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Abstract:

Resolved rotation curves (RCs) are the gold-standard measurements for inferring dark matter distributions in Lambda cold dark matter and testing alternative theories of dynamics in galaxies. However, they are expensive to obtain, making them prohibitive for large galaxy samples and at higher redshift. Spatially integrated flux profiles are more accessible and present the information in a different form, but – except in a highly compressed form, as linewidths – have not so far been compared in detail with RCs or employed for dynamical inferences. Here, we study the consistency of RCs and surface density profiles from SPARC with spatially integrated flux profiles from ALFALFA, by combining the resolved properties in a forward model for the flux profile. We define a new metric for asymmetry in the flux profiles, enabling us to cleanly identify those unsuitable for our axisymmetric method. Among all SPARC galaxies the agreement between RCs and flux profiles is satisfactory within the limitations of the data – with most galaxies having an uncertainty-normalized mean squared error (MSE) below 10 – whilst no galaxy deemed symmetric has a MSE above 1.2. Most cases of good agreement prefer an gas dispersion of 13 km s, consistent with resolved studies of gas dispersion from the literature. These results open the door for spatially integrated flux profiles to be used as proxies for spatially resolved dynamics, including a robust appraisal of the degree of asymmetry.

Abstract:

We perform a Bayesian analysis of anisotropy in binary galaxy spin directions in the Hyper-Suprime Cam Data Release 3 catalog, in response to a recent claim that it exhibits a dipole. We find no significant evidence for anisotropy, or for a direction-independent spin probability that differs from 0.5. These results are unchanged allowing for a quadrupole or simply searching for a fixed anisotropy between any two hemispheres, and the Bayes factor indicates decisive evidence for the isotropic model. Our principled method contrasts with the statistic employed by Shamir, which lacks a strong theoretical foundation. Our code is available at ✎.

Abstract:

Constrained cosmological simulations play an important role in modelling the local Universe, enabling investigation of the dark matter content of local structures and their formation. We introduce an internal method for quantifying the extent to which the variance of individual halo properties is suppressed by the constraints imposed on the initial conditions. We apply it to the Constrained Simulations in BORG (CSiBORG) suite of 101 high-resolution realizations across the posterior probability distribution of initial conditions from the Bayesian Origin Reconstruction from Galaxies (BORG) algorithm. The method is based on the overlap of the initial Lagrangian patch of a halo in one simulation with those in another, measuring the degree to which the haloes' particles are initially coincident. This addresses the extent to which the imposed large-scale structure constraints reduce the variance of individual halo properties. We find consistent reconstructions of M≳1014M⊙h-1 haloes, indicating that the constraints from the BORG algorithm are sufficient to pin down the masses, positions, and peculiar velocities of clusters to high precision, though we do not assess how well they reproduce observations of the local Universe. The effect of the constraints tapers off towards lower mass, and the halo spins and concentrations are largely unconstrained at all masses. We document the advantages of evaluating halo consistency in the initial conditions and describe how the method may be used to quantify our knowledge of the halo field given galaxy survey data analysed through the lens of probabilistic inference machines such as BORG.