Download THE CIRCINUS GALAXY - Observation and Data Reduction with the

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...
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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.