1. L B V I The highest redshift radio quasars with the highest resolution
Sándor Frey
(FÖMI Satellite Geodetic
Observatory, Hungary)
In collaboration with:
Leonid I. Gurvits (JIVE, NL)
Zsolt Paragi (JIVE, NL)
Krisztina Gabányi (FÖMI SGO, HU)
Dávid Cseh (Radboud Univ. Nijmegen, NL)
and more… L B V I
EVN Mini-symposium
30 June 2015
Институт прикладной астрономии РАН,
Санкт-Петербург

2. Quasars at z~6 became known quite recently (in the last ~15 years)
A brief introduction
Quasars at z~6 became known quite recently (in the last ~15 years)
First discoveries in the
Sloan Digital Sky Survey (SDSS)
To date, there are ~80 quasars
known at z~6; the record holder is at z=7.1
Most of the observed properties (e.g. metallicity, emission line strength, BH mass) are very similar to those of quasars at low redshifts
But: hot-dust-free quasars (2 out if 21) found
– they may represent the first generation
Apparently not all of the earliest quasars we see are completely evolved objects (lack of the dusty structures around the accretion disk)
Fan et al. (2001, 2003, 2004, 2006)
e.g. Willott et al. (2007, 2010)
Mortlock et al. (2011)
Jiang et al. (2010)

3. For comparison, ~8% of all SDSS quasars have FIRST radio counterparts
Radio quasars at z~6
Among the known z~6 quasars, only 4 are ”strong” continuum radio sources
For comparison, ~8% of all SDSS quasars have FIRST radio counterparts
Ivezić et al. (2002)
If the radio emission is compact, it should come from an AGN:
synchrotron jet in the vicinity of the central SMBH
This can be tested with Very Long Baseline Interferometry (VLBI) imaging

4. FIRST (VLA, 1.4 GHz) radio imageJ
z=5.77
Fan et al. (2001)
FIRST (VLA, 1.4 GHz) radio image
Weak (~1 mJy) radio sources
 VLBI imaging is challenging

5. example: Parkes Half-Jansky Flat-Spectrum Sample
SDSS J : luminosity
L5 = 1025 W Hz-1 sr-1
z=5.774
example: Parkes Half-Jansky Flat-Spectrum Sample
Jarvis & McLure (2002)

6. 1.6 GHz 5 GHz 20 mas 10 mas peak: 770 µJy/beam peak: 333 µJy/beam
1 mas angular size corresponds to ~6 pc linear size at around this z
compact but somewhat resolved structure
radio emission is confined to the central few tens of parsecs
steep radio spectrum (α = -0.8) , no indication of strong relativistic beaming
Frey et al. (2003, 2005)

7. 1.6 GHz 5 GHz J1427+3312 z=6.12 160 pc peak: 167 μJy/beam
McGreer et al. (2006); Stern et al. (2007)
5 GHz
160 pc
peak: 167 μJy/beam
peak: 460 μJy/beam
Frey et al. (2008);
Momjian et al. (2008)

8. J :
double structure seen at the lower frequency
again, compact but resolved (~ K brightness temperatures)
comparison with lower-resolution VLA & WRST data:
no significant ”missing” flux density, the total radio emission is also detected with VLBI
again, steep radio spectrum (α = -0.6)
The source is remarkably similar to the Compact Symmetric Objects (CSOs), known typically at z<1
Those are really young (up to ~104 yr) ”baby” radio AGNs
Their (kinematic) age is derived from the separation speed
Is our z>6 quasar a newborn radio AGN? – could be verified with VLBI monitoring over the time scale of decades

9. 5 GHz 1.6 GHz J1429+5447 z=6.21 20 pc peak: 0.67 mJy/beam
Willott et al. (2010)
5 GHz
1.6 GHz
20 pc
peak: 0.67 mJy/beam
peak: 2.32 mJy/beam
EVN images: similar compactness, steep spectrum
Frey et al. (2011)
EF022A was the very first EVN user experiment when Zelenchukskaya and Badary participated! (2010/2 session, L band, May 27)

10. A comparison of the z~6 sources with a famous CSO (J0713+4349)
Radio spectra
A comparison of the z~6 sources with a famous CSO (J )
Owsianik & Conway (1998)
Rest-frame frequencies
For J (z=0.52), the spectral data points taken from the NED, and scaled down to match the luminosity distance of the high-redshift quasars

11. found in the SDSS Stripe 82 area an even fainter radio source
z=5.95 J
found in the SDSS Stripe 82 area
an even fainter radio source
Zeimann et al. (2011)
VLA A-array image
Hodge et al. (2011)

12. EVN 1.6 GHz:
successful detection, with 0.3 mJy flux density (similar to the VLA value)
A feasibility test of the multi-phase-centre correlation technique with the EVN
Bd, Sv, Zc participated
(2011 Nov 1)
Cao et al. 2014

13. Summary
Among the known z~6 quasars, <10% is radio-emitting
The 4 imaged with high angular resolution show compact but resolved radio structures at ~ pc linear scales – no blazars
Their radio spectra are steep
One of them (at z=6.12) is double, and reminds us to the CSOs (very young radio AGNs at low redshifts)
The highest-resdhift radio quasars are still very rare
There must be a lot more, just waiting for discovery…

14. the first estimate of radio jet proper motion in a blazar at z>5
Bonus slides:
the first estimate of radio jet proper motion in a blazar at z>5
Confirmed blazars at extremely high redshifts (z>5) are very rare: there are only 4 known at present
The second most distant one is J at z=5.266
This source is unique at such a high redshift because it has a prominent radio jet
Frey et al. 2015

15. Apparent superluminal speeds (11 – 14c)
VLBA, 2006 Jan 28
Helmboldt et al. 2007
Over >7 years, component motions could be revealed (0.09 – 0.11 mas/yr)
Apparent superluminal speeds
(11 – 14c)
The moderate component proper motions are consistent with the cosmological interpretation of redshifts
Frey et al. 2015
EVN, 2013 May 28 (with Bd, Sv, Zc)