Physical conditions of the earliest phases of massive star formation: Single-dish and interferometric observations of ammonia and CCS in infrared dark clouds

Journal Article · Sun Nov 01 04:00:00 EST 2015 · The Astronomical Journal (Online)

DOI:https://doi.org/10.1088/0004-6256/150/5/159· OSTI ID:22890179

Dirienzo, William J.; Indebetouw, Rémy ^[1]; Brogan, Crystal ^[2]; Chandler, Claire J. ^[3]; Friesen, Rachel K. ^[4]

---

1. Department of Astronomy, University of Virginia, P.O. Box 3818, Charlottesville, VA 22903 (United States)
2. National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States)
3. National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801 (United States)
4. Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto M5S 3H4, Ontario (Canada)

Infrared Dark Clouds (IRDCs) harbor the earliest phases of massive star formation, and many of the compact cores in IRDCs, traced by millimeter continuum or by molecular emission in high critical density lines, host massive young stellar objects (YSOs). We used the Robert C. Byrd Green Bank Telescope and the Karl G. Jansky Very Large Array (VLA) to map NH{sub 3} and CCS in nine IRDCs to reveal the temperature, density, and velocity structures and explore chemical evolution in the dense (>10{sup 22} cm{sup −2}) gas. Ammonia is an excellent molecular tracer for these cold, dense environments. The internal structure and kinematics of the IRDCs include velocity gradients, filaments, and possibly colliding clumps that elucidate the formation process of these structures and their YSOs. We find a wide variety of substructure including filaments and globules at distinct velocities, sometimes overlapping at sites of ongoing star formation. It appears that these IRDCs are still being assembled from molecular gas clumps even as star formation has already begun, and at least three of them appear consistent with the morphology of “hub-filament structures” discussed in the literature. Furthermore, we find that these clumps are typically near equipartition between gravitational and kinetic energies, so these structures may survive for multiple free-fall times.

• OSTI ID: 22890179
• Journal Information: The Astronomical Journal (Online), Journal Name: The Astronomical Journal (Online) Journal Issue: 5 Vol. 150; ISSN 1538-3881
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
AMMONIA
COSMIC DUST
COSMIC GASES
EMISSION
MOLECULES
STAR EVOLUTION
STARS
TELESCOPES
VELOCITY