Astronomers discover two bright high-redshift quasars

An artistic rendering of a quasar. Credit: Robin Dienel /
Carnegie Institution for Science.

Using VST ATLAS and WISE surveys astronomers have identified
two new bright high-redshift quasars. The newly found
quasi-stellar objects, designated VST-ATLAS J158.6938-14.4211
and VST-ATLAS J332.8017-32.1036, could be helpful in
improving our understanding of the evolution of the universe.
The finding is reported March 4 in a paper published on

Quasars with high redshift (over 6.0) are of special interest
for astronomers because their ultraviolet light is absorbed by
the neutral hydrogen along the line of sight; thus, they can be
used to probe the intergalactic medium in the . They are the most luminous and
most distant, compact objects in the observable universe.

The spectrum of high-redshift quasars can be used to estimate
the mass of a , which constrains
the evolution and formation model of a quasar. Therefore, such
objects could serve as powerful tools to probe the early

However, high-redshift quasars are very difficult to find using
conventional color selections. This is due to their low spatial
density and high contaminants from cool dwarfs. Among more than
300,000 quasars discovered to date, only 290 of them are at
redshift higher than 5.0.

Now, a team of astronomers led by Ben Chehade of the Durham
University, UK, has found two new high-redshift quasars by
using the combination of the new Very Large Telescope Survey
Telescope ATLAS (VST ATLAS) and Wide-field Infrared Survey
Explorer (WISE). The detection was confirmed by follow-up
spectroscopic observations utilizing the Low Resolution Imaging
Spectrometer on the Keck I telescope and the European Southern
Observatory’s Faint Object Spectrograph and Camera 2 (EFOSC2)
on the 3.58m ESO New Technology Telescope (NTT).

“Here we report on our continued search for 5.7 2 of the
Southern Hemisphere. We have found two further z > 6
quasars, VST-ATLAS J158.6938-14.4211 at z = 6.07 and
J332.8017-32.1036 at z = 6.32,” the researchers wrote in the

As noted in the study, VST-ATLAS J158.6938-14.4211 (J158-14 for
short) has a redshift of 6.07, while VST-ATLAS
J332.8017-32.1036 (J332-32 for short) was found at a redshift
of 6.32. J158-14 and J332-32 have magnitudes of 19.4 and 19.7

Moreover, the researchers have conducted a preliminary estimate
of the black hole masses powering the two quasars. According to
the paper, J158-14 has a black hole with a mass of about 1.8
billion solar masses and when it comes to J332-32, its black
hole is approximately two billion times more massive than the

The astronomers noted that a more detailed analysis of black
hole masses of the two quasars will be published in another
research paper. However, the currently available preliminary
data, combined with previous studies, allowed Chehade’s team to
conclude that quasars identified by ATLAS survey are close to
having some of the most massive so far discovered.

Explore further:

High-redshift quasar discovered by Pan-STARRS

More information: Two more, bright, z > 6 quasars
from VST ATLAS and WISE, arXiv:1803.01424 [astro-ph.GA]

Recently, Carnall et al. discovered two bright high redshift
quasars using the combination of the VST ATLAS and WISE
surveys. The technique involved using the 3-D colour plane
i-z:z-W1:W1-W2 with the WISE W1 (3.4 micron) and W2 (4.5
micron) bands taking the place of the usual NIR J band to help
decrease stellar dwarf contamination. Here we report on our
continued search for 5.76 quasars, VST-ATLAS J158.6938-14.4211
at z=6.07 and J332.8017-32.1036 at z=6.32 with magnitudes of
z_AB=19.4 and 19.7 mag respectively. J158.6938-14.4211 was
confirmed by Keck LRIS observations and J332.8017-32.1036 was
confirmed by ESO NTT EFOSC-2 observations. Here we present VLT
X-shooter Visible and NIR spectra for the four ATLAS quasars.
We have further independently rediscovered two z>5.7 quasars
previously found by the VIKING/KiDS and PanSTARRS surveys. This
means that in ATLAS we have now discovered a total of six
quasars in our target 5.7

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