Feeding the dead: neutral gas inflow with suppressed star formation in a long-quenched ancient massive galaxy at z~2.7 observed with JWST/NIRSpec

TL;DR

The study presents the first spectroscopic detection of neutral gas inflow into a long-quenched massive galaxy at $z oughly 2.7$ using JWST/NIRSpec. By modeling the NaD absorption with VoigtFit and constraining the stellar population via pPXF with EMILES templates, the authors derive an inflow velocity of $278^{+79}_{-79}$ km s$^{-1}$, a hydrogen column density of $ H oughly 10^{20.66}$ cm$^{-2}$, an inflowing mass of $M_{in} oughly 1.6 imes 10^{8}$ M$_\odot$, and an inflow rate of $\dot{M}_{in} oughly 19^{+6}_{-7}$ M$_\odot$ yr$^{-1}$. Despite this inflow, the galaxy remains quiescent with an upper limit on the SFR of $0.2$ M$_\odot$ yr$^{-1}$ and a SFH indicating most stars formed by $z_{50} oughly 11$; the inflow is thus unlikely to trigger significant star formation and may instead fuel low-level AGN activity or replenish gas without reigniting SF. The findings demonstrate that quiescent galaxies can accrete cold gas post-quenching, particularly in overdense environments, and highlight the need for deeper, spatially resolved follow-up (JWST-IFU and ALMA) to constrain the inflow's origin and fate.

Abstract

We report the spectroscopic detection of neutral gas inflow into a massive ($M_* \simeq 4\times 10^{10} M_\odot$) quiescent galaxy observed at $z_{\rm{spec}} = 2.6576$ with JWST. From the redshifted absorption of the NaI doublet at $λλ5890, 5896 $ Ang, we estimate an inflow velocity $v=278^{+79}_{-79}$ km s$^{-1}$ and a column density $\log(N_{NaI}/\rm{cm^2}) = 13.02^{+0.03}_{-0.03}$. We derive the inflowing mass of the gas $M_{in} = 1.6^{+0.1}_{-0.1} \times 10^8 M_\odot$ and rate $\dot{M}_{in} = 19^{+6}_{-7} \, M_\odot \, \rm{yr}^{-1}$. The presence of several surrounding galaxies suggests that the galaxy may be accreting gas from nearby companions. However, we cannot confirm it with current data and the intergalactic medium or cosmic filaments are also viable sources of the inflowing gas. Despite the ongoing inflow, the galaxy remains quiescent, with an upper limit to the star formation rate of $0.2 \, M_\odot \, \rm{yr}^{-1}$. Moreover, its star formation history suggests that the galaxy has remained quiescent during the past $\sim1$ Gyr, with half of its stars formed by redshift $z_{50}=11^{+18}_{-3}$. We discuss that the inflow is not massive, dense, or long-lived enough to ignite significant star formation, or it is fueling low-level AGN activity instead. This is direct evidence that quiescent galaxies can accrete cold gas after their quenching while keeping their star formation subdued. Follow-up observations with JWST and ALMA will be needed to constraint the nature of the inflowing gas.

Figures (12)

• Figure 1: JWST spectrum and photometry of GLASS-180009. The top, middle, and bottom panels show the wavelength regions corresponding to the G140H/F100LP, G235H/F170LP, and G395H/F290LP gratings, respectively. In each panel, the grating and PRISM spectra are plotted with black and blue curves, respectively, while the photometric data are shown as orange circles. The two spectra are rescaled to the photometry. The missing wavelength regions of the grating spectrum are the detector gaps. The main absorption and emission lines detected are highlighted with dashed vertical lines. In the middle panel, we show a zoom-in of the NaD absorption feature from the grating spectrum. The vertical red dashed lines show the expected wavelengths of the two NaI absorption lines at $\lambda \lambda \, 5890, 5896 \, \AA$, while the observed features are evidently redshifted.
• Figure 2: Best-fit of the JWST high-resolution spectrum of GLASS-180009. Top panel: the black curve is the observed spectrum; the red curve is the best-fit stellar spectrum; the magenta curve is the best fit of the gas emission lines; the orange curve is the combined best fit of the stars and gas; the gray shaded regions are the spectral regions masked during the fit. The two insets in the upper right corner show the zoom-in of the [OII] and H$\alpha$+[NII] line fits. Bottom panel: the green diamonds, $\chi$, are the difference between the observed spectrum and best-fit model spectrum divided by the errors. The blue horizontal line is the median $\chi$ value.
• Figure 3: Left panel: map of the mass weights assigned by pPXF to each input template of given age and metallicity from the regularized fit. Right panel: fraction of mass weight as a function of the lookback time. The SFH is calculated as the cumulative sum of the weights. The red and blue lines indicate $t_{50}$ and $t_{95}$, respectively.
• Figure 4: NaD absorption features of the inflowing neutral gas. The black curve is the observed spectrum corrected for the stellar continuum. The gray regions indicate the errors on the flux. The red curve is the best-fitting solution of VoigtFit. The black (red) vertical lines indicate the wavelengths of the two expected (observed) NaI absorption lines.
• Figure 5: NIRCam imaging of GLASS-180009 in the F277W filter. The scale is shown in the lower left corner. The target galaxy is marked with a cross. The big dashed circle demarcate a surrounding region of about 150 kpc at the galaxy's redshift. The small circles highlight the 8 galaxies within 150 kpc projected distance having redshift comparable to that of our target galaxy. The UNCOVER catalog ID of each galaxy is reported close to each circle.