Dr. Francisco Pozo Nuñez

White paper from the "KIPAC Workshop: Rubin 2036" (August 3–5, 2026) exploring science enabled by new narrow-, medium-, and offset broad-band filters on the Vera C. Rubin Observatory after LSST. Seven science cases, from high-redshift cosmology and photometric redshifts to Galactic archaeology, exoplanet biosignatures, and Kuiper Belt objects, are assessed for science reach, figures of merit, data needs, and risks.

We present the first direct comparison between accretion-disk (AD) and broad-line region (BLR) sizes in quasars at z > 2. The comparison was possible because we combined continuum reverberation mapping with interferometric BLR constraints from GRAVITY and GRAVITY+. Using medium-band photometric monitoring with the MPG/ESO 2.2 m telescope, we measured interband continuum lags in two quasars: SDSS J092034.17+065718.0 at z = 2.33 (J0920) and SMSS J052915.80–435152.0 at z = 3.96 (J0529). These are two of the most luminous quasars known ( L bol ~ 10 48 erg s −1 ) and currently the only two quasars at z > 2 with spatially resolved BLRs and dynamical black hole masses measured via interferometry, making this comparison uniquely possible. We detect significant con-tinuum lags in both quasars that increase monotonically with wavelength. The inferred UV disk sizes are R AD = 4.35 −0.91 +0.78 light-days for J0529 and R AD = 3.15 −0.48 +0.50 light-days for J0920. For J0920, which accretes at λ Edd ~ 7–20, the disk size is consistent with standard thin-disk expectations, a surprising result given that the standard thin-disk approximation is not expected to hold in this super-Eddington regime. For J0529, the disk size is consistent with thin-disk predictions under the single-epoch black hole mass but would imply disk inflation by a factor of a few if the GRAVITY+ dynamical mass – which is an order of magnitude lower – is adopted instead. This tension illustrates that UV continuum disk sizes provide an independent physical scale that any self-consistent model of the black hole mass and accretion rate must satisfy. This provides an addition way of studying objects where BLR kinematics are dominated by outflows rather than virial motion. A comparison with the interferometric BLR sizes reveals pronounced radial hierarchies, with R BLR / R AD ~ 270 for J0529 (H β ) and ~ 115 for J0920 (H α ). The successful detection of lags in both quasars at L bol ~ 10 48 erg s −1 demonstrates that continuum reverberation mapping remains feasible even at the low-amplitude variability end expected for the most luminous systems, opening a path toward extending AD size measurements to larger samples with wide-field surveys such as the Vera C. Rubin Observatory’s LSST.

Abstract We report adaptive-optics K s -band imaging of the composite Seyfert 2 and Wolf–Rayet galaxy NGC 6764 ( D = 32 Mpc), obtained with LUCI/SOUL at the Large Binocular Telescope (LBT). The nucleus resolves into three compact sources with pairwise projected separations of 0 . ″ 07 – 0 . ″ 2 , corresponding to 11.0–30.9 pc. All three have indistinguishable H , K s , H 2 , and Br γ colors, so photometry alone cannot separate accretion from star formation. The system is consistent with a Seyfert nucleus and two star-forming regions, but a dual or triple active galactic nucleus (AGN) cannot be excluded. In case of the latter, the separations would be two orders of magnitude smaller than in any confirmed or candidate AGN triplet reported to date. Diffraction-limited near-infrared integral-field spectroscopy is required to establish the nature of each component.

Context. The broad-line region (BLR) radius–luminosity ( R–L ) relation underpins single-epoch black hole mass estimates in active galactic nuclei (AGNs). The published H β sample is heterogeneous in terms of observational quality and it remains unclear how much of its scatter is intrinsic, rather than caused by systematics in lag recovery. Aims. We aim to quantify the contribution of unreliable lag recovery to the observed scatter of the H β R–L relation and to provide the community with the tools required for such quality control measures. Methods. We compiled a publicly available database of reverberation mapping (RM) measurements for ~1200 AGNs from 32 campaigns spanning more than three decades, storing lags, luminosities, line widths, black hole masses, and observational metadata. On this basis, we developed a simulation-based consistency framework: damped random-walk light curves were sampled according to each campaign’s reported baseline, cadence, and signal-to-noise ratio, while the lags were recovered with the interpolated cross-correlation function. A comparison of the expected, reported, and simulation-retrieved lags defined the four-tier flagging scheme. The R–L relation was refit with the Bayesian nested-sampling code UltraNest for progressively cleaner subsamples, while the dependence on the assumed reference relation was removed by constructing consensus samples across three reference slopes. Results. Although some model-dependent biases could persist, of the 248 H β sources, ≈40% of them display a discrepancy between the reported and simulation-retrieved lags, while ≈5% exhibit a direct inconsistency between the expected and retrieved lags. Excluding flagged sources and correcting for model bias reduces the inferred intrinsic scatter from σ = 0.26 −0.01 +0.02 dex to σ = 0.11 ± 0.01 dex, with a model-bias-corrected slope of α = 0.48 ± 0.02. This is consistent with the photoionisation expectation of α = 0.5. Conclusions. A significant fraction of the observed scatter in the current H β R–L relation arises from observational limitations and lag-recovery biases, rather than from intrinsic AGN diversity. The database, simulation code, and the campaign-planning tool RM-Scout have been made publicly available.

