Ammonia Thermometry of Star-Forming Galaxies

Mangum, J. G.; Darling, Jeremy; Henkel, C.; Menten, K. M.; MacGregor, Meredith A.; Svoboda, Brian; Schinnerer, E.

doi:10.1088/0004-637x/779/1/33

Cited by 53 publications

(112 citation statements)

References 68 publications

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“…The model of C core indicates that the dust temperature is slightly higher than that required for rapid sublimation to occur while the gas temperature (189 ± 57 K) as estimated by Mangum et al (2013b) is somewhat lower than that needed for neutralneutral reactions to be effective. Also, we know that an additional, hotter, component is needed to model the continuum at wavelengths <10 μm.…”

Section: Why Is There So Much Water In Zw 049057?mentioning

confidence: 89%

Herschelspectroscopic observations of the compact obscured nucleus in Zw 049.057

Falstad

González-Alfonso

Aalto

et al. 2015

A&A

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Context. The luminous infrared galaxy Zw 049.057 contains a compact obscured nucleus where a considerable amount of the galaxy's luminosity is generated. This nucleus contains a dusty environment that is rich in molecular gas. One approach to probing this kind of environment and to revealing what is hidden behind the dust is to study the rotational lines of molecules that couple well with the infrared radiation emitted by the dust. Aims. We probe the physical conditions in the core of Zw 049.057 and establish the nature of its nuclear power source (starburst or active galactic nucleus). . We modeled the unresolved core of the galaxy using a spherically symmetric radiative transfer code. To account for the different excitation requirements of the various molecular transitions, we use multiple components and different physical conditions. Results. We present the full high-resolution SPIRE FTS spectrum of Zw 049.057, along with relevant spectral scans in the PACS range. We find that a minimum of two different components (nuclear and extended) are required in order to account for the rich molecular line spectrum of Zw 049.057. The nuclear component has a radius of 10−30 pc, a very high infrared surface brightness (∼10 14 L kpc −2 ), warm dust (T d > 100 K), and a very large H 2 column density (N H 2 = 10 24 −10 25 cm −2 ). The modeling also indicates high nuclear H 2 O (∼5 × 10 −6 ) and OH (∼4 × 10 −6 ) abundances relative to H 2 as well as a low 16 O/ 18 O-ratio of 50−100. We also find a prominent infall signature in the [O I] line. We tentatively detect a 500 km s −1 outflow in the H 2 O 3 13 → 2 02 line. Conclusions. The high surface brightness of the core indicates the presence of either a buried active galactic nucleus or a very dense nuclear starburst. The estimated column density towards the core of Zw 049.057 indicates that it is Compton-thick, making a buried X-ray source difficult to detect even in hard X-rays. We discuss the elevated H 2 O abundance in the nucleus in the context of warm grain and gas-phase chemistry. The H 2 O abundance is comparable to that of other compact (ultra-)luminous infrared galaxies such as NGC 4418 and Arp 220 -and also to hot cores in the Milky Way. The enhancement of 18 O is a possible indicator that the nucleus of Zw 049.057 is in a similar evolutionary stage as the nuclei of Arp 220 -and more advanced than NGC 4418. We discuss the origin of the extreme nuclear gas concentration and note that the infalling gas detected in [O I] implies that the gas reservoir in the central region of Zw 049.057 is being replenished. If confirmed, the H 2 O outflow suggests that the nucleus is in a stage of rapid evolution.

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Section: Why Is There So Much Water In Zw 049057?mentioning

confidence: 89%

Herschelspectroscopic observations of the compact obscured nucleus in Zw 049.057

Falstad

González-Alfonso

Aalto

et al. 2015

A&A

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“…Symmetric top molecules have been proven to be some of the best tracers of the gas kinetic temperature in the interstellar medium (Ho & Townes 1983;Mangum et al 2013). However, the results presented here suggest that they may sometimes fail as an interstellar thermometer under specific conditions.…”

Section: Discussionmentioning

confidence: 99%

Widespread Rotationally Hot Hydronium Ion in the Galactic Interstellar Medium

Lis

Schilke

Bergin

et al. 2014

ApJ

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We present new Herschel observations of the (6,6) and (9,9) inversion transitions of the hydronium ion toward Sagittarius B2(N) and W31C. Sensitive observations toward Sagittarius B2(N) show that the high, ∼500 K, rotational temperatures characterizing the population of the highly excited metastable H 3 O + rotational levels are present over a wide range of velocities corresponding to the Sagittarius B2 envelope, as well as the foreground gas clouds between the Sun and the source. Observations of the same lines toward W31C, a line of sight that does not intersect the Central Molecular Zone but instead traces quiescent gas in the Galactic disk, also imply a high rotational temperature of ∼380 K, well in excess of the kinetic temperature of the diffuse Galactic interstellar medium. While it is plausible that some fraction of the molecular gas may be heated to such high temperatures in the active environment of the Galactic center, characterized by high X-ray and cosmic-ray fluxes, shocks, and high degree of turbulence, this is unlikely in the largely quiescent environment of the Galactic disk clouds. We suggest instead that the highly excited states of the hydronium ion are populated mainly by exoergic chemical formation processes and the temperature describing the rotational level population does not represent the physical temperature of the medium. The same arguments may be applicable to other symmetric top rotors, such as ammonia. This offers a simple explanation of the long-standing puzzle of the presence of a pervasive, hot molecular gas component in the central region of the Milky Way. Moreover, our observations suggest that this is a universal process not limited to the active environments associated with galactic nuclei.

