What is the True HI Gas Content in Massive Quiescent Galaxies in the Local Universe?

TL;DR

Massive quiescent galaxies in the local universe exhibit an unprecedentedly wide range of atomic HI content, with two-thirds being extremely HI-poor. By conducting deep FAST HI observations on a morphology- and mass-selected, representative sample and comparing to ATLAS$^{3D}$ and xGASS, the study shows that HI-poor galaxies are not limited to early-type morphologies but are strongly linked to environment, particularly satellite status, though centrals can also be HI-poor. The results challenge existing HI mass estimators, which overpredict HI for non-detections in this population and reveal the need for non-Gaussian scatter and morphology–environment dependent calibrations. Overall, the work underscores that multiple physical processes beyond simple morphology or environment regulate the cold gas reservoirs in local massive quiescent galaxies, motivating deeper, unbiased HI surveys and refined models of gas content.

Abstract

While massive quiescent galaxies are known to be poor in atomic hydrogen (HI), their true HI content remains poorly constrained due to the limited sensitivity and morphological biases of existing surveys. We present deep HI observations using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) for a representative sample of 78 low-redshift massive quiescent galaxies, selected by stellar mass ($M_\ast > 10^{10} M_\odot$) and color (NUV$-r > 5$). Our observations reach an exceptional detection limit of $\log(M_{HI}/M_\ast) = -3$. We find that one-third of the sample follows the predicted HI mass fraction distribution based on previous surveys. However, the majority ($\sim$2/3) exhibit significantly lower HI content, with a $3σ$ upper limit of $\log(M_{HI}/M_\ast) < -3.46$ derived from stacking the non-detections. As a consequence of this enormous dynamic range and the high fraction of non-detections, the HI mass fraction shows no clear correlation with parameters tracing star formation, structure, or morphology. Our FAST sample shows remarkable similarity to the $ATLAS^{3D}$ sample which only includes early-type galaxies, both in its high fraction of HI-poor galaxies and its high satellite fraction among HI-poor galaxies, as indicated by three different environmental characteristics: projected cross-correlation functions, background-subtracted neighbour counts, and central/satellite classification in the SDSS galaxy group catalog. These results suggest that while early-type morphology and environment play crucial roles in suppressing HI reservoirs, neither factor alone fully explains the observed gas depletion, indicating that additional physical mechanisms must be responsible for the extreme HI deficiency prevalent in massive quiescent galaxies.

Figures (13)

• Figure 1: Hi mass fraction as a function of NUV$-r$ (left) and specific star formation rate (right). The gray contours represent the SDSS volume-limited sample. The magenta contours represent the ALFALFA 100 percent sample. The green points indicate the xGASS representative sample. The orange stars denote the $\rm ATLAS^{3D}$ sample. Hi upper limits are shown as downward arrows. The red regions highlight the parameter space of quiescent galaxies.
• Figure 2: NUV$-r$ (left) and Specific star formation rate (right) versus stellar mass. The gray contours represent the SDSS volume-limited sample. Contours from innermost to outermost include 15%, 30%, 45%, 60%, 75%, 90%, and 95% of the volume-limited sample, respectively. The colored symbols indicate the Hi samples (xGASS: green dots; FAST: blue dots; $\rm ATLAS^{3D}$: orange stars). The black dashed lines represent our sample selection criteria (vertical: $M_*>10^{10} M_{\odot}$, horizontal: $\log {\rm sSFR} < -11$ or NUV$-r > 5$).
• Figure 4: Hi fraction as a function of NUV$-r$ and specific star formation rate. The gray contours represent the SDSS volume-limited sample. The colored symbols indicate the Hi samples (xGASS: green dots; FAST: blue dots; $\rm ATLAS^{3D}$ in the Virgo cluster: red stars; $\rm ATLAS^{3D}$ outside the Virgo cluster: orange stars). Upper limits are denoted as downward arrows. The result of the Hi spectral stacking analysis for FAST Hi non-detections is represented by the large open blue circle with a downward arrow. The black horizontal dashed lines indicate $\log M_{\textsc{Hi}}/M_*=-1$ and $-2.4$.
• Figure 5: Hi fraction as a function of concentration and stellar surface mass density. The gray contours represent the volume-limited sample. The FAST sample is denoted as blue points. The orange(red) symbols indicate $\rm ATLAS^{3D}$ galaxies in(outside) the Virgo cluster. The xGASS sample is in green. Hi non-detections are denoted as downward arrows. The black horizontal dashed lines indicate $\log M_{\textsc{Hi}}/M_*=-1$ and $-2.4$.
• Figure 6: Left:Hi fraction as a function of T-type. Colored symbols represent different samples (blue: FAST, orange: $\rm ATLAS^{3D}$, green: xGASS). Hi non-detections are shown as arrows. The gray contours indicate the SDSS volume-limited sample. The horizontal dashed lines correspond to $\log M_{\textsc{Hi}}/M_*=-1$ and $-2.4$. Right:Hi fraction distribution of Hi samples. Real Hi observations are colored in green(detection) and orange(non-detection). Predicted Hi fractions are shown in pink.