TY - JOUR
T1 - Warm molecular gas in dwarf starburst galaxies
T2 - CO(3-2) observations
AU - Meier, David S.
AU - Turner, Jean L.
AU - Crosthwaite, Lucian P.
AU - Beck, Sara C.
PY - 2001/2
Y1 - 2001/2
N2 - Eight dwarf starburst galaxies have been observed with the Caltech Submillimeter Observatory telescope in the CO J = 3-2 transition. The galaxies observed are He 2-10, NGC 5253, 1569, and 3077, Haro 2, Haro 3, II Zw 40, and Mrk 86; all but the last two are detected. The central regions of He 2-10 and NGC 5253 were mapped and a CO(2-1) spectrum of NGC 5253 was obtained. The error-weighted mean CO(3-2)/CO(1-0) ratio of the detected galaxies is 0.60 ± 0.06, which is virtually identical to that found for starbursts in the nuclei of nearby spirals and suggests that the molecular gas is optically thick, warm (Tk > 20 K), and moderately dense (nH2 ∼ 103-104 cm-3). The CO(3-2)/CO(1-0) ratio peaks at or close to the starburst in all cases. CO emission does not appear to be optically thin in these dwarfs, despite the low metallicity and intense radiation fields, probably because for CO to exist in detectable amounts it must be self-shielding and hence optically thick. Physical properties of the molecular clouds in these dwarf starbursts appear to be essentially the same as those in nearby spiral nuclei, with the possible exception that CO is more confined to the cloud cores.
AB - Eight dwarf starburst galaxies have been observed with the Caltech Submillimeter Observatory telescope in the CO J = 3-2 transition. The galaxies observed are He 2-10, NGC 5253, 1569, and 3077, Haro 2, Haro 3, II Zw 40, and Mrk 86; all but the last two are detected. The central regions of He 2-10 and NGC 5253 were mapped and a CO(2-1) spectrum of NGC 5253 was obtained. The error-weighted mean CO(3-2)/CO(1-0) ratio of the detected galaxies is 0.60 ± 0.06, which is virtually identical to that found for starbursts in the nuclei of nearby spirals and suggests that the molecular gas is optically thick, warm (Tk > 20 K), and moderately dense (nH2 ∼ 103-104 cm-3). The CO(3-2)/CO(1-0) ratio peaks at or close to the starburst in all cases. CO emission does not appear to be optically thin in these dwarfs, despite the low metallicity and intense radiation fields, probably because for CO to exist in detectable amounts it must be self-shielding and hence optically thick. Physical properties of the molecular clouds in these dwarf starbursts appear to be essentially the same as those in nearby spiral nuclei, with the possible exception that CO is more confined to the cloud cores.
KW - Galaxies: ISM
KW - Galaxies: dwarf
KW - Galaxies: nuclei
KW - Galaxies: starburst
KW - Radio emission lines
UR - http://www.scopus.com/inward/record.url?scp=0001295924&partnerID=8YFLogxK
U2 - 10.1086/318782
DO - 10.1086/318782
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AN - SCOPUS:0001295924
SN - 0004-6256
VL - 121
SP - 740
EP - 752
JO - Astronomical Journal
JF - Astronomical Journal
IS - 2
ER -