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The interstellar medium in Andromeda's dwarf spheroidal galaxies - II. Multiphase gas content and ISM conditions

De Looze, Ilse, Baes, Maarten, Cormier, Diane, Kaneko, Hiroyuki, Kuno, Nario, Young, Lisa, Bendo, George J., Boquien, Médéric, Fritz, Jacopo, Gentile, Gianfranco, Kennicutt, Robert C., Madden, Suzanne C., Smith, Matthew W. L. and Wilson, Christine D. 2017. The interstellar medium in Andromeda's dwarf spheroidal galaxies - II. Multiphase gas content and ISM conditions. Monthly Notices of the Royal Astronomical Society 465 (3) , pp. 3741-3758. 10.1093/mnras/stw3001

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Abstract

We make an inventory of the interstellar medium material in three low-metallicity dwarf spheroidal galaxies of the Local Group (NGC 147, NGC 185 and NGC 205). Ancillary H I, CO, Spitzer Infrared Spectrograph spectra, Hα and X-ray observations are combined to trace the atomic, cold and warm molecular, ionized and hot gas phases. We present new Nobeyama CO(1–0) observations and Herschel SPIRE FTS [C I] observations of NGC 205 to revise its molecular gas content. We derive total gas masses of Mg = 1.9–5.5 × 105 M⊙ for NGC 185 and Mg = 8.6–25.0 × 105 M⊙ for NGC 205. Non-detections combine to an upper limit on the gas mass of Mg ≤ 0.3–2.2 × 105 M⊙ for NGC 147. 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 48–139 are also considerably lower compared to the expected GDR ∼ 370 and 520 for the low metal abundances in NGC 185 (0.36 Z⊙) and NGC 205 (0.25 Z⊙), 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 NGC 147, NGC 185 and NGC 205.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Publisher: Oxford University Press
ISSN: 00358711
Date of First Compliant Deposit: 25 July 2017
Date of Acceptance: 16 November 2016
Last Modified: 27 Jul 2017 11:06
URI: http://orca.cf.ac.uk/id/eprint/102958

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