Journal Article

Relics of structure formation: extra-planar gas and high-velocity clouds around the Andromeda Galaxy

T. Westmeier, C. Brüns and J. Kerp

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 390, issue 4, pages 1691-1709
Published in print November 2008 | ISSN: 0035-8711
Published online October 2008 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.13858.x
Relics of structure formation: extra-planar gas and high-velocity clouds around the Andromeda Galaxy

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Using the 100-m radio telescope at Effelsberg, we mapped a large area around the Andromeda Galaxy in the 21 cm line emission of neutral hydrogen to search for high-velocity clouds (HVCs) out to large projected distances in excess of 100 kpc. Our 3σ H i mass sensitivity for the warm neutral medium is 8 × 104M. We can confirm the existence of a population of HVCs near M31 with typical H i masses of a few times 105M. However, we did not detect any HVCs beyond a projected distance of about 50 kpc from M31, suggesting that HVCs are generally found in proximity of large spiral galaxies at typical distances of a few 10 kpc.

Comparison with cold dark matter (CDM)-based models and simulations suggests that only a few of the detected HVCs could be associated with primordial dark matter satellites, whereas others are most likely the result of tidal stripping. The lack of clouds beyond a projected distance of 50 kpc from M31 is also in conflict with the predictions of recent CDM structure formation simulations. A possible solution to this problem could be ionization of the HVCs as a result of decreasing pressure of the ambient coronal gas at larger distances from M31. A consequence of this scenario would be the presence of hundreds of mainly ionized or pure dark matter satellites around large spiral galaxies like the Milky Way and M31.

Keywords: galaxies: evolution; galaxies: individual: M31; intergalactic medium

Journal Article.  16162 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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