- ID:
- ivo://CDS.VizieR/J/A+A/658/A8
- Title:
- Resolved jet of 3C 273 at 150 MHz
- Short Name:
- J/A+A/658/A8
- Date:
- 02 Feb 2022 13:25:19
- Publisher:
- CDS
- Description:
- Since its discovery in 1963, 3C 273 has become one of the most widely studied quasars with investigations spanning the electromagnetic spectrum. While much has therefore been discovered about this historically notable source, its low-frequency emission is far less well understood. Observations in the MHz regime have traditionally lacked the resolution required to explore small-scale structures, such as knots and diffuse jet emission, that are key to understanding the processes that result in the observed emission. Advances in the processing of LOFAR international baseline data have now removed this limitation, providing the opportunity to explore this key area for the first time. In this paper we use the first sub-arcsecond images of 3C 273 at MHz frequencies to investigate the morphology of the compact jet structures and the processes that result in the observed spectrum. We will determine the jet's kinetic power, place constraints on the bulk speed and inclination angle of the jets, and look for evidence of the elusive counterjet at 150MHz. Using the full complement of LOFAR's international stations (German, Poland, France, UK, Sweden), we produce 0.31x0.21 arcsec images of 3C 273 at 150MHz. Using ancillary data at GHz frequencies, we fit free-free absorption (FFA) and synchrotron self-absorption (SSA) models to each region in order to determine their validity in explaining the observed spectra. The images presented display for the first time that robust, high-fidelity imaging of low-declination complex sources is now possible with the LOFAR international baselines. We show that the main small-scale structures of 3C 273 match those seen at higher frequencies, with a tenuous detection of an extension to the outer lobe. We find that FFA and SSA models are able to describe the spectrum of the knots and, while differentiating between model types requires further observations, conclude that absorption is present in the observed emission. We determine the kinetic power of the jet to be in the range of 3.5x10^43^-1.5x10^44^erg/s which agrees with estimates made using higher frequency observations. We derive lower limits for the bulk speed and Lorentz factor of beta>0.55 and Gamma>1.2 respectively. The counter-jet remains undetected at 150MHz, placing a limit on the peak brightness of S_cj_150<40mJy/beam.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/832/126
- Title:
- RESOLVE survey: 21cm obs. with GBT & Arecibo
- Short Name:
- J/ApJ/832/126
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the HI mass inventory for the REsolved Spectroscopy Of a Local VolumE (RESOLVE) survey, a volume-limited, multi-wavelength census of >1500 z=0 galaxies spanning diverse environments and complete in baryonic mass down to dwarfs of ~10^9^M_{sun}_. This first 21cm data release provides robust detections or strong upper limits (1.4M_HI_<5%-10% of stellar mass M*) for ~94% of RESOLVE. We examine global atomic gas-to-stellar mass ratios (G/S) in relation to galaxy environment using several metrics: group dark matter halo mass M_h_, central/satellite designation, relative mass density of the cosmic web, and distance to the nearest massive group. We find that at fixed M*, satellites have decreasing G/S with increasing M_h_ starting clearly at M_h_~10^12^M_{sun}_, suggesting the presence of starvation and/or stripping mechanisms associated with halo gas heating in intermediate-mass groups. The analogous relationship for centrals is uncertain because halo abundance matching builds in relationships between central G/S, stellar mass, and halo mass, which depend on the integrated group property used as a proxy for halo mass (stellar or baryonic mass). On larger scales G/S trends are less sensitive to the abundance matching method. At fixed M_h_<=10^12^M_{sun}_, the fraction of gas-poor centrals increases with large-scale structure density. In overdense regions, we identify a rare population of gas-poor centrals in low-mass (M_h_<10^11.4^M_{sun}_) halos primarily located within ~1.5x the virial radius of more massive (M_h_>10^12^M_{sun}_) halos, suggesting that gas stripping and/or starvation may be induced by interactions with larger halos or the surrounding cosmic web. We find that the detailed relationship between G/S and environment varies when we examine different subvolumes of RESOLVE independently, which we suggest may be a signature of assembly bias.
