Astro Seminar
When the galaxy looks the same, does the CGM remember? // The earliest phases of high-mass star formation
Speaker: Prachi Khatri // Maxime Valeille-Manet (Cardiff)
Date: Wednesday 13 May 2026
Time: 14:00
Venue: N3.28
The circumgalactic medium (CGM) acts as both the reservoir of gas that fuels star formation and galaxy growth, and the interface where galaxies deposit the products of stellar evolution and feedback, making it a crucial site for constraining galaxy formation physics. Observations of CGM absorption lines (like Mg II, O VI, C IV) can, in principle, constrain feedback physics in a galaxy formation model. In this talk, I will present a controlled simulation study exploring how variations in stellar feedback parameters, such as the energy and metal loading of galactic outflows, impact CGM properties and observables. I quantify how changes in these parameters influence the transport and distribution of metals in the CGM and alter its multi-phase structure. This allows one to ask: when the galaxy looks the same, does the CGM still remember its feedback history? // The formation of high-mass stars (M>8Msol) remains a complex process involving the interplay of gas dynamics, intense UV radiation, and magnetic fields. The sequence of events leading to the formation of a high-mass star is still not well constrained, and a key open question concerns the definition of the mass reservoir available for stellar assembly. It is therefore crucial to identify the earliest stages of high-mass star formation and to quantify the non-thermal support mechanisms that counteract gravity during gas assembly. The first part of this talk will present the first statistical sample of high-mass prestellar core candidates identified during my PhD (Valeille-Manet et al. 2025), within the protoclusters observed by the ALMA-IMF large program. These cores, with sizes of 1500–4000 au and mass reservoirs greater than 16 Msol, correspond to the formation sites of individual or multiple stellar systems. They represent prime targets for constraining the physical conditions of the massive prestellar phase. I will then present work carried out during my postdoctoral position at IPAG (Grenoble) on the study of turbulence and magnetic fields at the core scale in one of the ALMA-IMF protoclusters, combining ALMA spectral line and dust polarization data at matched physical resolution. Within the framework of a virial analysis, we find that more than 70% of the cores appear supported against gravity, a surprising result, particularly for protostellar cores whose envelopes are expected to be at least partially collapsing (Valeille-Manet et al. in review). We show that contributions from organized motions (infall, covergent flows, rotation) together with the omission of surface terms in the observational virial theorem can lead to an overestimation of the non-thermal support. Finally, I will introduce the LAGAF project, on which I’m working on here at Cardiff University with Nicolas Peretto, which focuses on the kinematics of dense gas in hub-filament systems bridging these core scale studies with the large scale dynamics that channel mass toward the cores.