Molecular gas in the outer disks of galaxies

J. Braine 1
1 FORMATION STELLAIRE 2017
LAB - Laboratoire d'Astrophysique de Bordeaux [Pessac]
Abstract : Molecular gas has still only been detected beyond the R25 radius in a few galaxies. Is this due to the low H2 content or to the difficulty of using Carbon Monoxide (CO) to trace H2? Similarly, star formation (SF) decreases sharply in the outer disks of spirals although HI is often plentiful; is the decrease in SF because there is little H2 or because the SF is very inefficient in the outer disk environment? Existing observations suggest that while outer disk clouds tend to be smaller (steeper mass function), their CO brightness temperature is only slightly lower than in the inner disk, at least when observed with sufficiently high angular resolution. In near-solar metallicity galaxies (Z >= 0.5Zsol ), the CO does not become intrinsically difficult to detect when H2 is present, even in the outer disk. While more observations of CO or other means of tracing H2 in the outer disks are necessary, current data tend to show that the SF rate per unit H2 remains approximately constant with galactocentric distance, indicating that the star formation proceeds normally but the transformation of HI into H2 is very slow in the outer disk.
Type de document :
Communication dans un congrès
2017IAUS.321.217B - Formation and Evolution of Galaxy Outskirts, Proceedings of the International Astronomical Union, IAU Symposium, Volume 321, pp. 217-219, 2017 held on march 14-18-, 2016 in Toledo, spain, Mar 2016, Toledo, Spain. 11 (S321), pp.217 - 219, <10.1017/S1743921316011777>
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https://hal.archives-ouvertes.fr/hal-01497751
Contributeur : Marie-Paule Pomies <>
Soumis le : mercredi 29 mars 2017 - 11:06:15
Dernière modification le : jeudi 30 mars 2017 - 01:07:40

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J. Braine. Molecular gas in the outer disks of galaxies. 2017IAUS.321.217B - Formation and Evolution of Galaxy Outskirts, Proceedings of the International Astronomical Union, IAU Symposium, Volume 321, pp. 217-219, 2017 held on march 14-18-, 2016 in Toledo, spain, Mar 2016, Toledo, Spain. 11 (S321), pp.217 - 219, <10.1017/S1743921316011777>. <hal-01497751>

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