Stacey Alberts

Infrared Surveys of (Proto-)clusters and Future Prospects

How the near-infrared, the Sunyaev-Zel'dovich (SZ) Effect, and rare galaxy populations have expanded our (proto-)cluster surveys and the order of magnitude increase expected for future surveys

The Near-Infrared: Stellar Mass Functions and Quenched Populations

What we know from the quiescent populations of clusters, from the stellar mass-dependence of quenching in clusters to pre-processing​​​

The Mid- to Far-Infrared: Dust-Obscured Star Formation and AGN​

How infrared observations have traced star formation activity in clusters to high redshift, revealing an epoch of vigorous activity (see next section). We also explore how Dusty Star Forming Galaxies are illuminating the nature of proto-clusters​

The Far-Infrared to Submillimeter: Dust and Gas Measurements

Molecular gas is fundamental to galaxy quenching. We cover the recent integrated to spatially resolved submillimeter measurements in low to high-z (proto-)clusters and what we can learn about environmental quenching

We've long known that galaxies in galaxy clusters (massive dark matter haloes that contain huge overdensities of galaxies and hot gas) live different lives than their cousins outside. They grow faster and shut down their star formation earlier, such that old, nearby galaxy clusters are full of old, red, dead galaxies.

Galaxy clusters start their lives as sprawling massive proto-clusters at high redshift (z>2) before collapsing into compact haloes. Do their galaxy population change at the proto-cluster stage or do they need the compact environment of the cluster?​​​

Using Herschel SPIRE imaging at 250μm, we studied the obscured star formation in mass-limited galaxy populations in 274 massive clusters spanning z=0.3-1.5. We found that while cluster galaxies have a more rapid evolution then field galaxies (as expected), at the highest redshifts (z~1.5), cluster galaxies have similar SFRs and specific-SFRs as field galaxies. This activity demonstrates that massive (virialized) clusters can still host significant star formation right into their cores, followed by a transition era to quenched populations. Read more: Alberts et al. 2014, MNRAS, 437, 437​

We followed up this study with targeted ultra-deep Herschel PACS imaging at 100 and 160μm to look at 11 massive clusters in detail. We found significant variation between the clusters (indicating the importance of statistical cluster studies), but with the same trend toward field-like star formation activity in the cluster cores at z~1.4. The evolution in the star formation activity in these suggests a rapid quenching mechanism at z~1.4 (perhaps mergers and AGN activity) followed by less rapid mechanisms taking over (perhaps gas stripping). Building on this, we revisited our full cluster sample and analysed the mass-limited galaxy populations for signs of AGN activity. Using SED fitting, we categorized galaxies as AGN-dominated, AGN-composite, host-composite, and host-dominated. Within the cores of the highest redshift clusters (left), we found clear signs of enhanced AGN activity. Read more: Alberts et al. 2016, ApJ, 825, 72

Directly connecting this activity to cluster galaxy quenching relied on ongoing studies of AGN feedback; however, these studies confirm that the epoch of z~1-2 is an active and important time in the lives of clusters, which must be connected to the precursor activity in proto-clusters at earlier epochs.

Coming Soon