VLBI observations of the water VLBI observations of the water megamaser in the nucleus of the megamaser in the nucleus of the Compton-thick AGN IRAS15480-Compton-thick AGN IRAS15480-

03440344

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 RSD = RS / θS

DU3789 = 49.6±5.1 Mpc

MBH = (1.16±0.12) × 107MSUN

(Reid et al. 2013)(Reid et al. 2009)

DN4258 = 7.2±0.5 Mpc

MBH = (3.9±0.3) × 107MSUN

(Herrnstein 1999)

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

10 kpc

WISE Multi-Colour image

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

An S0 galaxy at ~130 Mpc

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)

(Terashima & Wilson 2003)

GBT observations, April 7, 2012

Single-dish observations

COCO

VVsyssys

Line 1

• Broad (FWHM ~ 90 km/s)

• Blueshifted (V=8960 km/s)

• LH2O ~ 200 Lsun

Channel spacing 0.3 km/s

Line 2

• Narrow (FWHM < 1 km/s)

• Systemic (V=9106 km/s)

• LH2O ~ 15 Lsun

Single-dish observations

May 12, 2012

April 7, 2012

Channel spacing 3.3 km/sThe 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

VLBI observationsDetails 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

VLA, A-array, 8.4 GHz

(Schmitt et al. 2001) A

B

?

6 pc

VLBA, 22 GHz

Peak = 0.7 ± 0.1 mJy

TB > 3.6 x 106 K

P22 ~ 1.4 x 1021 W Hz-

1

Tentative

Peak ~ 0.5 mJy

Slightly resolved

300 pc

0.5”

VLBI observations

A

3 pc

B

?

Tentative!

Peak ~ 10 mJy

Ch. 1.8 km/s

Tentative!

Peak ~ 12 mJy

Ch. 1.8 km/s

Ch. 0.2 km/s

Peak ~ 42 mJy

Line parameters = single-dish spectrum

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