Evidence of Inside-out Multi-stage Formation History in UV-bright Early Type Galaxies Observed in the Mid-IR
Abstract
The origin of significant UV emission in quiescent early type galaxies (ETGs) is currently still debated, and strongly tied to a multi-epoch evolutionary process where much of the information is lost after progressing well beyond relaxation timescales. In order to address this topic, stellar synthesis and galaxy evolution must be disentangled, which can be more pragmatically done with well-resolved multi-wavelength images of nearby ETGs. We explore the radial distribution of FUV-NUV, NUV-r, and NUV-IR colors (GALEX, SDSS, and WISE) in a selection of nearby E/S0-type galaxies. Comparing these colors with stellar synthesis models, we find strong color gradients with the outer radii bluer than the inner half-light radii by ~1 magnitude, and account for it with an extreme horizontal branch fraction increase of 0.25 with radius. We estimated the average ages and determine that outer regions are likely to have formed ~1 Gyr after the inner regions. The results support inside-out formation: rapid star formation within the core at early epochs (>4 Gyr ago) and at least one later stage starburst event coinciding with 1.
- Publication:
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American Astronomical Society Meeting Abstracts #223
- Pub Date:
- January 2014
- Bibcode:
- 2014AAS...22312903P