- ID:
- ivo://CDS.VizieR/J/ApJS/94/615
- Title:
- Molecular outflow sources
- Short Name:
- J/ApJS/94/615
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A K'-band imaging survey with a ~8'x3' field of view of all regions associated with CO molecular outflow from the list of Fukui (1989) has been conducted. We present the individual images and describe individual nebulous objects and star clusters. The vast majority of all outflow sources are associated with nebulosity detectable in K', so such nebulae can be used as tracers for very young stars. We find a significant fraction (one-third) of molecular outflow sources to be associated with clusters of young stars. Most of the young embedded clusters show peaks in their K' magnitude histograms that, if interpreted as an evolutionary effect, indicate average ages of the embedded star population of <1x10^6yr.
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- ID:
- ivo://CDS.VizieR/J/ApJ/519/697
- Title:
- Molecular study of HC_3_NH^+^+e^-^
- Short Name:
- J/ApJ/519/697
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The dissociative recombination reaction between HC_3_NH^+^ and electrons is an important process in the chemistry of interstellar clouds. Motivated by the evidence that HCN and its metastable isomer HNC are both formed via the dissociative recombination reaction of HCNH^+^, we have examined the potential energy surface for the dissociation of the transient HC_3_NH following the recombination between HC_3_NH^+^ and electrons. We find that HC_3_NH^+^ gains 151 kcal mol^-1^ energy by the neutralization; this energy is high enough to isomerize HC_3_NH to HCCNCH, as well as to dissociate a hydrogen atom from either end of the molecule. The present calculation suggests, therefore, that the metastable linear and near-linear isomers of HC_3_N, namely, HNC_3_, HCCNC, and HCNCC, can be formed via the dissociative recombination between HC_3_NH^+^ and electrons. Two of these isomers, HNC3 and HCCNC, have already been detected in the dark cloud TMC-1. The unobserved species HCNCC is energetically the least stable. Since interstellar HC_3_N molecules are synthesized predominantly via neutral-neutral reactions, the HC_3_NH^+^ + e^-^ process serves mainly to produce the metastable isomers of HC_3_N.
- ID:
- ivo://CDS.VizieR/J/ApJ/851/76
- Title:
- Molecular transitions toward NGC5128 with ALMA
- Short Name:
- J/ApJ/851/76
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Centaurus A, with its gas-rich elliptical host galaxy, NGC 5128, is the nearest radio galaxy at a distance of 3.8Mpc. Its proximity allows us to study the interaction among an active galactic nucleus, radio jets, and molecular gas in great detail. We present ALMA observations of low-J transitions of three CO isotopologues, HCN, HCO+, HNC, CN, and CCH toward the inner projected 500pc of NGC 5128. Our observations resolve physical sizes down to 40pc. By observing multiple chemical probes, we determine the physical and chemical conditions of the nuclear interstellar medium of NGC 5128. This region contains molecular arms associated with the dust lanes and a circumnuclear disk (CND) interior to the molecular arms. The CND is approximately 400pc by 200pc and appears to be chemically distinct from the molecular arms. It is dominated by dense gas tracers while the molecular arms are dominated by ^12^CO and its rare isotopologues. The CND has a higher temperature, elevated CN/HCN and HCN/HNC intensity ratios, and much weaker ^13^CO and C^18^O emission than the molecular arms. This suggests an influence from the AGN on the CND molecular gas. There is also absorption against the AGN with a low velocity complex near the systemic velocity and a high velocity complex shifted by about 60km/s. We find similar chemical properties between the CND in emission and both the low and high velocity absorption complexes, implying that both likely originate from the CND. If the HV complex does originate in the CND, then that gas would correspond to gas falling toward the supermassive black hole.
