Warm Molecular Gas in Luminous Infrared Galaxies

Abstract

We present our initial results on the CO rotational spectral line energy distribution (SLED) of the $J$ to $J$$-$1 transitions from $J=4$ up to $13$ from Herschel SPIRE spectroscopic observations of 65 luminous infrared galaxies (LIRGs) in the Great Observatories All-Sky LIRG Survey (GOALS). The observed SLEDs change on average from one peaking at $J\le 4$ to a broad distribution peaking around $J\sim$6$-$7 as the IRAS 60-to-100 um color, $C(60/100)$, increases. However, the ratios of a CO line luminosity to the total infrared luminosity, $L_{\mathrm{IR}}$, show the smallest variation for $J$ around 6 or 7. This suggests that, for most LIRGs, ongoing star formation (SF) is also responsible for a warm gas component that emits CO lines primarily in the mid-$J$ regime ($5\lesssim J\lesssim 10$). As a result, the logarithmic ratios of the CO line luminosity summed over CO (5$-$4), (6$-$5), (7$-$6), (8$-$7) and (10$-$9) transitions to $L_{\mathrm{IR}}$, $\log R_{\mathrm{midCO}}$, remain largely independent of $C(60/100)$, and show a mean value of $-4.13$ ($\equiv \log R_{\mathrm{midCO}}^{\mathrm{SF}}$) and a sample standard deviation of only 0.10 for the SF-dominated galaxies. Including additional galaxies from the literature, we show, albeit with small number of cases, the possibility that galaxies, which bear powerful interstellar shocks unrelated to the current SF, and galaxies, in which an energetic active galactic nucleus contributes significantly to the bolometric luminosity, have their $R_{\mathrm{midCO}}$ higher and lower than $R_{\mathrm{midCO}}^{\mathrm{SF}}$, respectively.

Accepted for publication in the ApJ Letters; 5 pages, 4 figures

References in corpus (3)

• The 0.4 < z < 1.3 star formation history of the Universe as viewed in the far-infrared
• A Herschel Survey of the [N II] 205 micron Line in Local Luminous Infrared Galaxies --- The [N II] 205 micron Emission as a Star Formation Rate Indicator
• On the Detection of High Redshift Black Holes with ALMA through CO and H2 Emission

Cited by in corpus (24)

• CO excitation of normal star forming galaxies out to z=1.5 as regulated by the properties of their interstellar medium
• The Herschel Comprehensive (U)LIRG Emission Survey (HerCULES): CO Ladders, fine structure lines, and neutral gas cooling
• Turbulent Gas in Lensed Planck-selected Starbursts at redshifts 1-3.5
• CO emission in distant galaxies on and above the main sequence
• CO excitation, molecular gas density and interstellar radiation field in local and high-redshift galaxies
• Physical conditions of molecular gas in the Circinus galaxy: Multi-J CO and CI 1-0 observations
• Measuring Star-formation Rate and Far-Infrared Color in High-redshift Galaxies Using the CO (7-6) and [NII] 205 micron Lines
• Galaxy wide radio induced feedback in a radio quiet quasar
• HERUS: A CO Atlas from SPIRE Spectroscopy of local ULIRGs
• Spatially resolved CO SLED of the Luminous Merger Remnant NGC 1614 with ALMA
• Spatially resolved physical conditions of molecular gas and potential star formation tracers in M83, revealed by the Herschel SPIRE FTS
• Warm and Cold Molecular Gas Conditions Modeled in 87 Galaxies Observed by the Herschel SPIRE Fourier Transform Spectrometer
• Dense Gas in the Outer Spiral Arm of M51
• Suppressed CO emission and high G/D ratios in z=2 galaxies with sub-solar gas-phase metallicity
• The effect of active galactic nuclei on the cold interstellar medium in distant star-forming galaxies
• ALMA [NII] 205 micron Imaging Spectroscopy of the Interacting Galaxy System BRI 1202-0725 at Redshift 4.7
• Merger-induced star formation in low-metallicity dwarf galaxy NGC 4809/4810
• Unveiling the warm dense ISM in $z>6$ quasar host galaxies via water vapor emission
• The Unusual AGN Host NGC 1266: Evidence for Shocks in a Molecular Gas Rich S0 Galaxy with a Low Luminosity Nucleus
• A possible relation between global CO excitation and massive molecular outflows in local ULIRGs
• Investigating starburst-driven neutrino emission from galaxies in the Great Observatories All-Sky LIRG Survey
• Molecular gas content and high excitation of a massive main-sequence galaxy at z = 3
• ALMA Maps of Dust and Warm Dense Gas Emission in the Starburst Galaxy IC 5179${}^{\star }$
• Properties of Interstellar Medium in the S0 Galaxy NGC 1222: Evidence for Shocked-enhanced Line Emission