Min S. Yun

Radio Properties of Infrared-selected Galaxies in the IRAS 2 Jy Sample

The radio counterparts to the IRAS Redshift Survey galaxies are identified in the NRAO VLA Sky Survey (NVSS) catalog. Our new catalog of the IR flux-limited (S60 μm ≥ 2 Jy) complete sample of 1809 galaxies lists accurate radio positions, redshifts, and 1.4 GHz radio and IRAS fluxes. This sample is 6 times larger in size and 5 times deeper in redshift coverage (to z ≈ 0.15) than those used in earlier studies of the radio and far-IR (FIR) properties of galaxies in the local volume. The well-known radio-FIR correlation is obeyed by the overwhelming majority (≥98%) of the IR-selected galaxies, and the radio AGNs identified by their excess radio emission constitute only about 1% of the sample, independent of the IR luminosity. These FIR-selected galaxies can account for the entire population of late-type field galaxies in the local volume, and their radio continuum may be used directly to infer the extinction-free star formation rate in most cases. Both the 1.4 GHz radio and 60 μm IR luminosity functions are reasonably well described by linear sums of two Schechter functions, one representing normal, late-type field galaxies and the other representing starbursts and other luminous IR galaxies. The integrated FIR luminosity density for the local volume is (4.8 ± 0.5) × 107 L☉ Mpc-3, less than 10% of which is contributed by the luminous IR galaxies with LFIR ≥ 1011 L☉. The inferred extinction-free star formation density for the local volume is 0.015 ± 0.005 M☉ yr-1 Mpc-3.

Radio-to-Far-Infrared Spectral Energy Distribution and Photometric Redshifts for Dusty Starburst Galaxies

As a logical next step in improving the radio-to-submillimeter spectral index as a redshift indicator, we have investigated a technique of using the entire radio-to-far-infrared spectral energy distribution (SED) for deriving photometric redshifts for dusty starburst galaxies at high redshift. A dusty starburst SED template is developed from the theoretical understanding of various emission mechanisms related to massive star formation processes, and the template parameters are selected by examining the observed properties of 23 IR-selected starburst galaxies: Td = 58 K, β = 1.35, and fnth = 1. The major improvement in using this template SED for deriving photometric redshifts is the significant reduction in redshift uncertainty over the spectral index technique, particularly at higher redshifts. Intrinsic dispersion in the radio and far-infrared SEDs as well as absolute calibration and measurement errors contribute to the overall uncertainty of the technique. The derived photometric redshifts for five submillimeter galaxies with known redshifts agree well with their spectroscopic redshifts within the estimated uncertainty. Photometric redshifts for seven submillimeter galaxies without known spectroscopic redshifts (HDF 850.1, CUDSS 14.1, Lockman 850.1, SMM J00266+1708, SMM J09429+4658, SMM J14009+0252, and FIRBACK J1608+5418) are derived.

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

We present a 1.1mm wavelength imaging survey covering 0.3 deg^2 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 z ≈ 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^2 area which has a uniform sensitivity of ∼1.3 mJy beam^−1. 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^(12)L_☉ and star formation rates ≥1100M_☉ yr^(−1). 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.

The AzTEC mm-wavelength camera

AzTEC is a mm-wavelength bolometric camera utilizing 144 silicon nitride micromesh detectors. Here, we describe the AzTEC instrument architecture and its use as an astronomical instrument. We report on several performance metrics measured during a three-month observing campaign at the James Clerk Maxwell Telescope and conclude with our plans for AzTEC as a facility instrument on the Large Millimetre Telescope.

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.

CO luminosity functions for far-infrared- and B-band-selected galaxies and the first estimate for Omega(H I+H2)

We derive a nonparametric CO luminosity function using an FIR- and an optical B-band-selected sample of the galaxies included in the FCRAO Extragalactic CO Survey. The FIR-selected sample is defined using the IRAS bright galaxy samples (BGS; IRAS 60 μm flux density ≥5.24 Jy). Although our CO sample is not complete, the normalization using the BGS reproduces the IRAS 60 μm luminosity function in excellent agreement with those found in the literature. Similarly, a B-band-selected sample defined using the Revised Shapley-Ames catalog is used to derive a CO luminosity function for a comparison. A Schechter function describes both the derived CO luminosity functions reasonably well. Adopting the standard CO-to-H2 conversion factor, we derive a molecular gas density of ρ = (3.1 ± 1.2) × 107 h M☉ Mpc-3 for the local volume. Combining with the measurements of the local H I mass density and the helium contribution, we estimate that the total mass density of cold neutral gas in the local universe is Ωgas = (4.3 ± 1.1) × 10-4 h-1, which is about 20% of the total stellar mass density Ω*.

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.

THE AzTEC/SMA INTERFEROMETRIC IMAGING SURVEY OF SUBMILLIMETER-SELECTED HIGH-REDSHIFT GALAXIES

We present results from a continuing interferometric survey of high-redshift submillimeter galaxies with the Submillimeter Array, including high-resolution (beam size ~2 arcsec) imaging of eight additional AzTEC 1.1mm selected sources in the COSMOS Field, for which we obtain six reliable (peak S/N>5 or peak S/N>4 with multiwavelength counterparts within the beam) and two moderate significance (peak S/N>4) detections. When combined with previous detections, this yields an unbiased sample of millimeter-selected SMGs with complete interferometric followup. With this sample in hand, we (1) empirically confirm the radio-submillimeter association, (2) examine the submillimeter morphology - including the nature of submillimeter galaxies with multiple radio counterparts and constraints on the physical scale of the far infrared - of the sample, and (3) find additional evidence for a population of extremely luminous, radio-dim submillimeter galaxies that peaks at higher redshift than previous, radio-selected samples. In particular, the presence of such a population of high-redshift sources has important consequences for models of galaxy formation - which struggle to account for such objects even under liberal assumptions - and dust production models given the limited time since the Big Bang.

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.