Wednesday 20th Feb 2013


Herschel-ATLAS: a binary HyLIRG pinpointing a cluster of starbursting proto-ellipticals

R. J. Ivison (UK ATC and IfA, Edinburgh), A. M. Swinbank, Ian Smail, A. I. Harris, R. S. Bussmann, A. Cooray, P. Cox, Hai Fu, A. Kovacs, M. Krips, D. Narayanan, M. Negrello, R. Neri, J. Penarrubia, J. Richard, D. A. Riechers, K. Rowlands, J. G. Staguhn, T. A. Targett, S. Amber, A. J. Baker, N. Bourne, F. Bertoldi, M. Bremer, J. A. Calanog, D. L. Clements, H. Dannerbauer, A. Dariush, G. De Zotti, L. Dunne, S. A. Eales, D. Farrah, S. Fleuren, A.Franceschini, J. E. Geach, R. D. George, J. C. Helly, R. Hopwood, E. Ibar, M. J. Jarvis, J.-P. Kneib, S. Maddox, A. Omont, D. Scott, S. Serjeant, M. W. L. Smith, M. A. Thompson, E. Valiante, I. Valtchanov, J. Vieira, P. van der Werf

Exploiting the relationship between CO luminosity and line width determined for fainter starbursts, we identify and remove lensed sources from the widest Herschel extragalactic imaging survey to yield a sample of intrinsically luminous galaxies. Panchromatic observations of the best candidate HyLIRG then led to the discovery of at least four luminous galaxies across a ~100-kpc region at z=2.41. Our technique separates HyLIRGs from the more numerous, strongly lensed population, and can also pinpoint clusters of starbursting proto-ellipticals. Via sub-arcsecond interferometric imaging we have measured accurate gas and star-formation surface densities. The two brightest galaxies span ~3 kpc FWHM in submm/radio continuum and CO J=4-3, and double that in CO J=1-0. The broad CO line is due partly to the multitude of constituent galaxies and partly to large rotational velocities in two counter-rotating gas disks — a scenario predicted to lead to the most intense starbursts, which will therefore come in pairs. The disks have M(dyn) of several x 10^11 Msun, and gas fractions of ~40%. Velocity dispersions are modest so the disks are unstable, potentially on scales commensurate with their radii: these galaxies are undergoing extreme bursts of star formation, not confined to their nuclei, at close to the Eddington limit. Their specific star-formation rates place them ~>5x above the main sequence, which supposedly comprises large gas disks like these. Their high star-formation efficiencies are difficult to reconcile with a simple volumetric star-formation law. N-body and dark matter simulations suggest this system is the progenitor of a B(inary)-type ~10^14.6-Msun cluster.


Mid-Infrared Properties of Nearby Luminous Infrared Galaxies I: Spitzer IRS Spectra for the GOALS Sample

S. Stierwalt, L. Armus, J.A. Surace, H. Inami, A.O. Petric, T. Diaz-Santos, S. Haan, V. Charmandaris, J. Howell, D.C. Kim, J. Marshall, J.M. Mazzarella, H.W.W. Spoon, S. Veilleux, A. Evans, D. B. Sanders, P. Appleton, G. Bothun, C.R. Bridge, B. Chan, D. Frayer, K. Iwasawa, L.J. Kewley, S. Lord, B.F. Madore, J.E. Melbourne, E.J. Murphy, J.A. Rich, B. Schulz, E. Sturm, V. U, T. Vavilkin, K. Xu

The Great Observatories All-Sky LIRG Survey (GOALS) is a multiwavelength study of luminous infrared galaxies (LIRGs) in the local universe. Here we present low resolution Spitzer spectra covering 5-38um and provide a basic analysis of the mid-IR spectral properties for nearby LIRGs. In a companion paper, we discuss detailed fits to the spectra. The GOALS sample of 244 nuclei in 180 luminous and 22 ultraluminous IR galaxies represents a complete subset of the IRAS RBGS and covers a range of merger stages, morphologies and spectral types. The majority (>60%) of GOALS LIRGs have high 6.2um PAH equivalent widths (EQW > 0.4um) and low levels of silicate absorption (s_9.7um >-1.0). There is a general trend among the U/LIRGs for silicate depth and MIR slope to increase with LIR. U/LIRGs in the late stages of a merger also have on average steeper MIR slopes and higher levels of dust obscuration. Together these trends suggest that as gas & dust is funneled towards the center of a coalescing merger, the nuclei become more compact and obscured. The sources that depart from these correlations have very low PAH EQW (EQW < 0.1um) consistent with their MIR emission being dominated by an AGN. The most heavily dust obscured sources are the most compact in their MIR emission, suggesting that the obscuring (cool) dust is associated with the outer regions of the starburst. As the merger progresses a marked decline is seen for the fraction of high EQW (star formation dominated) sources while the fraction of composite sources increases but the fraction of AGN-dominated sources remains low. When compared to the MIR spectra of submillimeter galaxies (SMGs) at z~2, the average GOALS LIRG is more absorbed at 9.7um and has more PAH emission. However, when the AGN contributions to both the local LIRGs and the high-z SMGs are removed, the average local starbursting LIRG closely resembles the starbursting SMGs.


The 2013 Release of Cloudy

G. J. Ferland (1), R. L. Porter (2), P. A. M. van Hoof (3), R. J. R. Williams (4), N. P. Abel (5), M. L. Lykins (1), Gargi Shaw (6), W. J. Henney (7), P. C. Stancil (2)

This is a summary of the 2013 release of the plasma simulation code Cloudy. Cloudy models the ionization, chemical, and thermal state of material that may be exposed to an external radiation field or other source of heating, and predicts observables such as emission and absorption spectra. It works in terms of elementary processes, so is not limited to any particular temperature or density regime. This paper summarizes advances made since the last major review in 1998. Much of the recent development has emphasized dusty molecular environments, improvements to the ionization / chemistry solvers, and how atomic and molecular data are used. We present two types of simulations to demonstrate the capability of the code. We consider a molecular cloud irradiated by an X-ray source such as an Active Nucleus and show how treating EUV recombination lines and the full SED affects the observed spectrum. A second example illustrates the very wide range of particle and radiation density that can be considered.

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