AzTEC Millimetre Survey of the COSMOS field – II. Source count overdensity and correlations with large-scale structure

Austermann, J. E.,Aretxaga, I.,Hughes, D. H.,Kang, Y.,Kim, S.,Lowenthal, J. D.,Perera, T. A.,Sanders, D. B.,Scott, K. S.,Scoville, N.,Wilson, G. W.,Yun, M. S. Blackwell Publishing Ltd 2009 Monthly notices of the Royal Astronomical Society Vol.393 No.4

<P>ABSTRACT</P><P>We report an overdensity of bright submillimetre galaxies (SMGs) in the 0.15 deg<SUP>2</SUP> AzTEC/COSMOS survey and a spatial correlation between the SMGs and the optical-IR galaxy density at <I>z</I>≲ 1.1. This portion of the COSMOS field shows a ∼3σ overdensity of robust SMG detections when compared to a background, or ‘blank-field’, population model that is consistent with SMG surveys of fields with no extragalactic bias. The SMG overdensity is most significant in the number of very bright detections (14 sources with measured fluxes <I>S</I><SUB>1.1 mm</SUB> > 6 mJy), which is entirely incompatible with sample variance within our adopted blank-field number densities and infers an overdensity significance of ≫ 4σ. We find that the overdensity and spatial correlation to optical-IR galaxy density are most consistent with lensing of a background SMG population by foreground mass structures along the line of sight, rather than physical association of the SMGs with the <I>z</I>≲ 1.1 galaxies/clusters. The SMG positions are only weakly correlated with weak-lensing maps, suggesting that the dominant sources of correlation are individual galaxies and the more tenuous structures in the survey region, and not the massive and compact clusters. These results highlight the important roles cosmic variance and large-scale structure can play in the study of SMGs.</P>

AzTEC half square degree survey of the SHADES fields – I. Maps, catalogues and source counts

Austermann, J. E.,Dunlop, J. S.,Perera, T. A.,Scott, K. S.,Wilson, G. W.,Aretxaga, I.,Hughes, D. H.,Almaini, O.,Chapin, E. L.,Chapman, S. C.,Cirasuolo, M.,Clements, D. L.,Coppin, K. E. K.,Dunne, L.,Dy Blackwell Publishing Ltd 2010 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.401 No.1

<P>ABSTRACT</P><P>We present the first results from the largest deep extragalactic mm-wavelength survey undertaken to date. These results are derived from maps covering over 0.7 deg<SUP>2</SUP>, made at λ= 1.1 mm, using the AzTEC continuum camera mounted on the James Clerk Maxwell Telescope. The maps were made in the two fields originally targeted at λ= 850 μm with the Submillimetre Common-User Bolometer Array (SCUBA) in the SCUBA Half-Degree Extragalactic Survey (SHADES) project, namely the Lockman Hole East (mapped to a depth of 0.9–1.3 mJy rms) and the Subaru/<I>XMM–Newton</I> Deep Field (mapped to a depth of 1.0–1.7 mJy rms). The wealth of existing and forthcoming deep multifrequency data in these two fields will allow the bright mm source population revealed by these new wide-area 1.1 mm images to be explored in detail in subsequent papers. Here, we present the maps themselves, a catalogue of 114 high-significance submillimetre galaxy detections, and a thorough statistical analysis leading to the most robust determination to date of the 1.1 mm source number counts. These new maps, covering an area nearly three times greater than the SCUBA SHADES maps, currently provide the largest sample of cosmological volumes of the high-redshift Universe in the mm or sub-mm. Through careful comparison, we find that both the Cosmic Evolution Survey (COSMOS) and the Great Observatories Origins Deep Survey (GOODS) North fields, also imaged with AzTEC, contain an excess of mm sources over the new 1.1 mm source-count baseline established here. In particular, our new AzTEC/SHADES results indicate that very luminous high-redshift dust enshrouded starbursts (<I>S</I><SUB>1.1mm</SUB> > 3 mJy) are 25–50 per cent less common than would have been inferred from these smaller surveys, thus highlighting the potential roles of cosmic variance and clustering in such measurements. We compare number count predictions from recent models of the evolving mm/sub-mm source population to these sub-mm bright galaxy surveys, which provide important constraints for the ongoing refinement of semi-analytic and hydrodynamical models of galaxy formation, and find that all available models overpredict the number of bright submillimetre galaxies found in this survey.</P>

