High-redshift Radio-quiet Quasars Research Articles

Supermassive Black Hole Winds in X-rays -- SUBWAYS. III. A population study on ultra-fast outflows

The detection of blueshifted absorption lines likely associated with ionized iron K-shell transitions in the X-ray spectra of many active galactic nuclei (AGNs) suggests the presence of a highly ionized gas outflowing with mildly relativistic velocities (0.03c - 0.6c) named ultra-fast outflow (UFO). Within the SUBWAYS project, we characterized these winds starting from a sample of 22 radio-quiet quasars at an intermediate redshift (0.1 leq z leq 0.4) and compared the results with similar studies in the literature on samples of local Seyfert galaxies (i.e., 42 radio-quiet AGNs observed with XMM-Newton at z leq 0.1) and high redshift radio-quiet quasars (i.e., 14 AGNs observed with XMM-Newton and Chandra at z geq 1.4). The scope of our work is a statistical study of UFO parameters and incidence considering the key physical properties of the sources, such as supermassive black hole (SMBH) mass, bolometric luminosity, accretion rates, and spectral energy distribution (SED) with the aim of gaining new insights into the UFO launching mechanisms. We find indications that highly luminous AGNs with a steeper X-ray/UV ratio, $ ox $, are more likely to host UFOs. The presence of UFOs is not significantly related to any other AGN property in our sample. These findings suggest that the UFO phenomenon may be transient. Focusing on AGNs with UFOs, other important findings from this work include: (1) faster UFOs have larger ionization parameters and column densities; (2) X-ray radiation plays a more crucial role in driving highly ionized winds compared to UV; (3) the correlation between outflow velocity and luminosity is significantly flatter than what is expected for radiatively driven winds; (4) more massive black holes experience higher wind mass losses, suppressing the accretion of matter onto the black hole; (5) the UFO launching radius is positively correlated with the Eddington ratio. Furthermore, our analysis suggests the involvement of multiple launching mechanisms, including radiation pressure and magneto-hydrodynamic processes, rather than pointing to a single, universally applicable mechanism.

The Impact of Powerful Jets on the Far-infrared Emission of an Extreme Radio Quasar at z ∼ 6

Abstract The interactions between radio jets and the interstellar medium play a defining role for the coevolution of central supermassive black holes and their host galaxies, but observational constraints on these feedback processes are still very limited at redshifts z > 2. We investigate the radio-loud quasar PSO J352.4034–15.3373 at z ∼ 6 at the edge of the Epoch of Reionization. This quasar is among the most powerful radio emitters and the first one with direct evidence of extended radio jets (∼1.6 kpc) at these high redshifts. We analyze NOrthern Extended Millimeter Array and Atacama Large Millimeter/submillimeter Array millimeter data targeting the CO (6–5) and [C ii] far-infrared (FIR) emission lines, respectively, and the underlying continuum. The broad 440 ± 80 km s−1 and marginally resolved [C ii] emission line yields a systemic redshift of z = 5.832 ± 0.001. Additionally, we report a strong 215 MHz radio continuum detection, 88 ± 7 mJy, using the Giant Metrewave Radio Telescope. This measurement significantly improves the constraints at the low-frequency end of the spectral energy distribution of this quasar. In contrast to what is typically observed in high-redshift radio-quiet quasars, we show that cold dust emission alone cannot reproduce the millimeter continuum measurements. This is evidence that the strong synchrotron emission from the quasar contributes substantially to the emission even at millimeter (FIR in the rest-frame) wavelengths. This quasar is an ideal system to probe the effects of radio jets during the formation of a massive galaxy within the first gigayear of the universe.

