Molecular hydrogen emission in galaxies: Determination of excitation mechanism

Mouri, Hideaki

doi:10.1086/174184

Cited by 109 publications

(175 citation statements)

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“…Throughout the rest of the discussion, when we refer to H2 flux, we are referring to the strongest transition, 1-0 S(1) at 2.1218 µm, unless otherwise specified.) These vibrational transitions of H2 can be excited by shock heating, UV fluorescence or thermal excitation from O and B stars, and/or X-ray heating from a nearby AGN (Mouri 1994). Because we do not see a broad Brγ line, and because no AGN is evident from optical (Yuan et al 2010), mid-infrared (Stierwalt et al 2013), or X-ray (Iwasawa et al 2011) observations, the first two scenarios are more likely for this galaxy.…”

Section: Osiris Analysismentioning

confidence: 99%

Shocked gas in IRAS F17207-0014: ISM collisions and outflows

Medling

Vivian

Kewley

et al. 2015

Monthly Notices of the Royal Astronomical Society

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We combine optical and near-infrared AO-assisted integral field observations of the merging ULIRG IRAS F17207-0014 from the Wide-Field Spectrograph (WiFeS) and Keck/OSIRIS. The optical emission line ratios [N II]/Hα, [S II]/Hα, and [O I]/Hα reveal a mixing sequence of shocks present throughout the galaxy, with the strongest contributions coming from large radii (up to 100% at ∼5 kpc in some directions), suggesting galactic-scale winds. The nearinfrared observations, which have approximately 30 times higher spatial resolution, show that two sorts of shocks are present in the vicinity of the merging nuclei: low-level shocks distributed throughout our field-of-view evidenced by an H 2 /Brγ line ratio of ∼0.6-4, and strong collimated shocks with a high H 2 /Brγ line ratio of ∼4-8, extending south from the two nuclear disks approximately 400 pc (∼0. ′′ 5). Our data suggest that the diffuse shocks are caused by the collision of the interstellar media associated with the two progenitor galaxies and the strong shocks trace the base of a collimated outflow coming from the nucleus of one of the two disks.

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Section: Osiris Analysismentioning

confidence: 99%

Shocked gas in IRAS F17207-0014: ISM collisions and outflows

Medling

Vivian

Kewley

et al. 2015

Monthly Notices of the Royal Astronomical Society

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“…Therefore there has been a recent shift towards the idea that H 2 emission in galaxies may in some cases be mostly far-ultraviolet excited Israel and Koornneef, 1991;Tanaka et al, 1991;Pak et al, 1996). Mouri (1994) discusses spectroscopic methods of separating PDR, shock, and x-ray components of the H 2 emission. Goldader et al (1997), Sugai et al (1997), and Vanzi and Rieke (1997) present recent observations and discussion of the shock versus PDR origin of H 2 and [FeII] emission.…”

Section: Starburst Galactic Nucleimentioning

confidence: 99%

Photodissociation regions in the interstellar medium of galaxies

Hollenbach

Tielens²

1999

Rev. Mod. Phys.

