1. Ylva Pihlström University of New Mexico
Megamasers
Ylva Pihlström
University of New Mexico

2. What are megamasers?
Luminous, extragalactic masers with Lmegamaser > 106 Lgalactic maser
Detected species: SiO, CH, H2CO, OH and H2O
Associated with nuclear regions of active galaxies
Probes of high density regions
OH pumped by IR photons, H2O by collisions
Van Loon et al. 96; Whiteoak et al. 80; Baan et al. 86; Araya et al. 04

3. OH megamasers: history
First detected in Arp220
Association with host galaxy IR color
Surveys of IRAS galaxies
Detection rates high for high LFIR
Associated with nuclear regions of galaxies, in particular starburst nuclei of major mergers - ULIRGs.
Baan et al. 82
Henkel et al. 86
Stavely-Smith 87, 92; Norris et al. 89
Baan 89; Darling & Giovanelli 02
Sturm et al 96; Baan & Klöckner 06
Vignali et al. 05
1667 MHz OH
1665 MHz OH

4. Tracers of mergers Strong starburst/merger association
The OH 18cm lines favors dusty environments
Trace merger rate over cosmic time
Could help discriminating between different evolutionary scenarios
Darling & Giovanelli 02

5. Physical conditions
Detected in several lines (mainly 1667 and 1665 MHz lines)
Large supply of infrared photons
=> Inversion by infrared photons
Baan 85; Norris 95; Henkel et al. 87; Burdyuzha & Vikulov 90; Randell et al. 95
Radio - IR correlation + LOH  L60: Standard model with unsaturated maser emission amplifying nuclear continuum background.
Skinner et al. 97
Baan 85; Henkel & Wilson 90

6. OH megamasers with interferometers
Interferometric studies indicate molecular tori associated with massive central engines (Mrk231, IIIZw35, Mrk273, IC694)
Polatidis et al. 04; Klöckner et al. 03; Pihlström et al. 01; Richards et al. 06
Klöckner et al. 03

7. At VLBI resolution IIIZw35
Starburst related radio continuum resolved out
Masers in compact regions, large line widths (Arp220, IIIZw35)
Consistent with variability studies, indicating maser sizes <1.2pc (IRAS )
Lonsdale et al. 98; Diamond et al. 99
Darling & Giovanelli 02

8. Possible explanations
Parra et al. 05
Clumpy torus model, resulting in different emission spectra as compared to a smooth medium

9. New observations of Arp220
50 compact continuum sources (RSNe): 25% have associated bright, wide maser emission, also OH absorption.
Lonsdale et al. 06
Inverted gas local and associated with the radio supernova
Adds to the standard model
Lonsdale, Bialecki, Diamond in prep.

10. H2O megamasers: history
First detected in NGC4945
Circinus
NGC3079
NGC1068, NGC4258
Interferometric observations of NGC1068 and NGC4258
Survey
Associated with nuclear regions of galaxies, and in particular Seyfert 2s and LINERs.
Dos Santos & Lepine 79
Gardner & Whiteoak 82
Henkel et al. 84; Haschick & Baan 85
Claussen et al. 84
Claussen & Lo 86; Claussen et al. 88; Haschick et al. 90
Braatz et al. 94, 96, 97

11. H2O megamasers: types Circumnuclear AGN disks - e.g. NGC4258
Associated with radio jets - e.g. NGC1052 and Mrk348
Nakai et al. 93; Haschick & Baan 90; Haschick et al. 94; Greenhill et al. 95
Claussen et al. 98; Peck et al. 01
Other types: kilomasers - e.g. M51, M82, NGC253 and NGC2146
Ho et al. 87; Henkel et al. 84, 88; Claussen et al. 84, Tarchi et al. 02

12. Jet-driven megamasers
NGC1068 in jet-bending region (Gallimore et al. 96, 01)
NGC1052 along the SW jet (Claussen et al. 98)
Mrk348 toward the northern jet (Peck et al. 03)
Mrk348

13. Mrk348
Broad line (130 km/s) on < 0.3 pc, rapid variability => masers from shocked region
Temporal correlation between maser and continuum flux density suggest common origin
Spectra of jet-driven masers differs significantly from disk-masers
Peck et al. 03

14. Accretion disk H2O megamasers
Can be used to estimate black hole masses:
NGC1068
M=15x106 MS
Circinus
M=1.7x106 MS
NGC4258
M=39x106 MS
Miyoshi et al. 1994
Greenhill & Gwinn 97
Greenhill et al. 03

15. Test AGN unified schemes
Associated with obscuring column densities in Type 2 AGN
Type 2 AGN not well understood? Is the obscuring torus really a torus?
Warped accretion disks and outflows could be candidates for obscuring structures
Circinus
Greenhill et al. 03; Herrnstein et al. 97

16. Extragalactic distance scale (EDS)
Impacts cosmological key questions
Estimates of equation of state for dark energy requires constraints on expansion rate
Requires H0/H0 < 1% today > 10%
Most robust estimate: 889 Cepheids in 31 galaxies within 30 Mpc (PL relation in the LMC).
Hu 05
Freedman et al. 01

17. Geometric distances
Estimates of H0 directly via geometric distances should be more robust
Tie the EDS to galaxies with geometric distances
Broad Vrecession range
Obtained from water megamasers
VLBI mapping
Constrained geometry, high accuracy modeling
Acceleration distance
Proper motion distance

18. Uncertainty progress NGC4258
7.2 ±0.03 ±0.3 ±0.1 Mpc (4%)
Error Component
Type
Comparison with Herrnstein et al. 99
0.03 Mpc
Statistical
Reduction by factor 6
0.3 Mpc
Disk Model
Systematic
Work in progress: identifying all sources of modeling systematics
0.1 Mpc
Eccentricity Systematic
Investigation of e ≤ 0.1 space -> uncertainty reduced by factor 4
Acceleration fitting using 51 epochs of data, uses a 12 parameter 3D 2 fitting model.
Humphreys et al. 06

19. Towards 1% accuracy in H0
NGC4258: VLBI, HST (Cepheids) H0/H0 ~ a few %
Tie the EDS to maser galaxies:
Individual D/D ~ a few to 20%
N galaxies H0/H0 ~ (D/D)N-0.5
N~10 with the VLBA in 2010, SKA could increase N substantially ( , Morganti 04).

20. New H2O megamaser
183 GHz megamasers detected in Arp220, in the 31,3-22,0 line.
[A weaker detected in NGC3079]
350 km/s, probably starburst associated
Cernicharo et al. 06
Humphreys et al. 05

21. Extragalactic masers: future
Megamasers occur in nuclei of active galaxies - need VLBI.
OH: Even though most emission is in 100 pc scale tori, what about the compact spots with large line widths?
Why don't we see OH megamasers in every ULIRG? Can we use them as tracers of the merger rate as a function of z?
H2O: Look forward to more geometric distances!
What about the kilomasers - to date largely unexplored. Also includes 'outsider' masers.
Lonsdale et al.; Parra et al.
Spitzer and SMA data might help out!
Hagiwara et al. 01, Henkel et al. 06; Braatz et al. 04; Greenhill et al. 02; Nagar et al. 02; Tarchi et al. 03