The Arecibo Galaxy Environment Survey X: The Structure of Halo Gas Around M33

Abstract

As part of the HI Arecibo Galaxy Environments Survey (AGES) we have observed 5$\times$4 degrees of sky centred on M33, reaching a limiting column density of $\sim 1.5\times 10^{17}$ 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 HI 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 HI clouds total mass i.e. are the velocities indicative of virialised structures or have they been influenced by tidal interactions with other structures in the Local Group? We identify one particularly interesting HI cloud, AGESM33-31, that has many of the characteristics of HI distributed in the disc of a galaxy, yet there is no known optical counterpart associated with it. This object has a total HI mass of $1.22\times 10^7$ M${}_{\odot }$ and a diameter of 18 kpc if at the distance of M33 ($D_{M33}=840$ kpc). However, we also find that there are numerous other HI 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.

Accepted with minor revisions (corrected)

References in corpus (6)

• RR Lyrae Variables in M33. I. Evidence For a Field Halo Population
• The Arecibo Galaxy Environment Survey: Precursor Observations of the NGC 628 group
• The Arecibo Galaxy Environment Survey: II. A HI view of the Abell cluster 1367 and its outskirts
• HI clouds in the proximity of M33
• Formation of a giant HI bridge between M31 and M33 from their tidal interaction
• The Arecibo Galaxy Environment Survey VII : A Dense Filament With Extremely Long HI Streams

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• Faint and fading tails : the fate of stripped HI gas in Virgo cluster galaxies
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• The Arecibo Galaxy Environment Survey XII : Optically dark HI clouds in the Leo I Group
• Simulating the evolution of optically dark HI clouds in the Virgo cluster : will no-one rid me of this turbulent sphere ?
• The Arecibo Galaxy Environment Survey (AGES) XI: the expanded Abell 1367 field. Data catalogue and HI census over the surveyed volume
• The outskirts of M33: Tidally induced distortions versus signatures of gas accretion
• Neutral Gas Accretion onto Nearby Galaxies
• The case for gravitational millilensing in the multiply--imaged quasar B1152+199
• The Discovery and Origin of A Very-High Velocity Cloud Toward M33
• The Widefield Arecibo Virgo Extragalactic Survey: Early Results on Known Dark Sources
• Ultra Diffuse Galaxies in clusters : the peculiar gas loss of VCC 1964
• The Structure of Halo Gas Around M33