Morphology and Molecular Gas Fractions of Local Luminous Infrared Galaxies as a Function of Infrared Luminosity and Merger Stage

July 2016 • 2016ApJ...825..128L

Authors • Larson, K. L. • Sanders, D. B. • Barnes, J. E. • Ishida, C. M. • Evans, A. S. • U, V. • Mazzarella, J. M. • Kim, D. -C. • Privon, G. C. • Mirabel, I. F. • Flewelling, H. A.

Abstract • We present a new, detailed analysis of the morphologies and molecular gas fractions (MGFs) for a complete sample of 65 local luminous infrared galaxies from Great Observatories All-Sky Luminous Infrared Galaxies (LIRG) Survey using high resolution I-band images from The Hubble Space Telescope, the University of Hawaii 2.2 m Telescope and the Pan-STARRS1 Survey. Our classification scheme includes single undisturbed galaxies, minor mergers, and major mergers, with the latter divided into five distinct stages from pre-first pericenter passage to final nuclear coalescence. We find that major mergers of molecular gas-rich spirals clearly play a major role for all sources with {L}_{IR}\gt {10}^11.5{L}_⊙; however, below this luminosity threshold, minor mergers and secular processes dominate. Additionally, galaxies do not reach {L}_{IR}\gt {10}^12.0{L}_⊙ until late in the merger process when both disks are near final coalescence. The mean MGF ({MGF} = {M}_{{{H}}₂}/({M}_*+{M}_{{{H}}₂})) for non-interacting and early-stage major merger LIRGs is 18 ± 2%, which increases to 33 ± 3%, for intermediate stage major merger LIRGs, consistent with the hypothesis that, during the early-mid stages of major mergers, most of the initial large reservoir of atomic gas (HI) at large galactocentric radii is swept inward where it is converted into molecular gas (H₂).

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Joe Mazzarella

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