Daisuke Iono

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.

LUMINOUS INFRARED GALAXIES WITH THE SUBMILLIMETER ARRAY. II. COMPARING THE CO (3-2) SIZES AND LUMINOSITIES OF LOCAL AND HIGH-REDSHIFT LUMINOUS INFRARED GALAXIES

We present a detailed comparison of the CO (3-2) emitting molecular gas between a local sample of luminous infrared galaxies (U/LIRGs) and a high-redshift sample that comprises submm selected galaxies (SMGs), quasars, and Lyman Break Galaxies (LBGs). The U/LIRG sample consists of our recent CO (3-2) survey using the Submillimeter Array while the CO (3-2) data for the high-redshift population are obtained from the literature. We find that the and L FIR relation is correlated over five orders of magnitude, which suggests that the molecular gas traced in CO (3-2) emission is a robust tracer of dusty star formation activity. The near unity slope of 0.93 ? 0.03 obtained from a fit to this relation suggests that the star formation efficiency is constant to within a factor of 2 across different types of galaxies residing in vastly different epochs. The CO (3-2) size measurements suggest that the molecular gas disks in local U/LIRGs (0.3-3.1?kpc) are much more compact than the SMGs (3-16?kpc), and that the size scales of SMGs are comparable to the nuclear separation (5-40?kpc) of the widely separated nuclei of U/LIRGs in our sample. We argue from these results that the SMGs studied here are predominantly intermediate stage mergers, and that the wider line widths arise from the violent merger of two massive gas-rich galaxies taking place deep in a massive halo potential.

Luminous Infrared Galaxies with the Submillimeter Array. I. Survey Overview and the Central Gas to Dust Ratio

We present new data obtained with the Submillimeter Array for a sample of 14 nearby luminous and ultraluminous infrared galaxies. The galaxies were selected to have distances D_L 11.4. The galaxies were observed with spatial resolutions of order 1 kpc in the CO J = 3–2, CO J = 2–1,^(13)CO J = 2–1, and HCO+ J = 4–3 lines as well as the continuum at 880 μm and 1.3 mm. We have combined our CO and continuum data to measure an average gas-to-dust mass ratio of 120 ± 28 (rms deviation 109) in the central regions of these galaxies, very similar to the value of 150 determined for the Milky Way. This similarity is interesting given the more intense heating from the starburst and possibly accretion activity in the luminous infrared galaxies compared to the Milky Way. We find that the peak H_2 surface density correlates with the far-infrared luminosity, which suggests that galaxies with higher gas surface densities inside the central kiloparsec have a higher star formation rate. The lack of a significant correlation between total H_2 mass and far-infrared luminosity in our sample suggests that the increased star formation rate is due to the increased availability of molecular gas as fuel for star formation in the central regions. In contrast to previous analyses by other authors, we do not find a significant correlation between central gas surface density and the star formation efficiency, as traced by the ratio of far-infrared luminosity to nuclear gas mass. Our data show that it is the star formation rate, not the star formation efficiency, that increases with increasing central gas surface density in these galaxies.

Deep 1.1 mm-wavelength imaging of the GOODS-S field by AzTEC/ASTE – I. Source catalogue and number counts

We present the first results from a 1.1mm confusion-limited map of the Great Observatories Origins Deep Survey-South (GOODS-S) taken with the AzTEC camera on the Atacama Submillimeter Telescope Experiment. We imaged a 270arcmin 2 field to a 1� depth of 0.48 0.73mJy/beam, making this one of the deepest blank-field surveys at mm-wavelengths ever achieved. Although by traditional standards our GOODS-S map is extremely confused due to a sea of faint underlying sources, we demonstrate through simulations that our source identification and number counts analyses are robust, and the techniques discussed in this paper are relevant for other deeply confused surveys. We find a total of 41 dusty starburst galaxies with signal to noise ratios S/N > 3.5 within this uniformly covered region, where only two are expected to be false detections, and an additional seven robust source candidates located in the noisier (1� � 1mJy/beam) outer region of the map. We derive the 1.1mm number counts from this field using two different methods: a fluctuation or “P(d)” analysis and a semi-Bayesian technique, and find that both methods give consistent results. Our data are well-fit by a Schechter function model

Spatial correlation between submillimetre and Lyman-α galaxies in the SSA 22 protocluster

Lyman-α emitters are thought to be young, low-mass galaxies with ages of ∼108 yr (refs 1, 2). An overdensity of them in one region of the sky (the SSA 22 field) traces out a filamentary structure in the early Universe at a redshift of z ≈ 3.1 (equivalent to 15 per cent of the age of the Universe) and is believed to mark a forming protocluster. Galaxies that are bright at (sub)millimetre wavelengths are undergoing violent episodes of star formation, and there is evidence that they are preferentially associated with high-redshift radio galaxies, so the question of whether they are also associated with the most significant large-scale structure growing at high redshift (as outlined by Lyman-α emitters) naturally arises. Here we report an imaging survey of 1,100-μm emission in the SSA 22 region. We find an enhancement of submillimetre galaxies near the core of the protocluster, and a large-scale correlation between the submillimetre galaxies and the low-mass Lyman-α emitters, suggesting synchronous formation of the two very different types of star-forming galaxy within the same structure at high redshift. These results are in general agreement with our understanding of the formation of cosmic structure.

