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2017ApJ...846...64M - Astrophys. J., 846, 64-64 (2017/September-1)

The infrared and radio flux densities of Galactic H II regions.

MAKAI Z., ANDERSON L.D., MASCOOP J.L. and JOHNSTONE B.

Abstract (from CDS):

We derive infrared and radio flux densities of all ∼1000 known Galactic H II regions in the Galactic longitude range 17○ / . 5 ℓ65. Our sample comes from the Wide-Field Infrared Survey Explorer (WISE) catalog of Galactic H II regions. We compute flux densities at six wavelengths in the infrared (Spitzer GLIMPSE 8 µm, WISE 12 µm and 22 µm, Spitzer MIPSGAL 24 µm, and Herschel Hi-GAL 70 µm and 160 µm) and two in the radio (MAGPIS 20 cm and VGPS 21 cm). All H II region infrared flux densities are strongly correlated with their ∼20 cm flux densities. All H II regions used here, regardless of physical size or Galactocentric radius, have similar infrared to radio flux density ratios and similar infrared colors, although the smallest regions (r < 1 pc), have slightly elevated IR to radio ratios. The colors log10(F_24µm/F12µm_) 0 and log10(F_70µm/F12µm_) 1.2, and log10(F_24µm/F12µm_) 0 and log10(F_160µm/F70µm_) 0.67 reliably select H II regions, independent of size. The infrared colors of ∼22% of H II regions, spanning a large range of physical sizes, satisfy the IRAS color criteria of Wood & Churchwell for H II regions, after adjusting the criteria to the wavelengths used here. Because these color criteria are commonly thought to select only ultra-compact H II regions, this result indicates that the true ultra-compact H II region population is uncertain. Compared to a sample of IR color indices from star-forming galaxies, H II regions show higher log10(F_70µm/F12µm_) ratios. We find a weak trend of decreasing infrared to ∼20 cm flux density ratios with increasing Rgal, in agreement with previous extragalactic results, possibly indicating a decreased dust abundance in the outer Galaxy.

Abstract Copyright: © 2017. The American Astronomical Society. All rights reserved.

Journal keyword(s): H II regions - infrared: ISM - radio continuum: ISM - techniques: photometric - techniques: photometric

Simbad objects: 19

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