G. J. Stacey

Observatoire de Paris, Lutetia Parisorum, Île-de-France, France

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Publications (295)493.77 Total impact

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    ABSTRACT: We report the detection of 158 mum [C II] fine-structure line emission from MIPS J142824.0+352619, a hyperluminous (L IR ~ 1013 L sun) starburst galaxy at z = 1.3. The line is bright, corresponding to a fraction L [C II]/L FIR ≈ 2 × 10-3 of the far-IR (FIR) continuum. The [C II], CO, and FIR continuum emission may be modeled as arising from photodissociation regions (PDRs) that have a characteristic gas density of n ~ 104.2 cm-3, and that are illuminated by a far-UV radiation field ~103.2 times more intense than the local interstellar radiation field. The mass in these PDRs accounts for approximately half of the molecular gas mass in this galaxy. The L [C II]/L FIR ratio is higher than observed in local ultraluminous infrared galaxies or in the few high-redshift QSOs detected in [C II], but the L [C II]/L FIR and L CO/L FIR ratios are similar to the values seen in nearby starburst galaxies. This suggests that MIPS J142824.0+352619 is a scaled-up version of a starburst nucleus, with the burst extended over several kiloparsecs. Bibtex entry for this abstract Preferred format for this abstract (see Preferences) Find Similar Abstracts: Use: Authors Title Keywords (in text query field) Abstract Text Return: Query Results Return items starting with number Query Form Database: Astronomy Physics arXiv e-prints
    The Astrophysical Journal Letters 01/2010; 714. · 6.35 Impact Factor
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    ABSTRACT: We report the detection of the [CII]158 micron fine structure line from six submillimeter galaxies with redshifts between 1.12 and 1.73. This more than doubles the total number of [CII]158 micron detections reported from high redshift sources. These observations were made with the Redshift(z) and Early Universe Spectrometer(ZEUS) at the Caltech Submillimeter Observatory on Mauna Kea, Hawaii between December 2006 and March 2009. ZEUS is a background limited submm echelle grating spectrometer (Hailey-Dunsheath 2009). Currently we are constructing ZEUS-2. This new instrument will utilize the same grating but will feature a two dimensional transition-edge sensed bolometer array with SQUID multiplexing readout system enabling simultaneous background limited observations in the 200, 340, 450 and 650 micron telluric windows. ZEUS-2 will allow for long slit imaging spectroscopy in nearby galaxies and a [CII] survey from z 0.25 to 2.5.
    01/2010;
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    ABSTRACT: We have studied the molecular hydrogen energetics of the edge-on spiral galaxy NGC 891, using a 34 position map in the lowest three pure rotational H2 lines observed with the Spitzer Infrared Spectrograph. The S(0), S(1), and S(2) lines are bright with an extinction-corrected total luminosity of ~2.8 × 107 L sun, or 0.09% of the total-infrared luminosity of NGC 891. The H2 line ratios are nearly constant along the plane of the galaxy---we do not observe the previously reported strong drop-off in the S(1)/S(0) line intensity ratio in the outer regions of the galaxy, so we find no evidence for the very massive cold CO-free molecular clouds invoked to explain the past observations. The H2 level excitation temperatures increase monotonically indicating that there is more than one component to the emitting gas. More than 99% of the mass is in the lowest excitation (T ex ~ 125 K) "warm" component. In the inner galaxy, the warm H2 emitting gas is ~16% of the CO(1-0)-traced cool molecular gas, while in the outer regions the fraction is twice as high. This large mass of warm gas is heated by a combination of the far-UV photons from stars in photodissociation regions (PDRs) and the dissipation of turbulent kinetic energy. Including the observed far-infrared [O I] and [C II] fine-structure line emission and far-infrared continuum emission in a self-consistent manner to constrain the PDR models, we find essentially all of the S(0) and most (70%) of the S(1) line arise from low excitation PDRs, while most (80%) of the S(2) and the remainder of the S(1) line emission arise from low-velocity microturbulent dissipation.