Molecular Superbubbles in the Starburst Galaxy NGC 253

The central 2; 1 kpc of the starburst galaxy NGC 253 have been imaged using the Submillimeter Array at a 60 pc resolution in the J = 2 - 1 transitions of (12)CO, (13)CO, and C(18)O, as well as in the 1.3 mm continuum. Molecular gas and dust are distributed mainly in a circumnuclear disk of similar to 500 pc radius, with warm (similar to 40 K) and high area filling factor gas in its central part. Two gas shells or cavities have been discovered in the circumnuclear disk. They have similar to 100 pc diameters and have large velocity widths of 80 - 100 km s(-1), suggestive of expansion at similar to 50 km s(-1) . Modeled as an expanding bubble, each shell has an age of similar to 0.5 Myr and needed kinetic energy of similar to 1; 10(46) J, as well as mean mechanical luminosity of similar to 1; 10(33) W, for its formation. The large energy allows each to be called a superbubble. A similar to 10(6) M circle dot super star cluster can provide the luminosity and could be a building block of the nuclear starburst in NGC 253. Alternatively, a hypernova can also be the main source of energy for each superbubble, not only because it can provide the mechanical energy and luminosity but also because the estimated rate of superbubble formation and that of hypernova explosions are comparable. Our observations indicate that the circumnuclear molecular disk harboring the starburst is highly disturbed on 100 pc or smaller scales, presumably by individual young clusters and stellar explosions, in addition to being globally disturbed in the form of the well-known superwind.

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).

Atomic and Molecular Gas in Colliding Galaxy Systems. I. The Data

We present H I and CO (1-0) interferometric observations of 10 comparable-mass interacting systems obtained at the Very Large Array (VLA) and the Owens Valley Radio Observatory (OVRO) millimeter array. The primary intent of this study is to investigate the response of cold gas during the early stages of collision of massive disk galaxies. The sample sources are selected based on their luminosity (MB ≤ -19), projected separation (5-40 kpc), and single-dish CO (1-0) content (SCO ≥ 20 Jy km s-1). These selection criteria result in a sample that primarily consists of systems in the early stages of an interaction or a merger. Despite this sample selection, 50% of the systems show long H I tidal tails indicative of a tidal disruption in a prograde orbit. In addition, all (4/4) of the infrared luminous pairs (LIRGs) in the sample show long H I tails, suggesting that the presence of a long H I tail can be a possible signature of enhanced star formation activity in a collision of gas-rich galaxies. More than half of the groups show a displacement of H I peaks from the stellar disks. The CO (1-0) distribution is generally clumpy and widely distributed, unlike in most IR-selected late stage mergers—in fact, CO peaks are displaced from the stellar nucleus in 20% (4/18) of the galaxies with robust CO detection. H I and CO (1-0) position-velocity diagrams (PVDs) and rotation curves are also presented, and their comparison with the numerical simulation analyzed in Paper I show evidence for radial inflow and wide occurrences of nuclear molecular rings. These results are further quantified by examining physical and structural parameters derived in comparison with isolated systems in the BIMA SONG sample in our forthcoming paper.

High-Density Molecular Gas in the Infrared-bright Galaxy System VV 114

The new high-resolution CO (3-2) interferometric map of the IR-bright interacting galaxy system VV 114 observed with the Submillimeter Array reveals a substantial amount of warm and dense gas in the IR-bright but optically obscured galaxy, VV 114E, and the overlap region connecting the two nuclei. A 1.8 × 1.4 kpc concentration of CO (3-2) emitting gas with a total mass of 4 × 109 M☉ coincides with the peaks of near-IR, mid-IR, and radio continuum emission found previously by others, identifying the dense fuel for the active galactic nucleus and/or the starburst activity there. Extensive CO (2-1) emission is also detected, revealing detailed distribution and kinematics that are consistent with the earlier CO (1-0) results. The widely distributed molecular gas traced in CO (2-1) and the distributed discrete peaks of CO (3-2) emission suggest that a spatially extended intense starbursts may contribute significantly to its large IR luminosity. These new observations further support the notion that VV 114 is approaching its final stage of merger, when a violent central inflow of gas triggers intense starburst activity possibly boosting the IR luminosity above the ultraluminous threshold.

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.