Embedded Stellar Clusters
in the W3/W4/W5 Molecular Cloud Complex

John M. Carpenter
Department of Astronomy
California Institute of Technology
MS 105-24
Pasadena, CA 91125

Mark H. Heyer


Ronald L. Snell
Department of Astronomy
University of Massachusetts
Amherst, MA 01003


We analyze the embedded stellar content in the vicinity of the W3/W4/W5 HII regions using the FCRAO Outer Galaxy 12CO(J=1-0) Survey, the IRAS Point Source Catalog, published radio continuum surveys, and new near-infrared and molecular line observations. Thirty-four IRAS Point Sources are identified that have far-infrared colors characteristic of embedded star forming regions, and we have obtained K' mosaics and 13CO(J=1-0) maps for 32 of them. Ten of the IRAS sources are associated with an OB star and 19 with a stellar cluster, although three OB stars are not identified with a cluster. Half of the embedded stellar population identified in the K' images is found in just the 5 richest clusters, and 61% is contained in IRAS sources associated with an embedded OB star. Thus rich clusters around OB stars contribute substantially to the stellar population currently forming in the W3/W4/W5 region. Approximately 39% of the cluster population is embedded in small clouds with an average mass of ~130 Mo that are located as far as 100 pc from the W3/W4/W5 cloud complex. We speculate that these small clouds are fragments of a cloud complex dispersed by previous episodes of massive star formation. Finally, we find that 4 of the 5 known embedded massive star forming sites in the W3 molecular cloud are found along the interface with the W4 HII region despite the fact that most of the molecular mass is contained in the interior regions of the cloud. These observations are consistent with the classical notion that the W4 HII region has triggered massive star formation along the eastern edge of the W3 molecular cloud.

[paper from ADS]

(click on thumbnails to see enlarged versions)

Figure 1:
The location of the 34 IRAS point sources meeting our selection criteria (see text) overlaid on a grey scale image of the 12CO(1-0) integrated intensity between -57 km/s and -32 km/s from the FCRAO Outer Galaxy Survey (Heyer et al. 1998). Small circles represent IRAS point sources with far-infrared luminosities LFIR < 500 Lo, medium sized represent circles sources with 500 Lo <= LFIR < 5000 Lo, and large circles represent sources with LFIR >= 5000 Lo. The dash rectangle indicates the area that was searched for IRAS point sources.

Figure 2:
Contour map of the 12CO(1-0) integrated intensity shown in Figure 1 overlaid on the 21cm continuum image from the DRAO Galactic Plane Survey (Normandeau, Taylor, & Dewdney 1997, ApJS, 108, 279). The contour level shown is for an integrated intensity of 12 K km/s.

Figure 3:
Molecular line, near-infrared, and star count images for the 32 IRAS sources mosaicked at K' band. For each source, the left panel is an image of the 12CO(1-0) integrated intensity from the FCRAO Outer Galaxy survey (Heyer et al. 1988) integrated over a +/- 5 km/s interval around the velocity toward the IRAS source. Each 12CO image is shown over a 30' × 30' area centered on the IRAS point source position with a logarithmic intensity scale from log10(1.0 K km/s) to log10(60.0 K km/s). The adjacent panels show an image of the 13CO(1-0) integrated intensity centered on the IRAS source, the K' band mosaic, and a K' band stellar surface density map for stars with magnitudes between 11.5 mag and 17.5 mag. The contour levels for the 13CO maps begin at 1.0 K km/s with intervals of 2.0 K km/s, except for IRAS 02232+6138, 02245+6115, 02310+6133, 02455+6034, 02459+6029, 02531+6032, 02570+6028, 02593+6016, and 02575+6017, which have intervals of 8.0 K km/s. No 13CO data are present in any of the maps for declination offsets >= 1.5'. The contours in the stellar surface density images begin at 2 sigma above the mean derived stellar surface density (see text), with contours intervals of 3 sigma.

Figure 4:
Histogram of the far-infrared luminosity in the 12 micron, 25 micron and 60 micron IRAS bands for the 34 IRAS sources in our sample.

Figure 5:
The cumulative distribution of the total number of stars identified in clusters as a function of the number of stars in an individual cluster. The star counts have been normalized by the total cluster population (1595 stars). The richest clusters are labeled by their IRAS point source name, and the horizontal dashed line shows the 50% point in the cluster population. These results indicate that half of the detected cluster population is found in just the five richest clusters.