Study of Interstellar Molecular Clouds using Formaldehyde Absorption toward Extragalactic Radio Sources

Abstract

We present new Very Large Array 6cm H2CO observations toward four extragalactic radio continuum sources (B0212+735, 3C111, NRAO150, BL Lac) to explore the structure of foreground Galactic clouds as revealed by absorption variability. This project adds a new epoch in the monitoring observations of the sources reported by Marscher and collaborators in the mid 1990's. Our new observations confirm the monotonic increase in H${}_2$CO absorption strength toward NRAO150. We do not detect significant variability of our 2009 spectra with respect to the 1994 spectra of 3C111, B0212+735 and BL Lac; however we find significant variability of the 3C111 2009 spectrum with respect to archive observations conducted in 1991 and 1992. Our analysis supports that changes in absorption lines could be caused by chemical and/or geometrical gradients in the foreground clouds, and not necessarily by small scale (~10 AU) high density molecular clumps within the clouds.

25 pages, 7 figures

References in corpus (4)

• Formaldehyde Densitometry of Starburst Galaxies
• A First Look at the Auriga-California Giant Molecular Cloud With Herschel and the CSO: Census of the Young Stellar Objects and the Dense Gas
• A Search for H2CO 6cm Emission toward Young Stellar Objects III: VLA Observations
• Imaging galactic diffuse gas: Bright, turbulent CO surrounding the line of sight to NRAO150

Cited by in corpus (4)

• H2CO and CS in diffuse clouds: Excitation and abundance
• Shaken or stirred: the diffuse interstellar medium with exceptionally high SiO abundance
• Rethinking Habitability using Biogenic Precursors: Formaldehyde in Millimeter Molecular Clouds of the Inner Galaxy
• The role of neutral hydrogen in setting the abundances of molecular species in the Milky Way's diffuse interstellar medium. II. Comparison between observations and theoretical models