The interstellar medium in Andromeda's dwarf spheroidal galaxies – II. Multiphase gas content and ISM conditions
2016; Oxford University Press; Volume: 465; Issue: 3 Linguagem: Inglês
10.1093/mnras/stw3001
ISSN1365-2966
AutoresI. De Looze, M. Baes, D. Cormier, Hiroyuki Kaneko, Nario Kuno, L. M. Young, G. J. Bendo, M. Boquien, J. Fritz, Gianfranco Gentile, Robert C. Kennicutt, S. C. Madden, M. W. L. Smith, C. D. Wilson,
Tópico(s)Stellar, planetary, and galactic studies
ResumoWe make an inventory of the interstellar medium material in three low-metallicity dwarf spheroidal galaxies of the Local Group (NGC147, NGC185 and NGC205). Ancillary HI, CO, Spitzer IRS spectra, H{\alpha} and X-ray observations are combined to trace the atomic, cold and warm molecular, ionised and hot gas phases. We present new Nobeyama CO(1-0) observations and Herschel SPIRE FTS [CI] observations of NGC205 to revise its molecular gas content. We derive total gas masses of M_gas = 1.9-5.5x10^5 Msun for NGC185 and M_gas = 8.6-25.0x10^5 Msun for NGC205. Non-detections combine to an upper limit on the gas mass of M_gas =< 0.3-2.2x10^5 Msun for NGC147. The observed gas reservoirs are significantly lower compared to the expected gas masses based on a simple closed-box model that accounts for the gas mass returned by planetary nebulae and supernovae. The gas-to-dust mass ratios GDR~37-107 and GDR~48-139 are also considerably lower compared to the expected GDR~370 and GDR~520 for the low metal abundances in NGC 185 (0.36 Zsun) and NGC205 (0.25 Zsun), respectively. To simultaneously account for the gas deficiency and low gas-to-dust ratios, we require an efficient removal of a large gas fraction and a longer dust survival time (~1.6 Gyr). We believe that efficient galactic winds (combined with heating of gas to sufficiently high temperatures in order for it to escape from the galaxy) and/or environmental interactions with neighbouring galaxies are responsible for the gas removal from NGC147, NGC185 and NGC205.
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