ABSTRACT
Optical changing-look Active Galactic Nuclei (AGN) are a class of sources that change type within a short time-scale of years or decades. This change is characterized by the appearance or ...disappearance of broad emission lines, often associated with dramatic AGN continuum flux changes that are orders of magnitude larger than those expected from typical AGN variability. In this work we study for the first time the host galaxy of a changing-look AGN, Mrk 590, using high spatial resolution optical and near-infrared observations. We discover that after ∼10 yr absence, the optical broad emission lines of Mrk 590 have reappeared. The AGN optical continuum flux however is still ∼10 times lower than that observed during the most luminous state in the 1990s. The host galaxy shows a 4.5 kpc radius star-forming ring with knots of ionized and cold molecular gas emission. Extended ionized and warm molecular gas emission is detected in the nucleus, indicating that there is a reservoir of gas as close as 60 pc from the black hole. We observe a nuclear gas spiral between radii r ∼ 0.5 and 2 kpc, which has been suggested as a dynamical mechanism able to drive the necessary gas to fuel AGN. We also discover blue-shifted and high velocity dispersion O iii emission out to a radius of 1 kpc, tracing a nuclear gas outflow. The gas dynamics in Mrk 590 suggest a complex balance between gas inflow and outflow in the nucleus of the galaxy.
ABSTRACT
Mrk 590 is a known changing-look active galactic nuclei (AGNs) which almost turned off in 2012, and then in 2017 partially re-ignited into a repeat flaring state, unusual for an AGN. Our ...Swift observations since 2013 allow us to characterize the accretion-generated emission and its reprocessing in the central engine of a changing-look AGN. The X-ray and UV variability amplitudes are higher than those typically observed in ‘steady-state’ AGN at similar moderate accretion rates; instead, the variability is similar to that of highly accreting AGN. The unusually strong X-ray to UV correlation suggests that the UV-emitting region is directly illuminated by X-ray outbursts. We find evidence that the X-rays are reprocessed by two UV components, with the dominant one at ∼3 d and a faint additional reprocessor at near-zero lag. However, we exclude a significant contribution from diffuse broad line region continuum, known to contribute for bonafide AGN. A near-zero lag is expected for a standard ‘lamp-post’ disc reprocessing model with a driving continuum source near the black hole. That the overall UV response is dominated by the ∼3-d lagged component suggests a complicated reprocessing geometry, with most of the UV continuum not produced in a compact disc, as also found in recent studies of NGC 5548 and NGC 4151. None the less, the observed flares display characteristic time-scales of ∼100 rest-frame days, consistent with the expected thermal time-scale in an accretion disc.
Abstract
We study the host galaxies of four Iron Low-Ionization Broad Absorption-line Quasars (FeLoBALs), using Hubble Space Telescope imaging data, investigating the possibility that they represent ...a transition between an obscured active galactic nucleus (AGN) and an ordinary optical quasar. In this scenario, the FeLoBALs represent the early stage of merger-triggered accretion, in which case their host galaxies are expected to show signs of an ongoing or recent merger. Using PSF subtraction techniques, we decompose the images into host galaxy and AGN components at rest-frame ultraviolet and optical wavelengths. The ultraviolet is sensitive to young stars, while the optical probes stellar mass. In the ultraviolet we image at the BAL absorption trough wavelengths so as to decrease the contrast between the quasar and host galaxy emission. We securely detect an extended source for two of the four FeLoBALs in the rest-frame optical; a third host galaxy is marginally detected. In the rest-frame UV we detect no host emission; this constrains the level of unobscured star formation. Thus, the host galaxies have observed properties that are consistent with those of non-BAL quasars with the same nuclear luminosity, i.e. quiescent or moderately star-forming elliptical galaxies. However, we cannot exclude starbursting hosts that have the stellar UV emission obscured by modest amounts of dust reddening. Thus, our findings also allow the merger-induced young quasar scenario. For three objects, we identify possible close companion galaxies that may be gravitationally interacting with the quasar hosts.
