J/A+A/622/A92 Ultracompact extragalactic radio sources at 86GHz (Nair+, 2019)
Global millimeter VLBI array survey of ultracompact extragalactic radio sources
at 86 GHz.
Nair D.G., Lobanov A.P., Krichbaum T.P., Ros E., Zensus J.A., Kovalev Y.Y.,
Lee S.-S, Mertens F., Hagiwara Y., Bremer M., Lindqvist M., de Vicente P.
<Astron. Astrophys. 622, A92 (2019)>
=2019A&A...622A..92N 2019A&A...622A..92N (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; Galaxies, radio ; Active gal. nuclei ; QSOs ;
Radio continuum
Keywords: galaxies: active - galaxies: jets - galaxies: quasars: general -
radio continuum: galaxies - techniques: interferometric - surveys
Abstract:
Very long baseline interferometry (VLBI) observations at 86 GHz
(wavelength, λ=3mm) reach a resolution of about 50µas,
probing the collimation and acceleration regions of relativistic
outflows in active galactic nuclei (AGN). The physical conditions in
these regions can be studied by performing 86GHz VLBI surveys of
representative samples of compact extragalactic radio sources.
To extend the statistical studies of compact extragalactic jets, a
large global 86GHz VLBI survey of 162 compact radio sources was
conducted in 2010-2011 using the Global Millimeter VLBI Array
(GMVA).
The survey observations were made in a snapshot mode, with up to five
scans per target spread over a range of hour angles in order to
optimize the visibility coverage. The survey data attained a typical
baseline sensitivity of 0.1Jy and a typical image sensitivity of
5mJy/beam, providing successful detections and images for all of the
survey targets. For 138 objects, the survey provides the first ever
VLBI images made at 86GHz. Gaussian model fitting of the visibility
data was applied to represent the structure of the observed sources
and to estimate the flux densities and sizes of distinct emitting
regions (components) in their jets. These estimates were used for
calculating the brightness temperature (Tb) at the jet base (core) and
in one or more moving regions (jet components) downstream from the
core. These model-fit-based estimates of Tb were compared to the
estimates of brightness temperature limits made directly from the
visibility data, demonstrating a good agreement between the two
methods.
The apparent brightness temperature estimates for the jet cores in our
sample range from 2.5x109K to 1.3x1012K, with the mean value of
1.8x1011K. The apparent brightness temperature estimates for the
inner jet components in our sample range from 7.0x107K to
4.0x1011K. A simple population model with a single intrinsic value
of brightness temperature, T0, is applied to reproduce the observed
distribution. It yields T0=(3.77+0.100.14)1011K for the jet
cores, implying that the inverse Compton losses dominate the emission.
In the nearest jet components, T0=(1.42+0.160.19)1011K is found,
which is slightly higher than the equipartition limit of 5x1010K
expected for these jet regions. For objects with sufficient structural
detail detected, the adiabatic energy losses are shown to dominate the
observed changes of brightness temperature along the jet.
Description:
Dedicated VLBI observations at 86GHz are made with the GMVA and with
the Very Long Baseline Array (VLBA) working in a stand-alone mode
(VLBA also takes part in GMVA observations).
