UV emission line studies of NGC-low redshift Seyfert Galaxies, LINERS and HII regions
Keywords:Active Galaxies, Emission Lines, Low Redshift and Seyfert Galaxies
Active galaxies as a special class of galaxies are characterized by very strong and broad emission lines. The strong emission lines such as Lyα, NV, Si IV, C IV, and Mg II observed in the UV spectra of Seyfert galaxies and quasars can be used to probe the physical conditions of the gas in the BLR regions surrounding the central accretion discs of these most luminous and exotic objects. In the standard model of broad line emission regions for active galaxies it is assumed that the broad permitted lines are emitted by the photo-ionization of a large number of spherically distributed optically thick clouds which are in Keplerian motion surrounding a central continuum source. However, issues related to variability time-scales, delays in the light curves and BLR sizes etc., remain unexplained consistent with observations. In this paper, a study of emission line properties 9 objects satisfying good SNR (> 5.0) out of 98 NGC (catalogued) IUE observed low redshift active galaxies (z ≤ 0.017) is presented. The International Ultraviolet Explorer (IUE) satellite launched in 1978 by NASA has made low redshift UV spectroscopic observations of many different kinds of UV sources including active galaxies till 1996 and the flux calibrated spectral data of almost all observations have been hosted in NED-IUE database. In the present studies, IUE spectral data of a complete sample of NGC-catalogued active galaxies has been undertaken to understand the emission line properties of low luminosity and low z active galaxies. We find that the emission lines such as Lyα, N V, Si IV, O III], C III], C IV, and Mg II are observed as strong and broad lines in the spectra of only 9 objects owing to the criterion of S/N ≥ 5.0 adopted for the spectral analysis. The Lyα has not been found to be a strong line unlike in high z Seyfert galaxies and quasars observed by IUE satellite. C IV and Mg II lines are observed to be stronger lines in all the nine objects consistent with their usual presence in the remaining (~ 400) active galaxies observed by the IUE satellite. These observations are indicative of different physical and geometrical conditions in the BLR regions surrounding the central accretion disk compared to the intermediate and high redshift Seyfert galaxies and quasars.
observations of short-time scale variability in NGC 4151. IV. Analysis of multiwavelength continuum variability”, Astrophysical Journal, vol. 470, p. 364, 1996.
. P. Marziani, J. W. Sulentic, C. A. Negrette, et al., “UV spectral diagnostics for low redshift quasars: estimating physical conditions and radius of the broad line region,” Astro-ph.GA, arXiv:1410.3146v1, p. 1, October 2014.
. Martin J Rees, “Black hole model for active galactic nuclei“, Annual Review of Astronomy & Astrophysics, vol. 22, p. 471, 1984.
. J. A. Baldwin, “Luminosity Indicators in the spectra of Quasi-stellar objects“, Astrophysical Journal, vol. 214, p. 679, 1977.
. O. Smith, “Discovery and spectrophotometry of the Quasars in the 40 degree zone of the
CT10 Curtis-Schmidth Survey,” Astrophysical Journal Supplementary Series, vol. 42, p. 333, 1982.
. C. C. Wu, A. Boggess and T. R. Gull, “Prominent UV emission lines from type 1 Seyfert galaxies,” Astrophysical Journal, vol. 266, p. 28, 1983.
. G. A. Shields, “ I: Theory of active galactic Nuclei“, Publications of Astronomical Society of Pacific, vol. 98, p. 130, 1986.
. M. A. Malkan and W. L. W. Sargent, “The ultraviolet excess of Seyfert 1 galaxies and quasars“, Astrophysical Journal, vol. 254, p. 22, 1982.
. A. Boggess et al. “The IUE spacecraft and Instrumentation: In-flight performance of the
IUE,” Nature, vol. 275, p. 372, 1978.
. A. Robert, “Unified models for active galactic nuclei and quasars,” Annual Review of Astronomy and Astrophysics, vol. 31, p. 473, 1993.
. R. Walter et al. “Simultaneous observations of Seyfert 1 galaxies with IUE, ROSAT
and Ginga,” Astronomy & Astrophysics, vol. 285, p. 119, 1994.
. K. Davidson, “On photoionization analyses of emission spectra of quasars,” Astrophysical Journal, vol. 218, p. 20, 1977.
. K. Davidson and H. Netzer, “The emission lines of Quasars and similar Objects,” Review of Modern Physics, vol. 51, p. 715, 1979.
. G. J. Ferland and R. F. Mushotzky, “Broad line Region clouds and the absorbing material in NGC 4151)”, Astrophysical Journal Supplementary Series, vol. 262(1), p. 564, 1982.
. J. Kwan and J. H. Krolik, “The formation of emission lines in Quasars and Seyfert galaxy Nuclei,” Astrophysical Journal, vol. 250, p. 478, 1981.
. Vijayakumar H. Doddamani and P. Vedavathi, “Ultraviolet line-Continuum properties of Seyfert 1 galaxies and quasars “in the Proceedings of IAU Symposium 304: Multiwavelength AGN Surveys and Studies), (CUP), Edited by Areg M Mickaelian and David B Sanders, (ISBN-9781107045248, ISSN-17439213), p. 233, 2014.
. A. V. Filippenko, “New evidence for photoinoisation as the dominant excitation mechanism in LINERS,” Astrophysical Journal, vol. 289, p. 475, 1985.
. S. Collin-Souffrin, S. Dumont and J. Tully, “Hydrogen line spectrum in Quasars“, Astronomy and Astrophysics, vol. 106, p. 362, 1982.
. J. H. Krolik, “The origin of broad emission line clouds in active galactic nuclei,” Astrophysical Journal, vol. 325, p. 148, 1988.
. Hagai Netzer, “The spectrum of 3C 390.3 and the hydrogen line problem“, Monthly Notices of Royal Astronomical Society, vol. 198, p. 589, 1982.
. Online Data for E(B-V) values: http://heasarc.gsfc.nasa.gov/cgi-bin/tools/w3nh.pl
. F. J. Lockman and B. D. Savage, “Hubble space Telescope Quasar Absorption line key Project 10. Galactic HI 21 centimeter emission toward 143 Quasars and Active Galactic Nuclei,” Astrophysical Journal Supplementary Series, vol. 97(1), p. 1, 1995.
. B. W. Carroll and D. Aostlie, An introduction to modern astrophysics-IInd Edition, ch. 27, p. 1057, Addison-Pearson Wesley, New York, 2007.
. James Terrell, “The luminosity distance equation in Friedmann Cosmology“, American Journal
of Physics, vol. 45, p. 869, 1977.
. A. G. Riess, A. V. Filippenko, P. Challis, et al., “Observational evidence from Supernova for an accelerating Universe and a cosmological constant,” Astrophysical Journal, vol. 116, p. 1009, 1998.
. V. H. Doddamani and P. Vedavathi, “Luminosity- distances of IUE observed active galactic nuclei”, “in the Proceedings of IAU Symposium 304: Multiwavelength AGN Surveys and Studies), (CUP), Edited by Areg M Mickaelian and David B Sanders, (ISBN-9781107045248, ISSN-17439213), p. 37, 2014
. M. H. Ulrich, “Detailed ultraviolet observations of the quasar 3C273 with IUE”, Monthly Notices of Royal Astronomical Society, vol. 192, p. 561, 1980.
. I. Robson, “Active galactic nuclei”, ch. 3, p. 72, John Wiley and Sons, Chichester, 1996.