A Dust-Obscured Massive Maximum-Starburst Galaxy at a Redshift of 6.34
Dominik A. Riechers, C.M. Bradford, D.L. Clements, C.D. Dowell, I. Perez-Fournon, R.J. Ivison, C. Bridge, A. Conley, Hai Fu, J.D. Vieira, J. Wardlow, J. Calanog, A. Cooray, P. Hurley, R. Neri, J. Kamenetzky, J.E. Aguirre, B. Altieri, V. Arumugam, D.J. Benford, M. Bethermin, J. Bock, D. Burgarella, A. Cabrera-Lavers, S.C. Chapman, P. Cox, J.S. Dunlop, L. Earle, D. Farrah, P. Ferrero, A. Franceschini, R. Gavazzi, J. Glenn, E.A. Gonzalez Solares, M.A. Gurwell, M. Halpern, E. Hatziminaoglou, A. Hyde, E. Ibar, A. Kovacs, M. Krips, R.E. Lupu, P.R. Maloney, P. Martinez-Navajas, H. Matsuhara, E.J. Murphy, B.J. Naylor, H.T. Nguyen, S.J. Oliver, A. Omont, M.J. Page, G. Petitpas, N. Rangwala, I.G. Roseboom, D. Scott, A.J. Smith, J.G. Staguhn, A. Streblyanska, A.P. Thomson, I. Valtchanov, M. Viero, L. Wang, M. Zemcov, J. Zmuidzinas
AA Dust-Obscured Massive Maximum-Starburst Galaxy at a Redshift of 6.34
Dominik A. Riechers , C.M. Bradford , D.L. Clements , C.D. Dowell , I. Pérez-Fournon , R.J. Ivison , C. Bridge , A. Conley , Hai Fu , J.D. Vieira , J. Wardlow , J. Calanog , A. Cooray , P. Hurley , R. Neri , J. Kamenetzky , J.E. Aguirre , B. Altieri , V. Arumugam , D.J. Benford , M. Béthermin , J. Bock , D. Burgarella , A. Cabrera-Lavers , S.C. Chapman , P. Cox , J.S. Dunlop , L. Earle , D. Farrah , P. Ferrero , A. Franceschini , R. Gavazzi , J. Glenn , E.A. Gonzalez Solares , M.A. Gurwell , M. Halpern , E. Hatziminaoglou , A. Hyde , E. Ibar , A. Kovács , M. Krips , R.E. Lupu , P.R. Maloney , P. Martinez-Navajas , H. Matsuhara , E.J. Murphy , B.J. Naylor , H.T. Nguyen , S.J. Oliver , A. Omont , M.J. Page , G. Petitpas , N. Rangwala , I.G. Roseboom , D. Scott , A.J. Smith , J.G. Staguhn , A. Streblyanska , A.P. Thomson , I. Valtchanov , M. Viero , L. Wang , M. Zemcov , J. Zmuidzinas California Institute of Technology, 1200 East California Blvd., MC 249-17, Pasadena, CA 91125, USA Cornell University, 220 Space Sciences Building, Ithaca, NY 14853, USA Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109, USA Astrophysics Group, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK Instituto de Astrofisica de Canarias, E-38200 La Laguna, Tenerife, Spain Departamento de Astrofisica, Universidad de La Laguna, E-38205 La Laguna, Tenerife, Spain UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK Center for Astrophysics and Space Astronomy 389-UCB, University of Colorado, Boulder, CO 80309, USA Dept. of Physics & Astronomy, University of California, Irvine, CA 92697, USA Astronomy Centre, Dept. of Physics & Astronomy, University of Sussex, Brighton BN1 9QH, UK Institut de RadioAstronomie Millimetrique, 300 Rue de la Piscine, Domaine Universitaire, F-38406 Saint Martin d’Heres, France Dept. of Astrophysical and Planetary Sciences, CASA 389-UCB, University of Colorado, Boulder, CO 80309, USA Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104, USA Herschel Science Centre, European Space Astronomy Centre, Villanueva de la Cañada, 28691 Madrid, Spain Observational Cosmology Lab, Code 665, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA Laboratoire AIM-Paris-Saclay, CEA/DSM/Irfu - CNRS - Universite Paris Diderot, CEA-Saclay, point courrier 131, F-91191 Gif-sur-Yvette, France Institut d’Astrophysique Spatiale (IAS), batiment 121, Universite Paris-Sud 11 and CNRS, UMR 8617, F-91405 Orsay, France Aix-Marseille Universite, CNRS, Laboratoire d’Astrophysique de Marseille, UMR7326, F-13388 Marseille, France Grantecan S.A., Centro de Astrofisica de La Palma, Cuesta de San Jose, E-38712 Brena Baja, La Palma, Spain Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK Department of Physics, Virginia Tech, Blacksburg, VA 24061, USA Dipartimento di Fisica e Astronomia, Universita di Padova, vicolo Osservatorio, 3, I-35122 Padova, Italy Institut d’Astrophysique de Paris, UMR 7095, CNRS, UPMC Univ. Paris 06, 98bis boulevard Arago, F-75014 Paris, France Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA Department of Physics & Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada ESO, Karl-Schwarzschild-Str. 2, D-85748 Garching bei München, Germany Institute for Astrophysics, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455, USA Institute for Space and Astronautical Science, Japan Aerospace and Exploration Agency, Sagamihara, Kanagawa 229-8510, Japan Infrared Processing and Analysis Center, MS 100-22, California Institute of Technology, Pasadena, CA 91125, USA Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK Department of Physics & Astronomy, Johns Hopkins University, Baltimore, MD, 21218, USA
