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  1. Abstract We perform a systematic survey of active galactic nuclei (AGNs) continuum lags using ∼3 days cadence gri -band light curves from the Zwicky Transient Facility. We select a sample of 94 type 1 AGNs at z < 0.8 with significant and consistent inter-band lags based on the interpolated cross-correlation function method and the Bayesian method JAVELIN . Within the framework of the “lamp-post” reprocessing model, our findings are: (1) The continuum emission (CE) sizes inferred from the data are larger than the disk sizes predicted by the standard thin-disk model. (2) For a subset of the sample, the CE size exceeds the theoretical limit of the self-gravity radius (12 lt-days) for geometrically thin disks. (3) The CE size scales with continuum luminosity as R CE ∝ L 0.48±0.04 with a scatter of 0.2 dex, analogous to the well-known radius–luminosity relation of broad H β . These findings suggest a significant contribution of diffuse continuum emission from the broad-line region (BLR) to AGN continuum lags. We find that the R CE – L relation can be explained by a photoionization model that assumes ∼23% of the total flux comes from the diffuse BLR emission. In addition, the ratio of themore »CE size and model-predicted disk size anticorrelates with the continuum luminosity, which is indicative of a potential nondisk BLR lag contribution evolving with the luminosity. Finally, a robust positive correlation between the CE size and black hole mass is detected.« less
    Free, publicly-accessible full text available November 1, 2023
  2. Abstract In order to constrain the size of the optical continuum emission region in the dwarf Seyfert 1 galaxy NGC 4395 through reverberation mapping, we carried out high-cadence photometric monitoring in the griz filter bands on two consecutive nights in 2022 April using the four-channel MuSCAT3 camera on the Faulkes Telescope North at Haleakalā Observatory. Correlated variability across the griz bands is clearly detected, and the r -, i -, and z -band light curves show lags of 7.72 − 1.09 + 1.01 , 14.16 − 1.25 + 1.22 , and 20.78 − 2.09 + 1.99 minutes with respect to the g band when measured using the full-duration light curves. When lags are measured for each night separately, the Night 2 data exhibit lower cross-correlation amplitudes and shorter lags than the Night 1 light curves. Using the full-duration lags, we find that the lag–wavelength relationship is consistent with the τ ∝ λ 4/3 dependence found for more luminous active galactic nuclei. Combining our results with continuum lags measured for other objects, the lag between g and z band scales with optical continuum luminosity as τ gz ∝ L 0.56±0.05 , similar to the scaling of broad-line region size with luminosity,more »reinforcing recent evidence that diffuse continuum emission from the broad-line region may contribute substantially to optical continuum variability and reverberation lags.« less
    Free, publicly-accessible full text available August 1, 2023
  3. Abstract We present Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 2 observations of CO(2–1) emission from the circumnuclear disks in two early-type galaxies, NGC 1380 and NGC 6861. The disk in each galaxy is highly inclined ( i ∼ 75°), and the projected velocities of the molecular gas near the galaxy centers are ∼300 km s −1 in NGC 1380 and ∼500 km s −1 in NGC 6861. We fit thin disk dynamical models to the ALMA data cubes to constrain the masses of the central black holes (BHs). We created host galaxy models using Hubble Space Telescope images for the extended stellar mass distributions and incorporated a range of plausible central dust extinction values. For NGC 1380, our best-fit model yields M BH = 1.47 × 10 8 M ⊙ with a ∼40% uncertainty. For NGC 6861, the lack of dynamical tracers within the BH’s sphere of influence due to a central hole in the gas distribution precludes a precise measurement of M BH . However, our model fits require a value for M BH in the range of (1–3) × 10 9 M ⊙ in NGC 6861 to reproduce the observations. The BH masses are generally consistent with predictionsmore »from local BH–host galaxy scaling relations. Systematic uncertainties associated with dust extinction of the host galaxy light and choice of host galaxy mass model dominate the error budget of both measurements. Despite these limitations, the measurements demonstrate ALMA’s ability to provide constraints on BH masses in cases where the BH’s projected radius of influence is marginally resolved or the gas distribution has a central hole.« less
    Free, publicly-accessible full text available August 1, 2023
