G. Petitpas

Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, United States

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Publications (89)337.81 Total impact

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    ABSTRACT: We present an analysis of 11 bright far-IR/submm sources discovered through a combination of the Planck survey and follow-up Herschel-SPIRE imaging. Each source has a redshift z=2.2-3.6 obtained through a blind redshift search with EMIR at the IRAM 30-m telescope. Interferometry obtained at IRAM and the SMA, and optical/near-infrared imaging obtained at the CFHT and the VLT reveal morphologies consistent with strongly gravitationally lensed sources. Additional photometry was obtained with JCMT/SCUBA-2 and IRAM/GISMO at 850 um and 2 mm, respectively. All objects are bright, isolated point sources in the 18 arcsec beam of SPIRE at 250 um, with spectral energy distributions peaking either near the 350 um or the 500 um bands of SPIRE, and with apparent far-infrared luminosities of up to 3x10^14 L_sun. Their morphologies and sizes, CO line widths and luminosities, dust temperatures, and far-infrared luminosities provide additional empirical evidence that these are strongly gravitationally lensed high-redshift galaxies. We discuss their dust masses and temperatures, and use additional WISE 22-um photometry and template fitting to rule out a significant contribution of AGN heating to the total infrared luminosity. Six sources are detected in FIRST at 1.4 GHz. Four have flux densities brighter than expected from the local far-infrared-radio correlation, but in the range previously found for high-z submm galaxies, one has a deficit of FIR emission, and 6 are consistent with the local correlation. The global dust-to-gas ratios and star-formation efficiencies of our sources are predominantly in the range expected from massive, metal-rich, intense, high-redshift starbursts. An extensive multi-wavelength follow-up programme is being carried out to further characterize these sources and the intense star-formation within them.
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    ABSTRACT: We report the redshift of an unlensed, highly obscured submillimetre galaxy (SMG), HS1700.850.1, the brightest SMG (S850um =19.1 mJy) detected in the JCMT/SCUBA-2 Baryonic Structure Survey, based on the detection of its CO line emission. Using the IRAM PdBI-WIDEX with 3.6GHz band width, we serendipitously detect an emission line at 150.6 GHz. Confirmation of the identification of this line as CO(5-4) at z = 2.816 comes from a search over 14.5 GHz in the 3-mm and 2-mm atmospheric windows, meaning that it does not reside in the z~2.30 proto-cluster in this field. Measurement of the 870um source size (<0.74") from the Sub-Millimeter Array (SMA) confirms a compact emission in a S870um =14.5mJy, LIR~10^13 Lsun component, suggesting an Eddington-limited starburst. We use the double-peaked CO line profile measurements along with the SMA size constraints to study the gas dynamics of a HyLIRG, estimating the gas and dynamical masses of HS1700.850.1. While HS1700.850.1 is one of the most extreme galaxies known in the Universe, we find that it occupies a relative void in the Lyman-Break Galaxy distribution in this field. Comparison with other extreme objects at similar epochs (HyLIRG Quasars), and cosmological simulations, suggests such an anti-bias of bright SMGs could be relatively common, with the brightest SMGs rarely occupying the most overdense regions at z=2-4.
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    ABSTRACT: We report the blind detection of 12CO emission from a distant red galaxy, HS1700.DRG55. We have used the IRAM Plateau de Bure Interferometer WideX, with its 3.6 GHz of instantaneous dual-polarization bandwidth, to target 12CO(3–2) from galaxies lying in the protocluster at z = 2.300 in the field HS1700+64. If indeed this line in DRG55 is 12CO(3–2), its detection at 104.9 GHz indicates zCO = 2.296. None of the other eight known z ∼ 2.30 protocluster galaxies lying within the primary beam (PB) are detected in 12CO, although the limits are ∼2 × worse towards the edge of the PB where several lie. The optical/near-IR magnitudes of DRG55 (RAB > 27, KAB = 22.3) mean that optical spectroscopic redshifts are difficult with 10-m-class telescopes, but near-IR redshifts would be feasible. The 24-μm-implied star formation rate (210 M⊙ yr−1), stellar mass (∼1011 M⊙) and 12CO line luminosity (3.6 × 1010 K km s−1 pc2) are comparable to other normal 12CO-detected star-forming galaxies in the literature, although the galaxy is some ∼2 mag (∼6 ×) fainter in the rest-frame UV than 12CO-detected galaxies at z > 2. The detection of DRG55 in 12CO complements three other 12CO detected UV-bright galaxies in this protocluster from previous studies, and suggests that many optically faint galaxies in the protocluster may host substantial molecular gas reservoirs, and a full blind census of 12CO in this overdense environment is warranted.
