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SA COSMO

SA COSMO. Main aim is to provide a place where students and post-docs can meet and learn from each other, give talks, and start collaborations Usually about 50-70% of talks given by students/post-docs Meeting is very informal, so please ask questions

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SA COSMO

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  1. SA COSMO • Main aim is to provide a place where students and post-docs can meet and learn from each other, give talks, and start collaborations • Usually about 50-70% of talks given by students/post-docs • Meeting is very informal, so please ask questions • Speakers – remember your audience is very wide! • Should happen every ~4 months

  2. SCALPEL AND SALT BRUCE A. BASSETT ICG/SAAO Darragh O’Donoghue (SAAO) Ed Elson (SAAO/NASSP) Kurt van der Heyden (SAAO) Ricky Olivier (SAAO) Bob Nichol (ICG) Dan Carson (ICG) SCALPEL AND SALT BRUCE A. BASSETT ICG/SAAO Darragh O’Donoghue (SAAO) Kurt van der Heyden (SAAO) Ricky Olivier (SAAO) Bob Nichol (ICG) Dan Carson (ICG)

  3. The problem with modern cosmology • It doesn’t make sense – cosmos is accelerating! • The Universe on very large scales is dominated by an anti-gravity we call “dark energy” • What is this dark energy? • It requires negative pressure…a new form of energy!

  4. Correction for Brightness-Decline relation reduces scatter in nearby SN Ia Hubble Diagram Riess et al. 96 a(t)

  5. How can we hunt dark energy? • If we can measure a(t), the “size” of the universe as a function of time, we can learn about DE • Acceleration implies that currently

  6. Probes of a(t) • Type Ia supernovae – good but not well-understood • CMB – good, but not really sensitive to DE • Clusters – nice, but exponentially sensitive to systematic errors • Weak lensing – nice, but requires good seeing

  7. Cosmic chronometers • Excellent constraints on DE come from measuring the Hubble expansion rate where Then… redshift

  8. LRGs like to live here! But how do we measure dt? • Choose galaxy pairs at nearby redshifts (dz) • Estimate the difference in their ages, dt, from the difference of their spectra • But, can’t use any old galaxies! • Have to select very simple ones – Luminous Red Galaxies are the best…``red and dead”

  9. But why should this work? Simulated spectra for an LRG as a function of age from 10 million years to 13 billion years (top to bottom) Notice the steady Reddening with age… Z=0..2

  10. LCDM! The current state-of-the-art 32 LRG spectra Simon et al

  11. LRG Target Catalog SALT Cosmic Ages of Luminous Passive ELipticals survey • Use the fact that we can take many (~5) spectra simultaneously with RSS on SALT • Primary target: LRG’s at z=0.5 (optimal redshift window) • We will get 20-40 LRG spectra per night on SALT • Hence in 20 nights we should get 400-800 high-S/N LRG spectra

  12. So what? • We want to dissect the Universe at z=0.5, hence the name – SCALPEL • With 300 pairs of LRG spectra we get ~300 estimates of H(z) • If each estimate of H(z) is independent and accurate to ~30% we get an estimate of H(z) at z=0.5 accurate to

  13. Conclusions • Aim: to achieve an estimate of H(z) at z=0.5 that is as accurate as we have at z=0 • Since LRG’s are primarily found at the center of clusters we can estimate the cluster masses at the same time. • We will learn a lot about LRG’s • May make a key breakthrough regarding dark energy!

  14. Thanks to… • Joao, Robert and the CTP for hosting this event which we hope will be regular • The local organising committee for doing all the hard work: Martin Cook Norman Ives and the rest of the LOC… All the speakers and participants… See you at the next meeting!

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