Rubin-LSST

Abstract:

We present the fundamental plane (FP) for 38 early-type galaxies in the two rich galaxy clusters RX J0152.7-1357 (z = 0.83) and RX J1226.9+3332 (z = 0.89), reaching a limiting magnitude of MB = -19.8 in the rest frame of the clusters. While the zero-point offset of the FP for these high-redshift clusters relative to our low-redshift sample is consistent with passive evolution with a formation redshift of zform ≈ 3.2, the FP for the high-redshift clusters is not only shifted as expected for a mass-independent zform but rotated relative to the low-redshift sample. Expressed as a relation between the galaxy masses and the mass-to-light ratios, the FP is significantly steeper for the high-redshift clusters than for our low-redshift sample. We interpret this as a mass dependency of the star formation history, as has been suggested by other recent studies. The low-mass galaxies (10 ^10.3 M⊙) have experienced star formation as recently as z ≈ 1.35 (1.5 Gyr prior to their look-back time), while galaxies with masses larger than 10^11.3 M⊙ had their last major star formation episode at z > 4.5. © 2006, The American Astronomical Society. All rights reserved.

Abstract:

This article presents a measurement of the top quark mass using the CDF II detector at Fermilab. Colliding beams of protons and antiprotons at Fermilab's Tevatron (s=1.96TeV) produce top/antitop pairs, which decay to W+W-bb̄; events are selected where one W decays to hadrons and the other W decays to either e or μ plus a neutrino. The data sample corresponds to an integrated luminosity of approximately 318pb-1. A total of 165 tt̄ events are separated into four subsamples based on jet transverse energy thresholds and the number of b jets identified by reconstructing a displaced vertex. In each event, the reconstructed top quark invariant mass is determined by minimizing a χ2 for the overconstrained kinematic system. At the same time, the mass of the hadronically decaying W boson is measured in the same event sample. The observed W boson mass provides an in situ improvement in the determination of the hadronic jet energy scale. A simultaneous likelihood fit of the reconstructed top quark masses and the W boson invariant masses in the data sample to distributions from simulated signal and background events gives a top quark mass of 173.5-3.8+3.9GeV/c2. © 2006 The American Physical Society.