[Astro] Lunch Talk - 9/10/25

[Joseph Butler]

Gentle reminder of this today at 1pm.

Joe


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From: Joseph Butler <Joseph.Butler at nottingham.ac.uk>
Sent: Friday, October 3, 2025 3:19:18 PM
To: astro at nottingham.ac.uk <astro at nottingham.ac.uk>
Subject: Lunch Talk - 9/10/25

Hi all,

This week’s lunch talk will be given by Jesse Golden-Marx, and will take place on Thursday 9th October at 1pm in A113. Title and abstract below.

Title: The Metallicity of the ICL: A Euclid Q1 Story

Abstract: Colour provides key information for constraining the stellar population of the intracluster light (ICL), the diffuse light within galaxy clusters. Using the Euclid Q1 photometry for 174 DES-redMaPPer galaxy clusters (within the Q1 footprint) over the redshift range 0.1 < z < 0.75, we derive radial colour profiles of the brightest central galaxy (BCG) and ICL. Using elliptical annuli, we detect a colour gradient, such that the ICL is bluer than the BCG. By stacking these profiles, we can extend this gradient out to 600kpc. Using stellar population synthesis models, we find that near infrared colours are sensitive to metallicity, not age. Thus, we measure a metallicity gradient in the BCG+ICL out to 600kpc for the first time. We find that the metallicity of the BCG, which moderately evolves with redshift, is super-solar [log10 (Z/Zsun) > 0.2], while the ICL is metal-poor [log10(Z/Zsun)\sim -0.5 to -1.0], placing the first statistical constraint on the metallicity of the ICL as a population out to large radii. These results support our current understanding of BCG and ICL formation: BCGs form predominantly through mergers with massive galaxies or the cores of satellite galaxies, while the ICL grows via the tidal stripping of lower metallicity stars from the outskirts of massive satellite galaxies.

Thanks,
Joe
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