    Monthly Notices of the Royal Astronomical Society Letters 01/2015; 449(1). DOI:10.1093/mnrasl/slv010 · 5.52 Impact Factor
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    ABSTRACT: Studying molecular gas properties in merging galaxies gives us important clues to the onset and evolution of interaction-triggered starbursts. NGC4194 is particularly interesting to study since its FIR-to-CO luminosity ratio rivals that of ULIRGs,despite its lower luminosity compared to ULIRGs, which indicates a high star formation efficiency that is relative to even most spirals and ULIRGs.We study the molecular medium at an angular resolution of 0.65"x .52" through our observations of CO2-1 emission using the SMA. We compare our CO2-1 maps with optical HST and high angular resolution radio continuum images to study the relationship between molecular gas and other components of the starburst region. The molecular gas is tracing the complicated dust lane structure of NGC4194 with the brightest emission being located in an off-nuclear ring-like structure with ~320pc radius, the Eye of the Medusa. The bulk CO emission of the ring is found south of the kinematical center of NGC4194. The northern tip of the ring is associated with the galaxy nucleus, where the radio continuum has its peak. A prominent, secondary emission maximum in the radio continuum is located inside the molecular ring. This suggests that the morphology of the ring is partially influenced by massive supernova explosions. From the combined evidence, we propose that the Eye of the Medusa contains a shell of swept up material where we identify a number of giant molecular associations. We propose that the Eye may be the site of an efficient starburst of 5-7M_sun/yr, but it would still constitute only a fraction of the 30-50M_sun/yr SFR of NGC4194. Furthermore, we find that ~50% of the molecular mass of NGC4194 is found in extended filamentary-like structures tracing the minor and major axis dust lanes. We suggest that molecular gas is transported along these lanes providing the central starburst region with fuel.
    Astronomy and Astrophysics 07/2014; 569. DOI:10.1051/0004-6361/201423548 · 4.48 Impact Factor
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    ABSTRACT: At low redshift, a handful of gamma-ray bursts (GRBs) have been discovered with peak luminosities ($L_{\rm iso} < 10^{48.5}~\rm{erg\,s}^{-1}$) substantially lower than the average of the more distant ones ($L_{\rm iso} > 10^{49.5}~\rm{erg\,s}^{-1}$). The properties of several low-luminosity (low-$L$) GRBs indicate that they can be due to shock break-out, as opposed to the emission from ultrarelativistic jets. Owing to this, it is highly debated how both populations are connected, and whether there is a continuum between them. The burst at redshift $z=0.283$ from 2012 April 22 is one of the very few examples of intermediate-$L$ GRBs with a $\gamma$-ray luminosity of $L\sim10^{48.9}~\rm{erg\,s}^{-1}$ that have been detected up to now. Together with the robust detection of its accompanying supernova SN 2012bz, it has the potential to answer important questions on the origin of low- and high-$L$ GRBs and the GRB-SN connection. We carried out a spectroscopy campaign using medium- and low-resolution spectrographs at 6--10-m class telescopes, covering the time span of 37.3 days, and a multi-wavelength imaging campaign from radio to X-ray energies over a duration of $\sim270$ days. Furthermore, we used a tuneable filter centred at H$\alpha$ to map star formation in the host galaxy and the surrounding galaxies. We used these data to extract and model the properties of different radiation components and incorporate spectral-energy-distribution fitting techniques to extract the properties of the host galaxy. Modelling the light curve and spectral energy distribution from the radio to the X-rays revealed the blast-wave to expand with an initial Lorentz factor of $\Gamma_0\sim60$, low for a high-$L$ GRB, and that the afterglow had an exceptional low peak luminosity-density of $\lesssim2\times10^{30}~\rm{erg\,s}^{-1}\,\rm{Hz}^{-1}$ in the sub-mm. [Abridged]
