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- ID:
- ivo://CDS.VizieR/J/ApJ/626/887
- Title:
- HI clouds in Southern Galactic Plane Survey
- Short Name:
- J/ApJ/626/887
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an automated routine to search for HI self-absorption features within the Southern Galactic Plane Survey (SGPS). The data were taken with the Australia Telescope Compact Array (ATCA) and the Parkes Radio Telescope and encompass 3{deg}x105{deg} of sky in the Galactic plane. We apply our routine to this entire region and derive spin temperatures and column densities for 70 of the larger HISA complexes, finding spin temperatures ranging from 6 to 41K with HI number densities of a few cm^-3^. These "missing link" clouds fill in the spin temperature and density gaps between dense molecular clouds and diffuse atomic clouds. We compare the HI emission with ^12^CO emission and find that 60% of detected HI self-absorption is correlated in space and in velocity with a molecular counterpart. This is potentially due to a molecular/atomic gas transition. We also compare HI self-absorption with Galactic spiral arms and discuss the possibility of using it as a spiral arm tracer.
- ID:
- ivo://CDS.VizieR/J/A+A/651/A9
- Title:
- HIFI molecular line survey of SgrB2 (M)
- Short Name:
- J/A+A/651/A9
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We present a full analysis of a broadband spectral line survey of Sagittarius B2 (Main), one of the most chemically rich regions in the Galaxy located within the giant molecular cloud complex Sgr B2 in the Central Molecular Zone. Our goal is to derive the molecular abundances and temperatures of the high-mass star-forming region Sgr B2(M) and thus its physical and astrochemical conditions. Sgr B2(M) was observed using the Heterodyne Instrument for the Far-Infrared (HIFI) on board the Herschel Space Observatory in a spectral line survey from 480 to 1907GHz at a spectral resolution of 1.1MHz, which provides one of the largest spectral coverages ever obtained toward this high-mass star-forming region in the submillimeter with high spectral resolution and includes frequencies >1THz that are unobservable from the ground. We modeled the molecular emission from the submillimeter to the far-infrared using the XCLASS program, which assumes local thermodynamic equilibrium (LTE). For each molecule, a quantitative description was determined taking all emission and absorption features of that species across the entire spectral range into account. Because of the wide frequency coverage, our models are constrained by transitions over an unprecedented range in excitation energy. Additionally, we derived velocity resolved ortho/para ratios for those molecules for which ortho and para resolved molecular parameters are available. Finally, the temperature and velocity distributions are analyzed and the derived abundances are compared with those obtained for Sgr B2(N) from a similar HIFI survey. A total of 92 isotopologues were identified, arising from 49 different molecules, ranging from free ions to complex organic compounds and originating from a variety of environments from the cold envelope to hot and dense gas within the cores. Sulfur dioxide, methanol, and water are the dominant contributors. Vibrationally excited HCN (v2=1) and HNC (v2=1) are detected as well. For the ortho/para ratios, we find deviations from the high temperature values between 37 and 180%. In total 14% of all lines remain unidentified. Compared to Sgr B2(N), we found less complex molecules such as CH_3_OCH_3_, CH_3_NH_2_, or NH_2_CHO, but more simple molecules such as CN, CCH, SO, and SO_2_. However some sulfur bearing molecules such as H_2_CS, CS, NS, and OCS are more abundant in N than in M. The derived molecular abundances can be used for comparison to other sources and for providing further constraints for astrochemical models.
- ID:
- ivo://CDS.VizieR/J/A+A/594/A58
- Title:
- Hi-GAL l=224deg region CO(1-0) data cubes
- Short Name:
- J/A+A/594/A58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Stars form in dense, dusty structures, which are embedded in larger clumps of molecular clouds often showing a clear filamentary structure on large scales (>1pc). The origin (e.g., turbulence or gravitational instabilities) and evolution of these filaments, as well as their relation to clump and core formation, are not yet fully understood. A large sample of both starless and protostellar clumps can now be found in the Herschel Hi-GAL (Herschel Infrared GALactic Plane Survey) key project, which also provides striking images of the filamentary structure of the parent molecular clouds. Recent results indicate that populations of clumps on and off filaments may differ. One of the best studied regions in the Hi-GAL survey can be observed toward the l=224{deg} field. Here, a filamentary region has been studied and it has been found that protostellar clumps are mostly located along the main filament, whereas starless clumps are detected off this filament and are instead found on secondary, less prominent filaments. We want to investigate this segregation effect and how it may affect the clumps properties. We mapped the ^12^CO(1-0) line and its main three isotopologues toward the two most prominent filaments observed toward the l=224{deg} field using the Mopra radio telescope, in order to set observational constraints on the dynamics of these structures and the associated starless and protostellar clumps. Compared to the starless clumps, the protostellar clumps are more luminous, more turbulent and lie in regions where the filamentary ambient gas shows larger linewidths. We see evidence of gas flowing along the main filament, but we do not find any signs of accretion flow from the filament onto the Hi-GAL clumps. We analyze the radial column density profile of the filaments and their gravitational stability. The more massive and highly fragmented main filament appears to be thermally supercritical and gravitationally bound, assuming that all of the non-thermal motion is contributing thermal-like support, suggesting a later stage of evolution compared to the secondary filament. The status and evolutionary phase of the Hi-GAL clumps would then appear to correlate with that of the host filament.
