Seyfert galaxy isGalactic nucleusExtremely bright, strong and wideEmission lineOfActive galaxy, usually with rotating arm structure.It was first discovered by American astronomer Seyfert in 1943.Discipline: Astronomy (first-class discipline);Galaxies and the Universe (Secondary Discipline)
Carl Seyfert, an American astronomer, was engaged in infrared research of galaxies at the Wilson Observatory in 1943.He found that some galaxies have abnormal emission lines and obvious galactic nuclei, and the galactic nuclei have violent activities. This type of galaxy was later named Seifert galaxy.Soviet astronomermarkarian He has engaged in a large number of galaxy surveys and observations, and 10% of the objects in the "Makalian Catalog" published by him are Seyfert galaxies.By 2000, astronomers had discovered 1711 seyfertActive galaxy。Such galaxies are far away from us, most of them are hundreds of megaseconds away, and a few are 20-30 away from usMpc。[1]
Observational characteristics
Announce
edit
Seyfert galaxy NGC5728
The obvious observational feature of Seifert active galaxy is that the center has bright star shapeActive galactic nucleus, its size is only about 1pcThe brightness of the galactic nucleus is greater than that of usGalaxy10000 times brighter.There are faint vortex structures around the galactic nucleus, and the galaxies are generally of type Sa or SbSpiral galaxy。In addition, galactic nuclei have strong ultraviolet, infrared andRadio radiationSome people speculate that the center of Seyfert galaxy is a strongmagnetic fieldHigh speed rotating massive stars orblack hole。For example, the image of the Seiffert galaxy NGC5728, about 40 Mpc away from us, shows that the core of the galaxy has jets, which may be black holes.
There are obvious broad emission rays in the spectrum of such galactic nuclei, includingAtomic spectrumAllowable line, semi forbidden line andForbidden line。The allowable line width is generally wide, for example, the Doppler width of the Balmer line can reach 500~
km/s，There are even high ionization spectral lines, such as 13 times of ionization iron wire;The large red shift of the spectral line indicates that the matter in the nucleus leaves the galactic nucleus at a high speed.In addition to strong emitting rays, there are also relatively weak absorption lines in the spectrum.The continuous spectrum is blue or ultra violet, which is non thermal spectrum or not completely non thermal spectrum, so it can be inferred that the temperature of such galaxies is very high.Moreover, the continuous spectrum of such galaxies often changes in intensity within a few days to a year.
The seyfert galaxy is low luminosityActive galactic nucleus。The absolute magnitude of such galaxies
about
～
。[1]
Basic classification
Announce
edit
SAFET I and SAFET II
In the early 1970s, this type of galaxy was divided into two subtypes: Seyfert I and Seyfert II.The division of the two is mainly based onSpectral lineThe width, specifically, is the full width of the spectral line (FWHM) corresponding to half of the maximum value of the spectral line.Where the spectral line width
The unit of is nm, which can be determined by the formula（
/
）C=v, converted to km/s.Observations show that the allowable linewidth of Seyfert type I galaxies is very wide
The spectral line width of the line is greater than 3000 km/s;However, the allowable line width of Seyfert type II galaxies is about the same as the forbidden line width, which is generally 500~1000 km/s.
The typical judgment method in modern times is to compare spectral lines
(
=486.3 nm) and oxygen [O Ⅲ]（
=500.7 nm).
FWHM for Severt Type I（
)/FWHM[OⅢ]≈1。
FWHM for Severt II（
/FWHM[OⅢ]≈o．1。
In addition, according to [O Ⅲ]（
=500.7 nm) can also distinguish two subtypes of Seiffert galaxies, namely
FWHM for Severt Type I（
=500．7 nm)≈370 km/s。
FWHM for Severt II（
=500．7nm)≈500km/s。
In terms of light variation, Seifert I generally has light variationTime scaleFrom weeks to months;However, Seifert II generally has no light change.
stayDegree of polarizationIn terms of polarization, the degree of polarization of Seifert I is higher, reaching 1%~8%;The polarization degree of Seifert II is only 1%~4%.[1]
more
In the 1980s, some astronomers divided Seyfert galaxy into more subtypes when they studied it carefully.For example, according to the relative intensity of the spectral lines, if all the spectral lines are clearly outlined, it is Seifert 1.5;If in the transmission line of HI
Relatively weak but appearing
Seyfert 1.8;and
What can hardly be seen is the Seiffert 1.9 type, etc.[1]
Electromagnetic spectrum
Announce
edit
form
The spectrum of Seyfert galaxy is composed of continuous spectrum superimposed emission lines.The composition of the emission line is very similar to that of quasars. There are many forbidden lines with high excited states, such as [FeX]（
789.2 nm), the excitation potential is 262 eV;[FeXⅣ](
530.3 nm), the excitation potential is 361 eV.
Balmer Line in the Spectrum of Seyfert Galaxy
、
、
The strength ratio between them has an abnormal steep drop
Stronger than expected.There may be two reasons for this phenomenon: first, due to collision excitation or radiation excitation, or the self absorption of the Balmer linehydrogen atomThe energy state distribution of is abnormal.Second, the whole spectrum is reddened, which means that the energy is absorbed by the dust and then re radiated in the reddish band.Observations have proved that most of the Seyfert galaxies are very strongInfrared source。This shows that there is a large amount of dust near the core of Seyfert galaxy, which weakens the brightness of the core.
The continuous spectrum of Seyfert galaxy deviates significantly from the spectrum of galactic nucleus usually composed of stars, and presents a mixed spectrum of thermal spectrum and non thermal spectrum.The continuous spectrum of Seyfert I galaxy is mostly power law spectrum, while the continuous spectrum of Seyfert II galaxy is often mixed with the spectrum of stars and reddening caused by dust.It is generally believed that the radiation mechanism of the combination of thermal radiation and non thermal radiation has three situations: (1) relativistic electron synchrotron radiation;(2) Photospheric radiation of stars;(3) Infrared radiation of dust.[1]
Salient feature
The prominent feature of the continuous spectrum of Seyfert galaxy is thatinfrared radiation(From near infrared to more than 100
In the infrared band, the radiation also shows light variation and polarization.Most of the infrared sources discovered by IRAS satellite have been verified to be the new Seyfert galaxy.
Continuous spectralUltraviolet bandIt is non thermal spectrum, but the spectral index is smaller.The X-ray radiation of such galaxies is generally very strong, which, like the strong infrared radiation, is an important physical feature of such galaxies.The X-ray luminosity of Seyfert galaxy is
～
erg/s。In addition, X-ray radiation is light variableTime scaleFrom a few minutes to tens of days, the amplitude of light change can be doubled.The X-ray spectra (including soft X-ray) of many Seyfert galaxies can be fitted with a single spectral index.The radiation of X-ray is correlated with that of other wave bands, especially the optical wave band and infrared radiation.Some scientists have analyzed the relationship between X-ray and
、
[OⅢ](
500.7 nm) and even 21 cmRadio spectral lineThere are also connections between them.[1]
