The clustering of galaxies detected by neutral hydrogen emission
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Sean PassmoorProf. Catherine Cress
CollaboratorsAndreas Faltenbacher, Ando Ratsimbazafy Ben Hoyle, Russell Johnston, Mathew Smith
Galaxy Clustering in Radio surveys:HI & continuum sources
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Introduction
Why Measure Clustering:• Compare galaxy populations & relationship with dark
matter
• Evolution of clustering dependent on (ΩΛ; Ω
m)
• Constrains nature of Dark Matter (e.g. Hot Dark Matter Evolves Differently)
What is bias:• Relates fluctuations of DM to that of galaxies• Important for galaxy evolutionary theory• Predictions for SKA experiments
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Angular Correlation Function
Probability of Finding 2 sources separated by a given angle
For Random Samples ω(θ)=0
ω θ = DD θ RR θ
−1
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Illustration: Angular Correlation Function for an Artificial Distribution
•The fake data clustered on ±10° scale
• The Random Data is evenly distributed over the field
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Current Neutral Hydrogen Surveys
HIPASS Survey (Blue)• Area = 20 000 deg2
• Depth z ≈ 0.02• 4315 HI sources
ALFALFA Survey (Red)• Area ≈ 400 deg2
• Depth z ≈ 0.06• 1796 HI sources
Redshift Distribution
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Angular Correlation Function for HIPASS & ALFALFA
.Compare correlation function of HI-galaxies with dark matter to measure bias
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Recap
We find agreement between the clustering strengths of the two surveys.
Note : since bias < 1 → anti-biased
Measured BIAS parameter
ALFALFA 0.52 ± 0.1
HIPASS 0.68 ± 0.1
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Galaxy Clustering in Radio surveys:continuum sources
Continuum sources Synchrotron emission High redshift
• Faint Images of the Radio Sky at Twenty-Centimeters
~10000 deg2
~ 90 sources per deg2 at 1mJy
• Matched to SDSS (overlap ~4600 deg2)
Photometric Redshift Distribution
Matched Probe z < 1
• S3 Simulation – Theoretical Prediction of Redshift Distro.
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Galaxy Clustering in Radio surveys:continuum sources
Continuum sources Synchrotron emission High redshift
• Faint Images of the Radio Sky at Twenty-Centimeters
~10000 deg2
~ 90 sources per deg2 at 1mJy
• Matched to SDSS (overlap ~4600 deg2)
Photometric Redshift Distribution
Matched Probe z < 1
• S3 Simulation – Theoretical Prediction of Redshift Distro.
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Galaxy Clustering in Radio surveys:continuum sources
Continuum sources Synchrotron emission High redshift
• Faint Images of the Radio Sky at Twenty-Centimeters
~10000 deg2
~ 90 sources per deg2 at 1mJy
• Matched to SDSS (overlap ~4600 deg2)
Photometric Redshift Distribution
Matched Probe z < 1
• S3 Simulation – Theoretical Prediction of Redshift Distro.
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• Unmatched Sources– Probes deeper
• By Measuring the clustering of unmatched FIRST we probe bias at high-z
Faint Images of the Radio Sky at Twenty-Centimeters
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Ongoing ...
• Matched Sources– Matched Probe z < 1
• Unmatched Sources– Probes deeper
• Way Forward
– ???
Matched sample
contains a mixed
population?
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Summary
HI Clustering Studies
• Both ALFALFA & HIPASS indicate an anti-bias– i.e. less clustered than dark matter
Continuum Clustering Studies
• The Bias Calculation is ongoing