40 per cent of which have spectroscopic redshifts, while for the remaining objects photometric redshifts were used. The SPIRE LFs in different fields did not show any field-to-field variations beyond the small differences to be expected from cosmic variance. SPIRE flux densities were also combined with Spitzer photometry and multiwavelength archival data to perform a complete spectral energy distribution fitting analysis of SPIRE detected sources to calculate precise k -corrections, as well as the bolometric infrared (IR; 8–1000 μm) LFs and their low- z evolution from a combination of statistical estimators. Integration of the latter prompted us to also compute the local luminosity density and the comoving star formation rate density (SFRD) for our sources, and to compare them with theoretical predictions of galaxy formation models. The LFs show significant and rapid luminosity evolution already at low redshifts, 0.02 〈  z  〈 0.2, with L $_{\text{IR}}^{\ast } \propto (1+z)^{6.0\pm 0.4}$ and $\Phi _{\text{IR}}^{\ast } \propto (1+z)^{-2.1\pm 0.4}$ , L $_{250}^{\ast } \propto (1+z)^{5.3\pm 0.2}$ and $\Phi _{250}^{\ast } \propto (1+z)^{-0.6\pm 0.4}$ estimated using the IR bolometric and the 250 μm LFs, respectively. Converting our IR LD estimate into an SFRD assuming a standard Salpeter initial mass function and including the unobscured contribution based on the UV dust-uncorrected emission from local galaxies, we estimate an SFRD scaling of SFRD 0  + 0.08 z , where SFRD 0 ~= (1.9 ± 0.03)  x  10 –2 [M Mpc –3 ] is our total SFRD estimate at z  ~ 0.02.

Description: The intrinsic thermal (free–free) and non-thermal (synchrotron) emission components that comprise the radio continuum of galaxies represent unique, dust-free measures of star formation rates (SFR). Such high SFR galaxies will dominate the deepest current and future radio surveys. We disentangle the thermal and non-thermal emission components of the radio continuum of six ultraluminous infrared galaxies ( L FIR 〉 10 12.5  L ) at redshifts of 0.2 ≤ z ≤ 0.5 and 22 IR selected galaxies. Radio data over a wide frequency range (0.8 〈 〈 10 GHz) are fitted with a star-forming galaxy model comprising of thermal and non-thermal components. The luminosities of both radio continuum components are strongly correlated to the 60 μm luminosity across many orders of magnitude (consistent with the far-IR to radio correlation). We demonstrate that the spectral index of the radio continuum spectral energy distribution is a useful proxy for the thermal fraction. We also find that there is an increase in mean and scatter of the thermal fraction with FIR to radio luminosity ratio which could be influenced by different time-scales of the thermal and non-thermal emission mechanisms.