THE CIRCINUS GALAXY (ESO97-G013) SEEN BY VLTI/MIDI Lyuba Slavcheva-Mihova Lilit Hovhannisyan Aurea Garcia Rissmann Everton Ludke Kazuaki Ota

The Circinus Galaxy Circinus is an active galaxy in the Southern hemisphere (“Compass constellation”) RA=14h13m09.9s DEC= -65d20m21s emitting enough flux at 10m as to be observed by MIDI Flux (12 m ) = 37.8 Jy Vr = 434 km/s → 1mas = 0.028 pc Optical nucleus is a strong X-ray emitter.

Observational aspects... A nearby spiral galaxy only 4 degrees below the Galactic plane (Freeman et al. 1977). Due to galactic obscuration it has been detected in HI before the optical images were available (HST/WFPC - Wilson et al. 2003); Koribalski & Whiteoak (1996) mapped Circinus with several configurations of the ATCA – found evidence for a neutral gas bar in HI which is not evident in HST WFPC plates but it is seen in HCN and HCO+ millimeter lines (Curran et al. 1998); The nuclear activity is caused by star formation, a Seyfert 2 nucleus and giant radio lobes (perhaps associated with outflow), very similar to those in NGC 3079 (Koribalski & Whiteoak 1996); AAT Taurus Fabry-Perot interferometer and ESO NTT observations evidences fast-rotating nuclear ring and an ionization cone (Marconi et al. 1994) suggesting a complex nuclear dynamics at parsec scales; Circinus has a powerful water megamaser (Greenhill, 1982) suggesting an accretion disk and molecular outflow from 0.1-1 pc from the central engine; Our aims are to observe the nuclear region of the Circinus Galaxy with the VLTI and the MIDI telescope to impose better constraints in the measurements of sizes of the hot and cold dust streams associated with the inner parsec-scale regions to better probe the nuclear dynamics.

Observational Set-Up 2 UTs + MIDI at 10m (N band) (UT2-UT3, with baseline of about 43m) HIGH_SENS mode with PRISM dispersion Date of observation: May 26th 2005

Data Analysis Data provided by K. Tristram:  3 observations of a calibrator (HD 120404)  3 observations of the Circinus nucleus, made with UT2-UT3 with different position angles Analysis:  only possible for one of the target observations, given the low signal-to-noise ratio  calibration performed using the 3 observations of the star, and averaged at the end

Analysis Serious fringe detection problem for 2 out of the 3 target observations Region between around 9 and 11m not reliable given the visibility function sensitivity to different analysis parameters (binning, etc)

Modelling We assume a Gaussian distribution of intensities for the mid-IR emission of the galaxy core: FWHM = (/B)  0.5    sqrt(-ln 2  ln V) with VVisibility, which is a function of wavelength

Results Visibility could be estimated for one out of the three target observations available The emitting region, derived assuming a Gaussian distribution centered at the galaxy core, seems to have a single size component for wavelengths from 8 up to 9.2 m, and come from more extended regions for longer wavelengths. Further software development at MIA may be needed to cope with low signal-to-noise frames as it is the case for AGNs.