    The Astrophysical Journal 01/2010; 721(1):59-73. · 6.73 Impact Factor
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    ABSTRACT: We have made the first detections of the 88 mum [O III] line from galaxies in the early universe, detecting the line from the lensed active galactic nucleus (AGN)/starburst composite systems APM 08279+5255 at z = 3.911 and SMM J02399-0136 at z = 2.8076. The line is exceptionally bright from both systems, with apparent (lensed) luminosities ~1011 L sun. For APM 08279, the [O III] line flux can be modeled in a star formation paradigm, with the stellar radiation field dominated by stars with effective temperatures, T eff > 36,000 K, similar to the starburst found in M82. The model implies ~35% of the total far-IR luminosity of the system is generated by the starburst, with the remainder arising from dust heated by the AGN. The 88 mum line can also be generated in the narrow-line region of the AGN if gas densities are around a few 1000 cm-3. For SMM J02399, the [O III] line likely arises from H II regions formed by hot (T eff > 40,000 K) young stars in a massive starburst that dominates the far-IR luminosity of the system. The present work demonstrates the utility of the [O III] line for characterizing starbursts and AGN within galaxies in the early universe. These are the first detections of this astrophysically important line from galaxies beyond a redshift of 0.05.
    The Astrophysical Journal 01/2010; 714(1). · 6.73 Impact Factor
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    ABSTRACT: Within the framework of the HERM33ES key project, we are studying the star forming interstellar medium in the nearby, metal-poor spiral galaxy M33, exploiting the high resolution and sensitivity of Herschel. We use PACS and SPIRE maps at 100, 160, 250, 350, and 500 micron wavelength, to study the variation of the spectral energy distributions (SEDs) with galacto-centric distance. Detailed SED modeling is performed using azimuthally averaged fluxes in elliptical rings of 2 kpc width, out to 8 kpc galacto-centric distance. Simple isothermal and two-component grey body models, with fixed dust emissivity index, are fitted to the SEDs between 24 and 500 micron using also MIPS/Spitzer data, to derive first estimates of the dust physical conditions. The far-infrared and submillimeter maps reveal the branched, knotted spiral structure of M33. An underlying diffuse disk is seen in all SPIRE maps (250-500 micron). Two component fits to the SEDs agree better than isothermal models with the observed, total and radially averaged flux densities. The two component model, with beta fixed at 1.5, best fits the global and the radial SEDs. The cold dust component clearly dominates; the relative mass of the warm component is less than 0.3% for all the fits. The temperature of the warm component is not well constrained and is found to be about 60K plus/minus 10K. The temperature of the cold component drops significantly from about 24K in the inner 2 kpc radius to 13K beyond 6 kpc radial distance, for the best fitting model. The gas-to-dust ratio for beta=1.5, averaged over the galaxy, is higher than the solar value by a factor of 1.5 and is roughly in agreement with the subsolar metallicity of M33.
    Astronomy and Astrophysics. 01/2010;
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    ABSTRACT: We have detected the 158 mum [C II] line from 12 galaxies at z ~ 1-2. This is the first survey of this important star formation tracer at redshifts covering the epoch of maximum star formation in the universe and quadruples the number of reported high-z [C II] detections. The line is very luminous, between
    The Astrophysical Journal 01/2010; 724:957-974. · 6.73 Impact Factor
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    ABSTRACT: An updated Science Vision for the SOFIA project is presented, including an overview of the characteristics and capabilities of the observatory and first generation instruments. A primary focus is placed on four science themes: 'The Formation of Stars and Planets', 'The Interstellar Medium of the Milky Way', 'Galaxies and the Galactic Center' and 'Planetary Science'. Comment: 128 pages pdf format Version 2 corrects: Attribution for Figure 5-1 Definition of "SIS" Affiliation of one of the contributors to the Science Vision
    05/2009;
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    ABSTRACT: When and how did galaxies form and their metals accumulate? Over the last decade, this has moved from an archeological question to a live investigation: there is now a broad picture of the evolution of galaxies in dark matter halos: their masses, stars, metals and supermassive blackholes. Galaxies have been found and studied in which these formation processes are taking place most vigorously, all the way back in cosmic time to when the intergalactic medium (IGM) was still largely neutral. However, the details of how and why the interstellar medium (ISM) in distant galaxies cools, is processed, recycled and enriched in metals by stars, and fuels active galactic nuclei (AGNs) remain uncertain. In particular, the cooling of gas to fuel star formation, and the chemistry and physics of the most intensely active regions is hidden from view at optical wavelengths, but can be seen and diagnosed at mid- & far-infrared (IR) wavelengths. Rest-frame IR observations are important first to identify the most luminous, interesting and important galaxies, secondly to quantify accurately their total luminosity, and finally to use spectroscopy to trace the conditions in the molecular and atomic gas out of which stars form. In order to map out these processes over the full range of environments and large-scale structures found in the universe - from the densest clusters of galaxies to the emptiest voids - we require tools for deep, large area surveys, of millions of galaxies out to z~5, and for detailed follow-up spectroscopy. The necessary tools can be realized technically. Here, we outline the requirements for gathering the crucial information to build, validate and challenge models of galaxy evolution.
