J/ApJ/861/113 VLBA astrometry combined with Gaia DR1 epoch (Darling+, 2018)
Astrometric limits on the stochastic gravitational wave background.
Darling J., Truebenbach A.E., Paine J.
<Astrophys. J., 861, 113 (2018)>
=2018ApJ...861..113D 2018ApJ...861..113D
ADC_Keywords: Radio sources; Positional data; Proper motions; Redshifts; Optical
Keywords: astrometry; cosmology: observations; gravitational waves; inflation;
proper motions; techniques: high angular resolution
Abstract:
The canonical methods for gravitational wave detection are ground- and
space- based laser interferometry, pulsar timing, and polarization of
the cosmic microwave background. But as has been suggested by numerous
investigators, astrometry offers an additional path to gravitational
wave detection. Gravitational waves deflect light rays of
extragalactic objects, creating apparent proper motions in a
quadrupolar (and higher-order modes) pattern. Astrometry of
extragalactic radio sources is sensitive to gravitational waves with
frequencies between roughly 10-18 and 10-8Hz (H0 and 1/3yr-1),
overlapping and bridging the pulsar timing and CMB polarization
regimes. We present a methodology for astrometric gravitational wave
detection in the presence of large intrinsic uncorrelated proper
motions (i.e., radio jets). We obtain 95% confidence limits on the
stochastic gravitational wave background using 711 radio sources,
ΩGW<0.0064, and using 508 radio sources combined with the
first Gaia data release: ΩGW<0.011. These limits probe
gravitational wave frequencies 6x10-18Hz≲f≲1x10-9Hz. Using a
WISE-Gaia catalog of 567721 AGN, we predict a limit expected from Gaia
alone of ΩGW<0.0006, which is significantly higher than was
originally forecast. Incidentally, we detect and report on 22 new
examples of optical superluminal motion with redshifts 0.13-3.89.
Description:
We measure proper motions from astrometric time series using VLBA data
only and VLBA data combined with a single Gaia epoch.
The VLBA astrometric catalog is described and characterized in detail
in Truebenbach & Darling (2017, J/ApJS/233/3). In summary, the catalog
contains 713 objects with mean astrometric uncertainties of
24µas/yr. These were obtained from long-term astrometric monitoring
programs as well as new observations. The time baselines spanned by
the new and archival data cover the range 6.4-27.2 years (1.2x10-9Hz
to 5.0x10-9Hz).
The first Gaia data release (DR1) catalog (2016, I/337) contains a
single-epoch (2015.0) position for 2191 AGN in the International
Celestial Reference Frame (ICRF2) catalog. 577 of these are VLBA
sources in the Truebenbach & Darling (2017, J/ApJS/233/3) catalog, and
we use them to measure proper motions from the VLBA-Gaia time series.
Median uncertainties in the Gaia astrometry of these objects are
518µas and 459µas in RA and DEC, respectively.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table6.dat 81 45 Objects showing significant consistent radio and
optical proper motion
table7.dat 116 577 VLBA+Gaia astrometry and proper motions
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See also:
I/337 : Gaia DR1 (Gaia Collaboration, 2016)
J/ApJ/626/95 : Gamma-ray blazar candidates (Sowards-Emmerd+, 2005)
J/A+A/476/L17 : 86 and 43GHz observations of NRAO 150 (Agudo+, 2007)
J/ApJS/175/97 : CGRaBS: survey of γ-ray blazars (Healey+, 2008)
J/MNRAS/405/2302 : Improved redshifts for SDSS quasar spectra (Hewett+, 2010)
J/A+A/529/A91 : Proper motions of 555 quasars from VLBI (Titov+, 2011)
J/A+A/543/A100 : GaiaSimu Universe Model Snapshot (Robin+, 2012)
J/A+A/559/A95 : Fitted proper motions for the DR solution (Titov+, 2013)
J/MNRAS/430/2633 : The epoch ICRF (Xu+, 2013)
J/ApJ/783/130 : Parallaxes of high mass star forming regions (Reid+, 2014)
J/ApJS/233/3 : The VLBA Extragalactic PM Catalog (Truebenbach+, 2017)
