The clustering of galaxies detected by neutral hydrogen emission

1. Sean Passmoor Prof. Catherine Cress Collaborators Andreas Faltenbacher, Ando Ratsimbazafy Ben Hoyle, Russell Johnston, Mathew Smith The clustering of galaxies detected by neutral hydrogen emission Galaxy Clustering in Radio surveys: HI & continuum sources

2. Introduction • Why Measure Clustering: • Compare galaxy populations & relationship with dark matter • Evolution of clustering dependent on (ΩΛ; Ωm) • 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

3. Angular Correlation Function Probability of Finding 2 sources separated by a given angle For Random Samples ω(θ)=0

4. Illustration: Angular Correlation Function for an Artificial Distribution • The fake data clustered on ±10° scale • The Random Data is evenly distributed over the field

5. 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

6. Angular Correlation Function for HIPASS & ALFALFA • .Compare correlation function of HI-galaxies with dark matter to measure bias

7. Recap • We find agreement between the clustering strengths of the two surveys. • Note : since bias < 1 → anti-biased HI-selected galaxies less clustered than optically selected galaxies.- Stripping of could gas in dense environments The Clustering and bias of HI is important for SKA / MeerKAT.

8. 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.

9. 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.

10. 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.

11. Faint Images of the Radio Sky at Twenty-Centimeters • Unmatched Sources • Probes deeper • By Measuring the clustering of unmatched FIRST we probe bias at high-z

12. Ongoing ... • Matched Sources • Matched Probe z < 1 • Unmatched Sources • Probes deeper • Way Forward • ??? Matched sample contains a mixed population?

13. 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