Search

Start Over Subject interstellar medium Capability Type Simple Cone Search
31. Ammonia spectral atlas in Perseus
ID:
ivo://CDS.VizieR/J/ApJS/175/509
Title:
Ammonia spectral atlas in Perseus
Short Name:
J/ApJS/175/509
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present ammonia observations of 193 dense cores and core candidates in the Perseus molecular cloud made using the Robert F. Byrd Green Bank Telescope. We simultaneously observed the NH_3_(1,1), NH_3_(2,2), C_2_S (2_1_=>1_0_), and C^34^_2_S(2_1_=>1_0_) transitions near {nu}=23GHz for each of the targets with a spectral resolution of {delta}v~0.024km/s. We find ammonia emission associated with nearly all of the (sub)millimeter sources, as well as at several positions with no associated continuum emission. For each detection, we have measured physical properties by fitting a simple model to every spectral line simultaneously. Where appropriate, we have refined the model by accounting for low optical depths, multiple components along the line of sight, and imperfect coupling to the GBT beam. For the cores in Perseus, we find a typical kinetic temperature of T_k_=11K, a typical column density of N_NH3_~10^14.5^/cm2, and velocity dispersions ranging from {sigma}v=0.07 to 0.7km/s. However, many cores with {sigma}v>0.2km/s show evidence for multiple velocity components along the line of sight.
32. Analysis of B6-A9 stars from INES UV spectra
ID:
ivo://CDS.VizieR/J/AJ/143/28
Title:
Analysis of B6-A9 stars from INES UV spectra
Short Name:
J/AJ/143/28
Date:
21 Oct 2021
Publisher:
CDS
Description:
Main-sequence (MS) and giant late-B and early-A type stars are the best targets for searching for nearby interstellar (IS) SiIV and CIV resonance lines because they are not able to produce them, either in atmospheric layers or in their circumstellar environment, and because many stars of these spectral types are nearby and located in the local interstellar medium (LISM). In addition, the use of certain stars hotter than B6 can lead to misinterpretations (e.g., alpha Arae). This work analyzes the reliable Short-Wavelength Prime (SWP) high-resolution UV spectra of 558 B6-A9 type stars observed by the International Ultraviolet Explorer at distances lower than 400pc from the Sun. For the first time, this work utilizes the entire INES database to extract stellar and IS information in a systematic way from homogeneous data. Stars were classified into seven groups: normal (MS and subgiant), giant, peculiar, emission line, Algols, pre-main sequence or Herbig Ae/Be, and shell stars. Only 10 normal stars, located beyond 90pc, show weak SiIV and CIV absorptions and are clustered around the direction of Sco-Cen, while 85 located closer than 90pc, as well as another 89 beyond 90pc, do not show any absorptions at all.
33. Angular sizes of AGN cores at 2-43GHz
ID:
ivo://CDS.VizieR/J/MNRAS/452/4274
Title:
Angular sizes of AGN cores at 2-43GHz
Short Name:
J/MNRAS/452/4274
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have measured the angular sizes of radio cores of active galactic nuclei (AGN) and analyzed their sky distributions and frequency dependencies to study synchrotron opacity in AGN jets and the strength of angular broadening in the interstellar medium. We have used archival very long baseline interferometry (VLBI) data of more than 3000 compact extragalactic radio sources observed at frequencies, {nu}, from 2 to 43GHz to measure the observed angular size of VLBI cores. We have found a significant increase in the angular sizes of the extragalactic sources seen through the Galactic plane (|b|<10{deg}) at 2, 5 and 8GHz, about 1/3 of which show significant scattering. These sources are mainly detected in directions to the Galactic bar, the Cygnus region, and a region with galactic longitudes 220{deg}<l<260{deg} (the Fitzgerald window). The strength of interstellar scattering of the AGNs is found to correlate with the Galactic H{alpha} intensity, free-electron density, and Galactic rotation measure. The dependence of scattering strengths on source redshift is insignificant, suggesting that the dominant scattering screens are located in our Galaxy. The observed angular size of Sgr-A* is found to be the largest among thousands of AGN observed over the sky; we discuss possible reasons of this strange result. Excluding extragalactic radio sources with significant scattering, we find that angular size of opaque cores in AGN scales typically as {nu}^-1^ confirming predictions of a conical synchrotron jet model with equipartition.
