Spatially Resolved Spectroscopy of Passive Spiral Galaxies

TL;DR

This study uses spatially resolved spectroscopy to analyze stellar populations in passive spiral galaxies, revealing age differences between inner and outer regions and suggesting recent star formation cessation.

Contribution

It provides the first spatially resolved stellar population analysis of passive spiral galaxies, highlighting age gradients and potential quenching mechanisms.

Findings

Outer regions have younger stellar populations.

Strong Hδ absorption indicates recent star formation cessation.

Inner regions show older stellar populations.

Abstract

Passive spiral galaxies, despite their spiral morphological appearance, do not have any emission lines indicative of ongoing star formation in their optical spectra. Previous studies have suggested that passive spiral galaxies preferentially exist in infall regions of galaxy clusters, suggesting that the cluster environment is likely to be responsible for creating these galaxies. By carrying out spatially resolved long-slit spectroscopy on four nearby passive spiral galaxies with the Apache Point Observatory 3.5-m telescope, we investigated the stellar populations of passive spiral galaxies separately for their inner and outer regions. In the two unambiguously passive spiral galaxies among the four observed galaxies, H$\delta$ absorption lines are more prominent in the outer regions of the galaxies, whereas the 4000-{\AA} breaks (D$_{4000}$) are strongest in the inner regions of the galaxies. A comparison with a simple stellar population model for the two passive spiral galaxies indicates that the outer regions of the galaxies tend to harbour younger populations of stars. The strong H$\delta$ absorption observed in the outer regions of the sample galaxies is consistent with that of galaxies whose star formation ceased a few Gyrs ago. Because of the large uncertainty in the absorption indices in our samples, further observations are needed in order to place constraints on the mechanisms that quench star formation in passive spiral galaxies.