The Effectiveness of Mid IR / Far IR Blind, Wide Area, Spectral Surveys in Breaking the Confusion Limit

TL;DR

This study demonstrates that mid/far infrared wide-area spectroscopic surveys can effectively break the traditional confusion limit, enabling redshift determination for many previously inaccessible galaxies.

Contribution

The paper evaluates the effectiveness of SAFARI, a FIR spectrometer, in using spectral lines to resolve sources beyond the confusion limit in large-area surveys.

Findings

Accurately retrieve redshifts for 38/54% of brightest confused sources.

Recover redshifts for 38/29% of second brightest sources.

Deep spectral line surveys can surpass photometric confusion limits.

Abstract

Source confusion defines a practical depth to which to take large-area extragalactic surveys. 3D imaging spectrometers with positional as well as spectral information, however, potentially provide a means by which to use line emission to break the traditional confusion limit. In this paper we present the results of our investigation into the effectiveness of mid/far infrared, wide-area spectroscopic surveys in breaking the confusion limit. We use SAFARI, a FIR imaging Fourier Transform Spectrometer concept for the proposed JAXA-led SPICA mission, as a test case. We generate artificial skies representative of 100 SAFARI footprints and use a fully-automated redshift determination method to retrieve redshifts for both spatially and spectrally confused sources for bright-end and burst mode galaxy evolution models. We find we are able to retrieve accurate redshifts for 38/54% of the brightest spectrally confused sources, with continuum fluxes as much as an order of magnitude below the 120 $\mu$m photometric confusion limit. In addition we also recover accurate redshifts for 38/29% of the second brightest spectrally confused sources. Our results suggest that deep, spectral line surveys with SAFARI can break the traditional photometric confusion limit, and will also not only resolve, but provide redshifts for, a large number of previously inaccessible galaxies. To conclude we discuss some of the limitations of the technique, as well as further work.