Research and Publications
Below I have grouped my publications by topic, most active first.
Highlighted in green are the papers led by members of our group (students, postdocs and faculty of our current, closely linked collaboration).
We study the accretion flow feeding the central supermassive black hole in Active Galactic Nuclei (AGN). As this accretion disc is very small, we study it indirectly, through the information encoded in the variability of the flux it emits, mainly in the optical bands. Lately we have exploited the fantastic and massive variability data sets provided by the Zwicky Transient Facility to study the behavior of AGN with unprecedented precision. Combined with the ALeRCE machine learning classifier we are finding new populations of AGN and interesting events, such as AGN changing state from type II to type I and even newborn AGN.
We also use other surveys and proprietary data to constrain the accretion disc and its connection to the X-ray corona, dusty torus and relativistic jet.
Optical variability to find and study Quasars
Arévalo, et al., "The universal power spectrum of Quasars in optical wavelengths: Break timescale scales directly with both black hole mass and accretion rate", 2024 Astronomy and Astrophysics, 684, article number A133, link
Arévalo, et al., "A Newborn AGN in a Starforming Galaxy", 2024 Astronomy and Astrophysics Letters, 683, L8 link
Arévalo, et al., "Optical variability in quasars: scalings with black hole mass and Eddington ratio depend on the observed time-scales", 2023 Monthly Notices of the Royal Astronomical Society, 526, 6078, link
López-Navas, et al., "Improving the selection of changing-look AGNs through multiwavelength photometric variability", 2023 Monthly Notices of the Royal Astronomical Society, 524, 188, link
Sánchez-Sáez, et al., "Persistent and occasional: Searching for the variable population of the ZTF/4MOST sky using ZTF Data Release 11", 2023 Astronomy and Astrophysics, 675, A195, link
López-Navas, et al., "The Type 1 and Type 2 AGN dichotomy according to their ZTF optical variability", 2023 Monthly Notices of the Royal Astronomical Society, 518, 1531, link
López-Navas, et al., "Confirming new changing-look AGNs discovered through optical variability using a random forest-based light-curve classifier", 2022 Monthly Notices of the Royal Astronomical Society, 513, L57, link
Lira & Arévalo, "How massive is that black hole?", 2021 Science, 373, 734, link
Sánchez-Sáez, et al., "Alert Classification for the ALeRCE Broker System: The Light Curve Classifier", 2021 The Astronomical Journal, 161, 141, link
Horne, et al., "Space Telescope and Optical Reverberation Mapping Project. IX. Velocity-Delay Maps for Broad Emission Lines in NGC 5548", 2021 The Astrophysical Journal, 907, 76, link
Williams, et al., "Space Telescope and Optical Reverberation Mapping Project. XII. Broad-line Region Modeling of NGC 5548", 2020 The Astrophysical Journal, 902, 74, link
Kriss, et al., "Space Telescope and Optical Reverberation Mapping Project. VIII. Time Variability of Emission and Absorption in NGC 5548 Based on Modeling the Ultraviolet Spectrum", 2019 The Astrophysical Journal, 881, 153, link
Sánchez-Sáez, et al., "The QUEST-La Silla AGN Variability Survey: Selection of AGN Candidates through Optical Variability", 2019 The Astrophysical Journal Supplement Series, 242, 10, link
Sánchez-Sáez, et al., "The QUEST-La Silla AGN Variability Survey: Connection between AGN Variability and Black Hole Physical Properties", 2018 The Astrophysical Journal, 864, 87, link
Sánchez, et al., "Near-infrared Variability of Obscured and Unobscured X-Ray-selected AGNs in the COSMOS Field", 2017 The Astrophysical Journal, 849, 110, link
Mathur, et al., "Space Telescope and Optical Reverberation Mapping Project. VII. Understanding the Ultraviolet Anomaly in NGC 5548 with X-Ray Spectroscopy", 2017 The Astrophysical Journal, 846, 55, link
Pei, et al., "Space Telescope and Optical Reverberation Mapping Project. V. Optical Spectroscopic Campaign and Emission-line Analysis for NGC 5548", 2017 The Astrophysical Journal, 837, 131, link
