J/ApJ/878/92 Rotation measures in radio source pairs (Vernstrom+, 2019)
Differences in Faraday rotation between adjacent extragalactic radio sources as
a probe of cosmic magnetic fields.
Vernstrom T., Gaensler B.M., Rudnick L., Andernach H.
<Astrophys. J., 878, 92-92 (2019)>
=2019ApJ...878...92V 2019ApJ...878...92V (SIMBAD/NED BibCode)
ADC_Keywords: Radio continuum; Polarization; Redshifts; Intergalactic medium
Keywords: galaxies: magnetic fields; intergalactic medium; methods: statistical
radio continuum: galaxies
Abstract:
Faraday rotation measures (RMs) of extragalactic radio sources provide
information on line-of-sight magnetic fields, including contributions
from our Galaxy, source environments, and the intergalactic medium
(IGM). Looking at differences in RMs, ΔRM, between adjacent
sources on the sky can help isolate these different components. In
this work, we classify adjacent polarized sources in the NRAO VLA Sky
Survey (NVSS) as random or physical pairs. We recompute and correct
the uncertainties in the NVSS RM catalog, since these were
significantly overestimated. Our sample contains 317 physical and
5111 random pairs, all with Galactic latitudes |b|≥20°,
polarization fractions ≥2%, and angular separations between 1.5' and
20'. We find an rms ΔRM of 14.9±0.4 and 4.6±1.1rad/m2 for
the random and physical pairs, respectively. This means that polarized
extragalactic sources that are close on the sky but at different
redshifts have larger differences in RM than two components of one
source. This difference of ∼10rad/m2 is significant at 5σ and
persists in different data subsamples. While there have been other
statistical studies of ΔRM between adjacent polarized sources,
this is the first unambiguous demonstration that some of this RM
difference must be extragalactic, thereby providing a firm upper limit
on the RM contribution of the IGM. If the ΔRMs originate local
to the sources, then the local magnetic field difference between
random sources is a factor of 2 larger than that between components of
one source. Alternatively, attributing the difference in ΔRMs to
the intervening IGM yields an upper limit on the IGM magnetic field
strength of 40nG.
Description:
We make use of the Taylor+ (2009, J/ApJ/702/1230) catalog, which
provides 1.4GHz polarized intensities, polarized fractions, and
Faraday rotation measures (RMs) for 37543 sources and source
components from the NRAO VLA Sky Survey (NVSS; Condon+ 1998, VIII/65)
catalog, covering the sky north of DEC=-40°. See Section 2.
After classifying the pairs based on visual inspection of the images,
the RM source positions from Taylor+ (2009, J/ApJ/702/1230) are
cross-matched with the Hammond+ (2012, 1209.1438) and
Kimball & Ivezic (2008AJ....136..684K 2008AJ....136..684K) catalogs, which include
redshifts. See Section 3.3.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 215 5428 Details of Taylor+ (2009, J/ApJ/702/1230)
polarized pairs
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See also:
VIII/65 : 1.4GHz NRAO VLA Sky Survey (NVSS) (Condon+ 1998)
VII/250 : The 2dF Galaxy Redshift Survey (2dFGRS) (2dFGRS Team, 1998-2003)
VII/241 : The 2dF QSO Redshift Survey (Croom+ 2004)
VII/259 : 6dF galaxy survey final redshift release (Jones+, 2009)
V/139 : The SDSS Photometric Catalog, Release 9 (Adelman-McCarthy+, 2012)
J/A+A/370/409 : Large angular size radio galaxies. I. (Lara+, 2001)
J/ApJ/642/868 : Rotation measures for 223 pulsars (Han+, 2006)
J/ApJ/702/1230 : Rotation measure image of the sky (Taylor+, 2009)
J/ApJ/714/1170 : Faraday rotation at high Galactic latitude (Mao+, 2010)
J/ApJS/212/15 : Polarized NVSS sources SEDs (Farnes+, 2014)
