  The ATLAS liquid argon (LAr) calorimeter system consists of an
electromagnetic barrel calorimeter and two end-caps with electromagnetic,
hadronic and forward calorimeters. The construction of the full calorimeter
system is completed since mid-2004. The detector has been operated with LAr at
nominal high voltage and fully equipped with readout electronics. Online
software, monitoring tools and offline signal reconstruction have been
developed for data collection and processing. Extensive tests with calibration
pulses have been carried out, and the electronics calibration scheme for all
182468 channels has been exercised. Since Augst 2006, cosmic muon data have
been collected together with the rest of the ATLAS detector system as part of
the ATLAS commissioning program. The reconstructed LAr signals from energy
deposited by cosmic rays are compared to the prediction derived from measured
detector parameters and calibration pulses. The uniformity of the detector
response within regions that have sufficient cosmic muons are examined. The
expected performance of the LAr calorimeter for ATLAS physics, based on
previous beam tests and Monte Carlo simulation, is also summarised.
