Surveying the Giant H ii Regions of the Milky Way with SOFIA. I. W51A

Lim, Wanggi; Buizer, James M. De

doi:10.3847/1538-4357/ab0288

Cited by 24 publications

(25 citation statements)

References 86 publications

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“…Bisbas et al (2017) used radiative transfer calculations to show that the [CII] and CO lines show a significant offset in the process of the cloud collision. Such an offset is reported toward a few possible cloud-cloud collision sites (Bisbas et al 2018;Lim and De Buizer 2019). Nonetheless, it needs to be quantified how this signature differs from hierarchical gravitational collapse or feedback-driven outflows.…”

Section: High-mass Star Formation Triggered By Cloud-cloud Collisionsmentioning

confidence: 99%

The Molecular Cloud Lifecycle

et al. 2020

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Giant molecular clouds (GMCs) and their stellar offspring are the building blocks of galaxies. The physical characteristics of GMCs and their evolution are tightly connected to galaxy evolution. The macroscopic properties of the interstellar medium propagate into the properties of GMCs condensing out of it, with correlations between e.g. the galactic and GMC scale gas pressures, surface densities and volume densities. That way, the galactic environment sets the initial conditions for star formation within GMCs. After the onset of massive star formation, stellar feedback from e.g. photoionisation, stellar winds, and supernovae eventually contributes to dispersing the parent cloud, depositing energy, momentum and metals into the surrounding medium, thereby changing the properties of galaxies. This cycling of matter between gas and stars, governed by star formation and feedback, is therefore a major driver of galaxy evolution. Much of the recent debate has focused on the durations of the various evolutionary phases that constitute this cycle in galaxies, and what these can teach us about the physical mechanisms driving the cycle. We review results from observational, theoretical, and numerical work to build a dynamical picture of the evolutionary lifecycle of GMC evolution, star formation, and feedback in galaxies.

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Section: High-mass Star Formation Triggered By Cloud-cloud Collisionsmentioning

confidence: 99%

The Molecular Cloud Lifecycle

et al. 2020

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“…Various studies of Galactic high mass star forming regions have found dust temperatures to be greater than ∼ 50 − 60 K (see e.g. Kraemer et al 2001;Barbosa et al 2016;Lim & De Buizer 2019). This also applies to higher resolution observations of Arp 220 by Wilson et al (2014), among others, who derived average dust temperatures of 80 K and 197 K for the eastern and western nuclei, respectively.…”

Section: Expanding the Calculations Of Van Der Walt (2014)mentioning

confidence: 65%

Revisiting the formaldehyde masers

van der Walt,

Mfulwane

2021

Preprint

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Context. The 4.8 GHz formaldehyde (H 2 CO) masers are one of a number of rare types of molecular masers in the Galaxy. There still is not agreement on the mechanism responsible for the inversion of the 1 10 − 1 11 transition and the conditions under which an inversion can occur, and therefore how to interpret the masers. Aims. The aim of the present calculations is to explore a larger region of parameter space to improve on our previous calculations, thereby to better understand the range of physical conditions under which an inversion of the 1 10 − 1 11 transition occurs. We also aim to understand recently published results that H 2 CO masers are radiatively pumped. Methods. We solve the rate equations of the first 40 rotational levels of o-H 2 CO using a fourth-order Runge-Kutta method. We consider gas kinetic temperatures between 10 K and 300 K, H 2 densities between 10 4 cm −3 and 10 6 cm −3 , and a number of different dust temperatures and grey-body spectral energy density distributions. Results. We show that when using a black body radiation field the inversion of any transition will disappear as the kinetic temperature approaches the black-body radiation temperature since the system, consisting of the gas and radiation field, approaches thermodynamic equilibrium. Using a grey-body dust radiation field appropriate for Arp 220 we find that none of 1 10 − 1 11 , 2 11 − 2 12 , and 3 12 − 3 13 transitions are inverted for kinetic temperatures less than 100 K. Our calculations also show that in theory the 1 10 − 1 11 transition can be inverted over a large region of explored parameter space in the presence of an external far-infrared radiation field. Limiting the abundance of H 2 CO to less than 10 −5 , however, reduces the region where an inversion occurs to H 2 densities 10 5 cm −3 and kinetic temperatures 100 K. We propose a pumping scheme for the H 2 CO masers which can explain why collisions play a central role in inverting the 1 10 − 1 11 transition, and therefore why an external radiation field alone does not lead to an inversion. Conclusions. Collisions are an essential mechanism for the inversion of the 1 10 − 1 11 transition. Our results suggest that 4.8 GHz H 2 CO megamasers are associated with hot and dense gas typical of high mass star forming regions rather than with cold material. Although limiting the H 2 CO abundance to less than 10 −5 significantly reduces the region in parameter space where the 1 10 − 1 11 is inverted, it still is not clear whether this is the only reason why these masers are so rare.

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“…Moreover, since Class I YSOs are associated with dense molecular clouds, it would be harder for the blast wave to plow the dense gas, and instead, the shock wave would slow down where we observe both Class I and II YSOs at the boundary regions between HB 3 and W3 Complex. One needs to bear in mind that the comparison of separate evolutionary tracers of such SF activities, e.g., virial parameter (α vir ) vs. luminosity -mass ratio (L/M ) (Lim & De Buizer 2019) or unambiguous identification of YSOs with follow-up spectroscopy is still needed to support our conclusion.…”

Section: Objectsmentioning

confidence: 95%

Shocked Molecular Hydrogen and Broad CO lines from the Interacting Supernova Remnant HB 3

Rho,

Jarrett,

Tram

et al. 2021

Preprint

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We present the detections of shocked molecular hydrogen (H 2 ) gas in near-and mid-infrared and broad CO in millimeter from the mixed-morphology supernova remnant (SNR) HB 3 (G132.7+1.3) using Palomar WIRC, the Spitzer GLIMPSE360 and WISE surveys, and HHSMT. Our near-infrared narrow-band filter H 2 2.12 µm images of HB 3 show that both Spitzer IRAC and WISE 4.6µm emission originates from shocked H 2 gas. The morphology of H 2 exhibits thin filamentary structures and a large scale of interaction sites between the HB 3 and nearby molecular clouds. Half of HB 3, the southern and eastern shell of the SNR, emits H 2 in a shape of a "butterfly" or "W", indicating the interaction sites between the SNR and dense molecular clouds. Interestingly, the H 2 emitting region in the south-east is also co-spatial to the interacting area between HB 3 and the H II regions of the W3 complex, where we identified star-forming activity.We further explore the interaction between HB 3 and dense molecular clouds with detections of broad CO(3-2) and CO(2-1) molecular lines from the southern and southeastern shell along the H 2 emitting region. The widths of the broad lines are 8-20 km s −1 ; the detection of such broad lines is unambiguous, dynamic evidence of the interactions between the SNR and clouds. The CO broad lines are from two branches of the bright, southern H 2 shell. We apply the Paris-Durham shock model to the CO line profiles, which infer the shock velocities of 20 -40 km s −1 , relatively low densities of 10 3−4 cm −3 and strong (>200 µG) magnetic fields.

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Surveying the Giant H ii Regions of the Milky Way with SOFIA. I. W51A

Cited by 24 publications

References 86 publications

The Molecular Cloud Lifecycle

The Molecular Cloud Lifecycle

Revisiting the formaldehyde masers

Shocked Molecular Hydrogen and Broad CO lines from the Interacting Supernova Remnant HB 3

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