radioGalaxies detect radio radiationGalaxy。Ordinary galaxies have radio radiation.Generally, it refers to galaxies that emit strong radio radiation (102~106 times stronger than ordinary galaxies).The radio continuum spectrum of radio galaxies is generally power law spectrum, and there arepolarization，Spectral indexThe average is 0.75.Radio radiation has non thermal properties and originates from synchrotron acceleration radiation generated by relativistic electrons moving in a magnetic field.
Radio galaxies and related radio noise quasars andFlamboyant variant, are very bright active galaxies at radio wavelengths (frequencies from 10 MHz to 100 GHz, power up to 1038 W).The radio radiation comes from the synchronous acceleration process. The observed radio signal comes from the structure of a pair of gas jets and the external medium, and is emitted by the relativistic luminescence correction.Active galaxies with radio noise are interesting not only because they are galaxies themselves, but also because they can be observed at a long distance, which can be used as a useful tool for observing cosmology.Recently, a lot of work has been done effectively from theseIntergalactic mediumIn particular, galaxy clusters have obtained good results.
Broadly speaking, galaxies with obvious radio radiation can be called radio star systems.Galaxies with radio power of 10-10 ergs/s in the range of 10-10 Hz are called normal radio galaxies;Galaxies with radio power 10 to 10 times stronger than normal radio galaxies are called special radio galaxies (see extragalactic radio).In history, radio galaxies were regarded as "active" galaxies with abnormal optical characteristics.Now it seems that the optical characteristics of most radio galaxies are not special.Most radio galaxies areElliptical galaxy(E) , giant elliptical galaxies (D), ED galaxies in between and super giant elliptical galaxies (cD),Irregular galaxyvery seldom.They are often the brightest in galaxy clustersMember galaxyThe quality is also high.Some radio galaxies are N-type special galaxies andSeyfert galaxies 。
Galaxies with obvious radio radiation can be called radio galaxies. Galaxies with radio power of 1037~1041 ergs/s in the range of 10~10 Hz are called normal radio galaxies; galaxies with radio power 10~10 times stronger than normal radio galaxies are called special radio galaxies (see radio beyond rivers).In history, radio galaxies were regarded as "active" galaxies with abnormal optical characteristics.
Radio galaxy
From radio galaxies to otherActive galactic nucleusFrom both similarities and differences, some people think that radio radiation is just the performance of some types of celestial bodies at a certain stage of evolution.Radio galaxies may be an evolutionary result of quasars, which are "dead" quasars.In a word, the relationship between radio galaxies and optical objects needs further study.As for how the central celestial body generates huge energy, this is to study variousActive galaxy(See perturbing galaxies).The observation of M87 not long ago found that there is indeed a super massive object at its core, which is equivalent to
A solar mass, probably a black hole.Because radio galaxies are closer to us than quasars, if they have some common "activity" mechanism, then careful study of radio galaxies will be very helpful to solve the energy problem of quasars.
Ordinary galaxies have radio radiation.Usually refers to a galaxy that emits strong radio radiation (a hundred to one million times stronger than ordinary galaxies).The radio continuum spectrum of radio galaxies is generally a power law spectrum with polarization, and the average spectral index is 0.75.Radio radiation has non thermal properties and originates fromrelativitySynchrotron accelerating radiation produced by sexual electrons moving in a magnetic field.The radio flux and polarization of some radio galaxies often change.
Radio galaxies have various radio forms, which can be divided into compact type, nuclear halo type, double lobe type, head tail type and complex type with multiple sub sources.Most radio galaxies are elliptical galaxies, giant elliptical galaxies andSupergiant elliptical galaxy。The spectrum of radio galaxies is very similarSeyfert galaxies Most of them are similar to type II Seyfert galaxies, and a few are similar to type I Seyfert galaxies.However, the Seyfert system isSpiral galaxy。Radio galaxies and other galaxies that also emit strong radio radiation, such as quasars, Seyfert galaxiesBL Lacertae objects OthersActive galactic nucleusThe relationship between.Some radio galaxies also emit strong infrared radiation and X-ray.
