Poststarburst galaxies (PSBs), identified by strong Balmer absorption and weak nebular emission, provide a key laboratory for studying rapid quenching. Using the final data release of the Sloan Digital Sky Survey IV MaNGA survey, we follow the traditional PSB selection criteria of Y.-M. Chen et al. and develop a new method to identify regions that simultaneously exhibit PSB features and nuclear activities (AGN-PSBs). Our final sample comprises 48 AGN-PSBs, 92 central PSBs (CPSBs), 89 ringlike PSBs (RPSBs), and 828 irregular PSBs (IPSBs). We find the global and spatially resolved properties of CPSBs and RPSBs are consistent with the results of Y.-M. Chen et al. In this work, we focus on the properties of AGN-PSBs, comparing them with CPSBs, RPSBs, and control galaxies. Similar to CPSBs and RPSBs, AGN-PSBs show positive D _n 4000 gradients relative to negative D _n 4000 gradients of their controls, which indicates younger stellar populations in the central region than in the outskirts. Among the three subtypes, high-mass CPSBs (H-CPSBs; with $\mathrm{log}({M}_{* }/{M}_{\odot })\gt 9.5$ ) display the highest incidence of merger remnants and gas–star kinematic misalignment, consistent with a merger-/interaction-dominated origin. AGN-PSBs and RPSBs, however, show lower and comparable fractions of merger remnants and gas–star kinematic misalignment, favoring less violent external mechanisms. Based on radial profiles of the mass-weighted age and V _star / σ _star , we suggest that RPSBs can evolve into AGN-PSBs, whereas H-CPSBs likely follow a distinct evolutionary pathway. The existence of RPSBs and IPSBs also indicates that AGN feedback is not a necessary condition for the formation of PSBs.

We present a radio continuum study of photometrically selected post-starburst galaxies (PSBs) at cosmic noon (0.5 < z < 3) in the UKIRT Infrared Deep Sky Survey (or UKIDSS) Ultra Deep Survey field to assess if radio-mode active galactic nuclei (AGN) are linked to the quenching of star formation at cosmic noon. Cross-matching with deep Very Large Array imaging at 1.4 GHz results in a mean radio detection fraction (f(det)) of only 0.8% for PSBs above a radio luminosity threshold of L-1.4GHz >= 10(24) W Hz(-1), increasing to 5% +/- 2% for massive PSBs with stellar masses M-* > 10(11) M-circle dot. Massive PSBs exhibit a detection fraction comparable to that of massive quiescent galaxies (f(det) = 8% +/- 1%), though both classes have lower fractions than massive star-forming galaxies (f(det) = 13% +/- 1%) in the same field. The radio luminosities of detected PSBs, L-1.4(GHz) similar to 10(22.8)-10(24.9) W Hz(-1), exceed those expected from star formation by a median factor of 37, indicative of a possible AGN origin. Their compact morphologies (less than or similar to 15 kpc at z(med) = 1.5) suggest low-luminosity AGN hosting less powerful jets. Stacking the undetected PSBs reveals a weak radio detection (3.9 sigma) in the highest-mass bin (M-* > 10(11) M-circle dot). In contrast, 1.4 GHz-detected quiescent galaxies exhibit luminosities reaching the radio-loud regime and show a higher prevalence of extended morphologies indicative of large-scale jetted AGN. An AGN contribution is also detected in stacked measurements of quiescent galaxies. Overall, our results support a short radio AGN duty cycle in PSBs, characterized by weak radio jets, suggesting that radio-driven maintenance-mode feedback may become important at later evolutionary stages.

We present deep, medium-resolution lambda = 1-5 mu m JWST/NIRSpec spectroscopy for 14 quiescent galaxies at 3 < z < 5 with log(10) (M-*/M-circle dot) > 10, obtained as part of the EXCELS survey. We perform a complete re-reduction of these data, including a custom optimal-extraction approach to combat the spectral 'wiggles' that result from undersampling of the NIRSpec spatial PSF. We constrain the star-formation histories and stellar metallicities of these objects via full-spectral fitting, finding a clear stellar age versus stellar mass correlation, in which more massive galaxies assembled their stellar mass at earlier times. This confirms spectroscopically that the archaeological 'downsizing' trend was already in place by z similar or equal to 4. The slope of our measured relation (similar or equal to 2 Gyr per dex in stellar mass) is consistent with literature results at 0 < z < 3. We do not observe objects with log(10) (M-*/M-circle dot) less than or similar to 10.5 and ages of more than a few hundred Myr at this epoch, suggesting that recently reported examples of higher-redshift quiescent galaxies at these masses are likely to soon rejuvenate. We measure relatively high stellar metallicities for the majority of our sample, consistent with similar objects at 0 < z < 3. Finally, we explore evidence for alpha-enhancement in six older and more luminous galaxies within our sample, finding considerable disagreements in the chemical abundances measured using different stellar population models, different fitted rest-frame wavelength ranges, star-formation history models and fitting codes. We therefore conclude that inferring detailed stellar chemical abundances for the earliest quiescent galaxies remains challenging, and higher signal-to-noise spectra are required (observed frame SNR per resolution element similar or equal to 100 for R similar or equal to 1000).

