The enormous amount of data collected by the Dark Energy Survey (DES) provide a great opportunity to explore low surface brightness science topics, such as faint diffuse light in galaxies and galaxy clusters. In this talk, I will describe how we study diffuse intra-cluster light through stacking the images of hundreds of galaxy clusters from DES, reaching a surface brightness limit of 30 mag/arcsec^2, out to a radial distance of 1 Mpc from the cluster center. Despite their low surface brightness, our studies show that intra-cluster light is a significant component of the galaxy cluster stellar content. The stacking method has also been applied to characterizing the light profiles of luminous red galaxies, as well as studying the aureole component of the DES point spread function. Weak lensing and precision photometry calibration  methods may wish to consider these effects in the future.

Since the advent of large-area, high-quality astronomical surveys strong gravitational lensing has transitioned from a small-N to a large-N discipline. Galaxy cluster scale strong lensing, in particular, holds tremendous untapped potential. I will summarize our recent progress toward unlocking the scientific potential of large samples of strong lensing systems to address fundamental problems in astrophysics and cosmology. Focusing on recent results that highlight our sophisticated lensing analysis toolbox, I will present several pioneering measurements that lay the groundwork for future work that will use large numbers of highly magnified galaxies to answer outstanding questions about the physics of star formation and the properties of the interstellar medium in the epoch during which the Universe formed most of its stars. In addition to their value as natural telescopes, the massive structures that are responsible for the lensing action are, themselves, rare and powerful tools for testing the Lambda-CDM cosmological paradigm via the growth of structure and the mass distributions of lensing clusters.

before I will discuss the results of AGN studies with Swift.

The Galactic center excess has lingered as a possible, but ambiguous, signal of new physics for several years. It has previously been argued that certain details of the excess emission imply that it likely originates from a population of point sources, but this remains a topic of vigorous debate. In this talk, I will report on my recent work, relying on a new point source catalog (obtained by the Fermi-LAT collaboration), that sheds light on this controversial topic. After giving some background on the excess, I will discuss various metrics that have been used to try to understand its true nature. I will show that the large majority of bright sources that were previously suggested to be members of the excess are indeed contained in the new Fermi-LAT point source catalog -- and yet, despite masking out these sources (so that they cannot contribute to the excess), the excess remains just as bright in our new fit to the data. I will go on to discuss the implications of our findings for the two most popular interpretations of the excess.

The Cosmic Ultraviolet Baryon Survey (CUBS) is a large HST Cycle 25 GO

program designed to map 'dark' baryonic structures in the crucial but

unconstrained epoch between redshift z = 0.4 and z ~ 2.  The CUBS

program aims to combine absorption-line spectroscopy of 15 UV-bright

QSOs at z > 0.8 with matching deep galaxy survey data.  This legacy

sample enables systematic studies of the co-evolution of galaxies and

diffuse circumgalactic and intergalactic gas at a time when the star

formation rate density undergoes its most dramatic changes, and

provide key insights into how galaxy growth is regulated by accretion

and outflows.  In this talk, I will show some of the first results

from the CUBS program.

The AGN STORM (space telescope optical reverberation mapping) was an intense multi-wavelength campaign that observed NGC 5548, a type I Seyfert galaxy (z = 0.01717), for 180 months during 2014. The main goal was to determine the geometry and mass of the object through the reverberation mapping method, using 6 space-based and 21 ground-based telescopes.

NGC 5548 exhibited unusual behavior during the campaign: First, a strong soft X-ray absorption was present due to the appearance of a line of sight (LOS) obscurer between the central source and the observer. Then, it was discovered that broad emission lines and the UV continuum (emission-line holiday) decorrelated for 2 months during the observations. Finally, it was discovered that the same decorrelation happened between the narrow absorption lines and the continuum (absorption-line holiday).

We joined the campaign in 2017 to understand the behavior of NGC 5548 during the time of obscuration and holiday. We showed that LOS obscurer is the upper part of a symmetric continues disk-wind launched from the accretion disk. The base of this wind is called the equatorial obscurer and it persistently shields the BLR.  Based on Cloudy’s prediction, the variations of the covering factor of the LOS obscurer explains the absorption-line holiday, while changes in the column density/density of the equatorial obscurer explain the emission-line holiday.

Recently, we found out that the base of the wind has significant optical depth to electron scattering and must be a contributor to the Compton reflector. This reflector acts as a mirror and would reflect BLR emission. The wind’s optical depth explains why the far sides of the BLR are unexpectedly faint. During this talk, I will explain how our modeling resulted in this discovery, and also how the disk-wind model scenario fits into observations. 

I will report on the most recent discoveries by the NASA Neil Gehrels Swift mission of Active Galactic Nuclei (AGN) with high amplitude variabilities. While AGN typically vary with factors of 3 on times scales of days to years, some AGN exhibit outbursts or dramatic drops in the X-ray fluxes by factors of even more than 100. Among the most extreme cases are the Narrow-Line Seyfert 1 galaxy WPVS 007 which appears to be extremely X-ray faint, and the Seyfert 1.9 galaxy IC 3599 which has shown repeated X-ray flaring, most likely due to accretion disk instabilities. Swift capability of following objects for more than a decade with simultaneous X-ray and UV observations has allowed us to discover several of these extreme AGN.  Recent examples are IRAS 23226-3843, RX J2317-4422 and repeatedly Mkn 335 on which we triggered XMM/NuSTAR and HST observations several times in 2018 and 2019. In particular IRAS 23226-3843 is a so called changing look AGN that has changed its optical spectroscopic type several times. In most recent Swift observations IRAS 23226-3843 was found to be flaring again.

AGNs are the brightest persistent source of the electromagnetic radiation in the universe, enabling us to discover and study them across the cosmos. These are in the central regions of galaxies, and observing and tracing them informs us of the role of supermassive black holes (SBH) in the formation and evolution of galaxies. Fundamental properties such as the mass of the SBH and correlations with luminosity are based upon line-continuum reverberation mapping. Time delays between changes in the continuum luminosity and the response of the emission lines measure the physical size. The method is the basis for understanding phenomena near the SBH, which are far too small to be resolved even with the best telescopes.

During this talk, I will discuss how this correlation was broken in one of the well-studied AGNs, namely AGN NGC 5548.  In this object, the soft X-ray part of the SED was dramatically extinguished by an obscurer. During part of the time that this obscurer was present, the absorption and emission lines did not respond to variations of the continuum. We modeled the decorrelation of the absorption lines from the continuum in terms of a varying obscurer covering factor, and identify the physics which makes this possible. We identify a cycle in which the soft X-ray portion of the SED varies, causing changes in the ionization of helium.  The ionizing radiation produced in its recombination governs the ionization of the species observed with HST.  Photoionization models reproduce the sense of HST observations.  The obscurer is likely to be part of the broad-line region which happens to cover our sight line to the central object.  This shows the importance of cloud shadowing in understanding the physics of the emission-line clouds.