Colin Borys

The SCUBA Half-Degree Extragalactic Survey - II. Submillimetre maps, catalogue and number counts

We present maps, source catalogue and number counts of the largest, most complete and unbiased extragalactic submillimetre survey: the 850-μm SCUBA Half-Degree Extragalactic Survey (SHADES). Using the Submillimetre Common-User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope (JCMT), SHADES mapped two separate regions of sky: the Subaru/XMM–Newton Deep Field (SXDF) and the Lockman Hole East (LH). Encompassing 93 per cent of the overall acquired data (i.e. data taken up to 2004 February 1), these SCUBA maps cover 720 arcmin2 with a rms noise level of about 2 mJy and have uncovered >100 submillimetre galaxies. In order to ensure the utmost robustness of the resulting source catalogue, data reduction was independently carried out by four subgroups within the SHADES team, providing an unprecedented degree of reliability with respect to other SCUBA catalogues available from the literature. Individual source lists from the four groups were combined to produce a robust 120-object SHADES catalogue; an invaluable resource for follow-up campaigns aiming to study the properties of a complete and consistent sample of submillimetre galaxies. For the first time, we present deboosted flux densities for each submillimetre galaxy found in a large survey. Extensive simulations and tests were performed separately by each group in order to confirm the robustness of the source candidates and to evaluate the effects of false detections, completeness and flux density boosting. Corrections for these effects were then applied to the data to derive the submillimetre galaxy source counts. SHADES has a high enough number of detected sources that meaningful differential counts can be estimated, unlike most submillimetre surveys which have to consider integral counts. We present differential and integral source number counts and find that the differential counts are better fit with a broken power law or a Schechter function than with a single power law; the SHADES data alone significantly show that a break is required at several mJy, although the precise position of the break is not well constrained. We also find that a 850-μm survey complete down to 2 mJy would resolve 20–30 per cent of the far-infrared background into point sources.

The Hubble deep field-north SCUBA super-map – IV. Characterizing submillimetre galaxies using deep Spitzer imaging

We present spectral energy distributions (SEDs), Spitzer colours, and infrared (IR) luminosities for 850-μm selected galaxies in the Great Observatories Origins Deep Survey Northern (GOODS-N) field. Using the deep Spitzer Legacy images and new data and reductions of the Very Large Array-Hubble Deep Field (VLA-HDF) radio data, we find statistically secure counterparts for 60 per cent (21/35) of our submillimetre (submm) sample, and identify tentative counterparts for another 12 objects. This is the largest sample of submm galaxies with statistically secure counterparts detected in the radio and with Spitzer. Half of the secure counterparts have spectroscopic redshifts, while the other half have photometric redshifts. We find that in most cases the 850-μm emission is dominated by a single 24-μm source, with a median flux density of 241 μJy, leading to a median 24-to-850-μm flux density ratio of 0.040. A composite rest-frame SED shows that the submm sources peak at longer wavelengths than those of local ultraluminous infrared galaxies (ULIRGs). Using a basic grey-body model, 850-μm selected galaxies appear to be cooler than local ULIRGs of the same luminosity. This demonstrates the strong selection effects, both locally and at high redshift, which may lead to an incomplete census of the ULIRG population. The SEDs of submm galaxies are also different from those of their high-redshift neighbours, the near-IR selected BzK galaxies, whose mid-IR-to-radio SEDs are more like those of local ULIRGs. Using 24-μm, 850-μm and 1.4-GHz observations, we fit templates that span the mid-IR through radio to derive the integrated IR luminosity (LIR) of the submm galaxies and find a median value of LIR(8–1000 μm) = 6.0 × 1012 L. By themselves, 24-μm and radio fluxes are able to predict LIR reasonably well because they are relatively insensitive to temperature. However, the submm flux by itself consistently overpredicts LIR when using spectral templates which obey the local ULIRG temperature–luminosity relation. The shorter Spitzer wavelengths sample the stellar bump at the redshifts of the submm sources, and we find that the Spitzer photometry alone provides a model-independent estimate of the redshift, σ[Δz/(1 + z)] = 0.07. The median redshift for our secure submm counterparts is 2.0. Using X-ray and mid-IR data, only 5 per cent of our secure counterparts (1/21) show strong evidence for an active galactic nucleus dominating the LIR.

