M. S. Yun

AzTEC/ASTE 1.1-mm survey of the AKARI Deep Field South: source catalogue and number counts

We present the first results of a deep 1.1-mm survey of the AKARI Deep Field-South (ADF-S) with the AzTEC camera on the Atacama Submillimetre Telescope Experiment (ASTE ). This survey covers ∼400 arcmin, of which the central 202 arcmin is a uniform low-noise region with an rms noise level of 0.48–0.71 mJy. This is one of the deepest surveys at 1-mm wavelength, to cover such a large contiguous region. We detected 37 sources with a significance of 3.5–10 σ. The expected number of false detections at ≥3.5 σ is at most one, indicating that the detected sources are highly reliable. We construct differential and cumulative number counts and find a difference in number counts among 1-mm blank field surveys: the number counts of the ADF-S are less than those of GOODS-N and COSMOS fields. Most of the sources are not detected in the far-infrared bands of the AKARI, suggesting that they lie mostly at z ∼ > 1 given the detection limits. In this survey, about 10% of cosmic infrared background at 1.1 mm is resolved into discrete sources.

GOODS–Herschel: an infrared main sequence for star-forming galaxies

We present the deepest 100 to 500 μm far-infrared observations obtained with the Herschel Space Observatory as part of the GOODS-Herschel key program, and examine the infrared (IR) 3–500 μm spectral energy distributions (SEDs) of galaxies at 0 < z < 2.5, supplemented by a local reference sample from IRAS, ISO, Spitzer, and AKARI data. We determine the projected star formation densities of local galaxies from their radio and mid-IR continuum sizes. We find that the ratio of total IR luminosity to rest-frame 8 μm luminosity, IR8 (≡ L_(IR)^(tot)/L_8), follows a Gaussian distribution centered on IR8 = 4 (σ = 1.6) and defines an IR main sequence for star-forming galaxies independent of redshift and luminosity. Outliers from this main sequence produce a tail skewed toward higher values of IR8. This minority population (  3 × 10^(10) L_⊙ kpc^(-2)) and a high specific star formation rate (i.e., starbursts). The rest-frame, UV-2700 A size of these distant starbursts is typically half that of main sequence galaxies, supporting the correlation between star formation density and starburst activity that is measured for the local sample. Locally, luminous and ultraluminous IR galaxies, (U)LIRGs (L_(IR)^(tot)≥ 10^(11) L_☉), are systematically in the starburst mode, whereas most distant (U)LIRGs form stars in the “normal” main sequence mode. This confusion between two modes of star formation is the cause of the so-called “mid-IR excess” population of galaxies found at z > 1.5 by previous studies. Main sequence galaxies have strong polycyclic aromatic hydrocarbon (PAH) emission line features, a broad far-IR bump resulting from a combination of dust temperatures (T_(dust) ~ 15–50 K), and an effective T_(dust)  ~ 31 K, as derived from the peak wavelength of their infrared SED. Galaxies in the starburst regime instead exhibit weak PAH equivalent widths and a sharper far-IR bump with an effective T_(dust)~ 40 K. Finally, we present evidence that the mid-to-far IR emission of X-ray active galactic nuclei (AGN) is predominantly produced by star formation and that candidate dusty AGNs with a power-law emission in the mid-IR systematically occur in compact, dusty starbursts. After correcting for the effect of starbursts on IR8, we identify new candidates for extremely obscured AGNs.

The Canada-UK Deep Submillimeter Survey. IV. The Survey of the 14 Hour Field

We have used SCUBA to survey an area of simeq 50 arcmin2, detecting 19 sources down to a 3 σ sensitivity limit of ~3.5 mJy at 850 μm. Monte Carlo simulations have shown that the fluxes of sources in this and similar SCUBA surveys are biased upward by the effects of source confusion and noise, leading to an overestimate by a factor of ~1.4 in the fraction of the 850 μm background that has been resolved by SCUBA. Once a correction is made for this effect, about 20% of the background has been resolved. The simulations have also been used to quantify the effects of confusion on source positions. Of the 19 SCUBA sources, five are microjansky radio sources, and two are ISO 15 μm sources. The radio/submillmeter flux ratios imply that the dust in these galaxies is being heated by young stars rather than active galactic nuclei. The upper limit to the average 450 μm/850 μm flux ratio implies either that the SCUBA galaxies are at z G 2 or, if they are at lower redshifts, that the dust is generally colder than in ULIRGs. We have used simple evolution models to address the major questions about the SCUBA sources: (1) What fraction of the star formation at high redshift is hidden by dust? (2) Does the submillimeter luminosity density reach a maximum at some redshift? (3) If the SCUBA sources are protoellipticals, when exactly did ellipticals form? We show, however, that the observations are not yet good enough to answer these questions. There are, for example, acceptable models in which 10 times as much high-redshift star formation is hidden by dust as is seen at optical wavelengths, but also acceptable ones in which the amount of hidden star formation is less than that seen optically. There are acceptable models in which very little star formation occurred before a redshift of 3 (as might be expected in models of hierarchical galaxy formation), but also ones in which 30% of the stars have formed by this redshift. The key to answering these questions are measurements of the dust temperatures and redshifts of the SCUBA sources.

