Dust Reddening In Star-forming Galaxies And Exploring The Low-mass End Of The M_BH-σ* Relation With Active Galaxies

In last decade, it is one of the most important discovery in galaxy study that therelationshipbetweencentralblackholemassandgalaxybulgeproperties,whichimpliesthe co-evolution of black hole and star formation is a key problem in understandingthe galaxy formation and evolution. A significant uncertainty in comparison betweenthe theory and observation of star formation in galaxy is due to dust absorption andreradiation. The most uncertain relationship between central black hole and galaxy isthe low-mass end of M_BHσrelation. We search for low-mass central black holes inactive galaxies in the local Universe, and the host galaxies are mainly disk-dominated;the star formation is active in disk galaxies, therefore, the objects investigated in thisthesis work are mainly disk galaxies.We present empirical relations between the global dust reddening and other phys-ical galaxy properties including the Hαluminosity, Hαsurface brightness, metallicityand axial ratio for star-forming disk galaxies. The study is based on a large sampleof～22 000 well-defined star-forming galaxies selected from the Sloan Digital SkySurvey (SDSS). The reddening parameterized by color excess E(B V ) is derivedfrom the Balmer decrement. The galactic extinction curve is better than other extinc-tion/attenuation curves in dust-attenuation correction applied to star-forming regions ofdisk galaxies in local universe; and the intrinsic scatter between our SFR derived fromemission-line luminosity corrected for dust extinction and the SFR derived from far-infrared luminosity is less than 0.13dex, which is even less than the calibration uncer-tainty quoted in the literature. Besides the dependency of reddening on Hαluminosity/ surface brightness and gas phase metallicity, it is also correlated with the galaxy in-clination, in the sense that edge-on galaxies are more attenuated than face-on galaxiesat a give intrinsic luminosity. In light of these correlations and fundamental physicalconsiderations, we present the empirical formulae of E(B V ) as a function of thesegalaxy properties, with a scatter of only 0.07 mag, which could be almost explained bythe uncertainties in the physical variables involved. The offset between the observedreddening and predicted value from the empirical formulae, does not correlate with theany of the variables, including stellar mass, 4000 break strength or electron densitywithin the galaxy.We present a plane-parallel slab toy model to reproduce the observed trends be-tween E(B V ) and surface brightness in our sample. From the comparisons of the models to the observation, we find that the relative vertical scale of dust distributionto HII regions distribution may vary with Hαsurface brightness or metallicity. Theobserved trends can be reproduced if most dust attenuation to the HII region is dueto diffuse interstellar dust distributing in a disk thicker than that of HII regions. Theempirical relations, which suggest dust reddening is partially dependent on metallici-ty (∝Z^0.6～0.7), can be an observational constraints on the output of radiative-transfermodel calculations, and hence provides constraints on the assumed dust-to-gas ratio inthemodel. Theempiricalformulaecanbealsoincorporatedintosemi-analyticalmodelsofgalaxyformationandevolutiontoestimatethedustreddeningandenablecomparisonwith observations more practically.In order to investigate the low-mass end of M_BHσrelation, we select 76 Seyfer-t 1 galaxies from the recent catalog of Greene & Ho (2007), and get new measure-ments of stellar velocity dispersions, using spectra obtained with the Keck EchelletteSpectrograph and Imager (ESI) and the Magellan Echellette (MagE). These object-s were selected from the Sloan Digital Sky Survey (SDSS) to have estimated blackhole (BH) masses below 2×10⁶M⊙. Combining our results with previous ESI ob-servations of similar objects, we obtain an expanded sample of 93 active galaxies andexamine the relation between BH mass and velocity dispersion (the M_BHσrela-tion) for active galaxies with low BH masses. The low-mass active galaxies tend tofollow the extrapolation of the M_BHσrelation of inactive galaxies. Including re-sults for active galaxies of higher BH mass from the literature, we find a zero pointα= 7.68±0.08 and slope ofβ= 3.32±0.22 for the M_BHσrelation [in the formlogM_BH=α+βlog(σ/200 km s 1)], with intrinsic scatter of 0.46±0.03 dex. Thisresult is consistent, within the uncertainties, with the slope of the M_BHσrelationfor reverberation-mapped active galaxies with BH masses from 10⁶to 10⁹M⊙. Forthe subset of our sample having morphological information from Hubble Space Tele-scope images, we examine the slope of the M_BHσrelation separately for subsamplesof barred and unbarred host galaxies, and find no significant evidence for a differencein slope. We do find a mild offset between low-inclination and high-inclination diskgalaxies, such that more highly inclined galaxies tend to have largerσat a given valueof BH mass, presumably due to the contribution of disk rotation within the spectro-scopic aperture. We also find that the velocity dispersion of the ionized gas, measuredfrom narrow emission lines including [N II]λ6583, [S II]λλ6716,6731, and the core of[O III]λ5007 (with the blueshifted wing removed), trace the stellar velocity dispersionwell for this large sample of low-mass Seyfert 1 galaxies.