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J/ApJ/815/49    Spectropolarimetric survey of radio sources    (Anderson+, 2015)

Broadband radio polarimetry and Faraday rotation of 563 extragalactic radio sources. Anderson C.S., Gaensler B.M., Feain I.J., Franzen T.M.O. <Astrophys. J., 815, 49 (2015)> =2015ApJ...815...49A (SIMBAD/NED BibCode)
ADC_Keywords: Radio sources ; Magnetic fields ; Redshifts ; Surveys Keywords: galaxies: active - ISM: magnetic fields - magnetic fields - radio continuum: galaxies - techniques: polarimetric Abstract: We present a broadband spectropolarimetric survey of 563 discrete, mostly unresolved radio sources between 1.3 and 2.0 GHz using data taken with the Australia Telescope Compact Array. We have used rotation-measure synthesis to identify Faraday-complex polarized sources, those objects whose frequency-dependent polarization behavior indicates the presence of material possessing complicated magnetoionic structure along the line of sight (LOS). For sources classified as Faraday-complex, we have analyzed a number of their radio and multiwavelength properties to determine whether they differ from Faraday-simple polarized sources (sources for which LOS magnetoionic structures are comparatively simple) in these properties. We use this information to constrain the physical nature of the magnetoionic structures responsible for generating the observed complexity. We detect Faraday complexity in 12% of polarized sources at ∼1' resolution, but we demonstrate that underlying signal-to-noise limitations mean the true percentage is likely to be significantly higher in the polarized radio source population. We find that the properties of Faraday-complex objects are diverse, but that complexity is most often associated with depolarization of extended radio sources possessing a relatively steep total intensity spectrum. We find an association between Faraday complexity and LOS structure in the Galactic interstellar medium (ISM) and claim that a significant proportion of the Faraday complexity we observe may be generated at interfaces of the ISM associated with ionization fronts near neutral hydrogen structures. Galaxy cluster environments and internally generated Faraday complexity provide possible alternative explanations in some cases. Description: We obtained mosaicked observations of a 30 deg2 region of sky using the CABB correlator on the Australia Telescope Compact Array (ATCA; Wilson et al. 2011MNRAS.416..832W). Our observations were performed using the "CFB 1M" mode, which generates all polarization products from 1.1 to 3.1 GHz with 1 MHz channel widths. The mosaic consisted of 342 pointings laid out in a hexagonal grid. This grid spanned 7.5° in RA and 5.5° in DE and was centered on RA=03h29m40s and DE=-36°16'30" (J2000) in Fornax. The angular separation of the mosaic pointings was 0.323° and therefore spatially Nyquist-sampled at 1.4 GHz. To obtain adequate uv coverage, we broke the full mosaic up into seven submosaics and observed each submosaic on consecutive days. We completed the full seven-day observing run twice-once in each of the 1.5B and 750B array configurations, from 2011 May 5-11 and 2011 June 10-16, respectively. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 161 160 Selected Quantities Calculated or Determined for Polarized Sources in Our Sample. (from erratum ApJ, 820, 144)
See also: VII/6 : Polarization of Extragalactic Radio Sources (Eichendorf+ 1980) J/MNRAS/190/205 : Magnetic fields in extragalactic radio sources (Clarke+ 1980) J/ApJS/45/97 : Extragal. Radio Sources Faraday Rotation (Simard-Normandin+, 1981) J/ApJ/586/826 : Chandra X-ray observations of NGC 1316 (Kim+, 2003) J/MNRAS/362/9 : Radio-loud AGN in SDSS (Best+, 2005) J/ApJ/663/258 : Rotation measures of extragalactic sources in SGPS (Brown+, 2007) J/ApJ/702/1230 : Rotation measure image of the sky (Taylor+, 2009) J/AJ/144/105 : MOJAVE. VIII. Faraday rotation in AGN jets. (Hovatta+, 2012) J/MNRAS/469/4034 : Broadband polarisation of radio AGN (O'Sullivan+, 2017) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 13 A13 --- Name Source name (HHMMSS+DDMMSS) 15- 16 I2 h RAh Hour of Right Ascension (J2000) 18- 19 I2 min RAm Minute of Right Ascension (J2000) 21- 25 F5.2 s RAs Second of Right Ascension (J2000) 27 A1 --- DE- Sign of the Declination (J2000) 28- 29 I2 deg DEd Degree of Declination (J2000) 31- 32 I2 arcmin