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Bilicki, M.,Hoekstra, H.,Brown, M. J. I.,Amaro, V.,Blake, C.,Cavuoti, S.,de Jong, J. T. A.,Georgiou, C.,Hildebrandt, H.,Wolf, C.,Amon, A.,Brescia, M.,Brough, S.,Costa-Duarte, M. V.,Erben, T.,Glazebroo EDP Sciences 2018 Astronomy and astrophysics Vol.616 No.-
<P>We present a machine-learning photometric redshift (ML photo-<I>z</I>) analysis of the Kilo-Degree Survey Data Release 3 (KiDS DR3), using two neural-network based techniques: ANNz2 and MLPQNA. Despite limited coverage of spectroscopic training sets, these ML codes provide photo-<I>z</I>s of quality comparable to, if not better than, those from the Bayesian Photometric Redshift (BPZ) code, at least up to <I>z</I>phot ≲ 0.9 and <I>r</I> ≲ 23.5. At the bright end of <I>r</I> ≲ 20, where very complete spectroscopic data overlapping with KiDS are available, the performance of the ML photo-<I>z</I>s clearly surpasses that of BPZ, currently the primary photo-<I>z</I> method for KiDS. Using the Galaxy And Mass Assembly (GAMA) spectroscopic survey as calibration, we furthermore study how photo-<I>z</I>s improve for bright sources when photometric parameters additional to magnitudes are included in the photo-<I>z</I> derivation, as well as when VIKING and WISE infrared (IR) bands are added. While the fiducial four-band <I>ugri</I> setup gives a photo-<I>z</I> bias 〈<I>δz</I>/(1 + <I>z</I>)〉 = −2 × 10<SUP>−4</SUP> and scatter <I>σδz/(1+z)</I> < 0.022 at mean 〈<I>z</I>〉 = 0.23, combining magnitudes, colours, and galaxy sizes reduces the scatter by ~7% and the bias by an order of magnitude. Once the <I>ugri</I> and IR magnitudes are joined into 12-band photometry spanning up to 12 <I>μ</I>m, the scatter decreases by more than 10% over the fiducial case. Finally, using the 12 bands together with optical colours and linear sizes gives 〈<I>δz</I>/(1 + <I>z</I>)〉 < 4 × 10<SUP>−5</SUP> and <I>σ</I><I>δz</I>/(1+<I>z</I>) < 0.019. This paper also serves as a reference for two public photo-<I>z</I> catalogues accompanying KiDS DR3, both obtained using the ANNz2 code. The first one, of general purpose, includes all the 39 million KiDS sources with four-band <I>ugri</I> measurements in DR3. The second dataset, optimised for low-redshift studies such as galaxy-galaxy lensing, is limited to <I>r</I> ≲ 20, and provides photo-<I>z</I>s of much better quality than in the full-depth case thanks to incorporating optical magnitudes, colours, and sizes in the GAMA-calibrated photo-<I>z</I> derivation.</P>
Test of Special Relativity Using a Fiber Network of Optical Clocks
Delva, P.,Lodewyck, J.,Bilicki, S.,Bookjans, E.,Vallet, G.,Le Targat, R.,Pottie, P.-E.,Guerlin, C.,Meynadier, F.,Le Poncin-Lafitte, C.,Lopez, O.,Amy-Klein, A.,Lee, W.-K.,Quintin, N.,Lisdat, C.,Al-Maso American Physical Society 2017 Physical Review Letters Vol.118 No.22
<P>Phase compensated optical fiber links enable high accuracy atomic clocks separated by thousands of kilometers to be compared with unprecedented statistical resolution. By searching for a daily variation of the frequency difference between four strontium optical lattice clocks in different locations throughout Europe connected by such links, we improve upon previous tests of time dilation predicted by special relativity. We obtain a constraint on the Robertson-Mansouri-Sexl parameter |alpha| <= 1.1 x 10(-8), quantifying a violation of time dilation, thus improving by a factor of around 2 the best known constraint obtained with Ives-Stilwell type experiments, and by 2 orders of magnitude the best constraint obtained by comparing atomic clocks. This work is the first of a new generation of tests of fundamental physics using optical clocks and fiber links. As clocks improve, and as fiber links are routinely operated, we expect that the tests initiated in this Letter will improve by orders of magnitude in the near future.</P>
KiDS+2dFLenS+GAMA: testing the cosmological model with the EG statistic
Amon, A,Blake, C,Heymans, C,Leonard, C D,Asgari, M,Bilicki, M,Choi, A,Erben, T,Glazebrook, K,Harnois-Dé,raps, J,Hildebrandt, H,Hoekstra, H,Joachimi, B,Joudaki, S,Kuijken, K,Lidman, C,Loveday, J Oxford University Press 2018 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.479 No.3