J/ApJ/756/29 Scintillation of AGNs observed with the VLA (Koay+, 2012)
Why do compact active galactic nuclei at high redshift scintillate less?
Koay J.Y., Macquart J.-P., Rickett B.J., Bignall H.E., Jauncey D.L.,
Pursimo T., Reynolds C., Lovell J.E.J., Kedziora-Chudczer L., Ojha R.
<Astrophys. J., 756, 29 (2012)>
=2012ApJ...756...29K 2012ApJ...756...29K
ADC_Keywords: Active gal. nuclei ; Radio sources ; Interstellar medium
Keywords: cosmology: observations; galaxies: active; intergalactic medium;
ISM: structure; quasars: general; radio continuum: ISM
Abstract:
The fraction of compact active galactic nuclei (AGNs) that exhibit
interstellar scintillation (ISS) at radio wavelengths, as well as
their scintillation amplitudes, have been found to decrease
significantly for sources at redshifts z≳2. This can be attributed to
an increase in the angular sizes of the µas-scale cores or a
decrease in the flux densities of the compact µas cores relative to
that of the mas-scale components with increasing redshift, possibly
arising from (1) the space-time curvature of an expanding universe,
(2) AGN evolution, (3) source selection biases, (4) scatter broadening
in the ionized intergalactic medium (IGM) and intervening galaxies, or
(5) gravitational lensing. We examine the frequency scaling of this
redshift dependence of ISS to determine its origin, using data from a
dual-frequency survey of ISS of 128 sources at 0≲z≲4. We present a
novel method of analysis which accounts for selection effects in the
source sample.
Description:
We observed a sub-sample of 140 sources drawn from the original MASIV
Survey (Lovell et al. 2008, Cat. J/ApJ/689/108) over a duration of 11
days, from 2009 January 15 to 25, using the Very Large Array (VLA). Of
these sources, 70 have redshifts of z<2 (we refer to them as the
low-redshift sources) while another 70 have redshifts of z>2 (the
high-redshift sources). The telescope was divided into two subarrays,
one observing at 4.9GHz and the other observing at 8.4GHz
simultaneously.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 91 128 List of sources and their observed properties
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See also:
II/249 : WHAM Northern Sky Survey, V-1.1 (Haffner+, 2003)
VIII/72 : CLASS survey of radio sources (Myers+, 2003)
J/AJ/142/108 : Radio variability of compact, flat-spectrum AGNs (Koay+, 2011)
J/ApJ/737/45 : Variable 1.4GHz radio sources from NVSS and FIRST (Ofek+, 2011)
J/ApJS/194/29 : Observations of blazars at 15GHz (Richards+, 2011)
J/A+A/520/A62 : Radio-optical scrutiny of compact AGN (Arshakian+, 2010)
J/ApJ/689/108 : MASIV survey. II. First four epochs (Lovell+, 2008)
J/AJ/128/1570 : 8.4GHz VLBA observations of scintillating sources (Ojha+, 2004)
J/ApJ/614/607 : 8.4GHz obs. of scintillating sources (Ojha+, 2004)
J/A+A/421/455 : Interplanetary Scintillation Pushchino Survey (Kopylov+, 2004)
J/A+A/416/35 : Radio Emission from VLA FIRST Survey AGN (Wadadekar, 2004)
J/A+A/342/378 : 6 and 20cm flux densities of radio galaxies (Gurvits+ 1999)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- MASIV IAU name (JHHMM+DDMM)
12- 15 F4.2 Jy S4.9 [0.05/4.31] Mean 4.9GHz flux density
17- 20 F4.2 Jy S8.4 [0.05/5.25] Mean 8.4GHz flux density (1)
22- 26 F5.2 --- alpha Spectral index α (1)
28- 36 E9.2 --- D4.9 The 4.9GHz structure function D(τ=4d) (6)
38- 46 E9.2 --- e_D4.9 The 95% confidence error in D4.9
48- 56 E9.2 --- D8.4 The 8.4GHz structure function D(τ=4d) (6)
58- 66 E9.2 --- e_D8.4 The 95% confidence error in D8.4 (1)
68- 71 F4.2 --- RD ? The D8.4/D4.9 ratio (2)
73- 76 F4.2 --- e_RD ? The 95% confidence error in RD
78- 81 A4 --- OpID Optical identification (3)
83- 85 F3.1 --- z [0.1/4] Source redshift (4)
87- 91 F5.1 10+10m-2/s IHa [-0.2/147] Line-of-sight Hα intensity (5)
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Note (1): Spectral index defiedn as S∝να, may slightly
differ from values published in Paper I (J/AJ/142/108) following the
removal of data points on days in which the 4.9GHz subarray
encountered data losses, to avoid biases.
Note (2): Given only for ≥3σ variable sources.
Note (3): Obtained from NED, SIMBAD, and Pursimo et al. (2013ApJ...767...14P 2013ApJ...767...14P);
the classes are as follows:
fsrq = flat-spectrum radio-loud quasar;
bllc = BL Lac object;
NULL = no ID available, most likely fsrq;
nlrg = narrow-line radio galaxy;
syf1 = Seyfert 1 galaxy.
Note (4): Obtained from NED, SIMBAD, and Pursimo et al. (2013ApJ...767...14P 2013ApJ...767...14P).
Note (5): Obtained from Haffner et al. (2003, Cat. II/249).
In units of Rayleighs (1R=1010ph/m2/s)
Note (6): the structure function D(τ) is a characerisation of the source
variability at time lag τ defined by:
D(τ)=<[S(t+τ)-S(t)]2>
if S(t) is the normalized flux desnsity (<S(t)≥1)
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History:
From electronic version of the journal
References:
Koay et al. Paper I. 2011AJ....142..108K 2011AJ....142..108K Cat. J/AJ/142/108
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 18-Mar-2014