    04/2009;
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    ABSTRACT: The Molecular Hydrogen Explorer, H2 EX, was proposed in response to the ESA 2015 - 2025 Cosmic Vision Call as a medium class space mission with NASA and CSA participations. The mission, conceived to understand the formation of galaxies, stars and planets from molecular hydrogen, is designed to observe the first rotational lines of the H2 molecule (28.2, 17.0, 12.3 and 9.7 mum) over a wide field, and at high spectral resolution. H2 EX can provide an inventory of warm (>= 100 K) molecular gas in a broad variety of objects, including nearby young star clusters, galactic molecular clouds, active galactic nuclei, local and distant galaxies. The rich array of molecular, atomic and ionic lines, as well as solid state features available in the 8 to 29 mum spectral range brings additional science dimensions to H2 EX. We present the optical and mechanical design of the H2 EX payload based on an innovative Imaging Fourier Transform Spectrometer fed by a 1.2 m telescope. The 20'×20' field of view is imaged on two 1024×1024 Si:As detectors. The maximum resolution of 0.032 cm - 1 (full width at half maximum) means a velocity resolution of 10 km s - 1 for the 0 - 0 S(3) line at 9.7 mum. This instrument offers the large field of view necessary to survey extended emission in the Galaxy and local Universe galaxies as well as to perform unbiased extragalactic and circumstellar disks surveys. The high spectral resolution makes H2 EX uniquely suited to study the dynamics of H2 in all these environments. The mission plan is made of seven wide-field spectro-imaging legacy programs, from the cosmic web to galactic young star clusters, within a nominal two years mission. The payload has been designed to re-use the Planck platform and passive cooling design.
    Experimental Astronomy 03/2009; 23(1):277-302. · 2.97 Impact Factor
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    ABSTRACT: We report the first astronomical detection of a far-IR emission line at (69.524 ± 0.008) μm from aboard the Kuiper Airborne Observatory (KAO). We tentatively assign this line to the R-branch transition 43− → 33+ of H3O+. The wavelength of the discovered line lies between -112 and -60 km s-1 from predicted values. The position at which the emission line was detected is located about 20'' north of Orion BN, which is close to the shocked molecular hydrogen peak 1. We exclude hot shocked gas as the possible origin of the H3O+ emission. Hydrogen densities of 5 × 108 cm-3 and temperatures 100 K are required to match the observed integrated intensity of the 70 μm line. A speculative explanation for the 70 μm H3+O emission is that it might originate from very dense clumps.
