High‐resolution CO and radio imaging of ULIRGs: extended CO structures and implications for the universal star formation law

We present high spatial resolution (0.4 arcsec, ≃3.5 kpc) Plateau de Bure Interferometer interferometric data on three ultraluminous infrared galaxies (ULIRGs) at z ~ 2: two submillimetre galaxies (SMGs) and one submillimetre faint star-forming radio galaxy. The three galaxies have been robustly detected in CO rotational transitions, either ^(12)CO (J = 4→3) or ^(12)CO (J = 3→2), allowing their sizes and gas masses to be accurately constrained. These are the highest spatial resolution observations observed to date (by a factor of ~ 2) for intermediate-excitation CO emission in z ~ 2 ULIRGs. The galaxies appear extended over several resolution elements, having a mean radius of 3.7 kpc. High-resolution (0.3 arcsec) combined Multi-Element Radio-Linked Interferometer Network-Very Large Array observations of their radio continua allow an analysis of the star formation behaviour of these galaxies, on comparable spatial scales to those of the CO observations. This 'matched beam' approach sheds light on the spatial distribution of both molecular gas and star formation, and we can therefore calculate accurate star formation rates and gas surface densities: this allows us to place the three systems in the context of a Kennicutt–Schmidt (KS)-style star formation law. We find a difference in size between the CO and radio emission regions, and as such we suggest that using the spatial extent of the CO emission region to estimate the surface density of star formation may lead to error. This size difference also causes the star formation efficiencies within systems to vary by up to a factor of 5. We also find, with our new accurate sizes, that SMGs lie significantly above the KS relation, indicating that stars are formed more efficiently in these extreme systems than in other high- z star-forming galaxies.

[1]  A. Cimatti,et al.  High-redshift elliptical galaxies: are they (all) really compact? , 2009, 0909.3088.

[2]  J. Lee,et al.  On the interstellar medium and star formation demographics of galaxies in the local universe , 2009, 0908.1122.

[3]  Edinburgh,et al.  Confirming a population of hot-dust dominated, star-forming, ultraluminous galaxies at high redshift , 2009, 0906.5346.

[4]  I. Smail,et al.  A MID-INFRARED IMAGING SURVEY OF SUBMILLIMETER-SELECTED GALAXIES WITH THE SPITZER SPACE TELESCOPE , 2009 .

[5]  Lars Hernquist,et al.  The star-forming molecular gas in high-redshift Submillimetre Galaxies , 2009, 0905.2184.

[6]  I. Smail,et al.  MID-INFRARED SPECTROSCOPY OF SUBMILLIMETER GALAXIES: EXTENDED STAR FORMATION IN MASSIVE HIGH-REDSHIFT GALAXIES , 2009, 0903.4017.

[7]  J. Dunlop,et al.  Deep multi-frequency radio imaging in the Lockman Hole using the GMRT and VLA , 2009, 0903.3600.

[8]  D. Elbaz,et al.  A CO EMISSION LINE FROM THE OPTICAL AND NEAR-IR UNDETECTED SUBMILLIMETER GALAXY GN10 , 2009, 0903.3046.

[9]  U. Nottingham,et al.  Constraining Star Formation and AGN in z~2 Massive Galaxies using High Resolution MERLIN Radio Observations , 2009, 0902.1528.

[10]  R. Neri,et al.  New CO detections of lensed submillimetre galaxies in A2218: probing molecular gas in the LIRG regime at high redshift , 2008, 0812.3409.

[11]  R. Teyssier,et al.  Cold streams in early massive hot haloes as the main mode of galaxy formation , 2008, Nature.

[12]  A. M. Swinbank,et al.  The formation and assembly of a typical star-forming galaxy at redshift z ≈ 3 , 2008, Nature.

[13]  S. Rabien,et al.  From Rings to Bulges: Evidence for Rapid Secular Galaxy Evolution at z ~ 2 from Integral Field Spectroscopy in the SINS Survey , 2008, 0807.1184.

