Destry R. Saul

A High-resolution Study of the H I-H2 Transition across the Perseus Molecular Cloud

To investigate the fundamental principles of H2 formation in a giant molecular cloud, we derive the H I and H2 surface density (?H I and ?H2) images of the Perseus molecular cloud on sub-pc scales (~0.4?pc). We use the far-infrared data from the Improved Reprocessing of the IRAS Survey and the V-band extinction image provided by the COMPLETE Survey to estimate the dust column density image of Perseus. In combination with the H I data from the Galactic Arecibo L-band Feed Array H I Survey and an estimate of the local dust-to-gas ratio, we then derive the ?H2 distribution across Perseus. We find a relatively uniform ?H I ~ 6-8 M ??pc?2 for both dark and star-forming regions, suggesting a minimum H I surface density required to shield H2 against photodissociation. As a result, a remarkably tight and consistent relation is found between ?H2/?H I and ?H I + ?H2. The transition between the H I- and H2-dominated regions occurs at N(H I) + 2N(H2) ~ (8-14)?? 1020?cm?2. Our findings are consistent with predictions for H2 formation in equilibrium, suggesting that turbulence may not be of primary importance for H2 formation. However, the importance of a warm neutral medium for H2 shielding, an internal radiation field, and the timescale of H2 formation still remain as open questions. We also compare H2 and CO distributions and estimate the fraction of CO-dark gas, f DG ~ 0.3. While significant spatial variations of f DG are found, we do not find a clear correlation with the mean V-band extinction.

A SEARCH FOR RADIO TRANSIENTS IN VERY LARGE ARRAY ARCHIVAL IMAGES OF THE 3C 286 FIELD

We present a search for radio transients in the field of the bright radio source 3C 286 using archival observations from the Very Large Array. These observations span 23 years and include 1852 epochs at 1.4 GHz in the C and D configurations. We find no transients in the field. The sensitivity of the observations is limited by dynamic range effects in the images. At large flux densities (

Dust-to-gas ratios of the GALFA-H i Compact Cloud Catalog

> 0.2

Characterizing the turbulent properties of the starless molecular cloud MBM 16

Jy), single epoch observations provide a strong limit on the transient surface density. At flux densities near the dynamic range threshold, we use the requirement that transient sources must appear in consecutive epochs to be confirmed as real. This sets the sensitivity at low flux densities to transient durations of

The GALFA-HI Survey: Data Release 1

\tau \sim 1

THE CHANDRA ACIS SURVEY OF M33: X-RAY, OPTICAL, AND RADIO PROPERTIES OF THE SUPERNOVA REMNANTS

day, while

The GALFA-H I Compact Cloud Catalog

\tau > 1

Head–tail clouds: drops to probe the diffuse Galactic halo

minute for high flux densities. At 70 mJy, we find a 1-

COMPACT H I CLOUDS FROM THE GALFA-H I SURVEY

\sigma

ERRATUM: “THE GALFA-HI COMPACT CLOUD CATALOG” (2012, ApJ, 758, 44)

limit on the surface density