- ID:
- ivo://CDS.VizieR/J/ApJ/772/45
- Title:
- Hi-GAL obs.: star formation in the third quadrant
- Short Name:
- J/ApJ/772/45
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first Herschel PACS and SPIRE photometric observations in a portion of the outer Galaxy (216.5{deg}<~l<~225.5{deg} and -2{deg}<~b<~0{deg}) as a part of the Hi-GAL survey. The maps between 70 and 500{mu}m, the derived column density and temperature maps, and the compact source catalog are presented. NANTEN CO(1-0) line observations are used to derive cloud kinematics and distances so that we can estimate distance-dependent physical parameters of the compact sources (cores and clumps) having a reliable spectral energy distribution that we separate into 255 proto-stellar and 688 starless sources. Both typologies are found in association with all the distance components observed in the field, up to ~5.8kpc, testifying to the presence of star formation beyond the Perseus arm at these longitudes. Selecting the starless gravitationally bound sources, we identify 590 pre-stellar candidates. Several sources of both proto- and pre-stellar nature are found to exceed the minimum requirement for being compatible with massive star formation based on the mass-radius relation. For the pre-stellar sources belonging to the Local arm (d<~1.5kpc) we study the mass function whose high-mass end shows a power law N(logM){propto}M^-1.0+/-0.2^. Finally, we use a luminosity versus mass diagram to infer the evolutionary status of the sources, finding that most of the proto-stellar sources are in the early accretion phase (with some cases compatible with a Class I stage), while for pre-stellar sources, in general, accretion has not yet started.
- ID:
- ivo://CDS.VizieR/J/A+A/620/A158
- Title:
- High-mass IR-dark clumps MALT90 molecular content
- Short Name:
- J/A+A/620/A158
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- High mass stars form in groups or clusters in dense molecular clumps with sizes of 1pc and masses of 200M_{sun}_. Infrared-dark clumps and the individual cores within them with sizes <0.1pc and masses <100M_{sun}_ are important laboratories for high-mass star formation in order to study the initial conditions. We investigate the physical and chemical properties of high-mass clumps in order to better understand the early evolutionary stages and find targets which show star formation signs such as infall motions or outflows. We selected the high-mass clumps from ATLASGAL survey that were identified as dark at 8/24um wavelengths. We use MALT90 Survey data which provides a molecular line set (HCO^+^, HNC, HCN, N^13^CH^+^, H^13^CO^+^, HN^13^C (1-0), SiO) to investigate the physical and chemical conditions in early stages of star formation. Results. (1) Eleven sources have significant SiO detection (over 3{sigma}) which usually indicates outflow activity. (2) Thirteen sources are found with blue profiles in both/either HCO+ and/or HNC lines and clump mass infall rates are estimated to be in the range of 0.2x10^-3^M_{sun}_/yr-1.8x10^-2^M_{sun}_/yr. (3) The excitation temperature is obtained as <24K for all sources. (4) The column densities for optically thin lines of H^13^CO^+^ and HN^13^C (1-0) are in the range of 0.4-8.8(x10^12^)cm^-2^, and 0.9-11.9(x10^12^)cm^-2^, respectively, while it is in the range of 0.1-7.5(x10^14^)cm^-2^ for HCO^+^ and HNC lines. The column densities for N^13^CH^+^ were ranging between 4.4-275.7(x10^12^)cm^-2^ as expected from cold dense regions. (5) Large line widths of N^13^CH^+^ might indicate turbulence and large line widths of HCO^+^, HNC, and SiO indicate outflow activities. (6) Mean optical depths are 20.32, and 23.19 for optically thick HCO^+^ and HCN lines, and 0.39 and 0.45 for their optically thin isotopologues H^13^CO^+^ and HN^13^C (1-0), respectively. This study reveals the physical and chemical properties of 30 high-mass IR-dark clumps and the interesting targets among them based on their emission line morphology and kinematics.
