Spiral-like star-forming patterns in CALIFA early-type galaxies

TL;DR

This study reveals faint spiral-like star-forming features in the outskirts of early-type galaxies, indicating ongoing inside-out growth and providing insights into spiral structure formation in triaxial stellar systems.

Contribution

It reports the detection of faint spiral-arm-like features in early-type galaxies using combined SDSS imaging and CALIFA spectroscopy, highlighting ongoing growth and structural evolution.

Findings

Detection of faint spiral-like features in ETGs outskirts

Inner LINER and outer HII-region nebular zones identified

Implications for aperture effects in spectroscopic studies

Abstract

Based on a combined analysis of SDSS imaging and CALIFA integral field spectroscopy data, we report on the detection of faint (24 < {\mu}$_r$ mag/arcsec$^2$ < 26) star-forming spiral-arm-like features in the periphery of three nearby early-type galaxies (ETGs). These features are of considerable interest because they document the still ongoing inside-out growth of some local ETGs and may add valuable observational insight into the origin and evolution of spiral structure in triaxial stellar systems. A characteristic property of the nebular component in the studied ETGs, classified i+, is a two-radial-zone structure, with the inner zone that displays faint (EW(H\alpha)$\simeq$1{\AA}) low-ionization nuclear emission-line region (LINER) properties, and the outer one (3{\AA}<EW(H\alpha)<~20{\AA}) HII-region characteristics. This spatial segregation of nebular emission in two physically distinct concentric zones calls for an examination of aperture effects in studies of type i+ ETGs with single-fiber spectroscopic data.