J/MNRAS/490/2542 Unveiling weak radio quasar population at z≥4 (Perger+, 2019)
Unveiling the weak radio quasar population at z≥4.
Perger K., Frey S., Gabanyi K.E., Toth L.V.
<Mon. Not. R. Astron. Soc., 490, 2542-2549 (2019)>
=2019MNRAS.490.2542P 2019MNRAS.490.2542P (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Redshifts ; Radio sources
Keywords: methods: data analysis - galaxies: active - galaxies: high-redshift -
quasars: general - galaxies: star formation -
radio continuum: galaxies
Abstract:
We applied image stacking on empty field Faint Images of the Radio Sky
at Twenty-Centimeters (FIRST) survey maps centred on optically
identified high-redshift quasars at z≥4 to uncover the hidden µJy
radio emission in these active galactic nuclei (AGN). The median
stacking procedure for the full sample of 2229 optically identified
AGN uncovered an unresolved point source with an integrated flux
density of 52µJy, with a signal-to-noise ratio ∼10. We co-added the
individual image centre pixels to estimate the characteristic
monochromatic radio power at 1.4GHz considering various values for the
radio spectral index, revealing a radio population with
P1.4GHz∼1024W/Hz. Assuming that the entire radio emission
originates from star-forming (SF) activity in the nuclear region of
the host galaxy, we obtained an upper limit on the characteristic star
formation rate, ∼4200M☉/yr. The angular resolution of FIRST
images is insufficient to distinguish between the SF and AGN origin of
radio emission at these redshifts. However, a comparison with
properties of individual sources from the literature indicates that a
mixed nature is likely. Future very long baseline interferometry radio
observations and ultradeep Square Kilometre Array surveys are expected
to be sensitive enough to detect and resolve the central 1-10kpc
region in the host galaxies, and thus discriminate between SF and AGN
related emission.
Description:
The sample for the stacking analysis was defined by using the
high-redshift (z≥4) AGN catalogue by Perger et al.
(2017FrASS...4....9P 2017FrASS...4....9P). We selected optically identified AGN from the
catalogue with positions falling into the FIRST survey footprint. The
flux density of the objects selected is below the detection limit of
the survey (typically ∼1mJy). At the time of the analysis, the total
number of such AGN was 2232. Intensity fluctuations (rms noise) at the
optical AGN positions in the FIRST images vary in the range from tens
of µJy to ~<1mJy. To test an underlying high-redshift radio AGN
population, we stacked FIRST radio maps centred at these positions.
The images in Flexible Image Transport System (FITS) format (Wells,
Greisen & Harten 1981A&AS...44..363W 1981A&AS...44..363W) were obtained from the FIRST
image cut-out service. We downloaded images of 4.5x4.5arcmin2 size
for each individual AGN position. After excluding the largely
incomplete or entirely ragged maps, we obtained 2229 images for the
stacking process. The list of these 2229 AGNs is given in Table 1.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 75 2229 The AGN sample used for the stacking analysis
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 25 A25 --- Name AGN name
27- 28 I2 h RAh Right ascension (J2000)
30- 31 I2 min RAm Right ascension (J2000)
33- 37 F5.2 s RAs Right ascension (J2000)
39 A1 --- DE- Declination sign (J2000)
40- 41 I2 deg DEd Declination (J2000)
43- 44 I2 arcmin DEm Declination (J2000)
46- 50 F5.2 arcsec DEs Declination (J2000)
52- 55 F4.2 --- z Spectroscopic redshift
57- 75 A19 --- ref Literature reference of discovery (bibcode)
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 30-Jan-2023