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CLUSTERS OF GALAXIES AT THE FIRST EPOCHS OF ASSEMBLY

15 juin 2023 | 11h00 12h00

Simona Mei APC Paris

Visioconference ZOOM

At redshifts of z ≲ 1.3, early-type galaxies (ETGs) and passive galaxies are mainly found in dense environments, such as galaxy clusters. Our recent results from an in-depth study of galaxies in 16 spectroscopically confirmed clusters at 1.3 < z < 2.8 from the Clusters Around Radio-Loud AGN (CARLA) survey show that the morphology-density and passive-density relations are already in place at z ∼ 2. The cluster at z = 2.8 shows a similar fraction of ETG as in the other clusters in its densest region, however, only one cluster does not provide enough statistics to confirm that the morphology-density relation is already in place at z ∼ 3. The cluster ETG and passive fractions depend mainly on local environment and only slightly on galaxy mass; also, they do not depend on the global environment. Interestingly, we find evidence of high merger fractions in our clusters with respect to the CANDELS fields, but the merger fractions do not significantly depend on local environment. This suggests that merger remnants in the lowest density regions can reform disks fueled by cold gas flows, but those in the highest density regions are cut off from the gas supply and will become passive ETGs. 

Our sample passive ETGs (log(M/M) > 10.5) are systematically ≳0.2 − 0.3dex larger (≳3σ) than field ETGs at a similar redshift and mass from the CANDELS survey. The passive ETG average size evolution with redshift is slower at 1 < z < 2 when compared to the field. This could be explained by early-epoch differences in the formation and early evolution of galaxies in haloes of a different mass, as predicted by models. It does not exclude that other physical mechanisms, such as strong compaction and gas dissipation in field galaxies, followed by a sequence of mergers may have also played a significant role in the field ETG evolution, but not necessarily in the evolution of cluster galaxies. We will present and discuss our results in the context of a larger vision of the field.

Links to the papers: 

https://ui.adsabs.harvard.edu/abs/2023A%26A…670A..58M/abstract
https://ui.adsabs.harvard.edu/abs/2023A%26A…670A..95A/abstract

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