J/ApJS/236/37 : The Gaia-WISE extragalactic astrometric cat. (Paine+, 2018)
Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 1 I1 --- SL [0/1] Superluminal;
1=showing apparent superluminal motion
3- 10 A8 --- Name Name (HHMM+DDMM; B1950)
12- 12 A1 --- f_Name Flag on Name (1)
14- 18 F5.1 uarcsec/yr pmRA [-50/137] VLBA+Gaia Proper motion, in RA
20- 23 F4.1 uarcsec/yr e_pmRA [0.4/25.4] Uncertainty in pmRA, one sigma
25- 30 F6.1 uarcsec/yr pmDE [-111/108] VLBA+Gaia Proper motion, in DE
32- 35 F4.1 uarcsec/yr e_pmDE [0.4/17.0] Uncertainty in pmDE, one sigma
37- 40 F4.2 --- z [0.1/4]? Literature redshift
42- 43 I2 --- r_z [1/10]? Reference for z (2)
45- 48 I4 Mpc Dmu [542/7328]? Proper Motion Distance
50- 54 F5.2 c Vel-RA [-2.7/10.1]? Apparent velocity, in RA (3)
56- 59 F4.2 c e_Vel-RA [0.01/2]? Uncertainty in Vel-RA, one sigma
61- 65 F5.2 c Vel-DE [-7.2/4]? Apparent velocity, in DE (3)
67- 70 F4.2 c e_Vel-DE [0.02/1]? Uncertainty in Vel-DE, one sigma
72- 76 F5.2 c Vel-Tot [0.2/10.1]? Apparent Total velocity (3)
78- 81 F4.2 c e_Vel-Tot [0.02/2]? Uncertainty in Vel-Tot, one sigma
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Note (1):
b = 1657-562 and 1923+210 show VLBA+Gaia astrometric correspondence
and significant proper motion, but the redshifts for these objects are
unknown. If they have redshifts greater than 0.13 and 0.90,
respectively, then their observed proper motions would be superluminal.
Note (2): Literature References for redshift as follows:
1 = Wills & Wills (1976ApJS...31..143W 1976ApJS...31..143W);
2 = Healey et al. (2008, J/ApJS/175/97);
3 = Sowards-Emmerd et al. (2005, J/ApJ/626/95);
4 = Agudo et al. (2007, J/A+A/476/L17);
5 = Alvarez Crespo et al. (2016AJ....151...95A 2016AJ....151...95A);
6 = Hewett & Wild (2010, J/MNRAS/405/2302);
7 = Sbarufatti et al. (2009AJ....137..337S 2009AJ....137..337S);
8 = Hook et al. (1995MNRAS.273L..63H 1995MNRAS.273L..63H);
9 = Gelderman & Whittle (1994ApJS...91..491G 1994ApJS...91..491G);
10 = Smith & Spinrad (1980ApJ...236..419S 1980ApJ...236..419S).
Note (3): Apparent velocities are in the rest frame of each object, in units
of the speed of light, c (see Section 3.2).
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Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Name Name (HHMM+DDMM; B1950)
10- 11 I2 h RAh Hour of Right Ascension (J2000) (1)
13- 14 I2 min RAm Minute of Right Ascension
16- 23 F8.5 s RAs Second of Right Ascension
25- 27 I3 10-5s e_RAs [1/365] Uncertainty in position, RA
29- 29 A1 --- DE- Sign of the Declination (J2000) (1)
30- 31 I2 deg DEd Degree of Declination
33- 34 I2 arcmin DEm Arcminute of Declination
36- 42 F7.4 arcsec DEs Arcsecond of Declination
44- 46 I3 10-4arcsec e_DEs [1/938] Uncertainty in position, DE
48- 54 F7.1 uarcsec/yr pmRA-1 [-1191/393] VLBA Proper motion, in RA
56- 61 F6.1 uarcsec/yr e_pmRA-1 [0.4/1987] Uncertainty in pmRA-1, one sigma
63- 68 F6.1 uarcsec/yr pmDE-1 [-681/109] VLBA Proper motion, in DE
70- 75 F6.1 uarcsec/yr e_pmDE-1 [0.4/1588] Uncertainty in pmDE-1, one sigma
77- 83 F7.1 uarcsec/yr pmRA-2 [-1185/304] VLBA+Gaia Proper motion, in RA
85- 90 F6.1 uarcsec/yr e_pmRA-2 [0.4/2108] Uncertainty in pmRA-2, one sigma
92- 98 F7.1 uarcsec/yr pmDE-2 [-2285/502] VLBA+Gaia Proper motion, in DE
100-105 F6.1 uarcsec/yr e_pmDE-2 [0.4/2387] Uncertainty in pmDE-2, one sigma
107-110 F4.1 --- dpmRA [0/26] Gaia-VLBA Offset, RA, in sigma (2)
112-116 F5.1 --- dpmDE [0/160] Gaia-VLBA Offset, DE, in sigma (2)
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Note (1): Gaia coordinates are for epoch 2015.0, expressed in the J2000
reference frame.
Note (2): Gaia-VLBA offsets are expressed in standard deviations of the Gaia
astrometry from the VLBA time series fit, assuming that the error is
dominated by the sole Gaia epoch in each coordinate.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 15-Jul-2019