Speaker
Description
More than 200 quasars (QSOs) with spectroscopic redshift z > 6 have been discovered so far.
Multi-wavelength observations showed that these objects are evolved systems with large black hole masses ($10^8−10^{10} M_{\odot}$), and that their broad-band spectral energy distributions (SEDs) and rest-frame UV spectra have not significantly evolved over cosmic time.
The formation of their Super Massive Black Holes in less than 1 Gyr is still a challenge for theory, with many simulations claiming they formed at the center of primordial overdense regions.
I will present a study of all the 29 z∼6 QSOs observed so far in the X-rays, showing that the X-ray spectral properties of high-z QSOs do not differ significantly from those of QSOs at lower-z.
I will also present the results from a deep 500 ks Chandra observation of the field around z=6.31 QSO SDSS J1030+0524, which shows the best evidence of an overdense region around a z∼6 QSO. This is the deepest X-ray observation ever achieved for such a distant QSO. Comparing our results with those from previous XMM observation we found a hardening of the X-ray spectrum and a decrease of the flux by a factor 2.5. This is the first evidence of a variable QSO at such high redshift. I will discuss possible interpretations for the observed variability and discuss prospects for future X-ray observations of distant QSOs.
| Affiliation | INAF-OASBo |
|---|---|
| Topic | Active Galactic Nuclei: accretion physics and evolution across cosmic time |
