Astrophys. J., 853, 111-111 (2018/February-1)
First results from the Herschel and ALMA Spectroscopic surveys of the SMC: the relationship between [C II]-bright gas and co-bright gas at low metallicity.
JAMESON K.E., BOLATTO A.D., WOLFIRE M., WARREN S.R., HERRERA-CAMUS R., CROXALL K., PELLEGRINI E., SMITH J.-D., RUBIO M., INDEBETOUW R., ISRAEL F.P., MEIXNER M., ROMAN-DUVAL J., VAN LOON J.T., MULLER E., VERDUGO C., ZINNECKER H. and OKADA Y.
Abstract (from CDS):
The Small Magellanic Cloud (SMC) provides the only laboratory to study the structure of molecular gas at high resolution and low metallicity. We present results from the Herschel Spectroscopic Survey of the SMC (HS3), which mapped the key far-IR cooling lines [C II], [O I], [N II], and [O III] in five star-forming regions, and new ALMA 7 m array maps of 12CO and 13CO(2-1) with coverage overlapping four of the five HS3 regions. We detect [C II] and [O I] throughout all of the regions mapped. The data allow us to compare the structure of the molecular clouds and surrounding photodissociation regions using 13CO, 12CO, [C II], and [O I] emission at 10′′ ( 3 pc) scales. We estimate AV using far-IR thermal continuum emission from dust and find that the CO/[C II] ratios reach the Milky Way value at high AV in the centers of the clouds and fall to ∼1/5–1/10×the Milky Way value in the outskirts, indicating the presence of translucent molecular gas not traced by bright 12CO emission. We estimate the amount of molecular gas traced by bright [C II] emission at low AV and bright 12CO emission at high AV. We find that most of the molecular gas is at low AV and traced by bright [C II] emission, but that faint 12CO emission appears to extend to where we estimate that the H2-to-H I transition occurs. By converting our H2 gas estimates to a CO-to-H2 conversion factor (XCO), we show that XCO is primarily a function of AV, consistent with simulations and models of low-metallicity molecular clouds.
© 2018. The American Astronomical Society. All rights reserved.
galaxies: dwarf - galaxies: evolution - ISM: clouds - Magellanic Clouds - Magellanic Clouds
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