- ID:
- ivo://CDS.VizieR/J/ApJ/771/105
- Title:
- MWA Stokes I 189MHz sources
- Short Name:
- J/ApJ/771/105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a Stokes I, Q and U survey at 189MHz with the Murchison Widefield Array 32 element prototype covering 2400deg^2^. The survey has a 15.6' angular resolution and achieves a noise level of 15mJy/beam. We demonstrate a novel interferometric data analysis that involves calibration of drift scan data, integration through the co-addition of warped snapshot images, and deconvolution of the point-spread function through forward modeling. We present a point source catalog down to a flux limit of 4Jy. We detect polarization from only one of the sources, PMN J0351-2744, at a level of 1.8%+/-0.4%, whereas the remaining sources have a polarization fraction below 2%. Compared to a reported average value of 7% at 1.4GHz, the polarization fraction of compact sources significantly decreases at low frequencies. We find a wealth of diffuse polarized emission across a large area of the survey with a maximum peak of ~13K, primarily with positive rotation measure values smaller than +10rad/m2. The small values observed indicate that the emission is likely to have a local origin (closer than a few hundred parsecs). There is a large sky area at {alpha}>=2^h^30^m^ where the diffuse polarized emission rms is fainter than 1K. Within this area of low Galactic polarization we characterize the foreground properties in a cold sky patch at ({alpha},{delta})=(4^h^,-27.6{deg}) in terms of three-dimensional power spectra.
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Search Results
- ID:
- ivo://CDS.VizieR/J/other/PASA/33.20
- Title:
- MWA Survey of Galactic HII regions
- Short Name:
- J/other/PASA/33.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have compiled a catalogue of HII regions detected with the Murchison Widefield Array between 72 and 231MHz. The multiple frequency bands provided by the Murchison Widefield Array allow us identify the characteristic spectrum generated by the thermal Bremsstrahlung process in HII regions. We detect 306 HII regions between 260{deg}<l<340{deg} and report on the positions, sizes, peak, integrated flux density, and spectral indices of these HII regions. By identifying the point at which HII regions transition from the optically thin to thick regime, we derive the physical properties including the electron density, ionised gas mass, and ionising photon flux, towards 61 HII regions. This catalogue of HII regions represents the most extensive and uniform low frequency survey of HII regions in the Galaxy to date.
- ID:
- ivo://CDS.VizieR/VIII/82
- Title:
- 2nd Epoch Molonglo Galactic Plane Survey (MGPS-2)
- Short Name:
- VIII/82
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The MGPS-2 (second epoch Molonglo Galactic Plane Survey) was carried out with the Molonglo Observatory Synthesis Telescope at a frequency of 843MHz and with a restoring beam of 45"x45"csd|{delta}|, making it he highest resolution large scale radio survey of the southern Galactic plane. It covers the range |b|<10{deg} and 245<l<365{deg}; it is the Galactic counterpart to the SUMSS (Cat. VIII/81) which covers the southern sky ({delta}<-30{deg}, |b|>10{deg}). This catalogue (15-Aug-2007) consists of 48850 compact sources, made by fitting elliptical gaussians in the MGPS-2 mosaics to a limiting peak brightness of 10mJy/beam. We used a custom method (described in the associated publication) to remove extended sources from the catalogue. Positions in the catalogue are accurate to 1-2". See http://www.astrop.physics.usyd.edu.au/mosaics for access to the mosaic images.
- ID:
- ivo://CDS.VizieR/J/ApJ/753/27
- Title:
- New point sources in the WMAP 7yr data
- Short Name:
- J/ApJ/753/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have developed a new needlet-based method to detect point sources in cosmic microwave background (CMB) maps and have applied it to the Wilkinson Microwave Anisotropy Probe (WMAP) 7 year data. We use both the individual frequency channels as well as internal templates, the latter being the difference between pairs of frequency channels and hence having the advantage that the CMB component is eliminated. Using the area of the sky outside the Kq85 galactic mask, we detect a total of 2102 point sources at the 5{sigma} level in either the frequency maps or the internal templates. Of these, 1116 are detected either at 5{sigma} directly in the frequency channels or at 5{sigma} in the internal templates and >=3{sigma} at the corresponding position in the frequency channels. Of the 1116 sources, 603 are detections that have not been reported so far in WMAP data. We have made a catalog of these sources available with position and flux estimated in the WMAP channels where they are seen. In total, we identified 1029 of the 1116 sources with counterparts at 5GHz and 69 at other frequencies.
