arXiv subjects

Vivienne Wild

Publications and source records attributed to Vivienne Wild.

At least 19 recordsLinked to original sources

arXiv2026

JWST PRIMER: Post-starburst galaxies dominate the low-mass quiescent galaxy population since z~2

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.

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arXiv2026

Post-starburst Galaxies with Active Galactic Nucleus: Properties and Evolutionary Sequences

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 $\mathrm{D}_{n}4000$ gradients relative to negative $\mathrm{D}_{n}4000$ 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 $\log(M_{*}/M_{\odot})>9.5$) 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 $V_{\rm star}/\sigma_{\rm star}$, 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.

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arXiv2026

The multiwavelength structure of post-starburst galaxies at 0.5 < z < 3 with JWST PRIMER: compact morphologies and residual disturbances

We investigate the multi-wavelength structure of recently quenched post-starburst (PSB) galaxies at 0.5 < z < 3, using photometrically selected samples from the Ultra Deep Survey (UDS). Leveraging deep eight-band JWST/NIRCam imaging from the PRIMER programme, we analyze ~120 PSBs across the rest-frame optical-to-near-infrared, and compare with a reference sample of ~3000 passive and star-forming galaxies. Structural parameters (effective radius Re 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 Msun) 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 Msun) compact, disc-dominated systems akin to low-mass passive discs. Furthermore, for the first time, we systematically quantify disturbance indicators (residual flux fraction 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* > 10^10.25 Msun) 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.

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arXiv2026

No hidden monsters: Probing recently-quenched galaxies for obscured AGN with JWST-PRIMER MIRI and NIRCam

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 $\mu$m 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}\textrm{M}_\odot$) 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\%$. 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.

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arXiv2026

The quenching time and timescale distribution of z~2 quiescent galaxies from precise colour distribution analysis

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 1.7 10.3. 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}^{+31}Myr, 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.

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arXiv2026

Tracing Radio AGN-Driven Quenching in Post-Starburst Galaxies at Cosmic Noon

We present a radio continuum study of photometrically selected cosmic noon (0.5 10^{11}$M$_\odot$. Massive PSBs have a comparable detection fraction to that of massive quiescent galaxies ($f_{det}=8\pm1\%$), and both classes have lower fractions than that of massive star-forming galaxies ($f_{det}=13\pm1\%$) in the same field. The radio luminosities of detected PSBs, ${\rm L}_{1.4}\sim 10^{22.8}-10^{24.9}$W/Hz, exceed those from star formation by a median factor of 37 indicative of a possible AGN origin. Their compact morphologies ($\lesssim15$ kpc at $z_{med}=1.5$) suggest low-luminosity AGN with less powerful jets. Stacking the undetected PSBs reveals a weak radio detection ($3.9\sigma$) in the highest mass bin (M$_*>10^{11}$M$_\odot$). 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.

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arXiv2026

EMBERS I: Low redshift post-starburst galaxies are frequently depleted in molecular gas relative to star forming progenitors

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 (HI) and molecular gas (H2) in PSBs, observed with the Five Hundred-metre Aperture Spherical Telescope (FAST) and the Institut de radioastronomie millimetrique (IRAM) 30m telescope. We present new CO(1-0) observations for 52 PSBs with the IRAM 30m, which, combined with 9 archival observations, gives a total H2 sample of 61, of which 58/61 have ancillary HI measurements. We detect CO(1-0) in 34/61 galaxies, corresponding to molecular gas fractions (fH2 = MH2/M*) ranging from two 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 0.3-0.6 dex depleted in H2. However, considering both HI and H2, individual PSBs host diverse gas reservoirs ranging from gas-rich 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 gas-poor compared to SF controls, with the typical PSB hosting gas reservoirs intermediate to those found in star-forming and quenched galaxies.

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arXiv2026

Spatially resolved star-formation histories of local post-starburst galaxies: Starburst and quenching spatial patterns consistent with recent mergers

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 ($\sim0.3\,$kpc) 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 $\sim 1\,$Gyr 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.

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arXiv2026

A Multiwavelength Evaluation of AGN in the Post-Starburst Phase

The quenching of star formation is a crucial phase in galaxy evolution. Although active galactic nuclei (AGN) feedback 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/eFEDS (X-ray), WISE (mid-infrared), and FIRST (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$_{\rm obs}$/L$_{\rm SF}$) show that PSBs are consistent with star formation dominating their radio and X-ray emission. Although PSBs exhibit a 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 AGN's role in quenching at low redshift is more subtle than violently removing the gas -- the feedback is likely more "preventive" than "ejective".

