Search

We present results of a study of the correlation between the infrared (JHKL) and optical (B) fluxes of the nucleus of the Seyfert galaxy NGC 4151 for the years 2010–2015 using our own data (partially published) in combination with published data of Roberts and Rumstey (2012), Guo et al. (2014) and Schnülle et al. (2013, 2015). We find similar lags for each of the HKL passbands relative to the optical of 37 ± 3 days. The lags are the same to within the accuracy of measurement. We do not confirm a significant decrease in the lag for HKL in 2013–2014 previously reported by Schnülle et al. (2015), but we find that the lag of the short-lag component of J increased. We discuss our results within the framework of the standard model, where the variable infrared radiation is mainly due to the thermal re-emission of short-wave radiation by dust clouds close to a variable central source. There is also some contribution to the IR emission from the accretion disk, and this contribution increases with decreasing wavelength. The variability in J and K is not entirely simultaneous, which may be due to the differing contributions of the radiation from the accretion disk in these bands. The absence of strong wavelength-dependent changes in infrared lag across the HKL passbands can be explained by having the dust clouds during 2010–2015 be located beyond the sublimation radius. The relative wavelength independence of the infrared lags is also consistent with the hollow bi-conical outflow model of Oknyansky et al. (2015). [ABSTRACT FROM AUTHOR]

Optical and near-infrared photometry, optical spectroscopy and soft X-ray and UV monitoring of the changing-look active galactic nucleus NGC 2617 show that it continues to have the appearance of a type-1 Seyfert galaxy. An optical light curve for 2010-2016 indicates that the change of type probably occurred between 2010 October and 2012 February and was not related to the brightening in 2013. In 2016, NGC 2617 brightened again to a level of activity close to that in 2013 April. We find variations in all passbands and in both the intensities and profiles of the broad Balmer lines. A new displaced emission peak has appeared in Hβ. X-ray variations are well correlated with UV-optical variability and possibly lead by ∼2-3 d. The K band lags the J band by about 21.5 ± 2.5 d and lags the combined B + J filters by ∼25 d. J lags B by about 3 d. This could be because J-band variability arises from the outer part of the accretion disc, while K-band variability comes from thermal re-emission by dust.We propose that spectral-type changes are a result of increasing central luminosity causing sublimation of the innermost dust in the hollow bi-conical outflow. We briefly discuss various other possible reasons that might explain the dramatic changes in NGC 2617. [ABSTRACT FROM AUTHOR]

We investigate the torus size–luminosity relation of Type 1 active galactic nuclei (AGNs) based on the reverberation-mapping analysis using the light curves of the optical continuum and the IR continuum obtained with the W1 and W2 bands of the Wide-field Infrared Survey Explorer survey. The final sample consists of 446 and 416 AGNs, respectively, for W1- and W2-band light curves, covering a large dynamic range of bolometric luminosity from 1043.4 to 1047.6 erg s−1, which show reliable lag measurements based on our quality assessment analysis. After correcting for the accretion disk contamination in the observed IR flux, we constrain the torus size (R dust) and AGN bolometric luminosity (L bol) relationship with the best-fit slope of 0.39 (0.33) for the W1 (W2) band, which is shallower than expected from the dust radiation equilibrium model. By combining the previous K -band lag measurements, we find that the measured torus size depends on the observed wavelength of the dust radiation, as R dust, K : R dust,W1: R dust,W2 = 1.0:1.5:1.8 (R dust ∝ λ 0.80) at L bol = 1046 erg s−1, confirming a stratified structure of the torus, where wavelength-dependent emissions originate from distinct regions of the torus. By investigating the deviation from the best-fit torus size–luminosity relation, we find a moderate correlation between the offset from the R dust– L bol relation and Eddington ratio. This suggests a possible influence of the Eddington ratio on the observed flattening of the R dust– L bol relationship. [ABSTRACT FROM AUTHOR]

C/2019 Y4 (ATLAS) is an Oort cloud comet with an orbital period of ∼5895 yr. Starting in 2020 March, its nucleus underwent disintegration. In order to investigate the gas and dust properties of C/2019 Y4 (ATLAS) during its disintegration, we obtained long-slit spectra at 3600–8700 Å and BVRI multiband images with the Xinglong 2.16 m Telescope in 2020 April. Our observations revealed that C/2019 Y4 (ATLAS) exhibited strong emission bands of CN, C2, C3, and NH2, which are superimposed on a dust-scattering continuum, typical of cometary spectra in the optical. The production rates of CN, C2, and C3 derived using the Haser model and the corresponding C2/CN and C3/CN ratios suggest that C/2019 Y4 (ATLAS) is a "typical" Oort cloud comet under the A'Hearn classification, although it appears less dusty, as revealed by the Af ρ quantities. Its dust-scattering reflectivity is slightly red, with a gradient of ∼5% per 103Å. We model the reflectivity gradient in terms of porous dust and find that the red color is accounted for by porous dust. [ABSTRACT FROM AUTHOR]

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 H β compared to z = 2.040 ± 0.003 using Mg ii from the literature, signifying an extreme Mg ii blueshift of 2140 ± 530 km sâˆ'1 relative to H β. Using the H β -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 Ă— 108 M ⊙ and λ Edd ∼ 0.71, indicative of being in a rapidly accreting phase. Our investigations confirm the WLQ nature and the LoBAL â†' 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 âˆ' 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. [ABSTRACT FROM AUTHOR]