J/A+A/568/A126 : SDSS-DR9 photometric redshifts (Brescia+, 2014)
J/ApJS/224/18 : Identify giant radio sources from the NVSS (Proctor, 2016)
J/ApJ/829/5 : S-PASS & NVSS bright extragal. radio sources (Lamee+, 2016)
J/A+A/598/A78 : The GMRT 150MHz all-sky radio survey (Intema+, 2017)
J/MNRAS/474/5008 : Radio spectral index 147-1400MHz (de Gasperin+, 2018)
J/A+A/613/A58 : Polarized point sources in LOTSS-HETDEX (Van Eck+, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Seq [1/5428] Pair identifier number
6 A1 --- Class Class (1)
8- 9 I2 h RAh Source 1 Hour of Right Ascension (J2000)
11- 12 I2 min RAm Source 1 Minute of Right Ascension (J2000)
14- 18 F5.2 s RAs Source 1 Second of Right Ascension (J2000)
20 A1 --- DE- Source 1 Sign of the Declination (J2000)
21- 22 I2 deg DEd Source 1 Degree of Declination (J2000)
24- 25 I2 arcmin DEm Source 1 Arcminute of Declination (J2000)
27- 30 F4.1 arcsec DEs Source 1 Arcsecond of Declination (J2000)
32- 33 I2 h RA2h Source 2 Hour of Right Ascension (J2000)
35- 36 I2 min RA2m Source 2 Minute of Right Ascension (J2000)
38- 42 F5.2 s RA2s Source 2 Second of Right Ascension (J2000)
44 A1 --- DE2- Source 2 Sign of the Declination (J2000)
45- 46 I2 deg DE2d Source 2 Degree of Declination (J2000)
48- 49 I2 arcmin DE2m Source 2 Arcminute of Declination (J2000)
51- 54 F4.1 arcsec DE2s Source 2 Arcsecond of Declination (J2000)
56- 59 F4.1 arcmin Sep [1.5/20] Separation of sources in pair
61- 64 I4 rad/m2 RM1 [-231/214] Rotation Measure of source 1
66- 67 I2 rad/m2 e_RM1 [0/22] Uncertainty of RM source 1 (2)
69- 72 I4 rad/m2 RM2 [-209/180] Rotation Measure of source 2
74- 75 I2 rad/m2 e_RM2 [0/21] Uncertainty of RM source 2 (2)
77- 82 F6.1 rad/m2 DelRM [-141.3/104.4] Difference in RMs (RM1-RM2)
84- 87 F4.1 rad/m2 e_DelRM [0.7/28] Uncertainty of difference in RMs
89- 94 F6.2 mJy/beam P1 [2.29/337.53] Peak Polarized Intensity
source 1 (3)
96- 101 F6.2 mJy/beam P2 [2.27/776.65] Peak Polarized Intensity
source 2 (3)
103- 106 F4.2 mJy/beam sigQU [0.16/0.88] Average Q & U Image noise,
σQU (4)
108- 111 F4.2 % Leak1 [0.03/4.12] Leakage fraction percent source 1
113- 116 F4.2 % Leak2 [0.03/3.61] Leakage fraction percent source 2
118- 121 F4.1 % fPol1 [2/44.7] Polarization fraction percent
source 1
123- 126 F4.1 % fPol2 [2/62.5] Polarization fraction percent
source 2
128- 134 F7.3 --- z1 [0/4.71]?=-99.999 Redshift source 1
136- 142 F7.3 --- z2 [0/3.88]?=-99.999 Redshift source 2
144- 149 F6.2 --- SpInd1 [-1.37/0.9]?=-99.99 Spectral index source 1
151- 156 F6.2 --- SpInd2 [-1.39/1.05]?=-99.99 Spectral index source 2
158- 185 A28 --- Name1 Source 1 Name (5)
188- 215 A28 --- Name2 Source 2 Name (5)
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Note (1): Pair class as follows:
R = random: two physically unrelated sources with a given angular
separation on the sky (5111 sources)
P = physical: components of the same source (317 sources).
Note (2): In the RM column the uncertainty listed is not from the Taylor
catalog, but the uncertainty derived in this work following the
procedure described in Appendix A.
Note (3): The P column gives the frequency-averaged peak polarized intensity
as reported by Taylor+ (2009, J/ApJ/702/1230).
Note (4): The σQU values given are the average of the Q and U image
noise measured in this work from the single frequency NVSS postage
stamps multiplied by a factor of sqrt(2); for details see Appendix A.
Note (5): The Name1/Name2 columns give the NVSS source name for sources in
random pairs and gives the source name from published catalogs (usually
the optical or infrared core counterpart) if it is a physical pair.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 01-Mar-2022