scholarly journals The state of molecular gas in the Small Magellanic Cloud

2008 ◽  
Vol 4 (S256) ◽  
pp. 154-159
Author(s):  
Adam K. Leroy ◽  
Alberto D. Bolatto ◽  
Erik Rosolowsky ◽  
Snežana Stanimirović ◽  
Norikazu Mizuno ◽  
...  
Keyword(s):  
Molecular Clouds ◽  
Dust Emission ◽  
Line Emission ◽  
Stellar Mass ◽  
Magellanic Cloud ◽  
Molecular Gas ◽  
Giant Molecular Clouds ◽  
Small Magellanic Cloud ◽  
Irregular Galaxies ◽  
Low Mass

AbstractWe compare the resolved properties of giant molecular clouds (GMCs) in the Small Magellanic Cloud (SMC) and other low mass galaxies to those in more massive spirals. When measured using CO line emission, differences among the various populations of GMCs are fairly small. We contrast this result with the view afforded by dust emission in the Small Magellanic Cloud. Comparing temperature-corrected dust opacity to the distribution of Hisuggests extended envelopes of CO-free H2, implying that CO traces only the highest density H2in the SMC. Including this CO-free H2, the gas depletion time, H2-to-Hiratio, and H2-to-stellar mass/light ratio in the SMC are all typical of those found in more massive irregular galaxies.

scholarly journals CO Observations in the Small Magellanic Cloud

1984 ◽  
Vol 108 ◽  
pp. 399-400
Author(s):  
M. Rubio ◽  
R. Cohen ◽  
J. Montani
Keyword(s):  
Molecular Clouds ◽  
Milky Way ◽  
Dwarf Galaxies ◽  
Magellanic Cloud ◽  
Giant Molecular Clouds ◽  
Small Magellanic Cloud ◽  
Irregular Galaxies ◽  
The Galaxy ◽  
Co Emission ◽  
Co Observations

The dwarf Magellanic irregular galaxies apparently have a very low molecular content compared to the Milky Way. In the LMC, molecular clouds are fairly common, but the ratio of molecular to atomic gas is at least 5 times lower than in the Galaxy (Cohen et al. 1984). Elmegreen et al. (1980) searched for CO in 6 dwarf galaxies and failed to detect any emission even though their sensitivity was adequate to detect galactic giant molecular clouds placed at the distance of these galaxies. Israel (1984) observed the J=2→1 transition of CO at 15 points in the Small Magellanic Cloud and detected CO emission from five of them, but at a level two to six times lower than typical galactic values.

scholarly journals Rise and fall of molecular clouds across the M 33 disk

2019 ◽  
Vol 622 ◽  
pp. A171 ◽  
Author(s):  
Edvige Corbelli ◽  
Jonathan Braine ◽  
Carlo Giovanardi
Keyword(s):  
Molecular Clouds ◽  
Line Emission ◽  
Molecular Gas ◽  
Stellar Clusters ◽  
Giant Molecular Clouds ◽  
Hii Region ◽  
Star Forming ◽  
Outer Disk ◽  
Low Mass ◽  
The Mean

We carried out deep searches for CO line emission in the outer disk of M 33, at R >  7 kpc, and examined the dynamical conditions that can explain variations in the mass distribution of the molecular cloud throughout the disk of M 33. We used the IRAM-30 m telescope to search for CO lines in the outer disk toward 12 faint mid-infrared (MIR) selected sources and in an area of the southern outer disk hosting MA1, a bright HII region. We detect narrow CO lines at the location of two MIR sources at galactocentric distances of about 8 kpc that are associated with low-mass young stellar clusters, and at four locations in the proximity of MA1. The paucity of CO lines at the location of weak MIR-selected sources probably arises because most of them are not star-forming sites in M 33, but background sources. Although very uncertain, the total molecular mass of the detected clouds around MA1 is lower than expected given the stellar mass of the cluster, because dispersal of the molecular gas is taking place as the HII region expands. The mean mass of the giant molecular clouds (GMCs) in M 33 decreases radially by a factor 2 from the center out to 4 kpc, then it stays constant until it drops at R >  7 kpc. We suggest that GMCs become more massive toward the center because of the fast rotation of the disk, which drives mass growth by coalescence of smaller condensations as they cross the arms. The analysis of both HI and CO spectral data gives the consistent result that corotation of the two main arms in this galaxy is at a radius of 4.7 ± 0.3 kpc, and spiral shock waves become subsonic beyond 3.9 kpc. Perturbations are quenched beyond 6.5 kpc, where CO lines have been detected only around sporadic condensations associated with UV and MIR emission.

