Measuring And Studying Dust Attenuation In Galaxy With Full Spectral Fitting

The observed spectrum of a galaxy is a combination of several components:a contin-uum,absorption and emission lines.All these components are modified by the dust grains distributed in the inter-stellar space.Dust can affect galaxy spectra over a wide range of wavelengths,from ultraviolet(UV),optical to infrared,by absorbing short wavelength photons in UV/optical and re-emitting photons in the far-infrared,and the absorption is stronger in shorter wavelength.Because dust attenuation can cause changes in the overall shape and amplitude of a galaxy spectrum.Such attenuation has to be taken into account before one can measure the different components of an observed spectrum reliably.How to measure the dust attenuation better is always an important issue in the studies of galaxy formation and evolution.Motivated by previous studies,we develop a new method to estimate the dust attenuation of galaxies from full spectral fitting of their optical spectra.We firstly separate the small-scale features(S)from the large-scale spectral shape(L),by performing a moving average filter.We do the same decomposition to the model templates,and the intrinsic dust-free model spectrum is then derived by fitting the ob-served ratio of the small-scale to large-scale components(S/L)with the S,L components of the models.The selective dust attenuation curve is then determined by comparing the observed spectrum with the dust-free model spectrum.One important advantage of our method is that the estimated dust attenuation curve is independent of the shape of the-oretical dust attenuation curves,but we can measure the curve directly.We have done a series of tests on a set of mock spectra to test how reliable of our method in different cases.The tests show that our method is able to recover the input dust attenuation curves accurately,although the accuracy depends slightly on signal-to-noise ratio(SNR)of the spectra.We select a number of edge-on galaxies with obvious dust lanes from the SDSS? MaNGA survey,deriving and correcting their dust attenuation.The dust lane features largely disappear after we have corrected the effect of dust attenuation.The vertical bright-ness profiles of these galaxies become axis-symmetric and can be well fitted by a simple model proposed for the disk vertical structure.What our method measures is the stellar continuum dust attenuation,E(B-V)star.In addition,We also obtain the gas dust attenuation,E(B-V)_gas,by using the Balmer decrement.Firstly,we use a pipeline to find all the ionized gas regions of all MaNGA MPL9 galaxies.Then,we measure the E(B-V)star and E(B-V)_gas,and study their relation.By comparing this two attenuation,we find that:In H? regions,the two attenu-ation show tight correlation which becomes stronger in higher star formation rate regions.In diffuse ionized gas(DIG)regions,this two attenuation almost have no correlation.In H? regions,E(B-V)star/E(B-V)_gas is most related to the stellar age and has negative correlation with stellar age.Our main results support the two-components dust model in H? regions.In addition,we find that the younger H? regions have less dust while the older H? regions show larger E(B-V)_gas.