Post-starburst (PSB) galaxies, having recently experienced a starburst followed by rapid quenching, are excellent laboratories to probe physical mechanisms that drive starbursts and shutting down of star formation. Integral-field spectroscopy reveals the galaxies' spatially-resolved properties, where observed directional patterns can be linked to the galaxies' past evolution. We measure the resolved star-formation histories (SFHs), stellar metallicity evolution and dust properties of three local PSBs from the MaNGA survey, down to 0.5" resolution (∼0.3kpc) using a hierarchical Bayesian model. Local parameters were constrained simultaneously with parameters describing spatial trends. We found that all three galaxies first experienced an outer, weaker and slower quenching starburst, followed by a central, stronger and faster quenching starburst that peaked ∼ 1Gyr after the first. The central starbursts induced a significantly stronger rise in stellar metallicity compared to the outer starbursts. These results are consistent with the effects of a recent gas-rich (wet) merger, where the first pericentre passage triggered starbursts in the outer regions, while the later coalescence triggers a stronger centralised starburst. We find non-axisymmetric features in the maps of burst mass fraction and dust attenuation in all galaxies, which could be caused by tidal effects during the recent merger. Comparisons with literature binary merger simulations suggests that the galaxies' rapid quenching was driven by gas consumption and the stabilisation against gas gravitational collapse by a growing spheroid, while AGN feedback was not necessarily a primary cause.

The cold gas content of post-starburst galaxies (PSBs) provides important insight into the mechanisms that drive rapid quenching, but a multiphase assessment of both the atomic and molecular gas in PSBs does not yet exist. We introduce the Ensemble of Multiphase Baryons Evolving in Rapidly-quenching Systems, or EMBERS, a homogeneously selected, nearly mass- and redshift-complete survey of the global atomic (H i) and molecular gas (H-2) in PSBs, observed with the Five hundred-metre Aperture Spherical Telescope (FAST) and the Institut de Radioastronomie Millim & eacute;trique (IRAM) 30- m telescope. We present new CO(1-0) observations for 52 PSBs with the IRAM 30 m, which, combined with 9 archival observations, gives a total H-2 sample of 61, of which 58/61 have ancillary H i measurements. We detect CO(1-0) in 34/61 galaxies, corresponding to molecular gas fractions (fH(2) = MH2 /M & lowast;) ranging from 2 to 250 per cent. By comparing with a stellar-mass matched star-forming (SF) control sample from xCOLD GASS, we find that PSBs on average are similar to 0.3 - 0.6 dex depleted in H-2. However, considering both H i and H-2, individual PSBs host diverse gas reservoirs ranging from gasrich in both phases, elevated in one phase, or gas-poor, the latter of which is common at lower stellar mass. The existence of gas-normal and gas-depleted PSBs in both phases suggests that some PSBs may rejuvenate their star formation, but the rapid shutdown of star formation in others is likely terminal. Despite this diversity, the majority of EMBERS PSBs are gaspoor compared to SF controls, with the typical PSB hosting gas reservoirs intermediate to those found in SF and quenched galaxies.