    Astronomy and Astrophysics 01/2014; 566. DOI:10.1051/0004-6361/201423387 · 4.48 Impact Factor
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    ABSTRACT: We present a method for selecting $z>4$ dusty, star forming galaxies (DSFGs) using Herschel/SPIRE 250/350/500 $\mu m$ flux densities to search for red sources. We apply this method to 21 deg$^2$ of data from the HerMES survey to produce a catalog of 38 high-$z$ candidates. Follow-up of the first 5 of these sources confirms that this method is efficient at selecting high-$z$ DSFGs, with 4/5 at $z=4.3$ to $6.3$ (and the remaining source at $z=3.4$), and that they are some of the most luminous dusty sources known. Comparison with previous DSFG samples, mostly selected at longer wavelengths (e.g., 850 $\mu m$) and in single-band surveys, shows that our method is much more efficient at selecting high-$z$ DSFGs, in the sense that a much larger fraction are at $z>3$. Correcting for the selection completeness and purity, we find that the number of bright ($S_{500\,\mu m} \ge 30$ mJy), red Herschel sources is $3.3 \pm 0.8$ deg$^{-2}$. This is much higher than the number predicted by current models, suggesting that the DSFG population extends to higher redshifts than previously believed. If the shape of the luminosity function for high-$z$ DSFGs is similar to that at $z\sim2$, rest-frame UV based studies may be missing a significant component of the star formation density at $z=4$ to $6$, even after correction for extinction.
    The Astrophysical Journal 10/2013; 780(1). DOI:10.1088/0004-637X/780/1/75 · 6.28 Impact Factor
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    ABSTRACT: We present a ˜1″ (100 pc) resolution CO(3–2) map of the Antennae galaxies obtained with the Submillimeter Array. We find that only < 30% of the GMAs spatially coincides with the optically detected star clusters, suggesting that the bulk of the CO (3–2) emission traces the regions with very recent or near future star formation activity. A high CO (3–2)/(1–0) ratio is seen in both nuclei and the southern complexes in the overlap region. Higher radiation field associated with intense star formation can account for the nucleus of NGC 4038 and the overlap region, but the nuclear region of NGC 4039 show relatively little star formation or AGN activities and cannot easily explained. We show kinematical evidence that the high line ratio in NGC 4039 is possibly caused by gas inflow into the counter-rotating central disk.
    10/2013;
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    ABSTRACT: Gamma-ray bursts are the most luminous explosions that we can witness in the Universe. Studying the most extreme cases of these phenomena allows us to constrain the limits for the progenitor models. In this Letter, we study the prompt emission, afterglow, and host galaxy of GRB 120624B, one of the brightest GRBs detected by Fermi, to derive the energetics of the event and characterise the host galaxy in which it was produced. Following the high-energy detection we conducted a multi-wavelength follow-up campaign, including near-infrared imaging from HAWKI/VLT, optical from OSIRIS/GTC, X-ray observations from the Chandra X-ray Observatory and at sub-millimetre/millimetre wavelengths from SMA. Optical/nIR spectroscopy was performed with X-shooter/VLT. We detect the X-ray and nIR afterglow of the burst and determine a redshift of z = 2.1974 +/- 0.0002 through the identification of emission lines of [OII], [OIII] and H-alpha from the host galaxy of the GRB. This implies an energy release of Eiso = (3.0+/-0.2)x10^54 erg, amongst the most luminous ever detected. The observations of the afterglow indicate high obscuration with AV > 1.5. The host galaxy is compact, with R1/2 < 1.6 kpc, but luminous, at L ~ 1.5 L* and has a star formation rate of 91 +/- 6 Msol/yr as derived from H-alpha. As other highly obscured GRBs, GRB 120624B is hosted by a luminous galaxy, which we also proof to be compact, with a very intense star formation. It is one of the most luminous host galaxies associated with a GRB, showing that the host galaxies of long GRBs are not always blue dwarf galaxies, as previously thought.
