Surveying the Giant HII Regions of the Milky Way with SOFIA: VIII. W43 Main

TL;DR

The paper analyzes how the Galactic environment influences massive star formation in giant HII regions, focusing on W43 Main. It combines SOFIA-FORCAST mid-infrared imaging from 11–37 μm with archival Spitzer and Herschel data and applies SED fitting to characterize compact infrared sources and dust substructures. They identify 20 compact infrared sources, 16 of which are massive young stellar objects (MYSOs) or candidates, and find a total Lyman continuum photon rate of $\log N_{LyC} = 50.76^{+0.18}_{-0.22}$ s$^{-1}$; the most massive MYSO and MYSO density are near the survey medians, implying star formation activity similar to the Milky Way's typical GHII regions. Distance to W43 Main is anchored at 5.49 kpc from maser parallax measurements, enabling robust comparison of physical properties to other regions.

Abstract

In this eighth paper of the SOFIA-FORCAST series on Milky Way GHII regions, we present an analysis of the massive star-forming complex W43 Main. We compared our 11 - 37 micron maps with multi-wavelength observations from the near-infrared to radio, and investigated the physical nature of compact sources and dust substructures. We applied SED fitting to constrain properties of the compact infrared objects, and examined the evolutionary states of the extended subregions. We identified 20 compact infrared objects, 16 (80%) of which we classify as massive young stellar objects (MYSOs) or candidate MYSOs. W43 Main resides at the junction of the Scutum spiral arm and the Galactic Bar, a location where enhanced turbulence is anticipated and has been proposed as a potential influence on star-formation activity. Nevertheless, our analysis shows that its Lyman continuum photon production rate, the mass of its most massive MYSO, and its MYSO density are all consistent with the survey-wide median values. We therefore conclude that, despite W43 Main's unique Galactic environment, its present star formation activity appears broadly consistent with that of an average Galactic GHII region.

Figures (6)

• Figure 1: A 4-color image of the central $9\hbox{$.\mkern-4mu^\prime$}2\times10\hbox{$.\mkern-4mu^\prime$}3$ (14.7$\times$16.5 pc) region of W43 Main. Blue is the SOFIA-FORCAST 20 $\mu$m image, green is the SOFIA-FORCAST 37 $\mu$m image, and red is the Herschel-PACS 70 $\mu$m image. Overlaid in white is the Spitzer-IRAC 3.6 $\mu$m image, which traces the revealed stars within W43 Main, field stars, and hot dust.
• Figure 2: W43 Main image mosaic taken at 11 $\mu$m by SOFIA shown in inverse color (i.e. brighter features are darker in color). Sources labeled with numbers are the mid-infrared compact sources identified in this work. The positions of the mid-infrared sources marked with an 'x' are not seen at this wavelength. The small black dot in the lower left indicates the resolution of the image at this wavelength.
• Figure 3: W43 Main image mosaic taken at 20 $\mu$m by SOFIA shown in inverse color (i.e. brighter features are darker in color). See Figure \ref{['fig:fig2']} caption for further information.
• Figure 4: W43 Main image mosaic taken at 31 $\mu$m by SOFIA shown in inverse color (i.e. brighter features are darker in color). See Figure \ref{['fig:fig2']} caption for further information.
• Figure 5: W43 Main image mosaic taken at 37 $\mu$m by SOFIA shown in inverse color (i.e. brighter features are darker in color). See Figure \ref{['fig:fig2']} caption for further information.