We investigate the presence and origin of neutral gas outflows and inflows in 13 post-starburst and quiescent galaxies at redshifts 1.8 <= z <= 4.6, using James Webb Space Telescope NIRSpec spectroscopy from the EXCELS survey. Na d absorption profiles reveal that 3 out of 13 exhibit blueshifted absorption indicative of outflows, and a further 2 objects show signs of inflowing gas. Outflow velocities range from approximate to 300 to 1200 km s(-1), and we find gas flows are detected exclusively in objects that quenched < 600 Myr ago. We derive mass outflow rates overtwo orders of magnitude higherthan current levels of star formation in our sample, indicating that the winds are unlikely to be driven by supernovae. The majority of the outflow sample have anomalously high energy and momentum outflow rates compared to those predicted for current levels of star formation or active galactic nucleus (AGN) activity. We conclude that we are likely observing fossil outflows driven by previous, more luminous AGN activity which has since faded. We then compare with the eagle simulation to explore a potential 'outflow cycle', finding that our observations are consistent with a model in which z similar to 3 quiescent galaxies undergo short similar or equal to 5 Myr periods of AGN activity strong enough to drive outflows, which occur every similar or equal to 40 Myr on average. This AGN activity drives observable outflows that persist for up to similar or equal to 10 Myr after the AGN fades, followed by a similar or equal to 20 Myr lull, and a subsequent short inflow, which eventually re-ignites AGN activity, and the cycle repeats.

We investigate the multiwavelength structure of recently-quenched post-starburst (PSB) galaxies at 0.5 < z < 3, using photometrically selected samples from the Ultra Deep Survey. Leveraging deep eight-band James Webb Space Telescope/NIRCam imaging from the PRIMER programme, we analyse similar to 120 PSBs across the rest-frame optical-to-near-infrared, and compare with a reference sample of similar to 3000 passive and star-forming galaxies. Structural parameters (effective radius R-e} and Sersic index n) are derived independently in each waveband, and reveal that PSBs exhibit minimal structural variation with wavelength, indicating negligible stellar population age gradients or internal dust obscuration. We confirm that PSBs follow the established redshift-mass trends: at z > 1, massive PSBs (M-* > 10(10), M-circle dot) are compact spheroids resembling massive passive galaxies, albeit significantly more compact, whereas at 0.5 < z < 1, PSBs are typically low-mass (M-* < 10(10), M-circle dot ) compact, disc-dominated systems akin to low-mass passive discs. Furthermore, for the first time, we systematically quantify disturbance indicators (residual flux fraction {\it RFF}, asymmetry, residual asymmetry) across a large PSB sample. At all masses, PSBs exhibit low RFF and asymmetry values comparable to passive systems and consistent with smooth, largely undisturbed morphologies. However, at z > 1, massive PSBs (M-* > 1010.25, M-circle dot show enhanced residual asymmetry relative to the passive population, indicating a previously unrecognized level of structural disturbance masked beneath a smooth stellar distribution. These results suggest that, while structural transformation is largely complete by the PSB phase, residual disturbances persist at high redshift, supporting a scenario in which rapid quenching proceeds via two distinct pathways: highly disruptive events (e.g. major mergers) at high z and high mass, and comparatively gentle processes at later times.

Galaxy mergers and interactions have long been suggested as a significant driver of galaxy evolution. However, the exact extent to which mergers enhance star formation and AGN activity has been challenging to establish observationally. In previous work, we visually classified a sample of galaxies with various types of faint tidal features in DECaLS images. In this paper, we cross- correlate this sample with SDSS-derived data to investigate how the presence and specific nature of these features correlates with intense star formation and AGN activity. Averaged over all tidal classes, we find that our 688 tidal feature galaxies are 6.6 +/- 0.9 times more likely to be in a starburst phase and 19.6 +/- 5.0 times more likely to have rapidly quenched (post-starbursts) than a sample of 4073 controls matched in both stellar mass and redshift. Examining differences between tidal classes, galaxies with arm features were similar to 1.3-4.0 times more likely to be starbursting than the other categories, while those with shell features were similar to 2.3-5.3 times more likely to be in a quiescent state. In a similar analysis, we identify which galaxies show evidence of AGN activity (from a sample of similar to 2100) and find no significant difference between those with or without tidal features. Overall, our results reinforce the notion that mergers play an important role in driving star formation and rapid quenching in galaxies, and provide some of the first empirical evidence that the strength of this effect has a dependence on the detailed nature of the interaction, as traced by the tidal feature morphology.