    Astronomy and Astrophysics 09/2013; 557. DOI:10.1051/0004-6361/201322065 · 4.48 Impact Factor
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    ABSTRACT: We present high-resolution (~2.5") observations of 12CO J=6-5 towards the luminous infrared galaxy VV 114 using the Submillimeter Array. We detect 12CO J=6-5 emission from the eastern nucleus of VV 114 but do not detect the western nucleus or the central region. We combine the new 12CO J=6-5 observations with previously published or archival low-J CO observations, that include 13CO J=1-0 Atacama Large Millimeter/submillimeter Array cycle 0 observations, to analyze the beam-averaged physical conditions of the molecular gas in the eastern nucleus. We use the radiative transfer code RADEX and a Bayesian likelihood code to constrain the temperature (T_kin), density (n(H2)) and column density (N(12CO)) of the molecular gas. We find that the most probable scenario for the eastern nucleus is a cold (T_kin = 38 K), moderately dense (n(H2) = 10^2.89 cm^-3) molecular gas component. We find the most probable 12CO to 13CO abundance ratio ([12CO]/[13CO]) is 229, roughly three times higher than the Milky Way value. This high abundance ratio may explain the observed high 12CO/ 13CO line ratio (> 25). The unusual 13CO J=2-1/J=1-0 line ratio of 0.6 is produced by a combination of moderate 13CO optical depths (tau = 0.4 - 1.1) and extremely subthermal excitation temperatures. We measure the CO-to-H2 conversion factor, alpha_co to be 0.5 M_sol (K km s^-1 pc^2)^-1, which agrees with the widely used factor for ultra luminous infrared galaxies of Downes & Solomon (1998; alpha_co =0.8 M_sol (K km s^-1 pc^2)^-1).
    The Astrophysical Journal 09/2013; 777(2). DOI:10.1088/0004-637X/777/2/126 · 6.28 Impact Factor
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    ABSTRACT: Massive present-day early-type (elliptical and lenticular) galaxies probably gained the bulk of their stellar mass and heavy elements through intense, dust-enshrouded starbursts-that is, increased rates of star formation-in the most massive dark-matter haloes at early epochs. However, it remains unknown how soon after the Big Bang massive starburst progenitors exist. The measured redshift (z) distribution of dusty, massive starbursts has long been suspected to be biased low in z owing to selection effects, as confirmed by recent findings of systems with redshifts as high as ∼5 (refs 2-4). Here we report the identification of a massive starburst galaxy at z = 6.34 through a submillimetre colour-selection technique. We unambiguously determined the redshift from a suite of molecular and atomic fine-structure cooling lines. These measurements reveal a hundred billion solar masses of highly excited, chemically evolved interstellar medium in this galaxy, which constitutes at least 40 per cent of the baryonic mass. A 'maximum starburst' converts the gas into stars at a rate more than 2,000 times that of the Milky Way, a rate among the highest observed at any epoch. Despite the overall downturn in cosmic star formation towards the highest redshifts, it seems that environments mature enough to form the most massive, intense starbursts existed at least as early as 880 million years after the Big Bang.
    Nature 04/2013; 496(7445):329-333. DOI:10.1038/nature12050 · 42.35 Impact Factor
  • S. Martin · A. de Ugarte Postigo · G. Petitpas
  • Y. Matsuda · D. Iono · K. Ohta · T. Yamada · R. Kawabe · T. Hayashino · A. B. Peck · G. R. Petitpas
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    ABSTRACT: We present ∼ 2 ′ ′ resolution submillimeter observations of the submillimeter luminous giant Lyα blob (LAB1) in the SSA 22 protocluster at redshift z = 3.1 with the Submillimeter Array (SMA). Although the expected submillimeter flux density is 16 mJy at 880µm, no emission is detected with the 2. ′ ′ 4 × 1. ′ ′ 9 (18 × 14 kpc) beam at the 3σ level of 4.2 mJy beam −1 in the SMA field of view of 35 ′ ′. This is in contrast to the previous lower angular resolution (15 ′ ′ ) observations where a bright (17 mJy) unresolved submillimeter source was detected at 850µm toward the LAB1 using the Submillimeter Common-User Bolometer Array on the James Clerk Maxwell Telescope. The SMA non-detection suggests that the spatial extent of the submillimeter emission of LAB1 should be larger than 4 ′ ′ (> 30 kpc). The most likely interpretation of the spatially extended submillimeter emission is that starbursts occur throughout the large area in LAB1. Some part of the submillimeter emission may come from spatially extended dust expelled from starburst regions by galactic superwind. The spatial extent of the submillimeter emission of LAB1 is similar to those of high redshift radio galaxies rather than submillimeter galaxies.