Riechers et al. (2013), Nature, in the press (under press embargo until 13:00 US Eastern time on 17 April 2013) 1 assive 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 halos at early epochs. However, it remains unknown how soon after the Big Bang such massive starburst progenitors exist. The measured redshift ( z ) distribution of dusty, massive starbursts has long been suspected to be biased low in redshift owing to selection effects, as confirmed by recent findings of systems out to redshift z ~5. Here we report the identification of a massive starburst galaxy at redshift 6.34 through a submillimeter color-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 (ISM) in this galaxy, which constitutes at least 40% 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 of 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. We have searched 21 deg of the Herschel /SPIRE data of the HerMES blank field survey at 250 – 500 µ m for “ultra-red” sources with flux densities S µ m < S µ m < S µ m and S µ m / S µ m >1.3, i.e., galaxies that are significantly redder (and thus, potentially at higher redshift) than massive starbursts discovered thus far. This selection yields five candidate ultra-red sources down to a flux limit of 30 mJy at 500 µ m (>5 σ and above the confusion noise; see Supplementary Information Section 1 for additional details), corresponding to a source density of ≤ -2 . For comparison, models of number counts in the Herschel /SPIRE bands suggest a space density of massive starburst galaxies at z >6 with S µ m >30 mJy of 0.014 deg -2 (ref. 7). To understand the nature of galaxies selected by this technique, we have obtained full frequency scans of the 3-mm and 1-mm bands toward HFLS3 (also known as 1HERMES S350 J170647.8+584623; S µ m / S µ m = 1.45), the brightest candidate discovered in our study. These observations, augmented by selected follow-up over a broader wavelength range, unambiguously determine the galaxy redshift to be z =6.3369+/-0.0009 based on a suite of 7 CO lines, 7 H O lines, and OH, OH + , H O + , NH , [CI], and [CII] lines detected in emission and absorption (Figure 1). At this redshift, the Universe was just 880 million years old (or 1/16 th of its present age), and 1” on the sky corresponds to a physical scale of 5.6 kpc. Further observations from optical to radio wavelengths reveal strong continuum emission over virtually the entire wavelength range between 2.2 µ m and 20 cm, with no detected emission shortward of 1 µ m (see Supplementary Information Section 2 and Figures S1-S11 for additional details). HFLS3 hosts an intense starburst. The 870 µ m -flux of HFLS3 is >3.5 times higher than those of the brightest high-redshift starbursts in a 0.25-deg region containing the Hubble Ultra Deep Field (HUDF). From the continuum spectral energy distribution (Fig. 2), we find that the far-infrared (FIR) luminosity L FIR and inferred star formation rate (SFR) of 2,900 M sun yr -1 of HFLS3 are 15-20 times those of the prototypical local ultra-luminous starburst Arp 220, and >2,000 times those of the Milky Way (Table 1 and Supplementary Information Section 3). The SFR of HFLS3 alone corresponds to ~4.5 times the ultraviolet-based SFR of all z =5.5-6.5 star-forming galaxies in the HUDF combined, but the rarity and dust obscuration of ultra-red sources like HFLS3 implies that they do not dominate the UV photon density needed to reionize the universe. HFLS3 is a massive, gas-rich galaxy. From the spectral energy distribution and the intensity of the CO and [CII] emission, we find a dust mass of M d =1.3 x 10 M sun and total molecular and atomic gas masses of M gas =1.0 x 10 M sun and M HI =2.0 x 10 M sun . These masses are 