34. APEX CO and HI observations of Lupus I
ID:
ivo://CDS.VizieR/J/A+A/608/A102
Title:
APEX CO and HI observations of Lupus I
Short Name:
J/A+A/608/A102
Date:
21 Oct 2021
Publisher:
CDS
Description:
Lupus I cloud is found between the Upper Scorpius (USco) and Upper Centaurus-Lupus (UCL) subgroups of the Scorpius-Centaurus OB association, where the expanding USco HI shell appears to interact with a bubble currently driven by the winds of the remaining B stars of UCL. Aims. We investigate whether the Lupus I molecular could have formed in a colliding flow, and in particular, how the kinematics of the cloud might have been influenced by the larger scale gas dynamics. We performed APEX ^13^CO(2-1)and C^18^O(2-1) line observations of three distinct parts of Lupus I that provide kinematic information on the cloud at high angular and spectral resolution. We compare those results to the atomic hydrogen data from the GASS HI survey and our dust emission results presented in the previous paper. Based on the velocity information, we present a geometric model for the interaction zone between the USco shell and the UCL wind bubble. We present evidence that the molecular gas of Lupus Iis tightly linked to the atomic material of the USco shell. The CO emission in Lupus Iis found mainly at velocities between v_LSR_=3-6km/s, which is in the same range as the HI velocities. Thus, the molecular cloud is co-moving with the expanding USco atomic HI shell. The gas in the cloud shows a complex kinematic structure with several line-of-sight components that overlay each other. The nonthermal velocity dispersion is in the transonic regime in all parts of the cloud and could be injected by external compression. Our observations and the derived geometric model agree with a scenario in which Lupus Iis located in the interaction zone between the USco shell and the UCL wind bubble. The kinematics observations are consistent with a scenario in which the Lupus Icloud formed via shell instabilities. The particular location of Lupus I between USco and UCL suggests that counterpressure from the UCL wind bubble and pre-existing density enhancements, perhaps left over from the gas stream that formed the stellar subgroups, may have played a role in its formation.
35. Application of the D^3^PO algorithm
ID:
ivo://CDS.VizieR/J/A+A/581/A126
Title:
Application of the D^3^PO algorithm
Short Name:
J/A+A/581/A126
Date:
21 Oct 2021
Publisher:
CDS
Description:
We analyze the 6.5yr all-sky data from the Fermi LAT restricted to gamma-ray photons with energies between 0.6-307.2GeV. We present a non-parametric reconstruction of the diffuse photon flux up to several hundred GeV, its all-sky spectral index map, and its angular power spectrum. We decompose the diffuse emission into a cloud-like abd a bubble-like component and analyze their spectra. Additionally, we wrote up a catalog of source candidates that includes 3106 sources. For each source we report the location in the sky, flux, spectral index, and possible associations with sources from the second and third Fermi source catalog.
36. Are infrared dark clouds really quiescent?
ID:
ivo://CDS.VizieR/J/A+A/592/A21
Title:
Are infrared dark clouds really quiescent?
Short Name:
J/A+A/592/A21
Date:
21 Oct 2021
Publisher:
CDS
Description:
The dense, cold regions where high-mass stars form are poorly characterised, yet they represent an ideal opportunity to learn more about the initial conditions of high-mass star formation (HMSF), since high-mass starless cores (HMSCs) lack the violent feedback seen at later evolutionary stages. We present continuum maps obtained from the Submillimeter Array (SMA) interferometry at 1.1mm for four infrared dark clouds (IRDCs, G28.34S, IRDC 18530, IRDC 18306, and IRDC 18308). We also present 1mm/3mm line surveys using IRAM 30m single-dish observations. Our results are: (1) At a spatial resolution of 10^4^AU, the 1.1mm SMA observations resolve each source into several fragments. The mass of each fragment is on average >10M_{sun}_, which exceeds the predicted thermal Jeans mass of the whole clump by a factor of up to 60, indicating that thermal pressure does not dominate the fragmentation process. Our measured velocity dispersions in the 30m lines imply that non-thermal motions provides the extra support against gravity in the fragments. (2) Both non-detection of high-J transitions and the hyperfine multiplet fit of N_2_H^+^(1-0), C_2_H(1-0), HCN(1-0), and H^13^CN(1-0) indicate that our sources are cold and young. However, obvious detection of SiO and the asymmetric line profile of HCO^+^(1-0) in G28.34S indicate a potential protostellar object and probable infall motion. (3) With a large number of N-bearing species, the existence of carbon rings and molecular ions, and the anti-correlated spatial distributions between N_2_H^+^/NH_2_D and CO, our large-scale high-mass clumps exhibit similar chemical features as small-scale low-mass prestellar objects. This study of a small sample of IRDCs illustrates that thermal Jeans instability alone cannot explain the fragmentation of the clump into cold (~15K), dense (>10^5^cm^-3^) cores and that these IRDCs are not completely quiescent.
