1. Direct Probes of H0
Jim Braatz (NRAO)

2. Precision Cosmology with the CMB
Planck CMB sets framework for modern cosmological models, but it needs external constraint from the local universe to break fundamental degeneracies.
In the base ΛCDM cosmology with a cosmological constant in a geometrically flat universe, Planck predicts H0 = /- 0.9 km s-1 Mpc-1 (Ade et al. 2015)

3. WMAP and Planck Map the CMB
In the base ΛCDM cosmology, Planck predicts
H0 = /- 0.9 km s-1 Mpc (Ade et al. 2015; Planck paper XIII)
Best current measurements based on standard candles:
H0 = /- 2.5 km s-1 Mpc (Riess et al. 2011)
H0 = /- 2.6 km s-1 Mpc (Freedman et al. 2012)
Updated from
Ade et al. 2013; 2015

4. Measuring an Accurate, High-precision H0
Short-term goal (~2 years): A robust ~3% measurement that reaches general agreement from multiple, independent direct methods
Longer-term goal: A direct ~1% measurement to complement future CMB observations.
Independent H0 measurement can place strong constraints on basic physics models, especially neutrino mass (Σmν), and DE equation of state (e.g. Sekiguchi et al. 2010, Di Valentino et al. 2015).
Di Valentino et al. 2015

5. Constraints on Neutrino Mass
Oscillation experiments demonstrate Σmν > 50 meV
Without priors, the CMB-S4 detection of Σmν may be significant at only ~2σ
For a CMB-S4 experiment, a prior on H0 at the ~percent level provides the best additional constraint on neutrino mass
Manzotti, Dodelson & Park (2015)

6. Constraints on DE Equation of State
To complement Stage 4 CMB experiments, an external measurement of H0 provides the best constraint on the DE Equation of State
A 1% measurement of H0 will reduce the error on w by a factor of 2
Manzotti, Dodelson & Park (2015)

7. A 1% Goal for H0 with Standard Candles
To approach 1%, must simplify the distance ladder and improve anchor calibration. Two approaches:
Geometry => Cepheids => SNIa
(Only ~9 SNIa with Cepheid calibration)
Use RR Lyrae and TRGB rather than Cepheids (CHP II)
Gaia parallaxes will improve calibration of Cepheids, RR Lyrae zero point, and TRGB method

8. Gravitational Lens Time Delays (with apprecation to Sherry Suyu, Chris Fassnacht, Leon Koopmans)
RXJ1131
Time delay:
Obtain from lens mass model
Cosmography requires:
Identifying the best lenses
Time delays
Lens mass model
Mass along line of sight
Suyu et al. 2013

9. Current Focus of Lensing Studies (H0LiCOW)B
RXJ
Individual distances have ~5-8% uncertainties in best cases.

10. Current Constraints from CMB+RXJ1131
Lens data also show tension with Planck CMB
w = ± 0.2 “phantom” range
Most physical models of DE have w > -1
Suyu et al. (2014)

11. Optical Lensing Studies
Sensitive, high-res imaging required for lens mass model. So, HST.
Ground-based AO imaging also under investigation. Challenge: modeling the PSF
Current projects such as Hyper Suprime-Cam Survey (HSCS) and the Dark Energy Survey (DES) will discover ~103 lenses
Future telescopes and surveys, especially Euclid and LSST, will identify ~104 lensed QSOs

12. Radio Lensing Studies
Optical lensing surveys and monitoring will dominate the field until SKA turns on.
Radio discovery and monitoring would then lead; SKA expected to discover ~104 lensed QSOs.
The large sample will permit selectivity to minimize systematics in measuring distances.
SKA (radio) + Euclid (NIR) are well-matched in coverage, sensitivity, and resolution, making them complementary for studying both the lens and the background QSO.
B with HST and MERLIN 1.7 GHz
From these large samples, detailed studies of ~50 lensed QSOs would enable percent-level determination of H0

13. Measuring H0 with H2O Megamasers
The MCP is an NRAO “Key Project” with the goal of determining H0 precisely by measuring geometric distances to galaxies in the Hubble flow.
Mark Reid
Jim Condon
Fred Lo
Christian Henkel
Cheng-Yu Kuo
Feng Gao
Wei Zhao
Violetta Impellizzeri
Eugenia Litzinger
Jenny Greene
Anca Constantin
Lei Hao
Dom Pesce

14. Steps to Measuring H0 with the MCP
The MCP is an NRAO “Key Project” with the goal of determining H0 precisely by measuring geometric distances to galaxies in the Hubble flow.
Survey with the GBT to identify maser disk galaxies
Image the sub-pc disks with the High Sensitivity Array (VLBA+GBT+EB+VLA)
Measure accelerations in the disk with GBT monitoring
Model the maser disk dynamics and determine distance to the host galaxy

