An Extinction Threshold for Protostellar Cores in Ophiuchus

We have observed continuum emission at lambda = 850 microns over ~4 square degrees of the Ophiuchus star-forming cloud using SCUBA on the JCMT, producing a submillimetre continuum map twenty times larger than previous Ophiuchus surveys. Our sensitivity is 40 mJ/beam, 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 submillimetre continuum map with a map of visual extinction across the Ophiuchus cloud derived using a combination of 2MASS and R-band data. The total mass in submillimetre objects is ~ 50 Msun compared with ~ 2000 Msun in observed cloud mass estimated from the extinction. The submillimetre objects represent only 2.5% of the cloud mass. A clear association is seen between the locations of detected submillimetre objects and high visual extinction, with no objects detected at A_V<7 magnitudes. Using the extinction map, we estimate pressures within the cloud from P/k ~2x10^5 cm^-3 K in the less-extincted regions to P/k ~2x10^6 cm^-3 K at the cloud centre. Given our sensitivities, cold (T_d ~15K) 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 A_V because they may form only where A_V > 15, by some mechanism (e.g., loss of non-thermal support).Comment: 12 pages, 1 figure. Accepted by Astrophysical Journal Letter

Infrared Classification and Luminosities For Dusty AGN and the Most Luminous Quasars

Mid-infrared spectroscopic measurements from the Infrared Spectrometer on Spitzer (IRS) are given for 125 hard X-ray AGN (14-195 keV) from the Swift Burst Alert Telescope sample and for 32 AGN with black hole masses from reverberation mapping. The 9.7 um silicate feature in emission or absorption defines an infrared AGN classification describing whether AGN are observed through dust clouds, indicating that 55% of the BAT AGN are observed through dust. The mid-infrared dust continuum luminosity is shown to be an excellent indicator of intrinsic AGN luminosity, scaling closely with the hard X-ray luminosity, log vLv(7.8 um)/L(X) = -0.31 +- 0.35 and independent of classification determined from silicate emission or absorption. Dust luminosity scales closely with black hole mass, log vLv(7.8 um) = (37.2 +- 0.5) + 0.87 log BHM for luminosity in erg per sec and BHM in solar masses. The 100 most luminous type 1 quasars as measured in vLv(7.8 um) are found by comparing Sloan Digital Sky Survey optically discovered quasars with photometry at 22 um from the Wide-Field Infrared Survey Explorer, scaled to rest frame 7.8 um using an empirical template determined from IRS spectra. The most luminous SDSS/WISE quasars have the same maximum infrared luminosities for all 1.5 < z < 5, reaching total infrared luminosity L(IR) = 10^14.4 solar luminosities. Comparing with Dust Obscured Galaxies from Spitzer and WISE surveys, we find no evidence of hyperluminous obscured quasars whose maximum infrared luminosities exceed the maximum infrared luminosities of optically discovered quasars. Bolometric luminosities L(bol) estimated from rest frame optical or ultraviolet luminosities are compared to L(IR).Comment: accepted for publication in The Astrophysical Journa