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“…However, observed gas and dust temperatures do not agree with each other in the Galactic Central Molecular Zone (CMZ) and external galaxies (Güsten et al 1981;Ao et al 2013;Mangum et al 2013a;Ott et al 2014;Ginsburg et al 2016;Immer et al 2016). Dust temperatures in the LMC have been obtained by Gordon et al (2014) using Herschel 100 to 500 µm dust continuum emission data.…”

Section: Comparison Of Temperatures Derived From H 2 Co Co Nh 3 Amentioning

confidence: 99%

“…Multi-level observations of suitable molecules deliver the most reliable temperature determinations. The metastable lines of ammonia (NH 3 ) are frequently used as the standard molecular cloud thermometer in molecular clouds within our Galaxy and also in external galaxies (Ho & Townes 1983;Walmsley & Ungerechts 1983;Danby et al 1988;Henkel et al 2000Henkel et al , 2008Weiß et al 2001;Mauersberger et al 2003;Ao et al 2011;Lebrón et al 2011;Ott et al 2011;Wienen et al 2012;Mangum et al 2013a). However, the ammonia abundance can vary strongly in different molecular environments (e.g., 10…”

Section: Introductionmentioning

confidence: 99%

Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde

Tang

Henkel

Chen

et al. 2017

A&A

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Context. The kinetic temperature of molecular clouds is a fundamental physical parameter affecting star formation and the initial mass function. The Large Magellanic Cloud (LMC), the closest star forming galaxy with low metallicity, provides an ideal laboratory to study star formation in such an environment. Aims. The classical dense molecular gas thermometer NH 3 is rarely available in a low metallicity environment because of photoionization and a lack of nitrogen atoms. Our goal is to directly measure the gas kinetic temperature with formaldehyde toward six star-forming regions in the LMC. Methods. Three rotational transitions (J K A K C = 3 03 -2 02 , 3 22 -2 21 , and 3 21 -2 20 ) of para-H 2 CO near 218 GHz were observed with the Atacama Pathfinder EXperiment (APEX) 12 m telescope toward six star forming regions in the LMC. Those data are complemented by C 18 O 2-1 spectra. Results. Using non-LTE modeling with RADEX, we derive the gas kinetic temperature and spatial density, using as constraints the measured para-H 2 CO 3 21 -2 20 /3 03 -2 02 and para-H 2 CO 3 03 -2 02 /C 18 O 2-1 ratios. Excluding the quiescent cloud N159S, where only one para-H 2 CO line could be detected, the gas kinetic temperatures derived from the preferred para-H 2 CO 3 21 -2 20 /3 03 -2 02 line ratios range from 35 to 63 K with an average of 47 ± 5 K (errors are unweighted standard deviations of the mean). Spatial densities of the gas derived from the para-H 2 CO 3 03 -2 02 /C 18 O 2-1 line ratios yield 0.4 -2.9 × 10 5 cm −3 with an average of 1.5 ± 0.4 × 10 5 cm −3 . Temperatures derived from the para-H 2 CO line ratio are similar to those obtained with the same method from Galactic star forming regions and agree with results derived from CO in the dense regions (n(H 2 ) > 10 3 cm −3 ) of the LMC. A comparison of kinetic temperatures derived from para-H 2 CO with those from the dust also shows good agreement. This suggests that the dust and para-H 2 CO are well mixed in the studied star forming regions. A comparison of kinetic temperatures derived from para-H 2 CO 3 21 -2 20 /3 03 -2 02 and NH 3 (2,2)/(1,1) shows, however, a drastic difference. In the star forming region N159W, the gas temperature derived from the NH 3 (2,2)/(1,1) line ratio is ∼16 K (Ott et al. 2010), which is only half the temperature derived from para-H 2 CO and the dust. Furthermore, ammonia shows a very low abundance in a 30 ′′ beam. Apparently, ammonia only survives in the most shielded pockets of dense gas not yet irradiated by UV photons, while formaldehyde, less affected by photodissociation, is more widespread and is also sampling regions more exposed to the radiation of young massive stars. A correlation between the gas kinetic temperatures derived from para-H 2 CO and infrared luminosity, represented by the 250 µm flux, suggests that the kinetic temperatures traced by para-H 2 CO are correlated with the ongoing massive star formation in the LMC.

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Ammonia Thermometry of Star-Forming Galaxies

Cited by 53 publications

References 68 publications

Herschelspectroscopic observations of the compact obscured nucleus in Zw 049.057

Herschelspectroscopic observations of the compact obscured nucleus in Zw 049.057

Widespread Rotationally Hot Hydronium Ion in the Galactic Interstellar Medium

Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde

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