- ID:
- ivo://CDS.VizieR/J/A+A/592/A18
- Title:
- Molecule and grain abundances
- Short Name:
- J/A+A/592/A18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We develop a detailed chemical network relevant to calculate the conditions that are characteristic of prestellar core collapse. We solve the system of time-dependent differential equations to calculate the equilibrium abundances of molecules and dust grains, with a size distribution given by size-bins for these latter. These abundances are used to compute the different non-ideal magneto-hydrodynamics resistivities (ambipolar, Ohmic and Hall), needed to carry out simulations of protostellar collapse. For the first time in this context, we take into account the evaporation of the grains, the thermal ionisation of potassium, sodium, and hydrogen at high temperature, and the thermionic emission of grains in the chemical network, and we explore the impact of various cosmic ray ionisation rates. All these processes significantly affect the non-ideal magneto-hydrodynamics resistivities, which will modify the dynamics of the collapse. Ambipolar diffusion and Hall effect dominate at low densities, up to n_H_=10^12^cm-3, after which Ohmic diffusion takes over. We find that the time-scale needed to reach chemical equilibrium is always shorter than the typical dynamical (free fall) one. This allows us to build a large, multi-dimensional multi-species equilibrium abundance table over a large temperature, density and ionisation rate ranges. This table, which we make accessible to the community, is used during first and second prestellar core collapse calculations to compute the non-ideal magneto-hydrodynamics resistivities, yielding a consistent dynamical-chemical description of this process.
- ID:
- ivo://CDS.VizieR/J/A+A/607/A22
- Title:
- Monoceros R2 filament hub FIR observations
- Short Name:
- J/A+A/607/A22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present far-infrared observations of Monoceros R2 (a giant molecular cloud at approximately 830pc distance, containing several sites of active star formation), as observed at 70um, 160um, 250um, 350um, and 500um by the PACS and SPIRE instruments on the Herschel Space Observatory as part of the HOBYS Key programme. The Herschel data are complemented by SCUBA-2 data in the submillimetre range, and WISE and Spitzer data in the mid-infrared. In addition, C^18^O data from the IRAM 30-m Telescope are presented, and used for kinematic information. Sources were extracted from the maps with getsources, and from the fluxes measured, spectral energy distributions were constructed, allowing measurements of source mass and dust temperature. Of 177 Herschel sources robustly detected in the region (a detection with high signal-to-noise and low axis ratio at multiple wavelengths), including protostars and starless cores, 29 are found in a filamentary hub at the centre of the region (a little over 1% of the observed area). These objects are on average smaller, more massive, and more luminous than those in the surrounding regions (which together suggest that they are at a later stage of evolution), a result that cannot be explained entirely by selection effects. These results suggest a picture in which the hub may have begun star formation at a point significantly earlier than the outer regions, possibly forming as a result of feedback from earlier star formation. Furthermore, the hub may be sustaining its star formation by accreting material from the surrounding filaments.
- ID:
- ivo://CDS.VizieR/J/A+A/453/923
- Title:
- Morphologies in the Cepheus Flare region
- Short Name:
- J/A+A/453/923
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- These tables contain the data of the cloud sample on which the study of the relationships between cloud morphology, optical and IR properties, and star formation is based. The sample was defined using the extinction map of the Cepheus Flare region covering ~256 square degrees created from the B band star counts of the USNO-A2.0 catalogue (Cat. <I/252>) with a typical resolution of 3 arcminutes on a 1.5 arcminute grid. Cloud definition and description was carried out using automatized methods. The main table lists the positions, peak extinctions, sizes, morphological parameters and classes, distances, mass estimations, parent cloud complexes, and the number of YSO candidates associated. An additional table with the names of the previously catalogued associated clouds and their references is also available.
- ID:
- ivo://CDS.VizieR/J/A+A/633/A163
- Title:
- Mrk 231 CO(1-0) and CN(1-0) line observations
- Short Name:
- J/A+A/633/A163
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present interferometric observations of the CN(1-0) line emission in Mrk 231 and combine them with previous observations of CO and other H_2_ gas tracers to study the physical properties of the massive molecular outflow. We find a strong boost of the CN/CO(1-0) line luminosity ratio in the outflow of Mrk 231, which is unprecedented compared to any other known Galactic or extragalactic astronomical source. For the dense gas phase in the outflow traced by the HCN and CN emissions, we infer X_CN_=[CN]/[H_2_]>X_HCN_ by at least a factor of three, with H_2_ gas densities of n_H2_~10^5-6^cm^-3^. In addition, we resolve for the first time narrow spectral features in the HCN(1-0) and HCO^+^(1-0) high-velocity line wings tracing the dense phase of the outflow. The velocity dispersions of these spectral features, {sigma}_v_~7-20km/s, are consistent with those of massive extragalactic giant molecular clouds detected in nearby starburst nuclei. The H_2_ gas masses inferred from the HCN data are quite high, M_mol_~0.3-5x10^8^M_{sun}_. Our results suggest that massive complexes of denser molecular gas survive embedded into the more diffuse H_2_ phase of the outflow, and that the chemistry of these outflowing dense clouds is strongly aected by UV radiation.
