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

Thin and thick disks are found in most spiral galaxies, yet their formationscenarios remain uncertain. Whether thick disks form through slow or fast,internal or environmental, processes is unclear. The physical origin of outertruncations in thin and thick disks, observed as a drop in optical andnear-infrared (NIR) surface brightness profiles, is also a much debated topic.These truncations have been linked to star formation (SF) thresholds inMilky-Way type galaxies, but no such connection has been made for theirlow-mass counterparts or in thick disks. Our photometric analysis of theedge-on galaxy UGC 7321 offers a possible breakthrough. This well-studieddiffuse, isolated, bulgeless, ultra-thin galaxy is thought to be under-evolvedboth dynamically and in SF. It is an ideal target to disentangle internaleffects in the formation of thick disks and truncations. Our axial lightprofiles from deep far- and near-ultraviolet (UV; GALEX) images, tracing recentSF, and optical (DESI grz) and NIR (Spitzer 3.6 microns) images, tracing oldstellar populations, enable a detailed identification of an outer truncation inall probed wavelengths in both the thin and thick disks. After deprojecting toa face-on view, a sharp truncation signature is found at a stellar density ofroughly 1.5 solar masses per square parsec, in agreement with theoreticalexpectations of gas density SF thresholds. The redder colours beyond thetruncation radius are indicative of stellar migration towards the outerregions. We thus show that thick disks and truncations can form via internalmechanisms alone, given the pristine nature of UGC 7321. We report thediscovery of a truncation at and above the mid-plane of a diffuse galaxy thatis linked to a SF threshold; this poses a constraint on physically-motivateddisk size measurements among low-mass galaxies.

Linking star formation thresholds and truncations in the thin and thick disks of the low-mass galaxy UGC 7321