ABSTRACT
Since the start of ALMA (Atacama Large Millimeter Array) observatory operation, new and important chemistry of infrared cold core was revealed. Molecular transitions at millimetre range are ...being used to identify and to characterize these sources. We have investigated the 231 GHz ALMA archive observations of the infrared dark cloud region C9, focusing on the brighter source that we called as IRDC-C9 Main. We report the existence of two substructures on the continuum map of this source: a compact bright spot with high chemistry diversity that we labelled as core, and a weaker and extended one, that we labelled as tail. In the core, we have identified lines of the molecules OCS(19−18), 13CS(5−4), and CH3CH2CN, several lines of CH3CHO and the k-ladder emission of 13CH3CN. We report two different temperature regions, while the rotation diagram of CH3CHO indicates a temperature of 25 K, the rotation diagram of 13CH3CN indicates a warmer phase at temperature of ∼450 K. In the tail, only the OCS(19−18) and 13CS(5−4) lines were detected. We used the nautilus and the radex codes to estimate the column densities and the abundances. The existence of hot gas in the core of IRDC-C9 Main suggests the presence of a protostar, which is not present in the tail.
Abstract
Spectral line surveys reveal rich molecular reservoirs in G331.512–0.103, a compact radio source in the center of an energetic molecular outflow. In this first work, we analyze the physical ...conditions of the source by means of CH
3
OH and CH
3
CN. The observations were performed with the APEX Telescope. Six different system configurations were defined to cover most of the band within (292–356) GHz; as a consequence, we detected a forest of lines toward the central core. A total of 70 lines of
A
/
E
–CH
3
OH and
A
/
E
–CH
3
CN were analyzed, including torsionally excited transitions of CH
3
OH (
). In a search for all the isotopologues, we identified transitions of
13
CH
3
OH. The physical conditions were derived considering collisional and radiative processes. We found common temperatures for each
A
and
E
symmetry of CH
3
OH and CH
3
CN; the derived column densities indicate an
A
/
E
equilibrated ratio for both tracers. The results reveal that CH
3
CN and CH
3
OH trace a hot and cold component with
K and
K, respectively. In agreement with previous ALMA observations, the models show that the emission region is compact (
) with gas density
n
(H
2
) = (0.7–1)×10
7
cm
−3
. The CH
3
OH/CH
3
CN abundance ratio and the evidences for prebiotic and complex organic molecules suggest a rich and active chemistry toward G331.512–0.103.
Spectral line surveys reveal rich molecular reservoirs in G331.512-0.103, a compact radio source in the center of an energetic molecular outflow. In this first work, we analyze the physical ...conditions of the source by means of CH3OH and CH3CN. The observations were performed with the APEX Telescope. Six different system configurations were defined to cover most of the band within (292-356) GHz; as a consequence, we detected a forest of lines toward the central core. A total of 70 lines of A/E-CH3OH and A/E-CH3CN were analyzed, including torsionally excited transitions of CH3OH ( ). In a search for all the isotopologues, we identified transitions of 13CH3OH. The physical conditions were derived considering collisional and radiative processes. We found common temperatures for each A and E symmetry of CH3OH and CH3CN; the derived column densities indicate an A/E equilibrated ratio for both tracers. The results reveal that CH3CN and CH3OH trace a hot and cold component with K and K, respectively. In agreement with previous ALMA observations, the models show that the emission region is compact ( ) with gas density n(H2) = (0.7-1)×107 cm−3. The CH3OH/CH3CN abundance ratio and the evidences for prebiotic and complex organic molecules suggest a rich and active chemistry toward G331.512-0.103.
ABSTRACT
We present a catalog of low-mass dense cores observed with the SHARC-II instrument at 350
μ
m. Our observations have an effective angular resolution of 10″, approximately 2.5 times higher ...than observations at the same wavelength obtained with the
Herschel Space Observatory
, albeit with lower sensitivity, especially to extended emission. The catalog includes 81 maps covering a total of 164 detected sources. For each detected source, we tabulate basic source properties including position, peak intensity, flux density in fixed apertures, and radius. We examine the uncertainties in the pointing model applied to all SHARC-II data and conservatively find that the model corrections are good to within ∼3″, approximately 1/3 of the SHARC-II beam. We examine the differences between two array scan modes and find that the instrument calibration, beam size, and beam shape are similar between the two modes. We also show that the same flux densities are measured when sources are observed in the two different modes, indicating that there are no systematic effects introduced into our catalog by utilizing two different scan patterns during the course of taking observations. We find a detection rate of 95% for protostellar cores but only 45% for starless cores, and demonstrate the existence of a SHARC-II detection bias against all but the most massive and compact starless cores. Finally, we discuss the improvements in protostellar classification enabled by these 350
μ
m observations.
