An Unbiased CO Survey Toward the Northern Region of the Small Magellanic Cloud with the Atacama Compact Array. II. CO Cloud Catalog

Ohno, Takahiro; Tokuda, Kazuki; Konishi, Ayu; Matsumoto, Takeru; Sewiło, M.; Kondo, Hiroshi; Sano, Hidetoshi; Tsuge, Kisetsu; Zahorecz, Sarolta; Goto, Nao; Neelamkodan, Naslim; Wong, Tony; Fukushima, Hajime; Takekoshi, Tatsuya; Muraoka, Kazuyuki; Kawamura, Akiko; Tachihara, Kengo; Fukui, Y.; Onishi, Takaharu

doi:10.3847/1538-4357/accadb

Cited by 6 publications

(4 citation statements)

References 75 publications

(108 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Note that the amplitude of ( ) S r at 0.2 Z e is smaller by a factor of 2 than that at 1.0 Z e , as we see in d á ñ r v 2 (see Figure 6). This is consistent with the comparison of the CO line width between clouds in the LMC/SMC and the Milky Way (Bolatto et al 2008;Fukui & Kawamura 2010;Ohno et al 2023), except for those in extreme star-forming systems, such as 30 Dor R136 cluster (Indebetouw et al 2013). Also note that a variation at a given spatial displacement r is larger in the lower-metallicity environment because the shock-compressed layer is thicker, and thus the total number of cells in this analysis increases toward lower metallicity.…”

Section: The Properties/statistics Of the Cnm Clumpssupporting

confidence: 88%

“…Such a hierarchical structure may also determine the fractal nature of the young stellar structures in the LMC, suggested by the spatial clustering analysis of star clusters (e.g., Miller et al 2022). In addition, the similarity between the power-law spectrum of the molecular cloud mass function (e.g., µ a dn dm m where α = 1.7-1.9 in the LMC; Fukui et al 2001;Ohno et al 2023) and that of CNM clump mass function in our simulation also indicates that molecular cloud formation is predetermined by CNM structure (Figure 9). This implication requires further study to be confirmed in the future.…”

Section: Preexistence Of Cnm Structures In the Wnm: Cnmmentioning

confidence: 96%

See 1 more Smart Citation

Metallicity Dependence of Molecular Cloud Hierarchical Structure at Early Evolutionary Stages

Kobayashi,

Iwasaki,

Tomida

et al. 2023

ApJ

View full text Add to dashboard Cite

The formation of molecular clouds out of H i gas is the first step toward star formation. Its metallicity dependence plays a key role in determining star formation throughout cosmic history. Previous theoretical studies with detailed chemical networks calculate thermal equilibrium states and/or thermal evolution under one-zone collapsing background. The molecular cloud formation in reality, however, involves supersonic flows, and thus resolving the cloud internal turbulence/density structure in three dimensions is still essential. We here perform magnetohydrodynamics simulations of 20 km s−1 converging flows of warm neutral medium (WNM) with 1 μG mean magnetic field in the metallicity range from the solar (1.0 Z ⊙) to 0.2 Z ⊙ environment. The cold neutral medium (CNM) clumps form faster with higher metallicity due to more efficient cooling. Meanwhile, their mass functions commonly follow dn / dm ∝ m − 1.7 at three cooling times regardless of the metallicity. Their total turbulence power also commonly shows the Kolmogorov spectrum with its 80% in the solenoidal mode, while the CNM volume alone indicates the transition toward Larson’s law. These similarities measured at the same time in units of the cooling time suggest that the molecular cloud formation directly from the WNM alone requires a longer physical time in a lower-metallicity environment in the 1.0–0.2 Z ⊙ range. To explain the rapid formation of molecular clouds and subsequent massive star formation possibly within ≲10 Myr as observed in the Large/Small Magellanic Clouds, the H i gas already contains CNM volume instead of pure WNM.

show abstract

Section: The Properties/statistics Of the Cnm Clumpssupporting

confidence: 88%

Section: Preexistence Of Cnm Structures In the Wnm: Cnmmentioning

confidence: 96%

Metallicity Dependence of Molecular Cloud Hierarchical Structure at Early Evolutionary Stages

Kobayashi,

Iwasaki,

Tomida

et al. 2023

ApJ

View full text Add to dashboard Cite

show abstract

“…Both values are lower than GMCs in the other 10 external galaxies, while similar to those in M33 (Σ GMC = 30-40 M e pc −2 and σ v R 0.5 = 0.4-0.5). This suggests that low-surface density molecular clouds can be maintained even by the small turbulence (i.e., small velocity dispersion), which results in the observed R-σ v relation in M33 (see also Ohno et al 2023).…”

Section: Size-line-width Relationmentioning

confidence: 86%

“…Considering that the R-σ v relation obtained in M33 is similar to that in the PCC, it is suggested that many molecular clouds in M33 are not associated with active star formation like the PCC. However, this contradicts the fact that more than 70% of clouds in M33 are associated with star-forming regions (e.g., Gratier et al 2012, A. Konishi et al 2023. Indeed, Figure 6 shows that many high-mass (10) 12 CO(J = 2-1) intensity at its peak position of the cloud including uncertainty in units of K km s −1 .…”

Section: Size-line-width Relationmentioning

confidence: 93%

ACA CO(J = 2–1) Mapping of the Nearest Spiral Galaxy M33. I. Initial Results and Identification of Molecular Clouds