756

712

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The interstellar medium of galaxies is the reservoir out of which stars are born and into which stars inject newly created elements as they age. The physical properties of the interstellar medium are governed in part by the radiation emitted by these stars. Far-ultraviolet (6 eVϽh Ͻ13.6 eV) photons from massive stars dominate the heating and influence the chemistry of the neutral atomic gas and much of the molecular gas in galaxies. Predominantly neutral regions of the interstellar medium in which the heating and chemistry are regulated by far ultraviolet photons are termed PhotoDissociation Regions (PDRs). These regions are the origin of most of the non-stellar infrared (IR) and the millimeter and submillimeter CO emission from galaxies. The importance of PDRs has become increasingly apparent with advances in IR and submillimeter astronomy. The IR emission from PDRs includes fine structure lines of C, C ϩ , and O; rovibrational lines of H 2 ; rotational lines of CO; broad mid-IR features of polycyclic aromatic hydrocarbons; and a luminous underlying IR continuum from interstellar dust. The transition of H to H 2 and C ϩ to CO occurs within PDRs. Comparison of observations with theoretical models of PDRs enables one to determine the density and temperature structure, the elemental abundances, the level of ionization, and the radiation field. PDR models have been applied to interstellar clouds near massive stars, planetary nebulae, red giant outflows, photoevaporating planetary disks around newly formed stars, diffuse clouds, the neutral intercloud medium, and molecular clouds in the interstellar radiation field-in summary, much of the interstellar medium in galaxies. Theoretical PDR models explain the observed correlations of the [CII] 158 m with the CO Jϭ1 -0 emission, the CO Jϭ1 -0 luminosity with the interstellar molecular mass, and the [CII] 158 m plus [OI] 63 m luminosity with the IR continuum luminosity. On a more global scale, PDR models predict the existence of two stable neutral phases of the interstellar medium, elucidate the formation and destruction of star-forming molecular clouds, and suggest radiation-induced feedback mechanisms that may regulate star formation rates and the column density of gas through giant molecular clouds. [S0034-6861(99)01001-6] CONTENTS

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“…The 1-0S(2) / 1-0S(0) and 1-0S(3) / 1-0S(1) ratios, and the derived Trot values, in turn, show the dominant mechanism of the thermal component of excitation (Mouri 1994): the low Trot ∼ 1000 K temperatures of the Head and Tail suggest UV photon heating, such as in photodissociation regions, while the higher Trot ∼ 2000 K temperatures at the Heart and Body strongly suggest shock heating.…”

Section: Excitation Mechanismsmentioning

confidence: 83%

“…The differences between Trot and T vib , as well as the line-ratios involving ν = 1 and ν = 2 transitions, indicate (see e.g. Mouri 1994) that there are non-thermal processes (UV fluorescence) involved in the excitation. The Body aperture with 2-1S(1) / 1-0S(1) ∼ 0.5, in particular, appears to be dominated by non-thermal emission.…”

Section: Excitation Mechanismsmentioning

confidence: 99%

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Shutting down or powering up a (U)LIRG? Merger components in distinctly different evolutionary states in IRAS 19115−2124 (the Bird)

Vaïsänen

Reunanen

Kotilainen

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We present new SINFONI near-infrared integral field unit (IFU) spectroscopy and SALT optical long-slit spectroscopy characterising the history of a nearby merging luminous infrared galaxy, dubbed the Bird (IRAS19115-2114). The NIR line-ratio maps of the IFU data-cubes and stellar population fitting of the SALT spectra now allow dating of the star formation (SF) over the triple system uncovered from our previous adaptive optics data. The distinct components separate very clearly in a line-ratio diagnostic diagram. An off-nuclear pure starburst dominates the current SF of the Bird with 60-70% of the total, with a 4-7 Myr age, and signs of a fairly constant long-term star formation of the underlying stellar population. The most massive nucleus, in contrast, is quenched with a starburst age of > 40 Myr and shows hints of budding AGN activity. The secondary massive nucleus is at an intermediate stage. The two major components have a population of older stars, consistent with a starburst triggered 1 Gyr ago in a first encounter. The simplest explanation of the history is that of a triple merger, where the strongly star forming component has joined later. We detect multiple gas flows in different phases. The Bird offers an opportunity to witness multiple stages of galaxy evolution in the same system; triggering as well as quenching of SF, and the early appearance of AGN activity. It also serves as a cautionary note on interpretations of observations with lower spatial resolution and/or without infrared data. At high-redshift the system would look like a clumpy starburst with crucial pieces of its puzzle hidden, in danger of misinterpretations.

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Molecular hydrogen emission in galaxies: Determination of excitation mechanism

Cited by 109 publications

References 0 publications

Shocked gas in IRAS F17207-0014: ISM collisions and outflows

Shocked gas in IRAS F17207-0014: ISM collisions and outflows

Photodissociation regions in the interstellar medium of galaxies

Shutting down or powering up a (U)LIRG? Merger components in distinctly different evolutionary states in IRAS 19115−2124 (the Bird)

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