The quenching of star formation is a crucial phase in galaxy evolution. Although feedback from active galactic nuclei (AGN) has been proposed as a key driver of this transition, the lack of strong AGN in nearby quenching galaxies raises questions about its effectiveness. In this study, we investigate AGN activity in post-starburst galaxies (PSBs), star-forming galaxies (SFGs), and quiescent galaxies (QGs) at z < 0.2, using multiwavelength data from eROSITA Final Equatorial Depth Survey (X-ray), Wide-field Infrared Survey Explorer (mid-infrared), and Faint Images of the Radio Sky at Twenty cm (radio). We assess AGN incidence and strength across different stages and apply stacking techniques to undetected galaxies to recover average AGN properties. Comparisons between observed luminosity and that expected from star formation ( L _obs / L _SF ) show that PSBs are consistent with star formation dominating their radio and X-ray emission. Although PSBs exhibit a mid-infrared (MIR) AGN incidence rate twice that of SFGs, their estimated AGN luminosities are small compared to those of MIR AGN in the literature. PSBs overall do not display significantly enhanced AGN emission relative to mass- and redshift-matched SFGs and QGs. While the presence of obscured, low-luminosity AGN in PSBs cannot be excluded, such AGN, if present, could be fueled by residual gas from the preceding starburst and may not play a dominant role in quenching. Our findings suggest that the role of AGN in quenching at low redshift is more subtle than violently removing the gas—the feedback is likely more “preventive” than “ejective.”

Paul Hewett, pioneer of data science from wide-field digital astronomical surveys and expert in quasar demographics, died on 4 June 2026.

We present a radio continuum study of photometrically selected cosmic noon (0.510^11M_⊙. Massive PSBs have a comparable detection fraction to that of massive quiescent galaxies (f_det=8±1%), and both classes have lower fractions than that of massive star-forming galaxies (f_det=13±1%) in the same field. The radio luminosities of detected PSBs, L_1.4∼ 10^22.8-10^24.9W/Hz, exceed those from star formation by a median factor of 37 indicative of a possible AGN origin. Their compact morphologies (≲15 kpc at z_med=1.5) suggest low-luminosity AGN with less powerful jets. Stacking the undetected PSBs reveals a weak radio detection (3.9σ) in the highest mass bin (M_*>10^11M_⊙). In contrast, 1.4 GHz detected quiescent galaxies have radio luminosities reaching radio-loud levels, and a higher prevalence of extended morphologies indicative of large-scale jetted AGN. The AGN contribution is also detected in stacked measurements of quiescent galaxies. Overall, our results support a short radio AGN duty cycle for PSBs, characterized by weak radio jets, suggesting radio-driven maintenance mode feedback may become important at older ages.

We investigate the role of obscured active galactic nuclei (AGN) in recently quenched post-starburst galaxies (PSBs), using a sample of 65 photometrically selected PSBs in the PRIMER-UDS field at 1< z < 2. Combining JWST/MIRI 7.7 and 18 mu m (F770W and F1800W) imaging with eight NIRCam and three HST/ACS bands, we probe hot dust emission to test for hidden AGN or dust-enshrouded star formation. We find strong differences between the low- and high-mass PSBs. Most high-mass PSBs (>10(10)M(circle dot)) show no excess infrared emission (consistent with the quiescent population), indicating little or no dust-obscured activity, while low-mass PSBs display enhanced emission at 18 mu m, which we attribute to residual star formation. AGN template modelling indicates that the absence of mid-IR excess in massive PSBs limits any dust-enshrouded AGN to Eddington ratios of < 1 per cent. In addition, we show that the F770W-F1800W colour alone is a highly effective diagnostic for separating passive and star-forming galaxies, particularly at high stellar masses. Overall, our results provide further evidence for distinct quenching pathways within the PSB population, and confirm that massive PSBs show no evidence for excess AGN activity relative to older passive galaxies.

Post-starburst (PSB) galaxies, identified by strong Balmer absorption and weak nebular emission, provide a key laboratory for studying rapid quenching. Using the final data release of the SDSS-IV MaNGA survey, we follow the traditional PSB selection criteria of Chen et al. (2019) and develop a new method to identify regions that simultaneously exhibit PSB features and nuclear activities (AGN-PSBs). Our final sample comprises 48 AGN-PSBs, 92 central PSBs (CPSBs), 89 ring-like PSBs (RPSBs), and 828 irregular PSBs (IPSBs). We find the global and spatially resolved properties of CPSBs and RPSBs are consistent with the results of Chen et al. (2019). In this work, we focus on the properties of AGN-PSBs, comparing them with CPSBs, RPSBs, and control galaxies. Similar to CPSBs and RPSBs, AGN-PSBs show positive D_n4000 gradients relative to negative D_n4000 gradients of their controls, which indicates younger stellar populations in the central region than that in the outskirt. Among the three sub-types, high-mass CPSBs (H-CPSBs, with log(M_*/M_⊙)>9.5) display the highest incidence of merger remnants and gas–star kinematic misalignment, consistent with a merger/interaction-dominated origin. AGN-PSBs and RPSBs, however, show lower and comparable fractions of merger remnants and gas–star kinematic misalignment, favoring less violent external mechanisms. Based on radial profiles of mass-weighted age and V_ star/σ_ star, we suggest that RPSBs can evolve into AGN-PSBs, whereas H-CPSBs likely follow a distinct evolutionary pathway. The existence of RPSBs and IPSBs also indicates that AGN feedback is not a necessary condition for the formation of PSB.