37. A search for Compact High-Velocity Clouds
ID:
ivo://CDS.VizieR/J/A+A/391/159
Title:
A search for Compact High-Velocity Clouds
Short Name:
J/A+A/391/159
Date:
21 Oct 2021
Publisher:
CDS
Description:
An automated search is applied to the Leiden/Dwingeloo HI Survey (LDS) for high-velocity clouds north of Dec.=-28{deg}. From the general catalog we extract a sample of relatively small (less than about 8{deg}) and isolated high-velocity clouds, CHVCs: anomalous-velocity HI clouds which are sharply bounded in angular extent with no kinematic or spatial connection to other HI features down to a limiting column density of 1.5x10^18cm^-2. Unambiguously isolated objects are given the "CHVC" designation, while those with some degree of ambiguity in this classification or designated "CHVC:" or "CHVC?". The vast majority of features show diffuse connections at low column densities with the extended HVC complexes and are simply designated as "HVC" features. The automated search algorithm has been applied to the HIPASS and to the Leiden/Dwingeloo data sets. The results from the LDS are described here; Putman et al. (2002, Cat. <J/AJ/123/873>) describe application of this algorithm to the HIPASS material. Only those catalog entries which have and additional ID listed have been confirmed in independent data.
38. A search for pre-biotic molecules
ID:
ivo://CDS.VizieR/J/A+A/473/177
Title:
A search for pre-biotic molecules
Short Name:
J/A+A/473/177
Date:
21 Oct 2021
Publisher:
CDS
Description:
Low-noise, 0.8MHz resolution spectra around 90GHz towards four hot core sources: Orion KL, W51 e1/e2, S140, and W3(OH), are presented. The observations were performed using the 3mm SIS receiver at the Onsala 20m telescope. The observations were made in the beam-switching mode, the spectrum intensity is given in T_A_^*^ and high-order polynomial baselines have been subtracted. At 90GHz the Onsala 20m telescope has a beam FWHM of ~42arcsec and a main-beam efficiency of ~0.6. Due to changes in frequency setting during the observing period the frequency ranges are not identical for each source, but in all cases the ranges include the transitions used to determine the upper column densities of amino acetonitrile (H_2_NCH_2_CN), vinyl acetylene (C_2_H_3_CCH), oxiranecarbonitrile (c-C_3_H_3_NO), and amino-ethanol (NH_2_CH_2_CH_2_OH), presented in the paper. Note that the absorptions, seen in the S140 and the W3(OH) spectra around the strong HCN-line at 90.663GHz, are artificial.
39. Astrochemical study along M83 circumnuclear ring
ID:
ivo://CDS.VizieR/J/ApJ/884/100
Title:
Astrochemical study along M83 circumnuclear ring
Short Name:
J/ApJ/884/100
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report an astrochemical study on the evolution of interstellar molecular clouds and consequent star formation in the center of the barred spiral galaxy M83. We used the Atacama Large Millimeter/submillimeter Array (ALMA) to image molecular species indicative of shocks (SiO and CH_3_OH), dense cores (N_2_H^+^), and photodissociation regions (CN and CCH), as well as a radio recombination line (H41{alpha}) tracing active star-forming regions. M83 has a circumnuclear gas ring that is joined at two intersections by gas streams from the leading- edge gas lanes on the bar. We found elevated abundances of the shock and dense-core tracers in one of the orbit-intersecting areas, and found peaks of CN and H41{alpha} downstream. In the other orbit-intersection area, we found a similar enhancement of the shock tracers, but less variation of other tracers, and no sign of active star formation in the stream. We propose that the observed chemical variation or lack of it is due to the presence or absence of collision-induced evolution of molecular clouds and induced star formation. This work presents the clearest case of the chemical evolution in the circumnuclear rings of barred galaxies thanks to the ALMA resolution and sensitivity.
40. ATCA HI absorption survey in Magellanic clouds. I.
ID:
ivo://CDS.VizieR/J/ApJS/244/7
Title:
ATCA HI absorption survey in Magellanic clouds. I.
Short Name:
J/ApJS/244/7
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the first results from the Small Magellanic Cloud portion of a new Australia Telescope Compact Array HI absorption survey of both of the Magellanic Clouds, comprising over 800hr of observations. Our new HI absorption line data allow us to measure the temperature and fraction of cold neutral gas in a low-metallicity environment. We observed 22 separate fields, targeting a total of 55 continuum sources, against 37 of which we detected HI absorption; from this we measure a column-density-weighted mean average spin temperature of <Ts>=150K. Splitting the spectra into individual absorption line features, we estimate the temperatures of different gas components and find an average cold gas temperature of ~30K for this sample, lower than the average of ~40K in the Milky Way. The HI appears to be evenly distributed throughout the SMC, and we detect absorption in 67% of the lines of sight in our sample, including some outside the main body of the galaxy (N_HI_>2x10^21^cm^-2^). The optical depth and temperature of the cold neutral atomic gas show no strong trend with location spatially or in velocity. Despite the low-metallicity environment, we find an average cold gas fraction of ~20%, not dissimilar from that of the Milky Way.

Limit your search

more »

  • 2706