Starkey, et al., "Space Telescope and Optical Reverberation Mapping Project.VI. Reverberating Disk Models for NGC 5548", 2017 The Astrophysical Journal, 835, 65, link
Goad, et al., "Space Telescope and Optical Reverberation Mapping Project. IV. Anomalous Behavior of the Broad Ultraviolet Emission Lines in NGC 5548", 2016 The Astrophysical Journal, 824, 11, link
Fausnaugh, et al., "Space Telescope and Optical Reverberation Mapping Project. III. Optical Continuum Emission and Broadband Time Delays in NGC 5548", 2016 The Astrophysical Journal, 821, 56, link
Cartier, et al., "The QUEST-La Silla AGN Variability Survey", 2015 The Astrophysical Journal, 810, 164, link
Edelson, et al., "Space Telescope and Optical Reverberation Mapping Project. II. Swift and HST Reverberation Mapping of the Accretion Disk of NGC 5548", 2015 The Astrophysical Journal, 806, 129, link
De Rosa, et al., "Space Telescope and Optical Reverberation Mapping Project.I. Ultraviolet Observations of the Seyfert 1 Galaxy NGC 5548 with the Cosmic Origins Spectrograph on Hubble Space Telescope", 2015 The Astrophysical Journal, 806, 128, link
Lira, et al., "Optical and near-IR long-term monitoring of NGC 3783 and MR 2251-178: evidence for variable near-IR emission from thin accretion discs", 2011 Monthly Notices of the Royal Astronomical Society, 415, 1290, link
Correlating variability in different wavelengths
Hernández-García, et al., "Multiwavelength monitoring of the nucleus in PBC J2333.9-2343: the giant radio galaxy with a blazar-like core", 2023 Monthly Notices of the Royal Astronomical Society, 525, 2187, link
McHardy, et al., "X-ray/UV/optical variability of NGC 4593 with Swift: reprocessing of X-rays by an extended reprocessor", 2018 Monthly Notices of the Royal Astronomical Society, 480, 2881, link
Lira, et al., "Long-term monitoring of the archetype Seyfert galaxy MCG-6-30-15: X-ray, optical and near-IR variability of the corona, disc and torus", 2015 Monthly Notices of the Royal Astronomical Society, 454, 368, link
McHardy, et al., "Swift monitoring of NGC 5548: X-ray reprocessing and short-term UV/optical variability", 2014 Monthly Notices of the Royal Astronomical Society, 444, 1469, link
Cameron, et al., "Correlated X-ray/ultraviolet/optical variability in the very low mass AGN NGC 4395", 2012 Monthly Notices of the Royal Astronomical Society, 422, 902, link
Bell, et al., "X-ray and radio variability in the low-luminosity active galactic nucleus NGC 7213", 2011 Monthly Notices of the Royal Astronomical Society, 411, 402, link
Breedt, et al., "Twelve years of X-ray and optical variability in the Seyfert galaxy NGC 4051", 2010 Monthly Notices of the Royal Astronomical Society, 403, 605, link
Arévalo, et al., "Correlation and time delays of the X-ray and optical emission of the Seyfert Galaxy NGC 3783", 2009 Monthly Notices of the Royal Astronomical Society, 397, 2004, link
Breedt, et al., "Long-term optical and X-ray variability of the Seyfert galaxy Markarian 79", 2009 Monthly Notices of the Royal Astronomical Society, 394, 427, link
Arévalo, et al., "Correlated X-ray/optical variability in the quasar MR2251-178", 2008 Monthly Notices of the Royal Astronomical Society, 389, 1479, link
Arévalo, et al., "X-ray to UV variability correlation in MCG-6-30-15", 2005 Astronomy and Astrophysics, 430, 435, link
I started taking an interest in AGN variability by looking at the more vigorously varying X-ray emission. The X-rays in radio quiet AGN are produced by a so-called corona of hot electrons, that can be related to the accretion flow. Below are some papers that use the variability properties, sometimes combined with spectroscopic studies, to constrain the behavior of the X-ray corona.
The X-ray emission can penetrate large column densities of dust and gas, so it can reveal AGN activity in even very deeply buried AGN. We use this fact to find and study obscured AGN and even track the reflection of the X-rays over the surrounding gas to constrain its distribution around the supermassive black holes.
