Formação estelar e emissão de poeira em núcleos ativos de galáxias

Abstract

The energy coming from Active Nuclei of Galaxies (AGN) is attributed to the process of accretion of matter to a central Supermassive Black Hole (SMBH). The gases that flow towards the center of the galaxies (inflows of gas) can give rise to AGN but may also represent the accumulation of matter in the central region necessary to trigger star formation on scales of hundreds of parsecs. This work presents a study on the circumnuclear star formation for the Seyfert 1 Mrk 42 galaxy and a characterization of the dust emission in the nucleus of a sample of 15 Seyfert galaxies, in this way, relates intrinsic processes of AGN with properties of star formation regions. We use near-infrared spectroscopy data (J, H and K-band), obtained with the Near Infrared Integral Field Spectrograph (NIFS) installed on the Gemini North telescope. The Mrk 42 galaxy shows a ring of star-forming regions around the nucleus with a radius of ≈300 pc, clearly observed in the flux distributions of the infrared emission lines. Two main scenarios were proposed for the star formation rings in galaxies: the pop corn scenario, where material arriving in the central region is accumulated in the ring and forms stellar clusters at random positions without a sequence of ages and the pearls on the string scenario, for which the gas accumulates in the ring forming regions of high densities and there is movement of the star formation along the ring, observing a sequence of ages for the formed regions. Based on measurements for the equivalent width of Br we found evidence of age gradients for the star formation regions along the ring of Mrk 42, favoring the pearls on a string scenario. The full width at half maximum (FWHM) of the broad component of the Pa emission line measured in the nuclear spectrum is ∼1 480 kms−1, implying a mass of ≈ 2, 5 × 106 M⊙ for the central SMBH. Based on the ratios of emission lines we conclude that besides the active galactic nucleus, Mrk 42 has stellar formation activity in the nucleus. The kinematics of the gas are dominated by rotation in the plane of the galaxy, being well reproduced by a rotating disk model. However, for the central region (internal to the ring) we observe an additional component, probably originated by outflows of the AGN. In order to study the emission of nuclear dust from Seyferts galaxies, we fitted the nuclear continuum to 15 Seyferts galaxies from observations in the J and K bands. From the fits we obtain the contribution due to the components of law of power and black body function, attributed to the emission of accretion disk and the toroid of dust, respectively. We obtained values for the temperature ranging from 800 to 1 350 K and we derive masses of hot dust between 3,19×10−4 to 5,38×10−1 M⊙. There is a small tendency to have a larger number of Seyfert 1 galaxies with higher values for the hot dust than in Seyfert 2 galaxies. A correlation between the AGN bolometric luminosity and the hot dust mass, indicating that the AGN is responsible for heating the dust. The sample used to study the emission of dust is small and should be complemented in future works, as well as a better comparison with results of the literature is necessary.