ABSTRACT We use the distance probability density function formalism of Ellsworth-Bowers et al. to derive physical properties for the collection of 1,710 Bolocam Galactic Plane Survey (BGPS) version 2 ...sources with well-constrained distance estimates. To account for Malmquist bias, we estimate that the present sample of BGPS sources is 90% complete above and 50% complete above . The mass distributions for the entire sample and astrophysically motivated subsets are generally fitted well by a lognormal function, with approximately power-law distributions at high mass. Power-law behavior emerges more clearly when the sample population is narrowed in heliocentric distance (power-law index for sources nearer than 6.5 kpc and for objects between 2 and 10 kpc). The high-mass power-law indices are generally for various subsamples of sources, intermediate between that of giant molecular clouds and the stellar initial mass function. The fit to the entire sample yields a high-mass power-law . Physical properties of BGPS sources are consistent with large molecular cloud clumps or small molecular clouds, but the fractal nature of the dense interstellar medium makes it difficult to map observational categories to the dominant physical processes driving the observed structure. The face-on map of the Galactic disk's mass surface density based on BGPS dense molecular cloud structures reveals the high-mass star-forming regions W43, W49, and W51 to be prominent mass concentrations in the first quadrant. Furthermore, we present a 0.25 kpc resolution map of the dense gas mass fraction across the Galactic disk that peaks around 5%.
We present Herschel-HIFI, SPIRE, and PACS 50-670 mu m imaging and spectroscopy of six FU Orionis-type objects and candidates (FU Orionis, V1735 Cyg, V1515 Cyg, V1057 Cyg, V1331 Cyg, and HBC 722), ...ranging in outburst date from 1936 to 2010, from the "FOOSH" (FU Orionis Objects Surveyed with Herschel) program, as well as ancillary results from Spitzer Infrared Spectrograph and the Caltech Submillimeter Observatory. In their system properties (L sub(bol), T sub(bol), and line emission), we find that FUors are in a variety of evolutionary states. Additionally, some FUors have features of both Class I and II sources: warm continuum consistent with Class II sources, but rotational line emission typical of Class I, far higher than Class II sources of similar mass/luminosity. Combining several classification techniques, we find an evolutionary sequence consistent with previous mid-IR indicators. We detect OI in every source at luminosities consistent with Class 0/I protostars, much greater than in Class II disks. We detect transitions of super(13)CO (J sub(up) of 5-8) around two sources (V1735 Cyg and HBC 722) but attribute them to nearby protostars. Of the remaining sources, three (FU Ori, V1515 Cyg, and V1331 Cyg) exhibit only low-lying CO, but one (V1057 Cyg) shows CO up to J = 23 arrow right 22 and evidence for H sub(2)O and OH emission, at strengths typical of protostars rather than T Tauri stars. Rotational temperatures for "cool" CO components range from 20 to 81 K, for ~ 10 super(50) total CO molecules. We detect CI and NII primarily as diffuse emission.
ABSTRACT We present a catalog of low-mass dense cores observed with the SHARC-II instrument at 350 m. Our observations have an effective angular resolution of 10″, approximately 2.5 times higher than ...observations at the same wavelength obtained with the Herschel Space Observatory, albeit with lower sensitivity, especially to extended emission. The catalog includes 81 maps covering a total of 164 detected sources. For each detected source, we tabulate basic source properties including position, peak intensity, flux density in fixed apertures, and radius. We examine the uncertainties in the pointing model applied to all SHARC-II data and conservatively find that the model corrections are good to within ∼3″, approximately 1/3 of the SHARC-II beam. We examine the differences between two array scan modes and find that the instrument calibration, beam size, and beam shape are similar between the two modes. We also show that the same flux densities are measured when sources are observed in the two different modes, indicating that there are no systematic effects introduced into our catalog by utilizing two different scan patterns during the course of taking observations. We find a detection rate of 95% for protostellar cores but only 45% for starless cores, and demonstrate the existence of a SHARC-II detection bias against all but the most massive and compact starless cores. Finally, we discuss the improvements in protostellar classification enabled by these 350 m observations.
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 arrow right 0) and C super(18)O(J = 1 arrow right 0) lines with NANTEN, while its central region was mapped in CS(J = 2 arrow right 1 and J = 5 arrow right 4) with SEST, and in CS(J = 7 arrow right 6) and super(13)CO(J = 3 arrow right 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 super(3) M sub(middot in circle), molecular hydrogen density of 3.7 x 10 super(4) cm super(-3), dust temperature of 32 K, and integrated luminosity of 5.7 x 10 super(5) L sub(middot in circle), consistent with values found toward other massive star-forming dust clumps. The CS and super(13)CO spectra show the presence of two velocity components: a high-velocity component at ~ - 89 km s super(-1), seen toward four of the clumps, and a low-velocity component at ~ - 101 km s super(-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 + or - 0.2 and 1.2 + or - 0.2. A high-velocity molecular outflow is found at the center of the brightest clump, with a line width of 26 km s super(-1) (FWHM) in CS(J = 7 arrow right 6). Observations of SiO(J = 7 arrow right 6 and J = 8 arrow right 7), and SO(J sub(K) = 8 sub(8) arrow right 7 sub(7) and J sub(K) = 8 sub(7) arrow right 7 sub(6)) lines provide estimates of the gas rotational temperature toward this outflow >120 K and >75 K, respectively.
ABSTRACT We present 107 maps of continuum emission at 350 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 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 m compared to the mass of their parental clump is ∼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.
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