Scatter in the satellite galaxy SHMR: fitting functions, scaling relations, and physical processes from the IllustrisTNG simulation

A. Niemiec, C. Giocoli, E. Cohen, M. Jauzac, E. Jullo, and M. Limousin.


The connection between galaxies and their dark matter haloes is often described with the stellar-to-halo mass relation (SHMR). Satellite galaxies in clusters follow an SHMR distinct from central galaxies because of the environmental processes that they are subject to, and the variety of accretion histories leads to an important scatter in this relation. In this work, we use the suite of magnetohydrodynamical simulations IllustrisTNG to study the scatter in the satellite galaxy SHMR, and extract the parameters that can best allow to understand it. Active galaxies, that represent a very small fraction of cluster galaxies, follow a very different relation than their passive counterparts, mainly because they were accreted much more recently. For this latter population, we find that the distance to the cluster centre is a good predictor of variations in the SHMR, but some information on the galaxy orbital history, such as the distance of closest approach to the host centre, is an even better one, although it is in practice more difficult to measure. In addition, we found that galaxy compactness is also correlated with the SHMR, while the host cluster properties (mass and concentration, formation redshift, mass and size of BCG) do not play a significant role. We provide accurate fitting functions and scaling relations to the scientific community, useful to predict the subhalo mass given a set of observable parameters. Finally, we connect the scatter in the SHMR to the physical processes affecting galaxies in clusters, and how they impact the different satellite subpopulations.

Top panel: ShHMR measured for the satellite galaxies with total mass Msub > 10^10 h^-1Msun. The solid black line represents the median measured relation, and the grey shaded region the 16th - 84th percentiles. The best fit relation corresponding to equation (7) is shown as a dashed line. Middle top panel: SsHMR in bins in the 3D cluster-centric distance, with solid lines showing the median relations, and dashed lines the best fit relations according to Eq. (9). Bottom middle panel: same but using the minimum cluster-centric distance, throughout the galaxy accretion history. Bottom panel: residual distribution Delta(log m*) = log m* - log m* (m_sub) around the best fit relation, with the parameterization from Equation (8) shown a red solid line.

hybrid-Lenstool: A self-consistent algorithm to model galaxy clusters with strong- and weak-lensing simultaneously.

A. Niemiec, M. Jauzac, E. Jullo, M. Limousin, K. Sharon, J.-P. Kneib, P. Natarajan and J. Richard.


We present a new galaxy cluster lens modeling approach, hybrid-Lenstool, that is implemented in the publicly available modeling software Lenstool. hybrid-Lenstool combines a parametric approach to model the core of the cluster, and a non-parametric (free-form) approach to model the outskirts. hybrid-Lenstool optimizes both strong- and weak-lensing constraints simultaneously (Joint-Fit), providing a self-consistent reconstruction of the cluster mass distribution on all scales. In order to demonstrate the capabilities of the new algorithm, we tested it on a simulated cluster. hybrid-Lenstool yields more accurate reconstructed mass distributions than the former Sequential-Fit approach where the parametric and the non-parametric models are optimized successively. Indeed, we show with the simulated cluster that the mass density profile reconstructed with a Sequential-Fit deviates form the input by \(2-3\sigma\) at all scales while the Joint-Fit gives a profile that is within \(1-1.5\sigma\) of the true value. This gain in accuracy is consequential for recovering mass distributions exploiting cluster lensing and therefore for all applications of clusters as cosmological probes. Finally we found that the Joint-Fit approach yields shallower slope of the inner density profile than the Sequential-Fit approach, thus revealing possible biases in previous lensing studies.

Projected mass maps.Left column: input simulation, with the large scale potentials shown as white ellipses (top panel), and the potentials of the multiscale grid shown as white circles, which sizes are set to the core radii, s, of the potential (bottom panel). Middle Column: Sequential-Fit, with source density Ns= 45 sources/arcmin2 (top) and Ns= 100 sources/arcmin2(bottom). Right Column: Joint-Fit, with source density Ns= 45 sources/arcmin2 (top) and Ns= 100 sources/arcmin2 (bottom). The Sequential- and Joint-Fit mass maps are means over 1000 MCMC samples.

Dark matter stripping in galaxy clusters: a look at the Stellar to Halo Mass relation in the Illustris simulation.

