- ID:
- ivo://CDS.VizieR/J/A+A/621/A119
- Title:
- SgrA* and NRAS530 86GHz images
- Short Name:
- J/A+A/621/A119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The compact radio source Sagittarius A* (Sgr A*) in the Galactic centre is the primary supermassive black hole candidate. General relativistic magnetohydrodynamical (GRMHD) simulations of the accretion flow around Sgr A* predict the presence of sub-structure at observing wavelengths of ~3mm and below (frequencies of 86GHz and above). For very long baseline interferometry (VLBI) observations of Sgr A* at this frequency the blurring effect of interstellar scattering becomes sub-dominant, and arrays such as the high sensitivity array (HSA) and the global mm-VLBI array (GMVA) are now capable of resolving potential sub-structure in the source. Such investigations help to improve our understanding of the emission geometry of the mm-wave emission of Sgr A*, which is crucial for constraining theoretical models and for providing a background to interpret 1mm VLBI data from the Event Horizon Telescope (EHT). Following the closure phase analysis in our first paper, which indicates asymmetry in the 3 mm emission of Sgr A*, here we have used the full visibility information to check for possible sub-structure. We extracted source size information from closure amplitude analysis, and investigate how this constrains a combined fit of the size-frequency relation and the scattering law for Sgr A*. We performed high-sensitivity VLBI observations of Sgr A* at 3mm using the Very Long Baseline Array (VLBA) and the Large Millimeter Telescope (LMT) in Mexico on two consecutive days in May 2015, with the second epoch including the Greenbank Telescope (GBT). We confirm the asymmetry for the experiment including GBT. Modelling the emission with an elliptical Gaussian results in significant residual flux of ~10mJy in south-eastern direction. The analysis of closure amplitudes allows us to precisely constrain the major and minor axis size of the main emission component. We discuss systematic effects which need to be taken into account. We consider our results in the context of the existing body of size measurements over a range of observing frequencies and investigate how well-constrained the size-frequency relation is by performing a simultaneous fit to the scattering law and the size-frequency relation. We find an overall source geometry that matches previous findings very closely, showing a deviation in fitted model parameters less than 3% over a time scale of weeks and suggesting a highly stable global source geometry over time. The reported sub-structure in the 3mm emission of Sgr A* is consistent with theoretical expectations of refractive noise on long baselines. However, comparing our findings with recent results from 1mm and 7mm VLBI observations, which also show evidence for east-west asymmetry, we cannot exclude an intrinsic origin. Confirmation of persistent intrinsic substructure will require further VLBI observations spread out over multiple epochs.
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Search Results
- ID:
- ivo://CDS.VizieR/J/other/Sci/348.413
- Title:
- Sgr A East SNR multiwavelength images
- Short Name:
- J/other/Sci/348.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Dust formation in supernova ejecta is currently the leading candidate to explain the large quantities of dust observed in the distant, early universe. However, it is unclear whether the ejecta-formed dust can survive the hot interior of the supernova remnant (SNR). We present infrared observations of ~0.02 solar masses of warm (~100 kelvin) dust seen near the center of the ~10,000-year-old Sagittarius A East SNR at the Galactic center. Our findings indicate the detection of dust within an older SNR that is expanding into a relatively dense surrounding medium (electron density ~10^3^ centimeters^-3^) and has survived the passage of the reverse shock. The results suggest that supernovae may be the dominant dust-production mechanism in the dense environment of galaxies of the early universe.
- ID:
- ivo://CDS.VizieR/J/A+A/641/A40
- Title:
- S5 0836+710 Ground and Space VLBI images
- Short Name:
- J/A+A/641/A40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Detailed studies of relativistic jets in active galactic nuclei (AGN) require high-fidelity imaging at the highest possible resolution. This can be achieved using very long baseline interferometry (VLBI) at radio frequencies, combining worldwide (global) VLBI arrays of radio telescopes with a space-borne antenna on board a satellite. We present multiwavelength images made of the radio emission in the powerful quasar S5 0836+710, obtained using a global VLBI array and the antenna Spektr-R of the RadioAstron mission of the Russian Space Agency, with the goal of studying the internal structure and physics of the relativistic jet in this object. The RadioAstron observations at wavelengths of 18cm, 6cm, and 1.3cm are part of the Key Science Program for imaging radio emission in strong AGN. The internal structure of the jet is studied by analyzing transverse intensity profiles and modeling the structural patterns developing in the flow. The RadioAstron images reveal a wealth of structural detail in the jet of S5 0836+710 on angular scales ranging from 0.02mas to 200mas. Brightness temperatures in excess of 10^13^K are measured in the jet, requiring Doppler factors of >=100 for reconciling them with the inverse Compton limit. Several oscillatory patterns are identified in the ridge line of the jet and can be explained in terms of the Kelvin-Helmholtz (KH) instability. The oscillatory patterns are interpreted as the surface and body wavelengths of the helical mode of the KH instability. The interpretation provides estimates of the jet Mach number and of the ratio of the jet to the ambient density, which are found to be Mj~=12 and {eta}~=0.33. The ratio of the jet to the ambient density should be conservatively considered an upper limit because its estimate relies on approximations.
- ID:
- ivo://CDS.VizieR/J/A+AS/114/21
- Title:
- Shapley-Ames Galaxies at 2.8cm
- Short Name:
- J/A+AS/114/21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present measurements of the radio continuum emission at 2.8 cm of a nearly complete sample of spiral galaxies. The sample consists of the Shapley-Ames galaxies north of {delta}=-25deg and brighter than B_T_=+12. The large, nearby galaxies were not observed during the survey, but measured with high sensitivity in individual projects. The radioweak galaxies were also excluded. The observational results and the derived flux densities are given and compared with that of other observations. Pecularities of the radio emission of individual galaxies are discussed.
