PS J1721+8842: A gravitationally lensed dual AGN system at redshift 2.37 with two radio components

Dual-Active Galactic Nuclei (AGN) are a natural consequence of the hierarchical structure formation scenario, and can provide an important test of various models for black hole growth. However, due to their rarity and difficulty to find at high redshift, very few confirmed dual-AGN are known at the epoch where galaxy formation peaks. Here we report the discovery of a gravitationally lensed dual-AGN system at redshift 2.37 comprising two optical/IR quasars separated by 6.5 ± 0.6 kpc, and a third compact (Reff = 0.45 ± 0.02 kpc) red galaxy that is offset from one of the quasars by 1.7 ± 0.1 kpc. From Very Large Array imaging at 3 GHz, we detect 600 and 340 pc-scale radio emission that is associated with both quasars. The 1.4 GHz luminosity densities of the radio sources are about 1024.35 W Hz−1, which is consistent with weak jets. However, the low brightness temperature of the emission is also consistent with star-formation at the level of 850 to 1150 M⊙ yr−1. Although this supports the scenario where the AGN and/or star-formation is being triggered through an ongoing triple-merger, a post-merger scenario where two black holes are recoiling is also possible, given that neither has a detected host galaxy.

Symbiosis of radio-emitting winds and a jet in a super-Eddington active galactic nucleus

Super-critical accretion is the most powerful episode in nursing the black hole growth and works in several types of objects. Given that the inverse correlation between radio loudness and Eddington ratio, the super-Eddington active galactic nuclei (AGNs) hold the extremely radio-quiet end of AGNs. Regarding the existence of jet in super-Eddington or radio-quiet AGNs, it’s still unclear. Years of studies indicate nearly all types of super-Eddington accreting systems can launch a jet with one exception: no clear evidence to show jet in super-Eddington AGNs. Observations and theoretical works suggest that super-Eddington accretion can drive high-speed wind-like outflows, therefore produce radio emission through synchrotron (shocked wind) and bremsstrahlung mechanisms. However, such a radio-emitting wind has not been observed in super-Eddington systems except for the Galactic micro-quasar SS 433. In principle, high resolution very long baseline interferometry (VLBI) observation can directly map the inner structure of super-Eddington AGNs. Here, we report the discovery of the coupling of jet and radio-emitting winds in a nearby super-Eddington AGN, I Zw1. Its parsec-scale jet exhibits a wiggling, we interpret this as a jet precession. All the features make IZw1 act as a scaled-up version of SS 433. The observations favour that jet can be launched in extremely radio-quiet AGNs and ubiquitous in super-Eddington accreting systems. The jet wiggling or precession can produce a large aperture-angle shock, which emphasises the jet’s contribution to gas feedback. As the jet precession was also discovered in other super-Eddington systems such as SS 433 and V404 Cygni, it is possible that there is a correlation with each other.

The complementary graphene growth and etching revealed by large-scale kinetic Monte Carlo simulation

To fully understand the kinetics of graphene growth, large-scale atomic simulations of graphene islands evolution up to macro sizes (i.e., graphene islands of a few micrometers or with billions of carbon atoms) during growth and etching is essential, but remains a great challenge. In this paper, we developed a low computational cost large-scale kinetic Monte Carlo (KMC) algorithm, which includes all possible events of carbon attachments and detachments on various edge sites of graphene islands. Such a method allows us to simulate the evolution of graphene islands with sizes up to tens of micrometers during either growth or etching with a single CPU core. With this approach and the carefully fitted parameters, we have reproduced the experimentally observed evolution of graphene islands during both growth or etching on Pt(111) surface, and revealed more atomic details of graphene growth and etching. Based on the atomic simulations, we discovered a complementary relationship of graphene growth and etching—the route of graphene island shape evolution during growth is exactly the same as that of the etching of a hole in graphene and that of graphene island etching is exactly same as that of hole growth. The complementary relation brings us a basic principle to understand the growth and etching of graphene, and other 2D materials from atomic scale to macro size and the KMC algorithm is expected to be further developed into a standard simulation package for investigating the growth mechanism of 2D materials on various substrates.

Self-interacting dark matter and the delay of supermassive black hole growth

ABSTRACT Using cosmological hydrodynamic simulations with physically motivated models of supermassive black hole (SMBH) formation and growth, we compare the assembly of Milky Way-mass (Mvir ≈ 7 × 1011 M⊙ at z = 0) galaxies in cold dark matter (CDM) and self-interacting dark matter (SIDM) models. Our SIDM model adopts a constant cross-section of 1 cm2 g−1. We find that SMBH formation is suppressed in the early Universe due to SIDM interactions. SMBH–SMBH mergers are also suppressed in SIDM as a consequence of the lower number of SMBHs formed. Lack of initial merger-driven SMBH growth in turn delays SMBH growth by billions of years in SIDM compared to CDM. Further, we find that this delayed growth suppresses SMBH accretion in the largest progenitors of the main SIDM galaxies during the first 5 Gyr of their evolution. Nonetheless, by z = 0.8 the CDM and SIDM SMBH masses differ only by around 0.2 dex, so that both remain compatible with the MBH–M* relation. We show that the reduced accretion causes the SIDM SMBHs to less aggressively regulate star formation in their host galaxies than their CDM counterparts, resulting in a factor of 3 or more stars being produced over the lifetime of the SIDM galaxies compared to the CDM galaxies. Our results highlight a new way in which SIDM can affect the growth and merger history of SMBHs and ultimately give rise to very different galaxy evolution compared to the classic CDM model.

