Cosmic happenstance: 24-µm selected, multicomponent Herschel sources are line-of-sight projections

Scudder, Jillian M.; Oliver, Seb; Hurley, Peter D.; Wardlow, Julie L.; Wang, Lingyu; Farrah, Duncan

Abstract

In this paper, we investigate the physical associations between blended far-infrared (FIR)-emitting galaxies, in order to identify the level of line-of-sight projection contamination in the single-dish Herschel data. Building on previous work, and as part of the Herschel Extragalactic Legacy Project, we identify a sample of galaxies in the COSMOS field, which are found to be both FIR-bright (typically ∼15 mJy) and blended within the Herschel 250-μm beam. We identify a spectroscopic or photometric redshift for each FIR-bright source. We conduct a joint probability distribution analysis on the redshift probability density functions to determine the fraction of the FIR sources with multiple FIR-bright counterparts that are likely to be found at consistent (Δz < 0.01) redshifts. We find that only three (0.4 per cent) of the pair permutations between counterparts are >50 per cent likely to be at consistent redshifts. A majority of counterparts (72 per cent) have no overlap in their redshift probability distributions whatsoever. This is in good agreement with the results of recent simulations, which indicate that single-dish observations of the FIR sky should be strongly contaminated by line-of-sight projection effects. We conclude that for our sample of 3.6- and 24-μm selected, FIR-bright objects in the COSMOS field, the overwhelming majority of multicomponent FIR systems are line-of-sight projections within the 18.1-arcsec Herschel beam, rather than physical associations.

Citation

Scudder, J. M., Oliver, S., Hurley, P. D., Wardlow, J. L., Wang, L., & Farrah, D. (2018). Cosmic happenstance: 24-µm selected, multicomponent Herschel sources are line-of-sight projections. Monthly Notices of the Royal Astronomical Society, 480(3), 4124-4137. https://doi.org/10.1093/mnras/sty2009

• Journal Article Type: Article
• Acceptance Date: Jul 23, 2018
• Online Publication Date: Aug 1, 2018
• Publication Date: Nov 1, 2018
• Deposit Date: Nov 8, 2018
• Publicly Available Date: Nov 8, 2018
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Royal Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 480
• Issue: 3
• Pages: 4124-4137
• DOI: https://doi.org/10.1093/mnras/sty2009
• Public URL: https://durham-repository.worktribe.com/output/1313888