The progenitors of the intra-cluster light and intra-cluster globular clusters in galaxy groups and clusters

We use the IllustrisTNG50 cosmological hydrodynamical simulation, complemented by a catalog of tagged globular clusters, to investigate the properties and build up of two extended luminous components: the intra-cluster light (ICL) and the intra-cluster globular clusters (ICGC). We select the 39 most massive groups and clusters in the box, spanning the range of virial masses $5 \times 10^{12} < \rm M_{200}/\rm M_{\odot} < 2 \times 10^{14}$. We find good agreement between predictions from the simulations and current observational estimates of the fraction of mass in the ICL and its radial extension. The stellar mass of the ICL is only $\sim10\%-20\%$ of the stellar mass in the central galaxy but encodes useful information on the assembly history of the group or cluster. About half the ICL in all our systems is brought in by galaxies in a narrow stellar mass range, $M_*=10^{10}-10^{11}$ $\rm M_{\odot}$. However, the contribution of low-mass galaxies ($M_*<10^{10}$ $\rm M_{\odot}$) to the build-up of the ICL varies broadly from system to system, $\sim 5\%-45\%$, a feature that might be recovered from the observable properties of the ICL at $z=0$. At fixed virial mass, systems where the accretion of dwarf galaxies plays an important role have shallower metallicity profiles, less metal content and a lower stellar mass in the ICL than systems where the main contributors are more massive galaxies. We show that intra-cluster GCs are also good tracers of this history, representing a valuable alternative when diffuse light is not detectable

Simulating the spatial distribution and kinematics of globular clusters within galaxy clusters in illustris

We study the assembly of globular clusters (GCs) in 9 galaxy clusters using the cosmological simulation Illustris. GCs are tagged to individual galaxies at their infall time. The tidal removal of GCs from their galaxies and the distribution of the GCs within the cluster is later followed self-consistently by the simulation. The method relies on the simple assumption of a single power-law relation between halo mass (Mvir) and mass in GCs (MGC) as found in observations. We find that the GCs specific frequency SN as a function of V-band magnitude naturally reproduces the observed ‘U’-shape due to the combination of the power law MGC–Mvir relation and the non-linear stellar mass (M∗)–halo mass relation from the simulation. Additional scatter in the SN values is traced back to galaxies with early infall times due to the evolution of the M∗–Mvir relation with redshift. GCs that have been tidally removed from their galaxies form the present-day intracluster component, from which about ∼60 per cent were brought in by galaxies that currently orbit within the cluster potential. The remaining ‘orphan’ GCs are contributed by satellite galaxies with a wide range of stellar masses that are fully tidally disrupted at z = 0. This intracluster component is a good dynamical tracer of the dark matter potential. As a consequence of the accreted nature of most intracluster GCs, their orbits are fairly radial with a predicted orbital anisotropy β ≥ 0.5. However, local tangential motions may appear as a consequence of localized substructure, providing a possible interpretation to the β < 0 values suggested in observations of M87.Fil: Ramos Almendares, Felipe Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Sales, Laura Virginia. University of California; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Abadi, Mario Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Muriel, Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; Argentina. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; ArgentinaFil: Doppel, Jessica E.. University of California; Estados UnidosFil: Peng, Eric W.. Peking University; Chin

Imposters among us: globular cluster kinematics and the halo mass of ultra-diffuse galaxies in clusters

The velocity dispersion of globular clusters (GCs) around ultra-diffuse galaxies (UDGs) in the Virgo cluster spans a wide range, including cases where GC kinematics suggest haloes as massive as (or even more massive than) that of the Milky Way around these faint dwarfs. We analyse the catalogues of GCs derived in post-processing from the TNG50 cosmological simulation to study the GC system kinematics and abundance of simulated UDGs in galaxy groups and clusters. UDGs in this simulation reside exclusively in dwarf-mass haloes with M200 ≲ 1011.2 M⊙. When considering only GCs gravitationally bound to simulated UDGs, we find GCs properties that overlap well with several observational measurements for UDGs. In particular, no bias towards overly massive haloes is inferred from the study of bound GCs, confirming that GCs are good tracers of UDG halo mass. However, we find that contamination by intracluster GCs may, in some cases, substantially increase velocity dispersion estimates when performing projected mock observations of our sample. We caution that targets with less than 10 GC tracers are particularly prone to severe uncertainties. Measuring the stellar kinematics of the host galaxy should help confirm the unusually massive haloes suggested by GC kinematics around some UDGs

