Browsing by Subject "forming regions"

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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., II
We 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.
The Bolocam Galactic Plane Survey. XI. Temperatures and Substructure of Galactic Clumps Based on 350 ?M Observations
(2015-05) Merello, Manuel; Evans, Neal J., II; Shirley, Yancy L.; Rosolowsky, Erik; Ginsburg, Adam; Bally, John; Battersby, Cara; Dunham, Miranda M.; Merello, Manuel; Evans, Neal J., II
We present 107 maps of continuum emission at 350 mu m from Galactic molecular clumps. Observed sources were mainly selected from the Bolocam Galactic Plane Survey (BGPS) catalog, with three additional maps covering star-forming regions in the outer Galaxy. The higher resolution of the SHARC-II images (8."5 beam) compared with the 1.1 mm images from BGPS (33"beam) allowed us to identify a large population of smaller substructures within the clumps. A catalog is presented for the 1386 sources extracted from the 350 mu m maps. The color temperature distribution of clumps based on the two wavelengths has a median of 13.3 K and mean of 16.3 +/- 0.4 K, assuming an opacity law index of 1.7. For the structures with good determination of color temperatures, the mean ratio of gas temperature, determined from NH3 observations, to dust color temperature is 0.88 and the median ratio is 0.76. About half the clumps have more than 2 substructures and 22 clumps have more than 10. The fraction of the mass in dense substructures seen at 350 mu m compared to the mass of their parental clump is similar to 0.19, and the surface densities of these substructures are, on average, 2.2 times those seen in the clumps identified at 1.1 mm. For a well-characterized sample, 88 structures (31%) exceed a surface density of 0.2 g cm(-2), and 18 (6%) exceed 1.0 g cm(-2), thresholds for massive star Formation suggested by theorists.
The Gould's Belt Very Large Array Survey. III. The Orion Region
(2014-07) Kounkel, Marina; Hartmann, Lee; Loinard, Laurent; Mioduszewski, Amy J.; Dzib, Sergio A.; Ortiz-Leon, Gisela N.; Rodriguez, Luis F.; Pech, Gerardo; Rivera, Juana L.; Torres, Rosa M.; Boden, Andrew F.; Evans, Neal J.; Briceno, Cesar; Tobin, John; Evans, Neal J.
We present results from a high-sensitivity (60 mu Jy), large-scale (2.26 deg(2)) survey obtained with the Karl G. Jansky Very Large Array as part of the Gould's Belt Survey program. We detected 374 and 354 sources at 4.5 and 7.5 GHz, respectively. Of these, 148 are associated with previously known young stellar objects (YSOs). Another 86 sources previously unclassified at either optical or infrared wavelengths exhibit radio properties that are consistent with those of young stars. The overall properties of our sources at radio wavelengths such as their variability and radio to X-ray luminosity relation are consistent with previous results from the Gould's Belt Survey. Our detections provide target lists for follow-up Very Long Baseline Array radio observations to determine their distances as YSOs are located in regions of high nebulosity and extinction, making it difficult to measure optical parallaxes.
The Gould's Belt Very Large Array Survey. IV. The Taurus-Auriga Complex
(2015-03) Dzib, Sergio A.; Loinard, Laurent; Rodriguez, Luis F.; Mioduszewski, Amy J.; Ortiz-Leon, Gisela N.; Kounkel, Marina A.; Pech, Gerardo; Rivera, Juana L.; Torres, Rosa M.; Boden, Andrew F.; Hartmann, Lee; Evans, Neal J.; Briceno, Cesar; Tobin, John; Evans, Neal J.
We present a multi-epoch radio study of the Taurus-Auriga star-forming complex made with the Karl G. Jansky Very Large Array at frequencies of 4.5 GHz and 7.5 GHz. We detect a total of 610 sources, 59 of which are related to young stellar objects (YSOs) and 18 to field stars. The properties of 56% of the young stars are compatible with non-thermal radio emission. We also show that the radio emission of more evolved YSOs tends to be more non-thermal in origin and, in general, that their radio properties are compatible with those found in other star-forming regions. By comparing our results with previously reported X-ray observations, we notice that YSOs in Taurus-Auriga follow a Giidel Benz relation with k = 0.03, as we previously suggested for other regions of star formation. In general, YSOs in Taurus-Auriga and in all the previous studied regions seem to follow this relation with a dispersion of similar to 1 dex. Finally, we propose that most of the remaining sources are related with extragalactic objects but provide a list of 46 unidentified radio sources whose radio properties are compatible with a YSO nature.