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    ABSTRACT: We have used the Submillimeter Array (SMA) to make the first interferometric observations (beam size ∼ 1 ′ ′ , or ∼ 400 pc) of the 12 CO J=6-5 line and 435 µm (690 GHz) continuum emission toward the central region (half power field of view 17 ′ ′ ) of the nearby ultra-luminous infrared galaxy (ULIRG) Arp 220. These observations resolve the eastern and western nuclei from each other, in both the molecular line and dust continuum emission. At 435 µm, the peak intensity of the western nucleus is stronger than the eastern nucleus, and the difference in peak intensities is less than at longer wavelengths. Fitting a simple model to the dust emission observed between 1.3 mm and 435 µm suggests that dust emissivity power law index in the western nucleus is near unity and steeper in the eastern nucleus, about 2, and that the dust emission is optically thick at the shorter wavelength. Comparison with single dish measurements indicate that the interferometer observations are missing ∼ 60 % of the dust emission, most likely from a spatially extended component to which these observations are not sensitive. The 12 CO J=6-5 line observations clearly resolve kinematically the two nuclei. The distribution and kinematics of the 12 CO J=6-5 line appear to be very similar to lower J CO lies observed at similar resolution. Analysis of multiple 12 CO line intensities indicates that the molecular
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    ABSTRACT: 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 L ′ CO(3−2) and LFIR 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 two 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.
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    ABSTRACT: We have used the Submillimeter Array to image a flux limited sample of seven submillimeter galaxies, selected by the AzTEC camera on the JCMT at 1.1 mm, in the COSMOS field at 890 µm with ∼ 2 ′ ′ resolution. All of the sources – two radio–bright and five radio–dim – are detected as single point–sources at high significance (> 6σ), with positions accurate to ∼ 0.2 ′ ′ that enable counterpart identification at other wavelengths observed with similarly high angular resolution. All seven have IRAC counterparts, but only two have secure counterparts in deep HST/ACS imaging. As compared to the two radio–bright sources in the sample, and those in previous studies, the five radio–dim sources in the sample (1) have systematically higher submillimeter–to–radio flux ratios, (2) have lower IRAC 3.6–8.0 µm fluxes, and (3) are not detected at 24µm. These properties, combined with size constraints at 890 µm (θ ∼ < 1.2 ′ ′), suggest that the radio–dim submillimeter galaxies represent a population of very dusty starbursts, with physical scales similar to local ultraluminous infrared galaxies, and an average redshift higher than radio–bright sources.
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    ABSTRACT: 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.
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    ABSTRACT: We present high resolution images of the 12 CO(2–1) emission in the central 1 ′ (1 kpc) of NGC 5128 (Centaurus A), observed using the Submillimeter Array. We elucidate for the first time the distribution and kinematics of the molecular gas in this region with a resolution of 6. ′ ′ 0 × 2. ′ ′ 4 (100 pc × 40 pc). We spatially resolve the circumnuclear molecular gas in the inner 24 ′ ′ × 12 ′ ′ (400 pc × 200 pc), which is elongated along a position angle P.A. ≃ 155 ◦ and perpendicular to the radio/X-ray jet. The SE and NW components of the circumnuclear gas are connected to molecular gas found at larger radii. This gas appears as two parallel filaments at P.A. = 120 ◦ , which are coextensive with the long sides of the 3 kiloparsec parallelogram shape of the previously observed dust continuum, as well as ionized and pure rotational H2 lines. Spatial and kinematical asymmetries are apparent in both the circumnuclear and outer gas, suggesting non-coplanar and/or non-circular motions. We extend to inner radii (r < 200 pc) previously studied warped disk models built to reproduce the central parallelogram-shaped structure. Adopting the warped disk model we would confirm a gap in emission between the radii r = 200 – 800 pc (12 ′ ′ – 50 ′ ′), as has been suggested previously. Although this model explains this prominent feature, however, our 12 CO(2 − −1) observations show relevant deviations from this model. Namely, the physical connection between the circumnuclear gas and that at larger radii, brighter SE and NW sides on the parallelogram-shaped feature, and an outer curvature of its long sides. Overall it resembles more
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    ABSTRACT: The James Clerk Maxwell Telescope Nearby Galaxies Legacy Survey (NGLS) comprises an H?i-selected sample of 155 galaxies spanning all morphological types with distances less than 25?Mpc. We describe the scientific goals of the survey, the sample selection and the observing strategy. We also present an atlas and analysis of the CO J=3 - 2 maps for the 47 galaxies in the NGLS which are also part of the Spitzer Infrared Nearby Galaxies Survey. We find a wide range of molecular gas mass fractions in the galaxies in this sample and explore the correlation of the far-infrared luminosity, which traces star formation, with the CO luminosity, which traces the molecular gas mass. By comparing the NGLS data with merging galaxies at low and high redshift, which have also been observed in the CO J=3 - 2 line, we show that the correlation of far-infrared and CO luminosity shows a significant trend with luminosity. This trend is consistent with a molecular gas depletion time which is more than an order of magnitude faster in the merger galaxies than in nearby normal galaxies. We also find a strong correlation of the LFIR/LCO(3-2) ratio with the atomic-to-molecular gas mass ratio. This correlation suggests that some of the far-infrared emission originates from dust associated with atomic gas and that its contribution is particularly important in galaxies where most of the gas is in the atomic phase.