15-20 times those of Arp 220, and correspond to a gas-to-dust ratio of ~80 and a gas depletion timescale of M gas /SFR ~36 Myr. These values are comparable to lower-redshift submillimeter-selected starbursts. From the [CI] luminosity, we find an atomic carbon mass of 4.5 x 10 M sun . At the current star formation rate of HFLS3, this level of carbon enrichment could have been Riechers et al. (2013), Nature, in the press (under press embargo until 13:00 US Eastern time on 17 April 2013) 2 chieved through supernovae on a timescale of ~10 yr. The profiles of the molecular and atomic emission lines typically show two velocity components (Figs. 1, S5, and S7). The gas is distributed over a 1.7 kpc radius region with a high velocity gradient and dispersion (Fig. 3). This suggests a dispersion-dominated galaxy with a dynamical mass of M dyn = 2.7 x 10 M sun . The gas mass fraction in galaxies is a measure of the relative depletion and replenishment of molecular gas, and is expected to be a function of halo mass and redshift from simulations. In HFLS3, we find a high gas mass fraction of f gas = M gas / M dyn ~ 40%, comparable to what is found in submillimeter-selected starbursts and massive star-forming galaxies at z~2, but ~3 times higher than in nearby ultra-luminous infrared galaxies (ULIRGs) like Arp 220, and >30 times higher than in the Milky Way. From population synthesis modeling, we find a stellar mass of M * = 3.7 x 10 M sun , comparable to that of Arp 220 and about half that of the Milky Way. This suggests that at most ~40% of M dyn within the radius of the gas reservoir are due to dark matter. With up to ~10 M sun of dark matter within 3.4 kpc, HFLS3 likely resides in a dark matter halo massive enough to grow a present-day galaxy cluster. The efficiency for star formation is given by ε = t dyn x SFR/ M gas , where t dyn =( r /(2 GM )) is the dynamical (or free-fall) time, r is the source radius, M is the mass within radius r and G is the gravitational constant. For r =1.7kpc and M = M gas , this suggests ε =0.06, which is a few times higher than found in nearby starbursts and in Giant Molecular Cloud cores in the Galaxy. The properties of the atomic and molecular gas in HFLS3 are fully consistent with a highly enriched, highly excited interstellar medium, as typically found in the nuclei of warm, intense starbursts, but distributed over a large, ~3.5-kpc-diameter region. The observed CO and [CII] luminosities suggest that dust is the primary coolant of the gas if both are thermally coupled. The L [CII] / L FIR ratio of ~5 x 10 -4 is typical for high radiation environments in extreme starbursts and active galactic nucleus (AGN) host galaxies. The L [CII] / L CO(1-0) ratio of ~3,000 suggests that the bulk of the line emission is associated with the photon dominated regions of a massive starburst. At the L FIR of HFLS3, this suggests an infrared radiation field strength and gas density comparable to nearby ULIRGs without luminous AGN (Figs. 4 & 5 of ref. 19).
From the spectral energy distribution of HFLS3, we derive a dust temperature of T dust =56 +9-12 K, ~10 K less than in Arp 220, but ~3 times that of the Milky Way. CO radiative transfer models assuming collisional excitation suggest a gas kinetic temperature of T kin =144 +59-30 K and a gas density of log ( n (H ))=3.80 +0.28-0.17 cm -3 (Supplementary Information Section 4 and Figures S13/S14). These models suggest similar gas densities as in nearby ULIRGs, and prefer T kin >> T dust , which may imply that the gas and dust are not in thermal equilibrium, and that the excitation of the molecular lines may be partially supported by the underlying infrared radiation field. This is consistent with the finding that we detect H O and OH lines with upper level energies of E / k B > 300-450 K and critical densities of >10 cm -3 at line intensities exceeding those of the CO lines. The intensities and ratios of the detected H O lines cannot be reproduced by radiative transfer models assuming collisional excitation, but are consistent with being radiatively pumped by far-infrared photons, at levels comparable to those observed in Arp 220 (Figures S15/S16).