[14]  Spitzer Science Center,et al.  MORPHOLOGIES OF HIGH-REDSHIFT, DUST-OBSCURED GALAXIES FROM KECK LASER GUIDE STAR ADAPTIVE OPTICS , 2008, 0807.1115.

[15]  J. Surace,et al.  HST NICMOS Imaging of z ~ 2, 24 μm-selected Ultraluminous Infrared Galaxies , 2008, 0802.1050.

[16]  A. Cimatti,et al.  Kinemetry of SINS High-Redshift Star-Forming Galaxies: Distinguishing Rotating Disks from Major Mergers , 2008, 0802.0879.

[17]  A. Cimatti,et al.  Submillimeter Galaxies at z ~ 2: Evidence for Major Mergers and Constraints on Lifetimes, IMF, and CO-H2 Conversion Factor , 2008, 0801.3650.

[18]  R. Ivison,et al.  High-resolution radio observations of submillimetre galaxies , 2007, 0712.3047.

[19]  C. Conselice,et al.  The structures of distant galaxies – I. Galaxy structures and the merger rate to z∼ 3 in the Hubble Ultra-Deep Field , 2007, 0711.2333.

[20]  D. Elbaz,et al.  Mid-Infrared Spectral Diagnosis of Submillimeter Galaxies , 2007, 0711.1553.

[21]  James E. Larkin,et al.  Integral Field Spectroscopy of High-Redshift Star-forming Galaxies with Laser-guided Adaptive Optics: Evidence for Dispersion-dominated Kinematics , 2007, 0707.3634.

[22]  A. Cimatti,et al.  Dynamical Properties of z ~ 2 Star-forming Galaxies and a Universal Star Formation Relation , 2007, 0706.2656.

[23]  C. Carilli,et al.  HCN Observations of Dense Star-forming Gas in High-Redshift Galaxies , 2007, astro-ph/0703548.

[24]  J. Dunlop,et al.  The SCUBA HAlf Degree Extragalactic Survey - III. Identification of radio and mid-infrared counterparts to submillimetre galaxies , 2007, astro-ph/0702544.

[25]  D. Iono,et al.  High-Resolution Imaging of Warm and Dense Molecular Gas in the Nuclear Region of the Luminous Infrared Galaxy NGC 6240 , 2007, astro-ph/0701123.

[26]  Rethinking the N(H2)/I(CO) conversion factor , 2006, astro-ph/0610209.

[27]  R. Bender,et al.  Intense Star Formation and Feedback at High Redshift: Spatially Resolved Properties of the z = 2.6 Submillimeter Galaxy SMM J14011+0252 , 2006, astro-ph/0611769.

[28]  A. Cimatti,et al.  The rapid formation of a large rotating disk galaxy three billion years after the Big Bang , 2006, Nature.

[29]  C. Steidel,et al.  Hα Observations of a Large Sample of Galaxies at z ~ 2: Implications for Star Formation in High-Redshift Galaxies , 2006, astro-ph/0604388.

[30]  C. Steidel,et al.  The Stellar, Gas, and Dynamical Masses of Star-forming Galaxies at z ~ 2 , 2006, astro-ph/0604041.

[31]  R. Abuter,et al.  SINFONI Integral Field Spectroscopy of z ~ 2 UV-selected Galaxies: Rotation Curves and Dynamical Evolution , 2006, astro-ph/0603559.

[32]  J. Kneib,et al.  Galaxies under the cosmic microscope: resolved spectroscopy and new constraints on the z= 1 Tully–Fisher relation , 2006, astro-ph/0603042.

[33]  F. Bertoldi,et al.  High-Resolution Millimeter Imaging of Submillimeter Galaxies , 2005 .

[34]  Christopher F. McKee,et al.  A General Theory of Turbulence-regulated Star Formation, from Spirals to Ultraluminous Infrared Galaxies , 2005, astro-ph/0505177.

