BiCoQ Seminar: "Looking into the dark: how starless dark matter halos will help us constrain the nature of dark matter? "

Thursday 16 Apr 2026, 13:30 → 15:00 Europe/Zurich

U2-2016

Alejandro Benitez Llambay (Dipartimento di Fisica G. Occhialini, Università Milano Bicocca)

Abstract: Within the standard ΛCDM model, galaxy formation theories predict a redshift-dependent "critical dark matter mass" threshold for galaxies to form, implying a large population of dark matter halos just below this mass should be starless. The most massive of these objects are free of complex stellar feedback and retain enough neutral hydrogen (HI) to be detectable in 21cm emission. They thus represent a unique and clean test of galaxy formation (and cosmological) models at the smallest scales. These systems are referred to as Reionization-Limited-HI Clouds (RELHICs). In this talk, I will discuss the theoretical framework for these curious systems and present Cloud-9, a prime candidate for a starless halo. We have identified extended 21cm emission using the Five-hundred Aperture Radio Telescope (FAST), the Green Bank Observatory (GBT), and the Very Large Array (VLA). Follow-up observations with the Hubble Space Telescope (HST) have ruled out any luminous counterpart, making Cloud-9 the most compelling detection of a RELHIC to date. I will conclude by discussing current uncertainties and the future theoretical and observational directions needed to strengthen this detection and uncover a larger population of these elusive objects.

 

About the speaker: Alejandro Benitez-Llambay is an Assistant Professor at the University of Milano-Bicocca and a member of the Bicocca Center for Quantitative Cosmology (BiCoQ). His research focuses on numerical cosmology and extragalactic physics, specifically the formation of small-scale cosmic structures. He combines high-performance hydrodynamical simulations with theoretical modeling to investigate the nature of dark matter through the study of dwarf galaxies and their halos. He is also the creator of Py-SPHViewer, a widely used tool for the scientific visualization of complex astrophysical datasets.