How to do a physical examination classification for galaxies?

The following article comes from WeChat public account: Mr. Sai, author Chen Yanmei

The IC 427 (ARP 40) shot by Hubble Telescope, the source of the picture: NASA, ESA, and B. Holwerda (University of Louisville Research Foundation, Inc.)

Guide

In the vast universe, there are hundreds of millions of plackets, different forms of galaxies. These moving celestial bodies constitute the cornerstone of the universe building and witness the history of the universe tens of billions of years. In the long life trajectory, some galaxies call their friends and merge with other galaxies many times; some galaxies are alone and feel the changes in the years in their own corners. The different life journey of the galaxy has created its different physical properties. How to understand the complicated physical processes they experienced in the long river of the long river through the tens of billions of galaxy fossils, it is the lifelong pursuit of many celestial physicists. In this issue, Mr. Astronomy, let's do individual examinations for these galaxies and re -classify!

Written article | Chen Yanmei (Nanjing University)

Responsible editor | Wang Xinxin, Lu Haoran

Points Vision Spectrum Cattering: A whole body of galaxy

Observations of galaxy optical bands mainly include two aspects: imaging and spectrum. The image patrol, while depicting a deep and vivid galaxy form for us, also gives the galaxy's accurate QR projection position on the sky. The spectrum is the fingerprint that label the physical properties of the galaxy, and is the core of unlocking the mysteries of the origin of the galaxy. Only through spectral observations can we estimate the age of the galaxy and analyze the chemical composition of galaxies.

For more than 20 years, large-scale spectral patrols at home and abroad (such as Sloan Digital Sky Survey (SDSS; The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (Lamost) became a breakthrough of astronomical observation, and won 100,000, hundreds of thousands, and hundreds of thousands. Million or even tens of millions of celestial spectrum information.

Early spectrometer patrol (including SDSS I-III, Lamost) provided mainly is the single optical fiber spectrum: the radiation mirror at the center of the galaxy, and transmit the radiation collected by the telescope to the spectrometer through a single fiber. As a result, the information carried by the spectrum reflects the nature of the center of the galaxy (see Figure 1). The typical structure of a galaxy includes a nuclear ball + nuclear ball periphery of the elderly star in the central area. The two different structures of the two different structures of young stars have different properties and history. The so -called "pushing the leopard in the tube, just see it." If you only see the center of the galaxy, then the understanding of the galaxy will be as one -sided as a blind person.

Figure 1: Typical galaxy structure schematic diagram. The red circle in the figure above indicates the SDSS single optical fiber spectrum coverage area. Many collections bundled together by the root fiber, each optical fiber observes different areas, output the corresponding spectrum, picture source: Author's picture

Scientific needs have promoted the development of the Integral Field Unit (IFU) observation technology, which greatly improved the efficiency of two -dimensional spectrum observation with space resolution ability, and enabled a group of large samples near neighboring galaxies IFU observation projects to smoothly go smoothly. Expand (such as Sauron, Atlas3D, Califa, Sami, and SDSS-IV Manga). Taking the manga project as an example, the realization of its spatial resolution ability is reflected that it can be bundled together by binding multi -root fiber, and each optical fiber outputs the corresponding observation position to achieve the effect of a whole body check on the galaxy (in Figure 1, below, below, below ), Some inspection results examples are shown in Figure 2.

Figure 2: Manga galaxy observation example. From left to right are the star speed field, Hα emission radiation intensity, and gas speed field. In the speed field, green represents the relative observer, blue represents the observer movement, and red represents away from the observer.

From the shape of the Hubo Yin fork to the combination sequence

In the middle of the 20th century, the galaxies of various forms in the neighboring universe have been discovered. Facing the strange galaxies, Edwin Powell Hubble (1889-1953) proposed the concept of using sound fork maps to classify galaxies in 1936 (Figure 3 left). (S0) Put it on the fork handle (early galaxy), while the ordinary vortex galaxy and the rod galaxy (S and SB) are divided into two forks (collectively referred to as late galaxies). An excellent classification system can guide people to think about the physical nature behind phenomena. Further research on the nature of the galaxy found that from left to right along the Hubble fork, the star clan of the galaxy tended to be younger, the color changed from red to blue, and the central aggregation decreased. Since its proposal, the Hubble Classification Law has been popular in amateur and professional astronomical circles.