Studying the X-ray corona in AGN combining spectra and variability
Tortosa, et al., "BASS-XL: X-ray variability properties of unobscured active galactic nuclei", 2023 Monthly Notices of the Royal Astronomical Society, 526, 1687, link
Ricci, et al., "IC 751: A New Changing Look AGN Discovered by NuSTAR", 2016 The Astrophysical Journal, 820, 5, link
Marinucci, et al., "The Seyfert 2 galaxy NGC 2110: hard X-ray emission observed by NuSTAR and variability of the iron Kα line", 2015 Monthly Notices of the Royal Astronomical Society, 447, 160, link
Puccetti, et al., "The Variable Hard X-Ray Emission of NGC 4945 as Observed by NuSTAR", 2014 The Astrophysical Journal, 793, 26, link
Walton, et al., "NuSTAR and XMM-NEWTON Observations of NGC 1365: Extreme Absorption Variability and a Constant Inner Accretion Disk", 2014 The Astrophysical Journal, 788, 76, link
Marinucci, et al., "Simultaneous NuSTAR and XMM-Newton 0.5-80 keV spectroscopy of the narrow-line Seyfert 1 galaxy SWIFT J2127.4+5654", 2014 Monthly Notices of the Royal Astronomical Society, 440, 2347, link
Marinucci, et al., "The Broadband Spectral Variability of MCG-6-30-15 Observed by NuSTAR and XMM-Newton", 2014 The Astrophysical Journal, 787, 83, link
Arévalo, et al., "Deconvolving X-Ray Spectral Variability Components in the Seyfert 1.5 NGC 3227", 2014 The Astrophysical Journal, 783, 82, link
Emmanoulopoulos, et al., "The 'harder when brighter' X-ray behaviour of the low-luminosity active galactic nucleus NGC 7213", 2012 Monthly Notices of the Royal Astronomical Society, 424, 1327, link
Emmanoulopoulos, et al., "An XMM-Newton view of the `bare' nucleus of Fairall 9", 2011 Monthly Notices of the Royal Astronomical Society, 415, 1895, link
Papadakis, et al., "A correlation between the spectral and timing properties of AGN", 2009 Astronomy and Astrophysics, 494, 905, link
Arévalo, et al., "X-ray variability of the Seyfert 1 Markarian 335: power spectrum and time lags", 2008 Monthly Notices of the Royal Astronomical Society, 388, 211, link
Arévalo, et al., "Fourier-resolved energy spectra of the Narrow-Line Seyfert 1 Mkn 766", 2008 Monthly Notices of the Royal Astronomical Society, 387, 279, link
McHardy, et al., "Discovery of multiple Lorentzian components in the X-ray timing properties of the Narrow Line Seyfert 1 Ark 564", 2007 Monthly Notices of the Royal Astronomical Society, 382, 985, link
Summons, et al., "Timing evidence in determining the accretion state of the Seyfert galaxy NGC 3783", 2007 Monthly Notices of the Royal Astronomical Society, 378, 649, link
Markowitz, et al., "The Energy-dependent X-Ray Timing Characteristics of the Narrow-Line Seyfert 1 Mrk 766", 2007 The Astrophysical Journal, 656, 116, link
Arévalo, et al., "Spectral-timing evidence for a very high state in the narrow-line Seyfert 1 Ark 564", 2006 Monthly Notices of the Royal Astronomical Society, 372, 401, link
Arévalo, et al., "Investigating a fluctuating-accretion model for the spectral-timing properties of accreting black hole systems", 2006 Monthly Notices of the Royal Astronomical Society, 367, 801, link
Brinkmann, et al., "X-ray variability of the Narrow Line Seyfert 1 Galaxy PKS 0558-504", 2004 Astronomy and Astrophysics, 415, 959, link
Studying the environs of the accreting supermassive black holes through X-ray reflection and absorption
Diaz, et al., "Constraining the X-ray reflection in low accretion-rate active galactic nuclei using XMM-Newton, NuSTAR, and Swift", 2023 Astronomy and Astrophysics, 669, A114, link
Andonie, et al., "Localizing narrow Fe Kα emission within bright AGN", 2022 Astronomy and Astrophysics, 664, A46, link
Andonie, et al., "A multiwavelength-motivated X-ray model for the Circinus Galaxy", 2022 Monthly Notices of the Royal Astronomical Society, 511, 5768, link
Ricci, et al., "A hard X-ray view of luminous and ultra-luminous infrared galaxies in GOALS - I. AGN obscuration along the merger sequence", 2021 Monthly Notices of the Royal Astronomical Society, 506, 5935, link
Diaz, et al., "Constraining X-ray reflection in the low-luminosity AGN NGC 3718 using NuSTAR and XMM-Newton", 2020 Monthly Notices of the Royal Astronomical Society, 496, 5399, link
Ricci, et al., "Growing supermassive black holes in the late stages of galaxy mergers are heavily obscured", 2017 Monthly Notices of the Royal Astronomical Society, 468, 1273, link
Romero-Cañizales, et al., "Unveiling the AGN in IC 883: discovery of a parsec-scale radio jet", 2017 Monthly Notices of the Royal Astronomical Society, 467, 2504, link
Guainazzi, et al., "The nature of the torus in the heavily obscured AGN Markarian 3: an X-ray study", 2016 Monthly Notices of the Royal Astronomical Society, 460, 1954, link
