2021A&A...647A...5W


Query : 2021A&A...647A...5W

2021A&A...647A...5W - Astronomy and Astrophysics, volume 647A, 5-5 (2021/3-1)

First constraints on the AGN X-ray luminosity function at z ∼ 6 from an eROSITA-detected quasar.

WOLF J., NANDRA K., SALVATO M., LIU T., BUCHNER J., BRUSA M., HOANG D.N., MOSS V., ARCODIA R., BRUGGEN M., COMPARAT J., DE GASPERIN F., GEORGAKAKIS A., HOTAN A., LAMER G., MERLONI A., RAU A., ROTTGERING H.J.A., SHIMWELL T.W., URRUTIA T., WHITING M. and WILLIAMS W.L.

Abstract (from CDS):


Context. High-redshift quasars signpost the early accretion history of the Universe. The penetrating nature of X-rays enables a less absorption-biased census of the population of these luminous and persistent sources compared to optical/near-infrared colour selection. The ongoing SRG/eROSITA X-ray all-sky survey offers a unique opportunity to uncover the bright end of the high-z quasar population and probe new regions of colour parameter space.
Aims. We searched for high-z quasars within the X-ray source population detected in the contiguous ∼140deg2 field observed by eROSITA during the performance verification phase. With the purpose of demonstrating the unique survey science capabilities of eROSITA, this field was observed at the depth of the final all-sky survey. The blind X-ray selection of high-redshift sources in a large contiguous, near-uniform survey with a well-understood selection function can be directly translated into constraints on the X-ray luminosity function (XLF), which encodes the luminosity-dependent evolution of accretion through cosmic time.
Methods. We collected the available spectroscopic information in the eFEDS field, including the sample of all currently known optically selected z>5.5 quasars and cross-matched secure Legacy DR8 counterparts of eROSITA-detected X-ray point-like sources with this spectroscopic sample.
Results. We report the X-ray detection of eFEDSU J083644.0+005459, an eROSITA source securely matched to the well-known quasar SDSS J083643.85+005453.3 (z=5.81). The soft X-ray flux of the source derived from eROSITA is consistent with previous Chandra observations. The detection of SDSS J083643.85+005453.3 allows us to place the first constraints on the XLF at z>5.5 based on a secure spectroscopic redshift. Compared to extrapolations from lower-redshift observations, this favours a relatively flat slope for the XLF at z∼6 beyond L*, the knee in the luminosity function. In addition, we report the detection of the quasar with LOFAR at 145 MHz and ASKAP at 888 MHz. The reported flux densities confirm a spectral flattening at lower frequencies in the emission of the radio core, indicating that SDSS J083643.85+005453.3 could be a (sub-) gigahertz peaked spectrum source. The inferred spectral shape and the parsec-scale radio morphology of SDSS J083643.85+005453.3 indicate that it is in an early stage of its evolution into a large-scale radio source or confined in a dense environment. We find no indications for a strong jet contribution to the X-ray emission of the quasar, which is therefore likely to be linked to accretion processes.
Conclusions. Our results indicate that the population of X-ray luminous AGNs at high redshift may be larger than previously thought. From our XLF constraints, we make the conservative prediction that eROSITA will detect ∼90 X-ray luminous AGNs at redshifts 5.7<z<6.4 in the full-sky survey (De+RU). While subject to different jet physics, both high-redshift quasars detected by eROSITA so far are radio-loud; a hint at the great potential of combined X-ray and radio surveys for the search of luminous high-redshift quasars.

Abstract Copyright: © J. Wolf et al. 2021

Journal keyword(s): quasars: individual: SDSS J083643.85+005453.3 - galaxies: high-redshift - X-rays: galaxies

Status at CDS : Examining the need for a new acronym.

Simbad objects: 8

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Number of rows : 8
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
#notes
1 SDSS J010013.02+280225.8 QSO 01 00 13.0246669824 +28 02 25.791716364           ~ 111 0
2 PSO J047.4478+27.2992 Bla 03 09 47.44 +27 17 57.6           ~ 27 0
3 NAME Chandra Deep Field-South reg 03 32 28.0 -27 48 30           ~ 2001 1
4 NAME Extended Chandra Deep Field South reg 03 32 30.0 -27 48 20           ~ 728 0
5 SDSS J083643.85+005453.3 QSO 08 36 43.8598536120 +00 54 53.233681320   26.19 24.17     ~ 139 0
6 NAME Chandra Deep Field-North reg 12 36.8 +62 13           ~ 648 0
7 CFHQS J142952+544717 QSO 14 29 52.17 +54 47 17.7           ~ 44 0
8 2MASSI J1459584+333701 Sy1 14 59 58.4360286288 +33 37 01.776245988   16.89 16.70 16.5   ~ 55 0

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2023.01.27-22:03:57

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