The Megamaser Cosmology Project Jim Braatz NRAO Co-I’s: Mark Reid Lincoln Greenhill Fred Lo Jim Condon Christian Henkel Ingyin Zaw Avanti Tilak Lei Hao Cheng-Yu Kuo Liz Humphreys

The Impact of an H0 Prior on CMB Models H0 = 72 ± 3r ± 7s km s-1 Mpc-1 Freedman et al. 2001 H0 = 62 ± 1r ± 5s km s-1 Mpc-1 Sandage et al. 2006 WMAP Likelihood Surfaces Independent measurement of H0 is required to constrain the cosmological model.

Water masers in AGN Accretion Disks H2O emission at 22 GHz N(H2) ~ 108 - 1010 cm-3 T ~ 400 - 1000 K UGC 3789: Braatz & Gugliucci 2008

Measuring Distances to H2O Megamasers NGC 4258 NGC 4258 is the prototype for the maser distance method BUT this galaxy is too close to determine H0 directly Nearby maser galaxies like NGC 4258 can be used to recalibrate the Cepheid scale  Vr D = r/ 2Vr 2 a = Vr2/r D = Vr2/a Herrnstein et al. (1999) D = 7.2  0.5 Mpc

The Megamaser Cosmology Project In the framework of cosmology set by analysis of CMB anisotropies, a precise measurement of H0 will provide a strong constraint on the equation of state parameter, w, of dark energy. The MCP is an NRAO “Large Project” with the goal, in about 5 years, of determining H0 to 3% by measuring angular diameter distances to about 10 galaxies in the Hubble flow. The Process: Survey with the GBT to identify maser disk galaxies Image the sub-pc disks with the High Sensitivity Array (VLBA+GBT+EB) Measure accelerations in the disk with GBT monitoring Model the maser disk dynamics and determine distance to the host galaxy

Progress in Megamaser Surveys 112 Extragalactic maser galaxies are now known About 30% have h.v. components > 250 km s-1 About 10% are disk masers and are candidates for high precision distance measurements Primary sample for new surveys: Type 2 AGNs from SDSS

GBT Spectra of Maser Disks

UGC 3789 MBH ~ 1.0 x 107 Msun from acceleration analysis Braatz and Gugliucci, 2008

UGC 3789

UGC 3789 Reid et al, in prep.

UGC 3789 Preliminary Properties of UGC 3789 Maser Disk R ~ 0.09 - 0.20 pc (0.40 - 0.87 mas) V ~ 750 - 450 km/s Mbh ~ 1.2 x 107 Msun a ~ 3.6 km s-1 yr-1 (mean value) D ~ 51 Mpc (15%) H0 ~ 65 km s-1 Mpc-1 Braatz et al, in prep.

NGC 6323

Backup Slides

The Extragalactic Distance Scale Structures Largest NGC 4258 UGC 3789 NGC 3393 NGC 1194 NGC 6323 IC 2560 Mrk 1419 Cepheids Direct Measurement of H0 0 Mpc 100 Mpc 200 Mpc One method covers all scales out to the size of largest structures Maser distances can be used to calibrate other distance methods e.g. Cepheids, SN Ia, Tully-Fisher

The CMB and Cosmology “The single most important complement to the CMB for measuring the DE equation of state at z ~ 0.5 is a determination of the Hubble constant to better than a few percent.” Hu 2005 The CMB on its own does not measure many fundamental parameters; instead there are degemeracies. E.g. Ωmh2 Independent measurement of H0 is necessary Spergel et al., 2007 (WMAP 3-yr)

The Accretion Disk in NGC 4258 Warp in the disk is fully characterized Accelerations measured in both systemic and h.v. features Blue features absorbed by gas in the disk Disk characterization reduces systematic error in distance determination Alternative to LMC to anchor the extragalactic distance scale Humphreys et al. 2008 (CfA group)

A GBT Gallery of Extragalactic H2O masers Braatz and Gugliucci, 2008, ApJ, 678, 96

Measuring Distances to H2O Megamasers The Prototype: NGC 4258  Vr D = r/ a = Vr2/r D = Vr2/a 2Vr 2 Herrnstein et al. (1999) D = 7.2  0.5 Mpc Herrnstein et al. 1999

NGC 6323

Disk Masers in the Era of VSOP-2 Precision measurement of disk geometry Substructure: striation and spiral structure What fraction of the disk do masers trace? (skin structure) Accurate characterization of the disk is critical to minimize systematic errors Constraints on blended systemic features Elliptical orbits? Distinguish phase effects from maser clump effects Proper motion measurements? (~ 3 µas yr-1 for UGC 3789) Sensitivity (and flex scheduling) is essential (Baselines to GBT, EVLA, EB)