The Hubble Deep Field North SCUBA Super-map—I. Submillimetre maps, sources and number counts

We investigate the emission of submillimetre-wave radiation from galaxies in a 165 arcmin2 region surrounding the Hubble Deep Field North. The data were obtained from dedicated observing runs from our group and others using the SCUBA camera on the James Clerk Maxwell Telescope (JCMT), and combined using techniques specifically developed for low signal-to-noise ratio source recovery. The resulting ‘Super-map’ is derived from approximately 60 shifts of JCMT time, taken in a variety of observing modes and chopping strategies, and combined here for the first time. At 850 μm we detect 19 sources at >4σ, including five not previously reported. We also list an additional 15 sources between 3.5 and 4.0σ (where two are expected by chance). The 450-μm map contains five sources at >4σ. We present a new estimate of the 850- and 450-μm source counts. The number of submillimetre galaxies we detect account for approximately 40 per cent of the 850-μm submillimetre background, and we show that mild extrapolations can reproduce it entirely. A clustering analysis fails to detect any significant signal in this sample of SCUBA-detected objects. A companion paper describes the multiwavelength properties of the sources.

In-orbit performance of Herschel-HIFI

Aims. In this paper the calibration and in-orbit performance of the Heterodyne Instrument for the Far-Infrared (HIFI) is described. Methods. The calibration of HIFI is based on a combination of ground and in-flight tests. Dedicated ground tests to determine those instrument parameters that can only be measured accurately using controlled laboratory stimuli were carried out in the instrument level test (ILT) campaign. Special in-flight tests during the commissioning phase (CoP) and performance verification (PV) allowed the determination of the remaining instrument parameters. The various instrument observing modes, as specified in astronomical observation templates (AOTs), were validated in parallel during PV by observing selected celestial sources. Results. The initial calibration and in-orbit performance of HIFI has been established. A first estimate of the calibration budget is given. The overall in-flight instrument performance agrees with the original specification. Issues remain at only a few frequencies.

The relationship between stellar and black hole mass in submillimeter galaxies

We analyze deep X-ray, optical, and mid-infrared Spitzer observations of the CDF-N/GOODS-N region to study a sample of 13 submillimeter-detected galaxies with spectroscopic redshifts (median z = 2.2). These galaxies are among the most active and massive at this epoch. We find evidence for a power-law correlation between the estimated stellar and X-ray luminosity, implying that masses of the black holes may be related to the stellar masses of their host galaxies. We derive the rest-frame UV-near-infrared spectral energy distributions for these galaxies, believed to be young spheroids, and fit them with model templates. Using the rest-frame near-infrared luminosities, which are relatively insensitive to uncertainties in stellar ages and reddening in these young dusty galaxies, and theoretical mass-to-light ratios, we can estimate their stellar masses. Although the submillimeter emission implies that these galaxies are undergoing an epoch of intense star formation, the Spitzer data reveal a massive stellar population already in place. We find that our submillimeter galaxies have a median stellar mass of ~1011 M☉, which is roughly 10 times more massive than typical UV-selected star-forming systems at similar redshifts. These stellar masses are then compared to previously published black hole mass estimates derived from the X-ray luminosities under the assumption of Eddington-limit accretion. We find that the black hole masses for our high-redshift sample are approximately 1-2 orders of magnitude smaller than galaxies of comparable stellar mass in the local universe. Although our estimates of black hole masses will increase if the accretion is sub-Eddington, and our stellar masses will decrease if we assume a much younger stellar population or a different initial mass function, we find that only through a combination of effects is it possible to shift the high-redshift galaxies such that they lie on the local relation. This suggests that the black holes need to grow substantially between z = 2.2 and the present day, with much of the black hole growth occurring after the current obscured, far-infrared luminous phase of activity, which is likely associated with the formation of the spheroid. This interpretation supports a scenario in which submillimeter galaxies pass through a subsequent accretion-dominated phase, where they would appear as optically bright quasars.

The Hubble Deep Field North SCUBA Super‐map – III. Optical and near‐infrared properties of submillimetre galaxies

