Ultra-compact Embedded Clusters in the Galactic Plane

Abstract

We have identified a previously unrecognized population of very compact, embedded low-mass Galactic stellar clusters. These tight (r$\approx$0.14 pc) groupings appear as bright singular objects at the few arcsec resolution of the Spitzer Space Telescope at 8 and 24 $\mu$m but become resolved in the sub-arcsecond UKIDSS images. They average six stars per cluster surrounded by diffuse infrared emission and coincide with 100 -- 300 M$_{\sun}$ clumps of molecular material within a larger molecular cloud. The magnitudes of the brightest stars are consistent with mid- to early-B stars anchoring $\sim$80 M$_{\sun}$ star clusters. Their evolutionary descendants are likely to be Herbig Ae/Be pre-main sequence clusters. These ultra-compact embedded clusters (UCECs) may fill part of the low-mass void in the embedded cluster mass function. We provide an initial catalog of 18 UCECs drawn from infrared Galactic Plane surveys.

Accepted for publication in The Astrophysical Journals Letters

References in corpus (7)

• A Spitzer Survey of Young Stellar Clusters within One Kiloparsec of the Sun: Cluster Core Extraction and Basic Structural Analysis
• The Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey
• The UKIDSS Galactic Plane Survey
• The SCUBA Legacy Catalogue: Continuum Objects Detected by SCUBA
• The RMS Survey: Mid-Infrared Observations of Candidate Massive YSOs in the Southern Hemisphere
• Resolved 24.5 micron emission from massive young stellar objects
• Survey of intermediate/high-mass star-forming regions at centimeter and millimeter wavelengths

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• VERA astrometry toward the Perseus arm gap
• Do individual Spitzer young stellar object candidates enclose multiple UKIDSS sources?
• Extended Ionized Fe Objects in the UWIFE Survey