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The Effects of Charge Transfer Inefficiency (CTI) on Galaxy Shape Measurements

Rhodes, Jason and Leauthaud, Alexie and Stoughton, Chris and Massey, Richard and Dawson, Kyle S. and Kolbe, William and Roe, Natalie (2010) The Effects of Charge Transfer Inefficiency (CTI) on Galaxy Shape Measurements. Publications of the Astronomical Society of the Pacific, 122 (890). pp. 439-450. ISSN 0004-6280.

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We examine the effects of charge transfer inefficiency (CTI) during CCD readout on the demanding galaxy shape measurements required by studies of weak gravitational lensing. We simulate a CCD readout with CTI such as that caused by charged particle radiation damage in space-based detectors. We verify our simulations on real data from fully depleted p-channel CCDs that have been deliberately irradiated in a laboratory. We show that only charge traps with time constants of the same order as the time between row transfers during readout affect galaxy shape measurements. We simulate deep astronomical images and the process of CCD readout, characterizing the effects of CTI on various galaxy populations. Our code and methods are general and can be applied to any CCDs, once the density and characteristic release times of their charge trap species are known. We baseline our study around p-channel CCDs that have been shown to have charge transfer efficiency up to an order of magnitude better than several models of n-channel CCDs designed for space applications. We predict that for galaxies furthest from the readout registers, bias in the measurement of galaxy shapes, Δe, will increase at a rate of (2.65 ± 0.02) × 10^(-4) yr^(-1) at L2 for accumulated radiation exposure averaged over the solar cycle. If uncorrected, this will consume the entire shape measurement error budget of a dark energy mission surveying the entire extragalactic sky within about 4 yr of accumulated radiation damage. However, software mitigation techniques demonstrated elsewhere can reduce this by a factor of ~10, bringing the effect well below mission requirements. This conclusion is valid only for the p-channel CCDs we have modeled; CCDs with higher CTI will fare worse and may not meet the requirements of future dark energy missions. We also discuss additional ways in which hardware could be designed to further minimize the impact of CTI.

Item Type:Article
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URLURL TypeDescription
Leauthaud, Alexie0000-0002-3677-3617
Dawson, Kyle S.0000-0002-0553-3805
Additional Information:© 2010 The Astronomical Society of the Pacific. Received 2009 November 7; accepted 2010 February 3; published 2010 March 12. This work was supported in part by the Jet Propulsion Laboratory, operated by the California Institute of Technology under a contract with NASA. This work was also supported by the US Department of Energy under contract DE-AC02-05CH11231. We thank Chris Bebek, Mike Lampton, Michael Levi, and Roger Smith for useful discussions about CCDs and CTE. A. L. acknowledges support from the Chamberlain Fellowship at LBNL and from the Berkeley Center for Cosmological Physics. R. M. is supported by STFC Advanced Fellowship PP/E006450/1 and FP7 grant MIRG-CT-208994. C. S. was supported by funding from the Office of Science at LBNL and Fermilab.
Funding AgencyGrant Number
Department of Energy (DOE)DE-AC02-05CH11231
Science and Technology Facilities Council (STFC)PP/E006450/1
Lawrence Berkeley National Laboratory (LBNL)UNSPECIFIED
Issue or Number:890
Record Number:CaltechAUTHORS:20100412-140410010
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Official Citation:The Effects of Charge Transfer Inefficiency (CTI) on Galaxy Shape Measurements Jason Rhodes, Alexie Leauthaud, Chris Stoughton, Richard Massey, Kyle Dawson, William Kolbe, and Natalie Roe Publications of the Astronomical Society of the Pacific 2010 122:890, 439-450
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:17945
Deposited By: Tony Diaz
Deposited On:04 May 2010 01:34
Last Modified:09 Mar 2020 13:18

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