Galaxy disc scaling relations: A tight linear galaxy–halo connection challenges abundance matching

Lorenzo Posti,Filippo Fraternali,Benoit Famaey,Antonino Marasco

doi:10.1051/0004-6361/201935982

Abstract

In ΛCDM cosmology, to first order, galaxies form out of the cooling of baryons within the virial radius of their dark matter halo. The fractions of mass and angular momentum retained in the baryonic and stellar components of disc galaxies put strong constraints on our understanding of galaxy formation. In this work, we derive the fraction of angular momentum retained in the stellar component of spirals, fj, the global star formation efficiency fM, and the ratio of the asymptotic circular velocity (Vflat) to the virial velocity fV, and their scatter, by fitting simultaneously the observed stellar mass-velocity (Tully–Fisher), size–mass, and mass–angular momentum (Fall) relations. We compare the goodness of fit of three models: (i) where the logarithm of fj, fM, and fV vary linearly with the logarithm of the observable Vflat; (ii) where these values vary as a double power law; and (iii) where these values also vary as a double power law but with a prior imposed on fM such that it follows the expectations from widely used abundance matching models. We conclude that the scatter in these fractions is particularly small (∼0.07 dex) and that the linear model is by far statistically preferred to that with abundance matching priors. This indicates that the fundamental galaxy formation parameters are small-scatter single-slope monotonic functions of mass, instead of being complicated non-monotonic functions. This incidentally confirms that the most massive spiral galaxies should have turned nearly all the baryons associated with their haloes into stars. We call this the failed feedback problem.

Highlights

The current Λ cold dark matter (ΛCDM) cosmological model is very successful at reproducing observations of the large-scale structure of the Universe
We compare the goodness of fit of three models: (i) where the logarithm of f j, fM, and fV vary linearly with the logarithm of the observable Vflat; (ii) where these values vary as a double power law; and (iii) where these values vary as a double power law but with a prior imposed on fM such that it follows the expectations from widely used abundance matching models
In each row of this figure we show one of the three scaling relations considered; while in each column we present the comparison of the data with the three models

Summary

Introduction

The current Λ cold dark matter (ΛCDM) cosmological model is very successful at reproducing observations of the large-scale structure of the Universe. Bullock & Boylan-Kolchin 2017) These challenges could have important consequences on our understanding of the interplay between baryons and dark matter, or even on the roots of the cosmological model itself, including the very nature of dark matter. The most inner parts of galaxy rotation curves present a wide variety of shapes (Oman et al 2015, 2019), which might be indicative of a variety of central dark matter profiles ranging from cusps to cores and closely related to the observed central surface density of baryons Lelli et al 2013, 2016a; Ghari et al 2019) In addition to such surprising central correlations, the phenomenology of global galactic scaling laws, which relate fundamental galactic structural parameters of both baryons and dark matter, carries important clues that should inform us about the galaxy formation process in a cosmological context. Given the complexity of the baryon physics leading to the formation of galaxies, which involves for instance gravitational instabilities, gas dissipation, mergers and interactions with neighbours, or feedback from strong radiative sources, it is remarkable that many of the most basic structural scaling relations of disc galaxies are simple, tight power laws (see e.g. van der Kruit & Freeman 2011, for a review); these most basic structural scaling relations, for example, can be between the stellar or baryonic mass of the galaxy and its rotational velocity (Tully & Fisher 1977; Lelli et al 2016b), its stellar mass and size (Kormendy 1977; Lange et al 2016), and its stellar mass and stellar specific angular momentum (Fall 1983; Posti et al 2018a)

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Results

Conclusion