The survey observations have been made over a total of six days
(144-hours), scheduled within three separate GMVA sessions.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table5.dat 86 162 List of sources
table6.dat 88 174 Image parameters
table7.dat 99 380 Model fit parameters
list.dat 197 174 List of fits files
images/* . 174 Individual fits images
visib/* . 174 Individual fits visibility data
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Source IAU source name, J2000 (JHHMM+DDMM)
12- 19 A8 --- BName IAU source name, B1950 (HHMM+DDd)
21- 34 A14 --- Name Common name
36- 40 A5 --- Ep Observing epoch(s) (G1)
42- 43 I2 h RAh Right ascension (J2000)
45- 46 I2 min RAm Right ascension (J2000)
48- 56 F9.6 s RAs Right ascension (J2000)
58 A1 --- DE- Declination sign (J2000)
59- 60 I2 deg DEd Declination (J2000)
62- 63 I2 arcmin DEm Declination (J2000)
65- 72 F8.5 arcsec DEs Declination (J2000)
74- 79 F6.4 --- z ?=- Redshift
81 A1 --- Type Optical class (2)
83- 86 F4.1 mag Vmag ?=- V magnitude
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Note (2): Optical class as follows:
Q = quasar
B = BL Lac object
G = Galaxy
U = Unidentified source
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Source IAU source name, J2000 (JHHMM+DDMM)
12 A1 --- Ep Observing epoch (G1)
14- 18 F5.2 Jy S86GHz ?=- Total single dish flux density at
86GHz (1)
20- 25 F6.3 Jy SS ?=- Correlated flux densities measured on
projected baseline length listed in BS
27- 31 F5.3 Jy e_SS ?=- rms uncertainty on SS
33- 35 I3 --- BS ?=- Projected baseline length
37- 41 F5.3 --- SL ?=- Correlated flux densities measured on
projected baseline length listed in BL
43- 47 F5.3 --- e_SL ?=- rms uncertainty on SL
49- 52 I4 --- BL ?=- Projected baseline length
54- 57 I4 uas Ba Major axis of the restoring beam
59- 61 I3 uas Bb Minor axis of the restoring beam
63- 67 F5.1 deg BPA Position angle of the restoring beam
69- 73 I5 mJy St Total clean flux density
75- 79 I5 mJy/beam Sp Peak flux density
81- 83 I3 mJy/beam sigma Off-source rms noise in the residual image
85- 88 F4.2 --- Qual Quality factor of the residual noise in
the image
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Note (1): obtained from the pointing and calibration scan measurements at
Pico Veleta or Plateau de Bure.
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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- 10 A10 --- Source IAU source name, J2000 (JHHMM+DDMM)
12 A1 --- Ep Observing epoch (G1)
14- 15 I2 --- Comp ID number of Gaussian model fit component
17- 21 I5 mJy Stot Total flux density at 87GHz of the component
23- 26 I4 mJy e_Stot rms uncertainty on Stot
28- 31 I4 mJy/beam Speak Peak flux density at 87GHz of the component
33- 36 I4 mJy/beam e_Speak rms uncertainty on Speak
38 A1 --- l_d Limit flag on d
39- 41 I3 uas d ?=- Component size
43- 45 I3 uas e_d ?=- rms uncertainty on d
47- 50 I4 uas r ?=- Component's offset from the core
52- 54 I3 uas e_r ?=- rms uncertainty on r
56- 61 F6.1 deg theta ?=- Position angle of the offset
63- 66 F4.1 deg e_theta ?=- rms uncertainty on theta
68 A1 --- l_Tb Limit flag on Tb
69- 75 F7.3 10+10K Tb Brightness temperature obtained from the
model fits
77- 82 F6.3 10+10K e_Tb ?=- rms uncertainty on Tb
84- 90 F7.3 10+10K Tbmin ?=- Visibility based estimate of the minimum
brightness temperature
92- 99 F8.3 10+10K Tbmax ?=- Visibility based estimate of the maximum
resolved brightness temperature
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Source IAU source name, J2000 (JHHMM+DDMM)
12 A1 --- Ep [ABC] Observing epoch (G1)
14- 22 F9.5 deg RAdeg Right Ascension of center (J2000)
23- 31 F9.5 deg DEdeg Declination of center (J2000)
33- 36 I4 --- Nx Number of pixels along X-axis for
image (FileName1)
38- 41 I4 --- Ny Number of pixels along Y-axis for
image (FileName1)
43- 52 A10 "date" Obs.date Observation date
54- 64 E11.6 Hz Freq Observed frequency
66- 69 I4 Kibyte size1 Size of FITS file for image (FileName1)
71-100 A30 --- FileName1 Name of FITS file for image,
in the subdirectory images
102-127 A26 --- Title1 Title of the FITS file for image (FileName1)
129-132 I4 Kibyte size2 Size of FITS file for visibility (FineName2)
134-164 A31 --- FileName2 Name of FITS file for visibility,
in the subdirectory visib
166-197 A32 --- Title2 Title of the FITS file for visibility
(FileName2)
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Global notes:
Note (G1): Observing epochs as follows:
A = October 2010
B = May 2011
C = October 2011
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Acknowledgements:
Dhanya Nair, dhanya(at)mpifr-bonn.mpg.de
(End) Patricia Vannier [CDS] 21-Jan-2019