Soh Ikarashi

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.

Herschel reveals the obscured star formation in HiZELS Hα emitters at z = 1.47

We describe the far-infrared (far-IR; rest-frame 8–1000-μm) properties of a sample of 443 Hα-selected star-forming galaxies in the Cosmic Evolution Survey (COSMOS) and Ultra Deep Survey (UDS) fields detected by the High-redshift Emission Line Survey (HiZELS) imaging survey. Sources are identified using narrow-band filters in combination with broad-band photometry to uniformly select Hα (and [O ii] if available) emitters in a narrow redshift slice at z = 1.47 ± 0.02. We use a stacking approach in Spitzer-MIPS mid-IR, Herschel-PACS/SPIRE far-IR [from the PACS Evolutionary Prove (PEP) and Herschel Multi-tiered Extragalactic Survey (HerMES)] and AzTEC mm-wave images to describe their typical far-IR properties. We find that HiZELS galaxies with observed Hα luminosities of L(Hα)_(obs) ≈ 10^(8.1-9.1) L_⊙ ( ≈ 10^(41.7-42.7) erg s^(−1)) have bolometric far-IR luminosities of typical luminous IR galaxies, L(8−1000μm)≈10^(11.41)^(+0.04)_(−0.06) L_⊙. Combining the Hα and far-IR luminosities, we derive median star formation rates (SFRs) of SFR_(Hα), FIR = 32 ± 5 M_⊙ yr^(−1) and Hα extinctions of A_(Hα) = 1.0 ± 0.2 mag. Perhaps surprisingly, little difference is seen in typical HiZELS extinction levels compared to local star-forming galaxies. We confirm previous empirical stellar mass (M_*) to A_(Hα) relations and the little or no evolution up to z = 1.47. For HiZELS galaxies (or similar samples) we provide an empirical parametrization of the SFR as a function of rest-frame (u − z) colours and 3.6-μm photometry – a useful proxy to aid in the absence of far-IR detections in high-z galaxies. We find that the observed Hα luminosity is a dominant SFR tracer when rest-frame (u − z) colours are ≲0.9 mag or when Spitzer-3.6-μm photometry is fainter than 22 mag (Vega) or when stellar masses are lower than 10^(9.7) M_⊙. We do not find any correlation between the [O ii]/Hα and far-IR luminosity, suggesting that this emission line ratio does not trace the extinction of the most obscured star-forming regions, especially in massive galaxies where these dominate. The luminosity-limited HiZELS sample tends to lie above of the so-called main sequence for star-forming galaxies, especially at low stellar masses, indicating high star formation efficiencies in these galaxies. This work has implications for SFR indicators and suggests that obscured star formation is linked to the assembly of stellar mass, with deeper potential wells in massive galaxies providing dense, heavily obscured environments in which stars can form rapidly.

Detection of an ultrabright submillimetre galaxy in the Subaru/XMM-Newton Deep Field using AzTEC/ASTE

We report on the detection of an extremely bright (∼37 mJy at 1100 μm and ∼91 mJy at 880 μm) submillimetre galaxy (SMG), AzTEC-ASTE-SXDF1100.001 (hereafter referred to as SXDF1100.001 or Orochi), discovered in the 1100 μm observations of the Subaru/XMM–Newton Deep Field using AzTEC on ASTE. Subsequent CARMA 1300-μm and SMA 880-μm observations successfully pinpoint the location of Orochi and suggest that it has two components, one extended [full width at half-maximum (FWHM) of ∼4 arcsec] and one compact (unresolved). Z-Spec on CSO has also been used to obtain a wide-band spectrum from 190 to 308 GHz, although no significant emission/absorption lines were found. The derived upper limit to the line-to-continuum flux ratio is 0.1–0.3 (2σ) across the Z-Spec band. Based on the analysis of the derived spectral energy distribution from optical to radio wavelengths of possible counterparts near the SMA/CARMA peak position, we suggest that Orochi is a lensed, optically dark SMG lying at z ∼ 3.4 behind a foreground, optically visible (but red) galaxy at z ∼ 1.4. The deduced apparent (i.e., no correction for magnification) infrared luminosity (L_(IR)) and star formation rate (SFR) are 6 × 10^(13) L_⊙ and 11 000 M_⊙ yr^(−1), respectively, assuming that the L_(IR) is dominated by star formation. These values suggest that Orochi will consume its gas reservoir within a short time-scale (3 × 10^7 yr), which is indeed comparable to those in extreme starbursts like the centres of local ultraluminous infrared galaxies (ULIRGs).

