J/A+A/549/A139 Circinus galaxy CRIRES observations (Gnerucci+, 2013)
Spectroastrometry of rotating gas disks for the detection of supermassive black
holes in galactic nuclei.
III. CRIRES observations of the Circinus galaxy.
Gnerucci A., Marconi A., Capetti A., Axon D.J., Robinson A.
<Astron. Astrophys., 549, A139-139 (2013)>
=2013A&A...549A.139G 2013A&A...549A.139G
ADC_Keywords: Active gal. nuclei ; Galaxies, Seyfert ; Rotational velocities ;
Spectroscopy
Keywords: techniques: high angular resolution - techniques: spectroscopic -
galaxies: active - quasars: individual: Circinus -
galaxies: kinematics and dynamics - galaxies: nuclei
Abstract:
We present new CRIRES spectroscopic observations of the Brγ
emission line in the nuclear region of the Circinus galaxy, obtained
with the aim of measuring the black hole (BH) mass with the
spectroastrometric technique. The Circinus galaxy is an ideal
benchmark for the spectroastrometric technique given its proximity and
secure BH measurement obtained with the observation of its nuclear
H2O maser disk. The kinematical data have been analyzed both with
the classical method based on the analysis of the rotation curves and
with the new method developed by us that is based on
spectroastrometry. The classical method indicates that the gas disk
rotates in a gravitational potential resulting from an extended
stellar mass distribution and a spatially unresolved dynamical mass of
(1.7±0.2)x107M☉, concentrated within r<7pc, corresponding to
the seeing-limited resolution of the observations. The new method is
capable of probing the gas rotation at scales that are a factor ∼3.5
smaller than those probed by the rotation curve analysis, highlighting
the potential of spectroastrometry. The dynamical mass, which is
spatially unresolved with the spectroastrometric method, is a factor
∼2 smaller, 7.9+1.4-1.1x106M☉, indicating that
spectroastrometry has been able to spatially resolve the nuclear mass
distribution down to 2 pc scales. This unresolved mass is still a
factor ∼4.5 larger than the BH mass measurement obtained with the
H2O maser emission, indicating that even with spectroastrometry, it
has not been possible to resolve the sphere of influence of the BH.
Based on literature data, this spatially unresolved dynamical mass
distribution is likely dominated by warm molecular gas and has been
tentatively identified with the circum-nuclear torus that prevents a
direct view of the central BH in Circinus. This mass distribution,
with a size of ∼2pc, is similar in shape to that of the star cluster
of the Milky Way, suggesting that a molecular torus, forming stars at
a high rate, might be the earlier evolutionary stage of the nuclear
star clusters that are common in late-type spirals.
Description:
High spectra resolution, continuum subtracted longslit spectra of the
nuclear Br gamma line emission in the Circinus Galaxy. The spectra
have been obtained obtained with CRIRES at the ESO VLT with the slit
centered on the galaxy nucleus and oriented along three different
position angles, PA1=30°, PA2=90° and PA3=150°. Setup of
the observations: slit width 0.4", R=50000, wavelength
range=2.137-2.188um, dispersion 0.120Å, pixel scale along the slit
0.086"/pixel. Resulting spatial resolution along the slit is ∼0.7".
Spectra have been rebinned over 5 spectral channels, are wavelength
calibrated but not flux calibrated. The location of the nucleus along
the slit is at pixel 145.
Objects:
---------------------------------------------------------
RA (2000) DE Designation(s)
---------------------------------------------------------
14 13 09.91 -65 20 20.5 Circinus = NAME CIRCINUS GALAXY
---------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 132 3 List of fits files
fits/* . 3 Individual fits files
--------------------------------------------------------------------------------
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 I5 0.1nm lam.min [21648] Lower value of wavelength interval
6 A1 --- --- [/]
7- 11 I5 0.1nm lam.max [21752] Upper value of wavelength interval
13- 15 F3.1 0.1nm dlam [0.1] Wavelength resolution
18- 20 I3 deg PA [30/150] Position angle of slit (30, 90 or 150)
22- 25 I4 --- Nx [1024] Number of pixels along X-axis
26 A1 --- --- [x]
27- 29 I3 --- Ny [512] Number of pixels along Y-axis
31- 34 I4 Kibyte size [2056] Size of FITS file
36- 48 A13 --- FileName Name of FITS file in subdirectory fits
50-132 A83 --- Title Title of the file
--------------------------------------------------------------------------------
Acknowledgements:
Alessio Gnerucci, Alessandro Marconi,
alessandro.marconi(at)unifi.it
References:
Gnerucci et al., 2010A&A...511A..19G 2010A&A...511A..19G, Paper I
Gnerucci et al., 2011A&A...536A..86G 2011A&A...536A..86G, Paper II
(End) A. Marconi [Univ. Florence, Itay], P. Vannier [CDS] 21-Mar-2014