The CO and H O excitation is inconsistent with what is observed in quasar host galaxies like Mrk 231 and APM08279+5255 at z =3.9, which lends support to the conclusion that the gas is excited by a mix of collisions and infrared photons associated with a massive, intense starburst, rather than hard radiation associated with a luminous AGN. The physical conditions in the ISM of HFLS3 thus are comparable to those in the nuclei of the most extreme nearby starbursts, consistent with the finding that it follows the radio-FIR correlation for star-forming galaxies.
HFLS3 is rapidly assembling its stellar bulge through star formation at surface densities close to the theoretically predicted limit for “maximum starbursts”. At a rest-frame wavelength of 158 µ m, the FIR emission is distributed over a relatively compact area of 2.6 kpc x 2.4 kpc physical diameter along its major and minor axes respectively (Fig. 3; as determined by elliptical Gaussian fitting). This suggests an extreme star formation rate surface density of Σ SFR ~600 M sun yr -1 kpc -2 over a 1.3-kpc-radius region, and is consistent with near-Eddington-limited star formation if the starburst disk is supported by radiation pressure. This suggests the presence of a kiloparsec-scale hyper-starburst similar to that found in the z=6.42 quasar
Riechers et al. (2013), Nature, in the press (under press embargo until 13:00 US Eastern time on 17 April 2013) 3 Such high Σ SFR are also observed in the nuclei of local ULIRGs such as Arp 220, albeit on two orders of magnitude smaller scales. A starburst at such high Σ SFR may produce strong winds.
Indeed, the relative strength and broad, asymmetric profile of the OH Π (3/2-1/2) doublet detected in HFLS3 may indicate a molecular outflow, reminiscent of the OH outflow in Arp 220. The identification of HFLS3 alone is still consistent with the model-predicted space density of massive starburst galaxies at z >6 with S µ m > 30 mJy of 0.014 deg -2 (ref. 7). This corresponds to only 10 -3 -10 -4 times the space density of Lyman-break galaxies at the same redshift, but is comparable to the space density of the most luminous quasars hosting supermassive black holes (SMBHs, i.e., a different population of massive galaxies) at such early cosmic times. The host galaxies around these very distant SMBHs are commonly FIR-luminous, but less intensely star-forming, with typically a few times lower L FIR than ultra-red sources. This highlights the difference between selecting massive z>6 galaxies at the peak of their star formation activity through L FIR , and at the peak of their black hole activity through luminous AGN. The substantial population of ultra-red sources discovered with Herschel will be an ideal probe of early galaxy evolution and heavy element enrichment within the first billion years of cosmic time. These galaxies are unlikely to dominate the star formation history of the Universe at z>6, but they trace the highest peaks in SFR at early epochs. A detailed study of this galaxy population will reveal the mass and redshift distribution, number density and likely environments of such objects, which if confirmed in larger numbers may present a stern challenge to current models of early cosmic structure formation. References:
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Supplementary Information
Acknowledgments:
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. This research has made use of data from HerMES project (http://hermes.sussex.ac.uk/). HerMES is a Herschel Key Programme utilising Guaranteed Time from the SPIRE instrument team, ESAC scientists and a mission scientist. See Supplementary Information for further acknowledgments.
Author Contributions:
D.R. had the overall lead of the project. C.M.B., D.C., I.P.-F., R.I., C.B., H.F., J.V., and R.N. have contributed significantly to the taking and analysis of the follow-up data with different instruments by leading several telescope proposals and analysis efforts. C.D.D. has led the selection of the parent sample. A.C., J.W., J.C., A.C., P.H., and J.K. have contributed significantly to the data analysis and to fitting and modeling the results. All other authors contributed to the proposals, source selection, data analysis and interpretation, in particular through work on the primary
Herschel
SPIRE data in which the source was discovered through the HerMES consortium (led by J.B. and S.O.). All authors have reviewed, discussed, and commented on the manuscript.
