Dense gas in the Galactic central molecular zone is warm and heated by turbulence

Ginsburg, Adam; Henkel, C.; Ao, Yiping; Riquelme, D.; Kauffmann, Jens; Pillai, T.; Mills, Elisabeth A. C.; Requeña-Torres, M. A.; Immer, K.; Testi, L.; Ott, J.; Bally, John; Battersby, Cara; Darling, Jeremy; Aalto, S.; Stanke, T.; Kendrew, Sarah; Kruijssen, J. M. Diederik; Longmore, Steven N.; Dale, James E.; Guêsten, R.; Menten, K. M.

doi:10.1051/0004-6361/201526100

Cited by 219 publications

(371 citation statements)

References 108 publications

(174 reference statements)

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“…Other studies have shown that there is no significant difference in the kinetic temperature (Hüttemeister et al 1993;Ao et al 2013;Ginsburg et al 2016) or line width (Jones et al 2012) between the clouds in our study with relatively weak and bright HCN 1-0. Our RADEX analysis then indicates that for a constant column density, temperature, and linewidth, variations in volume density from n=10 5 − 10 7 should change the line brightness by less than a factor of 2.…”

Section: Variation In Excitation Conditionscontrasting

confidence: 67%

Origins of Scatter in the Relationship Between HCN 1-0 and Dense Gas Mass in the Galactic Center

Mills

Battersby

2017

ApJ

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We investigate the correlation of HCN 1-0 with gas mass in the central 300 pc of the Galaxy. We find that on the ∼ 10 pc size scale of individual cloud cores, HCN 1-0 is well correlated with dense gas mass when plotted as a log-log relationship. There is ∼0.75 dex of scatter in this relationship from clouds like Sgr B2, which has an integrated HCN 1-0 intensity of a cloud less than half its mass, and others that have HCN 1-0 enhanced by a factor of 2-3 relative to clouds of comparable mass. We identify the two primary sources of scatter to be self-absorption and variations in HCN abundance. We also find that the extended HCN 1-0 emission is more intense per unit mass than in individual cloud cores. In fact the majority (80%) of HCN 1-0 emission comes from extended gas with column densities below 7 × 10 22 cm −2 , accounting for 68% of the total mass. We find variations in the brightness of HCN 1-0 would only yield a ∼ 10% error in the dense gas mass inferred from this line in the Galactic center. However, the observed order of magnitude HCN abundance variations, and the systematic nature of these variations, warn of potential biases in the use of HCN as dense gas mass tracer in more extreme environments such as AGN and shock-dominated regions. We also investigate other 3 mm tracers, finding that HNCO is better correlated with mass than HCN, and might be a better tracer of cloud mass in this environment.

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Section: Variation In Excitation Conditionscontrasting

confidence: 67%

Origins of Scatter in the Relationship Between HCN 1-0 and Dense Gas Mass in the Galactic Center

Mills

Battersby

2017

ApJ

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“…Such discrepancy between gas and dust temperatures has been observed in the CMZ at 1 pc spatial scales (e.g., Ao et al 2013;Mills & Morris 2013;Ott et al 2014;Ginsburg et al 2016;Immer et al 2016;Krieger et al 2016). Our observations confirm that in the 20 km s −1 cloud high gas temperatures of 50 K continue down to 0.1-pc scales.…”

Section: Gas Temperatures At 01-pc Scalesmentioning

confidence: 86%

“…First, we search for correlations between temperatures and linewidths, assuming the latter to be an indicator of turbulent strength (cf. Ginsburg et al 2016;Immer et al 2016), and between temperatures and H 2 O maser luminosities, assuming the latter to be correlated with protostellar luminosities (Palla et al 1993). Second, we attempt to look for direct signatures of turbulent or protostellar heating from our temperature maps.…”

Section: Turbulent Heating and Protostellar Heatingmentioning

confidence: 99%

The Molecular Gas Environment in the 20 km s⁻¹ Cloud in the Central Molecular Zone

Zhang

Kauffmann

et al. 2017

ApJ

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We recently reported a population of protostellar candidates in the 20 km s −1 cloud in the Central Molecular Zone of the Milky Way, traced by H 2 O masers in gravitationally bound dense cores. In this paper, we report high-angular-resolution (∼3 ′′ ) molecular line studies of the environment of star formation in this cloud. Maps of various molecular line transitions as well as the continuum at 1.3 mm are obtained using the Submillimeter Array. Five NH 3 inversion lines and the 1.3 cm continuum are observed with the Karl G. Jansky Very Large Array. The interferometric observations are complemented with single-dish data. We find that the CH 3 OH, SO, and HNCO lines, which are usually shock tracers, are better correlated spatially with the compact dust emission from dense cores among the detected lines. These lines also show enhancement in intensities with respect to SiO intensities toward the compact dust emission, suggesting the presence of slow shocks or hot cores in these regions. We find gas temperatures of 100 K at 0.1-pc scales based on RADEX modelling of the H 2 CO and NH 3 lines. Although no strong correlations between temperatures and linewidths/H 2 O maser luminosities are found, in high-angular-resolution maps we notice several candidate shock heated regions offset from any dense cores, as well as signatures of localized heating by protostars in several dense cores. Our findings suggest that at 0.1-pc scales in this cloud star formation and strong turbulence may together affect the chemistry and temperature of the molecular gas.

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“…Formaldehyde (H 2 CO) is a ubiquitous molecule in the Galactic interstellar medium (ISM) of our and external galaxies (Downes et al 1980;Cohen & Few 1981;Bieging et al 1982;Cohen et al 1983;Baan et al 1986Baan et al , 1990Baan et al , 1993Henkel et al 1991;Zylka et al 1992;Hüttemeister et al 1997;Heikkilä et al 1999;Wang et al 2004Wang et al , 2009Mangum et al 2008;Zhang et al 2012;Mangum et al 2013b;Ao et al 2013;Tang et al 2013;Ginsburg et al 2015Ginsburg et al , 2016Guo et al 2016). H 2 CO is thought to be formed on the surface of dust grains by successive hydrogenation of CO (Watanabe & Kouchi 2002;Woon 2002;Hidaka et al 2004): CO → HCO → H 2 CO. Variations of the fractional abundance of H 2 CO do not exceed one order of magnitude.…”

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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Dense gas in the Galactic central molecular zone is warm and heated by turbulence

Cited by 219 publications

References 108 publications

Origins of Scatter in the Relationship Between HCN 1-0 and Dense Gas Mass in the Galactic Center

Origins of Scatter in the Relationship Between HCN 1-0 and Dense Gas Mass in the Galactic Center

The Molecular Gas Environment in the 20 km s⁻¹ Cloud in the Central Molecular Zone

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

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Dense gas in the Galactic central molecular zone is warm and heated by turbulence

Cited by 219 publications

References 108 publications

Origins of Scatter in the Relationship Between HCN 1-0 and Dense Gas Mass in the Galactic Center

Origins of Scatter in the Relationship Between HCN 1-0 and Dense Gas Mass in the Galactic Center

The Molecular Gas Environment in the 20 km s−1 Cloud in the Central Molecular Zone

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

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Product

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The Molecular Gas Environment in the 20 km s⁻¹ Cloud in the Central Molecular Zone