- ID:
- ivo://CDS.VizieR/J/ApJ/554/803
- Title:
- New VLA Sky Survey (NVSS) Cat of IRAS 2 Jy Galaxies
- Short Name:
- J/ApJ/554/803
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The radio counterparts to the IRAS Redshift Survey galaxies are identified in the NRAO VLA Sky Survey (NVSS) catalog. Our new catalog of the IR flux-limited (>2 Jy at 60 micron) complete sample of 1809 galaxies lists accurate radio positions, redshifts, and 1.4 GHz radio and IRAS flux densities and luminosities.
- ID:
- ivo://CDS.VizieR/J/A+A/632/A12
- Title:
- NGC 891 and NGC 4565 radio images
- Short Name:
- J/A+A/632/A12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Cosmic-ray electrons (CREs) originating from the star-forming discs of spiral galaxies frequently form extended radio haloes that are best observable in edge-on galaxies, where their properties can be directly investigated as a function of vertical height above the disc. For the present study, we selected two nearby edge-on galaxies from the Continuum Halos in Nearby Galaxies - an EVLA Survey (CHANG-ES), NGC 891 and 4565, which differ largely in their detectable halo extent and their star- formation rates (SFRs). Our aim is to figure out how such differences are related to the (advective and/or diffusive) CRE transport in the disc and in the halo. We use wide-band 1.5 and 6GHz Very Large Array (VLA) observations obtained in the B, C, and D configurations, and combine the 6GHz images with Effelsberg observations to correct for missing short spacings. After subtraction of the thermal emission, we investigate the spatially resolved synchrotron spectral index distribution in terms of CRE spectral ageing. We further compute total magnetic field strengths assuming equipartition between the cosmic-ray (CR) energy density and the magnetic field, and measure synchrotron scale heights at both frequencies. Based on the fitted vertical profiles of the synchrotron intensity and on the spectral index profile between 1.5 and 6GHz, we create purely advective and purely diffusive CRE transport models by numerically solving the 1D diffusion-loss equation. In particular, we investigate for the first time the radial dependence of synchrotron and magnetic field scale heights, advection speeds, and diffusion coefficients, whereas previous studies of these two galaxies only determined global values of these quantities.
- ID:
- ivo://CDS.VizieR/J/A+A/615/A98
- Title:
- NGC 891 LOFAR and AMI maps
- Short Name:
- J/A+A/615/A98
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Cosmic rays and magnetic fields play an important role for the formation and dynamics of gaseous halos of galaxies. Low-frequency radio continuum observations of edge-on galaxies are ideal to study cosmic-ray electrons (CREs) in halos via radio synchrotron emission and to measure magnetic field strengths. Spectral information can be used to test models of CRE propagation. Free-free absorption by ionized gas at low frequencies allows us to investigate the properties of the warm ionized medium in the disk. We obtained new observations of the edge-on spiral galaxy NGC 891 at 129-163MHz with the LOw Frequency ARray (LOFAR) and at 13-18GHz with the Arcminute Microkelvin Imager (AMI) and combine them with recent high-resolution Very Large Array (VLA) observations at 1-2GHz, enabling us to study the radio continuum emission over two orders of magnitude in frequency. The spectrum of the integrated nonthermal flux density can be fitted by a power law with a spectral steepening towards higher frequencies or by a curved polynomial. Spectral flattening at low frequencies due to free-free absorption is detected in star-forming regions of the disk. The mean magnetic field strength in the halo is 7+/-2{mu}G. The scale heights of the nonthermal halo emission at 146MHz are larger than those at 1.5GHz everywhere, with a mean ratio of 1.7+/-0.3, indicating that spectral ageing of CREs is important and that diffusive propagation dominates. The halo scale heights at 146MHz decrease with increasing magnetic field strengths which is a signature of dominating synchrotron losses of CREs. On the other hand, the spectral index between 146MHz and 1.5GHz linearly steepens from the disk to the halo, indicating that advection rather than diffusion is the dominating CRE transport process. This issue calls for refined modelling of CRE propagation. Free-free absorption is probably important at and below about 150MHz in the disks of edge-on galaxies. To reliably separate the thermal and nonthermal emission components, to investigate spectral steepening due to CRE energy losses, and to measure magnetic field strengths in the disk and halo, wide frequency coverage and high spatial resolution are indispensable.
- ID:
- ivo://CDS.VizieR/J/A+A/372/L41
- Title:
- NGC 2068/2071 protoclusters
- Short Name:
- J/A+A/372/L41
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on a wide-field submillimeter continuum survey of the NGC 2068/2071 protoclusters in the Orion B cloud complex. We used the SCUBA bolometer array on JCMT to map a 32'x18' region in size (~4pcx2pc) at 850 and 450 microns. Our survey shows that the dense cores mapped in CS(2-1) by Lada et al. (1991ApJ...368..432L) and labelled with LBS numbers break up into 82 small-scale (~5000AU) fragments. The latter include 70 starless condensations, believed to be the immediate progenitors of accreting protostars, and 5 circumstellar envelopes/disks around protostars. The nature of the 7 remaining cloud fragments is unclear because their dust continuum emission is largely contaminated by line emission.
