Browsing by Subject "initial conditions"

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The Bolocam Galactic Plane Survey. III. Characterizing Physical Properties Of Massive Star-Forming Regions In The Gemini Ob1 Molecular Cloud
(2010-07) Dunham, Miranda K.; Rosolowsky, Erik; Evans, Neal J.; Cyganowski, Claudia J.; Aguirre, James; Bally, John; Battersby, Cara; Bradley, Eric Todd; Dowell, Darren; Drosback, Meredith; Ginsburg, Adam; Glenn, Jason; Harvey, Paul; Merello, Manuel; Schlingman, Wayne; Shirley, Yancy L.; Stringfellow, Guy S.; Walawender, Josh; Williams, Jonathan P.; Dunham, Miranda K.; Evans, Neal J.; Harvey, Paul; Merello, Manue
We present the 1.1 mm Bolocam Galactic Plane Survey (BGPS) observations of the Gemini OB1 molecular cloud complex, and targeted NH3 observations of the BGPS sources. When paired with molecular spectroscopy of a dense gas tracer, millimeter observations yield physical properties such as masses, radii, mean densities, kinetic temperatures, and line widths. We detect 34 distinct BGPS sources above 5 sigma = 0.37 Jy beam(-1) with corresponding 5s detections in the NH3(1,1) transition. Eight of the objects show water maser emission (20%). We find a mean millimeter source FWHM of 1.12 pc and a mean gas kinetic temperature of 20 K for the sample of 34 BGPS sources with detections in the NH3(1,1) line. The observed NH3 line widths are dominated by non-thermal motions, typically found to be a few times the thermal sound speed expected for the derived kinetic temperature. We calculate the mass for each source from the millimeter flux assuming the sources are isothermal and find a mean isothermal mass within a 120 '' aperture of 230 +/- 180 M-circle dot. We find a total mass of 8400 M-circle dot for all BGPS sources in the Gemini OB1 molecular cloud, representing 6.5% of the cloud mass. By comparing the millimeter isothermal mass to the virial mass calculated from the NH3 line widths within a radius equal to the millimeter source size, we find a mean virial parameter (M-vir/M-iso) of 1.0 +/- 0.9 for the sample. We find mean values for the distributions of column densities of 1.0 x 10(22) cm(-2) for H-2, and 3.0 x 10(14) cm(-2) for NH3, giving a mean NH3 abundance of 3.0 x 10(-8) relative to H-2. We find volume-averaged densities on the order of 10(3)-10(4) cm(-3). The sizes and densities suggest that in the Gem OB1 region the BGPS is detecting the clumps from which stellar clusters form, rather than smaller, higher density cores where single stars or small multiple systems form.
Far-Infrared Observations Of The Very Low Luminosity Embedded Source L1521F-IRS In The Taurus Star-Forming Region
(2009-05) Terebey, Susan; Fich, Michael; Noriega-Crespo, Alberto; Padgett, Deborah L.; Fukagawa, Misato; Audard, Marc; Brooke, Tyler; Carey, Sean; Evans, Neal J.; Guedel, Manuel; Hines, Dean; Huard, Tracy; Knapp, Gillian R.; McCabe, Caer-Eve; Menard, Francois; Monin, Jean-Louis; Rebull, Luisa; Evans, Neal J.
We investigate the environment of the very low luminosity object L1521F-IRS using data from the Taurus Spitzer Legacy Survey. The MIPS 160 mu m image shows both extended emission from the Taurus cloud and emission from multiple cold cores over a 1 degrees x 2 degrees region. Analysis shows that the cloud dust temperature is 14.2 +/- 0.4 K and the extinction ratio is A(160)/A(K) = 0.010 +/- 0.001 up to A(V) similar to 4 mag. We find kappa(160) = 0.23 +/- 0.046 cm(2) g(-1) for the specific opacity of the gas-dust mixture. Therefore, for dust in the Taurus cloud we find that the 160 mu m opacity is significantly higher than that measured for the diffuse interstellar medium, but not too different from dense cores, even at modest extinction values. Furthermore, the 160 mu m image shows features that do not appear in the IRAS 100 mu m image. We identify six regions as cold cores, i.e., colder than 14.2 K, all of which have counterparts in extinction maps or C(18)O maps. Three of the six cores contain embedded young stellar objects, which demonstrates the cores are sites of current star formation. We compare the effects of L1521F-IRS on its natal core and find there is no evidence for dust heating at 160 or 100 mu m by the embedded source. From the infrared luminosity L(TIR) = 0.024 L(circle dot) we find L(bol_int) = 0.034 -0.046 L(circle dot), thus confirming the source's low luminosity. Comparison of L1521F-IRS with theoretical simulations for the very early phases of star formation appears to rule out the first core collapse phase. The evolutionary Stateappears similar to or younger than the class 0 phase, and the estimated mass is likely to be substellar.
Observational Constraints On Submillimeter Dust Opacity
(2011-02) Shirley, Yancy L.; Huard, Tracy L.; Pontoppidan, Klaus M.; Wilner, David J.; Stutz, Amelia M.; Bieging, John H.; Evans, Neal J.; Evans, Neal J.
Infrared extinction maps and submillimeter dust continuum maps are powerful probes of the density structure in the envelope of star-forming cores. We make a direct comparison between infrared and submillimeter dust continuum observations of the low-mass Class 0 core, B335, to constrain the ratio of submillimeter to infrared opacity (kappa(smm)/kappa(ir)) and the submillimeter opacity power-law index (kappa alpha lambda(-beta)). Using the average value of theoretical dust opacity models at 2.2 mu m, we constrain the dust opacity at 850 and 450 mu m. Using new dust continuum models based upon the broken power-law density structure derived from interferometric observations of B335 and the infall model derived from molecular line observations of B335, we find that the opacity ratios are kappa(850)/kappa(2.2) = (3.21-4.80)(-0.30)(+0.44) x 10(-4) and kappa(450)/kappa(2.2) = (12.8-24.8)(-1.3)(+2.4) x 10(-4)with a submillimeter opacity power-law index of beta(smm) = (2.18-2.58)(-0.30)(+0.30). The range of quoted values is determined from the uncertainty in the physical model for B335. For an average 2.2 mu m opacity of 3800 +/- 700 cm(2) g(-1), we find a dust opacity at 850 and 450 mu m of kappa(850) = (1.18-1.77)(-0.24)(+0.36) and kappa(450) = (4.72-9.13)(-0.98)(+1.9) cm(2) g(-1) of dust. These opacities are from (0.65-0.97) kappa(OH5)(850) of the widely used theoretical opacities of Ossenkopf and Henning for coagulated ice grains with thin mantles at 850 mu m.