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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 742451.0, MPI für Astronomie / Publikationen_mpia
Luminous infrared galaxies with the submillimeter array. V. Molecular gas in intermediate to late-stage mergers
Authors:Sliwa, K.; Wilson, C. D.; Matsushita, S.; Peck, A. B.; Petitpas, G. R.; Saito, T.; Yun, M.
Date of Publication (YYYY-MM-DD):2017
Title of Journal:The Astrophysical Journal
Issue / Number:1
Start Page:id. 8 (15 pp)
Audience:Not Specified
Abstract / Description:We present new high-resolution ALMA (13CO J = 1-0 and J = 2-1) and CARMA (12CO and 13CO J = 1-0) observations of two luminous infrared galaxies (LIRGs), Arp 55 and NGC 2623. The new data are complementary to published and archival submillimeter array observations of 12CO J = 2-1 and J = 3-2. We perform a Bayesian likelihood non-local thermodynamic equilibrium analysis to constrain the molecular gas physical conditions such as temperature, column, and volume densities and the [12CO]/[13CO] abundance ratio. For Arp 55, an early/intermediate-staged merger, the line measurements are consistent with cold (˜10-20 K), dense (>{10}3.5 cm-3) molecular gas. For NGC 2623, the molecular gas is warmer (˜110 K) and less dense (˜ {10}2.7 cm-3). Because Arp 55 is an early/intermediate stage merger, while NGC 2623 is a merger remnant, the difference in physical conditions may be an indicator of merger stage. Comparing the temperature and volume density of several LIRGs shows that the molecular gas, averaged over ˜kiloparsec scales, of advanced mergers is in general warmer and less dense than early/intermediate stage mergers. We also find that the [12CO]/[13CO] abundance ratio of NGC 2623 is unusually high (>250) when compared with the Milky Way; however, it follows a trend seen with other LIRGs in the literature. This high [12CO]/[13CO] value is very likely due to stellar nucleosynthesis enrichment of the interstellar medium. On the other hand, Arp 55 has a more Galactic [12CO]/[13CO] value with the most probable [12CO]/[13CO] value being 20-30. We measure the CO-to-H2 conversion factor, {α }{CO}, to be ˜0.1 and ˜0.7 (3 × 10-4/{x}{CO}) M (K km s-1 pc2)-1 for Arp 55 and NGC 2623, respectively. Because Arp 55 is an early/intermediate-stage merger, this suggests that the transition from a Galactic conversion factor to a LIRG value happens at an even earlier merger stage.
Free Keywords:galaxies: abundances; galaxies: individual: NGC 2623; Arp 55; galaxies: interactions; galaxies: starburst; submillimeter: galaxies
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
Identifiers:ISSN:0004-637X %R 10.3847/1538-4357/aa689b
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