Globular clusters as tracers of the dark matter content of dwarfs in galaxy clusters

Globular clusters (GCs) are often used to estimate the dark matter content of galaxies, especially dwarfs, where other kinematic tracers are lacking. These estimates typically assume spherical symmetry and dynamical equilibrium, assumptions that may not hold for the sparse GC population of dwarfs in galaxy clusters. We use a catalog of GCs tagged onto the Illustris simulation to study the accuracy of GC-based mass estimates. We focus on galaxies in the stellar mass range 10$^{8} - 10^{11.8}$ M$_{\odot}$ identified in $9$ simulated Virgo-like clusters. Our results indicate that mass estimates are, on average, quite accurate in systems with GC numbers $N_{\rm GC} \geq 10$ and where the uncertainty of individual GC line-of-sight velocities is smaller than the inferred velocity dispersion, $\sigma_{\rm GC}$. In cases where $N_{\rm GC} \leq 10$, however, biases may result depending on how $\sigma_{\rm GC}$ is computed. We provide calibrations that may help alleviate these biases in methods widely used in the literature. As an application, we find a number of dwarfs with $M_{*} \sim 10^{8.5}\, M_{\odot}$ (comparable to the ultradiffuse galaxy DF2, notable for the low $\sigma_{GC}$ of its $10$ GCs) with $\sigma_{\rm GC} \sim 7$ - $15\; \rm km \rm s^{-1}$. These DF2 analogs correspond to relatively massive systems at their infall time ($M_{200} \sim 1$ - $3 \times 10^{11}$ $M_{\odot}$) which have retained only $3$-$17$ GCs and have been stripped of more than 95$\%$ of their dark matter. Our results suggest that extreme tidal mass loss in otherwise normal dwarf galaxies may be a possible formation channel for ultradiffuse objects like DF2.Comment: 19 pages, 15 figures. Accepted to MNRAS Dec. 11 202

Modeling globular clusters in the TNG50 simulation: predictions from dwarfs to giant galaxies

We present a post-processing catalogue of globular clusters (GCs) for the 39 most massive groups and clusters in the TNG50 simulation of the IlllustrisTNG project (virial masses M200=[5×10^12−2×10^14] M⊙). We tag GC particles to all galaxies with stellar mass M* ≥ 5 × 10^6 M⊙, and we calibrate their masses to reproduce the observed power-law relation between GC mass and halo mass for galaxies with M200 ≥ 10^11 M⊙ (corresponding to M* ∼ 10^9 M⊙). Here, we explore whether an extrapolation of this MGC–M200 relation to lower mass dwarfs is consistent with current observations. We find a good agreement between our predicted number and specific frequency of GCs in dwarfs with M∗=[5×10^6−10^9] M⊙ and observations. Moreover, we predict a steep decline in the GC occupation fraction for dwarfs with M* &lt; 10^9 M⊙ that agrees well with current observational constraints. This declining occupation fraction is due to a combination of tidal stripping in all dwarfs plus a stochastic sampling of the GC mass function for dwarfs with M* &lt; 10^7.5 M⊙. Our simulations also reproduce available constraints on the abundance of intracluster GCs in Virgo and Centaurus A. These successes provide support to the hypothesis that the MGC–M200 relation holds, albeit with more scatter, all the way down to the regime of classical dwarf spheroidals in these environments. Our GC catalogues are publicly available as part of the IllustrisTNG data release