The Supersonic Project: Shining Light on SIGOs—A New Formation Channel for Globular Clusters

Abstract

Supersonically induced gas objects (SIGOs) with little to no dark matter component are predicted to exist in patches of the Universe with non-negligible relative velocity between baryons and the dark matter at the time of recombination. Using arepo hydrodynamic simulations we find that the gas densities inside these objects are high enough to allow stars to form. An estimate of the luminosity of the first star clusters formed within these SIGOs suggests that they may be observed at high redshift using future HST and JWST observations. Furthermore, our simulations indicate that SIGOs lie in a distinct place in the luminosity-radius parameter space, which can be used observationally to distinguish SIGOs from dark-matter hosting gas systems. Finally, as a proof-of-concept, we model star formation before reionization and evolve these systems to current times. We find that SIGOs occupy a similar part of the magnitude-radius parameter space as globular clusters. These results suggest that SIGOs may be linked with present-day metal-poor local globular clusters. Since the relative velocity between the baryons and dark matter is coherent over a few Mpc scales, we predict that if this is the dominant mechanism for the formation of globular clusters, their abundance should vary significantly over these scales.

The SLUGGS survey: measuring globular cluster ages using both photometry and spectroscopy

“…In the first class of models (e.g. Peebles 1984;Katz & Ricotti 2014;Trenti et al 2015;Chiou et al 2019) GC formation requires the special conditions of the early universe, forming before or during the epoch of reionization (z 6). In the second class (e.g.…”

The Supersonic Project: SIGOs, A Proposed Progenitor to Globular Clusters, and Their Connections to Gravitational-wave Anisotropies

“…This allows them to survive as independent, DM-depleted objects. Simulations suggest that these objects could potentially evolve into presentday globular clusters (Chiou et al 2019).…”

“…These objects, known as supersonically induced gas objects (SIGOs), have since been found in follow-up simulations (Popa et al 2016;Chiou et al 2018Chiou et al , 2019Chiou et al , 2021. However, there are still many outstanding questions about these objects.…”

“…The stream velocity is constant only on scales of a few Mpc (e.g., Tseliakhovich & Hirata 2010). Thus, the implementation of the initial conditions in numerical simulations can be done self-consistently only on smallbox simulations (e.g., Naoz et al 2012Stacy et al 2011;Schauer et al 2019;Chiou et al 2018Chiou et al , 2019Chiou et al , 2021. In these small-box simulations, the stream velocity is implemented as a uniform boost along one axis.…”

Young, old, massive: Steps to understanding globular cluster formation

“…This view, which might seem obvious now, is in itself a change in thinking from earlier times. Numerous early approaches suggested that GC formation might be special in some way, connected with the early universe; examples include Peebles & Dicke (1968); Fall & Rees (1985); Murray & Lin (1992); Moore et al (2006); Chiou et al (2019). However, those semi-cosmological ideas encounter fundamental and probably insurmountable obstacles: for example, there is no special mass scale for GCs (much current evidence indicates that their initial mass distribution has a power-law form, and the present-day GC luminosity function with its lognormal shape has been produced instead by dynamical evolution and preferential removal of lower-mass clusters).…”