Resolved star formation in the metal-poor star-forming region Magellanic Bridge C

Kalari, V.; Rubio, M.; Saldaño, H. P.; Bolatto, Alberto D.

doi:10.1093/mnras/staa2963

Cited by 12 publications

(13 citation statements)

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“…Molecular clouds with radii 0.3−1 pc, velocity FWHM 1−2 km s −1 and CO luminosities 10−100 K km s −1 pc 2 have been found in Magellanic Bridge B (Saldaño et al 2018). Magellanic Bridge C 12 CO(1−0) emission is concentrated in clouds with radii 0.9−1.5 pc and velocity FWHM 0.5−1.4 km s −1 (Kalari et al 2020), similar to the clouds we found in this work. The Magellanic Bridge A clouds have similar radii and slightly narrower linewidths and luminosities than regions in the LMC and SMC with active star formation, observed at similar (subparsec) resolution.…”

Section: Co(2-1) In Comparison With Previous Studiessupporting

confidence: 86%

ALMA resolves molecular clouds in metal-poor Magellanic Bridge A

Valdivia-Mena

Rubio

Bolatto

et al. 2020

A&A

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Context. The Magellanic Bridge is a tidal feature located between the Magellanic Clouds, containing young stars formed in situ. Its proximity allows high-resolution studies of molecular gas, dust, and star formation in a tidal low-metallicity environment. Aims. Our goal is to characterize gas and dust emission in Magellanic Bridge A, the source with the highest 870 μm excess of emission found in single-dish surveys. Methods. Using the ALMA telescope including the Morita Array, we mapped a 3′ field of view centered on the Magellanic Bridge A molecular cloud, in 1.3 mm continuum emission and 12CO(2−1) line emission at subparsec resolution. This region was also mapped in continuum at 870 μm and in 12CO(2−1) line emission at ~6 pc resolution with the APEX telescope. To study its dust properties, we also use archival Herschel and Spitzer data. We combine the ALMA and APEX 12CO(2−1) line cubes to study the molecular gas emission. Results. Magellanic Bridge A breaks up into two distinct molecular clouds in dust and 12CO(2−1) emission, which we call North and South. Dust emission in the North source, according to our best parameters from fitting the far-infrared fluxes, is ≈3 K colder than in the South source in correspondence to its less developed star formation. Both dust sources present large submillimeter excesses in LABOCA data: according to our best fits the excess over the modified blackbody (MBB) fit to the Spitzer/Herschel continuum is E(870 μm) ~ 7 and E(870 μm) ~ 3 for the North and South sources, respectively. Nonetheless, we do not detect the corresponding 1.3 mm continuum with ALMA. Our limits are compatible with the extrapolation of the MBB fits, and therefore we cannot independently confirm the excess at this longer wavelength. The 12CO(2−1) emission is concentrated in two parsec-sized clouds with virial masses of around 400 and 700 M⊙. Their bulk volume densities are n(H2) ~ 0.7−2.6 × 103 cm−3, higher than typical bulk densities of Galactic molecular clouds. The 12CO luminosity to H2 mass conversion factor αCO is 6.5 and 15.3 M⊙ (K km s−1 pc2)−1 for the North and South clouds, calculated using their respective virial masses and 12CO(2−1) luminosities. Gas mass estimates from our MBB fits to dust emission yields masses M ~ 1.3 × 103 M⊙ and 2.9 × 103 M⊙ for North and South, respectively, a factor of ~4 higher than the virial masses we infer from 12CO.

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Section: Co(2-1) In Comparison With Previous Studiessupporting

confidence: 86%

ALMA resolves molecular clouds in metal-poor Magellanic Bridge A

Valdivia-Mena

Rubio

Bolatto

et al. 2020

A&A

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“…From this value, Y DG 3.5 Y DG,M W would be expected in an environment like the Z = 0.2 Z SMC with f DG ∼ 0.8 (Jameson et al 2018). This corresponds very well to the observed ratio between the usual Galactic X CO,M W and X CO derived in SMC clumps: for sub-pc clumps in the SMC Wing Muraoka et al (2017) derived X CO ∼ 4 X CO,MW , and for pc-scale clumps in the Magellanic Bridge Kalari et al (2020) derived X CO ∼3 X CO,MW and Valdivia-Mena et al ( 2020) found X CO ∼1.5-3.5 X CO,MW . This suggests that Y DG (and f DG ) could be used as a check of measured X CO in clumps, or vice versa.…”

