MPIfR Colloquium, 23 April 2004 Yoshiaki Hagiwara ASTRON Collaborators: P.J.Diamond, W.A. Sherwood, W. Baan, N.Nakai M.Miyoshi, C.Henkel, E.Rovilos, K.Hachisuka H. Imai. R,Kawabe Extra-galactic Water Masers
Maser Transitions: H2O 6 16 5 23, 22 G Hz Several transitions were theoretically predicted at 22 – 321 G Hz, and detected around Galactic star-forming regions and late-type stars. (Neufeld & Melnick 1991; Menten & Melnick 1991) (from Elitzur 1991) Extra-galactic water masers – only at 22 G Hz The 1 st discovery was toward M33 by Churchwell et al. (1977) using the MPIfR100-m telescope.
Some VLBI studies on OH Megamasers (Kloeckner et al. 2003) Mrk231, distant ULFIRG, D=170 Mpc - 100 pc scale axis-symmetry torus (r ~ 65 pc) imaged by OH. - OH masers shield (obscure) a radio source in the galaxy. - dV/dx ~ 1 km/s/pc but no sign of Keplerian rotation.
Why study the water masers? Learn about the circum-nuclear region of AGN. - R < 1 pc scales (1,000-10,000 Rs) (OH Megamasers: R ~ 10 – 100 pc scales) - Kinematics around accretion disks (e.g. Miyoshi et al. 1995) Learn something about the extra-galactic star-formation - Kinematics and evolutions of star-formation in outer galaxies (e.g. Greenhill et al. 1990) Tools for Astrometry - VLBI measurement at 10 micro arcsec level - The 3-D kinematics in Local group of galaxies ( e.g. Argon et al. 1994; Brunthaler PhD. Thesis, 2004)
What do the maser spectra look like? (Greenhill 2003) (Quasi-) symmetric distribution of Doppler-shifted lines w.r.t Vsys. - High-velocity features - Presence of a rotating disk, or a receding and approaching gas ? Single broad-line ( FWHM ~ 100 km/s) emission.
Properties of the masers The masers are found towards ~ 40 objects. 1. The masers (< 10 Lsun) are exclusively found towards narrow- line AGNs (Type 2 Seyferts or LINERs). 2. High luminosity ~ 100 -1,000 Lsun (only ~ 1 Lsun for W49N ) 3. Intensity is highly variable (> 50-100 %). 4. Host galaxies contain kpc-scale radio/optical–jet. 5. Highly Doppler-shifted components within < 1000 km/s wrt Vsys. 6. Intensity of red-shifted features > blue- features
Water masers and VLBI VLBI imaging revealed that the masers trace the compact structures. - Very compact < ~ 1 mas - High surface brightness 10 7 – 10 15 K - Kinematics Vlos, dV/dt, (x,y) Credit: NRAO Very Long Baseline Interferometry (VLBI) since 1993 inspire astronomers.
The Keplerian disk toward NGC 4258 (Nakai et al. 1993; Miyoshi et al. 1995; Herrnstein et al. 1997, 1998) -R ~ 0.1 – 0.2 pc (~ 4,000 Rs) -Warped and thin Central binding mass ~10 7 Msun Vrot < 1,000 km/s dv/dt ~ 10 km/s/year for Vsys feature Distance to the galaxy ~7 %
Any other promising systems ? (Claussen et al. 1998; Greenhill et al. 2003) Circinus - sub-Keplerian disk Greenhill et al. 2003) Mccallum 2004 'Outflow' components NGC 1052 – Jet maser - The masers are associated with radio continuum. - NO hint of a disk or discernible structure. MPIfR 100-m spectra Braatz, Wilson, Henkel (1994)
Seyfert 2 galaxy NGC 5793 (Hagiwara et al. 2001) - Only blue-shifted components were detected with VLBI....... Where are the Vsys, red features? - The masers do not associate with any compact continuum like the case of NGC4258, Circinus......Obscuring a central engine?
- dV/d(RA) ~ 0.9 km/s/pc - Maser structure is unresolved. - Symmetric high-velocity features wrt Vsys – similar to NGC 4258. IC 2560 - LINER (Ishihara et al. 2001) NRO 45-m
NGC 6240 – Seyfert 2 (Hagiwara et al. 2002) - Redshifted (~ 450 km/s) components - The maser coincides with a nucleus. - The maser traces a 'hotspot' in a more dominant nucleus. VLA 1.3 cm K-band continuum
What did we learn from these masers using VLBI? Distribution: Resolved at < 1 pc Classification: - Disk: NGC 4258, NGC 1068, Circinus - r ~ 0.1 – 0.9 pc - dV/dt ~ several km/s/yr - dV/d(Dec, RA) ~ 1 – 10 km/s/pc - M bind – 10 6 ~ 10 7 Msun - Jet: NGC 1052, Mrk 348 - Outflow (large-scale): Circinus - Possible disk: NGC 3079, NGC 4945, NGC 5793, IC2560 (Greenhill et al. 1996, 1997, 2003; Hagiwara et al. 2001; Ishihara et al. 2001; Peck et al. 2003)
All these intense water masers (L H2O > 10 L sun ) are related to AGN-activity. --> Nuclear maser No masers are found r < ~ 0.1 pc ( ~ 1,000 Rs). - Water molecules are distroyed ?
