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Edinburgh, United Kingdom

Rhodes J.,Jet Propulsion Laboratory | Rhodes J.,California Institute of Technology | Leauthaud A.,Lawrence Berkeley National Laboratory | Leauthaud A.,University of California at Berkeley | And 5 more authors.
Publications of the Astronomical Society of the Pacific | Year: 2010

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. © 2010. The Astronomical Society of the Pacific. All rights reserved. Source

Amiaux J.,French Atomic Energy Commission | Scaramella R.,National institute for astrophysics | Mellier Y.,CNRS Paris Institute of Astrophysics | Altieri B.,European Space Agency | And 25 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

Euclid is an ESA Cosmic-Vision wide-field-space mission which is designed to explain the origin of the acceleration of Universe expansion. The mission will investigate at the same time two primary cosmological probes: Weak gravitational Lensing (WL) and Galaxy Clustering (in particular Baryon Acoustic Oscillations, BAO). The extreme precision requested on primary science objectives can only be achieved by observing a large number of galaxies distributed over the whole sky in order to probe the distribution of dark matter and galaxies at all scales. The extreme accuracy needed requires observation from space to limit all observational biases in the measurements. The definition of the Euclid survey, aiming at detecting billions of galaxies over 15 000 square degrees of the extragalactic sky, is a key parameter of the mission. It drives its scientific potential, its duration and the mass of the spacecraft. The construction of a Reference Survey derives from the high level science requirements for a Wide and a Deep survey. The definition of a main sequence of observations and the associated calibrations were indeed a major achievement of the Definition Phase. Implementation of this sequence demonstrated the feasibility of covering the requested area in less than 6 years while taking into account the overheads of space segment observing and maneuvering sequence. This reference mission will be used for sizing the spacecraft consumables needed for primary science. It will also set the framework for optimizing the time on the sky to fulfill the primary science and maximize the Euclid legacy. © 2012 SPIE. Source

Nyland K.,U.S. National Radio Astronomy Observatory | Nyland K.,Netherlands Institute for Radio Astronomy | Young L.M.,New Mexico Institute of Mining and Technology | Wrobel J.M.,U.S. National Radio Astronomy Observatory | And 28 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

We present the results of a high-resolution, 5 GHz, Karl G. Jansky Very Large Array study of the nuclear radio emission in a representative subset of the ATLAS3D survey of early-type galaxies (ETGs). We find that 51 ± 4 per cent of the ETGs in our sample contain nuclear radio emission with luminosities as low as 1018 W Hz-1. Most of the nuclear radio sources have compact (≲25-110 pc) morphologies, although ~10 per cent display multicomponent core+jet or extended jet/lobe structures. Based on the radio continuum properties, as well as optical emission line diagnostics and the nuclear X-ray properties, we conclude that the majority of the central 5 GHz sources detected in the ATLAS3D galaxies are associated with the presence of an active galactic nucleus (AGN). However, even at subarcsecond spatial resolution, the nuclear radio emission in some cases appears to arise from low-level nuclear star formation rather than an AGN, particularly when molecular gas and a young central stellar population is present. This is in contrast to popular assumptions in the literature that the presence of a compact, unresolved, nuclear radio continuum source universally signifies the presence of an AGN. Additionally, we examine the relationships between the 5 GHz luminosity and various galaxy properties including the molecular gas mass and - for the first time - the global kinematic state. We discuss implications for the growth, triggering, and fuelling of radio AGNs, as well as AGN-driven feedback in the continued evolution of nearby ETGs. © 2016 The Authors. Source

Young L.M.,New Mexico Institute of Mining and Technology | Young L.M.,Academia Sinica, Taiwan | Scott N.,University of Sydney | Serra P.,Netherlands Institute for Radio Astronomy | And 29 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present a study of the cold gas contents of the ATLAS3D early-type galaxies, in the context of their optical colours, near-ultraviolet colours and Hβ absorption line strengths. Early-type (elliptical and lenticular) galaxies are not as gas poor as previously thought, and at least 40 per cent of local early-type galaxies are now known to contain molecular and/or atomic gas. This cold gas offers the opportunity to study recent galaxy evolution through the processes of cold gas acquisition, consumption (star formation) and removal. Molecular and atomic gas detection rates range from 10 to 34 per cent in red sequence early-type galaxies, depending on how the red sequence is defined, and from 50 to 70 per cent in blue early-type galaxies. Notably, massive red sequence early-type galaxies (stellar masses >5 × 1010 {N-ary circled dot operator} , derived from dynamical models) are found to have HI masses up to M(H I)/M* 0.06 and H2 masses up to M(H2)/M* 0.01. Some 20 per cent of all massive early-type galaxies may have retained atomic and/or molecular gas through their transition to the red sequence. However, kinematic and metallicity signatures of external gas accretion (either from satellite galaxies or the intergalactic medium) are also common, particularly at stellar masses ≤5 × 1010 {N-ary circled dot operator} , where such signatures are found in 50 per cent of H2-rich early-type galaxies. Our data are thus consistent with a scenario in which fast rotator early-type galaxies are quenched former spiral galaxies which have undergone some bulge growth processes, and in addition, some of them also experience cold gas accretion which can initiate a period of modest star formation activity. We discuss implications for the interpretation of colour-magnitude diagrams. © 2014 The Authors. Source

Davis T.A.,European Southern Observatory | Young L.M.,New Mexico Institute of Mining and Technology | Young L.M.,Academia Sinica, Taiwan | Crocker A.F.,University of Toledo | And 27 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present measurements of the star formation rate (SFR) in the early-type galaxies (ETGs) of the ATLAS3D sample, based onWide-field Infrared Survey Explorer (WISE) 22 μmand Galaxy Evolution Explorer far-ultraviolet emission. We combine these with gas masses estimated from 12CO and HI data in order to investigate the star formation efficiency (SFE) in a larger sample of ETGs than previously available. We first recalibrate (based on WISE data) the relation between old stellar populations (traced at Ks band) and 22 μm luminosity, allowing us to remove the contribution of 22 μm emission from circumstellar dust. We then go on to investigate the position of ETGs on the Kennicutt-Schmidt (KS) relation. Molecular gas-rich ETGs have comparable star formation surface densities to normal spiral galaxy centres, but they lie systematically offset from the KS relation, having lower SFEs by a factor of ≈2.5 (in agreement with other authors). This effect is driven by galaxies where a substantial fraction of the molecular material is in the rising part of the rotation curve, and shear is high.We show here for the first time that although the number of stars formed per unit gas mass per unit time is lower in ETGs, it seems that the amount of stars formed per free-fall time is approximately constant. The scatter around this dynamical relation still correlates with galaxy properties such as the shape of the potential in the inner regions. This leads us to suggest that dynamical properties (such as shear or the global stability of the gas) may be important second parameters that regulate star formation and cause much of the scatter around star formation relations. © 2014 The Authors. Source

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