Discovery of a supercluster in the Zone of Avoidance in Vela

We report the discovery of a potentially major supercluster that extends across the Galactic plane in the constellation of Vela, at a mean recessional velocity of ~18 000 km s-1. Recent multiobject spectroscopic observations of this Vela supercluster (VSCL), using AAOmega+2dF and the Southern African Large Telescope, confirm an extended galaxy overdensity in the Zone of Avoidance (ZOA) located where residual bulk flows predict a considerable mass excess. We present a preliminary analysis of ~4500 new spectroscopic galaxy redshifts obtained in the ZOA centred on the Vela region (l = 272. ° 5 ± 20°, b = 0° ± 10°). The presently sparsely sampled data set traces an overdensity that covers 25° in Galactic longitude on either side of the Galactic plane, suggesting an extent of 25 × 20 deg2, corresponding to ~ 115×90 h70 Mpc at the supercluster redshift. In redshift space, the overdensity appears to consist of two merging wall-like structures, interspersed with clusters and groups. Both the velocity histogram and the morphology of the multibranching wall structure are consistent with a supercluster classification. Ks o galaxy counts show an enhancement of ~1.2 over the survey area for galaxies brighter than MK * at the VSCL distance, and a galaxy overdensity of δ = 0.50-0.77 within a photometric redshift shell around the VSCL, when compared with various Two Micron All-Sky Survey samples. Taking account of selection effects, the VSCL is estimated to contribute vLG ≳ 50 km s-1 to the motion of the Local GroupRCK-K, THJ, and MEC acknowledge research support from the NRF. MB is supported through grants #614.001.451 from the NWO, FP7 #279396 from the ERC, and #UMO-2012/07/D/ST9/02785 from the NC

The 2-degree Field Lensing Survey: Photometric redshifts from a large new training sample to r < 19.5

We present a new training set for estimating empirical photometric redshifts of galaxies, which was created as part of the 2-degree Field Lensing Survey project. This training set is located in a ∼700 deg2 area of the Kilo-Degree-Survey South field and is randomly selected and nearly complete at r < 19.5. We investigate the photometric redshift performance obtained with ugriz photometry from VST-ATLAS and W1/W2 from WISE, based on several empirical and template methods. The best redshift errors are obtained with kernel-density estimation (KDE), as are the lowest biases, which are consistent with zero within statistical noise. The 68th percentiles of the redshift scatter for magnitude-limited samples at r < (15.5, 17.5, 19.5) are (0.014, 0.017, 0.028). In this magnitude range, there are no known ambiguities in the colour–redshift map, consistent with a small rate of redshift outliers. In the fainter regime, the KDE method produces p(z) estimates per galaxy that represent unbiased and accurate redshift frequency expectations. The p(z) sum over any subsample is consistent with the true redshift frequency plus Poisson noise. Further improvements in redshift precision at r < 20 would mostly be expected from filter sets with narrower passbands to increase the sensitivity of colours to small changes in redshift.CW was supported by Australian Research Council Laureate Grant FL0992131. Parts of this research were conducted by the Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO), through project number CE110001020. MB is supported by the Netherlands Organization for Scientific Research, NWO, through grant number 614.001.451, through FP7 grant number 279396 from the European Research Council and by the Polish National Science Center under contract #UMO-2012/07/D/ST9/02785. CB acknowledges the support of the Australian Research Council through the award of a Future Fellowship. CH acknowledges support from the European Research Council under grant number 647112. HH was supported by the Deutsche Forschungsgemeinschaft under Emmy Noether grant Hi 1495/2-1. TE and DK are supported by the Deutsche Forschungsgemeinschaft in the framework of the TR33 ‘The Dark Universe’. This study is based in part on data acquired at the Australian Astronomical Observatory, through program A/2014B/08. KK acknowledges support by the Alexander von Humboldt Foundation. DP is supported by the Australian Research Council Future Fellowship Grant FT13010108

Testing gravity using galaxy-galaxy lensing and clustering amplitudes in KiDS-1000, BOSS, and 2dFLenS