Radio source Radiation+ self (collision)- pumping How do we model the rotating maser disk ? Vrot Longer gain path for self- amplification Disk edge Unseen Radiation pumping Vsys Vred = Vsys + Vrot Vbl = Vsys – Vrot
T hin disk or obscuring material Radio source Geometry and intensity of the maser Strongest Weak or unseen Intensity of unsaturated maser I n ~ h n A 21 N 2 n L exp[ t - 1]/ t t : optical depth L: path length N 2 n : population density of excited level Observable Unseen
Maser Intensity variability Single-dish or VLBI monitoringof the masers, for example, - Circinus (Maccllum et al. ) Long-term (~ an annual cycle) and rapid variation (maser flare ?) Interstellar Scintillation (ISS) (Greenhill et al. 1997) - NGC 3079 (Sherwood, Hagiwara, Baan) Search for a life-time of each feature - to study origin of the maser disc, outflow, supernova ? Effelsberg NGC 3079
Maser Intensity Variability Short-term : - Time scales on shorter than the light-crossing time for the maser - Instabilities in radiative transfer equation on timescale ~ L/c This causes hrs and minutes. - Observations with too wide a bandwidth (phase effects) (Evance 1972; Watson 1992, 1994; Gray 2004) Long-term: - Gains modified by bulk-flows and turbulence - May be connection to magnetic compensation (Cook 1966) - Links to age and evolution of SFRs - Observable with VLBI
Recent new results (black et al. 1992) VLA (Tarchi et al. 2003; 2004) 3C403, the first distinct detection from a radio galaxy (FRII), a most distant water maser, L H2O ~ 1,000 Lsun Mrk 1419, LINER (Henkel et al. 2002) Blue- and red-clusters are seen symmetrically offset by 475 km/s wrt Vsys. There i s a hint of velocity drift only for Vsys features.
The masers in 3C403, Mrk1419 are interesting systems but these new entries are very weak...... 50 mJy It's not easy for VLBI imaging. For imaging maser emission, ~100 mJy is limit using phase-referencing VLBI (plus the Eff 100-m). Which masers are worth to pursue ? Prototypes are NGC 4258, NGC 1068, Circinus, NGC 4945 (> 1 Jy). IC 2560 is weaker but look promising. NGC 3079 is just strong and look messy.
High-luminosity (L H2O > ~10 Lsun)... ca. 40 AGNs NGC4258, NGC3079, NGC4945, Circinus,...... Low-luminosity (L H2O < ~1 Lsun)... ca.10 nearby galaxies NGC253, M82, IC342, M33, M51,....... Found in nearby star-forming galaxies, starbursts, and also AGNs. NOTE: Strongest Galactic H2O maser (W49N) is ~ 1 Lsun. Low-luminosity water masers (Churchwell et al. 1977; Huchtmeier et al. 1988; Ho, Henkel et al. 1987; Greenhill 1993)
Learn something about the extragalactic star-formation. - The evolution and kinematics. - Structures of exotic star-formation in outer galaxies. Use the masers for extra-galactic Astrometry (IC10, M33). - The masers are obseved in nearby galaxies. - Parallaxes establish 3D-kinematics for the Local group. (Brunthaler PhD thesis 2004). - Proper motions yield galactic kinematics. Low-luminosity water masers Why Low-L water masers ?
H2O Maser Spectrum in M82 (Baudry, Henkel et al. 1994) OH masers (blue-shifted) imply star-formation in the expanding shell of SNR (Pedlar et al. 1999, Wills et al. 1999). Molecular super bubble structures in CO (Matsushita et al. 2000, Weiss et al. 2001) Weak (0.001-0.1 Lsun) H2O masers (Claussen et al. 1984) VLA -C at 1" res could not resolve the maser (Baudry & Brouillet 1996). Star-burst galaxy in M 82 ? (Hagiwara, in prep.)
-Angular res: 0.1 - 0.08 arcsec - A Configuration -Velocity range: V( LSR ) = 70 -155 km/s -Velocity res: 1.3 km/s Any other promising systems ? (Claussen et al. 1998; Greenhill et al. 2003) New VLA Observations
Xray source S1 S2 S1 New2 New1 New2 S2S2 M82 S1 : Compact HII Region S2 : 0.2 arcsec (3.5 pc) away from compact HII Region. - Followed up by MERLIN. New1 & 2 : Weak and narrow lines No nearby continuum
No continuum counterparts for these H2O masers. The masers are associated with neither thermal HII regions nor SNRs. The masers could trace the earlier phase of SF, like bipolar outflows in YSOs. Need for mapping at higher resolution ~ < 0.01 pc (Signatures of Galactic SF structures ~ < 0.01 pc) MERLIN, at res ~ 30 mas ~ 0.2 pc, barely resolved the maser. S2 MERLIN 22 GHz CO (2-1) Intensity map with PdBI & the 30m (Weiss et al. 2001) and positions of H2O masers. CO(2-1) H2OH2O What is S2?
