The half mass radius of MaNGA galaxies: Effect of IMF gradients

Abstract

Gradients in the stellar populations of galaxies -e.g., in age, metallicity, IMF -can result in gradients in the stellar mass to light ratio, M * /L. Such gradients imply that the distribution of the stellar mass and light are different. For old stellar populations, such as those typical of early-type galaxies at z ∼ 0, the M * /L gradients are weak if driven by variations in age and metallicity. However, if they are driven by variations in the stellar Initial Mass Function (IMF), then they can be significantly larger. An IMF-driven gradient which has M * /L decreasing outwards from the center increases the estimated total stellar mass (M * ) and reduces the scale which contains half this mass (R e, * ), compared to the values of mass and size when the gradient is ignored. We estimate IMF-gradients from spatially resolved spectra of early-type galaxies in the final release of the MaNGA survey, showing that the fractional decrease in R e, * can be significantly larger than the fractional M * increase, especially when the light is more centrally concentrated. The R e, * −M * correlation which results from the IMF-driven M * /L gradients at z ∼ 0 is offset by almost 0.3 dex to smaller sizes compared to when these gradients are ignored. Comparison with higher redshift samples is not straightforward. If it is fair to compare z ∼ 0 'early-type' galaxies with 'quiescent' galaxies at higher-z, then one must be able to consistently account for evolution in stellar population gradients (especially age and IMF) as well as changes in the steepness of the light profile before drawing conclusions about the evolution of the R e, * − M * relation.

JWST reveals a population of ultra-red, flattened disk galaxies at 2

“…Many quiescent, massive galaxies are either extremely flattened (lenticular) or significantly rotationally supported (fast-rotators; Cappellari et al 2011). We refer back to the the mass-weighted size-mass relation for S0 and fast-rotating galaxies from the MANGA survey (Bernardi et al 2022), as shown in Fig. 4a.…”

“…The grey points show the F444W sizes from Suess et al (2022a) for 1.0 < z < 2.5 galaxies at M * > 10 9 M , and the red symbols show UFOs. To guide the eye, the black lines show the relationship between half-mass radius and stellar mass at z ∼ 2(Suess et al 2019), and the blue lines show the size-mass relation for S0s and fast rotators fromBernardi et al (2022). Center: distribution of observed axis ratios and example population models with various intrinsic 3D shapes.…”

Coincidence between morphology and star formation activity through cosmic time: the impact of the bulge growth

“…The choice of the quantity of mock galaxies to be used for each object was taken as a good compromise between computational time and accuracy of the result. (Bernardi et al 2022) recently showed that a gradient in stellar population can reflect a gradient in the stellar mass-to-light (M/L) ratio within a galaxy, consequently affecting the 𝐵/𝑇. However, since we decide to use a constant IMF, the M/L is expected to be constant within a galaxy.…”

Rest-frame Near-infrared Sizes of Galaxies at Cosmic Noon: Objects in JWST's Mirror Are Smaller than They Appeared

“…However, these empirical structural measurements are fundamentally limited by the fact that even the longest wavelengths observed by HST (1.6 μm) correspond to restframe optical light at z ∼ 2, and shift into the rest-frame ultraviolet at higher redshifts. Local galaxies are known to exhibit radial gradients in their mass-to-light (M/L) ratios caused by gradients in their stellar ages, metallicities, or dust attenuation (e.g., Saglia et al 2000;La Barbera et al 2005;Tortora et al 2010;Greene et al 2015;Woo & Ellison 2019;Bernardi et al 2022). If these M/L gradients also exist at earlier time, then light-weighted size measurements at z ∼ 2 could differ significantly from mass-weighted sizes.…”