The absorption spectral line refers to the dark spectral line formed in the spectrum when the light of a certain band is absorbed by cold gas.Light from celestial bodies is selectively absorbed by atoms or molecules, resulting in that part of the light being eliminated from the starlight, leaving dark lines.
Chinese name
Absorption line
Foreign name
absorption line
Field
optics
Properties
Dark spectral lines formed in the spectrum
Cause
Selective absorption of light by atoms or molecules
The absorption spectral line refers to the darkness formed in the spectrum when the light of a certain band is absorbed by cold gasSpectral line。Light from celestial bodies is selectively absorbed by atoms or molecules, resulting in that part of the light being eliminated from the starlight, leaving dark lines.
Basic Introduction
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How do celestial bodies produce spectra?Imagine a large cloud of hydrogen atoms scattered in space, with a white hot bulb in the middle. The bulb lights up because the filament is heated to high temperature, producing black body radiation, so it radiates photons of all wavelengths, forming a continuous and uninterrupted color band, called continuous spectrum.
However, when these photons pass through the hydrogen surrounding the bulb before reaching our telescope, most of the photons that do not meet the energy level difference of the hydrogen atom pass through smoothly, but some photons whose wavelengths just match will be absorbed by the hydrogen atom that collides with them, and cannot reach the earth.In a short time after the hydrogen atom is excited, the electron returns to the original energy level and emits new photons, but the direction of the new photons is random rather than necessarily facing the earth, so only a few new photons can reach the earth again and be received by the telescope.So the spectrum received by the telescope is no longer the continuous spectrum of the bulb, but there are fewer photons with specific wavelengths that meet the energy level difference of the hydrogen atom. Black lines are formed at these wavelengths in the entire original complete spectrum. These black lines are called absorption lines, because they are the parts that are absorbed by the atom,The spectrum containing absorption lines is called absorption spectrum, also called dark line spectrum.
(1) The column density of UV absorption material in the wide absorption line area is 2 orders of magnitude higher than the original estimate, and the low ionization absorption line is formed in the saturated high ionization absorption line area;
(2) The absorption material of wide absorption quasars with quiet radio is mainly on the equatorial plane, and the distribution of absorption material of different sources is very different. In quasars with strong radio, equatorial and polar outflows are possible;
(3) The polarization of resonance scattered rays shows that the outflow material carries angular momentum.
Some galactic centralSupermassive black holeThe surrounding gas is accreted. When the gas falls into the black hole, it converts the huge gravitational binding energy into the thermal kinetic energy of particles, generating a large amount of electromagnetic radiation. At the same time, accretion is also a process of growth of the massive black hole.Their radiance is even 100 times more than that of the stars in the whole galaxy. We call these objectsActive galactic nucleus。Observations in the past 10 years show that almost all massive galaxies have supermassive black holes in their centers, and nuclear activity is a special stage of galaxy evolution.It is generally believed that the huge energy output of nuclear activity makes it play a key role in the process of galaxy evolution, resulting in a series of observed correlations between the mass of black holes and galaxy parameters.Quasars are high luminosity active galactic nuclei.
About 10% - 20% of quasars (QSOs) have wide, blue shifted ion absorption lines. These quasars are calledWide absorption line quasar(It is usually represented by BAL QSO).The most common ultraviolet absorption line is CIV1549,Resonant absorption lines of Li like ions such as NV1240, Ly α, SiIV1397, OVI1032, MgII2798, AlIII1870, etc. (as shown in Figure 1) are generated by the absorption continuous spectrum of high-speed outflow materials partially ionized by quasars, and the outflow speed can be as high as 0.1c-0.2c (c is the speed of light).If these outflows have sufficient mass outflow rates, they may be the key physical processes connecting nuclear activity and galaxy evolution, and will also have an important impact on the accretion process. Therefore, determining the physical parameters of quasars with wide absorption lines has received special attention in recent years.
Absorption line
Basic image of outflows in wide absorption quasars
At present, there are two kinds of completely different views on wide absorption line quasars: it is generally accepted that all quasars have wide absorption line outflows, but the outflows only cover a small part of the solid angles, in other words, outflows are only observed in some line of sight directions of quasars;Another view is that only some special quasars have outflows with wide absorption lines.
The main methods to observe and test these two viewpoints are:
(1) By comparing the coverage factor of the BAL QSO absorption line area with the proportion of the observed wide absorption line quasars, if the two are consistent, the first type of model is supported;
(2) Test the statistical differences between the properties of BAL QSO and non BAL QSO. If there are differences, they may be different.
