THE <i>SPITZER</i> SURVEY OF STELLAR STRUCTURE IN GALAXIES (S ⁴ G): PRECISE STELLAR MASS DISTRIBUTIONS FROM AUTOMATED DUST CORRECTION AT 3.6 <i>μ</i> m

Abstract

The mid-infrared is an optimal window to trace stellar mass in nearby\ngalaxies and the 3.6$\\mu m$ IRAC band has been exploited to this effect, but\nsuch mass estimates can be biased by dust emission. We present our pipeline to\nreveal the old stellar flux at 3.6$\\mu m$ and obtain stellar mass maps for more\nthan 1600 galaxies available from the Spitzer Survey of Stellar Structure in\nGalaxies (S$^{4}$G). This survey consists of images in two infrared bands (3.6\nand 4.5$\\mu m$), and we use the Independent Component Analysis (ICA) method\npresented in Meidt et al. (2012) to separate the dominant light from old stars\nand the dust emission that can significantly contribute to the observed 3.6$\\mu\nm$ flux. We exclude from our ICA analysis galaxies with low signal-to-noise\nratio (S/N &lt; 10) and those with original [3.6]-[4.5] colors compatible with an\nold stellar population, indicative of little dust emission (mostly early Hubble\ntypes, which can directly provide good mass maps). For the remaining 1251\ngalaxies to which ICA was successfully applied, we find that as much as 10-30%\nof the total light at 3.6$\\mu m$ typically originates from dust, and locally it\ncan reach even higher values. This contamination fraction shows a correlation\nwith specific star formation rates, confirming that the dust emission that we\ndetect is related to star formation. Additionally, we have used our large\nsample of mass estimates to calibrate a relationship of effective mass-to-light\nratio ($M/L$) as a function of observed [3.6]-[4.5] color: $\\log(M/L)=-0.339\n(\\pm 0.057) \\times ([3.6]-[4.5]) -0.336 (\\pm 0.002)$. Our final pipeline\nproducts have been made public through IRSA, providing the astronomical\ncommunity with an unprecedentedly large set of stellar mass maps ready to use\nfor scientific applications.\n