15. H2O Megamaser Disks NGC 6323 Mrk 1419 NGC 2273 IC 2560 J0437+2456
NGC 5765b
UGC 3789
NGC 6264
NGC 1194

16. UGC 3789

17. UGC 3789 dynamic spectra
Pesce et al. 2015

18. Bayesian Estimation of the H0 PDF from Megamasers
We use a custom MCMC code by Mark Reid
Inputs: (x, y, vLOS, aLOS) for each maser spot
Global parameters:
D (or H0 directly)
MBH
(x0, y0, V0) of dynamical center
PA, inclination
Up to 4 parameters to describe the position angle & inclination warping
[eccentricity]
For UGC 3789: D = ± 5.1 Mpc
H0 = ± 7.1 km s-1 Mpc-1 (Reid et al. 2013)

19. NGC 5765b

20. Estimation of H0 from Geometric Distances
H0 = 67.6 ± 4.0 km s-1 Mpc-1 (6%)
UGC ± 5.1 Mpc H0 = 69 ± 7 (Reid et al. 2013)
NGC ± 19 Mpc H0 = 68 ± 9 (Kuo et al. 2013)
NGC ± 42 Mpc H0 = 73 ± 26 (Kuo et al. 2015)
NGC 5765b 126 ± 11 Mpc H0 = 66 ± 6 (Gao et al. 2015)

21. Estimation of H0 from Geometric Distances
H0 = 67.6 ± 4.0 km s-1 Mpc-1 (6%)
UGC ± 5.1 Mpc H0 = 69 ± 7 (Reid et al. 2013)
NGC ± 19 Mpc H0 = 68 ± 9 (Kuo et al. 2013)
NGC ± 42 Mpc H0 = 73 ± 26 (Kuo et al. 2015)
NGC 5765b 126 ± 11 Mpc H0 = 66 ± 6 (Gao et al. 2015)
In ~2 years the MCP will finalize observations and analysis for 5 additional galaxies, and should achieve < 4% total uncertainty.
Along with other members of the H0 community, we are now adopting “blind” analysis strategies to eliminate personal bias

22. Most Recent Disk Maser Discovery
New megamaser in CGCG will be the focus of MCP observations in the coming year.

23. Toward a 1% H0 with Megamasers
Current suite of GBT+VLA+EB+VLBA, enables a ~4% H0 measurement.
With ~10X the VLA collecting area and continental baselines, we could set the goal to measure ~100 galaxies at ~10% each, to achieve 1% H0. A 5+ year project.
With ngVLA sensitivity, we would be able to measure galaxies out to ~300 Mpc, which would alleviate concerns over systematics induced by a local void (e.g. Bohringer et al. 2015).

24. Summary
Independent measurement of H0 will continue to be a powerful complement to analyses of the CMB, and enable accurate cosmology.
Current measurements of H0 at the ~3% level are in tension with Planck predictions based on ΛCDM.
A robust determination of H0 requires agreement from multiple, independent methods to counter unknown systematics.
Future 1% measurement of H0 will complement a CMB-S4 experiment to determine neutrino mass and constrain DE models.
Measurements from lensing and megamasers may be able to approach 1% solutions beyond the next decade.

25. The End

26. By Measuring SMBHs We Learn How Galaxies Evolve
M-σ Relation
M-σ Relation (Maser masses only)
McConnell & Ma (2013)
Updated from Greene et al. 2010

27. Multiple Methods for Measurement of H0
Update to Fig. 16
Ade et al (Planck paper XVI)

30. CMB-S4 sensitivity

31. NGC 4258, “The Maser Galaxy”
Miyoshi et al. 1995

32. Measuring Distances to H2O Megamasers: A Geometric Measurement
D = r/
a = Vr2/r
D = Vr2/a

33. Progress with Megamaser Surveys
162 galaxies detected out of > 3000 observed
~ 37 show spectra indicative of a disk and are suitable for MBH measurement
~ 10 suitable for distance measurement
Primary sample for surveys: Type 2 AGNs at z < 0.05

34. Ultra-high resolution mapping with the HSA: It’s all about the signal-to-noise
Should have mentioned that two of the key advocates for VLBA sitting in the audience: Marshall Cohen and Tony Readhead
For sensitivity, the MCP adds the GBT, EB, and phased VLA to the VLBA
The GBT enables self-cal on the maser line, greatly improving efficiency
/D ~ 0.33 mas

35. UGC 3789: Systemic Features

36. UGC 3789: Blue Features

37. Constraints on DE Equation of State
In the context of Stage 4 CMB experiments, an external measurement of H0 at the percent level provides the best additional constraint on the DE Equation of State
Manzotti, Dodelson & Park (2015)

38. A Sample of GBT Spectra of Disk Masers