List of Approved CAT Projects

This is a partial list. Not all CAT Reviews have been completed.

PI: D. Alexander

Title: Chandra-NuSTAR synergy in the NuSTAR serendipitous survey


A great breakthrough in resolving the peak of the cosmic X-ray background (CXB) is NuSTAR. The NuSTAR extragalactic survey has resolved ~35% of the CXB at the >10 keV peak, provided the first measurements of the >10 keV AGN luminosity function at z>0.1, and identified extreme heavily obscured AGNs. The NuSTAR serendipitous survey is the largest component of the extragalactic survey program and provides the majority of the (~75-80%) NuSTAR-detected sources. Through a combination of deep and shallow wide-area coverage it fills out the X-ray luminosity-redshift plane of AGN and detects intrinsically rare source populations. However, the NuSTAR data alone are insufficient to fully understand the physical properties of the NuSTAR sources and Chandra CATS observations are required to (i) provide reliable sub-arcsec optical counterpart identification for spectroscopic observations to obtain redshifts and identify Galactic sources and (ii) broad-band X-ray spectral to characterize the X-ray emission of the NuSTAR sources down to ~0.5-3 keV, where NuSTAR has no sensitivity. The Chandra CATS observations will allow for (i) the robust identification of optical counterparts, (ii) the characterization of the 0.5-24 keV spectra, (iii) the detection of multiple Chandra counterparts in spatially complex systems and crowded fields, (iv) a broad suite of analyses to constrain the properties and evolution of AGN at >10 keV, and (v) long-term (>1 year timescale) X-ray variability analyses for the NuSTAR sources with existing X-ray coverage. The Chandra CATS target list includes all of the NuSTAR sources that lie within 40 degrees of the ecliptic within the serendipitous survey to date.

PI: Nico Cappelluti

Title: Aiming at Stripe 82X Quasars as CATs: compelling targets while building area for the legacy survey.


High luminosity AGN (i.e., quasars) have a powerful impact on their host galaxies, via winds, jets, or intense radiation that can regulate star formation, and they likely represent the phase when the majority of mass was accreted onto black holes. We propose a series of pre-selected source populations (mostly bright Quasars) in Stripe 82 to target with ACIS-I within the Chandra CAT program, which will build area in the Stripe 82 while obtaining useful results from each pointing. In particular we will aim to observe: Bright Herschel-selected quasars in Stripe 82, Red Quasars, z>4 Quasars and Candidate AGN in low mass galaxies.

PI: Francesca Civano

Title: Calibration of the quasar Hubble diagram with z ≤ 0.7 quasars as CATs


Quasars are among the most luminous sources in the sky and as such can be detected up to very high redshifts (z = 7.54). For these reasons, scientists have long chased the possibility of using quasars to constrain cosmological models in a completely unexplored redshift range (z > 1.4, beyond which Supernovae (SN) are rarely detected). Despite several attempts, most of the proposed methods are affected by a high dispersion in the observational relations used, preventing high precision distance measurements. A new method, recently proposed by Risaliti & Lusso 2015, overcomes this difficulty by taking advantage of the very large statistic provided by the quasar surveys currently available. Building upon this result and the latest improvements about it, the goal of this CAT project is to increase the sample of low-z (z<0.7) quasars with good quality X-ray data from pointed observations to decrease the dispersion in the quasar Hubble diagram and calibrate a zero-point for it.

PI: Elena Gallo



Cosmological volume simulations are fast approaching the resolution necessary to follow the assembly and evolution of galactic structure well below the knee of the galaxy mass function, where the black hole occupation fraction remains essentially unconstrained. In the low stellar mass regime (i.e. below ~1e10 solar masses), the black hole occupation fraction determines the black hole mass function, sets tidal disruption event rates, affects star formation quenching and may even depend on the black hole seeding mechanisms at high-z. This program will contribute to a high accuracy measurement of the local black hole occupation fraction in the low mass regime through imaging observations of nearby dwarf galaxies.

PI: Mike Koss

Title: C-BASS: A Chandra Legacy Survey of AGN at the Highest Spatial Resolutions


Chandra has conducted over 30 extragalactic surveys, at depths between 100 ks to 7 Ms that cumulatively add up to several years of observations. This has led to the discovery of thousands of distant black holes and hundreds of refereed papers that have defined our current understanding of the growth of SMBHs, their radiative outputs, and how these may be linked to their host galaxies. The Swift-BAT 105-month survey all sky survey has detected 1181 of the nearest and brightest AGN, which have similar luminosities to the distant AGN typically found in deep, pencil-beam Chandra surveys. We propose a Chandra cool attitude program to survey the 537 BAT AGN that have yet to be observed by Chandra, within the ecliptic plane constraints. This will enable a high-spatial resolution study on the scales of 100s of pc (~0.025, i.e. 0.5"=250 pc) for a large number of AGN with an unprecedented collection of ancillary multiwavelength data for the first time to study dual, recoiling, and offset AGN, and to resolve jets, study AGN feedback, and look for extended profiles of plasma (Fe Ka) emission.