High Resolution Observations of OH Megamaser Galaxies

1. High Resolution Observations of OH Megamaser Galaxies MERLIN EVN Ylva Pihlström (NRAO) J. Conway (OSO) W. Baan (ASTRON) A. Polatidis (MPIfR) H.-R. Klöckner (Univ. of Groningen)

2. Early radio interferometry results • Standard model: • Starburst heats dust grains FIR radiation • FIR pumps a diffuse OH screen and seed photons stimulate • unsaturated, low-gain maser emission • Continuum and maser emission scales • Early results confirmed this picture • Arp 220(Norris et al 1985, Lonsdale et al 1994) • III Zw 35(Montgomery & Cohen 1992) Maser peaks Continuum peak MERLIN 0.28 arcsec resolution (Montgomery & Cohen 1992)

3. Global VLBI – III Zw 35 Diamond et al (1998) Trotter et al (1997) Single dish VLBA III Zw 35 • Failed to detect continuum high amplification factors • and standard model questioned (Diamond et al. 1998; Lonsdale et al 1999) • Missing flux is a potential problem

4. IIIZw35 1667 MHz Pihlström et al. 2001 50pc • EVN+MERLIN to pick up a larger fraction of the total flux density • A smooth distribution of emission, with a velocity gradient • Enclosed mass within 22pc radius is 7x10^6 solar masses

5. Geometrical model Pihlström et al. 2001 Pathlength A 22pc radius torus Inclination 30 deg. Path length and brightness maximized at tangent points Brightness Brightness EVN Global VLBI

6. Monte Carlo models Parra et al. 2003 in prep Tilted torus with pc-scale clouds in Keplerian orbits

7. Velocity field Parra et al. 2003 in prep Data Model

8. Brightness distribution Parra et al. 2003 in prep Model Data

9. Radio continuum The continuum distribution follows the OH maser emission • Diffuse continuum luminosity • agrees with radio luminosity • estimated from the FIR • luminosity • => Starburst dominated • Compact components • are either individual RSN • or super star clusters Pihlström et al. 2001

10. Mrk231 Klöckner et al. 2003 • Seyfert 1 galaxy with OHMM consistent with 65pc radius torus • Also a possible outflow component in the West

11. IRAS 12032+1707 Darling & Giovanelli 2001 100 pc • Redshift z = 0.217 • Very broad velocity extent: 1500 km/s • Observed with the VLBA in July 2002 • 100% of the flux density is recovered in the VLBA observations. • The emission is compact (100 x 100 pc)

12. IRAS 12032+1707 VLBA results Moment 1 • Velocity gradients are apparent, but a disturbed field • possibly two disks • 1667/1665MHz blending?

13. IRAS 14070+2505 Darling & Giovanelli 2000 Arecibo VLBA • Redshift z = 0.265 • Velocity extent 2000 km/s • Observed with an 8 element VLBA array • Only 20% of the flux density is recovered

14. IRAS 14070+2505 VLBA results Signs of a rotating disk with a gradient 8 km/s/pc. Estimated enclosed mass within 25 pc 10^8 solar masses.

15. Summary • VLBI observations demonstrate that the OHMM emission is • confined to sub-kpc scales • The velocity fields are ordered, with gradients • Best explained by rotating torus structures • Geometry can explain much of the emission characteristics • Probing the OH gas at all angular resolutions is important • to get a complete picture • Our data supports the standard model (Baan 1985)