- ID:
- ivo://CDS.VizieR/J/A+A/545/A65
- Title:
- S5 0836+710 image at 1.6GHz
- Short Name:
- J/A+A/545/A65
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The remarkable stability of extragalactic jets is surprising, given the reasonable possibility of the growth of instabilities. In addition, much work in the literature has invoked this possibility to explain observed jet structures and obtain information about the jet from these structures. For example, it has been shown that the observed helical structures in the jet in S5 0836+710 could be associated with helical pressure waves generated by a Kelvin-Helmholtz instability. Our aim is to resolve the arc-second structure of the jet in the quasar S5 0836+710 and confirm the lack of a hot-spot (reverse jet-shock) found by present observing arrays, as this lack implies a loss of jet collimation before interaction with the intergalactic medium.
- ID:
- ivo://CDS.VizieR/J/MNRAS/363/405
- Title:
- SIMBA observations of cold cores
- Short Name:
- J/MNRAS/363/405
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of a 1.2-mm continuum emission survey toward 131 star-forming complexes suspected of undergoing massive star formation. These regions have previously been identified as harbouring a methanol maser and/or a radio continuum source [ultracompact (UC) HII region], the presence of which is in most instances indicative of massive star formation. The 1.2-mm emission was mapped using the SIMBA instrument on the 15-m Swedish ESO Submillimetre Telescope (SEST). Emission is detected toward all of the methanol maser and UC HII regions targeted, as well as towards 20 others lying within the fields mapped, implying that these objects are associated with cold, deeply embedded objects. Interestingly, there are also 20 methanol maser sites and nine UC HII regions within the fields mapped which are devoid of millimetre continuum emission. In addition to the maser and UC HII regions detected, we have also identified 253 other sources within the SIMBA maps. All of these (253) are new sources, detected solely from their millimetre continuum emission. In total, 404 sources are detected, representing four classes of sources which are distinguished by the presence of the different combination of associated tracers.
- ID:
- ivo://CDS.VizieR/J/PASJ/58/529
- Title:
- SiO Maser Survey in Galactic Bulge
- Short Name:
- J/PASJ/58/529
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We surveyed 291 MSX/2MASS infrared objects in the 7{deg}x2{deg} area of the galactic center in the 43GHz SiO J=1-0 v=1 and 2 maser lines, obtaining accurate radial velocities of 163 detected objects. The surveyed area is the region where the IRAS catalog is incomplete due to contamination by high source density. The objects in the present MSX/2MASS sample were chosen to have similar infrared characteristics to those of the previous SiO-maser-survey samples based on the color-selected IRAS sources. The sampling based on the 2MASS catalog causes a bias to the foreside objects of the bulge due to heavy obscuration by interstellar dust; the detections considerably leaned on the V_lsr_<0 side.
- ID:
- ivo://CDS.VizieR/J/PASJ/56/261
- Title:
- SiO maser survey in Galactic center
- Short Name:
- J/PASJ/56/261
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have surveyed ~400 known large-amplitude variables within 15' of the galactic center in the SiO J=1-0 v=1 and 2 maser lines at 43GHz, resulting in 180 detections. SiO lines were detected from 16 other sources located within 20" of the program objects. The detection rate of 48% is comparable to that in bulge IRAS surveys.
- ID:
- ivo://CDS.VizieR/J/PASJ/56/765
- Title:
- SiO maser survey of IRAS sources
- Short Name:
- J/PASJ/56/765
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We surveyed 401 color-selected IRAS sources in the galactic disk in the SiO J=1-0, v=1 and 2 maser lines at 43GHz, resulting in 254 (239 new) detections. The observed sources lie mostly in a strip of the inner galactic disk with boundaries -10{deg}<l<40{deg} and |b|<3{deg}. This survey provides radial velocities of inner-disk stars for which optical measurements cannot be made due to interstellar extinction.
- ID:
- ivo://CDS.VizieR/J/AJ/125/2411
- Title:
- SIRTF First-Look Survey
- Short Name:
- J/AJ/125/2411
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The First-Look Survey (FLS) of the Space Infrared Telescope Facility (SIRTF) will cover about 5deg^2^ centered on J2000.0 (17:18+59:30) in order to characterize the extragalactic infrared sky 2 orders of magnitude deeper than the IRAS survey. We expect that most of the FLS far-infrared ({lambda} = 160, 70, and 24 {mu}m) sources will be star-forming galaxies obeying the very tight far-infrared/radio correlation and will be continuum radio sources with flux densities S>~100{mu}Jy at {nu}=1.4GHz. Conversely, radio sources stronger than 100{mu}Jy are usually powered by star-forming galaxies, plus some active galactic nuclei, and most should be detectable by the SIRTF FLS. Thus, a sensitive radio survey can be used to select and identify most of the SIRTF FLS source population before launch. We used the B configuration of the VLA to make an image of the FLS area at {nu}=1.4GHz with {sigma}=~23{mu}Jy/beam rms fluctuations, {theta}=5'' resolution, and {sigma}_{alpha}_=~{sigma}_{delta}_=~0.5'' rms uncertainties in right ascension and declination. The resulting radio image and catalog of 3565 radio components with peak flux densities Sp>=5{sigma}=115{mu}Jy/beam have been released via the Web to expedite follow-up optical identification and spectroscopy.