A. Niemiec, E. Jullo, C. Giocoli, M. Limousin and M. Jauzac. Monthly Notices of the Royal Astronomical Society, Volume 487, Issue 1, p.653-666. July 2019.


Satellite galaxies in galaxy clusters represent a significant fraction of the global galaxy population. Because of the unusual dense environment of clusters, their evolution is driven by different mechanisms than the ones affecting field or central galaxies. Understanding the different interactions they are subject to, and how they are influenced by them, is therefore an important step towards explaining the global picture of galaxy evolution. In this paper, we use the publicly-available high resolution hydrodynamical simulation Illustris-1 to study satellite galaxies in the three most massive host haloes (with masses \(M > 10^{14} h^{−1}M_{\odot}\) ) at z = 0. We measure the Stellar-to-Halo Mass Relation (hereafter SHMR) of the galaxies, and find that for satellites it is shifted towards lower halo masses compared to the SHMR of central galaxies. We provide simple fitting functions for both the central and satellite SHMR. To explain the shift between the two, we follow the satellite galaxies since their time of accretion into the clusters, and quantify the impact of dark matter stripping and star formation. We find that subhaloes start losing their dark matter as soon as they get closer than \(1.5 \times R_{\rm{vir}}\) to the centre of their host, and that up to 80% of their dark matter content gets stripped during infall. On the other hand, star formation quenching appears to be delayed, and galaxies continue to form stars for a few Gyr after accretion. The combination of these two effects impacts the ratio of stellar to dark matter mass which varies drastically during infall, from 0.03 to 0.3.

Evolution of subhalo properties as a function of time since accretion: halo-centric distance normalized by the host virial radius at accretion (top panel), subhalo dark matter mass normalized by the dark matter mass at accretion (second panel), stellar mass normalized by stellar mass at accretion (third panel), and specific star formation rate (SSFR) (bottom panel). Each column represents one of the cluster-like haloes. The black lines represent the evolution of each subhalo independently; the thick red line shows the median evolution, and the thin red lines mark the 16th and 84th percentiles.

Probing galaxy assembly bias with LRG weak lensing observations

A. Niemiec, E. Jullo, A. Montero-Dorta, F. Prada, S. Rodriguez-Torres, E. Perez and A. Klypin. Monthly Notices of the Royal Astronomical Society: Letters, Volume 477, Issue 1, p.L1-L5, June 2018.


In Montero-Dorta et al., we show that luminous red galaxies (LRGs) from the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS) at \(z \sim 0.55\) can be divided into two groups based on their star formation histories. So-called fast-growing LRGs assemble 80 per cent of their stellar mass at \(z \sim 5\), whereas slow-growing LRGs reach the same evolutionary state at \(z \sim 1.5\). We further demonstrate that these two subpopulations present significantly different clustering properties on scales of \(\sim 1-30\) Mpc. Here, we measure the mean halo mass of each subsample using the galaxy-galaxy lensing technique, in the \(\sim 190\deg^2\) overlap of the LRG catalogue and the CS82 and CFHTLenS shear catalogues. We show that fast- and slow-growing LRGs have similar lensing profiles, which implies that they live in haloes of similar mass: \(\log (M_{\rm{halo}}^{\rm{fast}}/h^{-1}M_{\odot}) = 12.85^{+0.16}_{-0.26}\) and \(\log (M_{\rm{halo}}^{\rm{slow}}/h^{-1}M_{\odot}) =12.92^{+0.16}_{-0.22}\). This result, combined with the clustering difference, suggests the existence of galaxy assembly bias, although the effect is too subtle to be definitively proven, given the errors on our current weak-lensing measurement. We show that this can soon be achieved with upcoming surveys like DES.

Lensing signal for the fast-growing (left-hand panel) and slow-growing (right-hand panel) LRGs, with the best-fitting model (solid blue line) and 68 per cent confidence interval (blue surface). The four terms of the model are also shown.

Stellar-to-halo mass relation of cluster galaxies

A. Niemiec, E. Jullo, M. Limousin, C. Giocoli, T. Erben, H. Hildebrant, J.-P. Kneib, A. Leauthaud, M. Makler, B. Moraes, M. E. S. Pereira, H. Shan, E. Rozo, E. Rykoff and L. Van Waerbeke. Monthly Notices of the Royal Astronomical Society, Volume 471, p.1153-1166, October 2017.