The physics of gravity on cosmological scales affects both the rate of assembly of large-scale structure and the gravitational lensing ofbackground light through this cosmic web. By comparing the amplitude of these different observational signatures, we can constructtests that can distinguish general relativity from its potential modifications. We used the latest weak gravitational lensing dataset fromthe Kilo-Degree Survey, KiDS-1000, in conjunction with overlapping galaxy spectroscopic redshift surveys, BOSS and 2dFLenS, toperform the most precise existing amplitude-ratio test. We measured the associatedEGstatistic with 15−20% errors in five∆z=0.1tomographic redshift bins in the range 0.2<z<0.7 on projected scales up to 100h−1Mpc. The scale-independence and redshift-dependence of these measurements are consistent with the theoretical expectation of general relativity in a Universe with matterdensityΩm=0.27 +- 0.04. We demonstrate that our results are robust against different analysis choices, including schemes forcorrecting the effects of source photometric redshift errors, and we compare the performance of angular and projected galaxy-galaxylensing statistics.the European Research Council under grant numbers 647112 (MA, BG, CH, TT), 770935 (AD, HH, JLvdB, AHW) and 693024 (SJ); the Polish Ministry of Science and Higher Education through grant DIR/WK/2018/12 and the Polish National Science Center through grant 2018/30/E/ST9/00698 (MB); the Max Planck Society and the Alexander von Humboldt Foundation in the framework of the Max Planck-Humboldt Research Award endowed by the Federal Ministry of Education and Research (CH); Heisenberg grant Hi 1495/5-1 of the Deutsche Forschungsgemeinschaft (HH); the Beecroft Trust (SJ); Vici grant 639.043.512 financed by the Netherlands Organisation for Scientific Research (AK); the Alexander von Humboldt Foundation (KK); the NSFC of China grant 11973070, the Shanghai Committee of Science and Technology grant 19ZR1466600 and Key Research Program of Frontier Sciences grant ZDBS-LY-7013 (HYS); and the European Union’s Horizon 2020 research and innovation programme under the Marie SklodowskaCurie grant 797794 (TT)

KiDS+2dFLenS+GAMA: Testing the cosmological model with the EG statistic

We present a new measurement of EG, which combines measurements of weak gravitational lensing, galaxy clustering, and redshift-space distortions. This statistic was proposed as a consistency test of General Relativity (GR) that is insensitive to linear, deterministic galaxy bias, and the matter clustering amplitude. We combine deep imaging data from KiDS with overlapping spectroscopy from 2dFLenS, BOSS DR12, and GAMA and find EG (z=0.267) = 0.43 ± 0.13(GAMA), EG (z=0.305) = 0.27 ± 0.08 (LOWZ+2dFLOZ), and EG (z=0.0554) = 0.26 ± 0.07 (CMASS + 2dFHIZ). We demonstrate that the existing tension in the value of the matter density parameter hinders the robustness of this statistic as solely a test of GR. We find that our EG measurements, as well as existing ones in the literature, favour a lower matter density cosmology than the cosmic microwave background. For a flat ΔCDM Universe, we find Ωm(z = 0) = 0.25 ± 0.03. With this paper, we publicly release the 2dFLenS data set at: http://2dflens.swin.edu.au.AA, CH, MA, and SJ acknowledge support from the European Research Council under grant numbers 647112 (CH and MA) and 693024 (SJ). CB acknowledges the support of the Australian Research Council through the award of a Future Fellowship. DL acknowledges support from the McWilliams Center for Cosmology, Department of Physics, Carnegie Mellon University. HHi acknowledges support from an Emmy Noether grant (No. Hi 1495/2-1) of the Deutsche Forschungsgemeinschaft. HHo acknowledges support from Vici grant 639.043.512, financed by the Netherlands Organisation for Scientific Research (NWO). BJ acknowledges support by an STFC Ernest Rutherford Fellowship, grant reference ST/J004421/1. JHD acknowledges support from the EuropeansCommission under a Marie-Sklodwoska-Curie European Fellowship (EU project 656869). SJ also acknowledges support from the Beecroft Trust. DP acknowledges the support of the Australian Research Council through the award of a Future Fellowship. MB is supported by the Netherlands Organisation for Scientific Research, NWO, through grant number 614.001.45

Photometric redshifts for the Kilo-Degree Survey Machine-learning analysis with artificial neural networks

We present a machine-learning photometric redshift analysis of the Kilo-Degree Survey Data Release 3, using two neural-network based techniques: ANNz2 and MLPQNA. Despite limited coverage of spectroscopic training sets, these ML codes provide photo-zs of quality comparable to, if not better than, those from the BPZ code, at least up to z(phot) less than or similar to 0.9 and r less than or similar to 23.5. At the bright end of r less than or similar to 20, where very complete spectroscopic data overlapping with KiDS are available, the performance of the ML photo-zs clearly surpasses that of BPZ, currently the primary photo-z method for KiDS. Using the Galaxy And Mass Assembly (GAMA) spectroscopic survey as calibration, we furthermore study how photo-zs improve for bright sources when photometric parameters additional to magnitudes are included in the photo-z derivation, as well as when VIKING and WISE infrared bands are added. While the fiducial four-band ugri setup gives a photo-z bias = -2 x 10(-4) and scatter sigma(delta z/(1+z)) = 0.23, combining magnitudes, colours, and galaxy sizes reduces the scatter by similar to 7% and the bias by an order of magnitude. Once the ugri and IR magnitudes are joined into 12-band photometry spanning up to 12 mu 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 < 4 x 10(-5) and sigma(delta z/(1+z)) < 0.019. This paper also serves as a reference for two public photo-z 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 ugri measurements in DR3. The second dataset, optimized for low-redshift studies such as galaxy-galaxy lensing, is limited to r less than or similar to 20, and provides photo-zs of much better quality than in the full-depth case thanks to incorporating optical magnitudes, colours, and sizes in the GAMA-calibrated photo-z derivation