The First Billion Years project: Finding infant globular clusters at z = 6

Abstract

Aims. We aim to conduct an assessment of the demographics of substructures in cosmological simulations to identify low-mass stellar systems at high redshift, with a particular focus on globular cluster (GC) candidates. Methods. We explored a suite of high-resolution cosmological simulations from the First Billion Years Project (FiBY) at z ≥ 6. All substructures within the simulations have been identified with the SUBFIND algorithm. From our analysis, two distinct groups of objects emerge. We hypothesise that the substructures in the first group, which appear to have a high baryon fraction (fb ≥ 0.95), are possible infant GC candidates. Objects belonging to the second group have a high stellar fraction (f* ≥ 0.95) and show a potential resemblance to infant ultra-faint dwarf galaxies. Results. The high baryon fraction objects identified in this study are characterised by a stellar content similar to the one observed in present-day GCs, but they still contain a high gas fraction (fgas ∼ 0.95) and a relatively low amount of dark matter. They are compact systems, with densities higher than the average population of FiBY systems at the same stellar mass. Their sizes are consistent with recent estimates based on the first observations of possible proto-GCs at high redshifts. These types of infant GC candidates appear to be more massive and more abundant in massive host galaxies, indicating that the assembly of galaxies via mergers may play an important role in building several GC-host scaling relations. Specifically, we express the relation between the mass of the most massive infant GC and its host stellar mass as log(Mcl) = (0.31 ± 0.15) log (M*, gal + (4.17 ± 1.06). We also report a new relation between the most massive infant GC and the parent specific star formation rate of the form log(Mcl) = (0.85 ± 0.30) log (sSFR)+α that describes the data at both low and high redshift. Finally, we assess the present-day GC mass (GC number) – halo mass relation offers a satisfactory description of the behaviour of our infant GC candidates at high redshift, suggesting that such a relation may be set at formation.

Exploring the physical properties of lensed star-forming clumps at $2\lesssim z \lesssim6$

“…In state-of-the art cosmological hydrodynamic simulations performed at very high resolution (i.e. dark matter particle mass resolution of ∼ 1000 M and, in some cases, pc-scale softening length for baryons, Ma et al 2020), bound and dense clumps in gas-rich highredshift galaxies have been identified, with sizes and masses below 100 pc, consistent with the typical values of star clusters (Kim et al 2018;Phipps et al 2020) and with the values measured in our sample. A systematic comparison between the properties of our clumps and the ones of current state-of-the art simulations is deferred to a future work.…”

Star Clusters Near and Far

“…At least in part motivated by the impending launch of JWST (and facilitated by technical improvements in hardware and modelling), a wide variety of recent studies has made predictions of the properties of young GC populations at high redshift. These range from back-of-the-envelope estimates, assuming simple scaling relations (e.g., Katz and Ricotti 2013;Renzini 2017;Boylan-Kolchin 2018), to expectations based on observations of nearby GC populations (e.g., Zick et al 2018) and high-redshift star formation (e.g., Vanzella et al 2017), and predictions from numerical simulations of galaxy formation, either by 'painting on' GCs using an ad-hoc model (e.g., Renaud et al 2017;Halbesma et al 2019;Madau et al 2019;Phipps et al 2019) or by including a physical description for GC formation and evolution (e.g., ). The resulting predictions for when GCs formed and what their corresponding detectability is with future observations with JWST or 30-m class telescopes vary greatly between these different approaches.…”

“…2 The first category of models takes a 'normal' galaxy formation simulation and uses some set of conditions (e.g. cuts in age, metallicity, or halo mass) to associate GCs to star particles (e.g., Renaud et al 2017;Halbesma et al 2019;Madau et al 2019;Phipps et al 2019). This 'particle tagging' technique has had difficulties to reproduce the observed demographics of GCs, such as their total number per unit galaxy mass and their age or metallicity distribution.…”

QuasarNet: A new research platform for the data-driven investigation of black holes

“…Simulations also place BH growth in its full astrophysical context against the backdrop of dark matter driven galaxy formation. Simulations have shown that the energy released from the accretion process has the capacity to impact a wide range of spatial scales -from the smallest scales where general relativity and magneto-hydrodynamic processes dominate to the largest scales wherein outflows driven by accreting black holes and their feedback are relevant (Beskin and Kuznetsova, 2000;Komissarov, 2001;Gammie et al, 2003;Komissarov, 2005;McKinney, 2005;Harrison et al, 2018;Phipps et al, 2020). This coupling of scales might hold the key to understanding the observed correlations.…”