Measuring the Hubble Constant Fundamental Cosmic Distance Scale Naples, May 3, 2011 Wendy Freedman Carnegie Observatories
Allan Sandage (1926-2010)
UnProgress in Measuring H o HST Factor of 2 Era Era of Percent Precision
Some history
Despite 60 years of effort, the Hubble constant was not measured to better than a factor of two
Solving the Twilight Zone Problem Use HST to measure Cepheids in galaxies to 20 Mpc, apply to calibrate a set of secondary distance indicators Use the secondary indicators to extend scale to 100 Mpc Twilight Zone
Philosophy of Key Project: Calibrate multiple methods to reduce risk of systematic errors Type Ia supernovae Tully-Fisher relation surface brightness fluctuations D n -σ relation fundamental plane
Cepheids
The Leavitt Law Leavitt (1908) Leavitt & Pickering (1912)
Cepheid Parameters: Optimizing Searches Cepheid amplitudes decrease with increasing λ Interstellar reddening decreases as λ 1 For detection: Cepheid searches best undertaken in the blue To minimize the effects of dust: observations best in the red Madore & Freedman (1991) HST: V and I
Multi-wavelength Distances Using Cepheids, HST M33 NGC 6822 A B ~1 mag I V R B A 4.5 ~ 0.01 mag WLF et al (1991) Madore et al (2009)
Larson objects in mirror
Key Project Sampling Strategy aliasing Equally-spaced observations Power-law sampling Madore & Freedman (2002, 2005)
The Hubble Key Project
Example Key Project Cepheids NGC 4414 NGC 2090 I V Turner et al.; Phelps et al.
M100 M100 Key Project Observations 12 V points 4 I points cosmic-ray split fixed roll angle ALLFRAME/ DoPHOT
Key Project Cepheids Composite I- band PL relation 24 galaxies ~800 Cepheids PL dispersion ~0.1 mag (LMC) Ferrarese et al. (2000)
Comparison of Cepheid Distances TRGB versus Cepheids SBF versus Cepheids Ferrarese et al. (2000): (Madore, Freedman, Lee, Sakai) PNLF versus Cepheids (Tonry et al.) GCLF versus Cepheids (Jacoby, Ciardullo) (Harris, Whitmore)
Key Project Results
Hubble H 0 Key Project (2001) Freedman et al. (2001) Hubble (1929) 1 st tick mark
Calibration of Secondary Methods Type Ia supernovae Cepheids Tully-Fisher relation Fundamental plane (ellipticals) Surface-brightness fluctuations Type II supernovae FP versus SBF SNIa versus SBF TF SNIa Blakeslee et al. (2001) Ahjar et al. (2001)
Calibration of the Tully-Fisher Relation H 0 = 71 ± 3 ± 7 km/sec/mpc Sakai et al. (2001)
Fundamental plane calibration Kelson et al. (2000) H 0 = 78 ± 5 ± 9 km/sec/mpc
Type Ia Supernovae BVI Hubble diagrams for SNIa Decline-rate relation (Phillips, Hamuy, Riess et al.) dispersion ~0.16 mag (8% in distance) 6 Cepheid calibrators H 0 = 71 2 7 km/sec/mpc Gibson et al. (2000)
Systematic Effects (1) Reddening: V 0.04 < E(B-V) < 0.36 V, I (H: NICMOS) agreement to 1% I H Macri et al. (2001), WLF et al. (1994)
Systematic Effects (con t) 2. Metallicity: 3. Calibration: (e.g., maser galaxy:ngc 4258, HST Cepheid parallaxes) 4. Velocity Flows: 1-2% at 30,000 km/s HST Key Project Sandage et al. 2004 Herrnstein et al. (1999); Macri et al 2006 Benedict et al. 2007
empirical tests: M31, M101 comparison with TRGB ~10% difference over a factor of 10 in [O/H] Metallicity
Final Combined Key Project Results H 0 = 72 ± 3 (stat.) ± 7 (sys.) km/sec/mpc WLF et al. (2001)
Recent Measurements Post HST KP
NGC 4258 s maser disk
Distance of NGC 4258 From proper motion and radial velocity 7.3 0.4 Mpc Herrnstein et al Nature From Cepheids 7.5 0.3 Mpc Macri et al ApJ 652 (alternatively equate the two and derive m-m(lmc) = 18.41 0.14)
SHOES program Supernovae and H 0 for the Equation of State Riess et al 2009, 2011 Differential Cepheid distances to NGC 4258 NGC 4536 NGC 4639 NGC 3982 NGC 3370 NGC 3021 NGC 1309 NGC 5584 NGC 4038 240 SNe Ia at z < 0.1 H 0 = 73.8 2.4 km/sec/mpc
Recent Measurements of H 0 240 SNe Ia z < 0.1 (Riess et al 2009) H 0 = 73.8 2.4 km/sec/mpc (Riess et al 2011)
Carnegie Supernova Project (CSP) Swope 1-meter Dupont 2.5-meter Magellan 6.5-meter Low z: High z: u BVg r i YJHK photometry 2.5-meter spectroscopy YJ photometry Magellan 6.5-meter 0 < z < 0.1 0.1 < z < 0.7
CSP Hubble Diagram for Low-z Supernovae Most of scatter is consistent with peculiar velocities. If confirmed, scatter in SN distances is 3-4%. Folatelli et al. 2009
