Triggered Star Formation in a Double Shell near W51A

Abstract

We present Heinrich Hertz Telescope CO observations of the shell structure near the active star-forming complex W51A to investigate the process of star formation triggered by the expansion of an HII region. The CO observations confirm that dense molecular material has been collected along the shell detected in Spitzer IRAC images. The CO distribution shows that the shell is blown out toward a lower density region to the northwest. Total hydrogen column density around the shell is high enough to form new stars. We find two CO condensations with the same central velocity of 59 km/s to the east and north along the edge of the IRAC shell. We identify two YSOs in early evolutionary stages (Stage 0/I) within the densest molecular condensation. From the CO kinematics, we find that the HII region is currently expanding with a velocity of 3.4 km/s, implying that the shell's expansion age is ~1 Myr. This timescale is in good agreement with numerical simulations of the expansion of the HII region (Hosokawa et al. 2006). We conclude that the star formation on the border of the shell is triggered by the expansion of the HII region.

9 pages, 10 figures, accepted for publication in ApJ

References in corpus (15)

• The Infrared Array Camera (IRAC) for the Spitzer Space Telescope
• GLIMPSE: I. A SIRTF Legacy Project to Map the Inner Galaxy
• A new calibration of stellar parameters of Galactic O stars
• Interpreting Spectral Energy Distributions from Young Stellar Objects. II. Fitting observed SEDs using a large grid of pre-computed models
• The Wavelength Dependence of Interstellar Extinction from 1.25 to 8.0 microns Using GLIMPSE Data
• Interpreting Spectral Energy Distributions from Young Stellar Objects. I. A grid of 200,000 YSO model SEDs
• First GLIMPSE Results on the Stellar Structure of the Galaxy
• IR Dust Bubbles: Probing the Detailed Structure and Young Massive Stellar Populations of Galactic HII Regions
• Triggered massive-star formation on the borders of Galactic HII regions. II. Evidence for the collect and collapse process around RCW 79
• Dynamical Expansion of Ionization and Dissociation Front around a Massive Star. II. On the Generality of Triggered Star Formation
• The Extended Environment of M17: A Star Formation History
• Triggered massive-star formation at the border of the HII region Sh 104
• Triggered star formation on the borders of the Galactic HII region RCW 82
• Large Scale CO and [CI] emission in the rho Ophiuchi Molecular Cloud
• A Near-Infrared Study of the Highly-Obscured Active Star-Forming Region W51B

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• Embedded Young Stellar Object Candidates in the Active Star Forming Complex W51: Mass Function and Spatial Distribution
• A Chandra Study of the Rosette Star-Forming Complex. III. The NGC 2237 Cluster and the Region's Star Formation History
• A CO Line and Infrared Continuum Study of the Active Star-Forming Complex W51
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