AzTEC millimetre survey of the COSMOS field – I. Data reduction and source catalogue

Scott, K. S.,Austermann, J. E.,Perera, T. A.,Wilson, G. W.,Aretxaga, I.,Bock, J. J.,Hughes, D. H.,Kang, Y.,Kim, S.,Mauskopf, P. D.,Sanders, D. B.,Scoville, N.,Yun, M. S. Blackwell Publishing Ltd 2008 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.385 No.4

<P>ABSTRACT</P><P>We present a 1.1 mm wavelength imaging survey covering 0.3 deg<SUP>2</SUP> in the COSMOS field. These data, obtained with the AzTEC continuum camera on the James Clerk Maxwell Telescope, were centred on a prominent large-scale structure overdensity which includes a rich X-ray cluster at <I>z</I>≈ 0.73. A total of 50 mm-galaxy candidates, with a significance ranging from 3.5 to 8.5σ, are extracted from the central 0.15 deg<SUP>2</SUP> area which has a uniform sensitivity of ∼1.3 mJy beam<SUP>−1</SUP>. 16 sources are detected with S/N ≥ 4.5, where the expected false-detection rate is zero, of which a surprisingly large number (9) have intrinsic (deboosted) fluxes ≥5 mJy at 1.1 mm. Assuming the emission is dominated by radiation from dust, heated by a massive population of young, optically obscured stars, then these bright AzTEC sources have far-infrared luminosities >6 × 10<SUP>12</SUP> L<SUB>⊙</SUB> and star formation rates >1100 M<SUB>⊙</SUB> yr<SUP>−1</SUP>. Two of these nine bright AzTEC sources are found towards the extreme peripheral region of the X-ray cluster, whilst the remainder are distributed across the larger scale overdensity. We describe the AzTEC data reduction pipeline, the source-extraction algorithm, and the characterization of the source catalogue, including the completeness, flux deboosting correction, false-detection rate and the source positional uncertainty, through an extensive set of Monte Carlo simulations. We conclude with a preliminary comparison, via a stacked analysis, of the overlapping MIPS 24-μm data and radio data with this AzTEC map of the COSMOS field.</P>

The source counts of submillimetre galaxies detected at λ= 1.1 mm

Scott, K. S.,Wilson, G. W.,Aretxaga, I.,Austermann, J. E.,Chapin, E. L.,Dunlop, J. S.,Ezawa, H.,Halpern, M.,Hatsukade, B.,Hughes, D. H.,Kawabe, R.,Kim, S.,Kohno, K.,Lowenthal, J. D.,Montañ,a, A. Blackwell Publishing Ltd 2012 Monthly notices of the Royal Astronomical Society Vol.423 No.1

<P><B>ABSTRACT</B></P><P>The source counts of galaxies discovered at submillimetre and millimetre wavelengths provide important information on the evolution of infrared‐bright galaxies. We combine the data from six blank‐field surveys carried out at 1.1 mm with AzTEC, totalling 1.6 deg<SUP>2</SUP> in area with root‐mean‐square depths ranging from 0.4 to 1.7 mJy, and derive the strongest constraints to date on the 1.1 mm source counts at flux densities <I>S</I><SUB>1100</SUB>= 1–12 mJy. Using additional data from the AzTEC Cluster Environment Survey to extend the counts to <I>S</I><SUB>1100</SUB>∼ 20 mJy, we see tentative evidence for an enhancement relative to the exponential drop in the counts at <I>S</I><SUB>1100</SUB>∼ 13 mJy and a smooth connection to the bright source counts at >20 mJy measured by the South Pole Telescope; this excess may be due to strong‐lensing effects. We compare these counts to predictions from several semi‐analytical and phenomenological models and find that for most the agreement is quite good at flux densities ≳ 4 mJy; however, we find significant discrepancies (≳ 3σ) between the models and the observed 1.1‐mm counts at lower flux densities, and none of them is consistent with the observed turnover in the Euclidean‐normalized counts at <I>S</I><SUB>1100</SUB>≲ 2 mJy. Our new results therefore may require modifications to existing evolutionary models for low‐luminosity galaxies. Alternatively, the discrepancy between the measured counts at the faint end and predictions from phenomenological models could arise from limited knowledge of the spectral energy distributions of faint galaxies in the local Universe.</P>