Understanding when and how galaxies quench their star formation is crucial for understanding the dominant physical processes at play. The spectral energy distribution (SED) of galaxies encodes significant information on their past histories: the relative importance of different physical processes influences the observed distribution of SED shapes in the galaxy population. We use a simulation based inference (SBI) approach to directly constrain the distribution of formation times, quenching times and quenching timescales within the massive galaxy population at z > 2 from their broad band photometric colour distribution at 1.710.3. We measure a quenched galaxy fraction of 0.24+/-0.02, with the number density of quenched galaxies rising rapidly 2.5Gyr after the Big Bang (z< 2.6). Galaxies must quench rapidly to achieve the precise bimodal colour distribution: defining the quenching timescale as the time from peak star formation rate (SFR_peak) -> 0.5xSFR_peak, the quenching timescale distribution has a mode at 97_-25^+31Myr, a median of 182+/-16Myr and a tail to 700Myr. To achieve full quiescence takes a median time of 400Myr. Comparing to direct number density measurements of quenched galaxies at z>2 the combination of recent and rapid quenching inferred from the fossil record suggests a substantial rejuvenation and/or merger rate for quenched galaxies observed directly at z>3.5.

We select a mass-complete sample of 225 quiescent galaxies at z > 2 with M-& lowast; > 10(10 )M(circle star) from PRIMER and JADES photometry spanning a total area of similar or equal to 320 sq. arcmin. Our analysis is restricted to only area with optical coverage in three Hubble Space Telescope ( HST ) ACS filters, which we show is important for selecting the most complete and clean samples. We investigate the contamination in our sample via James Webb Space Telescope (JWST) NIRSpec spectroscopy, Chandra X-ray imaging, and ALMA interferometry, calculating a modest contamination fraction of 12 . 9(-3.1)(+4.0) per cent. The removal of HST data increases star-forming galaxy contamination by similar or equal to 10 per cent and results in a similar or equal to 20 per cent loss of candidates recovered from HST + JWST data combined. We calculate massive quiescent galaxy number densities at 2 < z < 5, finding values three times larger than pre-JWST estimates, but generally in agreement with more-recent and larger-area JWST studies. In comparison with simulations, we find that most can now reproduce the observed number density at 2 < z < 3; however, they still increasingly fall short at z > 3, up to similar or equal to 1 dex. We place 14 of our z > 3 massive quiescent galaxies on the BPT and WHaN diagrams using medium-resolution spectroscopic data from the EXCELS survey, finding a very high incidence of weak active galactic nucleus ( similar or equal to 50 per cent), consistent with recent results at cosmic noon. This is interesting in the context of 'maintenance-mode' feedback, which is invoked in many simulations to prevent the re-ignition of quenched galaxies. To properly characterize the evolution of early massive quiescent galaxies, greater coverage in optical filters and significantly larger spectroscopic samples will be required.

We investigate the quenching of galaxies using a mock observational light-cone generated from the Semi-Analytic Model (SAM) L-Galaxies, closely matched to observations from the UKIDSS Ultra Deep Survey (UDS). The sample is used to study merging, rejuvenation, and visibility times for star-forming, quiescent, and post-starburst (PSB) galaxies, to assess the impact on the buildup of the passive galaxy mass functions. We find, for example, that a typical PSB (M-& lowast; > 10(10) M-circle dot) at z approximate to 1 has a 15 per cent likelihood of merging and around a 25 per cent likelihood of rejuvenating within 1 Gyr of being identified. Applying these rates and time-scales to the observational data, we estimate the fraction of quiescent galaxies that passed through a PSB phase. We find that 18-28 per cent of the build-up in the massive end (M-& lowast; > 10(10) M-circle dot) of the passive mass function at 1 < z < 2 can be explained by PSBs, with the contribution declining to similar to 5 per cent by z similar or equal to 0.5. Accounting for mergers and rejuvenation reduces the inferred PSB contribution by approximately a factor of two. At lower stellar masses (M-& lowast; > 10(10) M-circle dot), rapid quenching through a PSB phase explains a significantly larger fraction of the growth in the passive mass function. With a visibility time of similar to 0.75 Gyr, we find that around 60-80 per cent of low-mass passive galaxies underwent a PSB phase. Our findings provide further evidence that low- and high-mass galaxies follow different quenching pathways

