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The Arecibo Galaxy Environment Survey - X. The structure of halo gas around M33

Keenan, O. C., Davies, J. I., Taylor, R. and Minchin, R. F. 2016. The Arecibo Galaxy Environment Survey - X. The structure of halo gas around M33. Monthly Notices of the Royal Astronomical Society 456 (1) , pp. 951-960. 10.1093/mnras/stv2684

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As part of the H i Arecibo Galaxy Environment Survey (AGES), we have observed 5 × 4 deg of sky centred on M33, reaching a limiting column density of ∼1.5 × 1017 cm−2 (line width of 10 km s−1 and resolution 3.5 arcmin). We particularly investigate the absence of optically detected dwarf galaxies around M33, something that is contrary to galaxy formation models. We identify 22 discrete H i clouds, 11 of which are new detections. The number of objects detected and their internal velocity dispersion distribution is consistent with expectations from standard galaxy formation models. However, the issue remains open as to whether the observed velocity dispersions can be used as a measure of the H i clouds total mass, i.e. are the velocities indicative of virialized structures or have they been influenced by tidal interactions with other structures in the Local Group? We identify one particularly interesting H i cloud, AGESM33-31, that has many of the characteristics of H i distributed in the disc of a galaxy, yet there is no known optical counterpart associated with it. This object has a total H i mass of 1.22 × 107 M⊙ and a diameter of 18 kpc if at the distance of M33 (DM33 = 840 kpc). However, we also find that there are numerous other H i clouds in this region of sky that have very similar velocities and so it is plausible that all these clouds are actually associated with debris from the Magellanic stream.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Uncontrolled Keywords: galaxies: clusters: general; galaxies: dwarf; Local Group; radio lines: galaxies
Publisher: Oxford University Press
ISSN: 0035-8711
Date of First Compliant Deposit: 11 September 2017
Date of Acceptance: 13 November 2015
Last Modified: 05 May 2023 15:21

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