The Carnegie Hubble Program
Remaining Dominant Systematics in Key Project 1. Zero point of Cepheid 5% 1-σ PL relation (distance to the LMC) 2. Effects of Metallicity 3.5% 1-σ on Cepheid luminosities 3. WFPC-2 photometric 3.5% 1-σ zero point
Carnegie Hubble Project (CHP) Team Barry Madore Jane Rigby Vicky Scowcroft Wendy Freedman, PI Eric Persson Violet Mager Laura Sturch Mark Seibert
Two Major Recent Developments in the Cepheid Extragalactic Distance Scale 1. Benedict et al. (2007) Fine Guidance Sensors on HST: First high-precision parallaxes for 10 nearby Milky-Way Cepheids 2. Freedman et al. (2008), Ngeow & Kanbur (2008), Madore et al. (2008): First Spitzer mid-infrared Cepheid PL relations for LMC Cepheids
New Cepheid Parallaxes: HST Freedman et al. 2001 HST Key Project Benedict et al. 2007 Sandage et al. 2004 Freedman et al. No change to H 0 Sandage et al. H 0 increases Difference at long periods where extragalactic Cepheids lie. Absolute trig parallaxes 2-3 ± 0.2-0.3 milliarcsec
Galactic Parallax Calibration Calibrate Persson et al. JHK data with parallaxes from HST (m M) K = 18.45 ± 0.04 mag Milky Way parallax calibration State of the art: H 0 = 73 ± 2 ± 4 km/s/mpc near-infrared photometry zero point geometric parallax WLF + Madore ARAA (2010) Benedict et al. (2007)
Archival Spitzer Observations of LMC Cepheids Advantage of Spitzer for the extragalactic distance scale: At 3.6 µm, A λ is >20 times smaller than at optical (Bband) wavelengths Spitzer Infrared Telescope
Spitzer Hubble Constant Exploration Program Overview (PI: W. Freedman) 705 hours 3.6 µm observations of: 37 Milky Way Cepheids (and 4.5 µm) (anticipating GAIA sample) 85 LMC Cepheids (and 4.5 µm) Nearest spiral galaxy Cepheids Tests for metallicity effects 545 spiral Tully-Fisher galaxies 54 Carnegie Supernova Project galaxies
Spitzer Large Program Three Metallicity Tests Remaining dispersion in LMC Leavitt relation Radial gradients in M31 and M33 Mid-IR Cepheid TRGB comparison
Archival Spitzer Observations of Spitzer IRAC observations 3.6, 4.5, 5.8 µm LMC Cepheids SAGE LMC study of star formation (Meixner et al 2006) Serendipitous observations of 70 Cepheids Single phase σ = ± 0.16 mag WLF, Madore, Rigby, et al. (2008)
Spitzer Leavitt Relations for the LMC PL relations for the LMC at 3.6 and 4.5µm (average of 2 phases) compared to the optical B and V bands A B is a factor of 20 times larger than for 3.6 and 4.5µm
Spitzer: NGC 6822 A B ~1 mag A 4.5 ~ 0.01 mag Single-phase PL relations for NGC 6822 (4 IRAC bands) Madore et al (2009) Multiwavelength fit of Galactic extinction curve : BVRIK+ 3.6, 4.5, 5.8, 8 µm
Nearby Galaxies Sculptor Group: NGC 300: ~2 Mpc
Spitzer Tully-Fisher Relation ± 0.43 ± 0.43 0.36 ± 0.36 ± 0.12 B, I, H, 3.6 µm Tully-Fisher relations for Key Project Cepheid galaxies NOTE: The TF relation can be applied to any spiral galaxy.
Spitzer 3.6 and 4.5 µm Milky Way light curves 3.6 µm 4.5 µm
Spitzer 3.6 and 4.5 µm LMC light curves 3.6 µm 4.5 µm
Spitzer 3.6 and 4.5 µm SMC light curves 3.6 µm 4.5 µm
Spitzer LMC Leavitt Law 3.6 µm V 85 LMC Cepheids 24 phase points 3.6 µm: σ = 0.10 mag V-band: σ = 0.25 mag log P (days)
Near- and Mid-IR LMC PL Relations 4.5 3.6 4.5 3.6 K H J K H J log P
CHP Preliminary Results on H o LMC + Milky Way Spitzer 3.6 µm calibration H o = 73.6 1.5 (stat) 3.1 (sys) km/s/mpc To come: Additional nearby galaxies including N4258 GAIA parallaxes for Milky Way Cepheids Independent Mid-IR Tully-Fisher calibration
The Carnegie Hubble Project (CHP) : Summary 1. Cepheids LCO, HST, Spitzer, GAIA, JWST 2. Supernovae LCO (CSP), Spitzer 3. Mid-IRTF Spitzer, Magellan, JWST Consistent mid-infrared photometric zero point: from Milky Way through Local Group to Hubble flow. Eliminate current systematics.
Comparison of HST Key Project and CHP H 0 Error Budgets
Combining H 0 with Planck Results H 0 to ± 10% H 0 to ± 2% + SN + BAO 68 and 95% CL Freedman & Madore, Ann. Rev. 2010
Summary: An unprecedented decade of stability! WMAP, SHOES, CHP are all consistent with HST KP value of 73 km/s/mpc with an uncertainty of 5%. Accuracies of a few percent are now in sight. This will require independent measurements to test for robustness as done for Key Project.