The Fornax Cluster VLT Spectroscopic Survey III -- Kinematical characterisation of globular clusters across the Fornax galaxy cluster

Abstract

The Fornax cluster provides an unparalleled opportunity to investigate in detail the formation and evolution of early-type galaxies in a dense environment. We aim at kinematically characterizing photometrically detected globular cluster (GC) candidates in the core of the cluster. We used the VLT/VIMOS spectroscopic data from the FVSS survey in the Fornax cluster, covering one square degree around the central massive galaxy NGC 1399. We confirmed a total of 777 GCs, almost doubling the previously detected GCs, using the same dataset by Pota et al. (2018). Combined with previous literature radial velocity measurements of GCs in Fornax, we compiled the most extensive spectroscopic GC sample of 2341 objects in this environment. We found that red GCs are mostly concentrated around major galaxies, while blue GCs are kinematically irregular and are widely spread throughout the core region of the cluster. The velocity dispersion profiles of blue and red GCs show a quite distinct behaviour. Blue GCs exhibit a sharp increase in the velocity dispersion profile from 250 to 400 km s −1 within 5 arcminutes (∼29 kpc / ∼1 r eff of NGC 1399) from the central galaxy. The velocity dispersion profile of red GCs follows a constant value in between 200-300 km s −1 until 8 arcminutes (∼46 kpc/ ∼1.6 r eff ), and then rises to 350 km s −1 at 10 arcminutes (∼58 kpc/ ∼2 r eff ). Beyond 10 arcminutes and out to 40 arcminutes (∼230 kpc/ ∼8 r eff ), blue and red GCs show a constant velocity dispersion of 300±50 km s −1 , indicating that both GC populations are tracing the cluster potential. We have kinematically confirmed and characterized the previously photometrically discovered overdensities of intra-cluster GCs. We found that those substructured intra-cluster regions in Fornax are dominated mostly by blue GCs.

The Fornax Cluster VLT Spectroscopic Survey IV -- Cold kinematical substructures in the Fornax core from COSTA

“…In P+18 and S+18 we have discussed that this velocity dispersion raise is compatible with the scenario that both PN and GC populations at this distance start to feel the cluster potential, rather than the one of the central galaxy. This scenario has been recently confirmed with updated FVSS measurements of the PN and GC population (Chaturvedi et al 2021). An alternative scenario of a mix of populations producing an inflated profile as observed in Hydra cluster (Hilker et al 2018) cannot be excluded in Fornax, although does not seem to be supported by dynamical arguments (see S+18 and P+18).…”

“…Especially in its core, recent observations have revealed signatures of interactions between the cD, NGC 1399, and other bright galaxies, e.g. overdensities in the photometrically selected GCs, D'Abrusco et al ( 2016), C+20, Chaturvedi et al (2021); faint µ r ∼ 28 − 29 mag/arcsec 2 and diffuse intra-cluster patches of light (Iodice et al 2017), which were predicted in earlier dynamical studies (Napolitano et al 2002) and mirrored by asymmetries in the X-ray halo emission of NGC 1399 (Paolillo et al 2002;Su et al 2017).…”

“…The total size (> 2000 test particles) and velocity errors of the two datasets (∆ V 37 kms −1 for GCs, P+18, and between 30 and 45 kms −1 for PNe, S+18 -we will adopt an average error of 37.5 kms −1 in the following), are suitable for the detection and characterization of stream candidates, in hot environments like the stellar halo in cluster cores (see G+20). For the GC population we decided to use the P+18 catalog because this is based on a higher SNR sample that allows us to keep the statistical errors under a value (37 kms −1 ) smaller than the one of the new catalog (70-100 km s −1 , see Chaturvedi et al 2021) and similar to the one of the PNe 1 .…”

“…Despite its regular appearance, recent investigations have found that the assembly of Fornax is still ongoing, as shown by deep photometry with the ESO/VST, that found signatures of stellar and GC tidal streams (e.g. Iodice et al 2016, I+16 hereafter;Iodice et al 2017;D'Abrusco et al 2016, DA+16;Cantiello et al 2020, C+20; see also Chaturvedi et al 2021). Due to its proximity, Fornax gives us a unique opportunity to kinematically map the complexity of its core out to at least 200 kpc using discrete kinematical tracers (e.g.…”