We study 24 massive quiescent galaxies with logM(*)/M-circle dot>10 at 1 < z < 3 with JWST/NIRSpec medium-resolution observations from the Early Extragalactic Continuum and Emission Line Survey (EXCELS). We reconstruct their star formation histories and find that they have large bursts (100-1000 M-circle dot yr(-1)), followed by a rapid truncation of star formation. The number densities of the quenched galaxies in our sample that we predict underwent a submillimeter phase are consistent with submillimeter galaxies being the progenitors of our quenched population. The median post-starburst visibility time is similar to 600 Myr, with more massive galaxies ( logM(*)/M-circle dot>10.7 ) exhibiting shorter visibility times than lower-mass galaxies. The range of quenching times-defined as the time from the peak starburst to the time of quiescence-found in this sample (0.06-1.75 Gyr) suggests multiple quenching pathways, consistent with previous studies. We do not see evidence for quenching mechanisms varying with redshift between 1 < z < 3. We detect evidence for weak active galactic nucleus activity in four out of the eight galaxies with robust emission line detections, based on line ratio diagnostics. Our findings suggest that there is a diverse range of quenching mechanisms at Cosmic Noon, and support a scenario in which the primary quenching mechanisms are rapid (<500 Myr) following a starburst.

We present the evolution of the stellar mass functions for photometrically selected star-forming, passive and post-starburst galaxies, based on JWST PRIMER observations of the Ultra-Deep Survey (UDS) field. We identify over 800 post-starburst galaxies within the redshift range 0.5 < z < 3.0. We confirm the presence of a low-mass upturn in the quenched galaxy mass function at log(M*/M_sun) < 10 out to z 2, and show it is primarily driven by post-starburst galaxies. These findings imply that a rapid quenching pathway for low-mass galaxies is already active by z 2, which may be linked to environmental processes. If we assume that all post-starburst galaxies evolve into passive galaxies, adopting a typical visibility time for the post-starburst phase, we find a significant overprediction of low-mass passive galaxies at later times. We suggest a variety of factors that could contribute to reconciling this tension. If low-mass (M* < 10^10 M_sun) post-starburst galaxies quench through slower channels than high-mass systems then the post-starburst phase may be visible for longer periods, reducing their contribution to the passive population. However, the maximum realistic visibility timescale cannot account for all of the excess. We propose that additional factors inhibit the build-up of the low-mass passive galaxy mass function. These galaxies may be removed through mergers or tidal disruption, rejuvenate and return to the star-forming population, or represent systems observed during a dormant phase of stochastic star formation. We conclude that the emergence of the low-mass quenched population is likely governed by a complex interplay of processes, and cannot be explained by simple one-way evolutionary pathways.

Studying the gas content of post-starburst (PSB) galaxies can provide valuable clues regarding the process of fast quenching. Although previous works have studied the molecular gas content of PSBs, only a handful of HI measurements exist. Here, we present new Five hundred metre Aperture Spherical Telescope (FAST) 21cm observations of 44 PSBs, leading to 43 detections or sensitive upper limits of HI, which we combine with 25 archival measurements, for a total sample of 68 PSB MHI measurements. HI is detected in 57/68 galaxies, with HI masses ranging from MHI 10^8.5 up to 10^10 Msun and gas fractions (fHI = MHI/M*) from a few percent up to almost 30 percent. Post-starbursts therefore retain ample atomic gas reservoirs, despite no longer forming stars. By comparing with a stellar mass-matched sample of star-forming galaxies in xGASS, we find that PSBs have, on average, gas fractions lower by 0.2-0.4 dex, consistent with a mild reduction compared with their progenitor population. However, PSBs show a diversity of HI properties; about half have HI gas masses within the expected scatter of the star-forming population with the remaining 50 per cent up to a factor of 10 more gas-poor. Compared with galaxies in the green valley, about two thirds of PSBs have gas fractions within the expected range, with the remaining third up to a factor of 10 more gas-rich. Our results demonstrate that quenching in PSBs is not the result of wholesale removal of the atomic gas reservoir and that the population has atomic gas fractions that span the range from star-forming to green valley galaxies. We find no correlation between HI gas mass and time since burst; even galaxies a Gyr past their burst can remain HI-normal. The significant gas reservoirs remaining in many PSBs leaves open the possibility for future rekindling of star formation.