Now it seems that the optical characteristics of most radio galaxies are not special.Most radio galaxies areElliptical galaxy(E) , giant elliptical galaxies (D), ED galaxies in between and super giant elliptical galaxies (cD)Irregular galaxyvery seldom.They are often the brightest in galaxy clustersMember galaxyThe quality is also high.Some radio galaxies are N-type special galaxies and Seyfert galaxies.
In recent years, it has also been found that many radio star systems are also strongX-ray sourceAnd infrared source.It is not easy to understand the essence of celestial bodies simply from the radio characteristics.For example, radio data alone cannot distinguish between radio galaxies andQuasar radio sourceIt is also impossible to determine exactly which type of optical body it corresponds to.On the contrary, from the spectral analysis, we can divide them into two categories: wide and narrow, which are similar to type I and type II Seyfert galaxies respectively.
Launch process
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Radio wave emission from radio noisy active galaxies is synchrotron radiation, which is supposed to be very smooth, natural broadband and highly polarized.This implies that the plasma body that emits radio waves contains at leastRelativistic velocity(Lorentz factor is about~10).Therefore, the plasma body must be neutral, and protons or positrons must be one of its components, but there is no way to directly observe the type of particles from synchrotron radiation.Moreover, there is no way to determine the energy density of particles and magnetic fields from observations (that is, the same synchrotron radiation can come from a few electrons in a strong magnetic field or a large number of electrons in a weak magnetic field).It is the lowest energy state that can be measured under the lowest energy density at a given emissivity in a specific emission area (Burbidge 1956), but there is no special reason to believe that the energy anywhere is near the minimum energy in the real situation for many years.
One of the sister programs of synchrotron radiation is the inverse Compton process, in which the relativistic electrons interact with the surrounding photons and increase the energy through Thomson scattering.The particularly important result of inverse Compton emission from radio noise sources is X-ray (e.g. Croston et al. 2005), because it is only related to the density of electrons (and the known photon density)Inverse Compton scatteringThe measurement of allows us to estimate the energy density of particles and magnetic fields (depending on some models).This can be used to demonstrate whether most sources are close to the minimum energy.
Synchrotron accelerating radiation is not limited to the wavelength range of the radio wave: if the particles of the radio wave source can be accelerated to enough energy, the characteristics in the radio wave area can also be detected in infrared, optical, ultraviolet or even X-ray.However, the electrons in the latter state must obtain more than 1Tev of energy, while in the magnetic field under normal state, it is difficult for electrons to obtain such high energy.Once again, polarization and continuous spectrum are used to distinguish synchrotron radiation from other processes.Jets and hot spots are common sources of high-frequency synchrotron radiation.It is difficult to distinguish synchrotron radiation and inverse Compton radiation in observation. Fortunately, there will be some differences on some objects during the process, especially in X-ray.
In the process of producing relativistic particles, synchrotron radiation and inverse Compton radiation are both considered asParticle accelerator。Fermi acceleration seems to be an effective particle acceleration process in radio noisy active galaxies.[1-2]
morphological structure
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1. Dense type: about 15% of extragalactic radio sources have a fine structure of about 0.001 or less, which coincides with the optical positioning.useVery long baseline interferometerIt is observed that they are usually composed of several groups of sources, such as 3C84 (NGC1275).
2. Halo structure:The main body is a star like source, with halos around it, extending in two opposite directions.The center may have a composite structure composed of several dense sub sources.For example, Virgo A has a double dense sub source corresponding to the optical source (M87) in the center and is surrounded by a widely distributed radio emission area outside.Its most prominent optical feature is that it ejects a bright blue jet from the nuclear at a high speed of tens of thousands of kilometers per second, with a gap of 1.5 thousand seconds.These jets are also strong ultraviolet and X-ray sources, and are composed of several highly polarized agglomerates.The optical corona is 30 kiloseconds, and the radio corona is even larger.
3. Extended double lobe structure:About half of the extended source radio star systems roughly have this structure, that is, there are two discrete radio electron sources (epitaxial expansion lobes) outside, and the center is an optical object.For example, the two outer lobes of the Cygnus A radio star system are 186 thousand seconds apart, and each lobe is about 17 thousand seconds apart. The outside is bright, forming hot spots, which are basically in a straight line with the central object.Very long baseline interferometerIt is found that there is a weaker compact nucleus, which is located between the two optical sources in the center.In the meter band, there is a radiation bridge between the two outer lobes.
