A Search for Atomic Hydrogen and Molecular Gas Absorption in High-Velocity Clouds

Details A Search for Atomic Hydrogen and Molecular Gas Absorption in High-Velocity Clouds A Search for Atomic Hydrogen and Molecular Gas Absorption in High-Velocity Clouds

Sep 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999apj...523..163a&link_type=abstract

The Astrophysical Journal, Volume 523, Issue 1, pp. 163-170.

Astronomy and Astrophysics

Astronomy

12

Galaxies: Kinematics And Dynamics, Radio Lines: Ism, Ism: Structure

Scientific paper

We have searched for H I, CO, and HCO^+ in absorption along 16 lines of sight toward high-velocity clouds (HVCs). Of these, seven lines of sight are toward true HVCs, two are toward the Magellanic Stream, six are toward the outer arm complex, and one is toward a probable Galactic cloud. We detected absorption along two lines of sight toward the outer arm complex, at T_S=38 and 147 K, respectively. The detections are consistent with normal disk H I absorption. The nondetections suggest that HVCs are weak H I absorbers and that they contain primarily warm H I, with a surface filling fraction of cold (~50 K) gas of less than 7%. In one case, we obtained a 3 sigma lower limit to the spin temperature of 180-320 K. Upper limits for CO and HCO^+ emission along seven lines of sight are the most sensitive probes of molecular emission yet toward HVCs. The best upper limits imply N(CO)<5.5x10^14 and N(H_2)<5.5x10^18 cm^-2, assuming solar abundances and in one case a molecular gas fraction less than 17% at the 3 sigma level. Averaging the CO nondetections to test for broader, low-level absorption implies N(CO)<4.8x10^14 cm^-2.

Affiliated with

Also associated with

No associations

Rating

A Search for Atomic Hydrogen and Molecular Gas Absorption in High-Velocity Clouds 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 A Search for Atomic Hydrogen and Molecular Gas Absorption in High-Velocity Clouds, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and A Search for Atomic Hydrogen and Molecular Gas Absorption in High-Velocity Clouds will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1769310