Competing Interest Statement:
The authors declare that they have no competing financial interests.
Corresponding authors:
Correspondence and requests for material should be addressed to Dominik Riechers ([email protected]).
Riechers et al. (2013), Nature, in the press (under press embargo until 13:00 US Eastern time on 17 April 2013) 5 igures:
Figure 1:
Redshift identification through molecular and atomic spectroscopy of HFLS3. a , Black trace, wide-band spectroscopy in the observed-frame 19 - 0.95-mm (histogram; rest-frame 2,600 - 130 µ m) wavelength range with CARMA (3 mm; “blind” frequency scan of the full band), the PdBI (2 mm), the JVLA (19 - 6 mm), and CSO/Z-spec (1 mm; instantaneous coverage). (CARMA, Combined Array for Research in Millimeter-wave Astronomy; PdBI, Plateau de Bure Interferometer; JVLA, Jansky Very Large Array; and CSO, Caltech Submillimeter Observatory) This uniquely determines the redshift of HFLS3 to be z =6.3369 based on the detection of a series of H O, CO, OH, OH + , NH , [CI] and [CII] emission and absorption lines. b to o , Detailed profiles of detected lines (histograms; rest frequencies are indicated by corresponding letters in a ). 1-mm lines ( m - o ) are deeper, interferometric confirmation observations for NH , OH (both PdBI), and [CII] (CARMA) not shown in a . The line profiles are typically asymmetric relative to single Gaussian fits, indicating the presence of two principal velocity components at redshifts of 6.3335 and 6.3427. The implied CO, [CI], and [CII] line luminosities are 5.08+/-0.45 x 10 , 3.0+/-1.9 x 10 , and 1.55+/-0.32 x 10 L sun . Strong rest-frame submillimeter to far-infrared continuum emission is detected over virtually the entire wavelength range. For comparison, the Herschel /SPIRE spectrum of the nearby ultra-luminous infrared galaxy Arp 220 is overplotted in grey ( a ). Lines labeled in italic are tentative detections or upper limits (see Table S2). Most of the bright spectral features detected in Arp 220 are also detected in HFLS3 (in spectral regions not blocked by the terrestrial atmosphere). See Supplementary Information Sections 2-4 for more details. Riechers et al. (2013), Nature, in the press (under press embargo until 13:00 US Eastern time on 17 April 2013) 6 -1 (cid:104) obs ( µ m)10 -5 -4 -3 -2 -1 f l u x ( m Jy ) AB m ag (cid:105) rest (GHz) MBBArp220M82HR10Eyelash (a) HFLS3 0 1 2 3 4 5S /S S / S z=1 2 3 4 5678z=1 2 3 45 6 7 8 HFLS3 z=6.34HLS A773 z=5.24HATLAS ID141 z=4.24HFLS1 z=4.29HFLS5 z=4.44HLock102 z=5.29 S > S S > S S > 1.3 S Arp220M82HR10Eyelash(b)250 µm 500 µm1’ 350 µm
Figure 2:
Spectral energy distribution (SED) and
Herschel /SPIRE colors of HFLS3. a , HFLS3 was identified as a very high redshift candidate, as it appears red between the Herschel /SPIRE 250-, 350-, and 500- µ m bands (inset). The SED of the source (data points; λ obs , observed-frame wavelength; ν rest , rest-frame frequency; AB mag, magnitudes in the AB system; error bars are 1 σ r.m.s. uncertainties in both panels) is fitted with a modified black body (MBB; solid line) and spectral templates for the starburst galaxies Arp 220, M82, HR10, and the Eyelash (broken lines, see key). The implied FIR luminosity is 2.86 +0.32-0.31 x 10 L sun . The dust in HFLS3 is not optically thick at wavelengths longward of rest-frame 162.7 µ m (95.4% confidence; Figure S12). This is in contrast to Arp 220, in which the dust becomes optically thick (i.e., τ d =1) shortward of 234+/-3 µ m. Other high-redshift massive starburst galaxies (including the Eyelash) typically become optically thick around ~200 µ m. This suggests that none of the detected molecular/fine structure emission lines in HFLS3 require correction for extinction. The radio continuum luminosity of HFLS3 is consistent with the radio-FIR correlation for nearby star-forming galaxies. b , 350 µ m/250 µ m and 500 µ m/350 µ m flux density ratios of HFLS3. The colored lines are the same templates as in a , but redshifted between 1< z <8 (number labels indicate redshifts). Dashed grey lines indicate the dividing lines for red ( S µ m < S µ m < S µ m ) and ultra-red sources ( S µ m < S µ m and 1.3 x S µ m < S µ m ). Gray symbols show the positions of five spectroscopically confirmed red sources at 4