DEm Arcminute of Declination (J2000) 34- 38 F5.2 arcsec DEs Arcsecond of Declination (J2000) 40- 44 F5.3 deg Sep Angular separation from the position of the source nearest mosaic pointing center 46- 51 F6.1 deg PA [] Position angle from the position of the source nearest mosaic pointing center 53 A1 --- Res [ru] Resolved (r) or unresolved (u) source at the 90"x45" resolution of spectropolarimetric images 55- 59 F5.3 m lambda0 Reference wavelength to 3 significant figures 61- 66 F6.4 Jy Ilambda0 Interpolated value of Stokes I at λ0 68- 73 F6.4 Jy e_Ilambda0 Uncertainty in Ilambda0 75- 79 F5.2 --- alphal0 Value of α evaluated at λ0 (1) 81- 84 F4.2 --- e_alphal0 Uncertainty in alphal0 86 A1 --- Cat [cs] Complexity categorization of the source (2) 88- 89 I2 --- GES [6/10]? The highest RMCLEAN cutoff Gaussian-equivalent significance (GES) level at which the source appears complex, in equivalent Gaussian σ 91 A1 --- Weight [cn-] The weighting scheme under which a complex source attains its highest value of σΦ (3) 93- 98 F6.2 rad/m2 sigmaPhi Calculated value of the dispersion of the RMCLEAN model components, σΦ 100-104 F5.3 rad/m2/beam pcut The RMCLEAN cutoff value to 3 significant figures 106-112 F7.5 rad/m2/beam p Amplitude of the Faraday Dispersion Spectrum (FDS) at Φpeak 114-119 E6.1 rad/m2/beam e_p Uncertainty in p 121-124 F4.2 rad/m2/beam poff The fractional contribution of off-peak RMCLEAN components to the total polarized flux (4) 126-131 F6.1 rad/m2 Phipeak Faraday depth at which the FDS is maximum 133-135 F3.1 rad/m2 e_Phipeak Uncertainty in Phipeak 137-139 A3 --- Morph Stokes I morphology of the radio source at 15" resolution (5) 141-143 A3 --- IRc [yes-no off] Counterpart status of a source in IR (6) 145-147 A3 --- Oc [yes-no off] Counterpart status of a source in optical (6) 149-151 A3 --- UVc [yes-no off] Counterpart status of a source in UV (6) 153-155 A3 --- Xc [yes-no ] Counterpart status of a source in X-rays (7) 157-161 F5.3 --- z ? Cross-matched redshift
Note (1): Spectral index α (I(ν)∝να) Note (2): Categorization as follows: c = Faraday-complex source; s = Simple source. Note (3): Weighting scheme as follows: c = Constant rotation measure (RM) synthesis weighting scheme; n = Natural RM synthesis weighting scheme. Note (4): Those RMCLEAN components found in Φ bins apart from that in which the majority of components were found. Note (5): Morphology as follows: cj = "core-jet" if the total flux was dominated by an unresolved component in the presence of additional resolved components that were either (1) substantially fainter than the core or (2) radiated away from the core with linear morphology; lc = "lobe/jet component" if they either (1) possessed obvious radio lobe or jet morphology or (2) possessed a counterpart radio source within 3' of similar brightness (Hammond et al. 2012arXiv1209.1438H and refs therein); u = "unresolved" if the source was well fit by a Gaussian of the same dimensions as the restoring beam; ext = "extended" for resolved sources not meeting the above criteria. Note (6): In IR, optical, and UV, we manually identified counterparts by overlaying contours from the source-finding image onto the relevant survey images. Counterpart status as follows: yes = "match" when objects were present within 15" of the radio contour centroid (i.e., within the beam FWHM of the source-finding image); off = "match-off source" if either (1) the radio source was extended and a candidate counterpart source lay inside the 10% radio flux contour, (2) a second radio source was located within 3' and a candidate counterpart was located within 15" of the position of the flux centroid of the two sources (e.g., Best et al. 2005, J/MNRAS/362/9), or (3) NASA Extragalactic Database (NED) queries revealed an existing association in the literature; no = "no match" otherwise. Note (7): Our X-ray cross matches were made in a binary manner based on the distance to the nearest cataloged sources and the positional errors for the RASS-BSC and RASS-FSC (Parejko et al. 2008AJ....135...10P). Counterpart status as follows: yes = "match" if the radio emission centroid fell within 20" of a cataloged RASS-BSC source position or 40" of a RASS-FSC source position; no = "no match" otherwise.
History: From electronic version of the journal
(End) Prepared by Tiphaine Pouvreau [CDS] 17-Oct-2017
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