A close look at the dwarf AGN of NGC 4395: optical and near-IR integral field spectroscopy

Kavli Affiliate: Luis Ho

| First 5 Authors: Carine Brum, Marlon R. Diniz, Rogemar A. Riffel, Alberto Rodriguez-Ardila, Luis Ho

| Summary:

Intermediate mass black holes (10$^3$-10$^5$ M$_odot$) in the center of
dwarf galaxies are believed to be analogous to growing Active Galactic Nuclei
(AGN) in the early Universe. Their characterization can provide insight about
the early galaxies. We present optical and near-infrared integral field
spectroscopy of the inner $sim$50 pc of the dwarf galaxy NGC4395, known to
harbor an AGN. NGC 4395 is an ideal candidate to investigate the nature of
dwarf AGN, as it is nearby ($dapprox4.4$ Mpc) enough to allow a close look at
its nucleus. The optical data were obtained with the Gemini GMOS-IFU covering
the 4500 A to 7300 A spectral range at a spatial resolution of 10 pc. The J and
K-band spectra were obtained with the Gemini NIFS at spatial resolutions of
$sim$5 pc. The gas kinematics show a compact, rotation disk component with a
projected velocity amplitude of 25 km s$^{-1}$. We estimate a mass of
$7.7times10^5$ M$_odot$ inside a radius of 10 pc. From the H$alpha$ broad
line component, we estimate the AGN bolometric luminosity as $L_{
bol}=(9.9pm1.4)times10^{40}$ erg s$^{-1}$ and a mass $M_{
BH}=(2.5^{+1.0}_{-0.8})times10^5$ M$_odot$ for the central black hole. The
mean surface mass densities for the ionized and molecular gas are in the ranges
(1-2) M$_{odot} $pc$^{-2}$ and (1-4)$times10^{-3}$ M${_odot}$ pc$^{-2}$ and
the average ratio between ionized and hot molecular gas masses is $sim$500.
The emission-line flux distributions reveal an elongated structure at 24 pc
west of the nucleus, which is blueshifted relative to the systemic velocity of
the galaxy by $approx$30 km s$^{-1}$. We speculate that this structure is
originated by the accretion of a gas-rich small satellite or by a low
metallicity cosmic cloud.

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