the megamaser cosmology project
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
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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
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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
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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
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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
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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
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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
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GBT Spectra of Maser Disks
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UGC 3789
MBH ~ 1.0 x 107 Msun from acceleration analysis
Braatz and Gugliucci, 2008
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UGC 3789
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UGC 3789
Reid et al, in prep.
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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
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NGC 6323
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Backup Slides
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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
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• 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)
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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
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A GBT Gallery of Extragalactic H2O masers
Braatz and Gugliucci, 2008, ApJ, 678, 96
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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
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NGC 6323
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• 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