English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

In the local Universe, 10% of massive elliptical galaxies are observed toexhibit a peculiar property: a substantial excess of ultraviolet emission (UVX)over what is expected from their old, red stellar populations. Several originsfor the UVX have been proposed, including a population of hot young stars, or apopulation of old, blue horizontal branch or extended horizontal branch (BHB orEHB) stars that have undergone substantial mass loss from their outeratmospheres. We explore the radial distribution of ultraviolet excess (UVX) ina selection of 49 nearby E/S0-type galaxies by measuring the extendedphotometry in the UV-midIR with GALEX, SDSS and WISE. We compare UV/optical andUV/mid-IR colors with the Flexible Stellar Population Synthesis with EHB models(Conroy & Gunn 2010). We find that combined WISE mid-IR and GALEX UV colors aremore effective in distinguishing models than optical colors, and that theUV/mid-IR combination is sensitive to EHB fraction. There are strong colorgradients with the outer radii bluer than the inner half-light radii by ~1magnitude. This color difference is easily accounted for with a BHB fractionincrease of 0.25 with radius. We estimated the average ages for the inner andouter radii are 7.0+/-0.3 Gyr, and 6.2+/-0.2 Gyr, respectively, with theimplication that the outer regions are likely to have formed ~1 Gyr after theinner regions. Additionally, we find that metallicity gradients are likely nota significant factor in the color difference. The separation of color betweenthe inner and outer regions, which agrees with a specific stellar populationdifference (e.g., higher EHB populations), and the ~0.5-2 Gyr age differencesuggests multi-stage formation. Our results are best explained by inside-outformation: rapid star formation within the core at early epochs (>4 Gyr ago)and at least one later stage starburst event coinciding with z~1

UV-bright nearby early type galaxies observed in the mid-infrared: evidence for a multi-stage formation history by way of WISE and GALEX imaging