- ID:
- ivo://CDS.VizieR/J/MNRAS/474/4396
- Title:
- MASIV Survey. IV. Radio AGNs variability
- Short Name:
- J/MNRAS/474/4396
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the relationship between 5GHz interstellar scintillation (ISS) and 15GHz intrinsic variability of compact, radio-selected active galactic nuclei (AGNs) drawn from the Microarcsecond Scintillation-Induced Variability (MASIV) Survey and the Owens Valley Radio Observatory blazar monitoring program. We discover that the strongest scintillators at 5GHz (modulation index, m_5_>=0.02) all exhibit strong 15GHz intrinsic variability (m_15_>=0.1). This relationship can be attributed mainly to the mutual dependence of intrinsic variability and ISS amplitudes on radio core compactness at ~100{mu}s scales, and to a lesser extent, on their mutual dependences on source flux density, arcsec-scale core dominance and redshift. However, not all sources displaying strong intrinsic variations show high amplitude scintillation, since ISS is also strongly dependent on Galactic line-of-sight scattering properties. This observed relationship between intrinsic variability and ISS highlights the importance of optimizing the observing frequency, cadence, timespan and sky coverage of future radio variability surveys, such that these two effects can be better distinguished to study the underlying physics. For the full MASIV sample, we find that Fermi-detected gamma-ray loud sources exhibit significantly higher 5GHz ISS amplitudes than gamma-ray quiet sources. This relationship is weaker than the known correlation between gamma-ray loudness and the 15GHz variability amplitudes, most likely due to jet opacity effects.
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- ID:
- ivo://CDS.VizieR/J/AJ/127/501
- Title:
- 2MASS counterparts for OH/IR stars
- Short Name:
- J/AJ/127/501
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The positions of the IRAS counterparts to the 420 OH/IR stars in the Arecibo sky (0{deg}<{delta}<+38{deg}) are usually accurate to better than 10". But every star has recently been observed by the Two Micron All Sky Survey (2MASS, <II/246>), which provides 0.2" quality positions, while those with |b|<=4.5{deg} have also been observed by the Midcourse Space Experiment (MSX, <V/114>), which provides ~2" quality positions. We use the MSX and/or IRAS coordinates to guide us to 2MASS counterparts for the 134 Arecibo OH/IR stars with images in the second release of the 2MASS Point Source Catalog. An unexpected by-product of having the J-H versus H-K_s_ plot generated from the 2MASS fluxes is the realization that most (~85%) of the redder OH/IR stars have detached circumstellar shells. We identify five objects that probably, by contrast, have "normal" shells, and we confirm the status of AU Vul as a protoplanetary nebula.
- ID:
- ivo://CDS.VizieR/J/A+A/380/665
- Title:
- Massive dense cores with ^13^CO J=1-0 lines
- Short Name:
- J/A+A/380/665
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper reports ^13^CO J=1-0 line observations toward 107 IRAS or H2O maser sources with the 13.7m telescope of the Purple Mountain Observatory (PMO). Parameters of emission components are obtained and the profile characteristics are identified. Table1 lists the observed results. It contains source name and its coordinates. ^13^CO line parameters and profile characteristics are given out. Distance, IRAS color indices and bolometric luminosity are also presented.
- ID:
- ivo://CDS.VizieR/J/A+A/638/A105
- Title:
- 8 massive proto-cluster clumps NH2D & NH3 cubes
- Short Name:
- J/A+A/638/A105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The initial stage of star formation is very difficult to study because of its high density (n_H_2> 10^6^cm^-3^) and low temperature (T_dust_<18K). Under such conditions, many molecules become depleted from the gas phase by freezing out onto dust grains. However, the deuterated species could remain gaseous under these extreme conditions and are thus ideal tracers. We investigate the gas dynamics and NH_2_D chemistry in eight massive pre/protocluster clumps (G18.17, G18.21, G23.97N, G23.98, G23.44, G23.97S, G25.38, and G25.71). We present NH_2_D 1_11-1_01 (at 85.926GHz), NH_3_ (1,1) and (2,2) observations in the eight clumps using the PdBI and the VLA, respectively. We use 3D GAUSSCLUMPS to extract NH_2_D cores and provide a statistical view of their deuterium chemistry. We use NH_3_ (1,1) and (2,2) data to investigate the temperature and dynamics of dense and cold objects. We find that the distribution between deuterium fractionation and kinetic temperature shows a number density peak at around T_kin_=16.1K, and the NH_2_D cores are mainly located at a temperature range of 13.0 to 22.0K. The 3.5mm continuum cores have a kinetic temperature with the median width of 22.1+/-4.3K, which is obviously higher than the temperature in NH_2_D cores. We detect seven extremely high deuterium fractionation of 1.0<=D_frac_<=1.41. We find that the NH_2_D emission does not appear to coincide exactly with either dust continuum or NH3 peak positions, but often surrounds the star-formation active regions. This suggests that the NH_2_D has been destroyed by the central young stellar object (YSO) due to its heating. The detected NH_2_D lines are very narrow with a median width of 0.98+/-0.02km/s, which is dominated by non-thermal broadening. The extracted NH_2_D cores are gravitationally bound ({alpha}_vir_<1), are likely prestellar or starless, and can potentially form intermediate-mass or high-mass stars in future. Using NH3 (1,1) as a dynamical tracer, we find very complicated dynamical movement in all the eight clumps, which can be explained by a combined process with outflow, rotation, convergent flow, collision, large velocity gradient, and rotating toroids. High deuterium fractionation strongly depends on the temperature condition. NH_2_D is a poor evolutionary indicator of high-mass star formation in evolved stages, but a useful tracer in the starless and prestellar cores.
