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%arXiv:0904.4090

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\slugcomment{Submitted to ApJ}

\shorttitle{Images of SgrA*}

\begin{document}
\bibliographystyle{apj}

\title{Images of the radiatively inefficient accretion flow surrounding
a Kerr black hole: application in Sgr A*}

\author{Ye-Fei Yuan\altaffilmark{1}, Xinwu Cao\altaffilmark{2}, Lei
Huang\altaffilmark{1,2,3}and Zhi-Qiang Shen
\altaffilmark{2}}
Cosmology, University of Sciences and Technology of China,
Cosmology, Shanghai Astronomical Observatory, Chinese Academy of
Sciences, Shanghai 200030, China; cxw,zshen@shao.ac.cn}

\altaffiltext{3}{Academia Sinica, Institute of Astronomy and
Astrophysics, Taipei 106, Taiwan}

\begin{abstract}
In fully general relativity, we calculate the images of the
radiatively inefficient accretion flow (RIAF) surrounding a Kerr
black hole with arbitrary spins, inclination angles, and
observational wavelengths. For the same initial conditions, such as
the fixed accretion rate, it is found that the intrinsic size and
radiation intensity of the images become larger, but the images
become more compact in the inner region, while the size of the black
hole shadow decreases with the increase of the black hole spin. With
the increase of the inclination angles, the shapes of the black
hole shadows change and become smaller, even disappear at all due to
the obscuration by the thick disks. For median inclination angles,
the radial velocity observed at infinity is larger because of both
the rotation and radial motion of the fluid in the disk, which
results in the luminous part of the images is much brighter. For
larger inclination angles, such as the disk is edge on, the emission
becomes dimmer at longer observational wavelengths (such as at 7.0mm
and 3.5mm wavelengths), or brighter at shorter observational
wavelengths (such as at 1.3 mm wavelength) than that of the face on
case, except for the high spin and high inclination images.
These complex behaviors are due to the combination of the
Lorentz boosting effect and
the radiative absorption in the disk. We hope our results are
helpful to determine the spin parameter of the black hole in low
luminosity sources, such as the Galactic center. A primary
analysis by
comparison with the observed sizes of Sgr A* at millimeters strongly
suggests that the disk around the central black hole at Sgr A*
is  highly inclined or the central black hole is rotating fast.

\end{abstract}

\keywords{black hole physics -- Galaxy: center -- radiation
transfer -- sub-millimeter }

\end{document}