- ID:
- ivo://CDS.VizieR/J/A+A/552/A40
- Title:
- MSX high-contrast IRDCs with NH_3_
- Short Name:
- J/A+A/552/A40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Despite increasing research in massive star formation, little is known about its earliest stages. Infrared Dark Clouds (IRDCs) are cold, dense and massive enough to harbour the sites of future high-mass star formation. But up to now, mainly small samples have been observed and analysed. To understand the physical conditions during the early stages of high-mass star formation, it is necessary to learn more about the physical conditions and stability in relatively unevolved IRDCs. Thus, for characterising IRDCs studies of large samples are needed. We investigate a complete sample of 220 northern hemisphere high-contrast IRDCs using the ammonia (1,1)- and (2,2)-inversion transitions. We detected ammonia (1,1)-inversion transition lines in 109 of our IRDC candidates. Using the data we were able to study the physical conditions within the star-forming regions statistically. We compared them with the conditions in more evolved regions which have been observed in the same fashion as our sample sources. Our results show that IRDCs have, on average, rotation temperatures of 15K, are turbulent (with line width FWHMs around 2km/s), have ammonia column densities on the order of 10^14^cm^-2^ and molecular hydrogen column densities on the order of 10^22^cm^-2^. Their virial masses are between 100 and a few 1000M_{sun}_. The comparison of bulk kinetic and potential energies indicate that the sources are close to virial equilibrium. IRDCs are on average cooler and less turbulent than a comparison sample of high-mass protostellar objects, and have lower ammonia column densities. Virial parameters indicate that the majority of IRDCs are currently stable, but are expected to collapse in the future.
- ID:
- ivo://CDS.VizieR/J/ApJ/639/227
- Title:
- MSX IRDC candidate catalog
- Short Name:
- J/ApJ/639/227
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use 8.3{mu}m mid-infrared images acquired with the Midcourse Space Experiment satellite to identify and catalog infrared dark clouds (IRDCs) in the first and fourth quadrants of the Galactic plane. Because IRDCs are seen as dark extinction features against the diffuse Galactic infrared background, we identify them by first determining a model background from the 8.3{mu}m images and then searching for regions of high decremental contrast with respect to this background. IRDC candidates in our catalog are defined by contiguous regions bounded by closed contours of a 2{sigma} decremental contrast threshold. We identify 10,931 candidate IRDCs. For each IRDC, we also catalog cores. These cores, defined as localized regions with at least 40% higher extinction than the cloud's average extinction, are found by iteratively fitting two-dimensional elliptical Gaussian functions to the contrast peaks. We identify 12,774 cores. The catalog contains the position, angular size, orientation, area, peak contrast, peak contrast signal-to-noise, and integrated contrast of the candidate IRDCs and their cores.
- ID:
- ivo://CDS.VizieR/J/AJ/126/1423
- Title:
- MSX 8.3um fluxes of star-forming regions
- Short Name:
- J/AJ/126/1423
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have imaged seven nearby star-forming regions, the Rosette Nebula, the Orion Nebula, W3, the Pleiades, G300.2-16.8, S263, and G159.6-18.5, with the Spatial Infrared Imaging Telescope on the Midcourse Space Experiment (MSX) satellite at 18" resolution at 8.3, 12.1, 14.7, and 21.3{mu}m. The large angular scale of the regions imaged (~7.2-50deg^2^) makes these data unique in terms of the combination of size and resolution. In addition to the star-forming regions, two cirrus-free fields (MSXBG 160 and MSXBG 161) and a field near the south Galactic pole (MSXBG 239) were also imaged. Point sources have been extracted from each region, resulting in the identification over 500 new sources (i.e., no identified counterparts at other wavelengths), as well as over 1300 with prior identifications. The extended emission from the star-forming regions is described, and prominent structures are identified, particularly in W3 and Orion. The Rosette Nebula is discussed in detail. The bulk of the mid-infrared emission is consistent with that of photon-dominated regions, including the elephant trunk complex. The central clump, however, and a line of site toward the northern edge of the cavity show significantly redder colors than the rest of the Rosette complex.