Seyfert galaxies and "Unified Scheme"
From spectroscopic point of view Seyfert galaxies (as other Active Galactic Nuclei - AGN) basically are subdivided into two types: with and without broad permitted emission lines in their optical spectra (so called type I and type II Seyfert galaxies or AGNs). One of the most fundumental idea concer...
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| Cite this: | Seyfert galaxies and "Unified Scheme" / I.N. Pashchenko, S.V. Pilipenko, V.M. Vitrishchak // Advances in Astronomy and Space Physics. — 2011. — Т. 1., вип. 1-2. — С. 37-38. — Бібліогр.: 11 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1859823438162558976 |
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| author | Pahshchenko, I.N. Pilipenko, S.V. Vitrishchak, V.M. |
| author_facet | Pahshchenko, I.N. Pilipenko, S.V. Vitrishchak, V.M. |
| citation_txt | Seyfert galaxies and "Unified Scheme" / I.N. Pashchenko, S.V. Pilipenko, V.M. Vitrishchak // Advances in Astronomy and Space Physics. — 2011. — Т. 1., вип. 1-2. — С. 37-38. — Бібліогр.: 11 назв. — англ. |
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| description | From spectroscopic point of view Seyfert galaxies (as other Active Galactic Nuclei - AGN) basically are subdivided into two types: with and without broad permitted emission lines in their optical spectra (so called type I and type II Seyfert galaxies or AGNs). One of the most fundumental idea concerning AGN is that observed AGN type (I or II) is determined by inclination angle of AGN to the line of sight (LOS). At high inclination angles LOS crosses dusty torus which absorbs and scatters line emission. But in some recent papers the differences in close (< 100 kpc) environment of SyI and SyII (SyII have more close
companions), which are incompatible with Unification Scheme, were found and the possibility of physical (intrinsic) differences between Seyfert I and II was discussed. It was shown that this difference could be due to selection effects caused by the sample criteria. We sampled SyI and SyII galaxies from the Sloan Digital Sky Survey (SDSS) on the basis of their emission line properties thus excluding selection and discuss the properties of the environment of Seyfert galaxies.
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| first_indexed | 2025-12-07T15:27:00Z |
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Seyfert galaxies and �Uni�ed Scheme�
I. N. Pahshchenko1, S. V. Pilipenko1, V. M. Vitrishchak2
1Astro Space Center of Lebedev Physical Institute of RAS, Profsoyuznaya st. 84/32, 117997, Moscow, Russia
2Sternberg Astronomical Institute, Moscow State University, Universitetsky pr., 13, 119992, Moscow, Russia
in4pashchenko@gmail.com
From spectroscopic point of view Seyfert galaxies (as other Active Galactic Nuclei � AGN) basically
are subdivided into two types: with and without broad permitted emission lines in their optical spectra
(so called type I and type II Seyfert galaxies or AGNs). One of the most fundumental idea concerning
AGN is that observed AGN type (I or II) is determined by inclination angle of AGN to the line of sight
(LOS). At high inclination angles LOS crosses dusty torus which absorbs and scatters line emission. But in
some recent papers the di�erences in close (< 100 kpc) environment of SyI and SyII (SyII have more close
companions), which are incompatible with Uni�cation Scheme, were found and the possibility of physical
(intrinsic) di�erences between Seyfert I and II was discussed. It was shown that this di�erence could be due
to selection e�ects caused by the sample criteria. We sampled SyI and SyII galaxies from the Sloan Digital
Sky Survey (SDSS) on the basis of their emission line properties thus excluding selection and discuss the
properties of the environment of Seyfert galaxies.
Introduction
All AGNs can be classi�ed according to the presence (type I AGN) or the absence (type II AGN) of broad
(FWHM> 1000 km/s) permitted emission lines in their optical spectra [11]. Actually such classi�cation is
wider than just dichotomy (near 2/3 of all Seyfert galaxies are intermediate types), but division typeI/typeII
is clearly visible in SDSS data [6]. Traditional explanantion of type I/type II division is the existence of dusty
torus in Seyfert nuclei that absorbs and scatters emission when galaxy is observed edge on. Indeed, some
type II AGN displays broad lines in polarized (because of scattering) light [11]. This suggestion is called
Uni�ed Scheme (US) [8]. It has many observational evidences [4] (but see [7]) but in some recent papers its
insu�ciency has been found.
