Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userChandra Detection of Three X-ray Bright Quasars at z>5
129
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We report Chandra detection of three UV bright radio quiet quasars at $zgtrsim5$. We have collected a sufficient number of photons to extract an X-ray spectrum of each quasar to measure their basic X-ray properties, such as the X-ray flux, power law photon index ($Gamma$), and optical-to-X-ray spectral slope ($alpha_{rm OX}$). J074749+115352 at $z=5.26$ is the X-ray brightest radio-quiet quasar at $z>5$. It may have a short timescale variation (on a timescale of $sim3800rm~s$ in the observers frame, or $sim600rm~s$ in the rest frame) which is however largely embedded in the statistical noise. We extract phase folded spectra of this quasar. There are two distinguishable states: a high soft state with an average X-ray flux $sim2.7$ times of the low hard state, and a significantly steeper X-ray spectral slope ($Gamma=2.40_{-0.32}^{+0.33}$ vs $1.78_{-0.24}^{+0.25}$). We also compare the three quasars detected in this paper to other quasar samples. We find that J074749+115352, with a SMBH mass of $M_{rm SMBH}approx1.8times10^9rm~M_odot$ and an Eddington ratio of $lambda_{rm Edd}approx2.3$, is extraordinarily X-ray bright. It has an average $alpha_{rm OX}=-1.46pm0.02$ and a 2-10 keV bolometric correction factor of $L_{rm bol}/L_{rm2-10keV}=42.4pm5.8$, both significantly depart from some well defined scaling relations. We compare $Gamma$ of the three quasars to other samples at different redshifts, and do not find any significant redshift evolution based on the limited sample of $z>5$ quasars with reliable measurements of the X-ray spectral properties.
rate research
Read More
The X-ray luminosity function of distant (3<z<5.1) unabsorbed quasars has been measured. A sample of distant high-luminosity quasars ($10^{45} leq L_{{rm X},2-10} < 7.5 times 10^{45}$ erg/s in the 2--10 keV energy band) from the catalog given in Khorunzhev et al. (2016) compiled from the data of the 3XMM-DR4 catalog of the XMM-Newton serendipitous survey and the Sloan Digital Sky Survey (SDSS) has been used. This sample consists of 101 sources. Most of them (90) have spectroscopic redshifts $z_{spec}geqslant 3$. The remaining ones are quasar candidates with photometric redshift estimates $z_{phot}geqslant 3$. The spectroscopic redshifts of eight sources have been measured with AZT-33IK and BTA telescopes. Owing to the record sky coverage area ($simeq 250$ sq. deg at X-ray fluxes $sim 10^{-14}$ erg/s/cm$^{2}$ in the 0.5-2 keV), from which the sample was drawn, we have managed to obtain reliable estimates of the space density of distant X-ray quasars with luminosities $L_{{rm X},2-10} > 2 times 10^{45}$ erg/s for the first time. Their comoving space density remains constant as the redshift increases from z=3 to z=5 to within a factor of 2. The power-law slope of the X-ray luminosity function of high-redshift quasars in its bright end (above the break luminosity) has been reliably constrained for the first time. The range of possible slopes for the quasar luminosity and density evolution model is $gamma_2=2.78^{+0.00}_{-0.04}pm0.20$, where initially the lower and upper boundaries of $gamma_2$ with the remaining uncertainty in the detection completeness of X-ray sources in SDSS, and subsequently the statistical error of the slope are specified.
