SDSS-IV MaNGA: global stellar population and gradients for about 2000 early-type and spiral galaxies on the mass–size plane

Abstract

We perform full spectrum fitting stellar population analysis and Jeans\nAnisotropic modelling (JAM) of the stellar kinematics for about 2000 early-type\ngalaxies (ETGs) and spiral galaxies from the MaNGA DR14 sample. Galaxies with\ndifferent morphologies are found to be located on a remarkably tight mass plane\nwhich is close to the prediction of the virial theorem, extending previous\nresults for ETGs. By examining an inclined projection (`the mass-size' plane),\nwe find that spiral and early-type galaxies occupy different regions on the\nplane, and their stellar population properties (i.e. age, metallicity and\nstellar mass-to-light ratio) vary systematically along roughly the direction of\nvelocity dispersion, which is a proxy for the bulge fraction. Galaxies with\nhigher velocity dispersions have typically older ages, larger stellar\nmass-to-light ratios and are more metal rich, which indicates that galaxies\nincrease their bulge fractions as their stellar populations age and become\nenriched chemically. The age and stellar mass-to-light ratio gradients for\nlow-mass galaxies in our sample tend to be positive ($\\rm centre<outer$), while\nthe gradients for most massive galaxies are negative. The metallicity gradients\nshow a clear peak around velocity dispersion $\\log_{10} \\sigma_{\\rm e}\\approx\n2.0$, which corresponds to the critical mass $\\sim 3\\times 10^{10}M_{\\odot}$ of\nthe break in the mass-size relation. Spiral galaxies with large mass and size\nhave the steepest gradients, while the most massive ETGs, especially above the\ncritical mass $M_{\\rm crit}\\ge 2\\times 10^{11} M_{\\odot}$, where slow rotator\nETGs start dominating, have much flatter gradients. This may be due to\ndifferences in their evolution histories, e.g. mergers.\n