Simulated observations of sub-millimetre galaxies: the impact of single-dish resolution and field variance

Cowley, William I.; Lacey, Cedric G.; Baugh, Carlton M.; Cole, Shaun

Abstract

Recent observational evidence suggests that the coarse angular resolution [∼20 arcsec full width at half maximum (FWHM)] of single-dish telescopes at sub-mm wavelengths has biased the observed galaxy number counts by blending together the sub-mm emission from multiple sub-mm galaxies (SMGs). We use lightcones computed from an updated implementation of the galform semi-analytic model to generate 50 mock sub-mm surveys of 0.5 deg2 at 850 μm, taking into account the effects of the finite single-dish beam in a more accurate way than has been done previously. We find that blending of SMGs does lead to an enhancement of source extracted number counts at bright fluxes (S850 μm ≳ 1 mJy). Typically, three to six galaxies contribute 90 per cent of the flux of an S850 μm = 5 mJy source and these blended galaxies are physically unassociated. We find that field-to-field variations are comparable to Poisson fluctuations for our S850 μm > 5 mJy SMG population, which has a median redshift z50 = 2.0, but are greater than Poisson for the S850 μm > 1 mJy population (z50 = 2.8). In a detailed comparison to a recent interferometric survey targeted at single-dish detected sources, we reproduce the difference between single-dish and interferometer number counts and find a median redshift (z50 = 2.5) in excellent agreement with the observed value (z50 = 2.5 ± 0.2). We also present predictions for single-dish survey number counts at 450 and 1100 μm, which show good agreement with observational data.

Citation

Cowley, W. I., Lacey, C. G., Baugh, C. M., & Cole, S. (2015). Simulated observations of sub-millimetre galaxies: the impact of single-dish resolution and field variance. Monthly Notices of the Royal Astronomical Society, 446(2), 1784-1798. https://doi.org/10.1093/mnras/stu2179

• Journal Article Type: Article
• Acceptance Date: Oct 15, 2014
• Online Publication Date: Nov 21, 2014
• Publication Date: Jan 11, 2015
• Deposit Date: Nov 25, 2014
• Publicly Available Date: Nov 26, 2014
• 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: 446
• Issue: 2
• Pages: 1784-1798
• DOI: https://doi.org/10.1093/mnras/stu2179
• Keywords: Galaxies: evolution, Galaxies: formation, Galaxies: high-redshift, Galaxies: starburst, Submillimetre: diffuse background, Sub-millimetre: galaxies.
• Public URL: https://durham-repository.worktribe.com/output/1441214
• Related Public URLs: http://adsabs.harvard.edu/abs/2015MNRAS.446.1784C