S316p.09 ‐ IAU XXIX General Assembly, August 2015, Honolulu, HI

We obtained new deep Spitzer/IRAC warm mission observations of a sample of Infrared Dark Clouds (IRDCs), selected to have ancillary data available(deep near‐IR and Herschel) and to contain cores spanning a range of evolutionary states. The star formation activity of the sample ranges fromcandidate starless cores to IR−bright massive young stellar objects (YSOs). The primary goals of the project are (1) to detect additional 4.5 μm outflowsand massive protostars and (2) to study the low−mass YSO population associated with the IRDCs. Extended emission at 4.5 μm has been associatedwith shocked or ionized emission from outflows and has been shown to correlated with sites of massive star formation (Cyganowski et al.. 2008, 2009;Chambers et al. 2009). The new images improve by an order of magnitude our sensitivity to extended emission from outflows and to point sources(YSOs), and will allow us to address several questions important to understanding star and cluster formation in IRDCs and the meaning of extended 4.5μm emission as a star−forma on tracer.

A Survey for Outflows in Infrared Dark CloudsJoseph L. Hora (CfA), Claudia Cyganowski (University of St Andrews), Howard Smith (CfA), Jonathan Foster (Yale),James Jackson (BU), Susanna Finn (UMass/Lowell), Matthew Povich (CalPoly/Pomona)

Project Description

IRAS 18111‐17293.6 – 8 – 24 μm

Example: IRAS 18111‐1729The large color image (lower left) shows our new 3.6μm data along with 8 μm IRAC/GLIMPSE and 24 μmMIPSGAL data. The image is centered near IRAS18111‐1729., and shows several IRDC complexeswith many embedded sources and bright‐rimmedclouds. The white box shows the region which isenlarged in the small images at the top. The possibleoutflow sources are indicated with green arrows inthe 4.5 μm image. These objects are either absent orweak at 3.6 μm. Some of these potential outflowsources are also emit strongly in the 24 μm band.

We have surveyed ~75 regions, each with one ormore IRDCs such as this example. We will use Spitzercolor/color diagrams and SED fitting techniques toidentify young stellar objects and determine theirproperties, and study the clusters of stars associatedwith the IRDCs. We will follow up our identificationof possible outflow sources with IR spectroscopy andhigher resolution imaging.

4.5 μm 3.6 – 4.5 – 8 μm 3.6 – 8 – 24  μm3.6 μm

The image above is the IRAS 18111‐1729 region with the YSOcandidate positions plotted. Class 0 and I objects are plotted with redcrosses and Class II objects are green crosses. The Class 0/I objectscan be seen to be located primarily along the dark clouds. The ClassII objects are more distributed, although they are also clustered nearthe dark clouds. There are some clusters near dark clouds with onlyClass II objects, such as near the center of the image.

References:Chambers, E. T., Jackson, J. M., Rathborne, J. M., & Simon, R. 2009,ApJS, 181, 360Cyganowski, C. J., Whitney, B. A., Holden, E., et al. 2008, AJ, 136, 2391Cyganowski, C., Brogan, C., Hunter, T., & Churchwell, E. 2009, ApJ, 707, 1

8 μm

The image to the right shows the IRAS 18111‐1729 region with theclustered YSO candidate positions plotted (Class 0, I, and II). Eachidentified cluster is shown in a different color or symbol type. Themaximum distance between cluster members was 45 arcsec, or~1.1 pc at a distance of 5 kpc, and the minimum number of YSOsper cluster set at 8 members. A total of 67 clusters were identifiedin this region, containing about 60% of the total number of YSOcandidates. Most of the clustered YSOs are located in the lower leftpart of the image near the many IRDCs in this area. Some clustersare also associated with the bright rimmed clouds, such as in theupper left and lower right regions.

The largest three clusters (which contain about 1/3 of theclustered YSOs) have Class II/Class I ratios near 3, but the ratiovaries from 0.6 to clusters with no Class I objects. Typically theclusters with no or weak IRDCs have higher Class II/I ratios. We canuse these ratios to help determine the relative age of the clusters.

8 μm