G1B z = . HFLS3 z = . dust continuum velocity velocity dispersion [ C II ]( P / → P / ) ∆v =
100 km s − "" "" ◦ " "" D ec li n a t i o n . s . s h m . s ( J2000 ) + −
175 220 "" . "" × . ""
23 ∆v =
100 km s − Figure 3:
Gas dynamics, dust obscuration, and distribution of gas and star formation in HFLS3. a , b , High-resolution (FWHM 0.35”x0.23”) maps of the 158- µ m continuum ( a ) and [CII] line emission ( b ) obtained at 1.16 mm with the PdBI in A-configuration, overlaid on a Keck/NIRC2 2.2- µ m adaptive optics image (rest-frame UV/optical light). The r.m.s. uncertainty in the continuum ( a ) and line ( b ) maps is 180 and 400 µ Jy beam -1 , and contours are shown in steps of 3 and 1 σ , starting at 5 and 3 σ , respectively. A z =2.092 galaxy (labeled G1B) identified through Keck/LRIS spectroscopy is detected ~0.65” north of HFLS3, but is not massive enough to cause significant gravitational lensing at the position of HFLS3. Faint infrared emission is detected toward a region with lower dust obscuration in the north-eastern part of HFLS3 (not detected at <1 µ m). The Gaussian diameters of the resolved [CII] and continuum emission are 3.4 kpc x 2.9 kpc and 2.6 kpc x 2.4 kpc, suggesting gas and SFR surface densities of Σ gas = 1.4 x 10 M sun pc -2 and Σ SFR = 600 M sun yr -1 kpc -2 (~0.6 x 10 L sun kpc -2 ). The high Σ SFR is consistent with a maximum starburst at near-Eddington-limited intensity. Given the moderate optical depth of τ d <~1 at 158 µ m, this estimate is somewhat conservative. Peak velocity ( c ) and F.W.H.M. velocity dispersion ( d ) maps of the [CII] emission are obtained by Gaussian fitting to the line emission in each spatial point of the map. Velocity contours are shown in steps of 100 kms -1 . High-resolution CO J =7-6 and 10-9 and H O 3 -3 observations show consistent velocity profiles and velocity structure (Figures S5-S7). The large velocity dispersion suggests that the gas dynamics in this system are dispersion-dominated. See Supplementary Information Sections 3 and 5 for more details. Table 1: Observed and derived quantities for HFLS3, Arp 220 and the Galaxy
HFLS3 Arp 220* Milky Way* redshift M gas (M sun ) a (1.04+/-0.09) x 10 M dust (M sun ) b +0.32-0.30 x 10 ~1 x 10 ~6 x 10 M * (M sun ) c ~3.7 x 10 ~3-5 x 10 ~6.4 x 10 M dyn (M sun ) d (<20 kpc) f gase
40% 15% 1.2% L FIR (L sun ) f +0.32-0.31 x 10 SFR (M sun yr -1 ) g T dust (K) h +9.3-12.0
66 ~19
For details see Supplementary Information, Section 3. * Literature values for Arp 220 and the Milky Way are adopted from refs. 27, 20, 28, 29, and 30. The total molecular gas mass of the Milky Way is uncertain by at least a factor of 2. Quoted dust masses and stellar masses are typically uncertain by factors of 2-3 due to systematics. The dynamical mass for the Milky Way is quoted within the inner 20 kpc to be comparable to the other systems, not probing the outer regions dominated by dark matter. The dust temperature in the Milky Way varies by at least +/-5 K around the quoted value, which is used as a representative value. Both Arp 220 and the Milky Way are known to contain small fractions of significantly warmer dust. All error bars are 1 σ r.m.s. uncertainties. a Molecular gas mass, derived assuming α CO = M gas / L ’ CO = 1 M sun (K kms -1 pc ) -1 , see Supplementary Information, Section 3.3. b Dust mass, derived from spectral energy distribution fitting, see Supplementary Information, Section 3.1. c Stellar mass, derived from population synthesis fitting, see Supplementary Information, Section 3.4. d Dynamical mass, see Supplementary Information, Section 3.5. e Gas mass fraction, derived assuming f gas = M gas / M dyn , see Supplementary Information, Section 3.6. f Far-infrared luminosity as determined over the range of 42.5-122.5 µ m from spectral energy distribution fitting, see Supplementary Information, Section 3.1. g Star formation rate, derived assuming SFR[M sun yr -1 ] = 1.0 x 10 -10 L FIR [L sun ], see Supplementary Information, Section 3.2. h Dust temperature, derived from spectral energy distribution fitting, see Supplementary Information, Section 3.1.