    Monthly Notices of the Royal Astronomical Society 08/2012; 424(4):3050-3080. DOI:10.1111/j.1365-2966.2012.21453.x · 5.23 Impact Factor
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    ABSTRACT: The James Clerk Maxwell Telescope Nearby Galaxies Legacy Survey (NGLS) comprises an HI-selected sample of 155 galaxies spanning all morphological types with distances less than 25 Mpc. We describe the scientific goals of the survey, the sample selection, and the observing strategy. We also present an atlas and analysis of the CO J=3-2 maps for the 47 galaxies in the NGLS which are also part of the Spitzer Infrared Nearby Galaxies Survey. We find a wide range of molecular gas mass fractions in the galaxies in this sample and explore the correlation of the far-infrared luminosity, which traces star formation, with the CO luminosity, which traces the molecular gas mass. By comparing the NGLS data with merging galaxies at low and high redshift which have also been observed in the CO J=3-2 line, we show that the correlation of far-infrared and CO luminosity shows a significant trend with luminosity. This trend is consistent with a molecular gas depletion time which is more than an order of magnitude faster in the merger galaxies than in nearby normal galaxies. We also find a strong correlation of the L(FIR)/L(CO3-2) ratio with the atomic to molecular gas mass ratio. This correlation suggests that some of the far-infrared emission originates from dust associated with atomic gas and that its contribution is particularly important in galaxies where most of the gas is in the atomic phase.
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    ABSTRACT: We have constructed a five station 12 GHz atmospheric phase interferometer (API) for the Submillimeter Array (SMA) located near the summit of Mauna Kea, Hawaii. Operating at the base of unoccupied SMA antenna pads, each station employs a commercial low noise mixing block coupled to a 0.7 m off-axis satellite dish which receives a broadband, white noise-like signal from a geostationary satellite. The signals are processed by an analog correlator to produce the phase delays between all pairs of stations with projected baselines ranging from 33 to 261 m. Each baseline's amplitude and phase is measured continuously at a rate of 8 kHz, processed, averaged and output at 10 Hz. Further signal processing and data reduction is accomplished with a Linux computer, including the removal of the diurnal motion of the target satellite. The placement of the stations below ground level with an environmental shield combined with the use of low temperature coefficient, buried fiber optic cables provides excellent system stability. The sensitivity in terms of rms path length is 1.3 microns which corresponds to phase deviations of about 1 degree of phase at the highest operating frequency of the SMA. The two primary data products are: (1) standard deviations of observed phase over various time scales, and (2) phase structure functions. These real-time statistical data measured by the API in the direction of the satellite provide an estimate of the phase front distortion experienced by the concurrent SMA astronomical observations. The API data also play an important role, along with the local opacity measurements and weather predictions, in helping to plan the scheduling of science observations on the telescope.
    05/2012; 1(1). DOI:10.1142/S225117171250002X

Publication Stats

1k Citations
337.81 Total Impact Points

Institutions

  • 2007–2015
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
  • 2009
    • National Astronomical Observatory of Japan
      • Astronomy Data Center
      Edo, Tōkyō, Japan
  • 2004
    • Loyola University Maryland
      Baltimore, Maryland, United States
  • 2003
    • University of Maryland, College Park
      • Department of Astronomy
      Maryland, United States
  • 1997–2002
    • McMaster University
      • Department of Physics and Astronomy
      Hamilton, Ontario, Canada