Influencia de las propiedades de los núcleos galácticos activos en su clasificación óptica
- Autores: Lorenzo Barquín González
- Directores de la Tesis: Silvia Mateos Ibáñez (dir. tes.)
, Francisco Jesús Carrera Troyano (codir. tes.) - Lectura: En la Universidad de Cantabria ( España ) en 2024
- Idioma: español
- Títulos paralelos:
- Influence of active galactic nuclei properties on their optical classification
- Tribunal Calificador de la Tesis: José Ignacio González Serrano (presid.) , Silvia Bonoli (secret.) , Almudena Alonso Herrero (voc.)
- Enlaces
- Resumen
- español
El Modelo Unificado de los núcleos galácticos activos (AGNs) no proporciona una explicación clara sobre que propiedades son causantes del origen de los subtipos 1.0, 1.2, 1.5, 1.8 y 1.9. Para arrojar luz sobre esta cuestión, se ha utilizado una muestra de 165 AGNs con observaciones fotométricas y espectroscópicas desde el ultravioleta hasta el infrarrojo. Se ha estudiado el efecto del contraste, la extinción y las luminosidades del AGN, de la galaxia anfitriona y de las líneas de emisión en la determinación del subtipo. Se ha encontrado que los subtipos 1.8, 1.9 y 2 se clasifican como tales debido a menores contrastes observados, por un efecto combinado de extinción y aumento de la luminosidad de la galaxia huésped. La subclasificación en 1.0, 1.2 y 1.5 es consecuencia del aumento de la luminosidad relative de la línea de emisión [OIII]5007Å respecto a la del AGN. Se concluye, por tanto, que la luminosidad de la galaxia y la luminosidad relativa de [OIII]5007Å deben ser incluidas en el Modelo Unificado para proporcionar una explicación satisfactoria al origen de los subtipos ópticos.
- español
Active Galactic Nuclei (AGN) are the most luminous persistent phenomena in the observable Universe, emitting vast amounts of radiation all over the electromagnetic spectrum. AGN are fuelled by the accretion onto supermassive black holes (SMBHs) with masses 10^6 solar masses, which nowadays are believed to be in the centre of every massive galaxy. AGN have become a fundamental piece to understanding the formation and evolution of galaxies, as the properties of their SMBHs are tightly correlated with those of their host galaxies.
The most accepted explanation for the perceived diversity of AGN is the Unification Model. Among other achievements, it successfully explains the differences in the optical spectra between certain AGN and the associated classification into type 1, characterised by the detection of broad (FWHM> 1000 km/s) and narrow (FWHM < 1000 km/s) emission lines, and type 2, distinguished by the detection of solely the latter. In this model, a toroidal structure of gas and dust, known as the torus, would block certain emission lines, hampering the observation of the nuclear region, while others would be unaffected. However, the Unification Model does not provide a satisfactory answer on which physical properties are driving the subclassification of type 1 into subtypes 1.0, 1.2, 1.5, 1.8, and 1.9, based on the flux ratio of [OIII]5007Å and the broad component of Hb.
To achieve it, we drew our working sample from the Bright Ultra-hard XMM-Newton Survey (BUXS), an AGN sample composed of 258 X-ray bright (with fluxes greater than 6 x 10e14 erg s^-1 cm^2 at higher energies than 4 keV) sources detected with XMM-Newton. Using a combination of photometry information ranging from ultraviolet to mid-infrared and X-ray, optical, and near-infrared (NIR) spectra, we were able to construct a multi-wavelength sample composed of 159 AGN with complete, robust and uniform (based on the same set of emission lines for all objects) optical spectroscopic classification. The sample spans a rest frame 2 ß 10 keV X-ray luminosity range of 10^42 10^46 erg/s and redshifts between 0.05 and 0.75, a higher boundary than previous similar studies.
Using the photometry information collected, we built the spectral energy distributions (SED) of our sources. We decomposed the SEDs into a combination of host galaxy and AGN, with the latter including the accretion disk and torus emission components. To carry out the fits, we used the tool SEd Analysis using BAyesian Statistics (SEABASs). From these fits, we obtained the observed AGN over total (AGN plus galaxy) contrast, the total optical/ultraviolet line-of-sight extinction, and the host galaxy and AGN intrinsic luminosities.
