Spatially Resolving Stellar Mass-to-light Ratios Of Low-redshift Galaxies

The stellar mass-to-light ratio(M_*/L)in a given band shows tight correlations with optical colors,and these correlations have been widely used as cheap estimators of galaxy stellar mass.However,such estimators are usually calibrated either using broad band spectral energy distributions(SEDs)or spectroscopy at galactic centers.It is unclear whether the same estimators can provide unbiased M_*/L for different regions of galaxies.In this work we made use of the IFU spectra from Ma NGA and examine the spatially resolved M_*/L as obtained from full spectral fitting as a function of different color indices,as well as galaxy properties including morphology type,distance to galactic center and also stellar population parameters such as stellar age and metallicity.We aim to find a best color index that may provide accurate M*/L estimation for different types of galaxies and different regions within galaxies.Our analysis shows that considering combining multiple colors and/or including other properties to reduce the systematics and scatters of the estimator doesn't work better than a single color index defined by two bands.And thecolor is better than any other color indices,and it provides almost unbiased(M_*/L)for all the SDSS five bands and for all types of galaxies or regions,with only slight biases depending on stellar age and metallicity.We've applied our estimator to the Ma NGA galaxies and are able to well reproduce the M*/L map in most cases.The estimator may be applied in future to obtain surface mass density maps for large samples of galaxy images at both low-z and high-z.Bar structures are common in spiral galaxies,and there has been observational evidence that bar structures play an important role in inducing gas inflow to enhance the formation of stars in the center of galaxies and promote the growth of bulge.The study of the central drop down in the radial distribution of colors can help us verify the role of bars in galaxy evolution.In this work,we defined a sample of 23 galaxies with a drop down in the center of radial distribution of colors,and confirmed that they all have enhanced star formation in the center.We believeed that they are in the transition from'Blue Cloud'to'Red Sequence'and were not related to the active galactic nucleus and dust extinction.The correlation analysis between the color drop-down characteristics and galaxy structure shows that the bar structure is the main reason to promote the central star formation and cause the color's drop-down,which again confirms the previous research conclusion that the bar structure promotes the growth of bulge and consumes the gas in the galaxy center.