Molecular Line Observations Of The Small Protostellar Group L1251B
(2007-12) Lee, Jeong-Eun; Di Francesco, James; Bourke, Tyler L.; Evans, Neal J.; Wu, Jingwen; Evans, Neal J.
We present molecular line observations of L1251B, a small group of pre- and protostellar objects, and its immediate environment in the dense (CO)-O-18 core L1251E. These data are complementary to near-infrared, submillimeter, and millimeter continuum observations reported by Lee et al. The single-dish data of L1251B described here show very complex kinematics, including infall, rotation, and outflow motions, and the interferometer data reveal these in greater detail. Interferometer data of N2H+ 1-0 suggest a very rapidly rotating flattened envelope between two young stellar objects, IRS1 and IRS2. In addition, interferometer data of CO 2-1 resolve the outflow associated with L1251B seen in single-dish maps into a few narrow and compact components. Furthermore, the high-resolution data support recent theoretical studies of molecular depletions and enhancements that accompany the formation of protostars within dense cores. Beyond L1251B, single-dish data are also presented of a dense core located similar to 150 '' to the east that Lee et al. detected at 850 mu m, but that has no associated point sources at near- and mid-infrared wavelengths. The relative brightness between molecules, which have different chemical timescales, suggests that it is less chemically evolved than L1251B. This core may be a site for future star formation, however, since line profiles of HCO+, CS, and HCN show asymmetry with a stronger blue peak, which is interpreted as an infall signature.
Physical Characteristics Of G331.5-0.1: The Luminous Central Region Of A Giant Molecular Cloud
(2013-09) Merello, Manuel; Bronfman, Leonardo; Garay, Guido; Nyman, Lars-Ake; Evans, Neal J.; Walmsley, C. Malcom; Merello, Manuel; Evans, Neal J.
We report molecular line and dust continuum observations toward the high-mass star-forming region G331.5-0.1, one of the most luminous regions of massive star formation in the Milky Way, located at the tangent region of the Norma spiral arm, at a distance of 7.5 kpc. Molecular emission was mapped toward the G331.5-0.1 GMC in the CO(J = 1 -> 0) and (CO)-O-18(J = 1. 0) lines with NANTEN, while its central region was mapped in CS(J = 2 -> 1 and J = 5 -> 4) with SEST, and in CS(J = 7 -> 6) and (CO)-C-13(J = 3 -> 2) with ASTE. Continuum emission mapped at 1.2 mm with SIMBA and at 0.87 mm with LABOCA reveal the presence of six compact and luminous dust clumps, making this source one of the most densely populated central regions of a GMC in the Galaxy. The dust clumps are associated with molecular gas and they have the following average properties: size of 1.6 pc, mass of 3.2 x 10(3)M(circle dot), molecular hydrogen density of 3.7 x 10(4) cm(-3), dust temperature of 32 K, and integrated luminosity of 5.7 x 10(5) L-circle dot, consistent with values found toward other massive star-forming dust clumps. The CS and (CO)-C-13 spectra show the presence of two velocity components: a high-velocity component at similar to-89 km s(-1), seen toward four of the clumps, and a low-velocity component at similar to-101 km s(-1) seen toward the other two clumps. Radio continuum emission is present toward four of the molecular clumps, with spectral index estimated for two of them of 0.8 +/- 0.2 and 1.2 +/- 0.2. A high-velocity molecular outflow is found at the center of the brightest clump, with a line width of 26 km s(-1) (FWHM) in CS(J = 7 -> 6). Observations of SiO(J = 7 -> 6 and J = 8. 7), and SO(J(K) = 8(8) -> 7(7) and J(K) = 8(7) -> 7(6)) lines provide estimates of the gas rotational temperature toward this outflow > 120 K and > 75 K, respectively.
