Roberto Assef

Full Professor at Universidad Diego Portales (UDP, Santiago)

roberto.assef [at] mail.udp.cl

I am an Astronomy Professor of the newly formed Astronomy Nucleus at Universidad Diego Portales, in Santiago, Chile. Previously, I was a NASA Postdoctoral Program Fellow at the Jet Propulsion Laboratory, in Pasadena, CA, where I moved to after obtaining my Ph.D. at The Ohio State University.

My research is primarily on observations of Active Galactic Nuclei and their role in Galaxy Evolution. Please take a look at the Research section if you want to find out what I do in more detail.

Hot Dust Obscured Galaxies

One of the main focuses on my research has been the study of Hot Dust-Obscured Galaxies, or Hot DOGs for short. Hot DOGs are a rare population (~0.03 deg^-2) of hyper-luminous, heavily dust obscured quasars identified by the WISE mission (Eisenhardt et al. 2012, Wu et al. 2012). With bolometric luminosities exceeding 10¹³ L_Sun, and 10% exceeding 10¹⁴ L_Sun, these are some of the most luminous galaxies in the Universe, with virtually all of their luminosity powered by accretion onto their supermassive black hole. I am in particular interested in understanding the role that these objects may be playing in the evolution of their massive galaxy host galaxies.

AGN Selection

Part of my research has been dedicated to AGN identification techniques, in very close connection with my SED modeling work. My focus has been on infrared wavelengths, particularly on the WISE mission. In Stern et al. (2012) and in Assef et al. (2013) we defined selection criteria for AGN using photometry from the WISE AllSky catalog. Different criteria were tailored to improve either the reliability (R90/R75 for 90%/75% reliability) or the completeness (C90/75 for 90%/75% completeness) of the samples. We later updated the criteria in Assef et al. (2018a) to the AllWISE catalog photometry and produced catalogs of selected AGN over 30,000 deg².

Studying the most variable reliably AGN we identified in Assef et al. (2018a), we found a luminous transient in an AGN visible at both mid-IR and optical wavelengths, which we presented in Assef et al. (2018b). We show this transient is best modeled as a super luminous supernovae. We speculate it may be located within the torus of the AGN given a number of similar transients in the mid-IR without optical counterparts.

Vera Rubin Observatory Legacy Survey of Space and Time (LSST)

LSST will revolutionize our view of AGN and galaxy evolution. I am full member of the AGN Science Collaboration, and I am leading the photometric redshifts subgroup. I led three of the cadence notes submitted in 2021, which you can find linked below. I have contributed a quasar counting metric to MAF (which you can also find in this github repository).

You can find more about the AGN Science collaboration activities, including the collaboration roadmap in collaboration's official website.

4MOST ChANGES and SED Modeling

I led the development of LRT, as set of low resolution templates and algorithms to model the broad-band colors of AGN and galaxies using a very small set of parameters.

We are currently using these templates to select AGN targets for the upcoming 4MOST Chilean AGN and Galaxy Evolution Survey (ChANGES).