| 其他摘要 | One of the most important problems in the study of galaxies is the star formation,which is a basic process of the origin and evolution of celestial bodies at various scales throughout the history of the universe. It is one of the frontiers of observational astronomy and theoretical research. Understanding the instantaneous level of star formation (such as the star formation rate) can not only reveal the interstellar medium state, but also reveal the evolution and formation of galaxies. Therefore, a correct understanding of the relationship between the star formation rate and the star-forming gas in galaxies is the key to the study of the processes and laws related to star formation, and also the basis for further study of the astrophysical processes related to star formation in high-redshift galaxies and even the first generation galaxies. At present, the star formation rate has been measured in a wide range of wavelengths through continuum or emission lines. However, commonly used optical or infrared continuum emission is difficult to apply to high-redshift galaxies, because: (1). these spectral lines are redshifted to the band that is difficult to detect by ground equipments; (2). It is difficult or costly to obtain the complete infrared continuum. Therefore, alternative methods must be found.In the astrophysical environment, the (sub)millimeter band includes a large number of detectable line emission (e.g., the rotational emission of simple molecules, the ground state fine-structure transition of atoms and ions). These lines are the important coolant of interstellar medium, which can study the physical properties and chemical composition of gas and the energy source of gas emission. The research in (sub)millimeter band is not only of great significance to understand the physical properties of interstellar medium in nearby galaxies, but also can provide important reference for the study of high-redshift galaxies, and can provide key information for us to understand the formation and evolution of galaxies.Although (sub)millimeter lines have many advantages, only some of them can be detected by ground-based equipments, and most of them can only be detected by space telescope in nearby galaxies. However, for high redshift galaxies, they have been redshifted to the window that can be detected by ground-based equipments.Fortunately, with the use of new devices (e.g., Herschel, ALMA), we can make it possible to work with the (sub)millimeter lines. The ground state fine-structure transitions of atoms and ions in these lines are basically unaffected by dust extinction. At the same time, their self absorption is usually very weak (optically thin), and the emitted photons can basically escape from the gas cloud. In addition, because the excitation energy required by these lines is within a few hundred K, they are easy to collide with electrons, hydrogen atoms and hydrogen molecules, which makes them an important coolant for interstellar medium in various states and an excellent probe for the physical environment of gas cloud. As more and more fine-structure transitions of other atoms or ions are detected, the joint observation of these lines provides key diagnostics for the physical properties of atoms and ionized gas in interstellar medium, such as the hardness of the ultraviolet radiation field, the temperature density and mass of the gas, and the metallicity.In this paper, we first introduce how to explore the star formation properties (such as the calibration of star formation rate and the determination of the star formation mode) using different (sub)millimeter lines; Then, we review for the different methods of measuring the total molecular mass with (sub)millimeter lines, and make comparison among these methods. Meanwhile, we discuss the dependence of these methods on galactic properties. At last, we summarize the use of CO (CO spectral line energy distribution and the ratio of mid-J CO emission to infrared continuum) and other lines to diagnose the power sources in galaxies. At the end of the paper, we introduce the work (energy diagnosis and star formation rate calibration) and the main results of the target source-NGC 1266 using (sub)millimeter lines. |
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