| A galaxy is composed of stars, gas, and dust. Radiation from stars can ionize gaseous nebulae to produce spectral emission lines, and heat dust grains to yield ther-mal continuum emission; at the same time, dust grains obscure stellar emission with distorting spectral energy distributions of stellar populations, and also attenuate spec-tral emission lines from ionized gas. Electromagnetic radiation from galaxies we re-ceive reflects intrinsic properties of stars, gas, and dust, and contains information about the interaction between the three components. This thesis involves a series of stud-ies aimed at discovering stellar population properties and dust extinction influences in galaxies from ultraviolet and infrared radiation, and understanding physical environ-ments of ionized gas in galaxies from optical spectra.This thesis begins with a spatially resolved study of five nearby spiral galaxies, in order to investigate the correlation between infrared-to-ultraviolet luminosity ratio and ultraviolet color (the IRX-UV relation, a widely used recipe to cope with dust attenuation). Through comparison between observational data and relevant models, the results show that, at constant dust attenuation levels, aging of stellar populations tends to produce redder ultraviolet colors, but the diversity of star formation histories is suggested to disperse the age effects; in addition, integrated measurements of galaxies would weaken the age effects as well, due to the mixture of different stellar populations within galaxies. From this study, we can also understand that, an estimate of total infrared luminosity from infrared monochromatic luminosities is likely to be biased by variations in infrared continuum from dust heated by different stellar populations. In this work, the adopted models are constructed with one certain attenuation law, and definite discrepancies appear in the descriptions of some observational data with the model scenarios. In this case, the following part of this thesis focuses on the role of extinction law in the IRX-UV relation. The study of extinction law includes model prediction and observational evidence. From spectral synthesis modeling, linear background and the2175A bump in extinc-tion curve are expected to operate on the variations in ultraviolet color and infrared-to-ultraviolet luminosity ratio; observational signatures of the two extinction parameters are then diagnosed in four nearby spiral galaxies, and the different extinction features provide an description of the diverse IRX-UV properties for these galaxies, in partic-ular interpret the discrepancies between the observational data and the model scenar-ios when adopting one certain attenuation/extinction law. This work complements the characterization of the ultraviolet and infrared observations of galaxies.The dependence of the IRX-UV relation on far-ultraviolet luminosity and radial distance in galaxies is examined in this thesis. Most of the galaxies present weak trends except NGC3031where stellar population types are more relative to far-ultraviolet lu-minosity and radial distance. Two-dimensional maps of ultraviolet color and infrared-to-ultraviolet ratio are also displayed in this thesis, which enables more visual under-standing of the connection and the disparity between the two parameters in galaxies.The last part of this thesis introduces a preliminary study of radial spectra for star-forming regions inside NGC2403. Radial distributions of oxygen abundance within9star-forming regions inside NGC2403are obtained, which apparently shows an in-creasing gradient of oxygen abundance from center to edge for each of the star-forming regions. However, the values of oxygen abundance are estimated from the empirical method, where the adopted emission line indices are not only sensitive to chemical abundance, but also related to other parameters, and in this situation, the nature of the gradients on this small scale within star-forming regions still needs to be investigated. |
PDF Full Text Request