Fürst, et al., "NuSTAR and XMM-Newton Observations of the Hard X-Ray Spectrum of Centaurus A", 2016 The Astrophysical Journal, 819, 150, link
Ricci, et al., "NUSTAR Unveils a Heavily Obscured Low-luminosity Active Galactic Nucleus in the Luminous Infrared Galaxy NGC 6286", 2016 The Astrophysical Journal, 819, 4, link
Puccetti, et al., "Hard X-ray emission of the luminous infrared galaxy NGC 6240 as observed by NuSTAR", 2016 Astronomy and Astrophysics, 585, A157, link
Rivers, et al., "The NuSTAR View of Reflection and Absorption in NGC 7582", 2015 The Astrophysical Journal, 815, 55, link
Annuar, et al., "NuSTAR Observations of the Compton-thick Active Galactic Nucleus and Ultraluminous X-Ray Source Candidate in NGC 5643", 2015 The Astrophysical Journal, 815, 36, link
Bauer, et al., "NuSTAR Spectroscopy of Multi-component X-Ray Reflection from NGC 1068", 2015 The Astrophysical Journal, 812, 116, link
Ursini, et al., "The NuSTAR X-ray spectrum of the low-luminosity active galactic nucleus in NGC 7213", 2015 Monthly Notices of the Royal Astronomical Society, 452, 3266, link
Koss, et al., "Broadband Observations of the Compton-thick Nucleus of NGC 3393", 2015 The Astrophysical Journal, 807, 149, link
Brightman, et al., "Determining the Covering Factor of Compton-thick Active Galactic Nuclei with NuSTAR", 2015 The Astrophysical Journal, 805, 41, link
Rivers, et al., "The Multi-layer Variable Absorbers in NGC 1365 Revealed by XMM-Newton and NuSTAR", 2015 The Astrophysical Journal, 804, 107, link
Luo, et al., "Weak Hard X-Ray Emission from Broad Absorption Line Quasars: Evidence for Intrinsic X-Ray Weakness", 2014 The Astrophysical Journal, 794, 70, link
Gandhi, et al., "NuSTAR Unveils a Compton-thick Type 2 Quasar in Mrk 34", 2014 The Astrophysical Journal, 792, 117, link
Arévalo, et al., "The 2-79 keV X-Ray Spectrum of the Circinus Galaxy with NuSTAR, XMM-Newton, and Chandra: A Fully Compton-thick Active Galactic Nucleus", 2014 The Astrophysical Journal, 791, 81, link
Walton, et al., "NuSTAR and XMM-NEWTON Observations of NGC 1365: Extreme Absorption Variability and a Constant Inner Accretion Disk", 2014 The Astrophysical Journal, 788, 76, link
Marinucci, et al., "Simultaneous NuSTAR and XMM-Newton 0.5-80 keV spectroscopy of the narrow-line Seyfert 1 galaxy SWIFT J2127.4+5654", 2014 Monthly Notices of the Royal Astronomical Society, 440, 2347, link
Emmanoulopoulos, et al., "An XMM-Newton view of the `bare' nucleus of Fairall 9", 2011 Monthly Notices of the Royal Astronomical Society, 415, 1895, link
Markowitz, et al., "A Comprehensive X-Ray Spectral Analysis of the Seyfert 1.5 NGC 3227", 2009 The Astrophysical Journal, 691, 922, link
AGN in galaxy clusters can affect the hot gas that fills these structures, on very large spatial scales. The imprint of this AGN feedback can be tracked in the perturbations of the X-ray emission of the intra-cluster medium.
AGN feedback, perturbations in the surface brightness of the intra-cluster medium
Churazov, et al., "Arithmetic with X-ray images of galaxy clusters: effective equation of state for small-scale perturbations in the ICM", 2016 Monthly Notices of the Royal Astronomical Society, 463, 1057, link
Zhuravleva, et al., "The nature and energetics of AGN-driven perturbations in the hot gas in the Perseus Cluster", 2016 Monthly Notices of the Royal Astronomical Society, 458, 2902, link
Arévalo, et al., "On the Nature of X-ray Surface Brightness Fluctuations in M87", 2016 The Astrophysical Journal, 818, 14, link
Zhuravleva, et al., "Gas density fluctuations in the Perseus Cluster: clumping factor and velocity power spectrum", 2015 Monthly Notices of the Royal Astronomical Society, 450, 4184, link
Zhuravleva, et al., "Turbulent heating in galaxy clusters brightest in X-rays", 2014 Nature, 515, 85, link
For the topic above, we developed the Mexican Hat filter to extract the pattern of perturbations in images with sharp edges and irregular holes produced by masked-out foreground stars. This method can also be applied in 1 or 3 dimensions, and has now become extremely useful to estimate the power spectrum of optical lightcurves, in particular those produced by the ZTF, that are inevitably affeteced by yearly gaps and irregular sampling. This method is very quick to calculate and is used by the ALeRCE light curve classifier. It provides one of the key features that for example distinguishes AGN from long period variable stars. We have also used it in recent papers to characterize the optical variability of thousands of AGN.