The Spitzer c2d Survey Of Nearby Dense Cores. X. Star Formation In L673 And Cb188
(2010-12) Tsitali, Anastasia E.; Bourke, Tyler L.; Peterson, Dawn E.; Myers, Phillip C.; Dunham, Michael M.; Evans, Neal J.; Huard, Tracy L.; Dunham, Michael M.; Evans, Neal J.
L673 and CB188 are two low-mass clouds isolated from large star-forming regions that were observed as part of the Spitzer Legacy Project "From Molecular Clouds to Planet Forming disks" (c2d). We identified and characterized all the young stellar objects (YSOs) of these two regions and modeled their spectral energy distributions (SEDs) to examine whether their physical properties are consistent with values predicted from the theoretical models and with the YSO properties in the c2d survey of larger clouds. Overall, 30 YSO candidates were identified by the c2d photometric criteria, 27 in L673 and 3 in CB188. We confirm the YSO nature of 29 of them and remove a false Class III candidate in L673. We further present the discovery of two new YSO candidates, one Class 0 and another possible Class I candidate in L673, therefore bringing the total number of YSO candidates to 31. Multiple sites of star formation are present within L673, closely resembling other well-studied c2d clouds containing small groups such as B59 and L1251B, whereas CB188 seems to consist of only one isolated globule-like core. We measure a star formation efficiency (SFE) of 4.6%, which resembles the SFE of the larger c2d clouds. From the SED modeling of our YSO sample we obtain envelope masses for Class I and Flat spectrum sources of 0.01-1.0 M-circle dot. The majority of Class II YSOs show disk accretion rates from 3.3 x 10(-10) to 3 x 10(-8) M-circle dot yr(-1) and disk masses that peak at 10(-4) to 10(-3) M-circle dot. Finally, we examined the possibility of thermal fragmentation in L673 as the main star-forming process. We find that the mean density of the regions where significant YSO clustering occurs is of the order of similar to 10(5) cm(-3) using 850 mu m observations and measure a Jeans Length that is greater than the near-neighbor YSO separations by approximately a factor of 3-4. We therefore suggest that other processes, such as turbulence and shock waves, may have had a significant effect on the cloud's filamentary structure and YSO clustering.
Warm Gas Towards Young Stellar Objects In Corona Australis Herschel/PACS Observations From The Digit Key Programme
(2014-05) Lindberg, Johan E.; Jørgensen, Jes K.; Green, Joel D.; Herczeg, Gregory J.; Dionatos, Odysseas; Evans, Neal J.; Karska, Agata; Wampfler, Susanne F.; Green, Joel D.; Evans, Neal J.
Context. The effects of external irradiation on the chemistry and physics in the protostellar envelope around low-mass young stellar objects are poorly understood. The Corona Australis star-forming region contains the R CrA dark cloud, comprising several low-mass protostellar cores irradiated by an intermediate-mass young star. Aims. We study the effects of the irradiation coming from the young luminous Herbig Be star R CrA on the warm gas and dust in a group of low-mass young stellar objects. Methods. Herschel/PACS far-infrared datacubes of two low-mass star-forming regions in the R CrA dark cloud are presented. The distributions of CO, OH, H2O, [C II], [O I], and continuum emission are investigated. We have developed a deconvolution algorithm which we use to deconvolve the maps, separating the point-source emission from the extended emission. We also construct rotational diagrams of the molecular species. Results. By deconvolution of the Herschel data, we find large-scale (several thousand AU) dust continuum and spectral line emission not associated with the point sources. Similar rotational temperatures are found for the warm CO (282 4 K), hot CO (890 84 K), OH (79 +/- 4 K), and H2O (197 +/- 7 K) emission in the point sources and the extended emission. The rotational temperatures are also similar to those found in other more isolated cores. The extended dust continuum emission is found in two ridges similar in extent and temperature to molecular millimetre emission, indicative of external heating from the Herbig Be star R CrA. Conclusions. Our results show that nearby luminous stars do not increase the molecular excitation temperatures of the warm gas around young stellar objects (YSOs). However, the emission from photodissociation products of H2O, such as OH and O, is enhanced in the warm gas associated with these protostars and their surroundings compared to similar objects not subjected to external irradiation.