We present a new submillimetre (submm) super-map in the Hubble Deep Field North (HDF-N) region (Great Observatories Origins Deep Survey North, GOODS-N, field), containing 40 statistically robust sources at 850 μm. This map contains additional data, and several new sources, including one of the brightest blank-sky extragalactic submm sources ever detected. We have used the Advanced Camera for Surveys (ACS) Hubble Space Telescope (HST) images and ground-based near-infrared (IR) observations from the Great Observatories Origins Deep Survey (GOODS), along with deep radio observations, to develop a systematic approach for counterpart identification. With the depth achieved by this survey, optical counterparts have been found for all the radio-detected (RD) submm sources. We have used the colours, morphologies and photometric redshifts of these secure identifications to help identify counterparts to the radio-undetected (RU) sources, finding that certain combinations of optical properties can be used to successfully identify the counterpart to a submm source. 72 per cent of our sources with optical coverage have a unique optical counterpart using our new techniques for counterpart identification and an additional 18 per cent have more than one possibility that meet our criteria in the ACS images. Thus, only ∼10 per cent of our sources lack a plausible optical/near-IR counterpart, meaning that we have the first sample of Submillimetre Common User Bolometer Array (SCUBA) sources that is nearly completely identified in the optical. We have found a much higher extremely red object (ERO) rate than other submm surveys, as a result of the increased depth in the optical images. The median photometric redshift (and quartile range), from optical and near-IR data, is 1.7 (1.3-2.5) for the RD submm sources and rises to 2.3 (1.3-2.7) for the RU subsample. We find interesting correlations between the 850-μm flux and both the ι 775 magnitude and the photometric redshift, from which there appears to be an absence of high-redshift faint counterparts to the lower flux density SCUBA sources. While the quantitative morphologies span a range of values, in general the submm galaxies show larger sizes and a higher degree of asymmetry than other galaxy populations at the same redshifts. In the Appendix, we discuss several improvements in our data analysis procedure, including methods of testing for source reliability.

The SCUBA half-degree extragalactic survey - I. Survey motivation, design and data processing

he Submillimetre Common-User Bolometer Array (SCUBA) Half-Degree Extragalactic Survey (SHADES) is a major new blank-field extragalactic submillimetre (submm) survey currently underway at the James Clerk Maxwell Telescope (JCMT). Ultimately, SHADES aims to cover half a square degree at 450 and 850m to a 4 depth of ~= 8mJy at 850m. Two fields are being observed, the Subaru/XMM-Newton Deep Field (SXDF) (02h18m- 05) and the Lockman Hole East (10h52m+ 57). The survey has three main aims: (i) to investigate the population of high-redshift submm galaxies and the cosmic history of massive dust-enshrouded star formation activity; (ii) to investigate the clustering properties of submm-selected galaxies in order to determine whether these objects could be progenitors of present-day massive ellipticals; and (iii) to investigate the fraction of submm-selected sources that harbour active galactic nuclei. To achieve these aims requires that the submm data be combined with co-spatial information spanning the radio-to-X-ray frequency range. Accordingly, SHADES has been designed to benefit from ultra-deep radio imaging obtained with the Very Large Array (VLA), deep mid-infrared observations from the Spitzer Space Telescope, submm mapping by the Balloon-borne Large Aperture Submillimetre Telescope (BLAST), deep near-infrared imaging with the United Kingdom Infrared Telescope, deep optical imaging with the Subaru Telescope and deep X-ray observations with the XMM-Newton observatory. It is expected that the resulting extensive multiwavelength data set will provide complete photometric redshift information accurate to as well as detailed spectral energy distributions for the vast majority of the submm-selected sources. In this paper, the first of a series on SHADES, we present an overview of the motivation for the survey, describe the SHADES survey strategy, provide a detailed description of the primary data-analysis pipeline and demonstrate the superiority of our adopted matched-filter source-extraction technique over, for example, Emerson-II style methods. We also report on the progress of the survey. As of 2004 February, 720arcmin2 had been mapped with SCUBA (about 40 per cent of the anticipated final total area) to a median 1 depth of 2.2mJy per beam at 850m (25mJy per beam at 450m), and the source-extraction routines give a source density of 650 +/- 50 sources deg-2 > 3 at 850m. Although uncorrected for Eddington bias, this source density is more than sufficient for providing enough sources to answer the science goals of SHADES, once half a square degree is observed. A refined reanalysis of the original 8-mJy survey Lockman hole data was carried out in order to evaluate the new data-reduction pipeline. Of the 17 most secure sources in the original sample, 12 have been reconfirmed, including 10 of the 11 for which radio identifications were previously secured.

