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Fakultät für Physik - Digitale Hochschulschriften der LMU - Teil 05/05 Podcast
The large-scale environments of radio-loud active galactic nuclei and their evolution across cosmic time

The large-scale environments of radio-loud active galactic nuclei and their evolution across cosmic time

Fakultät für Physik - Digitale Hochschulschriften der LMU - Teil 05/05 vor 12 Jahren

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Emerging from the cosmic web, galaxy clusters are the most massive
gravitationally bound structures in the universe. Thought to have
begun their assembly at 2 < z < 3, i.e. 10 to 11 billion
years ago, clusters provide insights into the growth of large-scale
structure as well as the physics that drives galaxy evolution. The
redshift range 1 < z < 3 is a key epoch in their evolution.
At z ∼ 1.5, elliptical galaxies start to become the dominant
population in cluster cores, and star formation in spiral galaxies
is being quenched. But there is also evidence for a progressive
increase in the amount of star formation that occurs in galaxy
cluster cores at z ≳ 1.5. To understand the dependence of the
formation mechanisms of massive galaxies with environment, we must
focus on clusters at relatively unexplored redshifts z > 1.5
where major assembly is in progress. The search for galaxy clusters
at high redshift, so far, has been mildly successful and only a
handful of clusters at z > 1.5 have been confirmed. Because this
redshift range was essentially unreachable with previous
instrumentation, it was dubbed a ‘redshift desert’. The work
presented in this thesis has made a major contribution to this
field. The Clusters Around Radio- Loud AGN (CARLA) survey, a 400 hr
targeted Warm Spitzer program, observed 420 radio-loud AGN (active
galactic nuclei) at 1.3 < z < 3.2 across the full sky.
Extensive literature over several decades shows that powerful
radio-loud AGN preferentially reside in overdense environments.
From this survey, we have identified a sample of ∼ 200 galaxy
cluster candidates by selecting strong overdensities of
color-selected sources. By studying the luminosity function of the
CARLA cluster candidates, we showed that quenching is happening
much earlier in clusters around radio-loud AGN than in field galaxy
samples. This suggests that our targets may well be the most
massive and evolved structures known to date at z > 1.5. We also
showed that radio-loud AGN reside in denser environments than
similarly massive galaxies. This makes high-redshift clusters
around radio-loud AGN particularly interesting as they can reveal
how galaxies in the most massive dark matter halos assembled. A
complementary project, HERGE (Herschel Radio Galaxy Evolution
Project) observed a sample of 71 radio galaxies at 1 < z < 5
at far-IR wavelengths with the Herschel Space Observatory.
Supporting data in the mid-IR, partially in the near-IR and at
sub-mm wave- lengths allow to study cluster fields in more detail.
A pilot project on a single field showed that we can identify
cluster members and constrain their star-formation properties.
These projects laid the foundation for future work, which will make
a significant impact on understanding the formation of the most
massive structures over several billion years.