In the formation of galaxy groups and clusters, the dark matter haloes containing satellite galaxies are expected to be tidally stripped in gravitational interactions with the host. We use galaxy-galaxy weak lensing to measure the average mass of dark matter haloes of satellite galaxies as a function of projected distance to the centre of the host, since stripping is expected to be greater for satellites closer to the centre of the cluster. We further classify the satellites according to their stellar mass: assuming that the stellar component of the galaxy is less disrupted by tidal stripping, stellar mass can be used as a proxy of the infall mass. We study the stellar to halo mass relation of satellites as a function of the cluster-centric distance to measure tidal stripping. We use the shear catalogues of the DES science verification archive, the CFHTLenS and the CFHT Stripe 82 surveys, and we select satellites from the redMaPPer catalogue of clusters. For galaxies located in the outskirts of clusters, we find a stellar to halo mass relation in good agreement with the theoretical expectations from Moster, Naab & White (2013) for central galaxies. In the centre of the cluster, we find that this relation is shifted to smaller halo mass for a given stellar mass. We interpret this finding as further evidence for tidal stripping of dark matter haloes in high density environments.

Stellar-to-halo mass relation measured for the satellite galaxies in our sample, in blue for the galaxies in the inner part of clusters (Rs ∈ [0.1;0.55]h^{−1}Mpc) and in red for the galaxies in the outer part of clusters (Rs ∈ [0.55;1.]h^{−1}Mpc). The black line is the SHMR for field/central galaxies at z = 0.35, computed from simulations in Moster, Naab & White (2013).

Clustering properties of g-selected galaxies at z ∼ 0.8.

G. Favole, J. Comparat, F. Prada, G. Yepes, E. Jullo, A. Niemiec, J.-P. Kneib, S. A. Rodriguez-Torres, A. Klypin, R. A. Skibba, C. K. McBride, D. J Eisenstein, D. J. Schlegel, S. E. Nuza, C. H. Chuang, T. Delubac, C. Yeche and D. P. Schneider. Monthly Notices of the Royal Astronomical Society, Volume 461, Issue 4, p.3421-3431, October 2016.


Current and future large redshift surveys, as the Sloan Digital Sky Survey IV extended Baryon Oscillation Spectroscopic Survey (SDSS-IV/eBOSS) or the Dark Energy Spectroscopic Instrument (DESI), will use Emission-Line Galaxies (ELG) to probe cosmological models by mapping the large-scale structure of the Universe in the redshift range 0.6 < z < 1.7. With current data, we explore the halo-galaxy connection by measuring three clustering properties of g-selected ELGs as matter tracers in the redshift range 0.6 < z < 1: (i) the redshift-space two-point correlation function using spectroscopic redshifts from the BOSS ELG sample and VIPERS; (ii) the angular two-point correlation function on the footprint of the CFHT-LS; (iii) the galaxy-galaxy lensing signal around the ELGs using the CFHTLenS. We interpret these observations by mapping them onto the latest high-resolution MultiDark Planck N-body simulation, using a novel (Sub)Halo-Abundance Matching technique that accounts for the ELG incompleteness. ELGs at \(z \sim 0.8\) live in halos of \((1 \pm 0.5) \times 10^{12} h^{-1}M_{\odot}\) and \(22.5 \pm 2.5\%\) of them are satellites belonging to a larger halo. The halo occupation distribution of ELGs indicates that we are sampling the galaxies in which stars form in the most efficient way, according to their stellar-to-halo mass ratio.

Schematic diagram of possible ELG configurations. ELGs at z ~ 0.8 typically live in halos of mass Mh ~ (1±0.5) x 10^12 h^{-1}Msun and 22.5% are satellites belonging to larger halos, whose central galaxy is quiescent. Among these satellite configurations, 21.2% of parent halos with MhQ ~ 2.5 x 10^13 h^{-1}Msun host one satellite ELG, and only 1.3% of parents host more than one satellite ELG. The maxium number of satellites, n = 1.8, is achieved in the highest-mass case, MhQ ~ 6.8 x 10^13 h^{-1}Msun.

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