The Eddington ratio-dependent ‘changing look’ events in NGC 2992

We present an analysis of historical multiwavelength emission of the `Changing Look’ (CL) Active Galactic Nucleu (AGN) in NGC 2992, covering epochs ranging from 1978 to 2021, as well as new X-ray and optical spectra. The galaxy presents multiple Seyfert type transitions from Type 2 to intermediate-type, losing and regaining its Hα broad emission lines (BEL) recurrently. In X-rays, the source shows intrinsic variability with the absorption corrected luminosity varying by a factor of ∼ 40. We rule-out tidal disruption events or variable obscuration as causes of the type transitions, and show that the presence and the flux of th Hα BEL is directly correlated with the 2–10 keV X-ray luminosity (L2−10): the component disappears at L2−10 ≤ 2.6 × 1042 erg cm−2 s−1; this luminosity value translates into an Eddington ratio (λEdd) of ∼ 1 per cent. The λEdd in which the BEL transitions occur is the same as the critical value at which a state transition between a radiatively inefficient accretion flow and a thin accretion disk is expected, such similarity suggests that the AGN is operating at the threshold mass accretion rate between the two accretion modes. We find a correlation between the narrow Fe Kα flux and λEdd, and an anticorrelation between full-width at half maximum of Hα BEL and λEdd, in agreement with theoretical predictions. Two possible scenarios for type transitions are compatible with our results: either the dimming of the AGN continuum, which reduces the supply of ionizing photons available to excite the gas in the Broad Line Region (BLR), or the fading of the BLR structure itself occurs as the low accretion rate is not able to sustain the required cloud flow rate in a disc-wind BLR model

Exploring the AGN-Merger Connection in Arp 245 I: Nuclear Star Formation and Gas Outflow in NGC 2992

Galaxy mergers are central to our understanding of galaxy formation, especially within the context of hierarchical models. Besides having a large impact on the star formation history, mergers are also able to influence gas motions at the centre of galaxies and trigger an Active Galactic Nucleus (AGN). In this paper, we present a case study of the Seyfert galaxy NGC 2992, which together with NGC 2993 forms the early-stage merger system Arp 245. Using Gemini Multi-Object Spectrograph (GMOS) integral field unit (IFU) data from the inner 1.1 kpc of the galaxy we were able to spatially resolve the stellar populations, the ionisation mechanism and kinematics of ionised gas. From full spectral synthesis, we found that the stellar population is primarily composed by old metal-rich stars (t $\geq$ 1.4 Gyr, $Z \geq 2.0$\zsun), with a contribution of at most 30 per cent of the light from a young and metal-poor population (t $\leq$ 100 Myr, $Z \leq 1.0$\zsun). We detect \halpha and \hbeta emission from the Broad Line Region (BLR) with a Full Width at Half Maximum (FWHM) of $\sim$ 2000\kms. The Narrow Line Region (NLR) kinematics presents two main components: one from gas orbiting the galaxy disk and a blueshifted (velocity $\approx$ -200\kms) outflow, possibly correlated with the radio emission, with mass outflow rate of $\sim$ 2 M$_{\odot}$ yr$^{-1}$ and a kinematic power of $\sim$ 2 $\times 10^{40}$ erg s$^{-1}$ (\Eout/\Lbol $\approx$ 0.2 per cent). We also show even though the main ionisation mechanism is the AGN radiation, ionisation by young stars and shocks may also contribute to the emission line ratios presented in the innermost region of the galaxy.Comment: 20 pages, 13 Figs, Accepted for publication to the MNRA

Exploring the AGN-merger connection in Arp 245 : I: nuclear star formation and gas outflow in NGC 2992

Galaxy mergers are central to our understanding of galaxy formation, especially within the context of hierarchical models. Besides having a large impact on the star formation history, mergers are also able to influence gas motions at the centre of galaxies and trigger an active galactic nucleus (AGN). In this paper, we present a case study of the Seyfert galaxy NGC 2992, which together with NGC 2993 forms the early-stage merger system Arp 245. Using Gemini Multi-Object Spectrograph integral field unit data from the inner 1.1 kpc of the galaxy, we were able to spatially resolve the stellar populations, the ionization mechanism, and kinematics of ionized gas. From full spectral synthesis, we found that the stellar population is primarily composed by old metal-rich stars (t ≥ 1.4 Gyr, Z ≥ 2.0 Z⊙), with a contribution of at most 30 per cent of the light from a young and metal-poor population (t ≤ 100 Myr, Z ≤ 1.0 Z⊙). We detect H α and H β emission from the broad-line region with a full width at half-maximum of ∼2000 kms−1⁠. The narrow-line region kinematics presents two main components: one from gas orbiting the galaxy disc and a blueshifted (velocity ≈ −200 kms−1⁠) outflow, possibly correlated with the radio emission, with mass outflow rate of ∼2 M⊙ yr−1 and a kinematic power of ∼2 × 1040 erg s−1 (⁠E˙out/Lbol ≈ 0.2 per cent). We also show even though the main ionization mechanism is the AGN radiation, ionization by young stars and shocks may also contribute to the emission line ratios presented in the innermost region of the galaxy