The development of the ATLAS3D integration field of the field of vision, which made astronomers a qualitative change in the understanding of early galaxy sports, and also led to the advent of changes. In the visible light image, the early galaxy looks smooth and flat. It is generally believed that its star components are randomly moved in a smoother range. The angular movement of each other offsets each other, resulting in the net rotation of the entire system is not obvious. After combining images and rotation data, the ATLAS3D research group found that most of the early galaxies (even elliptical galaxies) are rapidly rotating ellipses. Self -rotation and "fast self -rotation". As a result, the members of the research group pointed out that "the appearance may be deceived. Our amazing new result is that for the galaxy categorized by professional astronomers, the proportion of error classification can be as high as 66%!" Research Based on these discoveries, the group proposed the classification of the Hubble Yin fork: ATLAS3D comb (Figure 3 right). It discharges the early galaxy along the handle, and the speed of rotation increases sequentially, while the vortex galaxy occupies three forks of three combed teeth instead of sound fork. The rapid rotation galaxy is located at the connection between the comb and the handle, and they may evolve from the vortex galaxy group.

Figure 3: (left) Hubble's sound fork map clearly divides the galaxy into three categories: ellipse (E), lens (S0), and vortex (S and SB); Right to the right. Image source: https://www-asstro.physics.ox.ac.uk/atlas3d/

Occasionally encounter with yin and yang: unexpected sports characteristics

Figure 4: Three examples of motion inconsistent galaxy venue. From top to bottom, the galaxy is reversed from the gas and the star, two reversed star disks, and two galaxies with reverse air disks. SDSS multi -color images were displayed from left to right. Pink purple hexagonal labeling Manga IFU coverage area, star speed field, gas speed field, and model diagram of different disks, blue represents gas disk, red represents the star disk Essence In the speed field, green represents the relative observer, blue represents the observer movement, and red represents away from the observer.

A very rough cognition about the formation of stars is that the cold gases in the galaxy are formed under the action of self -gravity. In this picture, the star originated from the gas, thereby inheriting the angular amount of the gas. Therefore, the star and gas ingredients have the same rotation direction (Figure 2). More than 30 years ago, based on the long-seam spectrum observation of a specific direction (such as the main axis) in a specific direction of the galaxy, astronomers successively reported some strange sports characteristics found in the source, mainly including gas-stars, stars-stars, gas, gas, gas -The gas rotation direction is inconsistent. These small samples have lasted about ten years, but they ended abruptly, which did not attract widespread attention from the academic community.

At the beginning of the 21st century, with the advancement of the large sample integral field of vision, the galaxy was inconsistent with sports science. Statistical research found that the occurrence probability of the inconsistency of galaxy sports has a strong dependence on the type of galaxy. Its proportion rose rapidly from 2 to 5%in the rich late galaxy to the early galaxies of lens galaxies and elliptical galaxies. 30 ～ 40%. Figure 4 shows the examples of the three types of sports. From top to bottom, the gas disk and the star disk are reversed. Two reversal star disks, and two reverse gas disk examples.

The emergence of inconsistencies in a large amount of exercise attracts people to explore its causes. If we regard the galaxy as an isolated system, because the star comes from the gas accumulation and the angle is conservatively conservative, the sports direction of the gas and star components in this process should be the same. Although a large amount of energy such as nuclear energy and central black holes in the outbreak of the supernova erupted by the galaxy will disturb the gas motion in the galaxy, the possibility of the galaxy -scale reversal of the galaxy is very small.

In fact, the evolutionary process of galaxies has a certain similarities with a person's growth process, which is based on internal and external causes. Since the internal process is difficult to cause the galaxy -scale sports inconsistency, we can only look at the external environmental factors. These factors include: the accumulation of harmony gas (including the accumulation of the cosmic network, dark matter halo, and small man's rich neighbor galaxy).

