VLBI observations of the water megamaser in the nucleus of the Compton-thick AGN IRAS15480-0344 Paola Castangia (INAF-OA Cagliari) Collaborators: Alessandro Caccianiga (INAF-OA Brera) Paola Severgnini (INAF-OA Brera) Andrea Tarchi (INAF-OA Cagliari) Roberto Della Ceca (INAF-OA Brera) Disk-masers • PV diagram θS,VR • Velocity drift RS D = RS / θ S DU3789 = 49.6±5.1 Mpc MBH = (1.16±0.12) × 107MSUN (Reid et al. 2013) DN4258 = 7.2±0.5 Mpc MBH = (3.9±0.3) × 107MSUN (Herrnstein 1999) (Reid et al. 2009) Jet-masers • Jet-cloud interaction Mrk 348 (Peck et al. 2003) •Continuum and line flux densities are correlated •Reverberation maps give: Vshock, ρj, ρ0 Outflow-masers: Circinus • H2O masers trace a warped edge-on accretion disk and a wide-angle outflow –Outflow l.o.s velocity: ± 160 km/s –The warps collimate the outflow (Greenhill et al. 2003) IRAS 15480-0344 An S0 galaxy at ~130 Mpc WISE Multi-Colour image The nucleus: • Sy2 with broad Hα in pol. (weak) (Young et al. 1996) • Unresolved radio source (VLA A, 8.4 GHz) (Schmitt et al. 2001) • Radio quiet (L5GHz/L2-10keV = -5) 10 kpc (Terashima & Wilson 2003) Compton-thick (NH > 1024 cm-2 ) AGN sample • Selection method: FIR and X-ray flux and colours (Severgnini et al. 2012) • Ongoing H2O maser survey Single-dish observations Line 2 GBT observations, April 7, 2012 • Narrow (FWHM < 1 km/s) • Systemic (V=9106 km/s) Vsys Line 1 • Broad (FWHM ~ 90 km/s) • Blueshifted (V=8960 km/s) • LH2O ~ 200 Lsun Channel spacing 0.3 km/s CO • LH2O ~ 15 Lsun Single-dish observations May 12, 2012 The broad line is variable: Peak and int. flux density decreased to ½ of their initial values in ~1 month The properties of the narrow component remained relatively constant April 7, 2012 Channel spacing 3.3 km/s VLBI observations Details of the observations • Telescope: VLBA • Dates: June 2 and 3, 2012 (2 x 5 hr) • Bands: 2 x 16 MHz IFs • Correlation: 128 ch per IF and pol. ch spacing 1.7 km/s “spectral zooming mode” ch spacing 0.2 km/s 22 GHz maps • Line low res. (rms = 2 mJy/beam) • Line high res (rms = 5 mJy/beam) • Continuum (from the line-free channels, rms = 0.1 mJy/beam) VLBI observations VLBA, 22 GHz Tentative Peak ~ 0.5 mJy Slightly resolved ? VLA, A-array, 8.4 GHz (Schmitt et al. 2001) Peak = 0.7 ± 0.1 mJy A TB > 3.6 x 106 K P22 ~ 1.4 x 1021 W Hz1 0.5” 300 pc 6 pc B Tentative! Peak ~ 12 mJy VLBI observations Peak ~ 42 mJy Line parameters = single-dish spectrum Ch. 1.8 km/s ? Ch. 0.2 km/s Tentative! Peak ~ 10 mJy A Ch. 1.8 km/s 3 pc B Investigating the obscured nucleus of IRAS 1548-0344 Radio continuum emission • TB of sources A and B suggest a non-thermal origin • P22 > 1021 W Hz-1 unlikely to be SNRs • P22 larger than average P5 in a sample of Sy (Panessa & Giroletti 2013) • If the tentative source is real 10-20 pc linear structure Origin of the maser? • Absence of the triple-peak profile jet/outflow maser • Systemic and blueshifted emission separeted by 15-20 pc disk-maser unlikely (R ≤ 1 pc) • Not associated with any compact continuum source at 22 GHz Conclusions and future plans Radio continuum emission: VLBA 22 GHz image show 2 (possibly 3) compact continuum sources in a linear structure of tenths of parsecs ejection processes in the nucleus of IRAS 15480-0344? The water megamaser in IRAS 15480-0344 Systemic and (tentative) blueshifted emission are separated by 15-20 pc jet/outflow origin still the most likely Multifrequency (L and C bands) EVN observations have been approved and await scheduling. These will be fundamental to establish the nature of the radio continuum emission from the nucleus Single dish monitoring of the water maser lines with Effelsberg will help shedding light on the origin of the maser
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