Overdensity of SMGs in fields containing z ∼ 0.3 galaxies: magnification bias and the implications for studies of galaxy evolution. Issue 4 (7th September 2020)

• Record Type: Journal Article
• Authors: Dunne, L; Bonavera, L; Gonzalez-Nuevo, J; Maddox, S J; Vlahakis, C
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 498:Issue 4(2020)
• Page Start: 4635
• Page End: 4649
• Publication Date: 2020-09-07
• Subjects: galaxies:haloes -- gravitational lensing:weak -- submillimetre:galaxies; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa2665
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We report a remarkable overdensity of high-redshift submillimetre galaxies (SMG), 4–7 times the background, around a statistically complete sample of twelve 250 μ m selected galaxies at z = 0.35, which were targeted by ALMA in a study of gas tracers. This overdensity is consistent with the effect of lensing by the haloes hosting the target z = 0.35 galaxies. The angular cross-correlation in this sample is consistent with statistical measures of this effect made using larger sub-mm samples. The magnitude of the overdensity as a function of radial separation is consistent with intermediate scale lensing by haloes of the order of $7\times 10^{13}\mbox{ $\rm M_{\odot }$ }$, which should host one or possibly two bright galaxies and several smaller satellites. This is supported by observational evidence of interaction with satellites in four out of the six fields with SMG, and membership of a spectroscopically defined group for a fifth. We also investigate the impact of these SMG on the reported Herschel fluxes of the z = 0.35 galaxies, as they produce significant contamination in the 350 and 500 μ m Herschel bands. The higher than random incidence of these boosting events implies a significantly larger bias in the sub-mm colours of Herschel sources associated with z < 0.7 galaxies than has previously been assumed, with f boost = 1.13, 1.26, 1.44 at 250, 350, and 500 μ m . This could have implications for studies of spectral energy distributions, source counts, and luminosity functions based on Herschel samples at z = 0.2–0.7.