The dense gas mass fraction in the W51 cloud and its protoclusters

Ginsburg, Adam; Bally, John; Battersby, Cara; Youngblood, Allison; Darling, Jeremy; Rosolowsky, Erik; Arce, Héctor G.; Santos, Mayra E. Lebron

doi:10.1051/0004-6361/201424979

Cited by 57 publications

(88 citation statements)

References 97 publications

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“…It shows a higher T kin value than our observed results. The spatial densities derived from the para-H 2 CO 3 03 -2 02 /C 18 O 2-1 ratio in our sample agree with the observed results in the Galactic clumps (Beuther et al 2002;Motte et al 2003;Wienen et al 2012Wienen et al , 2015, HII regions Ginsburg et al 2011), and giant molecular clouds (GMCs) (Wadiak et al 1988;Ginsburg et al 2015;Immer et al 2016). This agreement indicates that the physical conditions of the star forming regions should be similar in both the LMC and our Galactic disk.…”

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

confidence: 90%

“…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%

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

confidence: 90%

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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“…All MCCs hosting massive star clusters characterized by Murray (2011) are associated with MCCs in our catalog. We also cover wellknown MCCs such as W43 (Nguyen Luong et al 2011a), Cygnus X (Schneider et al 2006), W49 (Galván-Madrid et al 2013), and W51 (Ginsburg et al 2015). Therefore, we can conclude that our MCCs catalog is a robust catalog of nearby MCCs.…”

Section: Physical Propertiesmentioning

confidence: 81%

“…• W51 is near the tangent point of the Sagittarius arm, has a high dense gas fraction and host massive star formation events (Ginsburg et al 2015).…”

Section: Definition Of Mini-starburst Complexesmentioning

confidence: 99%

The Scaling Relations and Star Formation Laws of Mini-Starburst Complexes

Nguyen-Luong

Nguyen

Motte

et al. 2016

ApJ

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The scaling relations and the star formation laws for molecular cloud complexes in the Milky Way is investigated using data from the 12 CO 1-0 CfA survey and from the literatures. We compare their masses M gas , mass surface densities Σ Mgas , radii R, velocity dispersions σ, star formation rates SF R, and SFR densities Σ SFR with those of structures ranging from cores, clumps, Giant Molecular Clouds (GMCs), to Molecular Cloud Complexes (MCCs), and to Galaxies, spanning 8 orders of magnitudes in size and 13 orders of magnitudes in mass. MCC are mostly large (R > 50 pc), massive (∼ 10 6 M ⊙ ) gravitationally unbound cloud structures. This results in the following universal relations:Mgas , SF R ∼ M gas 0.9 , and SF R ∼ σ 2.7 .Variations in the slopes and the coefficients of these relations are found at individual scales signifying different physics acting at different scales. Additionally, there are breaks at the MCC scale in the σ − R relation and between the starburst and the normal star-forming objects in the SF R − M gas and Σ SFR -Σ Mgas relations. Therefore, we propose to use the Schmidt-Kennicutt diagram to distinguish the starburst from the normal star-forming structures by applying a Σ Mgas threshold of ∼ 100 M ⊙ pc −2 and a Σ SFR threshold of 1 M ⊙ yr −1 kpc −2 . Mini-starburst complexes are gravitationally unbound MCCs that have enhanced Σ SFR (>1 M ⊙ yr −1 kpc −2 ), probably caused by dynamic events such as radiation pressure, colliding flows, or spiral arm gravitational instability. Because of the dynamical evolution, gravitational boundedness does not play a significant role in characterizing the star formation activity of MCCs, especially the mini-starburst complexes, which leads to the conclusion that the formation of massive stars and clusters is dynamic. We emphasize the importance of understanding mini-starburst in investigating the physics of starburst galaxies.

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“…Sato et al (2010) reported the distance as 5.4 +0.31 −0.28 kpc with higher accuracy by using H 2 O masers and the trigonometric parallax method. There are studies based on maser emissions and velocity measurements showing the interaction between the star-forming region W51B and the supernova remnant W51C (i.e., Green et al 1997;Ginsburg et al 2015). Kang et al (2009) studied the YSO population of W51 by using Spitzer and 2MASS data and combining both the color selection criteria from Simon et al (2007) and the spectral energy distribution (SED) slope classification (Lada 1991;André et al 1993;Greene et al 1994), in addition to SED models from Robitaille et al (2006).…”

Section: Introductionmentioning

confidence: 99%

Young Stellar Objects in the Massive Star-forming Regions W51 and W43

Saral

Hora

Audard

et al. 2017

ApJ

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We present the results of our investigation of the star-forming complexes W51 and W43, two of the brightest in the first Galactic quadrant. In order to determine the young stellar object (YSO) populations in W51 and W43 we used color-magnitude relations based on Spitzer mid-infrared and 2MASS/UKIDSS near-infrared data. We identified 302 Class I YSOs and 1178 Class II/transition disk candidates in W51, and 917 Class I YSOs and 5187 Class II/transition disk candidates in W43. We also identified tens of groups of YSOs in both regions using the Minimal Spanning Tree (MST) method. We found similar cluster densities in both regions, even though Spitzer was not able to probe the densest part of W43. By using the Class II/I ratios, we traced the relative ages within the regions, and based on the morphology of the clusters, we argue that several sites of star formation are independent of one another in terms of their ages and physical conditions. We used spectral energy distribution-fitting to identify the massive YSO (MYSO) candidates since they play a vital role in the star formation process, and then examined them to see if they are related to any massive star formation tracers such as UCH II regions, masers, or dense fragments. We identified 17 MYSO candidates in W51, and 14 in W43, respectively, and found that groups of YSOs hosting MYSO candidates are positionally associated with H II regions in W51, though we do not see any MYSO candidates associated with previously identified massive dense fragments in W43.

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The dense gas mass fraction in the W51 cloud and its protoclusters

Cited by 57 publications

References 97 publications

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

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

The Scaling Relations and Star Formation Laws of Mini-Starburst Complexes

Young Stellar Objects in the Massive Star-forming Regions W51 and W43

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