High Velocity Clouds: Building Blocks of the Local Group

Details High Velocity Clouds: Building Blocks of the Local Group High Velocity Clouds: Building Blocks of the Local Group

1998-03-20

arxiv.org/abs/astro-ph/9803251v1

Astrophys.J.514:818-843,1999

Astronomy and Astrophysics

Astrophysics

65 pages, 27 figures (26 postscript, 1 gif). Submitted to Astrophysical Journal Full figures and paper available at http://w

Scientific paper

10.1086/306963

We suggest that the high--velocity clouds (HVCs) are large clouds, with typical diameters of 25 kpc and containing 5e7 solar masses of neutral gas and 3e8 solar masses of dark matter, falling onto the Local Group; altogether the HVCs contain 10$^{11}$ solar masses of neutral gas. Our reexamination of the Local-Group hypothesis for the HVCs connects their properties to the hierarchical structure formation scenario and to the gas seen in absorbtion towards quasars. We begin by showing that at least one HVC complex (besides the Magellanic Stream) must be extragalactic at a distance > 40 kpc from the Galactic center, with a diameter > 20 kpc and a mass > 1e8 solar masses. We interpret the more distant HVCs as dark matter ``mini--halos'' moving along filaments towards the Local Group. Most poor galaxy groups should contain HI structures to large distances bound to the group. The HVCs are local analogues of the Lyman--limit clouds We argue that there is a Galactic fountain in the Milky Way, but that the fountain does not explain the origin of the HVCs. Our analysis of the HI data leads to the detection of a vertical infall of low-velocity gas towards the plane. This implies that the chemical evolution of the Galactic disk is governed by episodic infall of metal-poor HVC gas that only slowly mixes with the rest of the interstellar medium. The Local--Group infall hypothesis makes a number of testable predictions. The HVCs should have sub-solar metallicities. Their H$\alpha $ emission should be less than that seen from the Magellanic Stream. The clouds should not be seen in absorption to nearby stars. The clouds should be detectable in both emission and absorption around other groups.

Affiliated with

Also associated with

No associations

Rating

High Velocity Clouds: Building Blocks of the Local Group does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with High Velocity Clouds: Building Blocks of the Local Group, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High Velocity Clouds: Building Blocks of the Local Group will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-680942