A New Route to the Hubble Constant (and Dark Energy) from HST Adam Riess (JHU, STScI) SHOES Collaboration

Anchor (NGC 4258): Galaxy with Cepheids whose distance we know by geometry SN Ia Host: Galaxy with Cepheids and an SN Ia, former calibrates latter Cepheids Variables, Period Indicates Luminosity Using a “distance ladder” we knit together progressively longer range distance indicators to ~300 million light years, measure the Hubble constant.

Eliminating sources of systematic error: 1) use same instrument 2) same Cepheid parameters (Period,Z) 3) better anchor REBUILD DISTANCE LADDER TO THE HUBBLE CONSTANT 3% Anchor: NGC4258 Hubble Flow 4.5% error ____ 1% 3% 0% NEW LADDER (100 Mpc) Hubble Flow 5% Anchor: LMC 4% SN Ia hosts, Metal poor to Metal rich 11% error ____ 1% # Modern, distant SNe Ia 3% # Modern, local hosts 5% Fast to Slow Cepheids 4% Ground to HST OLD DISTANCE LADDER (100 Mpc) H 0 =74+/-3.5 H 0 =72+/-8

g Expansion History reveals: THE ACCELERATING UNIVERSE XX Now need greater precision, longer history to understand Dark Energy! A more precise Hubble constant helps with this! High-z (Riess et al. 1998) SCP (Perlmutter et al. 1999) Dark Energy+Dark Matter

CMB 0.3 Myr Distant SNe Ia 2-9 Gyr ago BAO, 3 Gyr ago Hubble constant: Cepheids, local SNe Ia Dark Ages Different Tools delineate expansion history at different ages. Together, constrain the physics of Dark energy. BAO SN More data, More realism Test Robust- ness New H 0, ~5% w= /-0.10 Universe 300 Myr younger Dark Matter Dark Energy Old H 0 ~11% Big Bang WMAP Model uncertainty measurement uncertainty Cosmological model (stuff+physics)

WMAP+SHOES H 0 (wcdm) w= /-0.10 (for vacuum energy w=-1) compare to Hi-z SNe Ia+SDSS BAO: Wood-Vasey et al (ESSENCE) w= /-0.15 Astier et al (SNLS) w= /-0.10 SHOES WMAP5yr Komatsu et al. 2008

» A precise measurement of the Hubble constant is of comparable value to other leading methods for measuring dark energy. »This measurement can either provide a test of the model or allow for constraint in the face of additional complexity in the model. » We have halved the uncertainty in H 0 to under 5% by building a streamlined distance ladder in the near-IR with NICMOS, circumventing past sources of systematic error. »Future: More Maser anchors, more MW Cepheid parallaxes from GAIA, more local SNe Ia.  (H 0 )~1% may be possible SUMMARY