Integral field spectroscopy of the inner kpc of the elliptical galaxy NGC 5044

Abstract

We used Gemini Multi-Object Spectrograph in the integral field unit mode to map the stellar population, emission-line flux distributions and gas kinematics in the inner kpc of NGC 5044. From the stellar populations synthesis, we found that the continuum emission is dominated by old high metallicity stars (∼13 Gyr, 2.5 Z ). Also, its nuclear emission is diluted by a nonthermal emission, which we attribute to the presence of a weak active galactic nucleus (AGN). In addition, we report for the first time a broad component (FWHM ∼ 3000 km s−1) in the Hα emission line in the nuclear region of NGC 5044. By using emission-line ratio diagnostic diagrams, we found that two dominant ionization processes coexist, while the nuclear region (inner 200 pc) is ionized by a low-luminosity AGN, the filamentary structures are consistent with being excited by shocks. The Hα velocity field shows evidence of a rotating disc, which has a velocity amplitude of ∼240 km s−1 at ∼136 pc from the nucleus. Assuming a Keplerian approach, we estimated that the mass inside this radius is 1.9×109 M , which is in agreement with the value obtained through the M–σ relation, MSMBH = 1.8 ± 1.6 × 109M . Modelling the ionized gas velocity field by a rotating disc component plus inflows towards the nucleus along filamentary structures, we obtain a mass inflow rate of ∼0.4 M . This inflow rate is enough to power the central AGNs in NGC 5044.