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

Abstract

Intermediate mass black holes (10$^3$-10$^5$ M$_\\odot$) in the center of\ndwarf galaxies are believed to be analogous to growing Active Galactic Nuclei\n(AGN) in the early Universe. Their characterization can provide insight about\nthe early galaxies. We present optical and near-infrared integral field\nspectroscopy of the inner $\\sim$50 pc of the dwarf galaxy NGC4395, known to\nharbor an AGN. NGC 4395 is an ideal candidate to investigate the nature of\ndwarf AGN, as it is nearby ($d\\approx4.4$ Mpc) enough to allow a close look at\nits nucleus. The optical data were obtained with the Gemini GMOS-IFU covering\nthe 4500 A to 7300 A spectral range at a spatial resolution of 10 pc. The J and\nK-band spectra were obtained with the Gemini NIFS at spatial resolutions of\n$\\sim$5 pc. The gas kinematics show a compact, rotation disk component with a\nprojected velocity amplitude of 25 km s$^{-1}$. We estimate a mass of\n$7.7\\times10^5$ M$_\\odot$ inside a radius of 10 pc. From the H$\\alpha$ broad\nline component, we estimate the AGN bolometric luminosity as $L_{\nbol}=(9.9\\pm1.4)\\times10^{40}$ erg s$^{-1}$ and a mass $M_{\nBH}=(2.5^{+1.0}_{-0.8})\\times10^5$ M$_\\odot$ for the central black hole. The\nmean surface mass densities for the ionized and molecular gas are in the ranges\n(1-2) M$_{\\odot} $pc$^{-2}$ and (1-4)$\\times10^{-3}$ M${_\\odot}$ pc$^{-2}$ and\nthe average ratio between ionized and hot molecular gas masses is $\\sim$500.\nThe emission-line flux distributions reveal an elongated structure at 24 pc\nwest of the nucleus, which is blueshifted relative to the systemic velocity of\nthe galaxy by $\\approx$30 km s$^{-1}$. We speculate that this structure is\noriginated by the accretion of a gas-rich small satellite or by a low\nmetallicity cosmic cloud.\n