[35]  F. Israel.  Molecular gas in compact galaxies , 2005, astro-ph/0504569.

[36]  Edinburgh,et al.  An interferometric CO survey of luminous submillimetre galaxies , 2005 .

[37]  R. B. Partridge,et al.  High-resolution studies of radio sources in the Hubble Deep and Flanking Fields , 2005, astro-ph/0501679.

[38]  I. Smail,et al.  A Redshift Survey of the Submillimeter Galaxy Population , 2004, astro-ph/0412573.

[39]  Munich,et al.  The Supernova Rate-Velocity Dispersion Relation in the Interstellar Medium , 2005, astro-ph/0506339.

[40]  A. Dekel,et al.  Galaxy bimodality due to cold flows and shock heating , 2004, astro-ph/0412300.

[41]  Mark Swinbank,et al.  The Rest-Frame Optical Spectra of SCUBA Galaxies , 2004, astro-ph/0412050.

[42]  P. P. van der Werf,et al.  Detection of CO from SMM J16359+6612, the Multiply Imaged Submillimeter Galaxy behind A2218 , 2004, astro-ph/0409477.

[43]  R. J. Ivison,et al.  Evidence for Extended, Obscured Starbursts in Submillimeter Galaxies , 2004, astro-ph/0412051.

[44]  W. K. Huchtmeier,et al.  A Catalog of Neighboring Galaxies , 2004 .

[45]  F. Bertoldi,et al.  Interferometric Observations of Powerful CO Emission from Three Submillimeter Galaxies at z = 2.39, 2.51, and 3.35 , 2003 .

[46]  P. Solomon,et al.  Molecular Gas and Dust at z = 2.6 in SMM J14011+0252: A Strongly Lensed Ultraluminous Galaxy, Not a Huge Massive Disk , 2002, astro-ph/0210040.

[47]  Reinhard Genzel,et al.  Spatially Resolved Millimeter Interferometry of SMM J02399–0136: A Very Massive Galaxy at z = 2.8 , 2002, astro-ph/0210449.

[48]  M. Cappellari,et al.  Position-velocity diagrams of ionized gas in the inner regions of disk galaxies ? , 2002, astro-ph/0204006.

[49]  J. Kneib,et al.  Submillimeter Galaxies , 2002, astro-ph/0202228.

[50]  R. J. Ivison,et al.  The nature of faint submillimetre-selected galaxies , 2001 .

[51]  M. Yun,et al.  Radio Properties of Infrared-selected Galaxies in the IRAS 2 Jy Sample , 2001, astro-ph/0102154.

[52]  A. Weiss,et al.  The Effect of Violent Star Formation on the State of the Molecular Gas in M 82 , 2000, astro-ph/0010541.

[53]  M. Tecza,et al.  Gasdynamics in the Luminous Merger NGC 6240 , 1999, astro-ph/9905031.

[54]  Hilo,et al.  SCUBA: A Common - user submillimetre camera operating on the James Clerk Maxwell telescope , 1998, astro-ph/9809122.

[55]  Jean-Paul Kneib,et al.  Deep Counts of Submillimeter Galaxies , 1998, astro-ph/9812412.

[56]  STAR FORMATION IN GALAXIES ALONG THE HUBBLE SEQUENCE , 1998, astro-ph/9807187.

[57]  Jr.,et al.  The Global Schmidt law in star forming galaxies , 1997, astro-ph/9712213.

[58]  Simon J. E. Radford,et al.  The Molecular Interstellar Medium in Ultraluminous Infrared Galaxies , 1996, astro-ph/9610166.

[59]  D. Sanders,et al.  LUMINOUS INFRARED GALAXIES , 1996 .

[60]  S. Sakamoto.  Effects of molecular cloud properties on the CO-to-H2 conversion factor. , 1996 .

[61]  M. Schmidt.  The Rate of Star Formation , 1959 .