| A galaxy is a massive, gravitationally bound system consisting of stars, stellar remnants, an interstellar medium of gas and dust and dark matter. Hubble’s scheme divides galaxies into3broad classes:elliptical galaxies, spiral galaxies and irregular galaxy. Galaxy morphology has many structures that are suggestive of various processes or stages of secular evolution. This thesis performs spatial resolved study of nearby spiral galaxies from two aspects:star formation regions and pixel-to-pixel stellar population properties in nearby galaxies.Nearby galaxies supply us with the opportunity to study galaxy dynamic-s and star formation on large scales, yet are close enough to reveal the details. Star-formation regions in nearby galaxies provide an excellent laboratory to s-tudy star formation processes, evolution of massive stars and the properties of the surrounding interstellar medium. A wealth of information can be obtained from the spectral analysis of the bright emission lines and the stellar continuum. Considering these, we proposed a long-term project "Spectroscopic Observations of the Star Formation Regions in Nearby Galaxies".In the second chapter, we described a more detailed on the subject of scientific goals, sample definitions and observational strategies. Using these spectral data of star-forming regions, combined with multi-band image data, research can be carried out on dust extinction, star formation rate, metallicity, two-dimensional stellar population properties and other aspects.As the first step, we present spectroscopic observations from3650-8000A of a sample of80HⅡ regions in spiral galaxy NGC2403, using2.16m telescope at Xinglong Station of National Astronomical Observatory of China (NAOC).(1) We examine the physical properties of these HⅡ regions. Compared HeIλ5876/Hβ diagnostic with single-star nebular models suggests that the effective temperature (Teff) of the central stars～40000K. The electron density are consistent with the low electron density limit.(2) We separated the ionization parameter from the abundance used [NⅡ]/[OⅡ] vs.[OⅢ]/[OⅡ] diagnostic diagram. For a homo-geneous sample of HⅡ regions in one galaxy, ionization parameters have a widely coverage. Most of metallicity calibrators show strong dependence on ionization parameter excepted R23parameter.(3) Oxygen abundance and radial gradient are obtained. We fitted the slope of-0.045±0.001dexkpc-1. Considered pos-sible abundance break occurs in corotation radius, a two-slope linear fit is also presented and the inner disk is steeper to-0.071±0.002dexkpc-1.(4) Finally, we estimate stellar age in HⅡ region from EW(Eα) using STARBURST99mod-els. It shows no evidence of age gradient along galaxy radius. The ages of HⅡ regions are about2.5to7Myr. As a flocculent spiral, the driver of star formation in NGC2403maybe more complex.As a second part, multi-band photometric images from ultraviolet and optical to infrared are collected to derive spatially resolved properties of a nearby Scd type galaxy M101. With evolutionary stellar population synthesis models, two-dimensional distributions and radial profiles of age, metallicity, dust attenuation and star formation timescale in the form of the Sandage star formation history are obtained.(1) When fitting with the models, we use the IRX-AFUV relation, found to depend on a second parameter of birth rate b (ratio of present and past-averaged star formation rate), to constrain the dust attenuation. There are obvious parameter gradients in the disk of M101, which supports the theory of an "inside-out" disk growth scenario.(2) Two distinct disc regions with different gradients of age and color are discovered, similar to another late-type galaxy NGC628.(3) The metallicity gradient of the stellar content is flatter than that of HⅡ regions.(4) The stellar disk is optically thicker inside than outside and the global dust attenuation of this galaxy is lower, compared with galaxies of similar and earlier morphological type.(5) We highlight that a variational star formation timescale describes the real star formation history of a galaxy. The timescale increases steadily from the center to the outskirt. We also confirm that the bulge in this galaxy is a disk-like pseudo-bulge, whose evolution is likely to be induced by some secular processes of the small bar with relatively young age, rich metal, and much dust. |
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