Galaxy formation and evolution

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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.
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Herschel-SPIRE-Fourier Transform Spectroscopy of the nearby spiral galaxy IC342

Monthly Notices of the Royal Astronomical Society

Authors:

D Rigopoulou, PD Hurley, BM Swinyard, J Virdee, KV Croxall, RHB Hopwood, T Lim, GE Magdis, CP Pearson, E Pellegrini, E Polehampton, J-D Smith
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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
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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.
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Large Synoptic Survey Telescope White Paper; The Case for Matching U-band on Deep Drilling Fields

Authors:

BW Holwerda, A Baker, S Blyth, S Kannappan, D Obreschkow, S Ravindranath, E Elson, M Vaccari, S Crawford, M Bershady, N Hathi, N Maddox, R Taylor, MATTHEW Jarvis, J Bridge

Abstract:

U-band observations with the LSST have yet to be fully optimized in cadence. The straw man survey design is a simple coverage of the medium-deep-fast survey. Here we argue that deep coverage of the four deep drilling fields (XMM-LSS, ECDFS, ELAIS-S1 and COSMOS) has a much higher scientific return, given that these are also the target of the Southern Hemisphere's Square Kilometer Array Pathfinder, the MeerKAT specifically, deep radio observations.
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