The impact of galaxy selection on the splashback boundaries of galaxy clusters

O'Neil, Stephanie; Borrow, Josh; Vogelsberger, Mark; Diemer, Benedikt

doi:10.1093/mnras/stac850

Cited by 12 publications

(9 citation statements)

References 89 publications

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“…As we were motivated to study backsplash galaxies by the study of the splashback radius of galaxy clusters, we use the same sample of clusters as in O'Neil et al (2022). These are chosen to be isolated galaxy clusters with a mass M 200,mean > 10 13 M .…”

Section: Selecting Backsplash Galaxiesmentioning

confidence: 99%

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There and back again: understanding the critical properties of backsplash galaxies

Borrow¹,

Vogelsberger²,

O’Neil³

et al. 2022

Preprint

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Backsplash galaxies are galaxies that once resided inside a cluster, and have migrated back oustide as they move towards the apocenter of their orbit. The kinematic properties of these galaxies are well understood, thanks to the significant study of backsplashers in dark matter-only simulations, but their intrinsic properties are not well constrained due to modelling uncertainties in sub-grid physics, ram pressure stripping, dynamical friction, and tidal forces. In this paper, we use the Illustris-TNG-300-1 simulation, with a baryonic resolution of M b ≈ 1.1 × 10 7 M , to study backsplash galaxies around 1302 isolated galaxy clusters with mass 10 13.0 < M 200,mean /M < 10 15.5 . We employ a decision tree classifier to extract features of galaxies that make them likely to be backsplash galaxies, compared to nearby field galaxies, and find that backsplash galaxies have low gas fractions, high mass-to-light ratios, large stellar sizes, and low black hole occupation fractions. We investigate in detail the origins of these large sizes, and hypothesise their origins are linked to the tidal environments in the cluster. We show that the black hole recentering scheme employed in many cosmological simulations leads to the loss of black holes from galaxies accreted into clusters, and suggest improvements to these models. Generally, we find that backsplash galaxies are a useful population to test and understand numerical galaxy formation models.

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Section: Selecting Backsplash Galaxiesmentioning

confidence: 99%

“…This set of constraints esnures that the clusters move smoothly, and are the most dominant halo within their local neighborhood, to ensure a clean sample of infalling and backsplashing galaxies. The final selection of clusters rejects around 100 compared to O'Neil et al (2022), with 1302 clusters remaining.…”

Section: Selecting Backsplash Galaxiesmentioning

confidence: 99%

There and back again: understanding the critical properties of backsplash galaxies

Borrow¹,

Vogelsberger²,

O’Neil³

et al. 2022

Preprint

Self Cite

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“…Many previous investigations focused on relatively massive halos, so their results can only show the monotonic decline with halo mass at the massive end (e.g., More et al 2015;Diemer et al 2017;O'Neil et al 2022). In contrast, R c,mj is almost independent of halo mass, and its value, which is in the range of 0.6 ∼ 0.8R 200 , is less than that of R c,mn , which ranges from 1 to 1.4R 200 .…”

Section: Splashback Caustics and Their Dependencies On Halo Propertiesmentioning

confidence: 91%

Anisotropy and characteristic scales in halo density gradient profiles

Wang¹,

Wang²,

Mo³

2022

Preprint

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We use a large N -body simulation to study the characteristic scales in the density gradient profiles in and around halos with masses ranging from 10 12 to 10 15 h −1 M . We investigate the profiles separately along the major (T1) and minor (T3) axes of the local tidal tensor and how the characteristic scales depend on halo mass, formation time, and environment. We find two kinds of prominent characteristic features in the gradient profiles, a deep 'valley' and a prominent 'peak'. We use the Gaussian Process Regression to fit the gradient profiles and identify the local extrema to determine the scales associate with these features. Around the valley, we identify three types of distinct local minima, corresponding to caustics of particles orbiting around halos. The appearance and depth of the three caustics depend significantly on the direction defined by the local tidal field, formation time and environment of halos. The first caustic is located at a radius r > 0.8R200, corresponding to the splashback feature, and is dominated by particles at their first apocenter after infall. The second and third caustics, around 0.6R200 and 0.4R200 respectively, can be determined reliably only for old halos. The first caustic is always the most prominent feature along T3, but may not be the case along T1 or in azimuthally-averaged profiles, suggesting that caution must be taken when using averaged profiles to investigate the splashback radius. We find that the splashback feature is approximately isotropic when proper separations are made between the first and the other caustics. We also identify a peak feature located at ∼ 2.5R200 in the density gradient profile. This feature is the most prominent along T1 and is produced by mass accumulations from the structure outside halos. We also discuss the origins of these features and their observational implications.

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“…For the first time, we can rely on profiles that have been dynamically split into orbiting and infalling particles (using the algorithm presented in Diemer 2022, hereafter Paper I). Similar splits have recently been explored in observational data using galaxy properties such as color (Baxter et al 2017;Adhikari et al 2021;O'Donnell et al 2021;Shin et al 2021;Aung et al 2022;Dacunha et al 2022;O'Neil et al 2022), necessitating a fitting function that captures the shapes of the orbiting and infalling terms. We require that this fitting function should 1) describe the profiles accurately even in the transition region, 2) be flexible enough to apply to individual halos and to stacks with different selection criteria, 3) work across all halo masses, redshifts, cosmologies, and accretion rates, 4) rely on as few free parameters as possible with clear, physical interpretations, and 5) exhibit minimal parameter degeneracies.…”

Section: Introductionmentioning

confidence: 94%

A dynamics-based density profile for dark haloes -- II. Fitting function

Diemer¹

2022

Preprint

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The density profiles of dark matter haloes are commonly described by fitting functions such as the NFW or Einasto models, but these approximations break down in the transition region where halos become dominated by newly accreting matter. In Paper I we dynamically split simulation particles into orbiting and infalling components and analysed their separate profiles. Here we propose simple, accurate fitting functions designed to capture the asymptotic shapes of the two terms at large and small radii. The orbiting term is described as a truncated Einasto profile, ρ orb ∝ exp −2/α (r/r s ) α − 1/β (r/r t ) β , with a five-parameter space of normalization, physically distinct scale and truncation radii, and α and β, which control how rapidly the profiles steepen. The infalling profile is modelled as a power law in overdensity that smoothly transitions to a constant at the halo centre. We show that these formulae fit the averaged, total profiles in simulations to about 5% accuracy across almost all of an expansive parameter space in halo mass, redshift, cosmology, and accretion rate. When fixing α = 0.18 and β = 3, the formula becomes a three-parameter model for the orbiting term that fits individual halos better than the Einasto profile on average.

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The impact of galaxy selection on the splashback boundaries of galaxy clusters

Cited by 12 publications

References 89 publications

There and back again: understanding the critical properties of backsplash galaxies

There and back again: understanding the critical properties of backsplash galaxies

Anisotropy and characteristic scales in halo density gradient profiles

A dynamics-based density profile for dark haloes -- II. Fitting function

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