About CLEVeR

Key Scientific Challenges Tackled by CLEVeR & Our Approach

​

CLEVeR addresses some of the most pressing questions in galaxy evolution and large-scale structure formation. While theoretical models can successfully reproduce large-scale trends, they still struggle with predicting the detailed physics of feedback and baryon distribution at different cosmic scales. By leveraging multi-wavelength observations and state-of-the-art simulations, CLEVeR provides critical constraints on AGN and stellar feedback and their role in shaping the universe.

​

Challenge 1: Understanding Baryon Distribution in Low-Mass Halos

The Problem

​

While massive galaxy clusters have been extensively studied, low-mass halos (10¹² - 10¹³ M☉) remain poorly constrained. These halos are crucial because:
✔ They are the most common galaxy environments in the universe.
✔ Galaxies spend most of their evolutionary history in these environments before merging into larger clusters.
✔ Theoretical models diverge drastically in predicting how much gas these systems retain or expel.

Some simulations predict that low-mass halos are completely devoid of hot gas, while others suggest they retain substantial X-ray-bright atmospheres. The reality remains uncertain due to the lack of observational constraints.

​

CLEVeR’s Approach

•  Using eROSITA, CLEVeR provides an unprecedented census of galaxy groups, filling the "group desert"—a mass range where observational data has been lacking.

•  Cross-matching X-ray data with optical (SDSS, 4MOST), radio (LOFAR), and infrared (JWST, ALMA) surveys to determine the total baryonic content.

•  Comparing observational constraints with cutting-edge simulations (IllustrisTNG, Magneticum, BahamasXL) to refine our understanding of gas expulsion and retention mechanisms.

​

Challenge 2: The Role of AGN Feedback in Regulating Gas & Star Formation

The Problem

​

• Feedback from supermassive black holes (SMBHs) is thought to regulate the cooling of hot gas, preventing excessive star formation. However, current models struggle to reproduce key observations:

• How efficiently does AGN feedback eject gas from low-mass halos?

• Does feedback prevent star formation or trigger it in certain environments?

• Why do some clusters show ongoing star formation while others experience complete quenching?

 

CLEVeR’s Approach

• Measuring X-ray luminosity and gas temperature in galaxy groups to determine how much energy AGN inject into their surroundings.

• Identifying radio-loud AGN with LOFAR and eROSITA to map the energy output of SMBH jets.

• Using IFU spectrographs (MUSE, JWST, KCWI) to detect outflows, shocks, and gas filaments directly linked to feedback events.

By correlating AGN activity with gas properties, CLEVeR helps refine feedback models and determine when and where AGN regulate star formation.

​

Challenge 3: The Multiphase Nature of the Circumgalactic Medium (CGM)

The Problem

​

The CGM—the gaseous halo surrounding galaxies—plays a key role in fueling star formation and regulating feedback. However, observations reveal dramatic variations in CGM properties:

• Some galaxies have dense, cool CGM that sustains star formation.

• Others show hot, diffuse CGM, preventing gas accretion.

• The physics of CGM heating, cooling, and mixing remain poorly understood.

​

CLEVeR’s Approach

• Combining X-ray (eROSITA, XMM), UV (HST/COS), and radio (LOFAR, ALMA) data to create the most detailed multi-phase CGM map ever produced.

• Studying the metal content and temperature gradients to understand gas inflows and outflows.

• Comparing with simulations to test different CGM regulation models and their implications for galaxy evolution.

• ​

 

Challenge 4: Satellite Galaxy Evolution & Environmental Effects

The Problem

​

Satellite galaxies—smaller galaxies orbiting within a larger halo—experience harsh environmental processes that can either quench or sustain star formation. However, how this happens is still unclear:

• What determines whether a satellite retains or loses its gas?

• How do stripping processes affect galaxy structure?

• Do different environments (clusters vs. groups) lead to different satellite evolution paths?

​

CLEVeR’s Approach

• Using eROSITA and optical data (SDSS, 4MOST, GAMA) to track satellite galaxies within different environments.

• Studying ram-pressure stripping and tidal interactions by analyzing the gas content (HI, X-ray) and stellar properties (optical, IR) of satellites.

• Stacking analysis of thousands of satellite galaxies to detect large-scale trends in gas depletion, star formation history, and metal enrichment.

CLEVeR will directly test theories of environmental quenching by linking satellite properties to their host halo mass and gas conditions.

​

The CLEVeR Solution: A Multi-Scale, Multi-Wavelength Approach

By synthesizing data from X-ray, optical, UV, infrared, and radio telescopes, CLEVeR provides the most comprehensive observational constraints to date. The project bridges the gap between observations and simulations, refining our models of galaxy evolution and unraveling the complex feedback-driven processes that shape the universe.

​