Section: Relationship Between Fdg and The Co-to-h2 Conversion Factorsupporting

confidence: 84%

“…Lower-resolution observations run the risk of small clumps being diluted by large beam sizes, artificially inflating α vir and X CO and also increasing the likelihood of such clumps not being identified at all. Resolved observations of individual pc-scale clumps in distant low-Z environments have only recently become possible and typically yield smaller conversion factors (Muraoka et al 2017;Schruba et al 2017;Saldaño et al 2018;Kalari et al 2020;Valdivia-Mena et al 2020), approaching X CO,M W and in alignment with our expectations for clump f DG .…”

Section: Relationship Between Fdg and The Co-to-h2 Conversion Factorsupporting

confidence: 76%

“…Assessing the gravitational stability of clouds as measured by the virial parameter α vir (Bertoldi & McKee 1992) or if clouds conform to "Larson's relationships" between cloud radius, velocity dispersion, and surface density (Larson 1981) is ubiquitous in both theoretical and observational studies. In low-Z environments, departures from the typical values and relationships between these quantities for CO clouds under Galactic conditions have been observed (e.g., Bolatto et al 2008;Hughes et al 2013;Rubele et al 2015;Ochsendorf et al 2017;Kalari et al 2020). CO-dark (2010).…”

Section: Introductionmentioning

confidence: 99%

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Effects of CO-dark Gas on Measurements of Molecular Cloud Stability and the Size-Linewidth Relationship

O'Neill,

Indebetouw,

Bolatto

et al. 2022

Preprint

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Stars form within molecular clouds, so characterizing the physical states of molecular clouds is key in understanding the process of star formation. Cloud structure and stability is frequently assessed using metrics including the virial parameter and Larson (1981) scaling relationships between cloud radius, velocity dispersion, and surface density. Departures from the typical Galactic relationships between these quantities have been observed in low metallicity environments. The amount of H 2 gas in cloud envelopes without corresponding CO emission is expected to be high under these conditions; therefore, this "CO-dark" gas could plausibly be responsible for the observed variations in cloud properties. We derive simple corrections that can be applied to empirical clump properties (mass, radius, velocity dispersion, surface density, and virial parameter) to account for CO-dark gas in clumps following power-law and Plummer mass density profiles. We find that CO-dark gas is not likely to be the cause of departures from Larson's relationships in low-metallicity regions, but that virial parameters may be systematically overestimated. We demonstrate that correcting for CO-dark gas is critical for accurately comparing the dynamical state and evolution of molecular clouds across diverse environments.

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Section: Introductionmentioning

confidence: 99%

Effects of CO-dark Gas on Measurements of Molecular Cloud Stability and the Size–Linewidth Relationship

O'Neill

Indebetouw

Bolatto

et al. 2022

ApJ

View full text Add to dashboard Cite

Stars form within molecular clouds, so characterizing the physical states of molecular clouds is key to understanding the process of star formation. Cloud structure and stability are frequently assessed using metrics including the virial parameter and Larson scaling relationships between cloud radius, velocity dispersion, and surface density. Departures from the typical Galactic relationships between these quantities have been observed in low-metallicity environments. The amount of H2 gas in cloud envelopes without corresponding CO emission is expected to be high under these conditions; therefore, this CO-dark gas could plausibly be responsible for the observed variations in cloud properties. We derive simple corrections that can be applied to empirical clump properties (mass, radius, velocity dispersion, surface density, and virial parameter) to account for CO-dark gas in clumps following power-law and Plummer mass density profiles. We find that CO-dark gas is not likely to be the cause of departures from Larson’s relationships in low-metallicity regions, but that virial parameters may be systematically overestimated. We demonstrate that correcting for CO-dark gas is critical for accurately comparing the dynamical state and evolution of molecular clouds across diverse environments.

show abstract

Resolved star formation in the metal-poor star-forming region Magellanic Bridge C

Cited by 12 publications

References 74 publications

ALMA resolves molecular clouds in metal-poor Magellanic Bridge A

ALMA resolves molecular clouds in metal-poor Magellanic Bridge A

Effects of CO-dark Gas on Measurements of Molecular Cloud Stability and the Size-Linewidth Relationship

Effects of CO-dark Gas on Measurements of Molecular Cloud Stability and the Size–Linewidth Relationship

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