Initial phases of massive star formation in high infrared extinction clouds. I. Physical parameters

Abstract

The earliest phases of massive star formation are found in cold and dense infrared dark clouds (IRDCs). Since the detection method of IRDCs is very sensitive to the local properties of the background emission, we present here an alternative method to search for high column density in the Galactic plane by using infrared extinction maps. We find clouds between 1 and 5 kpc, of which many were missed by previous surveys. By studying the physical conditions of a subsample of these clouds, we aim at a better understanding of the initial conditions of massive star formation. We made extinction maps of the Galactic plane based on the 3.6-4.5 microns color excess between the two shortest wavelength Spitzer IRAC bands, reaching to visual extinctions of ~100 mag and column densities of 9x10^22 cm^-2. From this we compiled a new sample of cold and compact high extinction clouds. We used the MAMBO array at the IRAM 30m telescope to study the morphology, masses and densities of the clouds and the dense clumps within them. The latter were followed up by pointed ammonia observations with the 100m Effelsberg telescope, to determine rotational temperatures and kinematic distances. Extinction maps of the Galactic plane trace large scale structures such as the spiral arms. The 1.2 mm emission maps reveal that the high extinction clouds contain extended cold dust emission, from filamentary structures to still diffuse clouds. Most of the clouds are dark in 24 microns, but several show already signs of star formation via maser emission or bright infrared sources, suggesting that the high extinction clouds contain a variety of evolutionary stages. The observations suggest an evolutionary scheme from dark, cold and diffuse clouds, to clouds with a stronger 1.2 mm peak and to finally clouds with many strong 1.2 mm peaks, which are also warmer, more turbulent and already have some star formation signposts.

26 pages, 14 figures, 9 tables. Accepted for publication in Astronomy and Astrophysics, small corrections implemented

References in corpus (18)

• ATLASGAL - The APEX Telescope Large Area Survey of the Galaxy at 870 microns
• The Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey
• A Catalog of Extended Green Objects (EGOs) in the GLIMPSE Survey: A new sample of massive young stellar object outflow candidates
• Star formation through gravitational collapse and competitive accretion
• The initial conditions of stellar protocluster formation. I. A catalogue of Spitzer dark clouds
• A Minimum Column Density of 1 g cm^-2 for Massive Star Formation
• The earliest phases of high-mass star formation: a 3 square degree millimeter continuum mapping of Cygnus X
• The Bolocam Galactic Plane Survey -- II. Catalog of the Image Data
• The Mid-Infrared Extinction Law in the Ophiuchus, Perseus, and Serpens Molecular Clouds
• Lifting the Dusty Veil II: A Large-Scale Study of the Galactic Infrared Extinction Law
• The Slope of the Near Infrared Extinction Law
• Displacement of the Sun from the Galactic Plane
• Interferometric multi-wavelength (sub)millimeter continuum study of the young high-mass protocluster IRAS05358+3543
• SMA observations of Infrared Dark Clouds: A tale of two cores
• Millimetre Continuum Observations of Southern Massive Star Formation Regions II. SCUBA observations of cold cores and the dust grain emissivity index $\beta$
• Two Massive, Low-Luminosity Cores Toward Infrared Dark Clouds
• A general catalogue of 6.7GHz methanol masers II: statistical analysis
• Extinction techniques and impact on dust property determination

Cited by in corpus (26)

• Hi-GAL, the Herschel infrared Galactic Plane Survey: photometric maps and compact source catalogues. First data release for Inner Milky Way: +68°> l > -70°
• How Many Infrared Dark Clouds can form Massive Stars and Clusters?
• The ATLASGAL survey: a catalog of dust condensations in the Galactic plane
• Chemistry in Infrared Dark Cloud Clumps: a Molecular Line Survey at 3 mm
• High-dynamic-range extinction mapping of infrared dark clouds: Dependence of density variance with sonic Mach number in molecular clouds
• The identification of filaments on far infrared and submillimiter images. Morphology, physical conditions and relation with star formation of filamentary structure
• ATLASGAL-selected massive clumps in the inner Galaxy: I. CO depletion and isotopic ratios
• The Herschel view of massive star formation in G035.39--00.33: Dense and cold filament of W48 undergoing a mini-starburst
• Physical properties of high-mass clumps in different stages of evolution
• Properties of dense cores in clustered massive star-forming regions at high angular resolution
• Initial phases of massive star formation in high infrared extinction clouds. II. Infall and onset of star formation
• Mass reservoirs surrounding massive infrared dark clouds: A view by near-infrared dust extinction
• Deuterium fractionation and the degree of ionisation in massive clumps within infrared dark clouds
• A deep wide-field sub-mm survey of the Carina Nebula complex
• KFPA Examinations of Young STellar Object Natal Environments (KEYSTONE): Hierarchical Ammonia Structures in Galactic Giant Molecular Clouds
• 37 GHz methanol masers : Horsemen of the Apocalypse for the class II methanol maser phase?
• The SQUALO project (Star formation in QUiescent And Luminous Objects) I: clump-fed accretion mechanism in high-mass star-forming objects
• The Dynamical State of The Serpens South Filamentary Infrared Dark Cloud
• Deuterium Fractionation as an Evolutionary Probe in Massive Proto-stellar/cluster Cores
• Thermal balance and comparison of gas and dust properties of dense clumps in the Hi-GAL survey
• Testing the Hypothesis that Methanol Maser Rings Trace Circumstellar Disks: High Resolution Near-IR and Mid-IR Imaging
• A Herschel and BIMA study of the sequential star formation near the W48A HII region
• The Role of Magnetic Fields in the Formation of the Filamentary Infrared Dark Cloud G11.11-0.12
• New Massive Contact Twin Binary in a Radio-quiet HII Region Associated with the M17 Complex
• Extended Ionized Fe Objects in the UWIFE Survey
• Search for High-Mass Protostellar Objects in Cold IRAS Sources