Unveiling early black hole growth with multifrequency gravitational wave observations

ABSTRACT Third-generation ground-based gravitational wave interferometers, like the Einstein Telescope (ET), Cosmic Explorer, and the Laser Interferometer Space Antenna (LISA), will detect coalescing binary black holes over a wide mass spectrum and across all cosmic epochs. We track the cosmological growth of the earliest light and heavy seeds that swiftly transit into the supermassive domain using a semi-analytical model for the formation of quasars at z = 6.4, 2, and 0.2, in which we follow black hole coalescences driven by triple interactions. We find that light-seed binaries of several $10^2 \, {\rm M_\odot }$ are accessible to ET with a signal-to-noise ratio (S/N) of 10–20 at 6 < z < 15. They then enter the LISA domain with larger S/N as they grow to a few $10^4 \, {\rm M_\odot }$. Detecting their gravitational signal would provide first time evidence that light seeds form, grow, and dynamically pair during galaxy mergers. The electromagnetic emission of accreting black holes of similar mass and redshift is too faint to be detected even for the deepest future facilities. ET will be our only chance to discover light seeds forming at cosmic dawn. At 2 < z < 8, we predict a population of ‘starved binaries’, long-lived marginally growing light-seed pairs, to be loud sources in the ET bandwidth (S/N > 20). Mergers involving heavy seeds (${\sim} 10^5\!-\!10^6 \, {\rm M_\odot }$) would be within reach up to z = 20 in the LISA frequency domain. The lower z model predicts $11.25 \, (18.7)$ ET (LISA) events per year, overall.

X-ray properties of dust-obscured galaxies with broad optical/UV emission lines

ABSTRACT Dust-obscured galaxies (DOGs) with extreme infrared luminosities may represent a key phase in the co-evolution of galaxies and supermassive black holes. We select 12 DOGs at 0.3 ≲ z ≲ 1.0 with broad Mg ii or H β emission lines and investigate their X-ray properties utilizing snapshot observations (∼3 ks per source) with Chandra. By assuming that the broad lines are broadened due to virial motions of broad-line regions, we find that our sources generally have high Eddington ratios (λEdd). Our sources generally have moderate intrinsic X-ray luminosities (LX ≲ 1045 erg s−1), which are similar to those of other DOGs, but are more obscured. They also present moderate outflows and intense starbursts. Based on these findings, we conclude that high-λEdd DOGs are closer to the peaks of both host-galaxy and black hole growth compared to other DOGs, and that (active galactic nucleus) AGN feedback has not swept away their reservoirs of gas. However, we cannot fully rule out the possibility that the broad lines are broadened by outflows, at least for some sources. We investigate the relations among LX, AGN rest-frame 6 μm monochromatic luminosity, and AGN bolometric luminosity, and find the relations are consistent with the expected ones.

Quasar Sightline and Galaxy Evolution (QSAGE) survey – II. Galaxy overdensities around UV luminous quasars at z = 1–2

ABSTRACT We demonstrate that the UV brightest quasars at z = 1–2 live in overdense environments. This is based on an analysis of deep Hubble Space Telescope WFC3 G141 grism spectroscopy of the galaxies along the lines-of-sight to UV luminous quasars in the redshift range z = 1–2. This constitutes some of the deepest grism spectroscopy performed by WFC3, with four roll angles spread over a year of observations to mitigate the effect of overlapping spectra. Of the 12 quasar fields studied, 8 display evidence for a galaxy overdensity at the redshift of the quasar. One of the overdensities, PG0117 + 213 at z = 1.50, has potentially 36 spectroscopically confirmed members, consisting of 19 with secure redshifts and 17 with single-line redshifts, within a cylinder of radius ∼700 kpc. Its halo mass is estimated to be log (M/M⊙) = 14.7. This demonstrates that spectroscopic and narrow-band observations around distant UV bright quasars may be an excellent route for discovering protoclusters. Our findings agree with previous hints from statistical observations of the quasar population and theoretical works, as feedback regulated black hole growth predicts a correlation between quasar luminosity and halo mass. We also present the high signal-to-noise rest-frame optical spectral and photometric properties of the quasars themselves.