We investigate if the active galactic nucleus (AGN) of Mrk 590, whose supermassive black hole was until recently highly accreting, is turning off due to a lack of central gas to fuel it. We analyse ...new subarcsecond resolution Atacama Large Millimetre/submilllimetre Array maps of the ...CO(3-2) line and 344 GHz continuum emission in Mrk 590. We detect no ...CO(3-2) emission in the inner 150 pc, constraining the central molecular gas mass to M(H...) ... 1.6 x 10... M..., no more than a typical giant molecular gas cloud, for a CO luminosity to gas mass conversion factor of ... ~ 0.8 M...(K km s... pc...)... However, there is still potentially enough gas to fuel the black hole for another 2.6 x 10... yr assuming Eddington-limited accretion. We therefore cannot rule out that the AGN may just be experiencing a temporary feeding break, and may turn on again in the near future. We discover a ring-like structure at a radius of ~1 kpc, where a gas clump exhibiting disturbed kinematics and located just ~200 pc west of the AGN, may be refuelling the centre. Mrk 590 does not have significantly less gas than other nearby AGN host galaxies at kpc scales, confirming that gas reservoirs at these scales provide no direct indication of on-going AGN activity and accretion rates. Continuum emission detected in the central 150 pc likely originates from warm AGN-heated dust, although contributions from synchrotron and free-free emission cannot be ruled out. (ProQuest: ... denotes formulae/symbols omitted.)
Context. A significantly higher incidence of strong (rest equivalent width Wr > 1 Å) intervening Mg ii absorption is observed along gamma-ray burst (GRB) sight-lines relative to those of quasar ...sight-lines. A geometrical explanation for this discrepancy has been suggested: the ratio of the beam size of the source to the characteristic size of an Mg ii absorption system can influence the observed Mg ii equivalent width, if these two sizes are comparable. Aims. We investigate whether the differing beam sizes of the continuum source and broad-line region of Sloan Digital Sky Survey (SDSS) quasars produce a discrepancy between the incidence of strong Mg ii absorbers illuminated by the quasar continuum region and those of absorbers illuminated by both continuum and broad-line region light. Methods. We performed a semi-automated search for strong Mg ii absorbers in the SDSS Data Release 7 quasar sample. The resulting strong Mg ii absorber catalog is available at the CDS. We measured the sight-line number density of strong Mg ii absorbers superimposed on and off the quasar C iv λ 1550 and C iii λ 1909 emission lines. Results. We see no difference in the sight-line number density of strong Mg ii absorbers superimposed on quasar broad emission lines compared to those superimposed on continuum-dominated spectral regions. This suggests that the Mg ii absorbing clouds typically observed as intervening absorbers in quasar spectra are larger than the beam sizes of both the continuum-emitting regions and broad line-emitting regions in the centers of quasars, corresponding to a lower limit of the order of 1017 cm for the characteristic size of an Mg ii absorbing cloud.
In this paper, the authors investigate whether the differing beam sizes of the continuum source and broad-line region of Sloan Digital Sky Survey (SDSS) quasars produce a discrepancy between the ...incidence of strong MgII absorbers illuminated by the quasar continuum region and those of absorbers illuminated by both continuum and broad-line region light. The authors performed a semi-automated search for strong Mg II absorbers in the SDSS Data Release 7 quasar sample. The authors see no difference in the sight-line number density of strong MgII absorbers superimposed on quasar broad emission lines compared to those superimposed on continuum-dominated spectral regions. This suggests that the Mg II absorbing clouds typically observed as intervening absorbers in quasar spectra are larger than the beam sizes of both the continuum-emitting regions and broad line-emitting regions in the centers of quasars, corresponding to a lower limit of the order of 10 super( 17) cm for the characteristic size of an MgII absorbing cloud.
A Doppler broadening positron annihilation technique which allows for the study of near surface defects in bulk samples is described. The method is capable of observing changes in the homogeneous ...bulk defect concentration in a sample and is also able to characterize spatially localized near-surface defects in bulk materials with a resolution of about 1 mm. The applicability of this method is demonstrated by measurements on a sample of polycrystalline aluminum into which defects have been introduced by mechanical deformation. Isochronal annealing studies have been used to characterize the defect recovery in this material and are compared with results of conventional Doppler broadening measurements.
Room temperature
57Fe Mössbauer effect measurements of the one-and two-dimensional quasicrystalline phases of Al
75Pd
15Fe
10 are reported. Both materials show Mössbauer spectra with asymmetric ...doublets which have been analyzed in terms of a distribution of quadrupole splittings, and in terms of a discrete expansion of quadrupole splittings. The one-dimensional material shows the following characteristics compared with the two-dimensional material; (1) a larger mean quadrupole splitting, (2) a more positive mean isomer shift and (3) a broader distribution of quadrupole splittings. These results indicate that the local Fe environments in the one-dimensional material are less isotropic than in the two-dimensional material and that this material is characterized by a higher concentration of open volume defects.
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