NAOJ: Astronomers Rethink Quasar Environment

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NAOJ: Astronomers Rethink Quasar Environment

Post by bystander » Tue Mar 13, 2018 4:45 pm

Double or Nothing: Astronomers Rethink Quasar Environment
National Astronomical Observatory of Japan | Subaru Telescope | 2018 Mar 12

Using Hyper Suprime-Cam (HSC) mounted on the Subaru Telescope, astronomers have identified nearly 200 “protoclusters,” the progenitors of galaxy clusters, in the early universe, about 12 billion years ago, about ten times more than previously known. They also found that quasars don’t tend to reside in protoclusters; but if there is one quasar in a protocluster, there is likely a second nearby. This result raises doubts about the relation between protoclusters and quasars. ...

In order to understand protoclusters in the distant universe a larger observational sample was needed. A team including astronomers from the National Astronomical Observatory of Japan, the University of Tokyo, the Graduate University for Advanced Studies, and other institutes is now conducting an unprecedented wide-field systematic survey of protoclusters using the Subaru Telescope’s very wide-field camera, Hyper Suprime-Cam (HSC). By analyzing the data from this survey, the team has already identified nearly 200 regions where galaxies are gathering together to form protoclusters in the early universe 12 billion years ago.

The team also addressed the relationship between protoclusters and quasars. The team sampled 151 luminous quasars at the same epoch as the HSC protoclusters and to their surprise found that most of those quasars are not close to the overdense regions of galaxies. In fact, their most luminous quasars even avoid the densest regions of galaxies. These results suggest that quasars are not a good proxy for protoclusters and, more importantly, mechanisms other than galactic mergers may be needed to explain quasar activity. Furthermore, since they did not find many galaxies near the brightest quasars, that could mean that hard radiation from a quasar suppresses galaxy formation in its vicinity.

On the other hand, the team found two “pairs” of quasars residing in protoclusters. Quasars are rare, and pairs of them are even rarer. The fact that both pairs were associated with protoclusters suggests that quasar activity is perhaps synchronous in protocluster environments. ...

GOLDRUSH. III. A systematic search for protoclusters at z ∼ 4 based on the >100 deg2 area - Jun Toshikawa et al Luminous quasars do not live in the most overdense regions of galaxies at z ∼ 4 - Hisakazu Uchiyama et al Enhancement of galaxy overdensity around quasar pairs at z < 3.6
based on the Hyper Suprime-Cam Subaru Strategic Program Survey
- Masafusa Onoue et al
PASJ Special Issue: Subaru Hyper Suprime-Cam Survey
  • Publications of the Astronomical Society of Japan, Volume 70, Issue SP1 (Jan 2018)

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