Multiwavelength study of active galaxies a thesis submitted for the award of degree of doctor of philosophy in The Faculty of Science, University of Calicut, Calicut, Kerala
Singh, Veeresh
Multiwavelength study of active galaxies a thesis submitted for the award of degree of doctor of philosophy in The Faculty of Science, University of Calicut, Calicut, Kerala [Ph.D Thesis] Veeresh Singh - Bangalore Indian Institute of Astrophysics 2010 - xxxi, 251p.
Thesis Supervisor Prof. Prajval Shastri
Seyfert galaxies are categorized as nearby, low luminosity (MB _ -23), radio-quiet ( F5 GHz FB-band < 10) Active Galactic Nuclei (AGN) hosted in spiral or lenticular galaxies. Demographically, Seyfert galaxies may account for _ 10% of the entire population of active galaxies in the nearby universe. Seyfert galaxies are classi_ed mainly into two subclasses named as `type 1' and `type 2' Seyfert galaxies, based on the presence and absence of broad permitted emission lines in their optical spectra, respectively. Spectropolarimetric observations of Seyfert type 2s laid the foundation of the Seyfert uni_cation scheme, which hypothesizes that Seyfert type 1s and type 2s belong to the same parent population and appear di_erent solely due to the di_ering orientations of the obscuring material having a torus-like geometry around the AGN (Antonucci and Miller 1985; Antonucci 1993). The primary objective of this thesis work is to examine the validity and limitations of the orientation and obscuration based Seyfert uni_cation scheme using multiwavelength (mainly X-ray and radio) observations. The key issue in testing the Seyfert uni_cation scheme is acquiring a rigorously selected Seyfert sample
such that the two Seyfert subtypes are intrinsically similar within the framework of the uni_cation scheme. I study two samples of Seyfert galaxies which are rigorously
selected on the basis of the orientation-independent properties of AGN as well as the host galaxy. In our sample we ensure the intrinsic similarity of the two subtypes in cosmological redshift, [OIII] _5007_A emission line luminosity, absolute bulge magnitude, absolute stellar magnitude of the host galaxy and the Hubble stage of the host galaxy. Our sample selection criteria also mitigates the biases
generally inherent in most of the Seyfert samples derived from ux limited surveys at different wavelengths. The obscuring material supposedly having a torus-like geometry is optically thick for optical, UV and soft X-ray wavelengths. However, X-ray and radio studies are advantageous since X-ray spectral analysis enables to estimate the absorbing column density and radio emission is optically thin to the obscuring torus. I study the X-ray and radio properties of the Seyfert galaxies of our samples to test the predictions of the Seyfert uni_cation scheme. To derive the X-ray spectral properties I model the XMM-Newton pn X-ray spectra of our sample Seyfert galaxies. I perform statistical comparison of the X-ray spectral properties (i:e:; X-ray luminosities, absorbing column densities, hard X-ray spectral shapes, equivalent widths of Fe K_ line, soft excess, reection components etc.) of the two Seyfert subtypes in the framework of uni_cation. I also attempt to unveil the nature of obscuring material around a Compton-thick Seyfert galaxy NGC 5135 using Suzaku broadband X-ray spectral analysis. The correlations of the nuclear hard X-ray luminosity to the pc-scale and kpc-scale radio luminosities are also investigated for the two Seyfert subtypes. To test the predictions of the Seyfert uni_cation in the radio regime, I study the radio properties of Seyfert galaxies using Giant Meterwave Radio Telescope (GMRT) observations carried out at 240 MHz and 610 MHz, and NRAO VLA Sky Survey observations at 1.4 GHz and VLA 5 GHz observations from the literature. The radio luminosities and spectra are found to be similar for the Seyfert type 1s and type 2s. I also investigated radio - IR luminosity correlations and _nd that for both the Seyfert subtypes, the total 610 MHz and 240 MHz radio luminositie are moderately correlated with near-IR, mid-IR luminosities while the correlation becomes poorer with far-IR luminosities. Furthermore, the 12 _m, 25 _m, 60 _m and 100 _m IR luminosity distributions are not statistically different for the
Seyfert type 1s and type 2s. I conclude that the X-ray, radio and IR properties of the Seyfert galaxies of our rigorously selected samples are consistent with the unification scheme.
