OB Associations at the Upper End of the Milky Way Luminosity Function

Abstract

The Milky Way's most luminous, young and massive (M > 10^4 Msun) star clusters and OB associations have largely evaded detection despite knowledge of their surrounding H II regions. We search for these clusters and associations within the 40 star forming complexes from Rahman & Murray in the 13 most luminous WMAP free-free emission sources of the Galaxy. Selecting for objects with the dust-reddened colors of OB stars, we identify new candidate associations using the 2MASS point source catalog. In 40 star forming complexes searched, 22 contain cluster/association candidates with sizes and masses in the range of 3' - 26' and 10^{2.3} - 10^{5} Msun. Of the 22 candidates, at least 7 have estimated masses > 10^4 Msun, doubling the number of such massive clusters known in the Galaxy. Applying our method to a statistically similar set of test locations, we estimate that 3.0 +/- 0.6 of our 22 candidate associations are unrelated to the star forming complexes. In addition, the apparent extinctions of our candidate associations correlate well with the predictions from a Galactic model. These facts, along with the clear detection of a known OB association and the previous spectral verification of one cluster found by this method, validate our method. Only one of the searched WMAP sources remains without a candidate. In 8 of the most luminous WMAP sources, the candidate associations can account for the observed free-free flux. With our new compilation, the Galactic census of young, massive stellar associations may now be about half complete.

arXiv comment25 pages, 14 figures. To appear in ApJ

References in corpus (42)

• On the variation of the Initial Mass Function
• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• GLIMPSE: I. A SIRTF Legacy Project to Map the Inner Galaxy
• A new calibration of stellar parameters of Galactic O stars
• VISTA Variables in the Via Lactea (VVV): The public ESO near-IR variability survey of the Milky Way
• The Two Young Star Disks in the Central Parsec of the Galaxy: Properties, Dynamics and Formation
• Modelling the Galactic Interstellar Extinction Distribution in Three Dimensions
• The Luminosity & Mass Function of the Trapezium Cluster: From B stars to the Deuterium Burning Limit
• HST/NICMOS Observations of Massive Stellar Clusters Near the Galactic Center
• Interstellar Extinction Law toward the Galactic Center III: J, H, Ks bands in the 2MASS and the MKO systems, and 3.6, 4.5, 5.8, 8.0 micron in the Spitzer/IRAC system
• UBVJHK synthetic photometry of Galactic O stars
• The mass function of young star clusters in spiral galaxies
• A systematic survey for infrared star clusters with |b|<20deg using 2MASS
• New infrared star clusters in the southern Milky Way with 2MASS
• A massive cluster of Red Supergiants at the base of the Scutum-Crux arm
• New infrared star clusters in the Northern and Equatorial Milky Way with 2MASS
• The Initial Mass Function of the Massive Star-forming Region NGC 3603 from Near-Infrared Adaptive Optics observations
• Star Formation in Massive Clusters via the Wilkinson Microwave Anisotropy Probe and the Spitzer Glimpse Survey
• Discovery of an Extraordinarily Massive Cluster of Red Supergiants
• Interstellar Extinction Law toward the Galactic Center II: V, J, H, and Ks Bands
• Star Cluster Demographics. I. A General Framework and Application to the Antennae Galaxies
• The Luminosity, Mass, and Age Distributions of Compact Star Clusters in M83 Based on HST/WFC3 Observations
• Intermediate to low-mass stellar content of Westerlund 1
• Rotational Velocities For B0-B3 Stars in 7 Young Clusters: Further Study of the Relationship between Rotation Speed and Density in Star-Forming Regions
• The Massive Star Forming Region Cygnus OB2. II. Integrated Stellar Properties and the Star Formation History
• The Slope of the Near Infrared Extinction Law
• New Tests for Disruption Mechanisms of Star Clusters: Methods and Application to the Antennae Galaxies
• A third red supergiant rich cluster in the Scutum-Crux Arm
• A Census of the Carina Nebula -- II. Energy Budget and Global Properties of the Nebulosity
• Mass functions and structure of the young open cluster NGC\,6611
• MSX Mid infrared imaging of massive star birth environments. II: Giant HII regions
• Milky Way Star Forming Complexes and the Turbulent Motion of the Galaxy's Molecular Gas
• The initial luminosity and mass functions of the Galactic open clusters
• Candidate X-ray-Emitting OB Stars in the Carina Nebula Identified Via Infrared Spectral Energy Distributions
• Near Infrared Observations of the Giant HII Region W49A: A Starbirth Cluster
• Detection of a Large Arc of Ionized Hydrogen Far Above the Cas OB6 Association: A Superbubble Blowout into the Galactic Halo?
• Discovery of new Milky Way star cluster candidates in the 2MASS point source catalog III. Follow-up observations of cluster candidates in the Galactic Center region
• Massive Star Forming Regions in the Galaxy using the Spitzer GLIMPSE Survey
• Star clusters or asterisms? 2MASS CMD and structural analyses of 15 challenging targets
• Discovery of new Milky Way star cluster candidates in the 2MASS Point Source Catalog IV. Follow-up observations of cluster candidates in the Galactic plane
• Spectroscopic Confirmation of the Dragonfish Association: The Galaxy's Most Luminosity OB Association
• A Candidate for the Most Luminous OB Association in the Galaxy

Cited by in corpus (6)

• Old pre-main-sequence Stars: Disc reformation by Bondi-Hoyle accretion
• Extended Gamma-ray Emission from the G25.0+0.0 Region: A Star Forming Region Powered by the Newly Found OB Association?
• The seven most massive clumps in W43-Main as seen by ALMA: Dynamical equilibrium and Magnetic Fields
• Large-scale Map of Millimeter-wavelength Hydrogen Radio Recombination Lines around a Young Massive Star Cluster
• The Main Sequence of three Red Supergiant Clusters
• Massive Stars in Molecular Clouds Rich in High-energy Sources: The Bridge of G332.809-0.132 and CS 78 in NGC 6334