At the same time, we fitted the optical and NIR spectra of our sources. We developed an original code capable of fitting a progressively more complex model composed of several AGN/galaxy continuum and narrow and broad emission line components. The code allowed us to reliably determine the significance of the detection of the broad emission lines while avoiding overfitting. We obtained the emission line properties, like flux and width, and a robust intermediate classification.
We first studied the effect of observed contrast and contrast-related properties on the subtype determination. The contrast exhibits a clear decline with subtype, distinguishing two main groups: one composed of 1.0s, 1.2s, and 1.5s (1.0-5s) and the other of 1.8s, 1.9s y 2s (1.8-9/2s). This difference is partly driven by an increase in extinction following the same trend. For AGNs with low extinction (E(B - V ) < 0.65), we find that most, if not all, of the detected extinction can be associated with material in the host galaxy. For the rest, the extinction must have a significant contribution from material at circumnuclear scales.
Fifty percent of 1.9s and 2s lack sufficient extinction to explain the non-detection of detection of broad emission lines, unveiling the necessity of an additional effect. Our findings show that 1.8-9/2s preferentially reside in host galaxies with higher luminosities while displaying similar intrinsic AGN luminosities to 1.0-5s. Consequently, the AGN to host galaxy luminosity ratio diminishes, hindering the detection of the broad emission lines.
However, these results do not explain the origin of the intermediate subtypes from 1.0 to 1.5. To understand them, we studied the effect of the broad and narrow emission line relative luminosity on the subtype determination, using broad Hb and Ha and [OIII]5007Å. We found no differences in the intrinsic intensity of the broad component of Hb between 1.0, 1.2 and 1.5 subtypes. Similar results were found when we considered instead the broad component of Ha. We estimated the intensity of the broad component of Hb from the Ha observation for 1.9s with low extinction to account for the weakest broad Hb lines, which could have avoided detection. With these estimations, we reclassified them as 1.0/1.2/1.5/1.8. Even when these objects are included, we still did not find any significant difference between 1.0s, 1.2s and 1.5s. However, we found that the relative intensity of Hb might be lower in 1.8s than in 1.0-5s.
We found a clear decrease of the narrow emission line relative luminosity with increasing subtype for 1.0s, 1.2s and 1.5s, as traced by [OIII]5007Å. We also detected a decrease of the relative luminosity of [OIII]5007Å with the AGN luminosity, but not as strong as the former. We found that the trend with subtype is unlikely to be related to changes in the extinction suffered by the narrow emission lines, contamination from the host galaxy or variability. Our results suggest that it is most probably related to an increase in the covering factor of the narrow-line emitting region (NLR) with increasing subtype.
To sum up, this thesis showed that the intermediate classification of the AGN has a complex origin, and not a single parameter can explain the subtype differences. Therefore, we conclude that, on the one hand, the subtype classification into 1.0-5 and 1.8-9/2 is mainly driven by the combination of increasing extinction and decreasing AGN/galaxy luminosity ratio, primarily due to the rising luminosity of the host galaxy. At the same time, on the other hand, there is an increase in the relative luminosity of the narrow emission lines, particularly [OIII]5007Å, which is responsible for the subtype classification between 1.0, 1.2 and 1.5. These findings imply the need for the inclusion of additional parameters in the Unification Model to explain the observations, particularly the luminosity of the host galaxy and the properties of the NLR.
Future work would seek to expand the results presented here by studying the impact of the SMBH mass and the Eddington ratio on classification. For this purpose, the mass of the SMBH could be derived from its relation with the broad line properties for the 1.0-9s and with the stellar mass of the galaxy for the 2s. Additionally, direct measurements of the NLR properties (ionisation parameter, electron density and coverage factor) would be obtained by comparing the measured equivalent width of the [OIII]4363Å, [OIII]5007Å and the narrow Hb emission lines with theoretical models.
- español
