We present observations and analysis of the massive molecular outflow G331.512-0.103, obtained with ALMA band 7, continuing the work from Merello et al. (2013). Several lines were identified in the ...observed bandwidth, consisting of two groups: lines with narrow profiles, tracing the emission from the core ambient medium; and lines with broad velocity wings, tracing the outflow and shocked gas emission. The physical and chemical conditions, such as density, temperature, and fractional abundances are calculated. The ambient medium, or core, has a mean density of \(\sim 5\times 10^6\) cm\(^{-3}\) and a temperature of \(\sim 70\) K. The SiO and SO\(_2\) emission trace the very dense and hot part of the shocked outflow, with values of \(n_{\rm H_2}\sim10^9\) cm\(^{-3}\) and \(T \sim 160-200\) K. The interpretation of the molecular emission suggests an expanding cavity geometry powered by stellar winds from a new-born UCHII region, alongside a massive and high-velocity molecular outflow. This scenario, along with the estimated physical conditions, is modeled using the 3D geometry radiative transfer code MOLLIE for the SiO(J\(=8-7\)) molecular line. The main features of the outflow and the expanding shell are reproduced by the model.
We examined the response of demographic, morphological, and chemical parameters of turtle grass (Thalassia testudinum), to much-higher-than-normal rainfall associated with an El Niño event in the ...winter of 1997-1998. Up to 20 inches of added rain fell between December 1997 and March 1998. triggering widespread and persistent phytoplankton blooms along the west coast of Florida. Water-column chlorophyll concentrations estimated from serial Sea WiFS imagery were much higher during the El Niño event than in the previous or following years, although the timing and magnitude of phytoplankton blooms varied among sites. Seagrass samples collected in 1997, 1998, and 1999 provided an excellent opportunity to test the responsiveness of Thalassia to decline and subsequent improvement of water quality and clarity in four estuaries. Using a scoring technique based on temporal responsiveness, spatial consistency, and statistical strength of indicators, we found that several morphological parameters (Thalassia shoot density, blade width, blade number, and shoot-specific leaf area) were responsive and consistent measures of light stress. Some morphological parameters, such as rhizome apex density, responded to declines and subsequent improvement in water clarity, but lacked the statistical discriminating power necessary to be useful indicators. However, rhizome sugar, starch, and total carbohydrate concentrations also exhibited spatially and temporally consistent variation as well as statistical strength. Because changes in shoot density, as well as water clarity, affect rhizome carbohydrate levels, a composite metric based on Thalassia shoot density and rhizome carbohydrate levels together is probably more useful than either parameter alone as an indicator of seagrass health.
The evolutionary classification of massive clumps that are candidate progenitors of high-mass young stars and clusters relies on a variety of independent diagnostics based on observables from the ...near-infrared to the radio. A promising evolutionary indicator for massive and dense cluster-progenitor clumps is the L/M ratio between the bolometric luminosity and the mass of the clumps. With the aim of providing a quantitative calibration for this indicator we used SEPIA/APEX to obtain CH3C2H(12-11) observations, that is an excellent thermometer molecule probing densities > 10^5 cm^-3 , toward 51 dense clumps with M>1000 solar masses, and uniformly spanning -2 < Log(L/M) < 2.3. We identify three distinct ranges of L/M that can be associated to three distinct phases of star formation in massive clumps. For L/M <1 no clump is detected in CH3C2H , suggesting an inner envelope temperature below 30K. For 1< L/M < 10 we detect 58% of the clumps, with a temperature between 30 and 35 K independently from the exact value of L/M; such clumps are building up luminosity due to the formation of stars, but no star is yet able to significantly heat the inner clump regions. For L/M> 10 we detect all the clumps, with a gas temperature rising with Log(L/M), marking the appearance of a qualitatively different heating source within the clumps; such values are found towards clumps with UCHII counterparts, suggesting that the quantitative difference in T - L/M behaviour above L/M >10 is due to the first appearance of ZAMS stars in the clumps.
