A Photometrically and Spectroscopically Confirmed Population of Passive Spiral Galaxies

TL;DR

This study identifies a local population of passive spiral galaxies through photometry and spectroscopy, showing they have ceased star formation without transforming into early-type galaxies, challenging previous assumptions.

Contribution

It provides the first spectroscopic confirmation of passive spiral galaxies in the local universe, demonstrating star formation quenching without morphological transformation.

Findings

Passive spirals lack nebular emission indicative of star formation.

Spectra show old stellar populations with an average age of 2.3 Gyr.

Passive spirals exist locally, not just at high redshift.

Abstract

We have identified a population of passive spiral galaxies from photometry and integral field spectroscopy. We selected z<0.035 spiral galaxies that have WISE colours consistent with little mid-infrared emission from warm dust. Matched aperture photometry of 51 spiral galaxies in ultraviolet, optical and mid-infrared show these galaxies have colours consistent with passive galaxies. Six galaxies form a spectroscopic pilot study and were observed using the Wide-Field Spectrograph (WiFeS) to check for signs of nebular emission from star formation. We see no evidence of substantial nebular emission found in previous red spiral samples. These six galaxies possess absorption-line spectra with 4000\AA\ breaks consistent with an average luminosity-weighted age of 2.3 Gyr. Our photometric and IFU spectroscopic observations confirm the existence of a population of local passive spiral galaxies, implying that transformation into early-type morphologies is not required for the quenching of star formation.