Inference of Unresolved Point Sources at High Galactic Latitudes Using Probabilistic Catalogs
Abstract
The detection of point sources in images is a fundamental operation in astrophysics, and is crucial for constraining population models of the underlying point sources or characterizing the background emission. Standard techniques fall short in the crowdedfield limit, losing sensitivity to faint sources and failing to track their covariance with close neighbors. We construct a Bayesian framework to perform inference of faint or overlapping point sources. The method involves probabilistic cataloging, where samples are taken from the posterior probability distribution of catalogs consistent with an observed photon count map. In order to validate our method, we sample random catalogs of the gammaray sky in the direction of the North Galactic Pole (NGP) by binning the data in energy and pointspread function classes. Using three energy bins spanning 0.31, 13, and 310 GeV, we identify {270}_{10}^{+30} point sources inside a 40^\circ × 40^\circ region around the NGP above our pointsource inclusion limit of 3× {10}^{11} cm^{2} s^{1} sr^{1} GeV^{1} at the 13 GeV energy bin. Modeling the flux distribution as a power law, we infer the slope to be {1.92}_{0.05}^{+0.07} and estimate the contribution of point sources to the total emission as {18}_{2}^{+2}%. These uncertainties in the flux distribution are fully marginalized over the number as well as the spatial and spectral properties of the unresolved point sources. This marginalization allows a robust test of whether the apparently isotropic emission in an image is due to unresolved point sources or of truly diffuse origin.
 Publication:

The Astrophysical Journal
 Pub Date:
 April 2017
 DOI:
 10.3847/15384357/aa679e
 arXiv:
 arXiv:1607.04637
 Bibcode:
 2017ApJ...839....4D
 Keywords:

 gamma rays: diffuse background;
 gamma rays: galaxies;
 gamma rays: general;
 methods: data analysis;
 methods: statistical;
 Astrophysics  Instrumentation and Methods for Astrophysics;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 Astrophysics  Astrophysics of Galaxies;
 Astrophysics  High Energy Astrophysical Phenomena;
 High Energy Physics  Phenomenology
 EPrint:
 2017 ApJ 839 4