The circumnuclear region and long-term variability of the active nucleus in NGC 2992

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas, Programa de Pós-Graduação em Física, Florianópolis, 2021.Núcleos Galácticos Ativos (AGN) são regiões compactas no centro de galáxias capazes de gerar grandes quantidades de energia, de tal forma que não podem ser explicadas por fusão termonuclear pelas estrelas da galáxia, mas sim por acreção de matéria por um buraco negro supermassivo. Além de serem laboratórios para o estudo de física em condições extremas, acredita-se que AGNs são fundamentais para o entendimento da evolução das galáxias. Nesta dissertação apresentamos uma análise espacial e temporal do AGN presente na galáxia Seyfert em interação NGC 2992 usando observações em diferentes comprimentos de onda. Primeiramente, utilizando dados de Espectroscopia de Campo Integral do Telescópio Gemini, fomos capazes de resolver espacialmente as populações estelares, os mecanismos de ionização e a cinemática do gás ionizado. Utilizando síntese de populações estelares, nós mostramos que a população estelar é principalmente composta por estrelas velhas e ricas em metais, mas também por uma fração considerável, de até 30% da luz, por estrelas jovens e pobres em metais. A cinemática da Região de Linhas Estreitas (NLR) apresenta duas principais componentes: uma do gás orbitando o disco da galáxia e outra por uma ejeção (outflow) de gás, relacionada à emissão em rádio. Mostramos que apesar de a ionização pelo AGN ser o principal dos mecanismos, ionização por estrelas jovens e por choques também contribuem para as razões de linhas encontradas. Depois, apresentamos uma análise do histórico do espectro de emissão da galáxia em raios-X e no óptico. Mostramos que ela apresenta várias transições em sua classificação Seyfert, do tipo 2 para tipos intermediários, perdendo e readquirindo sua Linha de Emissão Larga (BEL) em Ha diversas vezes, portanto classificando-o como um ?Changing Look? AGN. Em raios-X, a fonte apresenta grande variabilidade com sua luminosidade corrigida por absorção variando por um fator de ~ 35. Mostramos que a presença (e o fluxo) da BEL em Ha está diretamente correlacionada com a taxa de acreção: com um valor mínimo 2.0% na razão de Eddington sendo necessário para a detecção da componente larga. Dois cenários são possíveis para explicar as transições de clasificação: o aumento (diminuição) da luminosidade do contínuo do AGN, que aumenta (diminui) a quantidade de fótons disponíveis para excitar o gás na Região de Linhas Largas (BLR), ou o desaparecimento da estrutura da BEL em si ocorre quando a baixa taxa de acreção não é capaz de suportar a taxa de fluxo de nuvens necessária. Este trabalho evidencia o papel das galáxias próximas no estudo dos fenômenos AGNs, nos quais as estruturas da escala parsec podem ser resolvidas e observações públicas em múltiplos comprimentos de onda e épocas estão disponíveis.Abstract: Active Galactic Nuclei (AGN) are compact regions at the center of galaxies that can generate large amounts of energy, such that it can not be explained by thermonuclear fusion in stars, but instead by accretion of matter onto a supermassive black hole (SMBH). Besides being a laboratory to study Physics in extreme conditions, AGNs are also believed to be fundamental for understanding galaxies? evolution. This dissertation presents a multi-wavelength spatial and temporal analysis of the AGN in the interacting Seyfert galaxy NGC 2992. First, using data taken with Gemini Multi-Object Spectrographs (GMOS), with the Integral Field Unit mode, from the inner 1.1 kiloparsecs of the galaxy, we were able to spatially resolve the stellar populations, the ionization mechanism, and kinematics of ionized gas. From full spectral synthesis, we found that the stellar population is primarily composed of old metal-rich stars with a smaller, but considerable, contributing of up to 30% of the light, from young and metal-poor populations. The Narrow Line Region kinematics presents two main components: one from gas orbiting the galaxy disk and another from a blueshifted outflow, correlated with the radio emission. We show that even though the primary ionization mechanism is the AGN radiation, ionization by young stars and shocks may also contribute to the emission line ratios found. Later, we present an analysis of the historical X-rays and optical spectra of the galaxy. We show that the nucleus of the galaxy presents multiple Seyfert type transitions from type 2 to intermediate-type, losing and regaining its Ha Broad Emission Line (BEL) recurrently, hence being a ?Changing Look? AGN. In X-rays, the source shows large intrinsic variability with the absorption corrected 2-10 keV luminosity varying by a factor of ~ 35. We show that the presence (and flux) of the Ha BEL is directly correlated with the accretion rate: a minimum Eddington ratio value of 2.0+2.0 ?1.3% is necessary for the broad line detection. Two possible scenarios for type transitions are still open: either there is a dimming (brightening) of the AGN continuum luminosity, which reduces (increases) the supply of ionizing photons available to excite the gas in the Broad Line Region (BLR), or the disappearance of the BLR structure itself occurs as the low accretion efficiency is not able to sustain the required cloud flow rate. This work evidences the role of the nearby galaxies in the study of the AGN phenomena, in which the parsec scale structures can be resolved and public multi-wavelength and multi-epoch observations are available