Jim BraatzNRAO
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 Megamaser Cosmology Project
The Impact of an H0 Prior on CMB Models
H0 = 72 ± 3r ± 7s km s-1 Mpc-1
H0 = 62 ± 1r ± 5s km s-1 Mpc-1
Freedman et al. 2001
Sandage et al. 2006
Independent measurement of H0 is required to constrain the cosmological model.
WMAP Likelihood Surfaces
Water masers in AGN Accretion Disks
UGC 3789: Braatz & Gugliucci 2008
• H2O emission at 22 GHz
• N(H2) ~ 108 - 1010 cm-3
• T ~ 400 - 1000 K
Measuring Distances to H2O Megamasers
• 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
NGC 4258
2Vr
2
D = r/
a = Vr2/r
D = Vr2/a
Vr
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:
1. Survey with the GBT to identify maser disk galaxies2. Image the sub-pc disks with the High Sensitivity Array (VLBA+GBT+EB)3. Measure accelerations in the disk with GBT monitoring4. 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
Braatz et al, in prep.
PreliminaryProperties of UGC 3789 Maser Disk
R ~ 0.09 - 0.20 pc (0.40 - 0.87 mas)V ~ 750 - 450 km/sMbh ~ 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
NGC 6323
Backup Slides
The Extragalactic Distance Scale
Cepheids Direct Measurement of H0
0 Mpc 100 Mpc 200 Mpc
NG
C 4
258
UG
C 3
789
NG
C 6
323
IC 2
560
NG
C 1
194
NG
C 3
393
Mrk
141
9
Larg
est
Str
uctu
res
• 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 on its own does not measure many fundamental parameters; instead there are degemeracies. E.g. Ωmh2
• Independent measurement of H0 is necessary
•“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 and Cosmology
Spergel et al., 2007 (WMAP 3-yr)
The Accretion Disk in NGC 4258
Humphreys et al. 2008(CfA group)
• 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
A GBT Gallery of Extragalactic H2O masers
Braatz and Gugliucci, 2008, ApJ, 678, 96
Measuring Distances to H2O Megamasers
The Prototype: NGC 4258
2Vr
2
D = r/
a = Vr2/r
D = Vr2/a
Vr
Herrnstein et al. (1999)
D = 7.2 0.5 Mpc
Herrnstein et al. 1999
NGC 6323
• 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)
Disk Masers in the Era of VSOP-2
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