- ID:
- ivo://CDS.VizieR/J/A+A/627/A85
- Title:
- 8 massive proto-cluster clumps observations
- Short Name:
- J/A+A/627/A85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Massive clumps tend to fragment into clusters of cores and condensations, some of which form high-mass stars. In this work, we study the structure of massive clumps at different scales, analyze the fragmentation process, and investigate the possibility that star formation is triggered by nearby HII regions. We present a high angular resolution study of a sample of 8 massive proto-cluster clumps. Combining infrared data, we use few-arcsecond resolution radio- and millimeter interferometric data to study their fragmentation and evolution. Our sample is unique in the sense that all the clumps have neighboring HII regions. Taking advantage of that, we test triggered star formation using a novel method where we study the alignment of the centres of mass traced by dust emission at multiple scales. The eight massive clumps have masses ranging from 228 to 2279M_{sun}_. The brightest compact structures within infrared bright clumps are typically associated with embedded compact radio continuum sources. The smaller scale structures of Reff~0.02pc observed within each clump are mostly gravitationally bound and massive enough to form at least a B3-B0 type star. Many condensations have masses larger than 8M_{sun}_ at small scale of Reff~0.02pc. Although the clumps are mostly infrared quiet, the dynamical movements are active at clump scale (~1pc). We studied the spatial distribution of the gas conditions detected at different scales. For some sources we find hints of external triggering, whereas for others we find no significant pattern that indicates triggering is dynamically unimportant. This probably indicates that the different clumps go through different evolutionary paths. In this respect, studies with larger samples are highly desired.
- ID:
- ivo://CDS.VizieR/J/A+A/432/921
- Title:
- Massive protostellar candidates
- Short Name:
- J/A+A/432/921
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have observed two rotational transitions of both CS and C^17^O, and the 1.2mm continuum emission towards a sample of 130 high-mass protostellar candidates with DE<-30{deg}. This work represents the first step of the extension to the southern hemisphere of a project started more than a decade ago aimed at the identification of massive protostellar candidates. Following the same approach adopted for sources with DE>=-30{deg}, we have selected from the IRAS Point Source Catalogue 429 sources which potentially are compact molecular clouds on the basis of their IR colours. The sample has then been divided into two groups according to the colour indices [25-12] and [60-12]: the 298 sources with [25-12]>=0.57 and [60-12]>=1.30 have been called High sources, the remaining 131 have been called Low sources. In this paper, we check the association with dense gas and dust in 130 Low sources. We have obtained a detection rate of ~85% in CS, demonstrating a tight association of the sources with dense molecular clumps.
- ID:
- ivo://CDS.VizieR/J/ApJS/243/13
- Title:
- Massive star-forming clump from MALT90
- Short Name:
- J/ApJS/243/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We selected 90 massive star-forming clumps with strong N2H+(1-0), HCO+(1-0), HCN(1-0), and HNC(1-0) emission from the Millimetre Astronomy Legacy Team 90 GHz survey. We obtained Herschel data for all 90 sources and NRAO VLA Sky Survey data for 51 of them. We convolved and regridded all images to the same resolution and pixel size and derived the temperature, H2 column density, molecules' abundances and abundance, and ratios of each pixel. Our analysis yields three main conclusions. First, the abundances of N2H+, HCO+, HCN, and HNC increase when the column density decreases and the temperature increases, with spatial variations in their abundances dominated by changes in the H2 column density. Second, the abundance ratios between N2H+, HCO+, HCN, and HNC also display systemic variations as a function of the column density due to the chemical properties of these molecules. Third, the sources associated with the 20cm continuum emission can be classified into four types based on the behavior of the abundances of the four molecules considered here as a function of this emission. The variations of the first three types could also be attributed to the variation of the H2 column density.