An AzTEC 1.1-mm survey for ULIRGs in the field of the Galaxy Cluster MS 0451.6−0305

Wardlow, J. L.,Smail, Ian,Wilson, G. W.,Yun, M. S.,Coppin, K. E. K.,Cybulski, R.,Geach, J. E.,Ivison, R. J.,Aretxaga, I.,Austermann, J. E.,Edge, A. C.,Fazio, G. G.,Huang, J.,Hughes, D. H.,Kodama, T.,K Blackwell Publishing Ltd 2010 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.401 No.4

<P>ABSTRACT</P><P>We have undertaken a deep (σ∼ 1.1 mJy) 1.1-mm survey of the <I>z</I>= 0.54 cluster MS 0451.6−0305 using the AzTEC camera on the James Clerk Maxwell Telescope. We detect 36 sources with signal-to-noise ratio (S/N) ≥ 3.5 in the central 0.10 deg<SUP>2</SUP> and present the AzTEC map, catalogue and number counts. We identify counterparts to 18 sources (50 per cent) using radio, mid-infrared, <I>Spitzer</I> InfraRed Array Camera (IRAC) and Submillimetre Array data. Optical, near- and mid-infrared spectral energy distributions are compiled for the 14 of these galaxies with detectable counterparts, which are expected to contain all likely cluster members. We then use photometric redshifts and colour selection to separate background galaxies from potential cluster members and test the reliability of this technique using archival observations of submillimetre galaxies. We find two potential MS 0451−03 members, which, if they are both cluster galaxies, have a total star formation rate (SFR) of ∼100 M<SUB>⊙</SUB> yr<SUP>−1</SUP>– a significant fraction of the combined SFR of all the other galaxies in MS 0451−03. We also examine the stacked rest-frame mid-infrared, millimetre and radio emission of cluster members below our AzTEC detection limit, and find that the SFRs of mid-IR-selected galaxies in the cluster and redshift-matched field populations are comparable. In contrast, the average SFR of the morphologically classified late-type cluster population is nearly three times less than the corresponding redshift-matched field galaxies. This suggests that these galaxies may be in the process of being transformed on the red sequence by the cluster environment. Our survey demonstrates that although the environment of MS 0451−03 appears to suppress star formation in late-type galaxies, it can support active, dust-obscured mid-IR galaxies and potentially millimetre-detected LIRGs.</P>

AzTEC 1.1 mm OBSERVATIONS OF THE MBM12 MOLECULAR CLOUD

Kim, M. J.,Kim, S.,Youn, S.,Yun, M. S.,Wilson, G. W.,Aretxaga, I.,Williams, J. P.,Hughes, D. H.,Humphrey, A.,Austermann, J. E.,Perera, T. A.,Mauskopf, P. D.,Magnani, L.,Kang, Y.-W. IOP Publishing 2012 The Astrophysical journal Vol.746 No.1

<P>We present 1.1 mm observations of the dust continuum emission from the MBM12 high-latitude molecular cloud observed with the Astronomical Thermal Emission Camera (AzTEC) mounted on the James Clerk Maxwell Telescope on Mauna Kea, Hawaii. We surveyed 6.34 deg(2) centered on MBM12, making this the largest area that has ever been surveyed in this region with submillimeter and millimeter telescopes. Eight secure individual sources were detected with a signal-to-noise ratio of over 4.4. These eight AzTEC sources can be considered to be real astronomical objects compared to the other candidates based on calculations of the false detection rate. The distribution of the detected 1.1 mm sources or compact 1.1 mm peaks is spatially anti-correlated with that of the 100 mu m emission and the (CO)-C-12 emission. We detected the 1.1 mm dust continuum emitting sources associated with two classical T Tauri stars, LkH alpha 262 and LkH alpha 264. Observations of spectral energy distributions (SEDs) indicate that LkH alpha 262 is likely to be Class II (pre-main-sequence star), but there are also indications that it could be a late Class I (protostar). A flared disk and a bipolar cavity in the models of Class I sources lead to more complicated SEDs. From the present AzTEC observations of the MBM12 region, it appears that other sources detected with AzTEC are likely to be extragalactic and located behind MBM12. Some of these have radio counterparts and their star formation rates are derived from a fit of the SEDs to the photometric evolution of galaxies in which the effects of a dusty interstellar medium have been included.</P>