Ministerio de Economía y Competitividad Gobierno de Canarias Universidad de La Laguna CSIC Centro de Excelencia Severo Ochoa

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A gigantic molecular cloud in a side of the low metallicity galaxy KISO 5639

Author/s: B. G. Elmegreen, C. Herrera, M. Rubio, D. M. Elmegreen, J. Sánchez Almeida, C. Muñoz-Tuñón, A. Olmo-García

Reference: 2018 ApJL 859 L22 | Link

Color image of Kiso 5639 from HST (Elmegreen et al. 2016, ApJ, 825, 145) in Hα, V, and B bands with superimposed CO contours tracing hydrogen molecules. The main molecular cloud contains ∼3 × 10<sup>7</sup> solar masses and is offset from the bright star formation region near the head of this tadpole galaxy. This lopsided structure is proposed to be the result of gaseous accretion or an impact event.
Color image of Kiso 5639 from HST (Elmegreen et al. 2016, ApJ, 825, 145) in Hα, V, and B bands with superimposed CO contours tracing hydrogen molecules. The main molecular cloud contains ∼3 × 107 solar masses and is offset from the bright star formation region near the head of this tadpole galaxy. This lopsided structure is proposed to be the result of gaseous accretion or an impact event.

A giant star-forming region in a metal-poor dwarf galaxy has been observed in optical lines with the 10-m  Gran Telescopio Canarias and in the emission line of CO(1-0) with the NOEMA mm-wave interferometer. The metallicity was determined to be around 15% solar, from which we estimate a molecular cloud mass of ~ 3 × 107 solar masses. This is an enormous concentration of molecular mass at one end of a small galaxy, suggesting a recent accretion. The molecular cloud properties seem normal, comparable to that of a standard giant molecular cloud. The virial ratio suggests the cloud to be gravitationally self-bound, and the gas consumption time, 0.5 Gyr, is typical for molecular regions. The low metallicity implies that the cloud is close to the threshold for molecule formation and so requires high internal pressure. High pressure is associated with the formation of massive clusters, therefore metal-poor galaxies such as dwarfs in the early universe could have been the hosts of metal-poor globular clusters.

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