Environmental impact: ripples in galaxy life are still the master of fate

The galaxy is different from the direction of the direction of the angle volume of its external accumulation. These gases accumulate to a certain extent, which will inevitably trigger the formation of new stars. Therefore, a direct problem is how to affect the subsequent evolution of the galaxy? Just stirring a hint of ripples in the life course of the galaxy, will it completely change the fate of the galaxy? To answer this question, we have to comprehensively consider internal factors and external factors. From the simplest assumptions and models, in three different cases, the possible impact of the obtaining external gas on the evolution of galaxies:

A early galaxy that can be ignored by gas content. The galaxy obtains a gas with different angular directions from its outside (top left). The torque effect of the star plate is approached to the star plate until the coexistence (Figure 5 below the left). In this process, the interaction between gas and stars can be ignored because of its small collision section. In this case, the acquisition of external gases is only an episode in the life of the early galaxy, so that it obtains a reverse air disk, which does not affect other properties of the galaxy. A rich vortex galaxy obtains the opposite air -conditioning of the direction of the angle volume, and the angular amount of the captured external gases is greater than the angular angular amount of the gase in the galaxy (in Figure 5). Due to the large collision section of gas and gas, the original gas in the galaxy interacts with the external gas, resulting in the rearracking volume. In extreme cases, we assume that the angular amount of the two parts of the gas offsets each other, the gases are free to fall to the center of the galaxy, and a large amount of gases gather in the center of the galaxy. At the same time, the star storm is triggered by the storm of the center of the galaxy.

Because the angular amount of external gas is greater than the original gas, the system will eventually show a galaxy -a star -reversing galaxy. The first galaxy in Figure 4 belongs to this kind of situation. Direct evidence that has occurred. This process has led to the birth of a nuclear ball component of the galaxy center and the fading of the external rotation arm. The galaxy has evolved from a vortex galaxy to a lens galaxy, and has since reborn. In addition, this process also provides a practical and effective way for the evolution of the three -filled teeth in the ATLAS3D comb. The reversal of the gas -star ingredients in the lens galaxy is higher than that of other types of galaxies. This observation phenomenon is the effective support of the evolutionary trajectory.

Figure 5: In the three different situations, the impact diagram of the accumulation of external gases on the evolution of galaxies. Red ellipse represents a star disk. The blue dot line and the solid line represent the gases and external accumulation gases in the galaxy. The blue solid circle in the situation 2 and 3 represents the newly formed nuclear -type ball. The length of the arrow represents the size of the angular movement, the same red is the angular amount of the star component, the blue is the gas component, the source of the picture: the author's picture

Similar to 2, the richer vortex galaxy obtains the air -conditioning of the opposite direction of the external angle, but the angular amount of the original gas is greater than the external gas (Figure 5 right). At this time, the final fate of the galaxy is also similar to 2). The final angular amount of the gas disk is dominated by the original gas, and the gas and the stars are turned together instead of turning. In addition, galaxies are also one of the possible origins of galaxy sports. Numerical simulation shows that the former and coincidence process will leave the images of galaxy fossils to leave dark relics such as tidal tails and shell structures (Figure 6). The system searched from the deep field patrol image and co -concentrated the characteristics of the ruins found that the contribution of galaxy and the inconsistent phenomenon of sports science was the highest in the early galaxy, which can reach about 20%. It can be seen that the contribution of external gas's accumulation to the inconsistency of sports science is much greater than and cooperated.

Figure 6: The tide tail in the galaxy (light rotary arm in the left) and the shell structure (right), picture source: The Dark Energy Spectroscopic Instrument (Desi) Legacy Imaging Surveys

Write to the end

Compared to the vast universe, humans are just a dust. Einstein said, "The most incomprehensible part of the universe is that it can be understood." The material components contained in the galaxy are different, and there are many physical processes involved. They are intertwined and influenced each other. So please allow a astronomer as a dust to sigh in the exploration of the rules of the universe: "There are too many problems, life is too short!"

It has been a long time since the integrity of the score visits to find a large number of sports science galaxies to this day, and it has only been more than ten years. It is still far from the complex physical process of the complicated and complicated physical processes. Combined, it will help us to unveil our mystery.

About the Author:

Chen Yanmei, a professor at the School of Astronomical and Space Science of Nanjing University. The research direction is the formation and evolution of galaxies.

references:

[1] "EXTRA-Galactic Nebulae", Edwin Hubble, The Astrophysical Journal, 64 (1926), 321-3699, 321-369

, Alatalo, K., Bois, Bois, M., Et Al., Monthly Notices of the Royal Astronomomical Society, 416 (2011), 1680-1696 [3] "Countr-Rotation in Disk Galaxies", Corsini E. M. M. M. M., Multi-SPIN Galaxies, Asp Conference Series, 486 (2014), 51

This article is authorized to reprint from WeChat public account: Mr. Sai Author: Chen Yanmei

Reprinted content only represents the author's point of view

It does not represent the high energy office of the Chinese Academy of Sciences

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