SDSS-IV MaNGA: Stellar M/L gradients and the M/L-colour relation in galaxies

The stellar mass-to-light ratio gradient in SDSS $r-$band $\nabla (M_*/L_r)$ of a galaxy depends on its mass assembly history, which is imprinted morphology and gradients age, metallicity, initial function (IMF). Taking MaNGA sample 2051 galaxies with masses ranging from $10^9$ to $10^{12}M_\odot$ released DR15, we focus face-on galaxies, without merger bar signatures, investigate the dependence 2D other properties, including $M_*/L_r$-colour relationships by assuming fixed Salpeter IMF as normalization reference. median M_*/L_r\sim -0.1$ (i.e., $M_*/L_r$ larger at centre) for massive becomes flat around $M_*\sim 10^{10} M_{\odot}$ change sign 0.1$ lowest masses. inside half light radius increases increasing mass; each bin, early-type have highest value, while pure-disk late-type smallest. Correlation analyses suggest that mass-weighted age dominant parameter influencing profile, since luminosity-weighted easily affected star formation when specific rate (sSFR) higher than $10^{-3} {\rm Gyr}^{-1}$. With increased sSFR gradient, one can obtain steeper negative (M_*/L_r)$. scatter slopes $M_*/L$-colour relations sSFR, example, slope post-starburst be flattened $0.45$ global value $0.87$ $M_*/L$ vs. $g-r$ diagram. Hence converting colours should done carefully, especially those young ages, quite different histories.