Star Formation Activity Beyond the Outer Arm II: Distribution and Properties of Star Formation

Abstract

The outer Galaxy beyond the Outer Arm represents a promising opportunity to study star formation in an environment vastly different from the solar neighborhood. In our previous study, we identified 788 candidate star-forming regions in the outer Galaxy (at galactocentric radii $R_{\mathrm{G}}$ $\ge$ 13.5 kpc) based on Wide-field Infrared Survey Explorer (WISE) mid-infrared (MIR) all-sky survey. In this paper, we investigate the statistical properties of the candidates and their parental molecular clouds derived from the Five College Radio Astronomy Observatory (FCRAO) CO survey. We show that the molecular clouds with candidates have a shallower slope of cloud mass function, a larger fraction of clouds bound by self-gravity, and a larger density than the molecular clouds without candidates. To investigate the star formation efficiency (SFE) at different $R_{\mathrm{G}}$, we used two parameters: 1) the fraction of molecular clouds with candidates and 2) the monochromatic MIR luminosities of candidates per parental molecular cloud mass. We did not find any clear correlation between SFE parameters and $R_{\mathrm{G}}$ at $R_{\mathrm{G}}$ of 13.5 kpc to 20.0 kpc, suggesting that the SFE is independent of environmental parameters such as metallicity and gas surface density, which vary considerably with $R_{\mathrm{G}}$. Previous studies reported that the SFE per year (SFE/yr) derived from the star-formation rate surface density per total gas surface density, HI plus H${}_2$, decreases with increased $R_{\mathrm{G}}$. Our results might suggest that the decreasing trend is due to a decrease in HI gas conversion to H${}_2$ gas.

40 pages, 26 figures, 5 tables, accepted for publication in ApJ

References in corpus (7)

• Inefficient Star Formation In Extremely Metal Poor Galaxies
• A Classification Scheme for Young Stellar Objects Using the WIDE-FIELD INFRARED SURVEY EXPLORER AllWISE Catalog: Revealing Low-Density Star Formation in the Outer Galaxy
• Stellar structures, molecular gas, and star formation across the PHANGS sample of nearby galaxies
• Chemical distribution of HII regions towards the Galactic anticentre
• Star Formation in the Most Distant Molecular Cloud in the Extreme Outer Galaxy: A Laboratory of Star Formation in an Early Epoch of the Galaxy's Formation
• Dispersal timescale of protoplanetary disks in the low-metallicity young cluster Dolidze 25
• Star formation activity beyond the outer Arm I: WISE-selected candidate star-forming regions

Cited by in corpus (4)

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• Overview Results of JWST Observations of Star-Forming Clusters in the Extreme Outer Galaxy
• Molecular Clouds at the Edge of the Galaxy I. Variation of CO J=2-1/1-0 Line Ratio
• Molecular Clouds at the Edge of the Galaxy II. Physical properties and scaling relations