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

Abstract

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 3-sigma HI mass sensitivity for the warm neutral medium is 8x10^4 solar masses. We can confirm the existence of a population of HVCs with typical HI masses of a few times 10^5 solar masses near the disc of M31. 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 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 ionisation 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 ionised or pure dark-matter satellites around large spiral galaxies like the Milky Way and M31.

21 pages, 15 figures, accepted for publication in MNRAS

References in corpus (11)

• Discovery and analysis of three faint dwarf galaxies and a globular cluster in the outer halo of the Andromeda galaxy
• The spatial distribution of the Milky Way and Andromeda satellite galaxies
• Distances to Galactic high-velocity clouds. I. Cohen Stream, complex GCP, cloud g1
• Distances to Galactic high-velocity clouds. Complex C
• An Accurate Distance to High-Velocity Cloud Complex C
• Investigating the Andromeda Stream: III. A Young Shell System in M31
• The Once and Future Andromeda Stream
• The origin of globular cluster systems from cosmological simulations
• The many streams of the Magellanic Stream
• The scattered debris of the Magellanic Stream
• Physical properties of two compact high-velocity clouds possibly associated with the Leading Arm of the Magellanic System

Cited by in corpus (11)

• Evidence for a Massive, Extended Circumgalactic Medium Around the Andromeda Galaxy
• The Smith Cloud and its dark matter halo: Survival of a Galactic disc passage
• Project AMIGA: A Minimal Covering Factor for Optically Thick Circumgalactic Gas Around the Andromeda Galaxy
• The HI Chronicles of LITTLE THINGS BCDS III: Gas Clouds in and around Mrk 178, VII Zw 403, AND NGC 3738
• Searching for Dark Matter Annihilation in the Smith High-Velocity Cloud
• The effect of rotation on the thermal instability of stratified galactic atmospheres - II. The formation of High Velocity Clouds
• A 5deg x 5deg deep HI survey of the M81 group: II. HI distribution and kinematics of IC 2574 and HIJASS J1021+68
• Solar-Metallicity Gas in the Extended Halo of a Galaxy at $z\sim 0.12$
• Evidence for a hot galactic halo around the Andromeda Galaxy using fast radio bursts along two sightlines
• A Component of the Smith High Velocity Cloud Now Crossing the Galactic Plane
• Cosmic Rays and Non-thermal Emission Induced by Accretion of Cool Gas onto the Galactic Disk