XMM-NewtonObservations of High-Redshift Quasars

We report on our XMM observations of the high redshift quasars BR 2237--0607 (z=4.558) and BR 0351--1034 (z=4.351), together with 14 other z>4 objects found in the XMM public archive. Contrary to former reports, we do not find high redshift radio-loud quasars to be more absorbed than their radio-quiet counterparts. We find that the optical to X-ray spectral index alpha-ox is correlated with the luminosity density at 2500 A, but does not show a correlation with redshift. The mean 2-10 keV power-law slope of the 9 high redshift radio-quiet quasars in our sample for which a spectral analysis can be performed is alpha-x1.23+-0.48, similar to alpha-x=1.19 found from the ASCA observations of low redshift Narrow-Line Seyfert 1 galaxies (NLS1s), and significantly different from alpha-x=0.78 found for low redshift Broad-Line Seyfert galaxies. While the optical/UV spectra of low to high redshift quasars look remarkably similar, we find a first indication of a difference in their X-ray spectrum. The steep X-ray spectral index suggests high Eddington ratios L/L_Edd. These observations give credence to the hypothesis of Mathur (2000) that NLS1s are low luminosity cousins of high redshift quasars, both likely to be in their early evolutionary stage.

Short-term optical variability of high-redshift quasi-stellar objects

In this paper we present the results of a search for short-term variability in the optical band of selected high-luminosity, high-redshift radio-quiet quasars. Each quasar has been monitored typically for 2–4 h with a time resolution of 2–5 min and a photometric accuracy of about 0.01–0.02 mag. As a result of the significant redshift (z > 2), the covered wavelength range falls into the ultraviolet region (typically 1500–2500 Å). We have found no statistical evidence for any continuum variations larger than 0.01–0.02 mag for any of the monitored objects. Our results suggest that the presence of a short-term variability in radio-quiet quasars is unlikely even in the ultraviolet region, contrary to reports by other authors. This conclusion holds true at least for high-luminosity (large black hole mass and accretion rate?) objects. The results are consistent with the idea that significant short-term (less than 1 h) variations in active galactic nuclei, where observed, should be attributed primarily to processes in a relativistic jet.

High-Redshift X-Ray–Selected Quasars: CXOCY J125304.0−090737 Joins the Club

We present a new X-ray selected high redshift quasar CXOCY J125304.0-090737 at z=4.179, discovered by the Calan-Yale Deep Extragalactic Research (CYDER) Survey. This quasar is the fifth X-ray selected high redshift radio quiet quasar ($z>4$) found so far. Here, we present its observed properties which are characterized by its relative optical and X-ray faintness, its X-ray hardness and its X-ray strength compared to optically selected quasars at high redshift. We also compare the X-ray selected high redshift radio quiet quasars to their optically selected counterparts. We find that the optical to X-ray spectral slope, $\alpha_{ox}$, is statistically harder (more X-ray luminous) for the X-ray selected radio quiet quasars than for the optically selected ones. This result, given the different range of rest frame ultraviolet luminosities studied and the selection of the samples, is consistent with the previously found correlation between X-ray and rest frame ultraviolet luminosities and would extend that result to a much wider luminosity range at high redshift. Finally, we discuss the prospects of unveiling the quasar luminosity function at high redshifts using X-ray surveys. The discovery of a high redshift object in the first field of our survey program provides suggestive evidence that X-ray selected surveys may identify more such objects than would be expected from an extrapolation of the optical luminosity function.

X-ray spectral evolution of high redshift quasars

At z approx. equals 3, the x-ray spectra of radio-loud and radio-quiet quasars are different. High-redshift radio-quiet quasars either have large absorbing columns, N(sub H), and steeper power law spectral indices, alpha(sub epsilon), than low redshift quasars, or no absorption and similar alpha(sub epsilon)'s. In contrast, the radio-loud quasars at high redshift have substantial absorption and similar alpha(sub epsilon)'s to low redshift quasars. Implications for the interpretation of the evolution of the luminosity function of quasars are discussed. If the absorption arises outside the central engine for both radio-loud and radio-quiet quasars, then radio-quiet quasars differ from the radio-loud quasars in that their emitted power law spectrum has evolved with redshift. We argue that this favors models where quasars are numerous and short-lived, rather than rare and long-lived.