Cosmology

Research group

Sub department

About

Group connectivity in COSMOS: a tracer of mass assembly history

Authors:

E Darragh-Ford, C Laigle, G Gozaliasl, C Pichon, JULIEN Devriendt, A Slyz, S Arnouts, Y Dubois, A Finoguenov, R Griffiths, K Kraljic, H Pan, S Peirani, F Sarron

Abstract:

Cosmic filaments are the channel through which galaxy groups assemble their mass. Cosmic connectivity, namely the number of filaments connected to a given group, is therefore expected to be an important ingredient in shaping group properties. The local connectivity is measured in COSMOS around X-Ray detected groups between redshift 0.5 and 1.2. To this end, large-scale filaments are extracted using the accurate photometric redshifts of the COSMOS2015 catalogue in two-dimensional slices of thickness 120 comoving Mpc centred on the group's redshift. The link between connectivity, group mass and the properties of the brightest group galaxy (BGG) is investigated. The same measurement is carried out on mocks extracted from the lightcone of the hydrodynamical simulation Horizon-AGN in order to control systematics. More massive groups are on average more connected. At fixed group mass in low-mass groups, BGG mass is slightly enhanced at high connectivity, while in high mass groups BGG mass is lower at higher connectivity. Groups with a star-forming BGG have on average a lower connectivity at given mass. From the analysis of the Horizon-AGN simulation, we postulate that different connectivities trace different paths of group mass assembly: at high group mass, groups with higher connectivity are more likely to have grown through a recent major merger, which might be in turn the reason for the quenching of the BGG. Future large-field photometric surveys, such as Euclid and LSST, will be able to confirm and extend these results by probing a wider mass range and a larger variety of environment.

Horizon-AGN virtual observatory - 1. SED-fitting performance and forecasts for future imaging surveys

MNRAS

Authors:

C Laigle, I Davidzon, O Ilbert, J Devriendt, D Kashino, C Pichon, P Capak, S Arnouts, S de la Torre, Y Dubois, G Gozaliasl, D Le Borgne, S Lilly, HJ McCracken, M Salvato, A Slyz

Abstract:

Using the ligthcone from the cosmological hydrodynamical simulation Horizon-AGN, we produced a photometric catalogue over $0

Improving Photometric Redshift Estimation using GPz: size information, post processing and improved photometry

Monthly Notices of the Royal Astronomical Society Blackwell Publishing Inc.

Authors:

Z Gomes, MJ Jarvis, IA Almosallam, SJ Roberts

Abstract:

The next generation of large scale imaging surveys (such as those conducted with the Large Synoptic Survey Telescope and Euclid) will require accurate photometric redshifts in order to optimally extract cosmological information. Gaussian Processes for photometric redshift estimation (GPz) is a promising new method that has been proven to provide efficient, accurate photometric redshift estimations with reliable variance predictions. In this paper, we investigate a number of methods for improving the photometric redshift estimations obtained using GPz (but which are also applicable to others). We use spectroscopy from the Galaxy and Mass Assembly Data Release 2 with a limiting magnitude of r<19.4 along with corresponding Sloan Digital Sky Survey visible (ugriz) photometry and the UKIRT Infrared Deep Sky Survey Large Area Survey near-IR (YJHK) photometry. We evaluate the effects of adding near-IR magnitudes and angular size as features for the training, validation and testing of GPz and find that these improve the accuracy of the results by ~15-20 per cent. In addition, we explore a post-processing method of shifting the probability distributions of the estimated redshifts based on their Quantile-Quantile plots and find that it improves the bias by ~40 per cent. Finally, we investigate the effects of using more precise photometry obtained from the Hyper Suprime-Cam Subaru Strategic Program Data Release 1 and find that it produces significant improvements in accuracy, similar to the effect of including additional features.

KiDS+VIKING-450 and DES-Y1 combined: Cosmology with cosmic shear

Astronomy and Astrophysics: a European journal EDP Sciences

Authors:

S Joudaki, H Hildebrandt, D Traykova, Ne Chisari, C Heymans, A Kannawadi, K Kuijken, Ah Wright, M Asgari, T Erben, H Hoekstra, B Joachimi, L Miller, T Tr枚ster, JL van den Busch

Abstract:

We present a combined tomographic weak gravitational lensing analysis of the Kilo Degree Survey (KV450) and the Dark Energy Survey (DES-Y1). We homogenize the analysis of these two public cosmic shear datasets by adopting consistent priors and modeling of nonlinear scales, and determine new redshift distributions for DES-Y1 based on deep public spectroscopic surveys. Adopting these revised redshifts results in a $0.8 \sigma$ reduction in the DES-inferred value for $S_8$. The combined KV450 + DES-Y1 constraint on $S_8 = 0.762^{+0.025}_{-0.024}$ is in tension with the Planck 2018 constraint from the cosmic microwave background at the level of $2.5\sigma$. This result highlights the importance of developing methods to provide accurate redshift calibration for current and future weak lensing surveys.

KiDS+VIKING-450: Cosmic shear tomography with optical+infrared data

Astronomy and Astrophysics: a European journal EDP Sciences

Authors:

H Hildebrandt, F K枚hlinger, JLVD Busch, B Joachimi, C Heymans, A Kannawadi, AH Wright, M Asgari, C Blake, H Hoekstra, S Joudaki, K Kuijken, LANCE Miller, CB Morrison, T Tr枚ster, A Amon, M Archidiacono, S Brieden, A Choi, JTAD Jong, T Erben, B Giblin, JA Peacock, A Mead, M Radovich

Abstract:

We present a tomographic cosmic shear analysis of the Kilo-Degree Survey (KiDS) combined with the VISTA Kilo-Degree Infrared Galaxy Survey (VIKING). This is the first time that a full optical to near-infrared data set has been used for a wide-field cosmological weak lensing experiment. This unprecedented data, spanning $450~$deg$^2$, allows us to improve significantly the estimation of photometric redshifts, such that we are able to include robustly higher-redshift sources for the lensing measurement, and - most importantly - solidify our knowledge of the redshift distributions of the sources. Based on a flat $\Lambda$CDM model we find $S_8\equiv\sigma_8\sqrt{\Omega_{\rm m}/0.3}=0.737_{-0.036}^{+0.040}$ in a blind analysis from cosmic shear alone. The tension between KiDS cosmic shear and the Planck-Legacy CMB measurements remains in this systematically more robust analysis, with $S_8$ differing by $2.3\sigma$. This result is insensitive to changes in the priors on nuisance parameters for intrinsic alignment, baryon feedback, and neutrino mass. KiDS shear measurements are calibrated with a new, more realistic set of image simulations and no significant B-modes are detected in the survey, indicating that systematic errors are under control. When calibrating our redshift distributions by assuming the 30-band COSMOS-2015 photometric redshifts are correct (following the Dark Energy Survey and the Hyper Suprime-Cam Survey), we find the tension with Planck is alleviated. The COSMOS-2015-calibrated KiDS redshift distributions are however discrepant with the results from our extensive spectroscopic calibration sample and the distributions recovered using angular clustering measurements, which we deem more reliable. The robust determination of source redshift distributions remains one of the most challenging aspects for future cosmic shear surveys.