A Quasar Shedding Its Dust Cocoon at Redshift 2

Abstract

We present the first near-IR spectroscopy and joint analyses of multiwavelength observations for SDSS J082747.14+425241.1, a dust-reddened, weak broad emission-line quasar (WLQ) undergoing a remarkable broad-absorption line (BAL) transformation. The systemic redshift is more precisely measured to be z = 2.070 ± 0.001 using Hβ compared to z = 2.040 ± 0.003 using Mg ii from the literature, signifying an extreme Mg ii blueshift of 2140 ± 530 km s−1 relative to Hβ. Using the Hβ-based single-epoch scaling relation with a systematic uncertainty of 0.3 dex, its black hole (BH) mass and Eddington ratio are estimated to be M BH ∼ 6.1 × 108 M ⊙ and λ Edd ∼ 0.71, indicative of being in a rapidly accreting phase. Our investigations confirm the WLQ nature and the LoBAL → HiBAL transformation, along with a factor of 2 increase in the Mg ii+Fe ii emission strength and a decrease of 0.1 in E(B − V) over two decades. The kinetic power of this LoBAL wind at R ∼ 15 pc from its BH is estimated to be ∼43% of the Eddington luminosity, sufficient for quasar feedback upon its host galaxy albeit with an order-of-magnitude uncertainty. This quasar provides a clear example of the long-sought scenario where LoBAL quasars are surrounded by dust cocoons, and wide-angle nuclear winds play a key role in the transition of red quasars evolving into the commonly seen blue quasars.

Quasar Winds Caught on Acceleration and Deceleration

“…J0136 shows kinematic acceleration signatures traced by both the C IV and Al III BAL troughs, in which the latter completely disappeared by MJD 59516 characteristic of a LoBAL → HiBAL transformation in tandem with the acceleration. Examining the MJD versus f 1700 panel, the continuum flux density at λ rest = 1700 Å brightened by a factor of ∼2 during the BAL transformation, a variability pattern that was also reported in another LoBAL quasar undergoing the same transformation (Yi et al 2022). However, the variability relation between velocity shift and continuum flux is unclear for J0136, given both the same and opposite trends observed over different time intervals, such that the largest velocity shift occurred in the interval with no or smallamplitude continuum variability, while the largest-amplitude continuum variability was detected in the interval having only a small velocity shift along with the Mg II BAL disappearance.…”

“…J0136 is the only one among the four quasars undergoing a LoBAL → HiBAL transformation and becoming brighter/ bluer in the rest-frame UV band at later epochs. Interestingly, such a time-variability trend is also seen in six LoBAL quasars that were caught in a LoBAL → HiBAL transformation (Yi & Timlin 2021); in particular, the C IV, Al III, and Mg II BALvariability trends in J0136 resemble closely another LoBAL quasar (J0827) that was captured in shedding its dust cocoon, despite the emergence of a new C IV BAL in J0827 (see Figure 4 in Yi et al 2022). Given the persistence of the BAL in J0136 and the LoBAL → HiBAL → non-BAL evolutionary path proposed in Yi & Timlin (2021), we argue that the SED of J0136 will become increasingly bluer/brighter, and ultimately, like the vast majority of non-BAL blue quasars, will peak at the rest-frame UV band as time passes.…”

“…The near-IR spectrum of J0136 at MJD 59503 exhibits strong Fe II and weak Hβ emission (see left panels of Figure 9). Following Yi et al (2022), we use a model with two Gaussians and one Fe II component to fit the Hα and Hβ lines. Our spectral fit reveals that the Hα/Hβ emission can be well fitted by two/one Gaussians, when their FWHMs are tied to each other and the Hα/Hβ flux ratio is constrained within a range between 2.9 and 3.5 for one set of the Gaussians during the fit.…”

“…As introduced above, time variability has become a widely used tool for probing the formation, acceleration, and evolution of BAL winds, due primarily to the fact that the vast majority of quasars and their host galaxies cannot be spatially resolved by current instruments. Generally, well-separated, multiepoch spectroscopy is a powerful technique for identifying genuine cases of BAL acceleration and for placing valuable constraints on the BAL physics, lifetime, and location (e.g., Aromal et al 2021;Yi et al 2022). In reality, however, BAL acceleration and BAL-profile variability may occur simultaneously, making a firm identification of BAL acceleration difficult or sometimes impossible, even with the aid of longterm, high-quality, and high-cadence sampling spectra (e.g., Kriss et al 2019;Yi & Timlin 2021;Byun et al 2022).…”

Changing-look Active Galactic Nuclei from the Dark Energy Spectroscopic Instrument. I. Sample from the Early Data

“…This could indicate that dust is being removed from these systems, which may be evidence that these AGNs are undergoing a "blow-out" phase, in which powerful outflows clear out the surrounding gas/dust (Glikman et al 2017;Fawcett et al 2022;Stacey et al 2022). Using spectroscopy over a 19 yr period, Yi et al (2022) discovered a turn-on CL AGN that hosted powerful outflows, concluding that the quasar was shedding a surrounding dust cocoon, transitioning to a blue quasar. However, it is still unclear whether changes in accretion disk could account for the change in continuum flux and also whether the difference in the dust extinction values over a 10-20 yr timescale is consistent with a blow-out phase.…”