COMPACT H I CLOUDS FROM THE GALFA-H I SURVEY

The GALFA-H i Survey: Techniques

We explain the entire process by which we conduct the Galactic Arecibo L-Band Feed Array Hi (GALFA-Hi) survey. The survey is a high resolution (3.4′), large area (13000 deg2), large Galactic velocity range (−750 to +750 km s−1), high spectral resolution (0.18 km s−1) survey of the Galaxy in the 21 cm line hyperfine transition of hydrogen conducted at Arecibo Observatory. We touch on some of the...

A Targeted Survey for H I Clouds in Galaxy Groups

Five galaxy groups with properties similar to those of the Local Group have been surveyed for H i clouds with the Arecibo Telescope. In total 300 pointings have been observed on grids of approximately 2.5 × 1.5 Mpc centred on the groups. The 4.5σ detection limit on the minimal detectable H i masses is approximately 7 × 10 M⊙ (H0 = 65 km s −1 Mpc). All detections could be attributed to optical g...

Isolated Ob Associations in Stripped H I Gas Clouds

HST ACS/HRC images in UV (F250W), V (F555W), and I (F814W) resolve three isolated OB associations that lie up to 30 kpc from the stellar disk of the S0 galaxy NGC 1533. Previous narrow-band Hα imaging and optical spectroscopy showed these objects as unresolved intergalactic H II regions having Hα luminosities consistent with single early-type O stars. These young stars lie in stripped H I gas w...

How Long Can Tiny H I Clouds Survive?

We estimate the evaporation timescale for spherical H I clouds consisting of the cold neutral medium surrounded by the warm neutral medium. We focus on clouds smaller than 1pc, which corresponds to tiny H I clouds recently discovered by Braun & Kanekar and Stanimirović & Heiles. By performing one-dimensional spherically symmetric numerical simulations of the two-phase interstellar medium (ISM),...

Magnetic Fields in Diffuse H I and Molecular Clouds