1 / 16

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

fausta
Download Presentation

SA COSMO

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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!

More Related