Understanding Cepheid Variable Lab - Appointment Available

1. TA: David Lin d-lin@northwestern.edu Office hours: For help with Cepheid variable lab, Make an appointment http://www.astro.edu/astro/faculty/ulmer/a01_fall2002.html Discussion section meetings start this week

2. We are here Approximate direction of 400 km/sec relative to Virgo & Ursa Major Group Mpc = 3 million light years

3. => After subtracting out 250 km/sec around the Galaxy (can ignore motion in local group), we get a motion with respect to the CMB close to this direction in the Local Super Cluster => it all fits with the CMB being “far away”

4. Where MAP goes “bad” First Peak Red model gives 20% to L

5. Update, notice L not needed by CMB yet

6. Get the MAP results first hand in this room, April 18, 2003, at 4:00 p.m. or watch the new papers in early January 2003. Results could disagree with Supernovae! Also, Jan 18, same time same place come for same general topic

7. Concept of “Error Bars”: • Any measurement must have an uncertainty assigned to it. • e.g. my mass is [about] 70 kg plus or minus… 0.5 kg. • =>If my mass were to be measured, 67% of the time the reading would be within 0.5 kg of 70 kg

8. <= wrong right =>

10. Position of first peak tells us the universe is flat!! • But this depends on interpretation • Why is flat or “not” flat such a key (and disturbing) issue? • Remember “flat” => k = 0, W0 = 1; W0 = 1 means relatively (20 times) higher density compared to the density of ordinary matter (as predicted, we see even less)

11. Key to interpretation: • Assume we can calculate angular size of CMB fluctuations

12. Matter and Size of Fluctuations: • Key “buzz word” is Adiabatic • = Light and Matter follow each other • Assume some sound speed in the gas and some ordinary (baryonic) and non-baryonic matter are mixed together WITH LIGHT • Mixed with light means Adiabatic in this context • With this model, calculate the angular size and intensity of the CMB (redshifted light) fluctuations from “acoustic waves.”

13. Angles appear larger for closed case versus open Observer Photons free stream to the observer on geodesics analogous to lines of longitude to the pole. Thus the same angular scale represents a smaller physical scale in a closed universe. Wayne Hu

14. Angles appear even smaller for open case Acoustic features appear at harmonics of a fixed physical scale at last scattering, the sound horizon. Measurement of the angular scale that such features subtend on the sky can thus measure the curvature of the universe through an angular size distance test. Wayne Hu

15. Adiabatic Fluctuations, cont. • Use theory to match observed galaxies and clusters CMB measurements • Structure formation driven by “seeds” • Can make it all work • In part because the theory is so flexible

16. Keep adding things to make the model agree with observations • Dark Energy • non-baryonic matter (2 kinds) • most of bayronic matter not seen (yet)

17. What we are looking for!! The “Goldilocks ordinary matter (not too hot and not too cold) so as not to have been detected yet 300 million light years on a side