Extinction and AGN over host galaxy contrast effects on the optical spectroscopic classification of AGN
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2024
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| author | Barquín-González, L. Mateos, S. Carrera, F. J. Ordovás-Pascual, I. Alonso-Herrero, A. Caccianiga, A. Cardiel, N. Corral, A. Domínguez, R. M. García-Bernete, I. Mountrichas, G. Severgnini, P. |
| author_facet | Barquín-González, L. Mateos, S. Carrera, F. J. Ordovás-Pascual, I. Alonso-Herrero, A. Caccianiga, A. Cardiel, N. Corral, A. Domínguez, R. M. García-Bernete, I. Mountrichas, G. Severgnini, P. |
| contents | The optical spectroscopic classification of active galactic nuclei (AGN) into type 1 and type 2 can be understood in the frame of the AGN unification models. However, it remains unclear which physical properties are driving the classification into intermediate sub-types (1.0,1.2,1.5,1.8,1.9). To shed light on this issue, we present an analysis of the effect of extinction and AGN and host galaxy luminosities on sub-type determination for a sample of 159 X-ray selected AGN with a complete and robust optical spectroscopic classification. The sample spans a rest-frame 2 - 10 keV X-ray luminosity range of $10^{42}-10^{46}$ erg s$^{-1}$ and redshifts between 0.05 and 0.75. From the fitting of their UV-to-mid-infrared spectral energy distributions, we extracted the observed AGN over total AGN+galaxy contrast, optical/UV line-of-sight extinction as well as host galaxy and AGN luminosities. The observed contrast exhibits a clear decline with sub-type, distinguishing two main groups: 1.0-5 and 1.8-9/2. This difference is partly driven by an increase in extinction following the same trend. Nevertheless, 50% of 1.9s and 2s lack sufficient extinction to explain the lack of detection of broad emission lines, unveiling the necessity of an additional effect. Our findings show that 1.8-9/2s preferentially live 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 emission of the broad emission lines, resulting in the 1.8-9/2 classification of those with insufficient extinction. Thus, the combination of increasing extinction and decreasing AGN/galaxy luminosity ratio, mainly driven by an increasing host galaxy luminosity, constitutes the main reasons behind the sub-type classification into 1.0-5 and 1.8-9/2. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2404_19544 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Extinction and AGN over host galaxy contrast effects on the optical spectroscopic classification of AGN Barquín-González, L. Mateos, S. Carrera, F. J. Ordovás-Pascual, I. Alonso-Herrero, A. Caccianiga, A. Cardiel, N. Corral, A. Domínguez, R. M. García-Bernete, I. Mountrichas, G. Severgnini, P. Astrophysics of Galaxies The optical spectroscopic classification of active galactic nuclei (AGN) into type 1 and type 2 can be understood in the frame of the AGN unification models. However, it remains unclear which physical properties are driving the classification into intermediate sub-types (1.0,1.2,1.5,1.8,1.9). To shed light on this issue, we present an analysis of the effect of extinction and AGN and host galaxy luminosities on sub-type determination for a sample of 159 X-ray selected AGN with a complete and robust optical spectroscopic classification. The sample spans a rest-frame 2 - 10 keV X-ray luminosity range of $10^{42}-10^{46}$ erg s$^{-1}$ and redshifts between 0.05 and 0.75. From the fitting of their UV-to-mid-infrared spectral energy distributions, we extracted the observed AGN over total AGN+galaxy contrast, optical/UV line-of-sight extinction as well as host galaxy and AGN luminosities. The observed contrast exhibits a clear decline with sub-type, distinguishing two main groups: 1.0-5 and 1.8-9/2. This difference is partly driven by an increase in extinction following the same trend. Nevertheless, 50% of 1.9s and 2s lack sufficient extinction to explain the lack of detection of broad emission lines, unveiling the necessity of an additional effect. Our findings show that 1.8-9/2s preferentially live 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 emission of the broad emission lines, resulting in the 1.8-9/2 classification of those with insufficient extinction. Thus, the combination of increasing extinction and decreasing AGN/galaxy luminosity ratio, mainly driven by an increasing host galaxy luminosity, constitutes the main reasons behind the sub-type classification into 1.0-5 and 1.8-9/2. |
| title | Extinction and AGN over host galaxy contrast effects on the optical spectroscopic classification of AGN |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2404.19544 |