- ID:
- ivo://CDS.VizieR/J/A+A/612/A56
- Title:
- Rest frequencies of dithioformic acid
- Short Name:
- J/A+A/612/A56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A better understanding of sulphur chemistry is needed to solve the interstellar sulphur depletion problem. A way to achieve this goal is to study new S-bearing molecules in the laboratory, obtaining accurate rest frequencies for an astronomical search. We focus on dithioformic acid, HCSSH, which is the sulphur analogue of formic acid. The aim of this study is to provide an accurate line list of the two HCSSH trans and cis isomers in their electronic ground state and a comprehensive centrifugal distortion analysis with an extension of measurements in the millimetre and submillimetre range. We studied the two isomers in the laboratory using an absorption spectrometer employing the frequency-modulation technique. The molecules were produced directly within a free-space cell by glow discharge of a gas mixture. We measured lines belonging to the electronic ground state up to 478GHz, with a total number of 204 and 139 new rotational transitions, respectively, for trans and cis isomers. The final dataset also includes lines in the centimetre range available from literature. The extension of the measurements in the mm and submm range lead to an accurate set of rotational and centrifugal distortion parameters. This allows us to predict frequencies with estimated uncertainties as low as 5kHz at 1mm wavelength. Hence, the new dataset provided by this study can be used for astronomical search.
- ID:
- ivo://CDS.VizieR/J/A+A/428/1019
- Title:
- Rest frequencies of methanol maser lines
- Short Name:
- J/A+A/428/1019
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report accurate laboratory measurements of selected methanol transition frequencies between 0.834 and 230GHz in order to facilitate astronomical velocity analyses. New data have been obtained between 10 and 27GHz and between 60 and 119GHz. Emphasis has been put on known or potential interstellar maser lines as well as on transitions suitable for the investigation of cold dark clouds. Because of the narrow line widths (<0.5km/s) of maser lines and lines detected in dark molecular clouds, accurate frequencies are needed for comparison of the velocities of different methanol lines with each other as well as with lines from other species. In particular, frequencies for a comprehensive set of transitions are given which, because of their low energy levels (<20cm^-1^ or 30K), are potentially detectable in cold clouds. Global Hamiltonian fits generally do not yet yield the required accuracy. Additionally, we report transition frequencies for other lines that may be used to test and to improve existing Hamiltonian models.
- ID:
- ivo://CDS.VizieR/J/A+AS/128/153
- Title:
- Revised GB/GB2 sample of radio sources
- Short Name:
- J/A+AS/128/153
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The revised sample of 373 extragalactic radio sources brighter than 0.2 Jy at 1.4GHz is presented. These sources, selected from the finding Green Bank surveys, were mapped at 1465 MHz using the VLA at different configurations. The biases introduced into the original GB (Maslowski, 1972AcA....22..227M) and GB2 (Machalski, 1978AcA....28..367M) catalogues by confusion as well as partial resolution by the VLA at its A-configuration, are eliminated. In effect, a number of sources have been excluded, and a few other are included into the revised sample. Now the sample is about 99, 97 and 95 per cent complete for sources with S_1.4_>=0.55Jy, 0.25Jy<=S_1.4_<0.55Jy, and 0.2Jy<=S_1.4_<0.25Jy, respectively. Table 3 gives the compilation of the radio, optical, and X-ray data available for the sample sources.
- ID:
- ivo://CDS.VizieR/VIII/31
- Title:
- Revised source list for the Rees 38-MHz survey
- Short Name:
- VIII/31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a revised machine-readable source list for the Rees 38-MHz (or '8C') survey with improved positions and no redundancy. The Rees 38-MHz survey covers an area of about 1 sr north of declination +60 degrees. The angular resolution is 4.5 x 4.5cosec(Dec) arcmin**2 and the limiting flux density over much of the survey area is about 1 Jy. Both of these figures are an improvement by nearly an order of magnitude on previous surveys at this frequency. Users of these data should consult and cite the original survey paper by Rees as primary reference (1990MNRAS.244..233R) with the present publication (1995MNRAS.274..447H) as a supplementary revision. The recommended style of reference is thus : "The revised Rees 38-MHz survey (Rees 1990, catalogue revised Hales et. al 1995)." Note that for interest the source list includes data on some sources at declinations lower than +60 degrees, but that the right ascension coverage is not complete below +60 degrees.
- ID:
- ivo://CDS.VizieR/J/MNRAS/420/1656
- Title:
- RMS compact HII regions distances
- Short Name:
- J/MNRAS/420/1656
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high-resolution HI data obtained using the Australia Telescope Compact Array to resolve the near/far distance ambiguities towards a sample of compact HII regions from the Red MSX Source (RMS) survey. The high-resolution data are complemented with lower resolution archival HI data extracted from the Southern and Very Large Array (VLA) Galactic Plane surveys. We resolve the distance ambiguity for nearly all of the 105 sources where the continuum was strong enough to allow analysis of the HI absorption line structure. This represents another step in the determination of distances to the total RMS sample, which with over 1000 massive young stellar objects and compact HII regions is the largest and most complete sample of its kind. The full sample will allow the distribution of massive star formation in the Galaxy to be examined.