Context. The high-resolution imaging of active galactic nuclei (AGNs) on subkiloparsec scales offers an important avenue for investigating their fueling. Observations in the near-infrared (NIR) are especially valuable as they minimize the absorption by dust. However, the inferred nuclear morphology may depend on the method used to analyze the images. Aims. The aim of this study is to assess whether ground-based adaptive-optics observations of the cores of Seyfert 2 galaxies in the Ks band provide advantages over HST observations at shorter wavelengths (i.e., in the V and H bands). We also investigate whether a dedicated 2D analysis is preferable to a 1D approach. Methods. A sample of 18 Seyfert 2 galaxies was observed with the adaptive optics (AO) system in the Ks band at the Large Binocular Telescope (LBT) and compared to archival HST V - or H -band images. The analysis included a 2D modeling procedure via GALFIT as well as an unsharp masking technique. Results. The results obtained in different filters are mutually consistent, indicating no clear advantage when using a redder filter. Using both GALFIT and unsharp-masking in tandem is preferable, as the two methods provide complementary strengths. We identified nuclear stellar rings in 8 of the 18 galaxies in our sample (44 ± 12%). This fraction is significantly higher than reported in previous studies and about a factor of 2 higher than what was reported in the most complete atlas of nuclear rings. The radii, size distribution, and inferred masses of the detected nuclear rings are similar to those observed in non-active galaxies. Low-luminosity AGNs seem to have little (if any) impact on the formation and evolution of nuclear rings. Conclusions. The high incidence of nuclear stellar rings in our study is unexpected and warrants further investigation. This could be tested further using the large number of suitable archival HST images available. If confirmed, it would imply that nuclear stellar rings are considerably more common than previously recognized.

Context. Anomalous Cepheids (ACEPs) are radially pulsating stars observed in dwarf galaxies, the Galactic bulge and halo, and globular clusters. Similarly to other radially pulsating stars, they can be used as distance indicators through their period-luminosity relations (PLRs) and the geometrical Baade-Wesselink (BW) method. Aims. We aim to calibrate the zero point of the distance scale of ACEPs using nearby representatives of this class of pulsating stars. Methods. We collected optical/near-infrared photometry and spectra for a sample of nearby ACEPs with two telescopes located at the RolfChini Cerro Murphy Observatory (formerly Observatory Cerro Armazones) and optical telescopes offered by the Las Cumbres Observatory, along with instruments hosted and operated by the European Southern Observatory. Using parallaxes measured by the Gaia space mission and mean magnitudes from our new photometry, we calibrated the zero point of the period-luminosity relations (PLRs) in Johnson B , V , 2MASS J , H , K S , and Pan-STARRS g , r , i passbands, as well as select Wesenheit indices. The slopes were adopted from the PLRs of the LMC ACEPs from the literature. Using the surface brightness-color relation version of the BW technique, we were also able to determine the projection factors (p-factors) and mean radii of three nearby ACEPs. Results. The precision of the measured zero points is at the level of 0.04–0.05 mag and their systematic uncertainty was estimated to be about 0.1 mag. We used our zero point values and literature photometry related to LMC ACEPs to measure the distance modulus of this galaxy. We obtained a value of 18.454 ± 0.045 (statistical) mag, which is in very good agreement with the most accurate value from eclipsing binaries. The p-factors were 1.38 ± 0.13, 1.59 ± 0.21, and 1.35 ± 0.14 for V716 Oph, XX Vir, and UY Eri, respectively. We suspect that the very high p-factor of XX Vir results from the underestimated parallax of this star in the Gaia catalog, as its radius and absolute brightness are also higher than expected for ACEPs at this period. Finally, the radii measured for V716 Oph and UY Eri are in agreement with the period-radius relation obtained from LMC ACEPs.

Abstract We introduce a numerical optimization method to extract the X-ray reverberation response functions from multiband light curves of active galactic nuclei. This approach does not require prior assumptions about the geometry of the accretion disk and corona, provided that the light curves result from the superposition of direct and singly convolved signals, consistently across all bands. By reformulating the light-curve equations into matrix form, the optimal response matrix is derived by minimizing the squared difference between the observed and reconstructed light curves using a gradient-based optimization algorithm. We demonstrate that the method can robustly accommodate up to two convolution processes, such as reverberation and propagation, simultaneously. When tested on the synthesized light curves, the method demonstrates robustness of the solutions to variations in the relative contributions of each light-curve component as the recovered response kernel remains acceptably close to the ground truth, as evaluated by both the response geometry and the reconstructed light curves. The method’s tolerance to random noise was also assessed. With appropriate denoising, the response kernel can be reliably recovered when the signal-to-noise ratio is at least 100. We show, as a proof of concept, that the proposed method is independent of the geometrical model and has the potential to offer a flexible complement to traditional approaches.

Direct measurements of accretion disc sizes have so far been confined to the Local Universe (z < 0.2), limiting our understanding of quasars during the peak of cosmic activity. Here, we report the first direct measurement of the accretion disc size in the quasar QSO J0455-4216 at z = 2.66, when the Universe was only ∼2 Gyrs old. Medium-band filters mounted on the MPG/ESO 2.2-metre telescope at La Silla Observatory were used to isolate continuum emission regions during a six-month monitoring campaign. The light curves exhibit pronounced variability features and enabled the detection of inter-band time delays from different parts of the disc. We mapped the disc and located its ultraviolet-emitting outermost region at ∼ 3 light-days from the black hole (∼500 AU). Given a supermassive black hole 900 million times the mass of the Sun, these measurements validate accretion disc theory at an unprecedented redshift and pave the way for efficient black hole mass estimates, reducing decades-long spectroscopic reverberation campaigns to just a few years or less.