Browsing by Subject "ii regions"
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Item The Bolocam Galactic Plane Survey. V. HCO+ and N2H+ Spectroscopy of 1.1 mm Dust Continuum Sources(2011-08) Schlingman, Wayne M.; Shirley, Yancy L.; Schenk, David E.; Rosolowsky, Erik; Bally, John; Battersby, Cara; Dunham, Miranda K.; Ellsworth-Bowers, Timothy P.; Evans, Neal J., II; Ginsburg, Adam; Stringfellow, Guy; Evans, Neal J., IIWe present the results of observations of 1882 sources in the Bolocam Galactic Plane Survey (BGPS) at 1.1 mm with the 10 m Henrich Hertz Telescope simultaneously in HCO+ J = 3-2 and N2H+ J = 3-2. We detect 77% of these sources in HCO+ and 51% in N2H+ at greater than 3 sigma. We find a strong correlation between the integrated intensity of both dense gas tracers and the 1.1 mm dust emission of BGPS sources. We determine kinematic distances for 529 sources (440 in the first quadrant breaking the distance ambiguity and 89 in the second quadrant). We derive the size, mass, and average density for this subset of clumps. The median size of BGPS clumps is 0.75 pc with a median mass of 330M(circle dot) (assuming T-Dust = 20 K). The median HCO+ linewidth is 2.9 km s(-1) indicating that BGPS clumps are dominated by supersonic turbulence or unresolved kinematic motions. We find no evidence for a size-linewidth relationship for BGPS clumps. We analyze the effects of the assumed dust temperature on the derived clump properties with a Monte Carlo simulation and find that changing the temperature distribution will change the median source properties (mass, volume-averaged number density, surface density) by factors of a few. The observed differential mass distribution has a power-law slope that is intermediate between that observed for diffuse CO clouds and the stellar initial mass function. BGPS clumps represent a wide range of objects (from dense cores to more diffuse clumps) and are typically characterized by larger sizes and lower densities than previously published surveys of high-mass star-forming regions. This collection of objects is a less-biased sample of star-forming regions in the Milky Way that likely span a wide range of evolutionary states.Item The First Galaxies: Chemical Enrichment, Mixing, And Star Formation(2010-06) Greif, Thomas H.; Glover, Simon C. O.; Bromm, Volker; Klessen, Ralf S.; Bromm, VolkerUsing three-dimensional cosmological simulations, we study the assembly process of one of the first galaxies, with a total mass of similar to 10(8) M(circle dot), collapsing at z similar or equal to 10. Our main goal is to trace the transport of the heavy chemical elements produced and dispersed by a pair-instability supernova exploding in one of the minihalo progenitors. To this extent, we incorporate an efficient algorithm into our smoothed particle hydrodynamics code that approximately models turbulent mixing as a diffusion process. We study this mixing with and without the radiative feedback from Population III (Pop III) stars that subsequently form in neighboring minihalos. Our simulations allow us to constrain the initial conditions for second-generation star formation, within the first galaxy itself, and inside of minihalos that virialize after the supernova explosion. We find that most minihalos remain unscathed by ionizing radiation or the supernova remnant, while some are substantially photoheated and enriched to supercritical levels, likely resulting in the formation of low-mass Pop III or even Population II (Pop II) stars. At the center of the newly formed galaxy, similar to 10(5) M(circle dot) of cold, dense gas uniformly enriched to similar to 10(-3) Z(circle dot) is in a Stateof collapse, suggesting that a cluster of Pop II stars will form. The first galaxies, as may be detected by the James Webb Space Telescope, would therefore already contain stellar populations familiar from lower redshifts.Item A Mid-Infrared Census Of Star Formation Activity In Bolocam Galactic Plane Survey Sources(2011-04) Dunham, Miranda K.; Robitaille, Thomas P.; Evans, Neal J.; Schlingman, Wayne M.; Cyganowski, Claudia J.; Urquhart, James; Dunham, Miranda K.; Robitaille, Thomas P.; Evans, Neal J.We present the results of a search for mid-infrared signs of star formation activity in the 1.1mm sources in the Bolocam Galactic Plane Survey (BGPS). We have correlated the BGPS catalog with available mid-IR Galactic plane catalogs based on the Spitzer Space Telescope GLIMPSE legacy survey and the Midcourse Space Experiment (MSX) Galactic plane survey. We find that 44% (3712 of 8358) of the BGPS sources contain at least one mid-IR source, including 2457 of 5067 (49%) within the area where all surveys overlap (10 degrees < l < 65 degrees). Accounting for chance alignments between the BGPS and mid-IR sources, we conservatively estimate that 20% of the BPGS sources within the area where all surveys overlap show signs of active star formation. We separate the BGPS sources into four groups based on their probability of star formation activity. Extended Green Objects and Red MSX Sources make up the highest probability group, while the lowest probability group is comprised of "starless" BGPS sources which were not matched to any mid-IR sources. The mean 1.1mm flux of each group increases with increasing probability of active star formation. We also find that the "starless" BGPS sources are the most compact, while the sources with the highest probability of star formation activity are on average more extended with large skirts of emission. A subsample of 280 BGPS sources with known distances demonstrates that mass and mean H-2 column density also increase with probability of star formation activity.