J/A+A/578/A67 AGN in IFRS. VLBA observations (Herzog+, 2015)
Active galactic nuclei cores in infrared-faint radio sources. Very long baseline
interferometry observations using the Very Long Baseline Array.
Herzog A., Middelberg E., Norris R.P., Spitler L.R., Deller A.T.,
Collier J.D., Parker Q.A.
<Astron. Astrophys., 578, A67-67 (2015)>
=2015A&A...578A..67H 2015A&A...578A..67H (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; VLBI ; Radio sources
Keywords: techniques: interferometric - galaxies: active -
galaxies: high-redshift - galaxies: nuclei - radio continuum: galaxies
Abstract:
Infrared-faint radio sources (IFRS) form a new class of galaxies
characterised by radio flux densities between tenths and tens of mJy
and faint or absent infrared counterparts. It has been suggested that
these objects are radio-loud active galactic nuclei (AGNs) at
significant redshifts (z>2). Whereas the high redshifts of IFRS have
been recently confirmed based on spectroscopic data, the evidence for
the presence of AGNs in IFRS is mainly indirect. So far, only two AGNs
have been unquestionably confirmed in IFRS based on very long baseline
interferometry (VLBI) observations. In this work, we test the
hypothesis that IFRS contain AGNs in a large sample of sources using
VLBI. We observed 57 IFRS with the Very Long Baseline Array (VLBA)
down to a detection sensitivity in the sub-mJy regime and detected
compact cores in 35 sources. Our VLBA detections increase the number
of VLBI-detected IFRS from 2 to 37 and provide strong evidence that
most - if not all - IFRS contain AGNs. We find that IFRS have a
marginally higher VLBI detection fraction than randomly selected
sources with mJy flux densities at arcsec-scales. Moreover, our data
provide a positive correlation between compactness - defined as the
ratio of milliarcsec- to arcsec-scale flux density - and redshift for
IFRS, but suggest a decreasing mean compactness with increasing
arcsec-scale radio flux density. Based on these findings, we suggest
that IFRS tend to contain young AGNs whose jets have not formed yet or
have not expanded, equivalent to very compact objects. We found two
IFRS that are resolved into two components. The two components are
spatially separated by a few hundred milliarcseconds in both cases.
They might be components of one AGN, a binary black hole, or the
result of gravitational lensing.
Description:
We selected all IFRS from the catalogue from Collier et al.
(2014MNRAS.439..545C 2014MNRAS.439..545C, Cat. J/MNRAS/439/545) which were located within
1° of a VLBA calibrator. Out of the 1317 IFRS presented by
Collier et al., 110 were found to provide a calibrator which fulfills
the given conditions.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 92 59 Component catalogue of 57 IFRS observed with
the VLBA
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See also:
J/MNRAS/439/545 : Infrared-faint radio sources catalog (Collier+, 2014)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- Name Identifier, FNNNN or FNNNN_N (1)
9- 12 A4 --- --- [NVSS]
14- 27 A14 --- NVSS NVSS name (JHHMMSS+DDMMSS) (2)
29- 30 I2 h RAh FIRST right ascension (J2000) (3)
32- 33 I2 min RAm FIRST right ascension (J2000)
35- 40 F6.3 s RAs FIRST right ascension (J2000)
42 A1 --- DE- FIRST declination sign (J2000) (3)
43- 44 I2 deg DEd FIRST declination (J2000)
46- 47 I2 arcmin DEm FIRST declination (J2000)
49- 53 F5.2 arcsec DEs FIRST declination (J2000)
55- 59 F5.1 mJy SpeakN NVSS peak flux (in mJy/beam) (3)
61- 65 F5.1 mJy SintN NVSS integrated flux (3)
67 A1 --- l_SpeakV Limit flag on SpeakV (4)
68- 72 F5.1 mJy SpeakV VLA peak flux (in mJy/beam) (3)
74- 77 F4.1 mJy SintV ?=- VLA integrated flux (3)
79- 83 F5.1 --- S/N ?=- VLBA signal-to-noise ratio
85- 88 F4.1 mag amaj ?=- Major axis of the VLBA beam
90- 92 F3.1 mag amin ?=- Minor axis of the VLBA beam
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Note (1): If a source is found to be composed of several components in the VLBA
observations, we list the components individually.
Note (2): The NVSS identifier follows the numbering by Collier et al.
(2014, Cat. J/MNRAS/439/545).
Note (3): NVSS and FIRST data are taken from Collier et al.
(2014, Cat. J/MNRAS/439/545).
Note (4): In case of a non-detection, we quote a 6.75σ peak flux density
upper limit.
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 24-Sep-2015