An Extinction Threshold for Protostellar Cores in Ophiuchus

By D. Johnstone, J. di Francesco, H. Kirk. 2004

151 citations recorded by the source corpus.

We have observed continuum emission at λ = 850 μm over ~4 deg2 of the Ophiuchus star-forming cloud using the Submillimeter Common-User Bolometric Array on the James Clerk Maxwell Telescope, producing a submillimeter continuum map 20 times larger than previous Ophiuchus surveys. Our sensitivity is 40 mJy beam-1, a factor of ~2 less sensitive than earlier maps. Using an automated identification algorithm, we detect 100 candidate objects. Only two new objects are detected outside the boundary of previous maps, despite the much wider area surveyed. We compare the submillimeter continuum map with a map of visual extinction across the Ophiuchus cloud derived using a combination of Two Micron All Sky Survey and R-band data. The total mass in submillimeter objects is ≈50 M☉ compared with ≈2000 M☉ in observed cloud mass estimated from the extinction. The submillimeter objects represent only 2.5% of the cloud mass. A clear association is seen between the locations of detected submillimeter objects and high visual extinction, with no objects detected at AV < 7 mag. Using the extinction map, we estimate pressures within the cloud from P/k ≈ 2 × 105 cm-3 K in the less-extincted regions to P/k ≈ 2 × 106 cm-3 K at the cloud center. Given our sensitivities, cold (Td ≈ 15 K) clumps supported by thermal pressure, had they existed, should have been detected throughout the majority of the map. Such objects may not be present at low AV because they may form only where AV > 15, by some mechanism (e.g., loss of nonthermal support).

Subfields: Astronomy and Astrophysics

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Citations in the corpus

A Preliminary VLBA Distance to the Core of Ophiuchus, with an Accuracy of 4% (2008, unknown): “…detail at numerous other wavelengths, including X-rays (Ozawa et al. 2005, Gagné et al. 2004), near-infrared (e.g. Haisch et al. 2002, Duchêne et al. 2004, and references therein), sub-millimeter (Motte et al. 1998, Johnstone et al. 2004), and radio (e.g. André et al. 1987, Leous et al. 1991).”
The SCUBA Legacy Catalogues: Submillimeter-Continuum Objects Detected by SCUBA (2008, methodology): “Previously published examples of SCUBAmapsmade via matrix inversion include those of molecular clouds in Ophiuchus (Johnstone et al. 2000b, 2004), Perseus (Kirk et al. 2006), and Orion (Johnstone et al. 2001, 2006; Johnstone & Bally 2006).”
The COMPLETE Survey of Star-Forming Regions: Phase I Data (2006, methodology): “This lack of detection is likely due to especially low sensitivity to extended, diffuse structures that may inhabit that location (see Johnstone et al. 2004).”
A General Theory of Turbulence-regulated Star Formation, from Spirals to Ultraluminous Infrared Galaxies (2005, background): “First, observations have confirmed that, in at least some clouds, the SFR is lower in the outer than the inner parts (Li et al. 1997; Johnstone et al. 2004), perhaps due to increased ionization there (McKee 1989).”
MAMBO Mapping Of Spitzer c2d Small Clouds And Cores (2008, background): “…surveys studied dense cores in large (up to several 10 pc) and massive (up to several 103 M ) complexes of molecular clouds (Motte et al. 1998; Johnstone et al. 2000, 2001, 2004, 2006; Johnstone & Bally 2006; Hatchell et al. 2005; Enoch et al. 2006, 2007; Young K. E. et al. 2006; Stanke et…”
Star Formation in the Milky Way and Nearby Galaxies (2012, background): “Other studies have found similar thresholds for efficient star formation or the presence of dense cores (Onishi et al. 1998; Enoch et al. 2007; Johnstone et al. 2004; André et al. 2010; Li et al. 1997; Lada 1992).”
THE STAR FORMATION RATE AND GAS SURFACE DENSITY RELATION IN THE MILKY WAY: IMPLICATIONS FOR EXTRAGALACTIC STUDIES (2010, unknown): “Similarly, both Johnstone et al. (2004) and André et al. (2010) find thresholds of AV ∼10 (150 M⊙ pc 2).”
The Global Evolution of Giant Molecular Clouds. I. Model Formulation and Quasi-Equilibrium Behavior (2006, unknown): “…rate were simply following the column density to some power, suggesting that magnetic fields may play a secondary role – Onishi et al. 1998, 1999, 2002; Johnstone et al. 2004 – though see Hatchell et al. 2005 who find that low column densities reduce but do not completely prevent star formation.)”
ATLASGAL - The APEX telescope large area survey of the galaxy at 870 μm (2009, methodology): “Using the Submillimetre Common User Bolometer Array (SCUBA) instrument, Johnstone et al. (2004) mapped 4 deg2 of the Ophiuchus star-forming cloud, and Hatchell et al. (2005) covered 3 deg2 of the Perseus molecular cloud.”
Star formation in Perseus - Clusters, filaments and the conditions for star formation (2005, methodology): “As the cores in Ophiuchus were identified in the same way as in this study of Perseus, that is, from SCUBA 850 µm observations, there must either be a real difference between star formation in the two clouds, or a significant difference in the way that optical/IR extinction and C18O trace column den”
DIRECT OBSERVATION OF A SHARP TRANSITION TO COHERENCE IN DENSE CORES (2010, background): “Lada et al. (2008) argued that most of the cores in the Pipe can be pressure confined by the MC’s own weight, see also Bertoldi & McKee (1992) and Johnstone et al. (2004).”
Comparing Star Formation on Large Scales in the c2d Legacy Clouds: Bolocam 1.1 mm Dust Continuum Surveys of Serpens, Perseus, and Ophiuchus (2007, methodology): “Johnstone et al. (2004) find a mass ratio of 2.5% in a survey of approximately 4 deg2 of Ophiuchus, quite similar to our result.”
STAR FORMATION RELATIONS IN NEARBY MOLECULAR CLOUDS (2014, result): “This relation was consistent with many studies of star formation in the Galaxy showing that star formation was highly correlated with relatively dense gas within the molecular cloud (Onishi et al. 1998; Enoch et al. 2007; Johnstone et al. 2004; André et al. 2010; Li et al. 1997; Lada 1992).”
A census of dense cores in the Aquila cloud complex: SPIRE/PACS observations from the Herschel Gould Belt survey (2015, background): “The existence of such a threshold had been suspected for a long time, based on the results of ground-based millimeter and submillimeter surveys for cores in, e.g., the Taurus, Ophiuchus, and Perseus clouds (e.g., Onishi et al. 1998; Johnstone et al. 2004; Kirk et al. 2006).”