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We present the size–mass relation of the brightest cluster galaxies (BCGs) at 0.1 < z < 1.4 using the imaging data obtained by the Hyper Suprime-Cam Subaru Strategic Program. Our sample consists of 471 photometrically selected BCGs with stellar mass log M */M⊙ = 11–12. We measure the size of the BCGs using i -band imaging and model fits based on a single Sérsic light profile. Stellar masses are determined through spectral energy distribution fitting using Sérsic-modelled photometry data across five optical bands (grizy). The size–mass scaling relation of BCGs is |$r_\mathrm{ e}\propto M_*^{0.73-1.00}$| at z < 1, with a slope that does not evolve significantly. The slope of the size–mass relation for BCGs is steeper than other non-BCG galaxies, which implies that BCGs are a special galaxy population. The size of BCGs at a given stellar mass evolves rapidly as ∝ (1 + z)−1.58 ± 0.13 and increases with redshift by a factor of 2.5 from z ∼ 1.2 to z ∼ 0.2. The rapid size growth is in agreement with semi-analytical model results, indicating that the BCG growth is dominated by frequent minor mergers. Furthermore, we explore the size–mass relationship of BCGs with respect to the halo mass of the cluster and find there is no significant correlation, which might imply that a dependence on the environment predominantly affects the outer envelope of the BCGs. [ABSTRACT FROM AUTHOR]

We propose that observations of supermassive galaxies contain cosmological statistical constraining power similar to conventional cluster cosmology, and we provide promising indications that the associated systematic errors are comparably easier to control. We consider a fiducial spectroscopic and stellar mass complete sample of galaxies drawn from the Dark Energy Spectroscopic Instrument (DESI) and forecast how constraints on Ωm–σ8 from this sample will compare with those from number counts of clusters based on richness λ. At fixed number density, we find that massive galaxies offer similar constraints to galaxy clusters. However, a mass-complete galaxy sample from DESI has the potential to probe lower halo masses than standard optical cluster samples (which are typically limited to λ ≳ 20 and M halo ≳ 1013.5 M⊙  h −1); additionally, it is straightforward to cleanly measure projected galaxy clustering w p for such a DESI sample, which we show can substantially improve the constraining power on Ωm. We also compare the constraining power of M *-limited samples to those from larger but mass-incomplete samples [e.g. the DESI Bright Galaxy Survey (BGS) sample]; relative to a lower number density M *-limited samples, we find that a BGS-like sample improves statistical constraints by 60 per cent for Ωm and 40 per cent for σ8, but this uses small-scale information that will be harder to model for BGS. Our initial assessment of the systematics associated with supermassive galaxy cosmology yields promising results. The proposed samples have a ∼10 per cent satellite fraction, but we show that cosmological constraints may be robust to the impact of satellites. These findings motivate future work to realize the potential of supermassive galaxies to probe lower halo masses than richness-based clusters and to potentially avoid persistent systematics associated with optical cluster finding. [ABSTRACT FROM AUTHOR]

We perform a consistent comparison of the mass and mass profiles of massive (M ⋆ > 1011.4 M⊙) central galaxies at z ∼ 0.4 from deep Hyper Suprime-Cam (HSC) observations and from the Illustris, TNG100, and Ponos simulations. Weak lensing measurements from HSC enable measurements at fixed halo mass and provide constraints on the strength and impact of feedback at different halo mass scales. We compare the stellar mass function (SMF) and the Stellar-to-Halo Mass Relation (SHMR) at various radii and show that the radius at which the comparison is performed is important. In general, Illustris and TNG100 display steeper values of α where |$M_{\star } \propto M_{\rm vir}^{\alpha }$|⁠. These differences are more pronounced for Illustris than for TNG100 and in the inner rather than outer regions of galaxies. Differences in the inner regions may suggest that TNG100 is too efficient at quenching in situ star formation at M vir ≃ 1013 M⊙ but not efficient enough at M vir ≃ 1014 M⊙. The outer stellar masses are in excellent agreement with our observations at M vir ≃ 1013 M⊙, but both Illustris and TNG100 display excess outer mass as M vir ≃ 1014 M⊙ (by ∼0.25 and ∼0.12 dex, respectively). We argue that reducing stellar growth at early times in |$M_\star \sim 10^{9-10} \, \mathrm{M}_{\odot }$| galaxies would help to prevent excess ex-situ growth at this mass scale. The Ponos simulations do not implement AGN feedback and display an excess mass of ∼0.5 dex at r < 30 kpc compared to HSC which is indicative of overcooling and excess star formation in the central regions. The comparison of the inner profiles of Ponos and HSC suggests that the physical scale over which the central AGN limits star formation is r ≲ 20 kpc. Joint comparisons between weak lensing and galaxy stellar profiles are a direct test of whether simulations build and deposit galaxy mass in the correct dark matter haloes and thereby provide powerful constraints on the physics of feedback and galaxy growth. Our galaxy and weak lensing profiles are publicly available to facilitate comparisons with other simulations. [ABSTRACT FROM AUTHOR]