Di�erent environment or selection?
The evidence of US insu�ciency comes from observational fact that SyI galaxies lack of close companions
as compared to SyII. According to the US isotropical properties of typeI and typeII AGN (properties that do
not depend on direction of observation) must be the same. These are richness of the environment, luminosity
of narrow emission lines (narrow lines are believed to originate far from nuclei � outside of dusty torus),
radio luminosities. However, some papers do reveal di�erent number of close (with projected separation less
than 100 kpc) companions in SyI and SyII (see [5] and references there). Authors explain such discrepancy
by evolution along SyII-SyI sequence due to decrease of star-formation rate with time after initial star-burst
induced by interaction with close companion or oppositly � evolution along SyI-SyII due to decreasing AGN
activity comparing to star formation. But probably such results are caused by selection. Authors of [9] claim
that it is selection criteria of [5] sample that cause such selection e�ects. Studied in [5] SyII sample selection
criteria is based on the UV-excess. But as SyII could be edge-on AGN direct view of UV-source (acretion
disc) is closed and UV-�ux is only available via star-formation activity that is triggered by interaction with
close companions. So SyII samples constructed in this way are subject to selection of galaxies with an excess
of close companions respective to other samples.
37
Advances in Astronomy and Space Physics I. N. Pashchenko, S. V. Pilipenko, V. M. Vitrishchak
The sample
We used SDSS Data Release 7 [1] Main Galaxy Sample (MGS) to select SyI and SyII galaxies. Sample
criteria based on emission lines were used to form samples. Value of 2000 km/s (in objects rest frame) for
FWHM of Hα and Hβ and its equivalent width (EW) of 10 Å were used to identify SyI galaxies. Flux ratios
of [O iii] 5007Å/Hβ>3, [N ii] 6583Å/Hα>0.6 [2] and EW= 2 Å for these lines were used for identifying SyII
galaxies. Also we used S
N = 5 criteria for spectra and galaxies with redening Ar < 0.2 mag. Quasars (in
common sense: type I AGN of high luminosity) were excluded from SyI sample and quasars (in terms of
SDSS: any galaxy with emission lines broader than 1000 km/s) were excluded from SyII sample. It resulted
in 856 SyI and 1276 SyII galaxies. For each SyI galaxy we found SyII with nearly same z -band (e�ective
wavelength 9000 Å) luminosity and redshift. The �nal samples of SyI and SyII galaxies consist of 480 pairs.
Results and conclusions
Firstly we checked the basic parameter that traces inclination of galaxies from SyI and SyII samples.
As all of them are mainly Sc, Sb�spirals, their inclination could be infered from axis ratio of photometric
isophots measured by SDSS pipeline in r -band. We found that SyI have more rounded isophotes than it
is basically expected in US. Then we used concentration parameter [10] that is a ratio of radius containing
90% of �ux of the galaxy to radius containing 50% of �ux as a proxy to morphology type of Seyfert galaxies.
Being corrected for pointlike AGN-contribution (we estimated it from SyI galaxies with known spectral
decomposition), SyI and SyII galaxies do have the same mean concentrations. Finally we compared the
richness of the environment of two samples on di�erent scales. We used Minimal Spanning Tree algorithm
[3] to determine the frequency of falling in large scale (∼ 5 Mpc) regions of low density. It turned out to be
the same (less then 1σ di�erence) for Seyferts I and II. Then we used direct counting of close (with small
projected distances and photometric redshifts) companions to compare environment on small (∼ 50 kpc)
scale. For projected separation of 30 kpc we found frequencies of galaxies with at least one companion
0.118±0.016 and 0.105±0.015 and for separation 50 kpc we found 0.20±0.03 and 0.21±0.03 for SyI and SyII
correspondingly. Thus, in contrary to the conclusions of [5], close environment of Seyfert galaxies appears
to be the same. Therefore samples of Seyfert galaxies that are free of selection reveal results predicted by
Uni�cation Scheme.
