Locuss: The Mid-Infrared Butcher-Oemler Effect

Abstract

We study the mid-infrared properties of galaxies in 30 massive galaxy clusters at 0.02≤z≤0.40, using panoramic Spitzer/MIPS 24µm and near-infrared data, including 27 new observations from the LoCuSS and ACCESS surveys. This is the largest sample of clusters to date with such high-quality and uniform mid-infrared data covering not only the cluster cores, but extending into the infall regions. We use these data to revisit the so-called Butcher-Oemler effect, measuring the fraction of massive infrared luminous galaxies (K<K ⋆ +1.5, L IR >5×10 10 L ⊙ ) within r 200 , finding a steady increase in the fraction with redshift from ∼3% at z=0.02 to ∼10% by z=0.30, and an rms cluster-to-cluster scatter about this trend of 0.03. The best-fit redshift evolution model of the form f SF ∝ (1 + z) n has n = 5.7 +2.1 −1.8 , which is stronger redshift evolution than that of L ⋆ IR in both clusters and the field. We find that, statistically, this excess is associated with galaxies found at large clustercentric radii, specifically r 500 <r<r 200 , implying that the mid-infrared Butcher Oemler effect can be explained by a combination of both the global decline in star-formation in the universe since z ∼ 1 and enhanced star formation in the infall regions of clusters at intermediate redshifts. This picture is supported by a simple infall model based on the Millennium Simulation semi-analytic galaxy catalogs, whereby star-formation in infalling galaxies is instantaneously quenched upon their first passage through the cluster, in that the observed radial trends of f SF trace those inferred from the simulations. The observed f SF however lie systematically above the predictions, suggesting an overall excess of star-formation, either due to triggering by environmental processes, or a gradual quenching. We also find that f SF does not depend on simple indicators of the dynamical state of clusters, including the offset between the brightest cluster galaxy and the peak of the X-ray emission. This is consistent with the picture described above in that most new star-formation in clusters occurs in the infall regions, and is thus not sensitive to the details of cluster-cluster mergers in the core regions.

LoCuSS: Shedding new light on the massive lensing cluster Abell 1689 – the view fromHerschel

“…Over March-May 2009 we obtained 1006 spectra with MMT/Hectospec, targeting probable cluster members (based on their M K and J − K colour as in Haines et al 2009a) with K < K * + 2 over the full WFCAM field, prioritising those detected at 24 μm, and giving the highest priority to all sources with f 24 > 1 mJy (irrespective of their NIR colour), identifying 387 cluster members. A1689 already had extensive spectroscopic coverage, most notably from Czoske (2004) and the survey of ISOCAM detections by D02, taking us up to a total of 989 unique cluster members.…”

“…These issues have motivated the Local Cluster Substructure (LoCuSS 1 ) Herschel key programme to study a large statistical sample of 30 massive galaxy clusters at z ∼ 0.2 with panoramic FUV-FIR data from GALEX, Spitzer and Herschel (Haines et al 2009a;Smith et al 2010). These provide a complete census of star formation in cluster galaxies extending to the infall regions, which can then be related to the dynamical status of the cluster as determined from complementary lensing, X-ray and dynamical analyses (Haines et al 2009b;Pereira et al 2010).…”

LoCuSS: AHerschelview of obscured star formation in Abell 1835

“…We decompose the 0.5-2 keV combined XMM image into unresolved and extended emission, following the wavelet technique of Finoguenov et al (2009), before extracting point source fluxes at the locations of Herschel sources. Additionally, we make use of previously published wide-field data from Spitzer/MIPS 24 μm and UKIRT/WFCAM J, K bands (Haines et al 2009), and Subaru/Suprime-CAM (Okabe et al 2010). …”

“…Some studies have claimed to observe triggered star formation in strongly disrupted, merging clusters (e.g. Geach et al 2006) but the intrinsic scatter in this correlation is large, with some seemingly relaxed clusters presenting much higher star formation activity than their actively merging counterparts (Haines et al 2009). …”

LoCuSS: Probing galaxy transformation physics withHerschel

“…Figure 4 is only available in electronic form at http://www.aanda.org star-formation (SF) has been recently quenched, through optical spectral features including Balmer absorption lines, to mid/farinfrared (IR) emission from dust heated by SF (e.g. Moran et al 2007;Poggianti et al 2000;Haines et al 2009b).…”