Megamasers

1. 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 Baan et al. 82 Henkel et al. 86 • 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. 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 (IRAS12032+1707) Lonsdale et al. 98; Diamond et al. 99 Darling & Giovanelli 02

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

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

10. H2O megamasers: history Dos Santos & Lepine 79 • 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. 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 Nakai et al. 93; Haschick & Baan 90; Haschick et al. 94; Greenhill et al. 95 • Circumnuclear AGN disks - e.g. NGC4258 • Associated with radio jets - e.g. NGC1052 and Mrk348 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%) 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 (100-1000, 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