A massive protocluster of galaxies at a redshift of z ≈ 5.3.

Massive clusters of galaxies have been found that date from as early as 3.9 billion years (3.9 Gyr; z = 1.62) after the Big Bang, containing stars that formed at even earlier epochs. Cosmological simulations using the current cold dark matter model predict that these systems should descend from ‘protoclusters’—early overdensities of massive galaxies that merge hierarchically to form a cluster. These protocluster regions themselves are built up hierarchically and so are expected to contain extremely massive galaxies that can be observed as luminous quasars and starbursts. Observational evidence for this picture, however, is sparse because high-redshift protoclusters are rare and difficult to observe. Here we report a protocluster region that dates from 1 Gyr (z = 5.3) after the Big Bang. This cluster of massive galaxies extends over more than 13 megaparsecs and contains a luminous quasar as well as a system rich in molecular gas. These massive galaxies place a lower limit of more than 4 × 1011 solar masses of dark and luminous matter in this region, consistent with that expected from cosmological simulations for the earliest galaxy clusters.

Where is the neutral atomic gas in Hickson groups

We have analyzed the total HI contents of 72 Hickson compact groups of galaxies (HCGs) and the detailed spatial distributions and kinematics of HI within a subset of 16 groups using the high angular resolution observations obtained with the VLA in order to investigate a possible evolutionary scenario for these densest systems in the present day galaxy hierarchy. For the more homogeneous subsample of 48 groups, we found a mean HI deciency of DefHI =0 :40 0:07, which corresponds to 40% of the expected HI for the optical luminosities and morphological types of the member galaxies. The individual galaxies show larger degrees of deciency than the groups globally, DefHI =0 :62 0:09 (24% of the expected HI), due in most cases to ecient gas stripping from individual galaxies into the group environment visible in the VLA maps. The degree of deciency is found to be similar to the central galaxies of Virgo and Coma cluster, and Coma I group, in spite of the signicantly dierent characteristics (number of galaxies, velocity dispersion) of these environments. It does not seem plausible that a signicant amount of extended HI has been missed by the observations. Hence phase transformation of the atomic gas should explain the HI deciency. The groups richer in early type galaxies or more compact with larger velocity dispersions show a weak tendency to be more HI decient. The detection rate of HCGs at X-ray wavelengths is larger for HI decient groups, although the hot gas distribution and hence its origin is only known for a few cases. In the evolutionary scenario we propose, the amount of detected HI would decrease further with evolution, by continuous tidal stripping and/or heating. The H2 content also tends to be lower than expected for the galaxies in HI decient groups, this may suggest that the HI stripping by frequent tidal interaction breaks the balance between the disruption of molecular clouds by star formation and the replenishment from the ambient HI.

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

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 deg2, 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/XMM–Newton 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 (S1.1mm > 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.

The Canada-UK Deep Submillimeter Survey. VI. The 3 Hour Field

We present the complete submillimeter data for the Canada-UK Deep Submillimeter Survey (CUDSS) 3h field. The observations were taken with the Submillimeter Common-User Bolometric Array (SCUBA) on the James Clerk Maxwell Telescope (JCMT) on Mauna Kea. The 3h field is one of two main fields in our survey and covers 60 arcmin2 to a 3 ? depth of ~3 mJy. In this field we have detected 27 sources above 3 ? and 15 above 3.5 ?. We assume that the differential source counts follow the form N(S) S-? and measure ? = 3.3, in good agreement with previous studies. We estimate that SCUBA sources brighter than 3 mJy are responsible for ~13% of the extragalactic background at 850 ?m (after correcting for flux boosting, 20% with no correction), which is in general agreement with previous estimates made by other groups. Using preliminary Infrared Space Observatory 15 ?m maps and VLA 1.4 GHz data, we have identified counterparts for 10 objects and have detected two sources at 450 ?m. With this information we estimate a lower limit on the median redshift of the sample of z > 1.4 with 6%-10% lying at z 3 mJy sources using the source catalogs from the CUDSS two main fields, the 3h and 14h fields, and find ?(?) = 4.4