Active galaxies-Theses
Multiwavelength study-Theses
X-ray-Theses
(043.2)524.6 / SIN
Multiwavelength study of active galaxies a thesis submitted for the award of degree of doctor of philosophy in The Faculty of Science, University of Calicut, Calicut, Kerala [Ph.D Thesis] Veeresh Singh - Bangalore Indian Institute of Astrophysics 2010 - xxxi, 251p.
Thesis Supervisor Prof. Prajval Shastri
Seyfert galaxies are categorized as nearby, low luminosity (MB _ -23), radio-quiet ( F5 GHz FB-band < 10) Active Galactic Nuclei (AGN) hosted in spiral or lenticular galaxies. Demographically, Seyfert galaxies may account for _ 10% of the entire population of active galaxies in the nearby universe. Seyfert galaxies are classi_ed mainly into two subclasses named as `type 1' and `type 2' Seyfert galaxies, based on the presence and absence of broad permitted emission lines in their optical spectra, respectively. Spectropolarimetric observations of Seyfert type 2s laid the foundation of the Seyfert uni_cation scheme, which hypothesizes that Seyfert type 1s and type 2s belong to the same parent population and appear di_erent solely due to the di_ering orientations of the obscuring material having a torus-like geometry around the AGN (Antonucci and Miller 1985; Antonucci 1993). The primary objective of this thesis work is to examine the validity and limitations of the orientation and obscuration based Seyfert uni_cation scheme using multiwavelength (mainly X-ray and radio) observations. The key issue in testing the Seyfert uni_cation scheme is acquiring a rigorously selected Seyfert sample
such that the two Seyfert subtypes are intrinsically similar within the framework of the uni_cation scheme. I study two samples of Seyfert galaxies which are rigorously
selected on the basis of the orientation-independent properties of AGN as well as the host galaxy. In our sample we ensure the intrinsic similarity of the two subtypes in cosmological redshift, [OIII] _5007_A emission line luminosity, absolute bulge magnitude, absolute stellar magnitude of the host galaxy and the Hubble stage of the host galaxy. Our sample selection criteria also mitigates the biases
generally inherent in most of the Seyfert samples derived from ux limited surveys at different wavelengths. The obscuring material supposedly having a torus-like geometry is optically thick for optical, UV and soft X-ray wavelengths. However, X-ray and radio studies are advantageous since X-ray spectral analysis enables to estimate the absorbing column density and radio emission is optically thin to the obscuring torus. I study the X-ray and radio properties of the Seyfert galaxies of our samples to test the predictions of the Seyfert uni_cation scheme. To derive the X-ray spectral properties I model the XMM-Newton pn X-ray spectra of our sample Seyfert galaxies. I perform statistical comparison of the X-ray spectral properties (i:e:; X-ray luminosities, absorbing column densities, hard X-ray spectral shapes, equivalent widths of Fe K_ line, soft excess, reection components etc.) of the two Seyfert subtypes in the framework of uni_cation. I also attempt to unveil the nature of obscuring material around a Compton-thick Seyfert galaxy NGC 5135 using Suzaku broadband X-ray spectral analysis. The correlations of the nuclear hard X-ray luminosity to the pc-scale and kpc-scale radio luminosities are also investigated for the two Seyfert subtypes. To test the predictions of the Seyfert uni_cation in the radio regime, I study the radio properties of Seyfert galaxies using Giant Meterwave Radio Telescope (GMRT) observations carried out at 240 MHz and 610 MHz, and NRAO VLA Sky Survey observations at 1.4 GHz and VLA 5 GHz observations from the literature. The radio luminosities and spectra are found to be similar for the Seyfert type 1s and type 2s. I also investigated radio - IR luminosity correlations and _nd that for both the Seyfert subtypes, the total 610 MHz and 240 MHz radio luminositie are moderately correlated with near-IR, mid-IR luminosities while the correlation becomes poorer with far-IR luminosities. Furthermore, the 12 _m, 25 _m, 60 _m and 100 _m IR luminosity distributions are not statistically different for the
Seyfert type 1s and type 2s. I conclude that the X-ray, radio and IR properties of the Seyfert galaxies of our rigorously selected samples are consistent with the unification scheme.
Active galaxies-Theses
Multiwavelength study-Theses
X-ray-Theses
(043.2)524.6 / SIN