  4. Abstract We present a new empirical template for iron emission in active galactic nuclei (AGNs) covering the 4000–5600 Å range. The new template is based on a spectrum of the narrow-line Seyfert 1 galaxy Mrk 493 obtained with the Hubble Space Telescope. In comparison with the canonical iron template object I Zw 1, Mrk 493 has narrower broad-line widths, lower reddening, and a less extreme Eddington ratio, making it a superior choice for template construction. We carried out a multicomponent spectral decomposition to produce a template incorporating all the permitted and forbidden lines of Fe ii identified in the Mrk 493 spectrum over this wavelength range, as well as lines from Ti ii , Ni ii , and Cr ii . We tested the template by fitting it to AGN spectra spanning a broad range of iron emission properties, and we present a detailed comparison with fits using other widely used monolithic and multicomponent iron emission templates. The new template generally provides the best fit (lowest χ 2 ) compared to other widely used monolithic empirical templates. In addition, the new template yields more accurate spectral measurements including a significantly better match of the derived Balmer line profiles (H βmore », H γ , H δ ), in contrast with results obtained using the other templates. Our comparison tests show that the choice of iron template can introduce a systematic bias in measurements of the H β line width, which consequently impacts single-epoch black hole mass estimates by ∼0.1 dex on average and possibly up to ∼0.3–0.5 dex individually.« less
  5. Abstract Photoionization modeling of active galactic nuclei (AGN) predicts that diffuse continuum (DC) emission from the broad-line region makes a substantial contribution to the total continuum emission from ultraviolet through near-infrared wavelengths. Evidence for this DC component is present in the strong Balmer jump feature in AGN spectra, and possibly from reverberation measurements that find longer lags than expected from disk emission alone. However, the Balmer jump region contains numerous blended emission features, making it difficult to isolate the DC emission strength. In contrast, the Paschen jump region near 8200 Å is relatively uncontaminated by other strong emission features. Here, we examine whether the Paschen jump can aid in constraining the DC contribution, using Hubble Space Telescope Space Telescope Imaging Spectrograph spectra of six nearby Seyfert 1 nuclei. The spectra appear smooth across the Paschen edge, and we find no evidence of a Paschen spectral break or jump in total flux. We fit multicomponent spectral models over the range 6800–9700 Å and find that the spectra can still be compatible with a significant DC contribution if the DC Paschen jump is offset by an opposite spectral break resulting from blended high-order Paschen emission lines. The fits imply DC contributions rangingmore »from ∼10% to 50% at 8000 Å, but the fitting results are highly dependent on assumptions made about other model components. These degeneracies can potentially be alleviated by carrying out fits over a broader wavelength range, provided that models can accurately represent the disk continuum shape, Fe ii emission, high-order Balmer line emission, and other components.« less
    Free, publicly-accessible full text available March 1, 2023
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  7. Abstract We report the results of near-infrared spectroscopic observations of 37 quasars in the redshift range 6.3 < z ≤ 7.64, including 32 quasars at z > 6.5, forming the largest quasar near-infrared spectral sample at this redshift. The spectra, taken with Keck, Gemini, VLT, and Magellan, allow investigations of central black hole mass and quasar rest-frame ultraviolet spectral properties. The black hole masses derived from the Mg ii emission lines are in the range (0.3–3.6) × 10 9 M ⊙ , which requires massive seed black holes with masses ≳10 3 –10 4 M ⊙ , assuming Eddington accretion since z = 30. The Eddington ratio distribution peaks at λ Edd ∼ 0.8 and has a mean of 1.08, suggesting high accretion rates for these quasars. The C iv –Mg ii emission-line velocity differences in our sample show an increase of C iv blueshift toward higher redshift, but the evolutionary trend observed from this sample is weaker than the previous results from smaller samples at similar redshift. The Fe ii /Mg ii flux ratios derived for these quasars up to z = 7.6, compared with previous measurements at different redshifts, do not show any evidence of strong redshift evolution,more »suggesting metal-enriched environments in these quasars. Using this quasar sample, we create a quasar composite spectrum for z > 6.5 quasars and find no significant redshift evolution of quasar broad emission lines and continuum slope, except for a blueshift of the C iv line. Our sample yields a strong broad absorption line quasar fraction of ∼24%, higher than the fractions in lower-redshift quasar samples, although this could be affected by small sample statistics and selection effects.« less