RECONSTRUCTING THE STELLAR MASS DISTRIBUTIONS OF GALAXIES USING S⁴G IRAC 3.6 AND 4.5 μm IMAGES. II. THE CONVERSION FROM LIGHT TO MASS

Abstract

We present a new approach for estimating the 3.6 µm stellar mass-to-light ratio Υ 3.6 in terms of the [3.6]-[4.5] colors of old stellar populations. Our approach avoids several of the largest sources of uncertainty in existing techniques using population synthesis models. By focusing on mid-IR wavelengths, we gain a virtually dust extinction-free tracer of the old stars, avoiding the need to adopt a dust model to correctly interpret optical or optical/NIR colors normally leveraged to assign the mass-to-light ratio Υ. By calibrating a new relation between NIR and mid-IR colors of giant stars observed in GLIMPSE we also avoid the discrepancies in model predictions for the [3.6]-[4.5] colors of old stellar populations due to uncertainties in the molecular line opacities assumed in template spectra. We find that the [3.6]-[4.5] color, which is driven primarily by metallicity, provides a tight constraint on Υ 3.6 , which varies intrinsically less than at optical wavelengths. The uncertainty on Υ 3.6 of ∼0.07 dex due to unconstrained age variations marks a significant improvement on existing techniques for estimating the stellar M/L with shorter wavelength data. A single Υ 3.6 =0.6 (assuming a Chabrier IMF), independent of [3.6]-[4.5] color, is also feasible as it can be applied simultaneously to old, metalrich and young, metal-poor populations, and still with comparable (or better) accuracy (∼0.1 dex) as alternatives. We expect our Υ 3.6 to be optimal for mapping the stellar mass distributions in S 4 G galaxies, for which we have developed an Independent Component Analysis technique to first isolate the old stellar light at 3.6 µm from non-stellar emission (e.g. hot dust and the 3.3 PAH feature). Our estimate can also be used to determine the fractional contribution of non-stellar emission to global (rest-frame) 3.6 µm fluxes, e.g. in WISE imaging, and establishes a reliable basis for exploring variations in the stellar IMF.

SUPERMASSIVE BLACK HOLES AND THEIR HOST SPHEROIDS. II. THE RED AND BLUE SEQUENCE IN THE MBH–M*,SPH DIAGRAM

“…Bulge luminosities 9 (Table 1) from Paper Iwere converted into stellar masses using a constant 3.6 m m mass-to-light ratio, 0.6 3.6 G = (Meidt et al 2014). We additionally explored a more sophisticated way to compute mass-to-light ratios, using the color-3.6 G relation published by Meidt et al (2014), their Equation (4)), which allows one to estimate 3.6 G of a galaxy from its Table 1) when available for our galaxies, or were estimated from the bulge stellar velocity dispersion, σ, using the color-σ relation presented by Peletier et al (2012, their Figure 6).…”

“…We additionally explored a more sophisticated way to compute mass-to-light ratios, using the color-3.6 G relation published by Meidt et al (2014), their Equation (4)), which allows one to estimate 3.6 G of a galaxy from its Table 1) when available for our galaxies, or were estimated from the bulge stellar velocity dispersion, σ, using the color-σ relation presented by Peletier et al (2012, their Figure 6). We found that the range in [3.6]-[4.5] color is small (0.06 mag), and thus the range in 3.6 G is also small (0.04).…”

Asymmetric mass models of disk galaxies

“…Velocity fields of these types of galaxies are rich with information that are worth investigating. Furthermore, as resolved SPS models as in Zibetti et al (2009), Corbelli et al (2014, Meidt et al (2014), and Rahmani et al (2016) are in their early stages, derivations of many more stellar density maps is strongly encouraged to be able to quantify the asymmetries of the gravitational potential of stellar disks directly. This is more straightforward for the gas component since atomic and molecular surface density maps are routinely acquired with mm and cm arrays.…”

Large scale kinematics and dynamical modelling of the Milky Way nuclear star cluster

“…Under this assumption, McGaugh & Schombert (2013) found a mean value of (0.5 ± 0.1) M /L ,3.6 µm in disk galaxies. Meidt et al (2014) constrained the mean value to 0.6 M /L ,3.6 µm . The mass-to-light ratio at 4.5 µm should be similar or even less than the massto-light ratio at 3.6 µm (Oh et al 2008).…”