scholarly journals Enhanced UV radiation and dense clumps in the molecular outflow of Mrk 231

2020 ◽  
Vol 633 ◽  
pp. A163 ◽  
Author(s):  
Claudia Cicone ◽  
Roberto Maiolino ◽  
Susanne Aalto ◽  
Sebastien Muller ◽  
Chiara Feruglio
Keyword(s):  
Gas Phase ◽  
Uv Radiation ◽  
Molecular Clouds ◽  
Line Emission ◽  
Molecular Gas ◽  
Spectral Features ◽  
Giant Molecular Clouds ◽  
Dense Phase ◽  
Molecular Outflow ◽  
First Time

We present interferometric observations of the CN(1–0) line emission in Mrk 231 and combine them with previous observations of CO and other H2 gas tracers to study the physical properties of the massive molecular outflow. We find a strong boost of the CN/CO(1–0) line luminosity ratio in the outflow of Mrk 231, which is unprecedented compared to any other known Galactic or extragalactic astronomical source. For the dense gas phase in the outflow traced by the HCN and CN emissions, we infer XCN ≡ [CN]/[H2]> XHCN by at least a factor of three, with H2 gas densities of nH2 ∼ 105−6 cm−3. In addition, we resolve for the first time narrow spectral features in the HCN(1–0) and HCO+(1–0) high-velocity line wings tracing the dense phase of the outflow. The velocity dispersions of these spectral features, σv ∼ 7−20 km s−1, are consistent with those of massive extragalactic giant molecular clouds detected in nearby starburst nuclei. The H2 gas masses inferred from the HCN data are quite high, Mmol ∼ 0.3−5 × 108 M⊙. Our results suggest that massive complexes of denser molecular gas survive embedded into the more diffuse H2 phase of the outflow, and that the chemistry of these outflowing dense clouds is strongly affected by UV radiation.

scholarly journals Molecular gas in the Small Magellanic Cloud

1991 ◽  
Vol 148 ◽  
pp. 429-430
Author(s):  
Monica Rubio
Keyword(s):  
Molecular Hydrogen ◽  
Molecular Clouds ◽  
Column Density ◽  
Angular Resolution ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Molecular Gas ◽  
Small Magellanic Cloud ◽  
Hydrogen Column Density ◽  
Co Emission

We summarize the results of observations of molecular gas from the Small Magellanic Cloud (SMC) made with low angular resolution (8'.8). These observations show that the CO emission is weak (TA˜ 0.04K) and that the CO luminosities of the Clouds are low compared to those of Galactic molecular clouds. The factor to convert the CO luminosity to molecular hydrogen column density for the SMC is ˜20 and three times larger than those derived for clouds in our Galaxy and in the Large Magellanic Cloud (LMC) respectively. In addition, we present preliminary results of high resolution (40″) observations of SMC molecular clouds made with the SEST telescope.

scholarly journals LABOCA observations of giant molecular clouds in the southwest region of the Small Magellanic Cloud

2010 ◽  
Vol 524 ◽  
pp. A52 ◽  
Author(s):  
C. Bot ◽  
M. Rubio ◽  
F. Boulanger ◽  
M. Albrecht ◽  
A. Leroy ◽  
...  
Keyword(s):  
Molecular Clouds ◽  
Magellanic Cloud ◽  
Giant Molecular Clouds ◽  
Small Magellanic Cloud ◽  
Southwest Region

scholarly journals Tracing the cold molecular gas reservoir through dust emission in the SMC

2008 ◽  
Vol 4 (S256) ◽  
pp. 148-153
Author(s):  
Caroline Bot ◽  
Mónica Rubio ◽  
François Boulanger ◽  
Marcus Albrecht ◽  
Frank Bertoldi ◽  
...  
Keyword(s):  
Molecular Clouds ◽  
Virial Theorem ◽  
Spectral Energy Distribution ◽  
Dust Emission ◽  
Spectral Energy ◽  
Molecular Gas ◽  
Giant Molecular Clouds ◽  
Gas Reservoir ◽  
Co Emission ◽  
Co Observations

