Cosmology

Abstract:

GRAVITY+ is the upgrade for GRAVITY and the Very Large Telescope Interferometer (VLTI) with wide-separation fringe tracking, new adaptive optics, and laser guide stars on all four 8 m Unit Telescopes (UTs) to enable ever-fainter, all-sky, high-contrast, milliarcsecond interferometry. Here we present the design and first results of the first phase of GRAVITY+, known as GRAVITY Wide. GRAVITY Wide combines the dual-beam capabilities of the VLTI and the GRAVITY instrument to increase the maximum separation between the science target and the reference star from 2 arcseconds with the 8 m UTs up to several 10 arcseconds, limited only by the Eartha's turbulent atmosphere. This increases the sky-coverage of GRAVITY by two orders of magnitude, opening up milliarcsecond resolution observations of faint objects and, in particular, the extragalactic sky. The first observations in 2019-2022 include the first infrared interferometry of two redshift z ~ 2 quasars, interferometric imaging of the binary system HD 105913A, and repeat observations of multiple star systems in the Orion Trapezium Cluster. We find the coherence loss between the science object and fringe-tracking reference star well described by the turbulence of the Eartha's atmosphere. We confirm that the larger apertures of the UTs result in higher visibilities for a given separation due to the broader overlap of the projected pupils on the sky and provide predictions for visibility loss as a function of separation to be used for future planning.

Abstract:

Cosmological N-body simulations of the dark matter component of the universe typically use initial conditions with a fixed power spectrum and random phases of the density field, leading to structure consistent with the local distribution of galaxies only in a statistical sense. It is, however, possible to infer the initial phases which lead to the configuration of galaxies and clusters that we see around us. We analyse the CSiBORG suite of 101 simulations, formed by constraining the density field within 155 Mpc h⁻¹ with dark matter particle mass 4.38 × 10⁹ M_⊙, to quantify the degree to which constraints imposed on 2.65 Mpc h⁻¹ scales reduce variance in the halo mass function and halo–halo cross-correlation function on a range of scales. This is achieved by contrasting CSiBORG with a subset of the unconstrained Quijote simulations and expectations for the ΛCDM average. Using the FOF, PHEW, and HOP halofinders, we show that the CSiBORG suite beats cosmic variance at large mass scales (≳10¹⁴ M_⊙ h⁻¹), which are most strongly constrained by the initial conditions, and exhibits a significant halo–halo cross-correlation out to ∼30 Mpc h⁻¹. Moreover, the effect of the constraints percolates down to lower mass objects and to scales below those on which they are imposed. Finally, we develop an algorithm to ‘twin’ haloes between realizations and show that approximately 50 per cent of haloes with mass greater than 10¹⁵ M_⊙ h⁻¹ can be identified in all realizations of the CSiBORG suite. We make the CSiBORG halo catalogues publicly available for future applications requiring knowledge of the local halo field.