- ID:
- ivo://CDS.VizieR/J/A+A/632/A13
- Title:
- NGC 4013 radio and polarization maps
- Short Name:
- J/A+A/632/A13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- From the Continuum HAloes in Nearby Galaxies - an EVLA Survey (CHANG-ES) radio continuum data from the Karl G. Jansky Very Large Array (VLA), observed in two frequency bands, 6GHz (C-band) and 1.5GHz (L-band), we present the radio maps, including polarization of the edge-on spiral galaxy NGC 4013. Supplemantary X-ray data are also presented here. The central point source of NGC 4013 dominates the radio continuum emission in both CHANG-ES bands. Complementary X-ray data from Chandra show one dominant point source in the central part. The XMM-Newton spectrum shows hard X-rays, but no clear AGN classification is possible at this time. The radio continuum halo of NGC 4013 in C-band is rather small, while the low-frequency LOFAR data reveal a large halo. The scale height analysis shows that Gaussian fits better represent the intensity profiles than do exponential fits. The frequency dependence gives clear preference to diffusive CRE transport. The radio halo of NGC 4013 is relatively faint. Diffusion is the dominating transport process up to heights of 1-2kpc. The polarization data reveal plane-parallel, regular magnetic fields within the entire disk and vertical halo components indicating the presence of an axisymmetric field having a radial component pointing outwards. The mean magnetic field strength of the disk of NGC 4013 of 6.6{mu}G is rather small. Large-scale vertical fields are observed in the halo out to heights of about 6kpc. The interaction and the low star formation rate (SFR) across the disk of NGC 4013 probably influence the appearance of its radio continuum halo and are correlated with the low total magnetic field strength. Several observable quantities give consistent evidence that the CR transport in the halo of NGC 4013 is diffusive: the frequency dependence of the synchrotron scale height, the disk/halo flux density ratio, the vertical profile of the synchrotron spectral index, the small propagation speed measured modeled with spinnaker, and the low temperature of the X-ray emitting hot gas.
- ID:
- ivo://CDS.VizieR/J/A+A/639/A111
- Title:
- NGC 4217 radio and polarization maps
- Short Name:
- J/A+A/639/A111
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the radio continuum halo, the magnetic field, and the transport processes of the CRs of the edge-on spiral galaxy NGC 4217 using Continuum HAlos in Nearby Galaxies - an Evla Survey (CHANG-ES) radio data at two frequencies, 6GHz (C-band) and 1.5GHz (L-band), and supplemental LOFAR data of this galaxy at 150MHz. With additional X-ray Chandra data, we study the connection of radio features to the diffuse hot gas around NGC 4217. NGC 4217 shows a large-scale X-shaped magnetic field structure, covering a major part of the galaxy with a mean total magnetic field strength in the disk of 9G. From the analysis of the rotation measure map at C-band, we found that the direction of the disk magnetic field is pointing inward. A helical outflow structure is furthermore present in the northwestern part of the galaxy, which is extended nearly 7 kpc into the halo. More polarized emission is observed on the approaching side of the galaxy, indicating that Faraday depolarization has to be considered at C-band. With a simplified galaxy disk model, we are able to explain the finding of higher polarized intensity on the approaching side. We generalize the model to predict that roughly 75% of edge-on spiral galaxies will show higher polarized intensity on the approaching side. Many loop and shell structures are found throughout the galaxy in total intensity at C-band. One structure, a symmetric off-center (to the southwest of the disk) superbubble-like structure is prominent in total and polarized intensity, as well as in Halpha and optical dust filaments. This is at a location where a second peak of total intensity (to the southwest of the disk) is observed, making this superbubble-like structure a possible result of a concentrated star formation region in the disk. The X-ray diffuse emission shows similarities to the polarized diffuse emission of NGC 4217. The flux density extension of the radio continuum halo increases toward lower frequencies. While the total flux density of the disk and halo are comparable at C-band, the contribution of the disk flux density decreases toward LOFAR to 18% of the total flux density. Dumbbell-shaped structures are present at C-band and at the LOFAR frequency. Total intensity profiles at the two CHANG-ES bands and the LOFAR frequency show a clear two-component behavior and were fit best with a two-component exponential fit. The halo scale heights are 1.10+/-0.04kpc, 1.43+/-0.09kpc, and 1.55+/-0.04kpc in C-band, L-band, and 150MHz, respectively. The frequency dependence of these scale heights between C-band and L-band suggests advection to be the main transport process. The 1D CRE transport modeling shows that advection appears to be more important than diffusion.