Muraoka,

Konishi,

Tokuda

et al. 2023

ApJ

Self Cite

View full text Add to dashboard Cite

We present the results of ALMA-ACA 7 m array observations in 12CO(J = 2–1), 13CO(J = 2–1), and C18O(J = 2–1) line emission toward the molecular-gas disk in the Local Group spiral galaxy M33 at an angular resolution of 7.″31 × 6.″50 (30 × 26 pc). We combined the ACA 7 m array 12CO(J = 2–1) data with the IRAM 30 m data to compensate for emission from diffuse molecular-gas components. The ACA+IRAM combined 12CO(J = 2–1) map clearly depicts the cloud-scale molecular-gas structure over the M33 disk. Based on the ACA+IRAM 12CO(J = 2–1) cube data, we cataloged 848 molecular clouds with a mass range from 103–106 M ⊙. We found that high-mass clouds (≥105 M ⊙) tend to associate with the 8 μm bright sources in the spiral arm region, while low-mass clouds (<105 M ⊙) tend to be apart from such 8 μm bright sources and to exist in the inter-arm region. We compared the cataloged clouds with GMCs observed by the IRAM 30 m telescope at 49 pc resolution (IRAM GMC), and found that a small IRAM GMC is likely to be identified as a single molecular cloud even in ACA+IRAM CO data, while a large IRAM GMC can be resolved into multiple ACA+IRAM clouds. The velocity dispersion of a large IRAM GMC is mainly dominated by the line-of-sight velocity difference between small clouds inside the GMC rather than the internal cloud velocity broadening.

show abstract

Modeling the molecular gas content and CO-to-H₂ conversion factors in low-metallicity star-forming dwarf galaxies

Ramambason,

Lebouteiller,

Madden

et al. 2023

A&A

View full text Add to dashboard Cite

Context. Low-metallicity dwarf galaxies often show no or little CO emission, despite the intense star formation observed in local samples. Both simulations and resolved observations indicate that molecular gas in low-metallicity galaxies may reside in small dense clumps, surrounded by a substantial amount of more diffuse gas that is not traced by CO. Constraining the relative importance of CO-bright versus CO-dark H2 star-forming reservoirs is crucial to understanding how star formation proceeds at low metallicity. Aims. We test classically used single component radiative transfer models and compare their results to those obtained on the assumption of an increasingly complex structure of the interstellar gas, mimicking an inhomogeneous distribution of clouds with various physical properties. Methods. Using the Bayesian code MULTIGRIS, we computed representative models of the interstellar medium as combinations of several gas components, each with a specific set of physical parameters. We introduced physically motivated models assuming power-law distributions for the density, ionization parameter, and the depth of molecular clouds. Results. This new modeling framework allows for the simultaneous reproduction of the spectral constraints from the ionized gas, neutral atomic gas, and molecular gas in 18 galaxies from the Dwarf Galaxy Survey. We confirm the presence of a predominantly CO-dark molecular reservoir in low-metallicity galaxies. The predicted total H2 mass is best traced by [C II]158 μm and, to a lesser extent, by [C I] 609 μm, rather than by CO(1–0). We examine the CO-to-H2 conversion factor (αCO) versus metallicity relation and find that its dispersion increases significantly when different geometries of the gas are considered. We define a “clumpiness” parameter that is anti-correlated with [C II]/CO and explains the dispersion of the αCO versus metallicity relation. We find that low-metallicity galaxies with high clumpiness parameters may have αCO values as low as the Galactic value, even at low metallicity. Conclusions. We identify the clumpiness of molecular gas as a key parameter for understanding variations of geometry-sensitive quantities, such as αCO. This new modeling framework enables the derivation of constraints on the internal cloud distribution of unresolved galaxies, based solely on their integrated spectra.

show abstract

An Unbiased CO Survey Toward the Northern Region of the Small Magellanic Cloud with the Atacama Compact Array. II. CO Cloud Catalog

Cited by 6 publications

References 75 publications

Metallicity Dependence of Molecular Cloud Hierarchical Structure at Early Evolutionary Stages

Metallicity Dependence of Molecular Cloud Hierarchical Structure at Early Evolutionary Stages

ACA CO(J = 2–1) Mapping of the Nearest Spiral Galaxy M33. I. Initial Results and Identification of Molecular Clouds

Modeling the molecular gas content and CO-to-H₂ conversion factors in low-metallicity star-forming dwarf galaxies

Contact Info

Product

Resources

About

An Unbiased CO Survey Toward the Northern Region of the Small Magellanic Cloud with the Atacama Compact Array. II. CO Cloud Catalog

Cited by 6 publications

References 75 publications

Metallicity Dependence of Molecular Cloud Hierarchical Structure at Early Evolutionary Stages

Metallicity Dependence of Molecular Cloud Hierarchical Structure at Early Evolutionary Stages

ACA CO(J = 2–1) Mapping of the Nearest Spiral Galaxy M33. I. Initial Results and Identification of Molecular Clouds

Modeling the molecular gas content and CO-to-H2 conversion factors in low-metallicity star-forming dwarf galaxies

Contact Info

Product

Resources

About

Modeling the molecular gas content and CO-to-H₂ conversion factors in low-metallicity star-forming dwarf galaxies