the clustering of galaxies detected by neutral hydrogen emission

Sean PassmoorProf. Catherine Cress

CollaboratorsAndreas Faltenbacher, Ando Ratsimbazafy Ben Hoyle, Russell Johnston, Mathew Smith

Galaxy Clustering in Radio surveys:HI & continuum sources

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

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

Illustration: Angular Correlation Function for an Artificial Distribution

•The fake data clustered on ±10° scale

• The Random Data is evenly distributed over the field

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

Angular Correlation Function for HIPASS & ALFALFA

.Compare correlation function of HI-galaxies with dark matter to measure bias

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

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.

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.

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.

• 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

Ongoing ...

• Matched Sources– Matched Probe z < 1

• Unmatched Sources– Probes deeper

• Way Forward

– ???

Matched sample

contains a mixed

population?

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