2024ApJ...974..238L

We analyze the properties of a rare population, the strongly bulge-dominated early-type galaxies (sBDEs) with significant H I gas, using the databases from the FAST All Sky H I survey (FASHI) and the Arecibo Legacy Fast ALFA (ALFALFA) survey. We select the sBDEs from the Sloan Digital Sky Survey and crossmatch with the FASHI-ALFALFA combined H I sample, resulting in 104 H I-rich sBDEs. These sBDEs tend to have extremely high H I reservoirs, which is rare in previous studies such as ATLAS^3D. A total of 70% of the selected sBDEs are classified as quiescent galaxies, even though they have a large H I reservoir. We study the properties of these sBDEs from four main aspects: stellar population, gas-phase metallicity, stacked H I spectra, and environment. The majority of H I-rich sBDEs appear to show lower gas-phase metallicity and are located in significantly lower-density environments, suggesting an external origin for their H I gas. We find that star-forming sBDEs exhibit statistically higher star formation efficiency and slightly older stellar populations compared to normal star-forming galaxies, suggesting a recent star formation on the Gyr timescale. They also show narrower and more concentrated H I profiles compared to control star-forming galaxies, which may explain their higher star formation efficiency.