ALMA Deep Field in SSA22: A Concentration of Dusty Starbursts in a z = 3.09 Protocluster Core

The version of record is available at: http://iopscience.iop.org/article/10.1088/2041-8205/815/1/L8/meta;jsessionid=E0003CC36F8A1587DB4A86725C658FE2.c2.iopscience.cld.iop.org

AzTEC/ASTE 1.1-mm survey of SSA22: Counterpart identification and photometric redshift survey of submillimetre galaxies

This article has been accepted for publication in Monthly Notices Of The Royal Astronomical Society ©: 2014 H. Umehata et al. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

SXDF–ALMA 2-arcmin2 deep survey: 1.1-mm number counts

We report 1.1-mm number counts revealed with the Atacama Large Millimeter/submillimeter Array (ALMA) in the Subaru/XMM-Newton Deep Survey Field (SXDF). The advent of ALMA enables us to reveal millimeter-wavelength number counts down to the faint end without source confusion. However, previous studies are based on the ensemble of serendipitously detected sources in fields originally targeting different sources and could be biased due to the clustering of sources around the targets. We derive number counts in the flux range of 0.2-2 mJy by using 23 (≥4σ) sources detected in a continuous 2.0-arcmin2 area of the SXDF. The number counts are consistent with previous results within errors, suggesting that the counts derived from serendipitously detected sources are not significantly biased, although there could be field-to-field variation due to the small survey area. By using the best-fitting function of the number counts, we find that ˜40% of the extragalactic background light at 1.1 mm is resolved at S1.1mm > 0.2 mJy.

Obscured star formation in Lyα blobs at z = 3.1

We present results from the AzTEC/ASTE 1.1-mm imaging survey of 35 Lyα blobs (LABs) found in the SSA22 protocluster at z = 3.1. These 1.1-mm data reach an rms noise level of 0.7–1 mJy beam^(−1), making this the largest millimetre-wave survey of LABs to date. While one (or possibly two) out of 35 LABs might be detected at 3σ level, no significant (≥3.5σ) emission is found in any of individual 35 LABs. From this, we estimate 3σ upper limits on the far-infrared luminosity of L_FIR < 2 × 10^(12) L_⊙ (the dust temperature of 35 K and the emissivity index of 1.5 are assumed). Stacking analysis reveals that the 1.1-mm flux density averaged over the LABs is S_(1.1 mm) < 0.40 mJy (3σ), which places a constraint of LFIR < 4.5 × 10^(11) L_⊙. These data constrain the dust spectral energy distributions of the LABs more tightly than ever if their spectral indices at rest-frame wavelength of ≈ 240 μm are similar to those found in (ultra-)luminous infrared galaxies at 0.2 < z < 0.3. Our results suggest that LABs on average have little ultraluminous obscured star formation, in contrast to a long-believed picture that LABs undergo an intense episode of dusty star formation activities with star formation rates of ∼10^3  M_⊙ yr^(−1). Observations with the Atacama Large Millimeter/submillimeter Array are needed to directly study the obscured part of star formation activity in the LABs.

SXDF-ALMA 1.5 arcmin2 Deep Survey: A Compact Dusty Star-forming Galaxy at z = 2.5

We present the first results from the SXDF-Atacama Large Millimeter/submillimeter Array (ALMA) 1.5 arcmin2 deep survey at 1.1 mm using ALMA. The map reaches a 1σ depth of 55 μJy/beam and covers 12 Hα-selected star-forming galaxies (SFGs) at z = 2.19 or z = 2.53. We have detected continuum emission from three of our Hα-selected sample, including one compact SFG with high stellar surface density, NB2315-07. They are all red in the rest-frame optical and have stellar masses of log (M*/M⊙) > 10.9, whereas the other blue, main-sequence galaxies with {log}({M}*/{M}⊙ ) = 10.0-10.8 are exceedingly faint,

Extremely Red Submillimeter Galaxies: New z ≳ 4-6 Candidates Discovered using ALMA and Jansky VLA

We present the detailed characterization of two extremely red submillimeter galaxies (SMGs), ASXDF1100.053.1 and 231.1, with the Atacama Large Millimeter/submillimeter Array (ALMA) and the Jansky Very Large Array. These SMGs were originally selected using AzTEC at 1100 μm, and are observed by Herschel to be faint at 100–500 μm. Their (sub)millimeter colors are as red as—or redder—than known z ≳ 5 SMGs; indeed, ASXDF1100.053.1 is redder than HFLS 3, which lies at z = 6.3. They are also faint and red in the near-/mid-infrared: ∼1 μJy at IRAC 4.5 μm and

SXDF-UDS-CANDELS-ALMA 1.5 arcmin2 deep survey

We have conducted 1.1 mm ALMA observations of a contiguous 105″ × 50″ or 1.5 arcmin2 window (achieved by 19 point mosaic) in the SXDF-UDS-CANDELS. We achieved a 5σ sensitivity of 0.28 mJy, giving a flat sensus of dusty star-forming galaxies with LIR ~6 × 1011 L⊙ (if Tdust = 40 K) or SFR ~100 M⊙ yr-1 up to z~10 thanks to the negative K-correction at this wavelength. We detect 5 brightest sources (S/N>6) and 18 low-significant sources (5 > S/N > 4; they may contain spurious detections, though) in the field. We find that these discrete sources are responsible for a faint filamentary emission seen in low-resolution (~30″) heavily confused AzTEC 1.1mm and SPIRE 0.5mm images. One of the 5 brightest ALMA sources is very dark in deep WFC3 and HAWK-I NIR images as well as VLA 1.4 GHz images, demonstrating that deep ALMA imaging can unveil new obscured star-forming galaxy population.