Star Formation: High-Mass:
SMA view of star formation in the DR21 Ridge
Star formation regions are dominated by filamentary structures, but the role that those filaments play in turning gas and dust into stars is still unclear. DR21 is a massive filament, around 15,000 solar masses, in the Cygnus-X region of the Milky Way. At a 1.4 kpc distance, it is relatively close to the Solar System, which makes it an excellent laboratory for studying how massive filaments produce massive stars. The DR21 Ridge is a particularly interesting part of DR21 because its northern and southern halves are both very massive, but the southern half shows more massive star formation activity and infrared luminosity output. We observed the DR21 Ridge with the SMA to do a census of dense material along the filament at 0.02 pc spatial resolution to help unravel this mystery. This is the first high-resolution, interferometric view of a contiguous ~2 pc stretch of the ridge around the massive DR21(OH) core. With the SMA data, we see that the material in the southern section of the DR21 Ridge has been driven to higher density than the northern section; at a given radius, we find higher mass clumps and cores in the south, above empirically derived massive star formation mass-size limits. The SMA data supports the view that high density is needed drive massive star formation, not just high mass. But where does the high density in the southern section of the DR21 Ridge come from? We propose that this higher density is driven by overlapping sub-filaments of the DR21 Ridge, which we see in ancillary spectral line data from other telescopes, that are present in the south but not in the north. This points to an overall picture where intersecting sub-filaments within massive filaments lead to local over-densities that then lead to massive stellar birth.
Left: SMA continuum image of the DR21 Ridge. The SMA is sensitive to emission from cold dust along this star forming filament. This image has spatial resolution near 0.02 pc, which means it can detect individual star-forming cores that may form one or multiple protostars in the near future. Center: Spitzer three-color RGB image of the DR21 Ridge. The red, green, and blue images are from the Spitzer IRAC camera operating 5.8, 4.5, and 3.6 micron, respectively. This image shows existing protostars along this star forming filament. Right: The Spitzer image with SMA continuum contours overlaid. This view shows how the SMA is sensitive to star-forming material along the DR21 Ridge from select regions where we do detect protostars in the infrared, as well as from select regions where no protostars are detected. The ability to detect cold, star-forming material with no associated infrared counterpart demonstrates the power of the SMA and millimeter interferometry to probe the earliest stages of star formation in massive molecular cloud filaments.
