Kavli Affiliate: Risa Wechsler
| First 5 Authors: Tara Dacunha, Tara Dacunha, , ,
| Summary:
The diffuse starlight extending throughout massive galaxy clusters, known as
intracluster light (ICL), has the potential to be read as a memoir of mass
accretion: informative, individual, and yet imperfect. Here, we combine dark
matter-only zoom-in simulations from the Symphony suite with the Nimbus
"star-tagging" model of the stellar halo to assess how much information about
the mass assembly of an individual galaxy cluster can be gleaned from idealized
measurements of ICL outskirts. We show that the edges of a cluster’s stellar
profile — the primary (Rsp*1) and secondary (Rsp*2) stellar "splashback" radii
— are sensitive to both continuous mass accretion histories and discrete
merger events, making them potentially powerful probes of a cluster’s past. We
find that Rsp*1 strongly correlates with the cluster’s mass ~1 dynamical time
ago, while Rsp*2 traces more recent mass accretion history to a slightly lesser
degree. In combination, these features can further distinguish between clusters
that have and have not undergone a major merger within the past dynamical time.
We use both to predict realistic cluster mass accretion histories with the
MultiCAM framework. These outer ICL features are significantly more sensitive
to mass accretion and merger histories than the stellar mass gap and halo
concentration, and perform comparably to the commonly used X-ray-based tracer
of relaxedness, x_off. While our analysis is idealized, the relevant ICL
features are potentially detectable in next-generation deep imaging of nearby
clusters. This work highlights the promise of ICL measurements and lays the
groundwork for more detailed forecasts of their power.
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