Acknowledgement
The work was supported by Russian Federation President grant MK-2839.2009.2
References
[1] Abazajian K. N., Adelman-McCarthy J. K., Agueros M. A. et al. Astrophys. J. Suppl. Ser., V. 182, pp. 543-558 (2009)
[2] Baldwin J. A., Phillips M. M., Terlevich R. Astron. Soc. of the Paci�c, Publications, V. 93, pp. 5-19 (1981)
[3] Barrow J. D., Bhavsar S. P., Sonoda D. H. Mon. Notic. Roy. Astron. Soc., V. 216, pp. 17-35 (1985)
[4] Barthel P. D. ASP Conf. Ser., V. 54, pp. 175-186 (1994)
[5] Dultzin-Hacyan D., Krongold Y., Fuentes-Guridi I., Marziani P. Astrophys. J., V. 513, pp. 111-114 (1999)
[6] Hao L., Strauss M. A., Tremonti C. A. Astron. J., V. 129, pp. 1783-1794 (2005)
[7] Komberg B.V. Astron. Rep., V. 39, pp. 1-8 (1995)
[8] Padovani P. Mon. Notic. Roy. Astron. Soc., V. 257, pp. 404-414 (1992)
[9] Schmitt H. R. Astron. J., V. 122, pp. 2243-2256 (2001)
[10] Strateva I., Ivezic Z., Knapp G. R. et al. Astron. J., V. 122, pp. 1861-1874 (2001)
[11] Urry M. C., Padovani P. Astron. Soc. of the Paci�c, Publications, V. 107, pp. 803-845 (1995)
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| id | nasplib_isofts_kiev_ua-123456789-118980 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| isbn | 987-966-439-367-3 |
| language | English |
| last_indexed | 2025-12-07T15:27:00Z |
| publishDate | 2011 |
| publisher | Advances in astronomy and space physics |
| record_format | dspace |
| spelling | Pahshchenko, I.N. Pilipenko, S.V. Vitrishchak, V.M. 2017-06-02T18:32:57Z 2017-06-02T18:32:57Z 2011 Seyfert galaxies and "Unified Scheme" / I.N. Pashchenko, S.V. Pilipenko, V.M. Vitrishchak // Advances in Astronomy and Space Physics. — 2011. — Т. 1., вип. 1-2. — С. 37-38. — Бібліогр.: 11 назв. — англ. 987-966-439-367-3 https://nasplib.isofts.kiev.ua/handle/123456789/118980 From spectroscopic point of view Seyfert galaxies (as other Active Galactic Nuclei - AGN) basically are subdivided into two types: with and without broad permitted emission lines in their optical spectra (so called type I and type II Seyfert galaxies or AGNs). One of the most fundumental idea concerning AGN is that observed AGN type (I or II) is determined by inclination angle of AGN to the line of sight (LOS). At high inclination angles LOS crosses dusty torus which absorbs and scatters line emission. But in some recent papers the differences in close (< 100 kpc) environment of SyI and SyII (SyII have more close companions), which are incompatible with Unification Scheme, were found and the possibility of physical (intrinsic) differences between Seyfert I and II was discussed. It was shown that this difference could be due to selection effects caused by the sample criteria. We sampled SyI and SyII galaxies from the Sloan Digital Sky Survey (SDSS) on the basis of their emission line properties thus excluding selection and discuss the properties of the environment of Seyfert galaxies. The work was supported by Russian Federation President grant MK-2839.2009.2. en Advances in astronomy and space physics Advances in Astronomy and Space Physics Seyfert galaxies and "Unified Scheme" Article published earlier |
| spellingShingle | Seyfert galaxies and "Unified Scheme" Pahshchenko, I.N. Pilipenko, S.V. Vitrishchak, V.M. |
| title | Seyfert galaxies and "Unified Scheme" |
| title_full | Seyfert galaxies and "Unified Scheme" |
| title_fullStr | Seyfert galaxies and "Unified Scheme" |
| title_full_unstemmed | Seyfert galaxies and "Unified Scheme" |
| title_short | Seyfert galaxies and "Unified Scheme" |
| title_sort | seyfert galaxies and "unified scheme" |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/118980 |
| work_keys_str_mv | AT pahshchenkoin seyfertgalaxiesandunifiedscheme AT pilipenkosv seyfertgalaxiesandunifiedscheme AT vitrishchakvm seyfertgalaxiesandunifiedscheme |