Implications for galaxy formation models from observations of globular clusters around ultradiffuse galaxies

Abstract

We present an analysis of Hubble Space Telescope observations of globular clusters (GCs) in six ultra-diffuse galaxies (UDGs) in the Coma cluster, a sample that represents UDGs with large effective radii (Re), and use the results to evaluate competing formation models. We eliminate two significant sources of systematic uncertainty in the determination of the number of GCs, NGC by using sufficiently deep observations that (i) reach the turnover of the GC luminosity function and (ii) provide a sufficient number of GCs with which to measure the GC number radial distribution. We find that NGC for these galaxies is on average ∼ 20, which implies an average total mass, Mtotal, ∼ 1011 M⊙ when applying the relation between NGC and Mtotal. This value of NGC lies at the upper end of the range observed for dwarf galaxies of the same stellar mass and is roughly a factor of two larger than the mean. The GC luminosity function, radial profile and average colour are more consistent with those observed for dwarf galaxies than with those observed for the more massive (L*) galaxies, while both the radial and azimuthal GC distributions closely follow those of the stars in the host galaxy. Finally, we discuss why our observations, specifically the GC number and GC distribution around these six UDGs, pose challenges for several of the currently favoured UDG formation models.

HIPASS study of southern ultradiffuse galaxies and low surface brightness galaxies

“…Recently Gault et al (2021) imaged H i in about ten UDGs and found the H i mass and the H i disk diameter to follow the correlation in Wang et al (2016), however the H i mass range covered in this work is less than 2 × 10 9 M ⊙ , in the range of dwarf galaxies. A scaling relation between the UDG R e and the DM halo mass was proposed by Zaritsky (2017) and is consistent with a globular cluster count study of six Coma UDGs with R e ≥ 3 kpc by Saifollahi et al (2022). However the R e -DM halo mass relation is yet to be confirmed with DM halo mass estimates based on H i rotation curves.…”

Galaxy populations in the Hydra I cluster from the VEGAS survey

“…major-to-minor axis ratio from SExtractor) ≤ 2 in both bands; v) CI X within ±0.1 mag of the local sequence of point sources. The choices of 4 and 8 pixels, and ∆CI x = ±0.1 mag, were made after several tests, as a compromise between the completeness and contamination (see also Saifollahi et al 2021Saifollahi et al , 2022, where the same compactness parameter is adopted).…”

“…Nevertheless, assuming that it holds also for UDGs, in the Coma cluster of galaxies, S N appears to be larger in UDGs than in dwarf galaxies of similar luminosity (Lim et al 2020;Forbes et al 2020a), which could indicate the presence of DM halos more massive for this class of objects than for similar luminosity dwarfs (M h ≥ 10 11 M ). On the other hand, UDGs with S N similar to dwarf galaxies are found in other clusters of galaxies (Prole et al 2019a;Saifollahi et al 2021Saifollahi et al , 2022Marleau et al 2021). In this respect, the DM content of the UDGs is one of the open and most debated issues.…”

Metallicity profiles of Ultra Diffuse Galaxies in NIHAO simulations

“…There has been a large effort in the community to explore the different properties that emerge from the different formation mechanisms (e.g. Sales et al 2020;Carleton et al 2021;Saifollahi et al 2022;Trujillo-Gomez et al 2022). While several of the formation mechanisms shown in the literature are able to explain, with more or less success, the average properties of UDGs, the radial variation of such properties has yet to be explored in detail.…”