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arXiv2026

The JWST EXCELS survey: The ages and abundances of $3<z<5$ massive quiescent galaxies show that downsizing was already in place by $z\simeq4$

We present deep, medium-resolution $\lambda=1-5\,\mu$m JWST/NIRSpec spectroscopy for 14 quiescent galaxies at $3 \,}10$, 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 vs 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 $z\simeq4$. The slope of our measured relation ($\simeq2$ Gyr per dex in stellar mass) is consistent with literature results at $0 < z < 3$. We do not observe objects with $\log_{10}(M_*/\mathrm{M_\odot})\lesssim10.5$ 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 (SNR per resolution element $>100$ for $R\simeq1000$).

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arXiv2026

The JWST EXCELS survey: Outflows in 1.5 < z < 5 quiescent and recently quenched galaxies are likely relics from episodic AGN activity

We investigate the presence and origin of neutral gas outflows and inflows in 13 post-starburst (PSB) and quiescent galaxies at redshifts 1.8 $\leq$ z $\leq$ 4.6, using JWST NIRSpec spectroscopy from the EXCELS survey. NaD 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 $\approx$ 300 - 1200 kms$^{-1}$, and we find gas flows are detected exclusively in objects that quenched $\lt$ 600 Myr ago. This result holds when we include comparable objects from recent literature. We derive mass outflow rates over two orders of magnitude higher than current levels of star formation in our sample, indicating that the winds are unlikely to be driven by supernovae, and likely play a significant role in keeping the galaxies quenched. 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 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 $\sim$ 3 quiescent galaxies undergo short $\simeq$ 5 Myr periods of AGN activity strong enough to drive outflows, which occur every $\simeq$ 40 Myr on average. This AGN activity drives observable outflows that persist for up to $\simeq$ 10 Myr after the AGN fades, followed by a $\simeq$ 20 Myr lull, and a subsequent short inflow, which eventually re-ignites AGN activity, and the cycle repeats.

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arXiv2025

The role of mergers and rejuvenation in the buildup of the quiescent population at cosmic noon

We investigate the quenching of galaxies using a mock observational lightcone 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 build-up of the passive galaxy mass functions. We find, for example, that a typical PSB ($M_\ast\sim10^{10}$\,M$_\odot$) at $z\approx1$ 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 timescales 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 ($M_\ast>10^{10}$\,M$\,_\odot$) of the passive mass function at $1<z<2$ can be explained by PSBs, with the contribution declining to $\sim5$ per cent by $z \simeq 0.5$. Accounting for mergers and rejuvenation reduces the inferred PSB contribution by approximately a factor of two. At lower stellar masses ($M_\ast < 10^{10}$\,M$_\odot$), rapid quenching through a PSB phase explains a significantly larger fraction of the growth in the passive mass function. With a visibility time of $\sim$ 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.

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arXiv2025

The JWST EXCELS survey: Insights into the nature of quenching at cosmic noon

We study 24 massive quiescent galaxies with $\log \textrm{M}_*/\textrm{M}_\odot > 10$ 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 ($100\textrm{ M}_{\odot} \textrm{yr}^{-1} -1000 \textrm{ M}_{\odot} \textrm{yr}^{-1}$), 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 $\sim600$ Myr, with more massive galaxies ($\log \textrm{M}_*/\textrm{M}_\odot > 10.7$) 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 AGN activity in 4 out of the 8 galaxies with robust emission line detections, based on line ratio diagnostics. Our findings suggest that there are 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.

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arXiv2025

Stellar populations of quasar host galaxies with MFICA decomposition

Galaxy evolution theories require co-evolution between accreting supermassive black holes (SMBH) and galaxies to explain many properties of the local galaxy population, yet observational evidence for the mechanisms driving this co-evolution is lacking. The recent star-formation histories of the host galaxies of accreting SMBHs (Active Galactic Nuclei, AGNs) can help constrain the processes that feed SMBHs and halt star formation in galaxies, but are difficult to obtain for the most luminous AGNs (quasars). We introduce Mean-Field Independent Component Analysis (MFICA) to decompose quasar spectra and obtain recent star formation histories of their host galaxies. Applying MFICA to quasar spectra from the Sloan Digital Sky Survey (SDSS) DR7 Quasar Catalogue in the redshift range $0.16 \leq z \leq 0.76$, we find that 53 per cent of quasar host galaxies are star-forming, 17 per cent lie in the green-valley, while only 5 per cent are quiescent. This contrasts with 14, 11, and 74 per cent of a mass-matched control sample that are star-forming, green-valley, and quiescent, respectively. We find that $\sim25$ per cent of quasars are hosted by post-starburst galaxies, an excess of $28\pm1$ compared to our control sample. While the heterogeneity of recent star formation histories implies multiple SMBH feeding mechanisms, the excess of post-starburst host galaxies demonstrates the link between accreting SMBHs and a recent starburst followed by rapid quenching. Given that massive post-starburst galaxies are predominantly caused by gas-rich major mergers, our results indicate that $30-50$ per cent of quasars originate from merger-induced starbursts.

