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HELP : xid+, the probabilistic de-blender for Herschel SPIRE maps.

Hurley, P. D. and Oliver, S. and Betancourt, M. and Clarke, C. and Cowley, W. I. and Duivenvoorden, S. and Farrah, D. and Griffin, M. and Lacey, C. and Le Floc'h, E. and Papadopoulos, A. and Sargent, M. and Scudder, J. M. and Vaccari, M. and Valtchanov, I. and Wang, L. (2017) 'HELP : xid+, the probabilistic de-blender for Herschel SPIRE maps.', Monthly notices of the Royal Astronomical Society., 464 (1). pp. 885-896.


We have developed a new prior-based source extraction tool, xid+, to carry out photometry in the Herschel SPIRE (Spectral and Photometric Imaging Receiver) maps at the positions of known sources. xid+ is developed using a probabilistic Bayesian framework that provides a natural framework in which to include prior information, and uses the Bayesian inference tool Stan to obtain the full posterior probability distribution on flux estimates. In this paper, we discuss the details of xid+ and demonstrate the basic capabilities and performance by running it on simulated SPIRE maps resembling the COSMOS field, and comparing to the current prior-based source extraction tool desphot. Not only we show that xid+ performs better on metrics such as flux accuracy and flux uncertainty accuracy, but we also illustrate how obtaining the posterior probability distribution can help overcome some of the issues inherent with maximum-likelihood-based source extraction routines. We run xid+ on the COSMOS SPIRE maps from Herschel Multi-Tiered Extragalactic Survey using a 24-μm catalogue as a positional prior, and a uniform flux prior ranging from 0.01 to 1000 mJy. We show the marginalized SPIRE colour–colour plot and marginalized contribution to the cosmic infrared background at the SPIRE wavelengths. xid+ is a core tool arising from the Herschel Extragalactic Legacy Project (HELP) and we discuss how additional work within HELP providing prior information on fluxes can and will be utilized. The software is available at We also provide the data product for COSMOS. We believe this is the first time that the full posterior probability of galaxy photometry has been provided as a data product.

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Publisher statement:This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:16 September 2016
Date deposited:02 March 2017
Date of first online publication:16 September 2016
Date first made open access:02 March 2017

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