- ID:
- ivo://CDS.VizieR/J/ApJ/815/130
- Title:
- High-mass molecular clumps from MALT90
- Short Name:
- J/ApJ/815/130
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present dust column densities and dust temperatures for ~3000 young, high-mass molecular clumps from the Millimeter Astronomy Legacy Team 90GHz survey, derived from adjusting single-temperature dust emission models to the far-infrared intensity maps measured between 160 and 870{mu}m from the Herschel/Herschel Infrared Galactic Plane Survey (Hi-Gal) and APEX/APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) surveys. We discuss the methodology employed in analyzing the data, calculating physical parameters, and estimating their uncertainties. The population average dust temperature of the clumps are 16.8+/-0.2K for the clumps that do not exhibit mid-infrared signatures of star formation (quiescent clumps), 18.6+/-0.2K for the clumps that display mid-infrared signatures of ongoing star formation but have not yet developed an HII region (protostellar clumps), and 23.7+/-0.2 and 28.1+/-0.3K for clumps associated with HII and photo-dissociation regions, respectively. These four groups exhibit large overlaps in their temperature distributions, with dispersions ranging between 4 and 6K. The median of the peak column densities of the protostellar clump population is 0.20+/-0.02g/cm2, which is about 50% higher compared to the median of the peak column densities associated with clumps in the other evolutionary stages. We compare the dust temperatures and column densities measured toward the center of the clumps with the mean values of each clump. We find that in the quiescent clumps, the dust temperature increases toward the outer regions and that these clumps are associated with the shallowest column density profiles. In contrast, molecular clumps in the protostellar or HII region phase have dust temperature gradients more consistent with internal heating and are associated with steeper column density profiles compared with the quiescent clumps.
- ID:
- ivo://CDS.VizieR/J/other/ApSS/361.191
- Title:
- High-mass star forming clumps from MALT90
- Short Name:
- J/other/ApSS/361
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A total of 197 relatively isolated high-mass star-forming clumps were selected from the Millimeter Astronomy Legacy Team 90GHz (MALT90) survey data and their global chemical evolution investigated using four molecular lines, N_2_H^+^(1-0), HCO^+^(1-0), HCN(1-0), and HNC(1-0). The results suggest that the global averaged integrated intensity ratios I(HCO^+^)/I(HNC), I(HCN)/I(HNC), I(N_2_H^+^)/I(HCO^+^), and I(N_2_H^+^)/ I(HCN) are promising tracers for evolution of high-mass star-forming clumps. The global averaged column densities and abundances of N_2_H^+^, HCO^+^, HCN, and HNC increase as clumps evolve. The global averaged abundance ratios X(HCN)/X(HNC) could be used to trace evolution of high-mass star forming clumps, X(HCO^+^)/X(HNC) is more suitable for distinguishing high-mass star-forming clumps in prestellar (stage A) from those in protostellar (stage B) and HII/PDR region (stage C). These results suggest that the global averaged integrated intensity ratios between HCN(1-0), HNC(1-0), HCO^+^(1-0) and N_2_H^+^(1-0) are more suitable for tracing the evolution of high-mass star forming clumps. We also studied the chemical properties of the target high-mass star-forming clumps in each spiral arm of the Galaxy, and got results very different from those above. This is probably due to the relatively small sample in each spiral arm. For high-mass star-forming clumps in Sagittarius arm and Norma-Outer arm, comparing two groups located on one arm with different Galactocentric distances, the clumps near the Galactic Center appear to be younger than those far from the Galactic center, which may be due to more dense gas concentrated near the Galactic Center, and hence more massive stars being formed there.
- ID:
- ivo://CDS.VizieR/J/MNRAS/445/1412
- Title:
- HII regions and GMC in the Antennae
- Short Name:
- J/MNRAS/445/1412
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have combined observations of the Antennae galaxies from the radio interferometer ALMA (Atacama Large Millimeter/submillimeter Array) and from the optical interferometer GH{alpha}FaS (Galaxy H{alpha} Fabry-Perot System). The two sets of observations have comparable angular and spectral resolutions, enabling us to identify 142 giant molecular clouds (GMCs) and 303 HII regions. We have measured, and compared, their basic physical properties (radius, velocity dispersion, luminosity).
- ID:
- ivo://CDS.VizieR/J/A+A/485/155
- Title:
- HK photometry of rho Oph PMS stars
- Short Name:
- J/A+A/485/155
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Variability is a common characteristic of pre-main-sequence stars (PMS). Near-IR variability surveys of young stellar objects (YSOs) can probe stellar and circumstellar environments and provide information about the dynamics of the ongoing magnetic and accretion processes. Furthermore, variability can be used as a tool to uncover new cluster members in star formation regions. We hope to achieve the deepest near-IR variability study of YSOs targeting the rho Ophiuchi cluster. Fourteen epochs of observations were obtained with the Wide Field Camera (WFCAM) at the UKIRT telescope scheduled in a manner that allowed the study of variability on timescales of days, months, and years. Statistical tools, such as the multi-band cross correlation index and the reduced chi-square, were used to disentangle signals of variability from noise. Variability characteristics are compared to existing models of YSOs in order to relate them to physical processes, and then used to select new candidate members of this star-forming region. Variability in the near-IR is found to be present in 41% of the known population of rho Ophiuchi recovered in our sample. The behaviours shown are several and can be associated with the existence of spots on the stellar surface, variations in circumstellar extinction, or changes in the geometry of an accretion disc. Using variability, a new population of objects has been uncovered, that is believed to be part of the rho Ophiuchi cluster.