    The Astrophysical Journal 01/2009; 463(2):L109. · 6.73 Impact Factor
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    ABSTRACT: We report measurements of the [C II] fine-structure line at 157.714 μm in 30 normal star-forming galaxies with the Long Wavelength Spectrometer (LWS) on the Infrared Space Observatory (ISO). The ratio of the line to total far-infrared (FIR) luminosity, LC II/LFIR, measures the ratio of the cooling of gas to that of dust, and thus the efficiency of the grain photoelectric heating process. This ratio varies by more than a factor of 40 in the current sample. About two-thirds of the galaxies have LC II/LFIR ratios in the narrow range of (2-7) × 10−3. The other one-third show trends of decreasing LC II/LFIR with increasing dust temperature, as measured by the flux ratio of infrared emission at 60 and 100 μm, Fν(60 μm)/Fν(100 μm), and with increasing star formation activity, measured by the ratio of FIR and blue-band luminosity, LFIR/LB. We also find three FIR-bright galaxies that are deficient in the [C II] line, which is undetected with 3 σ upper limits of LC II/LFIR < (0.5-2) × 10−4. The trend in the LC II/LFIR ratio with the temperature of dust and with star formation activity may be due to decreased efficiency of photoelectric heating of gas at high UV radiation intensity as dust grains become positively charged, decreasing the yield and the energy of the photoelectrons. The three galaxies with no observed photodissociation region lines have among the highest LFIR/LB and Fν(60 μm)/Fν(100 μm) ratios. Their lack of [C II] lines may be due to a continuing trend of decreasing LC II/LFIR with increasing star formation activity and dust temperature seen in one-third of the sample with warm IRAS colors. In that case, the upper limits on LC II/LFIR imply a ratio of UV flux to gas density of G0/n>10 cm3 (where G0 is in units of the local average interstellar field). The low LC II/LFIR ratio could also be due to either weak [C II], owing to self-absorption, or a strong FIR continuum from regions weak in [C II], such as dense H II regions or plasma ionized by hard radiation of active galactic nuclei. The mid-infrared and radio images of these galaxies show that most of the emission comes from a compact nucleus. CO and H I are detected in these galaxies, with H I seen in absorption toward the nucleus.
    The Astrophysical Journal 01/2009; 491(1):L27. · 6.73 Impact Factor
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    ABSTRACT: We report measurements of the [C II] 157.74 μm fine-structure line in a sample of seven ultraluminous infrared galaxies (ULIGs) (LIR > 1012 L☉) with the Long Wavelength Spectrometer on the Infrared Space Observatory. The [C II] line is an important coolant in galaxies and arises in interstellar gas exposed to far-ultraviolet photons (hν≥11.26 eV); in ULIGs, this radiation stems from the bursts of star formation and/or from the active galactic nuclei that power the tremendous infrared luminosity. The [C II] 158 μm line is detected in four of the seven ULIGs; the absolute line flux (about a few times 10-20 W cm-2) represents some of the faintest extragalactic[C II] emission yet observed. Relative to the far-infrared continuum, the [C II] flux from the observed ULIGs is ~10% of that seen from nearby normal and starburst galaxies. We discuss possible causes for the [C II] deficit, namely (1) self-absorbed or optically thick [C II] emission, (2) saturation of the [C II] emission in photodissociated gas with high gas density n (3 × 103 cm-3) or with a high ratio of incident UV flux G0 to n (G0/n 10 cm3), or (3) the presence of a soft ultraviolet radiation field caused, for example, by a stellar population deficient in massive main-sequence stars. As nearby examples of colliding galaxies, ULIGs may resemble high-redshift protogalaxies in both morphology and spectral behavior. If true, the suggested [C II] deficit in ULIGs poses limitations on the detection rate of high-z sources and on the usefulness of [C II] as an eventual tracer of protogalaxies.
    The Astrophysical Journal 01/2009; 504(1):L11. · 6.73 Impact Factor
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    ABSTRACT: We present the first complete far-infrared spectrum (43-197 μm) of M82, the brightest infrared galaxy in the sky, taken with the Long Wavelength Spectrometer of the Infrared Space Observatory (ISO). We detected seven fine structure emission lines, [O I] 63 and 145 μm, [O III] 52 and 88 μm , [N II] 122 μm, [N III] 57 μm, and [C II] 158 μm, and fitted their ratios to a combination starburst and photodissociation region (PDR) model. The best fit is obtained with H II regions with n=250 cm-3, an ionization parameter of 10-3.5, and PDRs with n=103.3 cm-3 and a far-ultraviolet flux of G0=102.8. We applied both continuous and instantaneous starburst models, with our best fit being a 3-5 Myr old instantaneous burst model with a 100 M☉ cutoff. We also detected the ground-state rotational line of OH in absorption at 119.4 μm. No excited level OH transitions are apparent, indicating that the OH is almost entirely in its ground state with a column density ~4×1014 cm-2. The spectral energy distribution over the long-wavelength spectrometer wavelength range is well fitted with a 48 K dust temperature and an optical depth, τDust λ-1.
