Galaxy evolution as seen by Herschel
Authors:   , Ma Zhiyuan 
Published: April 2021

The unprecedented Herschel data have revolutionized our view of the IR universe, providing new insights to galaxy formation and evolution. However, the Herschel data are still far away from being fully explored, mainly due to three reasons. First, in most of the Herschel wide fields, we are still lacking ancillary data even in the optical/near-IR, which prevents us from doing any follow-up analysis. Second, even in the few fields that have sufficient ancillary data in various archives, there is no homogeneous reduction such that the data can be readily used. Third, but not the least, the long-standing problem of poor spatial resolution in FIR/sub-mm observations severely limits our capability of counterpart identification, and hence creates tremendous obstacles in obtaining redshifts, modeling the spectral energy distributions, deriving star formation rates, etc. In this thesis, I present our approach to attack these problems. My basic task is to establish a methodology that can be applied to all the Herschel wide-field survey data, with the science goal of constructing the largest, well-defined sample of highredshift Ultra-Luminous InfarRed Galaxies (ULIRGs) whose optical-to-far-IR SEDs are accurately measured. We first conduct a comprehensive search of the available archival optical data in the public domain. Moreover, we have been conducting our own deep optical survey, Mizzou WIYN Survey, to observe those fields that lack full range optical data coverage. To facilitate the data reduction process, I have developed APUS, a pipeline building and management tool that offers great repeatability, scalability, and maintainability. With this tool, we can reduce all these data in a uniform manner and create deep optical mosaics. To combat the problem of poor spatial resolution in the Herschel data, we have developed a source de-blending algorithm, which I have implemented as a software tool called CIDer. Using this tool, we can extract the major contributors to the FIR fluxes based on the position priors from the high-resolution optical data. Treating all the Herschel wide-field data is obviously beyond the scope of an individual thesis. Therefore, my thesis mainly focuses on one field, namely the "First Look Survey" field. As the first study case, we compiled and reduced the full-range multi-wavelength data in this field, and constructed the panchromatic SEDs from optical to FIR using CIDer. The redshifts of the sources were found to be ranging from z = 0 to ~ 3. We derived the total IR luminosities by fitting modified black body model or starbursting templates, which are found to be ranges from 3 x 10[superscript 10] to ~ 10[superscript 13] L[SYMBOL]_ after taking into account the cut to ensure reliability of the CIDer result. On the L[subscript IR]-T plane, the sources show the similar turning over behavior as in our previous study Yan and Ma (2016), implies a limited size of the dust star forming sites. Also presented in the thesis is our earlier work on the Herschel-detected SDSS quasars. The project was conducted before we have the CIDer to obtain the fullrange SEDs and thereby the redshifts. Instead, we aimed at the quasars, which we can measure the redshift spectroscopically and to a high redshift. In the project, it is found that the Herschel-detected quasars are mostly ULIRGs, and are forming stars very actively. This implies the co-evolution of extreme AGNs and star formation.