The Role of Bulge Formation in the Homogenization of Stellar Populations at $z\sim 2$ as revealed by Internal Color Dispersion in CANDELS

Abstract

We use data from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey to study how the spatial variation in the stellar populations of galaxies relate to the formation of galaxies at $1.5<z<3.5$. We use the Internal Color Dispersion (ICD), measured between the rest-frame UV and optical bands, which is sensitive to age (and dust attenuation) variations in stellar populations. The ICD shows a relation with the stellar masses and morphologies of the galaxies. Galaxies with the largest variation in their stellar populations as evidenced by high ICD have disk-dominated morphologies (with Sérsic indexes $<2$) and stellar masses between $10<\mathrm{Log}M/{\mathrm{M}}_{\odot }<11$. There is a marked decrease in the ICD as the stellar mass and/or the Sérsic index increases. By studying the relations between the ICD and other galaxy properties including sizes, total colors, star-formation rate, and dust attenuation, we conclude that the largest variations in stellar populations occur in galaxies where the light from newly, high star-forming clumps contrasts older stellar disk populations. This phase reaches a peak for galaxies only with a specific stellar mass range, $10<\mathrm{Log}M/{\mathrm{M}}_{\odot }<11$, and prior to the formation of a substantial bulge/spheroid. In contrast, galaxies at higher or lower stellar masses, and/or higher Sérsic index ($n>2$) show reduced ICD values, implying a greater homogeneity of their stellar populations. This indicates that if a galaxy is to have both a quiescent bulge along with a star forming disk, typical of Hubble Sequence galaxies, this is most common for stellar masses $10<\mathrm{Log}M/{\mathrm{M}}_{\odot }<11$ and when the bulge component remains relatively small ($n<2$).

15 pages, 14 figures

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• Star-Forming Galaxies at Cosmic Noon
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• Predicting Quiescence: The Dependence of Specific Star Formation Rate on Galaxy Size and Central Density at 0.5<z<2.5
• Physical Properties of Sub-galactic Clumps at 0.5 $\le z\le$ 1.5 in the UVUDF
• The MOSDEF Survey: An Improved Voronoi Binning Technique on Spatially Resolved Stellar Populations at z~2
• The MOSDEF Survey: Probing Resolved Stellar Populations at $z\sim 2$ Using a New Bayesian-defined Morphology Metric Called Patchiness
• Improved SED-Fitting Assumptions Result in Inside-Out Quenching at $z\sim 0.5$ and Quenching at All Radii Simultaneously at $z\sim 1$
• Low-redshift analogues of cosmic noon galaxies as laboratories for clumpy star formation