- ID:
- ivo://CDS.VizieR/J/A+A/598/A30
- Title:
- Massive star forming molecular clumps Tkin
- Short Name:
- J/A+A/598/A30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- For a general understanding of the physics involved in the star formation process, measurements of physical parameters such as temperature and density are indispensable. The chemical and physical properties of dense clumps of molecular clouds are strongly affected by the kinetic temperature. Therefore, this parameter is essential for a better understanding of the interstellar medium. Formaldehyde, a molecule which traces the entire dense molecular gas, appears to be the most reliable tracer to directly measure the gas kinetic temperature.We aim to determine the kinetic temperature with spectral lines from formaldehyde and to compare the results with those obtained from ammonia lines for a large number of massive clumps.Three 218 GHz transitions (J_KAKC_=3_03_-2_02_, 3_22_-2_21_, and 3_21_-2_20_) of para-H_2_CO were observed with the 15m James Clerk Maxwell Telescope (JCMT) toward 30 massive clumps of the Galactic disk at various stages of high-mass star formation. Using the RADEX non-LTE model, we derive the gas kinetic temperature modeling the measured para-H_2_CO 3_22_-2_21_/3_03_-2_02_ and 3_21_-2_20_/3_03_-2_02_ ratios. The gas kinetic temperatures derived from the para-H2CO (3_21_-2_20_/3_03_-2_02_) line ratios range from 30 to 61K with an average of 46K. A comparison of kinetic temperature derived from para-H_2_CO, NH3, and the dust emission indicates that in many cases para-H_2_CO traces a similar kinetic temperature to the NH_3_ (2,2)/(1,1) transitions and the dust associated with the HII regions. Distinctly higher temperatures are probed by para-H_2_CO in the clumps associated with outflows/shocks. Kinetic temperatures obtained from para-H_2_CO trace turbulence to a higher degree than NH_3_ (2,2)/(1,1) in the massive clumps. The non-thermal velocity dispersions of para-H_2_CO lines are positively correlated with the gas kinetic temperature. The massive clumps are significantly influenced by supersonic non-thermal motions.
- ID:
- ivo://CDS.VizieR/J/ApJ/566/945
- Title:
- Massive star forming regions at 1.2mm
- Short Name:
- J/ApJ/566/945
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed 1.2mm continuum and CS spectral line study of a large sample of 69 massive star forming regions in very early stages of evolution, most of them prior to building up an ultracompact H II region.
- ID:
- ivo://CDS.VizieR/J/ApJ/864/136
- Title:
- Massive star-forming regions multiwavelength study
- Short Name:
- J/ApJ/864/136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a multiwavelength study of 28 Galactic massive star-forming HII regions. For 17 of these regions, we present new distance measurements based on Gaia DR2 parallaxes. By fitting a multicomponent dust, blackbody, and power-law continuum model to the 3.6{mu}m through 10mm spectral energy distributions, we find that ~34% of Lyman continuum photons emitted by massive stars are absorbed by dust before contributing to the ionization of HII regions, while ~68% of the stellar bolometric luminosity is absorbed and reprocessed by dust in the HII regions and surrounding photodissociation regions. The most luminous, infrared-bright regions that fully sample the upper stellar initial mass function (ionizing photon rates N_C_>=10^50^s^-1^ and dust-processed L_TIR_>=10^6.8^L_{sun}_) have on average higher percentages of absorbed Lyman continuum photons (~51%) and reprocessed starlight (~82%) compared to less luminous regions. Luminous HII regions show lower average polycyclic aromatic hydrocarbon (PAH) fractions than less luminous regions, implying that the strong radiation fields from early-type massive stars are efficient at destroying PAH molecules. On average, the monochromatic luminosities at 8, 24, and 70{mu}m combined carry 94% of the dust-reprocessed L_TIR_. L70 captures ~52% of L_TIR_, and is therefore the preferred choice to infer the bolometric luminosity of dusty star-forming regions. We calibrate star formation rates (SFRs) based on L24 and L70 against the Lyman continuum photon rates of the massive stars in each region. Standard extragalactic calibrations of monochromatic SFRs based on population synthesis models are generally consistent with our values.