LoCuSS: Luminous infrared galaxies in the merging cluster Abell 1758 at z = 0.28

We present the first galaxy evolution results from the Local Cluster Substructure Survey (LoCuSS), a multiwavelength survey of 100 X-ray selected galaxy clusters at 0.15 ≤ z ≤ 0.3. LoCuSS combines far-ultraviolet (UV) through far-infrared (IR) observations of cluster galaxies with gravitational lensing analysis and X-ray data to investigate the interplay between the hierarchical assembly of clusters and the evolution of cluster galaxies. Here we present new panoramic Spitzer/Multiband Imaging Photometer 24-μm observations of the merging cluster Abell 1758 at z = 0.279 spanning 6.5 × 6.5 Mpc² and reaching a 90 per cent completeness limit of S _{24 μm} = 400 μJy. We estimate a global cluster star formation rate of SFR_{24 μm} = 910 ± 320 M_⊙ yr ^-1 within R < 3 Mpc of the cluster centre, originating from 42 galaxies with L_{8-1000 μm} > 5 × 10¹⁰ L _⊙. The obscured activity in A1758 is therefore comparable with that in Cl 0024+1654, the most active cluster previously studied at 24 μm. The obscured galaxies faithfully trace the cluster potential as revealed by the weak-lensing mass map of the cluster, including numerous mass peaks at R ∼ 2-3 Mpc that are likely associated with infalling galaxy groups and filamentary structures. However, the core (R ≲ 500 kpc) of A1758N is ∼two times more active in the IR than that of A1758S, likely reflecting differences in the recent dynamical history of the two clusters. The 24-μm results from A1758 therefore suggest that dust-obscured cluster galaxies are common in merging clusters and suggest that obscured activity in clusters is triggered by both the details of cluster-cluster mergers and processes that operate at larger radii including those within in-falling groups. Our ongoing far-UV through far-IR observations of a large sample of clusters should allow us to disentangle the different physical processes responsible for triggering obscured star formation in clusters.