AbstractThe amount of molecular gas is a key for understanding the future star formation in a galaxy. However, this quantity is difficult to infer as the cold H2 is almost impossible to observe and, especially at low metallicities, CO only traces part of the clouds, keeping large envelopes of H2 hidden from observations. In this context, millimeter dust emission tracing the cold and dense regions can be used as a tracer to unveil the total molecular gas masses. I present studies of a sample of giant molecular clouds in the Small Magellanic Cloud. These clouds have been observed in the millimeter and sub-millimeter continuum of dust emission: with SIMBA/SEST at 1.2 mm and the new LABOCA bolometer on APEX at 870 μm. Combining these with radio data for each cloud, the spectral energy distribution of dust emission are obtained and gas masses are inferred. The molecular cloud masses are found to be systematically larger than the virial masses deduced from CO emission. Therefore, the molecular gas mass in the SMC has been underestimated by CO observations, even through the dynamical masses. This result confirms what was previously observed by Bot et al. (2007). We discuss possible interpretations of the mass discrepancy observed: in the giant molecular clouds of the SMC, part of cloud's support against gravity could be given by a magnetic field. Alternatively, the inclusion of surface terms in the virial theorem for turbulent clouds could reproduce the observed results and the giant molecular clouds could be transient structures.

scholarly journals ALMA resolves molecular clouds in metal-poor Magellanic Bridge A

2020 ◽  
Vol 641 ◽  
pp. A97 ◽  
Author(s):  
M. T. Valdivia-Mena ◽  
M. Rubio ◽  
A. D. Bolatto ◽  
H. P. Saldaño ◽  
C. Verdugo
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Dust Emission ◽  
Line Emission ◽  
Far Infrared ◽  
Continuum Emission ◽  
Molecular Gas ◽  
The North ◽  
Mass Conversion ◽  
North And South

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.

scholarly journals Molecules in the Magellanic Clouds

1991 ◽  
Vol 148 ◽  
pp. 415-420 ◽  
Author(s):  
R. S. Booth ◽  
Th. De Graauw
Keyword(s):  
High Resolution ◽  
Molecular Clouds ◽  
Short Review ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Giant Molecular Clouds ◽  
Interstellar Molecules ◽  
First Time ◽  
Excitation Conditions

In this short review we describe recent new observations of millimetre transitions of molecules in selected regions of the Magellanic Clouds. The observations were made using the Swedish-ESO Submillimetre Telescope, SEST, (Booth et al. 1989), the relatively high resolution of which facilitates, for the first time, observations of individual giant molecular clouds in the Magellanic Clouds. We have mapped the distribution of the emission from the two lowest rotational transitions of 12CO and 13CO and hence have derived excitation conditions for the molecule. In addition, we have observed several well-known interstellar molecules in the same regions, thus doubling the number of known molecules in the Large Magellanic Cloud (LMC). The fact that all the observations have been made under controlled conditions with the same telescope enables a reasonable intercomparison of the molecular column densities. In particular, we are able to observe the relative abundances among the different isotopically substituted species of CO.

scholarly journals The global star formation law: from dense cores to extreme starbursts

2006 ◽  
Vol 2 (S237) ◽  
pp. 331-335
Author(s):  
Yu Gao
Keyword(s):  
Star Formation ◽  
Linear Correlation ◽  
Molecular Clouds ◽  
High Redshift ◽  
Gas Content ◽  
Molecular Gas ◽  
Giant Molecular Clouds ◽  
Active Star ◽  
Dense Cores ◽  
The Galaxy

AbstractActive star formation (SF) is tightly related to the dense molecular gas in the giant molecular clouds' dense cores. Our HCN (measure of the dense molecular gas) survey in 65 galaxies (including 10 ultraluminous galaxies) reveals a tight linear correlation between HCN and IR (SF rate) luminosities, whereas the correlation between IR and CO (measure of the total molecular gas) luminosities is nonlinear. This suggests that the global SF rate depends more intimately upon the amount of dense molecular gas than the total molecular gas content. This linear relationship extends to both the dense cores in the Galaxy and the hyperluminous extreme starbursts at high-redshift. Therefore, the global SF law in dense gas appears to be linear all the way from dense cores to extreme starbursts, spanning over nine orders of magnitude in IR luminosity.

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