1468. RMS survey
- ID:
- ivo://CDS.VizieR/J/MNRAS/452/4029
- Title:
- RMS survey
- Short Name:
- J/MNRAS/452/4029
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of ammonia observations towards 66 massive star forming regions identified by the Red Midcourse Space Experiment Source survey. We have used the Green Bank Telescope and the K-Band Focal Plane Array to map the ammonia (NH_3_) (1,1) and (2,2) inversion emission at a resolution of 30 arcsec in 8 arcmin regions towards the positions of embedded massive star formation. We have identified a total of 115 distinct clumps, approximately two-thirds of which are associated with an embedded massive young stellar object or compact HII region, while the others are classified as quiescent. There is a strong spatial correlation between the peak NH3 emission and the presence of embedded objects. We derive the spatial distribution of the kinetic gas temperatures, line widths, and NH3 column densities from these maps, and by combining these data with dust emission maps we estimate clump masses, H_2_ column densities and ammonia abundances. The clumps have typical masses of ~1000M_{sun}_ and radii ~0.5pc, line widths of ~2km/s and kinetic temperatures of ~16-20K. We find no significant difference between the sizes and masses of the star-forming and quiescent subsamples; however, the distribution maps reveal the presence of temperature and line width gradients peaking towards the centre for the star-forming clumps while the quiescent clumps show relatively uniform temperatures and line widths throughout. Virial analysis suggests that the vast majority of clumps are gravitationally bound and are likely to be in a state of global free fall in the absence of strong magnetic fields. The similarities between the properties of the two subsamples suggest that the quiescent clumps are also likely to form massive stars in the future, and therefore provide an excellent opportunity to study the initial conditions of massive pre-stellar and protostellar clumps.
- ID:
- ivo://CDS.VizieR/J/A+A/501/539
- Title:
- RMS survey. 6cm observations of YSOs
- Short Name:
- J/A+A/501/539
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Red MSX Source (RMS) survey is an ongoing multi-wavelength observational programme designed to return a large, well-selected sample of massive young stellar objects (MYSOs). We have identified ~2000 MYSO candidates located throughout the Galaxy by comparing the colours of MSX and 2MASS point sources to those of known MYSOs. The aim of these follow-up observations is to identify other objects with similar colours such as ultra compact (UC) HII regions, evolved stars and planetary nebulae (PNe) and distinguish between genuine MYSOs and nearby low-mass YSOs. To identify the populations of UCHII regions and PNe within the sample and examine their Galactic distribution. We have conducted high resolution radio continuum observations at 6cm towards 659 MYSO candidates in the northern hemisphere (10{deg}<l<250{deg}) using the Very Large Array (VLA). These observations have a spatial resolution of ~1-2" and typical image rms noise values of ~0.22mJy - sensitive enough to detect a HII region powered by B0.5 star at the far side of the Galaxy. In addition to these targeted observations we present archival data towards a further 315 RMS sources extracted from a previous VLA survey of the inner Galaxy.
- ID:
- ivo://CDS.VizieR/J/MNRAS/437/1791
- Title:
- RMS survey: molecular observations
- Short Name:
- J/MNRAS/437/1791
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used the well-selected sample of ~1750 embedded, young, massive stars identified by the Red MSX Source (RMS) survey to investigate the Galactic distribution of recent massive star formation. We present molecular line observations for ~800 sources without existing radial velocities. We describe the various methods used to assign distances extracted from the literature and solve the distance ambiguities towards approximately 200 sources located within the solar circle using archival Hi data. These distances are used to calculate bolometric luminosities and estimate the survey completeness (~2x10^4^L_{sun}_). In total, we calculate the distance and luminosity of ~1650 sources, one third of which are above the survey's completeness threshold. Examination of the sample's longitude, latitude, radial velocities and mid-infrared images has identified ~120 small groups of sources, many of which are associated with well-known star formation complexes, such as G305, G333, W31, W43, W49 and W51. We compare the positional distribution of the sample with the expected locations of the spiral arms, assuming a model of the Galaxy consisting of four gaseous arms. The distribution of young massive stars in the Milky Way is spatially correlated with the spiral arms, with strong peaks in the source position and luminosity distributions at the arms' Galactocentric radii. The overall source and luminosity surface densities are both well correlated with the surface density of the molecular gas, which suggests that the massive star formation rate per unit molecular mass is approximately constant across the Galaxy. A comparison of the distribution of molecular gas and the young massive stars to that in other nearby spiral galaxies shows similar radial dependences. We estimate the total luminosity of the embedded massive star population to be ~0.76x10^8^L_{sun}_, 30 per cent of which is associated with the 10 most active star-forming complexes. We measure the scaleheight as a function of the Galactocentric distance and find that it increases only modestly from ~20-30pc between 4 and 8kpc, but much more rapidly at larger distances.