-T ype 1 Seyfert, D=9.7 Mpc (VLA-A: 0.1 arcsec = ~ 5pc) -Narrow-line Seyfert 1 (Osterbrock & Pogge 1985) -Weak H 2 O emission (~2 Lsun) (Hagiwara et al. 2004) -H 2 O maser in a type 1 nucleus is rather unique. Water Maser in narrow-line Seyfert 1 (NLS1) galaxy in NGC 4051
Effelsberg and VLA Spectra Quasi-symmetric velocity distribution w.r.t Vlsr = 710 km/s. VLA-A could not resolve the masers at 0.1 arcsec, or 5pc. Vsys No high-velocity emission was seen at rms ~ 5 mJy/ch within +- 800 km/s w.r.t Vsys.
What is the maser in NGC 4051? The radio continuum peak coincides with the maser. -AGN-activity -But, why is the low-luminosity (~ 2 Lsun) ? Because... -Narrow-line Seyfert 1 -Low inclination disc-like configuration Lower column density in the line-of-site Dense and warm molecular gas environment (HCN, HCO+). -Star-forming activity ??
The H 2 O maser in M51 Terashima & Wilson (2004) + : Hard Xray point source Hagiwara, Henkel, et al. (2001) Vsys ~ 470 km/s -Nearby star-forming galaxy, hosting a low-luminosity AGN -Weak (0.1-1 Lsun) H2O maser (Ho et al. 1986) -Hagiwara, Henkel et al. (2001) pinpointed the maser in the vicinity (0.1", ~5pc) of the radio continuum nucleus with the VLA-A snap-shot. What is the origin ? AGN-activity or Star-forming-activity?
Monitoring with the 100-m (Hagiwara, Henkel, Menten et al. 2001) Vsys
New VLA Observations of M51 A weak blue-shifted (V=445 km/s) and red-shifted (V=538-585 km/s) components were detected. Higher resolution ~ 0.08 arcsec.
Red-shifted maser: 0.1" (~ 5pc ) north the radio (3.6-cm) nucleus -Confirmed the results in Hagi, Henkel et al. (2001) A blue-shifted maser: 0.6" (~30pc) north-west the nucleus. Where is the maser in M51 ? 3.6-cm VLA map: Bradley, Kaiser, Baan (2004)
Origin of the maser in M51 VLA maps: Bradley, Kaiser, Baan (2004) The red-shifted masers are likely to be related to AGN-activity. The blue-shifted maser might be originated from the gas-rich environment in star-forming region. VLBA resolved the maser ! The presence of a thin disc (Moran et al. 2003)? Blue-shifted emission Red-shifted emission VLA 3.6-cm
Jet Maser in NGC1068 C Weak (~10 Lsun) H2O maser at the radio knot (C), located ~30 pc north the nucleus. - The maser intensity is variable. - Proper motion over 2 epochs (1983 and 1987)? The origin of the maser (Gallimore et al. 2001) - Molecular outflows in YSOs - Amplifying the radio jet - Shock in molecular clouds in star-forming site Nakai et al. (1995) Gallimore et al. (1996)
MERLIN Observations of the Jet Maser According to preliminary data analysis... The jet maser was not detected in these observations Because of... -Intensity variability -Maser is resolved at 30 mas, ~ 3pc. -MERLIN sensitivity ( rms ~ 4 mJy/beam/ch) Nucleus S1 Knot C NGC1068 1.3-cm Radio Continuum
What do the Low-L H 2 O Masers tell us ? Particular conditions required for H 2 O masers -Density (10 8 - 10 10 /cm 3 ) -Warm (500 - 800 K) What do low-luminosity masers trace? Low-luminosity H 2 O masers are outside of the nucleus (e.g. Claussen & Lo 1986).
- Extra-galactic Young Stellar Object (YSO): disc, inflow/outflow (M82) Scales of Galactic YSOs are < 0.001 -0.01 pc. - VLBI cannot resolve - Thermal radio continuum, i.e. Compact HII region (M33, IC10, M 82, NGC2146) - Non-thermal SNR (e.g. Expanding shells) - Startburst nucleus (NGC 253 ?) - Disc or torus around an active nucleus (M51 ?) (Greenhill et al. 1993; Tarchi et al. 2002; Henkel et al. 2003; Moran et al. 2003)
Low-luminosity masers observed with VLA or VLBI
21-cm VLA radio continuum - FIR (100 um + 60 um) 21cmVLA data from Condon et al. (1990) ( Hagiwara, in prep ) Radio-excess galaxies = H2O Masers FIR-excess galaxies = OH Masers Arp200 Arp220, Mrk231, Mrk273 NGC4258, NGC3079, NGC1068, NGC5506, NGC5793 M82, NGC253, M51
The future is...... Water masers in general are very useful for probing sub-pc scale kinematics can also be used as iagnosing tools in extragalactic objects -Tracers of High density, warm regions, i.e. Hotspots Low-luminosity H 2 O masers -Extragalactic star-forming regions OH, H 2 CO masers And, of course, we need more H 2 O masers