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(2013), Nature, in the press (under press embargo until 13:00 US Eastern time on 17 April 2013) 18 " , M"! , W%,7)3%,&/8%$%8,(7%,gJ,%6?0()(0/',$)88%*,0',OZ[!E,"20'5, (7%, R`VUk, *)80)(03%, (*)'2.%*, ?/8%>, )22"&0'5,)',%2?) PM , `2, 0' * LF ! <, )'8, Y ! M, $0'%2, /.,,,YMf, H&2 A< >, )'8, ), hgJIO F i, )4"'8)'?%, *)(0/, /., <@ AN B,W%,."*(7%*,.06%8,(7%,?/2&0?,&0?*/G)3%,4)?H5*/"'8,(%& ! LYBEN, (/, > g1c> ! 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X<@@, )'8,FM@,o,)'8, E F =X<@ FBY ,)'8,<@ MB@, ?& AE >,*%2 ,, M": : = , \03%', (7%, $0&0(%8, ?/'2(*)0'(2, /', (7%, O F J, %6?0()(0/',$)88%*, 9Z05"*%, ! L<@ L<@ A<@ ! <@ F B, W%,5%'%*)(%8, Pj , 1n[C-]U!C, 02, ),c)+%20)',(//$,20&0$)*,(/,1g1g>,4"(,02,&/*%,%..0?0%'(,G7%', 8%)$0'5, G0(7, &"$(0A&/8)$, *%50/'2, 0', F JIO F i>, )'8, (7"2>, A >, )*%, F J, 8)(), )$/'%B, !/$"(0/'2, G0(7, > H0' X<@@ ! PBM, ?& AE , )*%, F J,%6?0()(0/',0',`* , C/, ."*(7%*, %6 J " IH c , aXF@@, o, Riechers et al. (2013), Nature, in the press (under press embargo until 13:00 US Eastern time on 17 April 2013) 19 '(/, )??/"'(B, !/$"(0/'2, G0(7, $%22, %6(*%&%, 5)2,8%'20(0%2, /., <@ j ! <@ P, ?& AE , )*%, > H0' , /., .%G, 7"'8*%82, (/, ;<@@@, oB, C7%, 4%2(A.0((0'5,&/8%$2, 2(0$$, /'$+, F J,$%3%$2,%0(7%*B, , W%,8%(%?(,%&0220/',.*/&,O F J,$0'%2,G0(7," J I O c ,;,E@@ ! NM@,o>,G70?7,G/"$8,*%K"0*%,5)2,8%'20(0%2,0',%6?%22,/.,<@ PBM, ?& AE ,(/,*% * o)o? LE F< , )'8, N FF , %'%*5+, $%3%$2, /.,/*(7/A,)'8, F J,?)',4%,%..0?0%'($+, * o)o? LF IN@@,H&2 A< = A B, `(, (7%, 802()'?%, /., OZ[!E>, (702,2"55%2(2, ), $%'20'5, &)5'0.0?)(0/', .)?(/*, /., P [ L Wavelength Frequency Flux Density Error Observatory [ ! m] [GHz] [mJy] [mJy] v%**/*,4)*2,/',!T-RU,.$"6%2,)*%,/4()0'%8,.*/&,.0((0'5,)'8,8/,'/(,)??/"'(,./*,?/'."20/','/02%>,G70?7,02,)(,$%)2(,XY&S+,0',)$$,!T-RU,4)'82B, Riechers et al. (2013), Nature, in the press (under press embargo until 13:00 US Eastern time on 17 April 2013) 21 %>+( ! T ! Transition Rest Frequency Peak flux density Velocity FWHM Line Intensity Line Luminosity Obs. [GHz] [mJy] [km/s] [Jy km/s] [10 L l ] CO J =1-0 CO J =2-1 CO J =3-2 CO J =5-4 CO J =6-5 CO J =7-6 CO J =9-8 CO J =10-9 CO J =12-11 CO J =13-12 CO J =14-13 CO J =15-14 CO J =16-15 CO J =17-16 CO J =18-17 CO J =19-18 H O 2 -2 H O 2 -1 H O 3 -3 H O 3 -2 H O 3 -3 H O 4 -4 H O 5 -5 H O 4 -4 H O 2 -2 H O 2 -1 H O 3 -2 H O 6 -6 H O 6 -6 H O 7 -7 H O 5 -5 H O 5 -4 H O 3 -3 H O 4 -4 H O 4 -3 H O 3 -2 H O 3 -3 H O 5 -5 H O + -1 J =5/2-3/2 J =3/2-3/2 Riechers et al. (2013), Nature, in the press (under press embargo until 13:00 US Eastern time on 17 April 2013) 22 ransition Rest Frequency Peak flux density Velocity FWHM Line Intensity Line Luminosity Obs. [GHz] [mJy] [km/s] [Jy km/s] [10 L l ] OH OH + F -0 F ~1,033.0582 -0.56 0.18 -0.92 0.29 PdBI* CH + J =1-0 CH + J =2-1 NH K a-2 K s ~1,763.6496 -1.56 0.51 648 290 -1.07 0.37 -0.60 0.21 PdBI* -5.68 2.83 -3.2 1.6 Z-spec* NH 2 -1 ~1,958.2068 -7.06 3.10 -3.2 1.4 Z-spec* HF J =2-1 [CI] P - P [CII] P - P [NII] P - P [NII] P - P [OI] P - P w $0'%,$"&0'/20(+,02,503%',0',"'0(2,/., @ ( ,L,o,H&I2, F, v(%'()(03%,8%(%?(0/'2,/'$+>,0'8% Parameter Median value 1 ! range 1D Max 4D Max T kin [K] log n (H ) [cm -3 ] log N CO [cm -2 ] log ' A ! ! ! ! ! log P [K cm -2 ] log < N CO > [cm -2 ] d v /d r [kms -1 pc -1 ] Riechers et al. (2013), Nature, in the press (under press embargo until 13:00 US Eastern time on 17 April 2013) 23 %>+( Parameter Value L’ CO ± " K kms -1 pc L CO ± " L sun L [CI] ± " L sun L [CII] ± " L sun L FIR +0.32-0.31 " L sun M gasa " M sun M CIb " M sun M HIc " M sun M dust +0.32-0.30 " M sun M * " M sun M dyn " M sun SFR d sun yr -1 % gas " M sun pc -2 % SFR 600 M sun yr -1 kpc -2 f gas gas-to-dust ratio t dep ( d [CII] " d FIR " T dust +9.3-12.0 K ± ) )22"&0'5 & gJ, L, A I @ t gJ ,L,<,1 ,9o,H&2 A<, F = A< ,9*%.2B,Fj>Yf=, )22"&0'5,),hg-i,%6?0()(0/',(%& j<,? EBP, ?& AE , )22"&0'5,!ZRh1 +* A< i,L,,4)2%8,/',),g7)4*0%*,0'0(0)$,&)22,."'?(0/' YF>YE , Riechers et al. (2013), Nature, in the press (under press embargo until 13:00 US Eastern time on 17 April 2013) 24 " , ^-'1&( , `880(0/')$, 80)5'/2(0?, $0'%2, /., (7%, 2()*A./*&0'5, 0'(%*2(%$$)*, &%80"&, 0', OZ[!EB, C%'()(03%,8%(%?(0/'2,)'8," * LM ! 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