Beecroft Institute for Particle Astrophysics and Cosmology

Research group

Research theme

Sub department

About

A ghost in the toast: TESS background light produces a false “transit” across τ Ceti

Research Notes of the AAS American Astronomical Society 3:10 (2019) 145

Authors:

Nora Eisner, Benjamin Pope, Suzanne Aigrain, Oscar Barragan Villanueva, Timothy R White, Chelsea X Huang, Chris Lintott, Andrey Volkov

Inferring high redshift large-scale structure dynamics from the Lyman-alpha forest

A&A 2019

Authors:

Natalia Porqueres, Jens Jasche, Guilhem Lavaux, Torsten Enßlin

Abstract:

One of the major science goals over the coming decade is to test fundamental physics with probes of the cosmic large-scale structure out to high redshift. Here we present a fully Bayesian approach to infer the three-dimensional cosmic matter distribution and its dynamics at z>2 from observations of the Lyman-α forest. We demonstrate that the method recovers the unbiased mass distribution and the correct matter power spectrum at all scales. Our method infers the three-dimensional density field from a set of one-dimensional spectra, interpolating the information between the lines of sight. We show that our algorithm provides unbiased mass profiles of clusters, becoming an alternative for estimating cluster masses complementary to weak lensing or X-ray observations. The algorithm employs a Hamiltonian Monte Carlo method to generate realizations of initial and evolved density fields and the three-dimensional large-scale flow, revealing the cosmic dynamics at high redshift. The method correctly handles multi-modal parameter distributions, which allow constraining the physics of the intergalactic medium (IGM) with high accuracy. We performed several tests using realistic simulated quasar spectra to test and validate our method. Our results show that detailed and physically plausible inference of three-dimensional large-scale structures at high redshift has become feasible.

Growth of massive scalar hair around a Schwarzschild black hole

Physical Review D American Physical Society 100 (2019) 063014

Authors:

Katherine Clough, PG Ferreira, M Lagos

The SAMI Galaxy Survey: First detection of a transition in spin orientation with respect to cosmic filaments in the stellar kinematics of galaxies

(2019)

Authors:

C Welker, J Bland-Hawthorn, J Van de Sande, C Lagos, P Elahi, D Obreschkow, J Bryant, C Pichon, L Cortese, SN Richards, SM Croom, M Goodwin, JS Lawrence, S Sweet, A Lopez-Sanchez, A Medling, MS Owers, Y Dubois, J Devriendt

Massive spheroids can form in single minor mergers

Monthly Notices of the Royal Astronomical Society Oxford University Press 489:4 (2019) 4679-4689

Authors:

RA Jackson, G Martin, S Kaviraj, C Laigle, Julien Devriendt, Y Dubois, C Pichon

Abstract:

Understanding how rotationally supported discs transform into dispersion-dominated spheroids is central to our comprehension of galaxy evolution. Morphological transformation is largely merger-driven. While major mergers can efficiently create spheroids, recent work has highlighted the significant role of other processes, like minor mergers, in driving morphological change. Given their rich merger histories, spheroids typically exhibit large fractions of ‘ex situ’ stellar mass, i.e. mass that is accreted, via mergers, from external objects. This is particularly true for the most massive galaxies, whose stellar masses typically cannot be attained without a large number of mergers. Here, we explore an unusual population of extremely massive (M* > 1011M⊙) spheroids, in the Horizon-AGN simulation, which exhibit anomalously low ex situ mass fractions, indicating that they form without recourse to significant merging. These systems form in a single minor-merger event (with typical merger mass ratios of 0.11–0.33), with a specific orbital configuration, where the satellite orbit is virtually co-planar with the disc of the massive galaxy. The merger triggers a catastrophic change in morphology, over only a few hundred Myr, coupled with strong in situ star formation. While this channel produces a minority (∼5 per cent) of such galaxies, our study demonstrates that the formation of at least some of the most massive spheroids need not involve major mergers – or any significant merging at all – contrary to what is classically believed.