    The Astrophysical Journal 01/2009; 511(2):721. · 6.73 Impact Factor
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    V. Charmandaris, G. J. Stacey, and G. Gull
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    ABSTRACT: We present new 37.7 μm far-infrared imaging of the infrared luminous (LIR ~ 5.16 × 1011 L☉) interacting galaxy Arp 299 (= IC 694 + NGC 3690). We show that the 38 μm flux, like the 60 and 100 μm emission, traces the luminosity of star forming galaxies but at considerably higher spatial resolution. Our data establish that the major star formation activity of the galaxy originates from a point source in its eastern component, IC 694, which is inconspicuous in the optical, becoming visible only at the near- and mid-infrared. We find that IC 694 is 2 times more luminous than NGC 3690, contributing to more than 46% of the total energy output of the system at this wavelength. The spectral energy distribution of the different components of the system clearly shows that IC 694 has 6 times the infrared luminosity of M82, and it is the primary source responsible for the bolometric luminosity of Arp 299.
    The Astrophysical Journal 12/2008; 571(1):282. · 6.73 Impact Factor
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    ABSTRACT: Using the large multiwavelength data set in the Chandra/SWIRE Survey (0.6 deg2 in the Lockman Hole), we show evidence for the existence of highly obscured (Compton-thick) AGNs, estimate a lower limit to their surface density, and characterize their multiwavelength properties. Two independent selection methods based on the X-ray and infrared spectral properties are presented. The two selected samples contain (1) five X-ray sources with hard X-ray spectra and column densities 1024 cm-2 and (2) 120 infrared sources with red and AGN-dominated infrared SEDs. We estimate a surface density of at least 25 Compton-thick AGNs deg-2 detected in the infrared in the Chandra/SWIRE field, of which ~40% show distinct AGN signatures in their optical/near-infrared SEDs, the remaining being dominated by the host galaxy emission. Only ~33% of all Compton-thick AGNs are detected in the X-rays at our depth [F(0.3-8 keV) > 10-15 ergs cm-2 s-1]. We report the discovery of two sources in our sample of Compton-thick AGNs, SWIRE J104409.95+585224.8 (z = 2.54) and SWIRE J104406.30+583954.1 (z = 2.43), which are the most luminous Compton-thick AGNs at high z currently known. The properties of these two sources are discussed in detail with an analysis of their spectra, SEDs, luminosities, and black hole masses.
    The Astrophysical Journal 12/2008; 642(2):673. · 6.73 Impact Factor
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    ABSTRACT: We report the first detection of the 205 μm 3P1 P0 [N II] line from a ground-based observatory using a direct detection spectrometer. The line was detected from the Carina star formation region using the South Pole Imaging Fabry-Perot Interferometer (SPIFI) on the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) at the South Pole. The [N II] 205 μm line strength indicates a low-density (n ~ 32 cm-3) ionized medium, similar to the low-density ionized halo previously reported in its [O III] 52 and 88 μm line emission. When compared with the Infrared Space Observatory [C II] observations of this region, we find that 27% of the [C II] line emission arises from this low-density ionized gas, but the large majority (~73%) of the observed [C II] line emission arises from the neutral interstellar medium. This result supports and underpins prior conclusions that most of the observed [C II] 158 μm line emission from Galactic and extragalactic sources arises from the warm, dense photodissociated surfaces of molecular clouds. The detection of the [N II] line demonstrates the utility of Antarctic sites for THz spectroscopy.
    The Astrophysical Journal 12/2008; 652(2):L125. · 6.73 Impact Factor
  • Thomas Nikola, Gordon J. Stacey, C. Matt Bradford
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    ABSTRACT: We present a trade study for a submillimeter direct-detection spectrometer operating at the background limit for the Cornell Caltech Atacama Telescope (CCAT). In this study we compare the classical echelle spectrometer ZEUS with the waveguide grating spectrometer Z-Spec. The science driver for this instrument is spectroscopic investigation of high redshift galaxies as their far-IR fine structure line emission is redshifted into the telluric submillimeter windows. The baseline detector consists of SQUID multiplexed TES bolometers and the ideal spectrometer to detect weak lines from distant extragalactic sources is a grating with a resolution of ~103 and a large bandwidth, covering an entire telluric submillimeter window instantaneously. Since the density of high-z sources on the sky is ~100 within a 10'×10' field of view and a redshift range of Deltaz~0.2 we also explore multi-object (~50 objects) capability, including articulated mirrors and flexible waveguide fibers.