We present new X-ray observations of luminous heavily dust-reddened quasars (HRQs) selected from infrared sky surveys. HRQs appear to be a dominant population at high redshifts and the highest luminosities, and may be associated with a transitional blowout phase of black hole and galaxy co-evolution models. Despite this, their high-energy properties have been poorly known. We use the overall sample of $10$ objects with XMM-Newton coverage to study the high-energy properties of HRQs at $left< L_{rm bol} right> = 10^{47.5}$ erg/s and $left< z right>= 2.5$. For the seven sources with strong X-ray detections, we perform spectral analyses. These find a median X-ray luminosity of $left< L_{rm 2-10,keV} right> = 10^{45.1}$ erg/s, comparable to the most powerful X-ray quasars known. The gas column densities are $N_{rm H}=(1$-$8)times 10^{22}$ cm$^{-2}$, in agreement with the amount of dust extinction observed. The dust to gas ratios are sub-Galactic, but are higher than found in local AGN. The intrinsic X-ray luminosities of HRQs are weak compared to the mid-infrared ($L_{rm 6mu m}$) and bolometric luminosities ($L_{rm bol}$), in agreement with findings for other luminous quasar samples. For instance, the X-ray to bolometric corrections range from $kappa_{rm bol}approx 50$-$3000$. The moderate absorption levels and accretion rates close to the Eddington limit ($left< lambda_{rm Edd} right>=1.06$) are in agreement with a quasar blowout phase. Indeed, we find that the HRQs lie in the forbidden region of the $N_{rm H}$-$lambda_{rm Edd}$ plane, and therefore that radiation pressure feedback on the dusty interstellar medium may be driving a phase of blowout that has been ongoing for a few $10^{5}$ years. The wider properties, including [OIII] narrow-line region kinematics, broadly agree with this interpretation.
Chandra snapshot observations of the three most distant quasars then known, at redshifts 5.82, 5.99, and 6.28, gave signficant detections even in the short, 6 -- 8 ks, observations. The X-ray to optical luminosity ratios indicate that quasars will be detectable in X-rays if they exist at even larger redshifts. The present observations hint at two exciting discoveries. An extended X-ray source 23 arcsec from SDSS1306+0356 may be a jet emitting inverse Compton radiation from the Cosmic Microwave Background. SDSS 1030+0524 does not appear to be a point source, and may be a gravitationally lensed system, or contain a small scale X-ray jet.
We present a comprehensive analysis of Chandra X-ray observations of 15 young radio quasars at redshifts $4.5 < z < 5.0$. All sources are detected in the $0.5-7.0$ keV energy band. Emission spectra are extracted, and the average photon index for the sample is measured to be $1.5pm0.1$. Unabsorbed rest-frame $2-10$ keV luminosities are found to range between $(0.5-23.2) times 10^{45}$ erg s$^{-1}$. The optical-X-ray power-law spectral index $alpha_{ox}$ is calculated for each source using optical/UV data available in the literature. The $alpha_{ox}$-UV relationship is compared with other quasar surveys, and an anticorrelation is observed that agrees with independent estimates. Rest-frame radio and X-ray luminosities are established for the sample, and a correlation between the luminosities is detected. These multiwavelength results reinforce a lack of spectral evolution for quasars over a broad redshift range. We additionally identify three quasars from our multiwavelength analysis that are statistically significant outliers, with one source being a Compton-thick candidate in the early universe, and discuss each in detail.
We present the discovery and properties of DESJ014132.4-542749.9 (DES0141-54), a new powerful radio-loud active galactic nucleus (AGN) in the early Universe (z=5.0). It was discovered by cross-matching the first data release of the Dark Energy Survey (DES DR1) with the Sidney University Molonglo Survey (SUMSS) radio catalog at 0.843 GHz. This object is the first radio-loud AGN at high redshift discovered in the DES. The radio properties of DES0141-54, namely its very large radio-loudness (R>10$^{4}$), the high radio luminosity (L$_{0.8 GHz}$=1.73$times$10$^{28}$ W Hz$^{-1}$), and the flatness of the radio spectrum ($alpha$=0.35) up to very high frequencies (120 GHz in the sources rest frame), classify this object as a blazar, meaning, a radio-loud AGN observed along the relativistic jet axis. However, the X--ray luminosity of DESJ0141-54 is much lower compared to those of the high redshift (z$geq$4.5) blazars discovered so far. Moreover its X-ray-to-radio luminosity ratio (log($frac{L_{[0.5-10]keV}}{L_{1.4GHz}}$)=9.96$pm$0.30 Hz) is small also when compared to lower redshift blazars: only 2% of the low-z population has a similar ratio. By modeling the spectral energy distribution we found that this peculiar X--ray weakness and the powerful radio emission could be related to a particularly high value of the magnetic field. Finally, the mass of the central black hole is relatively small (M$_{BH}$ = 3-8 $times$10$^8$ M$_{odot}$) compared to other confirmed blazars at similar redshift, making DES0141-54 the radio-loud AGN that host the smallest supermassive black hole ever discovered at z$geq$5.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