We present a comparative study of physical properties derived from gas and dust emission in a sample of 1068 dense Galactic clumps. The sources are selected from the crossmatch of the Hi-GAL survey ...with 16 catalogues of NH\(_3\) line emission in its lowest inversion (1,1) and (2,2) transitions. The sample covers a large range in masses and bolometric luminosities, with surface densities above \(\Sigma=0.1\) g cm\(^{-2}\) and with low virial parameters \(\alpha<1\). The comparison between dust and gas properties shows an overall agreement between \(T_{\textit{kin}}\) and \(T_{\textit{dust}}\) at volumetric densities \(n\gtrsim1.2\times10^{4}\) cm\(^{-3}\), and a median fractional abundance \(\chi\)(NH\(_3\))\(=1.46\times10^{-8}\). While the protostellar clumps in the sample have small differences between \(T_{\textit{kin}}\) and \(T_{\textit{dust}}\), prestellar clumps have a median ratio \(T_{\textit{kin}}/T_{\textit{dust}}=1.24\), suggesting that these sources are thermally decoupled. A correlation is found between the evolutionary tracer \(L/M\) and the parameters \(T_{\textit{kin}}/T_{\textit{dust}}\) and \(\chi\)(NH\(_3\)) in prestellar sources and protostellar clumps with \(L/M<1\) L\(_\odot\) M\(_\odot^{-1}\). In addition, a weak correlation is found between non-thermal velocity dispersion and the \(L/M\) parameter, possibly indicating an increase of turbulence with protostellar evolution in the interior of clumps. Finally, different processes are discussed to explain the differences between gas and dust temperatures in prestellar candidates, and the origin of non-thermal motions observed in the clumps.
Since the start of ALMA observatory operation, new and important chemistry of infrared cold core was revealed. Molecular transitions at millimeter 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 sub-structures 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), \(^{13}\)CS(5-4) and CH\(_{3}\)CH\(_{2}\)CN, several lines of CH\(_{3}\)CHO and the k-ladder emission of \(^{13}\)CH\(_{3}\)CN.We report two different temperature regions: while the rotation diagram of CH\(_{3}\)CHO indicates a temperature of 25 K, the rotation diagram of \(^{13}\)CH\(_{3}\)CN indicates a warmer phase at temperature of \(\sim450\)K. In the tail, only the OCS(19-18) and \(^{13}\)CS(5-4) lines were detected. We used the \(Nautilus\) and the \textsc{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.
The degradation of spatial resolution in star-forming regions observed at large distances (\(d\gtrsim1\) kpc) with Herschel,can lead to estimates of the physical parameters of the detected compact ...sources (clumps) which do not necessarily mirror the properties of the original population of cores. This paper aims at quantifying the bias introduced in the estimation of these parameters by the distance effect. To do so, we consider Herschel maps of nearby star-forming regions taken from the Herschel-Gould-Belt survey, and simulate the effect of increased distance to understand what amount of information is lost when a distant star-forming region is observed with Herschel resolution. In the maps displaced to different distances we extract compact sources, and we derive their physical parameters as if they were original Hi-GAL maps of the extracted source samples. In this way, we are able to discuss how the main physical properties change with distance. In particular, we discuss the ability of clumps to form massive stars: we estimate the fraction of distant sources that are classified as high-mass stars-forming objects due to their position in the mass vs radius diagram, that are only "false positives". We give also a threshold for high-mass star-formation \(M>1282 \ \left(\frac{r}{\mathrm{pc}}\right)^{1.42} M_{\odot}\). In conclusion, this paper provides the astronomer dealing with Herschel maps of distant star-forming regions with a set of prescriptions to partially recover the character of the core population in unresolved clumps.
We present a catalog of low-mass dense cores observed with the SHARC-II instrument at 350 microns. 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 micron observations.
We use the distance probability density function (DPDF) formalism of Ellsworth-Bowers et al. (2013, 2015) 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 400 \(M_\odot\) and 50% complete above 70 \(M_\odot\). 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 \(\alpha = 2.0\pm0.1\) for sources nearer than 6.5 kpc and \(\alpha = 1.9\pm0.1\) for objects between 2 kpc and 10 kpc). The high-mass power-law indices are generally \(1.85 \leq \alpha \leq 2.05\) 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 \(\hat{\alpha} = 1.94_{-0.10}^{+0.34}\). 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 difficult the mapping of 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 as 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 107 maps of continuum emission at 350 microns from Galactic molecular clumps. Observed sources were mainly selected from the Bolocam Galactic Plane Survey (BGPS) catalog, with 3 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 micron 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 two substructures and 22 clumps have more than 10. The fraction of the mass in dense substructures seen at 350 microns 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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