LOCATING THE YOUNGEST H II REGIONS IN M82 WITH 7 mm CONTINUUM MAPS

Journal Article · Mon Jun 15 04:00:00 EDT 2009 · Astronomical Journal (New York, N.Y. Online)

DOI:https://doi.org/10.1088/0004-6256/137/6/4655; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)· OSTI ID:21255749

Tsai, C -W; Turner, Jean L ^[1]; Beck, Sara C ^[2]; Meier, David S ^[3]; Ho, Paul T. P. , ^[4]

---

1. Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095-1547 (United States)
2. Department of Physics and Astronomy, Tel Aviv University, Ramat Aviv (Israel)
3. Jansky Fellow: National Radio Astronomy Observatory, P. O. Box 0, Socorro, NM 87801 (United States)
4. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)

We present 7 mm Very Large Array continuum images of the starburst galaxy M82. On arcsecond scales, two-thirds of the 7 mm continuum consists of free-free emission from H II regions. In the subarcsecond resolution map, we identify 14 compact sources, including 9 bright H II regions with N {sub lyc} > 10{sup 51} s{sup -1}. Four of the H II regions have rising spectra, implying emission measures >10{sup 8} cm{sup -6} pc. Except for one compact source with peculiar features, all other compact radio sources are found in dust lanes and do not have optical or near-infrared continuum counterparts. Four regions of extended, high brightness (EM >10{sup 7} cm{sup -6} pc) radio emission are found in our high-resolution map, including some as large as {approx}2'', or 30 pc, representing either associations of small H II regions, or sheet-like structures of denser gas. The good correlation between 7 mm emission and Spitzer IRAC 8 {mu}m continuum-removed polycyclic aromatic hydrocarbon (PAH) feature suggests that PAH emission may track the recently formed OB stars. We find an excellent correlation between molecular gas and star formation, particularly dense gas traced by HCN, down to the {approx}45 pc scale in M82. We also find star formation efficiencies (SFEs) of 1%-10% on the same scale, based on CO maps. The highest SFE are found in regions with the highest dense gas fractions.

• OSTI ID: 21255749
• Journal Information: Astronomical Journal (New York, N.Y. Online), Journal Name: Astronomical Journal (New York, N.Y. Online) Journal Issue: 6 Vol. 137; ISSN 1538-3881
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
99 GENERAL AND MISCELLANEOUS
BRIGHTNESS
DUSTS
EMISSION
GALAXIES
HYDROCYANIC ACID
MAPS
POLYCYCLIC AROMATIC HYDROCARBONS
RESOLUTION
STAR CLUSTERS
STARS