ASpitzer Space TelescopeInfrared Spectrograph Survey of Warm Molecular Hydrogen in Ultraluminous Infrared Galaxies

Abstract

We have conducted a survey of ultraluminous infrared galaxies (ULIRGs) with the Infrared Spectrograph on the Spitzer Space Telescope, obtaining spectra from 5.0 to 38.5 m for 77 sources with 0:02 < z < 0:93. Observations of the pure rotational H 2 lines S(3) 9.67 m, S(2) 12.28 m, and S(1) 17.04 m are used to derive the temperature and mass of the warm molecular gas. We detect H 2 in 77% of the sample, and all ULIRGs with F 60 m > 2 Jy. The average warm molecular gas mass is $2 ; 10 8 M . High extinction, inferred from the 9.7 m silicate absorption depth, is not observed along the line of sight to the molecular gas. The derived H 2 mass does not depend on F 25 m /F 60 m , which has been used to infer either starburst or AGN dominance. Similarly, the molecular mass does not scale with the 25 or 60 m luminosities. In general, the H 2 emission is consistent with an origin in photodissociation regions associated with star formation. We detect the S(0) 28.22 m emission line in a few ULIRGs. Including this line in the model fits tends to lower the temperature by $50Y100 K, resulting in a significant increase in the gas mass. The presence of a cooler component cannot be ruled out in the remainder of our sample, for which we do not detect the S(0) line. The measured S(7) 5.51 m line fluxes in six ULIRGs implies $3 ; 10 6 M of hot ($1400 K ) H 2 . The warm gas mass is typically less than 1% of the cold gas mass derived from 12 CO observations.

Turbulent and fast motions of H2gas in active galactic nuclei

“…2; lower panel) shows the natural logarithm of the number of electrons n e that descended from the upper to the lower state, normalized by the statistical weight g of the transition, as a function of the temperature that corresponds to the energy of the upper state E up divided by the Boltzmann constant k. The value of n e is computed as L/(αhν), where h is the Planck constant, α is the Einstein coefficient of the transition, and ν is the frequency of the emitted line. For a single temperature of 374 K we find that the mass of the H 2 gas at systemic velocity is 1.4 × 10 8 M (see also Higdon et al 2006). Assuming (for simplicity) that T is the same for both H 2 kinematic components (see Fig.…”

LIGHTING THE DARK MOLECULAR GAS: H2 AS A DIRECT TRACER

“…In the MOlecular Hydrogen Emission Galaxies (MOHEGs) of Ogle et al (2010), M(H 2 )<1500 K contributes only 0.01% of the total H 2 . M(H 2 )<300 K contributes less than 1% in ULIRGs (Higdon et al 2006). …”

“…The H 2 rotational line fluxes for QSO PG 1440+356 were taken from the Spitzer Quasar and ULIRG Evolution Study (QUEST) sample of Veilleux et al (2009), and those for the 19 ULIRGs were obtained from Higdon et al (2006). The fluxes of H 2 rotational lines for the NGC 6240 and other LIRGs in the sample are from Armus et al (2006) and Pereira-Santaella et al (2010), respectively.…”

Energetics of the molecular gas in the H2luminous radio galaxy 3C 326: Evidence for negative AGN feedback

“…By "astrophysical conditions" we refer to the galaxy properties and the mechanism which is causing the observed gas properties. Typically, in gas-rich, actively starforming galaxies the amount of cold molecular gas exceeds the masses of warm molecular and ionized gas by factors 10−100 (see Roussel et al 2007;Higdon et al 2006, for samples of nearby galaxies and ULIRGs, respectively). We will now show that this ratio is much smaller for 3C 326 N. All masses, luminosities, and kinetic energies are summarized in Table 5.…”