A 250 GHz Survey of High-Redshift Quasars from the Sloan Digital Sky Survey

We present observations at 250 GHz (1.2 mm), 43 GHz, and 1.4 GHz of a sample of 41 QSOs at z > 3.7 found in the Sloan Digital Sky Survey. We detect 16 sources with a 250 GHz flux density greater than 1.4 mJy. The combination of centimeter and millimeter wavelength observations indicates that the 250 GHz emission is most likely thermal dust emission. Assuming a dust temperature of 50 K, the implied dust masses for the 16 detected sources are in the range 1.5-5.9 × 108 M☉, and the dust emitting regions are likely to be larger than 1 kpc in extent. The radio-through-optical spectral energy distributions for these sources are within the broad range defined by lower redshift, lower optical luminosity QSOs. We consider possible dust heating mechanisms, including UV emission from the active galactic nucleus (AGN) and a starburst concurrent with the AGN, with implied star formation rates between 500 and 2000 M☉ yr-1.

An AzTEC 1.1 mm survey of the GOODS-N field - I. Maps, catalogue and source statistics

We have conducted a deep and uniform 1.1 mm survey of the Great Observatories Origins Deep Survey-North (GOODS-N) field with AzTEC on the James Clerk Maxwell Telescope. Here, we present the first results from this survey including maps, the source catalogue and 1.1 mm number counts. The results presented here were obtained from a 245 arcmin2 region with a near uniform coverage to a depth of 0.96–1.16 mJy beam−1. Our robust catalogue contains 28 source candidates detected with S/N ≥ 3.75, only ∼1– 2 of which are expected to be spurious detections. Of these source candidates, eight are also detected by Submillimetre Common-User Bolometer Array (SCUBA) at 850 μm in regions where there is a good overlap between the two surveys. The major advantage of our survey over that with SCUBA is the uniformity of coverage. We calculate number counts using two different techniques: the first using a frequentist parameter estimation and the second using a Bayesian method. The two sets of results are in good agreement. We find that the 1.1 mm differential number counts are well described in the 2–6 mJy range by the functional form dN/dS=N′(S′/S) exp(−S/S′) with fitted parameters S′= 1.25 ± 0.38 mJy and dN/dS= 300 ± 90 mJy−1 deg−2 at 3 mJy.

A deep ALMA image of the Hubble Ultra Deep Field

We present the results of the first, deep Atacama Large Millimeter Array (ALMA) imaging covering the full ≃4.5 arcmin2 of the Hubble Ultra Deep Field (HUDF) imaged with Wide Field Camera 3/IR on HST. Using a 45-pointing mosaic, we have obtained a homogeneous 1.3-mm image reaching σ1.3 ≃ 35 μJy, at a resolution of ≃0.7 arcsec. From an initial list of ≃50 > 3.5σ peaks, a rigorous analysis confirms 16 sources with S1.3 > 120 μJy. All of these have secure galaxy counterparts with robust redshifts (〈z〉 = 2.15). Due to the unparalleled supporting data, the physical properties of the ALMA sources are well constrained, including their stellar masses (M*) and UV+FIR star formation rates (SFR). Our results show that stellar mass is the best predictor of SFR in the high-redshift Universe; indeed at z ≥ 2 our ALMA sample contains seven of the nine galaxies in the HUDF with M* ≥ 2 × 1010 M⊙, and we detect only one galaxy at z > 3.5, reflecting the rapid drop-off of high-mass galaxies with increasing redshift. The detections, coupled with stacking, allow us to probe the redshift/mass distribution of the 1.3-mm background down to S1.3 ≃ 10 μJy. We find strong evidence for a steep star-forming ‘main sequence’ at z ≃ 2, with SFR ∝M* and a mean specific SFR ≃ 2.2 Gyr−1. Moreover, we find that ≃85 per cent of total star formation at z ≃ 2 is enshrouded in dust, with ≃65 per cent of all star formation at this epoch occurring in high-mass galaxies (M* > 2 × 1010 M⊙), for which the average obscured:unobscured SF ratio is ≃200. Finally, we revisit the cosmic evolution of SFR density; we find this peaks at z ≃ 2.5, and that the star-forming Universe transits from primarily unobscured to primarily obscured at z ≃ 4.