4 research outputs found
Impact of the CMB on the evolution of AGNs and their relativisitc jets at the highest redshift
Radio-Loud (RL) Active Galactic Nuclei (AGNs) are among the brightest
astrophysical sources at all wavelengths. Their relativistic jets can affect
both their Supermassive Black Holes (SMBHs) growth and the surrounding
intergalactic medium. While in the radio band these jets can be observed at all
scales (from pc to Mpc scales), their X-ray and {\gamma}-ray emission is
expected to be concentrated on very small scales (<10 pc). However, after the
launch of the Chandra X-ray telescope, several kpc-scale jets were detected and
the mechanism responsible for their high-energy radiation at these scales is
still under debate. Understanding its origin is crucial also to derive the
physical properties of these jets (e.g. the power) at large scales and, as a
consequence, their impact on the environment. In the following, we explore the
Inverse Compton interaction of the relativistic electrons within relativistic
jets with the Cosmic Microwave background photons (IC/CMB) as possible
interpretation. Moreover, we also estimate how this interpretation could also
affect the observed evolution across cosmic times of the SMBHs hosted in jetted
systems.Comment: Published on the Hypatia Colloquium 2022 book of proceeding
The space density of z>4 blazars
High redshift blazars are an important class of Active Galactic Nuclei (AGN)
that can provide an independent estimate of the supermassive black-hole mass
function in high redshift radio-loud AGN without the bias due to absorption
along the line-of-sight. Using the Cosmic Lens All Sky Survey (CLASS) we built
a complete radio flux-limited sample of high redshift (z>4) blazars suitable
for statistical studies. By combining dedicated optical observations and the
SDSS spectroscopic database, we obtained a sample of 26 blazar candidates with
a spectroscopic redshift above 4. On the basis of their radio spectrum we
distinguish between blazars and QSO with a Gigahertz Peaked Spectrum (GPS) like
spectrum. Out of the 18 confirmed blazars 14 constitute a completely
identified, flux-limited sample down to a magnitude of 21 (AB). Using this
complete sample we derive a space density of blazars with 4<z<5.5 of rho=0.13
(+0.05,-0.03) Gpc^-3. This is the first actual estimate of the blazar space
density in this range of redshift. This value is in good agreement with the
extrapolation of the luminosity function and cosmological evolution based on a
sample of flat-spectrum radio quasars selected at lower redshifts and it is
consistent with a cosmological evolution peaking at z2 similar to
radio-quiet QSO. We do not confirm, instead, the presence of a peak at z~4 in
the space density evolution, recently suggested using an X-ray selected sample
of blazars. It is possible that this extreme peak of the evolution is present
only among the most luminous blazars.Comment: 14 pages, accepted for publication on MNRAS
(https://doi.org/10.1093/mnras/sty3526
Minute-timescale Variability in the X-ray Emission of the Highest Redshift Blazar
We report on two Chandra observations of the quasar PSO J0309+27, the most distant blazar observed so far (z = 6.1), performed eight months apart, in 2020 March and November. Previous Swift-XRT observations showed that this object is one of the brightest X-ray sources beyond redshift 6.0 ever observed so far. This new dataset confirmed the high flux level and unveiled a spectral change that occurred on a very short timescale (250 s rest frame), caused by a significant softening of the emission spectrum. This kind of spectral variability, on such a short interval, has never been reported in the X-ray emission of a flat-spectrum radio quasar. A possible explanation for this is given by the emission produced by the inverse Compton scatter of the quasar UV photons by the cold electrons present in a fast shell moving along the jet. Although this bulk Comptonization emission should be an unavoidable consequence of the standard leptonic jet model, this would be the first time that it has been observed
The central engine of the highest redshift blazar
We report on a LUCI/Large Binocular Telescope near-infrared (NIR) spectrum of
PSO J030947.49+271757.31 (hereafter PSO J0309+27), the highest redshift blazar
known to date (z6.1). From the C1549 broad emission line
we found that PSO J0309+27 is powered by a
1.4510M supermassive black hole (SMBH)
with a bolometric luminosity of 810 erg s and an
Eddington ratio equal to 0.44. We also obtained new
photometric observations with the Telescopio Nazionale Galileo in J and K bands
to better constrain the NIR Spectral Energy Distribution of the source. Thanks
to these observations, we were able to model the accretion disk and to derive
an independent estimate of the black hole mass of PSO J0309+27, confirming the
value inferred from the virial technique. The existence of such a massive SMBH
just 900 million years after the Big Bang challenges models of the
earliest SMBH growth, especially if jetted Active Galactic Nuclei are
associated to a highly spinning black hole as currently thought. Indeed, in a
Eddington-limited accretion scenario and assuming a radiative efficiency of
0.3, typical of a fast rotating SMBH, a seed black hole of more than 10
M at z = 30 is required to reproduce the mass of PSO J0309+27 at
redshift 6. This requirement suggests either earlier periods of rapid black
hole growth with super-Eddington accretion and/or that only part of the
released gravitational energy goes to heat the accretion disk and feed the
black hole.Comment: 10 pages, 5 figures, 2 tables; Accepted to publication in A&