    Proc SPIE 08/2008;
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    ABSTRACT: We propose to accurately trace molecular gas excitation and mass along the plane of the two nearby nearby edge-on spiral galaxies, NGC 4905 and 5907 through deep IRS spectroscopy of four pure rotational lines (S(3), S(2), S(1), and S(0)) of H2. Our primary goal is to investigate the physical state, mass, and heating processes in the molecular ISM in these galaxies, and compare them with our on-going study of the edge-on galaxy NGC 891. Prior modeling of the S(1) and S(0) emission from NCG 891 suggests an enormous amount of cool (T< 90K) H2 (5 to 15 times the atomic mass) for this galaxy if the ortho to para H2 ratio is 3. However, these models are hampered by the degeneracy between gas excitation and the (assumed) o/p ratio. Including the S(3) and S(2) lines in the analysis breaks the degeneracy, enabling independent determination of gas excitation for the ortho and para species, and a measure of the o/p ratio. Using three lines (S(2), S(1), and S(0)) for NGC 891, we find gas excitation near 220 K, with an o/p ratio near unity, resulting in greatly reduced molecular gas mass. We were awarded time in Cycle 4 to verify this model through deeper integrations of the S(0), S(1), and S(2) lines, and observations of the S(3) line in NGC 891. {These observations have not yet been scheduled}. Here we propose to extend our study by mapping all four lines in the disks of galaxies with different gas contents than NGC 891: the early type Sb NGC 4565 and the late type Sc NGC 5907. We are particularly intrigued with the regions outside of the CO emitting disk where the gas is likely not heated in a PDR scenario but rather by modest velocity cloud-cloud collisions in the outer galaxy. The proposed observations address the heating source as the ortho and para ratio depends on the formation temperature: a larger ratio indicates a larger formation temperature. Did H2 form in a relatively warm far-UV bathed environment near stars, or in a cold environment devoid of young stars?
    Spitzer Proposal. 03/2008;
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    ABSTRACT: We report the first detection of a mid-J isotopic CO line from an external galaxy. We detected the 13CO (6-5) line from the starburst nucleus of NGC 253. The line is suprisingly bright with an integrated intensity 7% of the 12CO (6-5) line, indicating optical depth in the 12CO line. Our LVG modeling shows that a single warm (T ~ 120 K), dense (n ~ 104 cm-3) component emits most of the 12CO and 13CO line emission from J = 2-1 through J = 7-6. The CO(1-0) line comes from an additional lower excitation envelope. About 60% of the total molecular gas mass within 70 pc of the nucleus is in the warm, dense component. We show that stellar far-UV photons or X-ray photons from a nuclear source are unlikely to be the primary sources of the gas heating. The most likely sources of heat are cosmic rays from the nuclear starburst or microturbulence within molecular clouds.
    EAS Publications Series 01/2008; 31:151-154.

Publication Stats

2k Citations
493.77 Total Impact Points

Institutions

  • 2014
    • Observatoire de Paris
      Lutetia Parisorum, Île-de-France, France
  • 2013
    • Arizona State University
      • School of Earth and Space Exploration
      Phoenix, Arizona, United States
  • 2012
    • University of Hawaiʻi at Hilo
      Hilo, Hawaii, United States
  • 1992–2012
    • Cornell University
      • Department of Astronomy
      Ithaca, New York, United States
  • 1991–2009
    • University of California, Berkeley
      • Department of Physics
      Berkeley, CA, United States
  • 2001–2005
    • California Institute of Technology
      • Infrared Processing and Analysis Center
      Pasadena, California, United States
  • 1999
    • University of Texas at Austin
      • Department of Astronomy
      Austin, Texas, United States
  • 1997
    • Cornell College
      Cornell, Wisconsin, United States
  • 1996
    • University of Wyoming
      Laramie, Wyoming, United States