Astronomical instrumentation

Abstract:

{abridged} We present imaging and spectroscopy of Abell 1689 (z=0.183) from GEMINI/GMOS-N and HST/ACS. We measure integrated photometry from the GMOS g' and r' images (for 531 galaxies) and surface photometry from the HST F625W image (for 43 galaxies) as well as velocities and velocity dispersions from the GMOS spectra (for 71 galaxies). We construct the Kormendy relation (KR), Faber-Jackson relation (FJR) and colour-magnitude relation (CMR) for early-type galaxies in Abell 1689 using this data and compare them to those of the Coma cluster. We measure the intrinsic scatter of the CMR in Abell 1689 to be 0.054 \pm 0.004 mag which places degenerate constraints on the ratio of the assembly timescale to the time available (beta) and the age of the population. Making the assumption that galaxies in Abell 1689 will evolve into those of Coma over an interval of 2.26 Gyr breaks this degeneracy and limits beta to be > 0.6 and the age of the red sequence to be > 5.5 Gyr (formed at z > 0.55). Without corrections for size evolution but accounting for magnitude cuts and selection effects, the KR & FJR are inconsistent and disagree at the 2 sigma level regarding the amount of luminosity evolution in the last 2.26 Gyr. However, after correcting for size evolution the KR & FJR show similar changes in luminosity (0.22 \pm 0.11 mag) that are consistent with the passive evolution of the stellar populations from a single burst of star formation 10.2 \pm 3.3 Gyr ago (z = 1.8+inf-0.9). Thus the changes in the KR, FJR & CMR of Abell 1689 relative to Coma all agree and suggest old galaxy populations with little or no synchronisation in the star formation histories. Furthermore, the weak evidence for size evolution in the cluster environment in the last 2.26 Gyr places interesting constraints on the possible mechanisms at work, favouring harassment or secular processes over merger scenarios.

Abstract:

This Letter presents a search for contact interactions in the dielectron and dimuon channels using data from proton-proton collisions produced by the LHC at s=7 TeV and recorded by the ATLAS detector. The data sample, collected in 2011, corresponds to an integrated luminosity of 1.08 and 1.21 fb-1 in the e+e- and μ+μ- channels, respectively. No significant deviations from the standard model are observed. Using a Bayesian approach with a prior flat in 1/Λ2, the following 95% CL lower limits are placed on the energy scale of ℓℓqq contact interactions: Λ->10.1 TeV (Λ+>9.4 TeV) in the electron channel and Λ->8.0 TeV (Λ+>7.0 TeV) in the muon channel for constructive (destructive) interference in the left-left isoscalar contact interaction model. Limits are also provided for a prior flat in 1/Λ4. © 2012 CERN.

Abstract:

This Letter presents a search for singly produced vector-like quarks, Q, coupling to light quarks, q. The search is sensitive to both charged current (CC) and neutral current (NC) processes, pp→Qq→Wqq' and pp→Qq→Zqq' with a leptonic decay of the vector gauge boson. In 1.04fb-1 of data taken in 2011 by the ATLAS experiment at a center-of-mass energy √s=7 TeV, no evidence of such heavy vector-like quarks is observed above the expected Standard Model background. Limits on the heavy vector-like quark production cross section times branching ratio as a function of mass mQ are obtained. For a coupling κqQ=v/mQ, where v is the Higgs vacuum expectation value, 95% C.L. lower limits on the mass of a vector-like quark are set at 900 GeV and 760 GeV from CC and NC processes, respectively. © 2012 CERN.