DIAGNOSTICS OF AGN-DRIVEN MOLECULAR OUTFLOWS IN ULIRGs FROM HERSCHEL-PACS OBSERVATIONS OF OH AT 119 μm

We report on our observations of the 79 and 119µm doublet transitions of OH for 24 local (z<0.262) ULIRGs observed with Herschel-PACS as part of the Herschel ULIRG Survey (HERUS). Some OH119 profiles display a clear P-Cygni shape and therefore imply outflowing OH gas, other profiles are predominantly in absorption or are completely in emission. We find that the relative strength of the OH emission component decreases as the silicate absorption increases. This locates the OH outflows inside the obscured nuclei. The maximum outflow velocities for our sources range from less than 100 to �2000km s −1 , with 15/24 (10/24) sources showing OH absorption at velocities exceeding 700km s −1 (1000km s −1 ). Three sources show maximum OH outflow velocities exceeding that of Mrk231. Since outflow velocities above 500–700km s −1 are thought to require an active galactic nucleus (AGN) to drive them, about 2/3 of our ULIRG sample may host AGN-driven molecular outflows. This finding is supported by the correlation we find between the maximum OH outflow velocity and the IR-derived bolometric AGN luminosity. No such correlation is found with the IR-derived star formation rate. The highest outflow velocities are found among sources which are still deeply embedded. We speculate that the molecular outflows in these sources may be in an early phase of disrupting the nuclear dust veil before these sources evolve into less obscured AGN. Four of our sources show high-velocity wings in their [C II] fine-structure line profiles implying neutral gas outflow masses of at least 2–4.5×10 8 M⊙. Subject headings: infrared: galaxies – galaxies: ISM – quasars: absorption lines – galaxies: evolution – ISM: jets and outflows

Far-infrared Fine-Structure Line Diagnostics of Ultraluminous Infrared Galaxies

We present Herschel observations of 6 fine-structure lines in 25 ultraluminous infrared galaxies at z < 0.27. The lines, [O III]52 μm, [N III]57 μm, [O I]63 μm, [N II]122 μm, [O I]145 μm, and [C II]158 μm, are mostly single Gaussians with widths <600 km s^(–1) and luminosities of 10^7-10^9 L_☉. There are deficits in the [O I]63/L_(IR), [N II]/L_(IR), [O I]145/L_(IR), and [C II]/L_(IR) ratios compared to lower luminosity systems. The majority of the line deficits are consistent with dustier H II regions, but part of the [C II] deficit may arise from an additional mechanism, plausibly charged dust grains. This is consistent with some of the [C II] originating from photodissociation regions or the interstellar medium (ISM). We derive relations between far-IR line luminosities and both the IR luminosity and star formation rate. We find that [N II] and both [O I] lines are good tracers of the IR luminosity and star formation rate. In contrast, [C II] is a poor tracer of the IR luminosity and star formation rate, and does not improve as a tracer of either quantity if the [C II] deficit is accounted for. The continuum luminosity densities also correlate with the IR luminosity and star formation rate. We derive ranges for the gas density and ultraviolet radiation intensity of 10^1 < n < 10^(2.5) and 10^(2.2) < G_0 < 10^(3.6), respectively. These ranges depend on optical type, the importance of star formation, and merger stage. We do not find relationships between far-IR line properties and several other parameters: active galactic nucleus (AGN) activity, merger stage, mid-IR excitation, and SMBH mass. We conclude that these far-IR lines arise from gas heated by starlight, and that they are not strongly influenced by AGN activity.

The properties of Microjansky radio sources in the Hubble Deep Field-North, SSA 13, and SSA 22 fields

We present multiwavelength observations for a large sample of microjansky radio sources detected in ultradeep 1.4GHz maps centered on the Hubble Deep Field-North (HDF-N) and the Hawaii Survey Fields SSA13 and SSA22. Our spectroscopic redshifts for 169 radio sources reveal a flat median redshift distribution, and these sources are hosted by similarly luminous optical Lgalaxies, regardless of redshift. We suggest that the absence of low optical luminosity galaxies at low redshifts, where there are no selection effects, is due to small galaxies not being efficientat retaining the cosmic rays necessary to host microjansky radio sources. This is a serious concern for radio estimates of the local star formation rate density, as a substantial fraction of the ultraviolet luminosity density is generated by sub-Lgalaxies at low redshifts. From our submillimeter measurements for 278 radio sources, we find error-weighted mean 850µm fluxes of 1.72±0.09mJy for the total sample, 2.37±0.13mJy for the optically-faint (I > 23.5) subsample, and 1.04±0.13mJy for the optically-bright (I 3�) detect in the submillimeter 50 of the radio sources, 38 with I > 23.5. Spectroscopic redshifts for three of the I 23.5. We also find that 66±7% of the S850µm> 5mJy (> 4�) sources are radio-identified. We use our spectroscopic sample to determine the evolution with redshift of the radio power, and hence the far-infrared (FIR) luminosity (through the local FIR-radio correlation). We find that millimetric redshift estimates at low redshifts are best made with a FIR template intermediate between a Milky Way type galaxy and a starburst galaxy, and at high redshifts with an Arp 220 template. Subject headings: cosmology: observations — galaxies: evolution — galaxies: formation — galaxies: starburst