分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: The correlation between the mass of supermassive black holes (SMBHs; $\mathcal{M}_{\rm BH}$) and their host galaxies ($\mathcal{M}_\star$) in the reionization epoch provides valuable constraints on their early growth. High-redshift quasars typically have a $\mathcal{M}_{\rm BH}$/$\mathcal{M}_\star$ ratio significantly elevated in comparison to the local value. However, the degree to which this apparent offset is driven by observational biases is unclear for the most distant quasars. To address this issue, we model the sample selection and measurement biases for a compilation of 20 quasars at $z\sim6$ with host properties based on ALMA observations. We find that the observed distribution of quasars in the $\mathcal{M}_{\rm BH} - \mathcal{M}_\star$ plane can be reproduced by assuming that the underlying SMBH population at $z\sim6$ follows the relationship in the local universe. However, a positive or even a negative evolution in $\mathcal{M}_{\rm BH}$/$\mathcal{M}_\star$ can also explain the data, depending on whether the intrinsic scatter evolves and the strength of various systematic uncertainties. To break these degeneracies, an improvement in the accuracy of mass measurements and an expansion of the current sample to lower $\mathcal{M}_{\rm BH}$ limits are needed. Furthermore, assuming a radiative efficiency of 0.1 and quasar duty cycles estimated from the active SMBH fraction, significant outliers in $\mathcal{M}_{\rm BH}$/$\mathcal{M}_\star$ tend to move toward the local relation given their instantaneous BH growth rate and star formation rate. This may provide evidence for a self-regulated SMBH-galaxy coevolution scenario that is in place at $z\sim6$, with AGN feedback being a possible driver.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: The relationship between quasars and their host galaxies provides clues on
how supermassive black holes (SMBHs) and massive galaxies are jointly
assembled. To elucidate this connection, we measure the structural and
photometric properties of the host galaxies of ~5000 SDSS quasars at 0.2
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: This study aims at identifying luminous quasars at $z>5.7$ among X-ray-selected sources in the eROSITA Final Equatorial-Depth Survey (eFEDS) in order to place a lower limit on black hole accretion well into the epoch of re-ionisation. We confirm the low significance detection with eROSITA of a previously known, optically faint $z=6.56$ quasar from the Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs) survey. We obtained a pointed follow-up observation of the source with the Chandra X-ray telescope in order to confirm the eROSITA detection. Using new near-infrared spectroscopy, we derived the physical properties of the super-massive black hole. Finally, we used this detection to infer a lower limit on the black hole accretion density rate at $z>6$. The Chandra observation confirms the eFEDS source as the most distant blind X-ray detection to date. The derived X-ray luminosity is high with respect to the rest-frame optical emission of the quasar. With a narrow MgII line, low derived black hole mass, and high Eddington ratio, as well as its steep photon index, the source shows properties that are similar to local narrow-line Seyfert 1 galaxies, which are thought to be powered by young super-massive black holes. In combination with a previous high-redshift quasar detection in the field, we show that quasars with $L_{2-10 \, \mathrm{keV}} >10^{45} \, \mathrm{erg \, s^{-1}}$ dominate accretion onto super-massive black holes at $z\sim 6$.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We construct the eROSITA X-ray catalog of radio galaxies discovered by the
WERGS survey that is made by the cross-matching of the wide-area Subaru/HSC
optical survey and VLA/FIRST 1.4 GHz radio survey. We find 393 eROSITA detected
radio galaxies in the 0.5--2 keV band in the eFEDS field covering 140~deg$^2$.
Thanks to the wide and medium depth eFEDS X-ray survey, the sample contains the
rare and most X-ray luminous radio galaxies above the knee of the X-ray
luminosity function, spanning 4422$. Those obscured
and radio AGN reside in $0.4
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We report on a spectroscopic program to search for dual quasars using Subaru Hyper Suprime-Cam (HSC) images of SDSS quasars which represent an important stage during galaxy mergers. Using Subaru/FOCAS and Gemini-N/GMOS, we identify three new physically associated quasar pairs having projected separations less than 20 kpc, out of 26 observed candidates. These include the discovery of the highest redshift ($z=3.1$) quasar pair with a separation $<$ 10 kpc. Based on the sample acquired to date, the success rate of identifying physically associated dual quasars is $19\%$ when excluding stars based on their HSC colors. Using the full sample of six spectroscopically confirmed dual quasars, we find that the black holes in these systems have black hole masses ($M_{BH} \sim 10^{8-9}M_{\odot}$) similar to single SDSS quasars as well as their bolometric luminosities and Eddington ratios. We measure the stellar mass of their host galaxies based on 2D image decomposition of the five-band ($grizy$) optical emission and assess the mass relation between supermassive black holes (SMBHs) and their hosts. Dual SMBHs appear to have elevated masses relative to their host galaxies. Thus mergers may not necessarily align such systems onto the local mass relation, as suggested by the Horizon-AGN simulation. This study suggests that dual luminous quasars are triggered prior to the final coalescence of the two SMBHs, resulting in early mass growth of the black holes relative to their host galaxies.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: The existence of high-redshift supermassive black holes (SMBHs) -- shining brightly as quasars during the first billion years of our universe -- presents a conundrum in astrophysics. A broad variety of physical mechanisms have been proposed for the formation and rapid growth of these early SMBHs. Promising diagnostics are the relative properties of the black hole and its host galaxy. However, up to now, the detection of stars in quasar host galaxies has been elusive beyond $z>2$, even with deep HST observations. Here, we report the first detections of the stellar component of the host galaxies of two relatively low-luminosity quasars at $z>6$ observed with JWST using NIRCam. After modeling and subtracting the glare from the quasar itself, we find that the host galaxies are massive (stellar mass of $2.5\times$ and $6.3\times10^{10}$ M$_{\odot}$), compact, and disk-like. Unlike most SMBHs in the nearby universe, these quasars are displaced from the centers of their host galaxies in the rest-frame optical, in one case by $0.9$ kpc. These first positive detections of quasar hosts at $z>6$ are a pivotal milestone; we can now assess the stellar environment along with star formation and black hole accretion to determine the physical conditions that govern the formation and evolution of the first SMBHs.