The first type of test is mainly determined by comparing the intensity of the ion resonance scattering spectral line with the prediction of the theoretical model.For most absorption lines, the interaction between ions and photons is not true absorption but resonance scattering, so the area covered by the scattering material can be determined by measuring the light scattered from other directions.This method gives an upper limit of coverage factor of 30% in the wide absorption line area, but to some extent, it is related to the model.
The second method finds that BAL and non BAL QSO only have slight differences in the emission line contour,The CIV line of BAL QSO is more blue shifted, which may indicate that they are different, or it is only caused by the different perspective directions of Class II systems. The former supports the first view, while the latter supports the second view. Therefore, Class II methods do not give a clear trend.
The outflow of the wide absorption line is accelerated by radiation. If the ionization degree of the outflow is appropriate,Active galactic nucleusStrong ultraviolet radiation can effectively accelerate the material outflow.
For a typical Li like ion ionized material, the ratio of the resonance scattering cross section to the photoelectric absorption cross section is 105.However, resonance scattering can only occur near the resonance frequency of the common coordinate system of the absorbing material and is easy to be saturated, so its importance depends on the velocity gradient of the absorbing material.For materials with thick resonance scattering optics, the relative importance of the two is determined by the velocity gradient of column density (n (dr/d ν)) and the shape of ionization continuum spectrum,λ is estimated between 10 and 10000.In some cases, dust absorption is also an important source of radiation.Some characteristics of the absorption line profile are also found in the observation, which indicates that the radiation pressure of the resonance line is an important acceleration mechanism of the outflow. For example, there is sometimes a peak of residual flow at the speed of 5800km/s in the CIV absorption pit, which is caused by the reduction of the number of ions in the velocity segment due to the additional acceleration obtained by the NV ions after absorbing the strong Ly α emission line of the quasar.
The depth of the absorption pits of some wide absorption line quasars is deeper than the local continuous spectrum, which requires that the wide absorption line material also absorbs the emission line, in other words, the wide absorption line area is outside the emission line area.For quasars, the scale of the typical wide radiation region is 1016-1017cm. For comparison, the radius of a typical 108M mass black hole is 1.5 × 1013cm.The wide absorption line region may extend to pc (second difference) scale.From the UV absorption pit, we can estimate the lower limit of the absorption ion column density, which corresponds to a material column density of only 1021cm-2. From the absorption line outline, the absorption material is continuously flowing out, so it is estimated that the absorption material density is only 105-106cm-3.This low-density material is exposed to the strong radiation field of the quasar, and the ionization degree of the material is very high, so Li like ions are difficult to exist.One solution is that there are highly ionized absorption materials inside the wide absorption line, which absorb soft X-ray, thus ensuring the existence of Li like ions outside.Strong soft X-ray absorption observed in wide absorption line quasars supports this solution.[1]
Absorption line intensity
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definition
The energy absorbed by the incident beam at a given frequency per unit time and per unit area cross section is called the intensity of the absorption spectral line.[2]
Related nouns
Absorption spectrum: the ground state atom absorbs its resonance radiation.
Emission spectrum: due to the influence of external energy, the electrons in the yard may absorb energy to become an excited state, and then transition from the excited state to the ground state or a lower energy state.
Franckondun principle: the electronic transition is much faster than the molecular vibration. Although the state of the electron has changed, the atom in the molecule has not yet had time to change its position significantly
Chromophore: the atomic group and its related chemical bond in the molecule that determine the electronic absorption band, connected with the chromophore, and the group that makes the absorption wavelength shift and the absorption intensity increase is the chromophore.
Rayleigh scattering: when illuminated by a monochromatic beam, the scattered light has the same frequency as the incident light.
Stark: The spectral lines of matter move in an electric field.
Nuclear statistics: the rotational dynamics of molecules are subject to the Pauli principle. The rotational dynamics that meet the Pauli principle can be established, and those that do not meet the Pauli principle cannot be established.
State superposition principleThe linear combination of eigenfunctions corresponding to different eigenvalues is no longer the eigenfunction of this operator, but they are still a possible state of the system.
Principle of non intersection: the two original energy curves are mutually exclusive, and the two final curves will never intersect.
Molecular system and radiation generation: similar energy, symmetry matching.