Radio galaxy
4. Complex source:A narrow and long radiation belt composed of multiple sub sources is generally composed of two strong sub sources on both sides of the optical body, and there is one or more group sources and low brightness areas on the inside. The shape is complex and the linear distribution is irregular, such as 3C288.
5. Head and tail structure:In front of it is a compact source corresponding to an optical galaxy, followed by several pairs of increasing dual radio electron sources, which drag a radio tail with gradually broadened range, gradually steepened spectral index, and gradually weakened intensity.The tail can reach tens to hundreds of thousands of seconds.They are all members of galaxy clusters.
The radio spectrum and the radio continuum spectrum of polarized radio galaxies are generally written as power-law spectra. Most radio galaxies have linear spectra, with an average value of 0.75, and the radiation flow is generally unchanged.Its dense structure has flat spectrum (about 0~0.25) or complex spectrum, that is, there are one or more maxima or minima, and the radiation flow is mostly variable.In recent years, centimeter band polarization measurements show that almost all radio galaxies are linearly polarized, from a few tenths of a percent to a few percent.
From the perspective of a source, the linear polarization is low, only a few percent, in a relatively dense region;But in the extended low brightness area, it can be as high as 60%.By observing thespectrumAnd polarization inference, the radio radiation mechanism belongs to the relativistic electronmagnetic fieldSynchrotron accelerating radiation generated by the motion in.In the extended region, the straight line spectrum is obtained due to its transparency;In the dense area, due to the non transparency, self absorption can produce Pintan spectrum and complex spectrum formed by superposition of various source spectra.Spectra and energy. The spectral characteristics of radio galaxies are very similar to those of Seyfert galaxies, and can also be divided into two categories.The spectrum of the central optical source of most radio galaxies has a narrow profile, such as type II Seyfert galaxies.A few of them have wide line outlines, such as type I Seyfert galaxies.From synchrotron radiation magnetic energy toElectron energyThe total internal energy of the radio galaxy can be as high as 1060 ergs by averaging.The lifetime of radio galaxies is about 107~9 years.
Radio galaxies have obvious symmetrical double structure for the central optical body, and there are many correlation characteristics between the external sub source and the optical body.High resolution in recent yearsRadio interferometerIt is found that there are also
Experimental basis
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Radio galaxy
Radio star system used in the 1960sSynthetic aperture radio telescopeA large number of observations have shown that the number of dark and weak radio sources with galaxy level energy is much more than expected by the assumption of uniform distribution of radio sources in space, that is, radio star systems are actually not evenly distributed in space.It is inferred that radio galaxies evolve from stronger sources to weaker ones on cosmological timescale.
Tencent Technology NewsAccording to foreign media reports, recently, Australian astronomers announcedCentaurA's radio galaxy image, they have successfully drawn a detailed image of radio galaxies, which is conducive to our further understanding of this strange astronomical phenomenon of radio galaxies.
It is reported that the team led by Australian scientist Dr. Lena Fein publicly released their images at the academic conference on the diversity of the Centaurus galaxy held in Sydney last week.Scientists throughCommonwealth Scientific and Industrial Research Organization of AustraliaThe National Astronomical Telescope found: "Only a few galaxies are of this shape. They are like a blue whale in the vast space.
”In order to draw this detailed image, scientists used small arrays and Parker models in Australiaradio telescopeThe group continued to observe for 1200 hours, took 406 pictures, and spent 10000 hours using computers to process these pictures.
CentaurA is a galaxy in the Centaur Galaxy Group, 14 million light-years away from Earth, densely surrounded by radio nebula.The new image shows that the structure of the nebula is piled up by a stream of ray particles emitted by a supermassive black hole with a mesocentric center.When the particle stream releases energy in the galaxy, different halves are formed.Professor Ken Freeman from Mount Stroll University in Canberra said: "This detailed picture gives us an overall impression and view of this nebula. The nebula is like a cloud in the sky, just like clouds have different shapes, so are radio galaxies."
Scientists said that in order to study radio galaxies, it is necessary to do a lot of research on a series of spectra, such as visual spectrum and X-ray spectrum, and understanding the differences between them is what astronomy focuses on.[3]