We probe the dusty environment of the archetypical Type 1 active galactic nucleus (AGN) in NGC 4151 with comprehensive IR reverberation mapping over several decades, in the J (∼1.22 μm), H (∼1.63 μm), K (∼2.19 μm), L (∼3.45 μm), and N bands (∼10.6 μm), plus multiple measurements at 20–40 μm. At 1–4 μm, the hot dust reverberation signals come from two distinct dust populations at separate radii (∼0.033 pc and ∼0.076 pc), with temperatures of ∼1500–2500 K and ∼900–1000 K, consistent with the expected properties of sublimating graphite and silicate dust grains. The domination of the torus infrared output by carbon and silicate grains near their sublimation temperatures and radii may account for the general similarity of AGN near-IR spectral energy distributions. The torus inner edge defined by the hottest dust remains at roughly the same radius independent of the AGN optical luminosity over ∼25 yr. The emission by hot dust warmed directly by the optical/UV AGN output has increased gradually by ∼4% yr−1, indicating a possibly growing torus. A third dust component at ∼700 K does not seem to participate directly in the IR reverberation behavior, and its emission may originate deep in the circumnuclear torus. We find a reverberation signal at ∼10 μm with an inferred radius for the warm dust of ∼2.2–3.1 pc. The lack of variability at 20–40 μm indicates that the far-IR emission comes from even more extended regions. The torus properties revealed by dust reverberation analysis are inconsistent with predictions from pure clumpy torus models. Instead, the longer-wavelength emission possibly originates in a flared torus or the polar wind. [ABSTRACT FROM AUTHOR]

The size of the dust torus in active galactic nuclei (AGNs) and their high-luminosity counterparts, quasars, can be inferred from the time delay between UV/optical accretion disk continuum variability and the response in the mid-infrared (MIR) torus emission. This dust reverberation mapping (RM) technique has been successfully applied to ∼70 z ≲ 0.3 AGNs and quasars. Here we present first results of our dust RM program for distant quasars covered in the Sloan Digital Sky Survey Stripe 82 region combining ∼20 yr ground-based optical light curves with 10 yr MIR light curves from the WISE satellite. We measure a high-fidelity lag between W1 band (3.4 μm) and g band for 587 quasars over 0.3 ≲ z ≲ 2 () and two orders of magnitude in quasar luminosity. They tightly follow (intrinsic scatter ∼0.17 dex in lag) the IR lag–luminosity relation observed for z < 0.3 AGNs, revealing a remarkable size–luminosity relation for the dust torus over more than four decades in AGN luminosity, with little dependence on additional quasar properties such as Eddington ratio and variability amplitude. This study motivates further investigations in the utility of dust RM for cosmology and strongly endorses a compelling science case for the combined 10 yr Vera C. Rubin Observatory Legacy Survey of Space and Time (optical) and 5 yr Nancy Grace Roman Space Telescope 2 μm light curves in a deep survey for low-redshift AGN dust RM with much lower luminosities and shorter, measurable IR lags. The compiled optical and MIR light curves for 7384 quasars in our parent sample are made public with this work. [ABSTRACT FROM AUTHOR]

Observed extinction curves of active galactic nuclei (AGNs) are significantly different from those observed in the Milky Way. The observations require preferential removal of small grains at the AGN environment; however, the physics for this remains unclear. In this paper, we propose that dust destruction by charging, or Coulomb explosion, may be responsible for AGN extinction curves. Harsh AGN radiation makes a dust grain highly charged through photoelectric emission, and grain fission via Coulomb explosion occurs when the electrostatic tensile stress of a charge grain exceeds its tensile strength. We show that Coulomb explosion can preferentially remove both small silicate and graphite grains and successfully reproduce both flat extinction curve and the absence of 2175 Å bump. [ABSTRACT FROM AUTHOR]

We present the results of a dust-reverberation survey of quasars at redshifts z < 0.6. We found a delayed response of the K-band flux variation after the optical flux variation in 25 out of 31 targets, and obtained the lag time between them for 22 targets. Combined with the results for nearby Seyfert galaxies, we provide the largest homogeneous collection of K-band dust-reverberation data for 36 type 1 active galactic nuclei (AGNs). This doubles the sample and includes the most distant AGN and the largest lag so far measured. We estimated the optical luminosity of the AGN component of each target using three different methods: spectral decomposition, the flux-variation-gradient method, and image decomposition. We found a strong correlation between the reverberation radius for the innermost dust torus and the optical luminosity over a range of approximately four orders of magnitude in luminosity, as is already known for Seyfert galaxies. We estimated the luminosity distances of the AGNs based on their dust-reverberation lags, and found that the data in the redshift–distance diagram are consistent with the current standard estimates of the cosmological parameters. We also present the radius–luminosity relations for isotropic luminosity indicators such as the hard X-ray (14–195 keV), [O IV] 25.89 μm, and mid-infrared (12 μm) continuum luminosities, which are applicable to obscured AGNs. [ABSTRACT FROM AUTHOR]

Dust plays a central role in the unification theory of active galactic nuclei (AGNs). Whether the dust that forms the torus around an AGN is micron-sized, like interstellar grains, or much larger, has a profound impact on correcting for the obscuration of the dust torus to recover the intrinsic spectrum and luminosity of the AGN. Here we show that the ratio of the optical extinction in the visual band () to the optical depth of the 9.7 μm silicate absorption feature () could potentially be an effective probe of the dust size. The anomalously lower ratio of / ≈ 5.5 of AGNs compared to that of the Galactic diffuse interstellar medium of / ≈ 18 reveals that the dust in AGN tori could be substantially larger than the interstellar grains of the Milky Way and those of the Small Magellanic Cloud, and therefore, one could expect a flat extinction curve for AGNs. [ABSTRACT FROM AUTHOR]