👉Scientists are deeply concerned about how galaxies are distributed and how they detect dark matter because this relationship holds important clues to understanding the structure, evolution, and fundamental physics of the universe.
- Dark Matter’s Role:
- Galaxies form and move within the "framework" of dark matter halos.
🌀 1. Galaxy Power Spectrum
It’s a way to measure how galaxies are spread out in the universe—are they clumped together? Or spread evenly?
📊 2. Power Spectrum Estimation
What it means:
This is the process of calculating the power spectrum from data. You take the positions of galaxies and turn it into a graph that shows clustering strength vs. scale.
📐 3. Angular Power Spectrum
It measures clustering of galaxies across angles in the sky, not actual 3D distances.
How galaxies are clumped together at different scales.
The galaxy angular power spectrum describes the clustering of galaxies on the sky as a function of angular scale (multipole moment ℓ).
Simple example:
Think of looking at the sky like looking at a flat screen. If two galaxies are 10° apart on the sky, the angular power spectrum tells you how often you find galaxy pairs at that angle.
🧲 4. Bias Estimation
Galaxies don’t perfectly follow where the invisible dark matter is. Bias tells you how closely galaxies follow dark matter.
Bias: Galaxies don’t perfectly trace dark matter; they’re "biased tracers." Measuring bias reveals how different galaxies populate dark matter halos.
For example: Massive galaxies cluster more strongly (higher bias) than dwarf galaxies.
Galaxy bias (A Bridge Between Light and Dark): This tells us how galaxies sit in the cosmic web made of dark matter.
🌌 5. Theoretical Matter Power Spectrum
This is a prediction from cosmology about how dark matter is spread out in the universe, assuming we know how the universe works.
🧮 6. Cosmological Parameters (from Planck)
These are the key numbers that describe the universe: how fast it's expanding, how much matter it has, etc. Planck is a satellite that measured them very precisely.
➗ 7. Linear Biasing
It assumes the relationship between galaxies and dark matter is simple:
📦 8. Redshift Bins
Redshift tells us how far a galaxy is.
Binning means dividing the galaxy sample into groups by distance (e.g., nearby, middle, far).
🌈 9. Photometric Redshifts
It’s an estimated distance to a galaxy based on its color (brightness in different filters), not a precise one.
👉 10. Some Important Points:
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LOFAR (Low-Frequency Array) is a big radio telescope that listens to low-frequency radio waves from space.
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LoTSS (LOFAR Two-Metre Sky Survey) is a project that maps a large part of the sky using LOFAR.
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The First Data Release (DR1) of LoTSS gave images of 2% of the sky, detecting over 300,000 galaxies. The data is good enough for cosmology (after cleaning).
Galaxy clustering is a fossil record of how gravity built the cosmos over billions of years.
ΛCDM Model: Describes the universe's structure formation via cold dark matter halos hosting galaxies.
Importance:
The way galaxies are spread out fits well with the standard model of the universe (ΛCDM).
This shows that radio galaxy surveys like LoTSS can be used to study the structure and evolution of the universe.
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It’s a foundation for bigger studies in the future using more LOFAR data.
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It helps us connect the visible universe (galaxies) with the invisible parts (dark matter and early universe physics).