We use the UniverseMachine to analyse the source of scatter between the central galaxy mass, the total stellar mass in the halo, and the dark matter halo mass, for massive (M vir > 1013 M⊙) haloes. We also propose a new halo mass estimator, the cen+N mass: the sum of the stellar mass of the central and the N most massive satellites. We show that, when real space positions are perfectly known, the cen+N mass has scatter competitive with that of richness-based estimators. However, in redshift space, using a simple cluster finder, the cen+N mass suffers less from projection effects in the UniverseMachine model. The cen+N mass is therefore a potential candidate to constrain cosmology with upcoming spectroscopic data from DESI. We analyse the scatter in stellar mass at fixed halo mass and show that the total stellar mass in a halo is uncorrelated with secondary halo properties, but that the central stellar mass is a function of both halo mass and halo age. This is because central galaxies in older haloes have had more time to grow via accretion. If the UniverseMachine model is correct, this implies that haloes selected using the centrals stellar mass will be biased old and that accurate galaxy-halo modelling of mass selected samples therefore needs to consider halo age in addition to mass. [ABSTRACT FROM AUTHOR]

Using deep images from the Hyper Suprime-Cam (HSC) survey and taking advantage of its unprecedented weak lensing capabilities, we reveal a remarkably tight connection between the stellar mass distribution of massive central galaxies and their host dark matter halo mass. Massive galaxies with more extended stellar mass distributions tend to live in more massive dark matter haloes. We explain this connection with a phenomenological model that assumes, (1) a tight relation between the halo mass and the total stellar content in the halo, (2) that the fraction of in situ and ex situ mass at r <10 kpc depends on halo mass. This model provides an excellent description of the stellar mass functions (SMFs) of total stellar mass (⁠|$M_{\star }^{\mathrm{max}}$|⁠) and stellar mass within inner 10 kpc (⁠|$M_{\star }^{10}$|⁠) and also reproduces the HSC weak lensing signals of massive galaxies with different stellar mass distributions. The best-fitting model shows that halo mass varies significantly at fixed total stellar mass (as much as 0.4 dex) with a clear dependence on |$M_{\star }^{10}$|⁠. Our two-parameter |$M_{\star }^{\mathrm{max}}$| – |$M_{\star }^{10}$| description provides a more accurate picture of the galaxy–halo connection at the high-mass end than the simple stellar–halo mass relation (SHMR) and opens a new window to connect the assembly history of haloes with those of central galaxies. The model also predicts that the ex situ component dominates the mass profiles of galaxies at r < 10 kpc for log  M ⋆ ≥ 11.7. The code used for this paper is available online https://github.com/dr-guangtou/asap [ABSTRACT FROM AUTHOR]

We study the faint stellar halo of isolated central galaxies, by stacking galaxy images in the HSC survey and accounting for the residual sky background sampled with random points. The surface brightness profiles in HSC r band are measured for a wide range of galaxy stellar masses (9.2 < log10 M ∗/M⊙ < 11.4) and out to 120 kpc. Failing to account for the stellar halo below the noise level of individual images will lead to underestimates of the total luminosity by ≤15%. Splitting galaxies according to the concentration parameter of their light distributions, we find that the surface brightness profiles of low-concentration galaxies drop faster between 20 and 100 kpc than those of high-concentration galaxies. Albeit the large galaxy-to-galaxy scatter, we find a strong self-similarity of the stellar halo profiles. They show unified forms once the projected distance is scaled by the halo virial radius. The colour of galaxies is redder in the centre and bluer outside, with high-concentration galaxies having redder and more flattened colour profiles. There are indications of a colour minimum, beyond which the colour of the outer stellar halo turns red again. This colour minimum, however, is very sensitive to the completeness in masking satellite galaxies. We also examine the effect of the extended PSF in the measurement of the stellar halo, which is particularly important for low-mass or low-concentration galaxies. The PSF-corrected surface brightness profile can be measured down to ∼31  |$\mathrm{mag}\, \mathrm{arcsec}^{-2}$| at 3σ significance. PSF also slightly flattens the measured colour profiles. [ABSTRACT FROM AUTHOR]