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arXiv2025

PRIMER & JADES reveal an abundance of massive quiescent galaxies at 2 < z < 5

We select a mass-complete sample of 225 quiescent galaxies at $z>2$ with $M_* > 10^{10}\ \mathrm{M}_\odot$ from PRIMER and JADES photometry spanning a total area of $\simeq320$ sq. arcmin. We restrict our analysis to only area with optical coverage in three $HST$ ACS filters, and provide evidence that this is important for selecting the most complete and clean samples of $z>2$ massive quiescent galaxy candidates. We investigate the contamination in our sample via $JWST$ NIRSpec spectroscopic validation, $Chandra$ X-ray imaging, and ALMA interferometry, calculating a modest total contamination fraction of $12.9_{-3.1}^{+4.0}$ per cent. The removal of $HST$ data increases star-forming galaxy contamination by $\simeq10$ per cent and results in a $\simeq20$ per cent loss of candidates recovered from $HST$+$JWST$ data combined. We calculate massive quiescent galaxy number densities at $2 3$, with discrepancies of up to $\simeq 1$ 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. We find a very high incidence of faint AGN in our sample, at a level of $\simeq50$ 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 quenched galaxies from re-igniting star formation. To properly characterise the evolution of early massive quiescent galaxies, greater coverage in optical filters and significantly larger spectroscopic samples will be required.

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arXiv2025

The diverse quenching pathways of post-starburst galaxies in SDSS-IV MaNGA

The quenching of star formation in galaxies is an important aspect of galaxy evolution, but the physical mechanisms that drive it are still not understood. Measuring the spatial distribution of quenching can help determine these mechanisms. We present the star-formation histories (SFHs) and stellar metallicity evolution of rapidly quenched regions in 86 local post-starburst (PSB) galaxies from the MaNGA integral field survey, obtained through Bayesian full spectral fitting of their rest-frame optical spectra. We found that regardless of spatial location, the PSB regions have similar past SFHs and chemical evolution, once radial metallicity gradients are accounted for. This suggests that all PSB regions are regulated by a common set of local scale processes in the interstellar medium, regardless of the broader triggering mechanism. We show that the centres of galaxies with outer PSB regions are also quenching. The central specific star-formation rate (sSFR) has declined by $\sim1.0\;$dex on average during the last 2 Gyr, a significantly steeper decline than main sequence galaxies over the same period ($\approx0.2\;$dex). This central quenching can be either synchronous, outside-in or inside-out, and slower or as fast as the outer regions, highlighting the diversity of quenching pathways for local galaxies. Our results imply a primary quenching mechanism that is both catastrophic and global in rapidly halting star formation in local galaxies. We suggest the predominant cause is galaxy mergers or interactions, with large scale feedback from a starburst or a central supermassive black hole playing a lesser role.

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arXiv2025

Linking enhanced star formation and quenching to faint tidal features in galaxies

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$\pm$0.9 times more likely to be in a starburst phase and 19.6$\pm$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 \textit{arm} features were $\sim$1.3-4.0 times more likely to be starbursting than the other categories, while those with \textit{shell} features were $\sim$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 $\sim$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.

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arXiv2025

Cool Gas in the Circumgalactic Medium of Massive Post Starburst Galaxies

Observing the interplay between galaxies and their gaseous surroundings is crucial for understanding how galaxies form and evolve, including the roles of long-lived cool gas reservoirs, starburst and AGN driven outflows. We use stacked Mg II absorption lines in the spectra of background quasars to study the cool gas out to 9Mpc from massive quiescent, star-forming and post-starburst galaxies with stellar masses $\log_{10}(M_{\mathrm{gal}}/M_\odot) \gtrsim 11.4$ and $0.4 \lesssim z \lesssim 0.8$ selected from the Baryon Oscillation Spectroscopic Survey (BOSS) CMASS galaxies. Consistent with previous studies, we observe a decline in absorption strength indicating a decrease in cool gas content with increasing distance from the galaxies, as well as decreasing star formation rate of the galaxies. Beyond 1Mpc, this decline levels off to the same absorption strength in all galaxy types, suggesting a transition from the circumgalactic medium (CGM) to the intergalactic medium (IGM) at approximately the virial radius of the host dark matter haloes. We find that post-starburst galaxies, that have experienced a recent burst of star formation that has rapidly quenched, exhibit significantly stronger Mg II absorption within 1Mpc than star-forming or quiescent galaxies of the same stellar mass. Because post-starburst galaxies are a potentially significant pathway for the formation of quiescent elliptical galaxies, our results have wide reaching implications for understanding the mechanisms involved in quenching star formation in galaxies. We speculate that the excess cool gas absorption out to 1Mpc around post-starburst galaxies is related to their observed high velocity ($\sim$1000\,km/s) cool gas outflows. Thus, strong, short-lived bursts of star formation impact the CGM around galaxies on Mpc distances and Gyr timescales.

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