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Abstract Post-starburst (PSB) galaxies are galaxies that have undergone a large burst of star formation followed by rapid quenching. Understanding their properties as a population can help us better understand how galaxies evolve to quiescence. This project aims to use star formation history (SFH) measurements from the integral field spectroscopy (IFS) surveys MaNGA, CALIFA, and AMUSING++ processed with the Pipe3D analysis pipeline in order to select PSB galaxies as well as PSB regions in galaxies. Most PSB selection methods use cutoffs determined by spectral features, but in this work, we introduce a new PSB selection method based directly on the property we are most interested in: inferred SFHs. IFS data allows us to probe a galaxy’s star formation on a spatially resolved scale, enabling us to examine the size, shape, and location of PSB regions within a galaxy. We select 107 PSB galaxies, only seven of which are among known PSBs selected by other methods. Unlike traditional PSB selection methods, our approach is not biased against active galactic nuclei (AGNs). Despite this, we still find no evidence for a significant Seyfert 2 PSB population, suggesting that strong AGN activity is uncommon throughout the PSB phase. Our spatially resolved SFH selection identifies a wide range of galaxies, including globally quiescent elliptical galaxies with centrally concentrated PSB spaxels, galaxies with ring-like PSB spaxels, and a preference for inside-out age gradients (contrary to what has previously been observed in the literature), and galaxies with widespread PSB regions that have significant star formation elsewhere in the galaxy. 

Many poststarburst galaxies at z ∼ 0.7 have been shown to retain substantial molecular gas reservoirs yet host low ongoing star formation, suggesting that the remaining gas may be inefficient at forming stars during the early postburst phase. We present new Atacama Large Millimeter/submillimeter Array CO(5-4) observations of nine gas-rich poststarburst galaxies at z ~ 0.7 from the Studying Quenching in Intermediate-z Galaxies: Gas, anguLar momentum, and Evolution (SQuIGGLE) survey, providing a view of the molecular gas excitation in these systems. Combined with existing CO(2-1) data, we detect CO(5─4) in eight out of nine targets and find that most have moderate CO excitation with r52 = L'CO(5−4)/L'CO(2−1) ~ 0.1−0.3 . These systems show no clear trend between r52 and either total or surface-density of star formation. Specifically, all objects have ΣSFR ∼ 0.01─1 M⊙ yr−1 kpc−2, consistent with compact, modest star formation, even when allowing for buried activity, as these galaxies decline from their peak. One object, J1448+1010, which has clear optical, mid-infrared, and radio indicators of an active galactic nucleus, is an outlier with r52 ~ 0.6; its elevated excitation likely requires significant nonstellar heating, with a contribution from potentially obscured star formation. Together, most gas-rich SQuIGGLE poststarbursts have moderately excited molecular gas alongside little to modest star-forming activity, indicating that the remaining gas hosts relatively suppressed star formation efficiencies instead of strong buried starburst activity. 

Abstract Outflows and jets launched from the nuclei of galaxies emit radio synchrotron emission that can be used to study the impact of accretion energy on the host galaxy. The decades-long baseline now enabled by large radio surveys allows us to identify cases where new outflows or jets have been launched. Here, we present the results of a targeted Very Large Array program observing four poststarburst galaxies that have brightened significantly in radio emission over the past ∼20 yr. We obtain quasi-simultaneous observations in five bands (1–18 GHz) for each source. We find peaked spectral energy distributions, indicative of self-absorbed synchrotron emission. While all four sources have risen significantly over the past ∼20 yr in the 1–2 GHz band, two also show clear recent flares in the 2–4 GHz band. These sources are less luminous than typical peaked-spectrum radio active galactic nucleus (AGN). It remains unclear whether these sources are low luminosity analogs of the peaked radio AGN from accreted gas, or driven by tidal disruption events with missed optical flares. Regardless of the source of the accreted material, these newly launched outflows contain sufficient energy to drive the molecular gas outflows observed in poststarburst galaxies and to drive turbulence, suppressing star formation. 

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.” 

Observational and theoretical studies have long held that rapid gas consumption in starbursts is responsible for the formation of the most massive quiescent galaxies at high redshift. However, studies of recently quenched “post-starburst” galaxies have discovered that a number of them are surprisingly luminous in CO, challenging this assumption. We present deep Atacama Large Millimeter/submillimeter Array CO(2–1) observations of 50 massive (log(M⋆/M⊙)∼11.2) post-starburst galaxies from the SQuIGGLE sample at z ∼ 0.7. We detect a large fraction (27/50) of the galaxies in CO(2–1). We perform new spectral energy distribution (SED) fits incorporating mid- and far-IR photometry to measure the star formation rates (SFRs) and histories that can reproduce both the rest-optical and dust properties of these galaxies. We find that the CO luminosity correlates with the age of the recent starburst, suggesting a gas-removal timescale of ≲150 Myr, an order of magnitude shorter than is implied by their SFRs under standard birth cloud dust assumptions. We find that while allowing for significantly more attenuation in birth clouds can raise SFRs by ∼0.5 dex, for almost all galaxies, it is neither required to fit the observed IR SED, nor is it sufficient to explain the observed depletion trend. Even the combination of significant buried star formation and ULIRG-like α_CO is not enough to explain this decay in CO luminosity. Furthermore, there is no strong evidence to support either of those modifications to the depletion time. Therefore, it remains a distinct possibility that the age–CO luminosity trend should not be interpreted as an evolutionary sequence, and that gas-rich SQuIGGLE galaxies will soon rejuvenate. 

Abstract We conduct an analysis of over 60,000 dwarf galaxies ( $7\lesssim \log M_{*}/M_{\odot }\lesssim 10$ ) in search of photometric variability indicative of active galactic nuclei (AGNs). Using data from the Young Supernova Experiment, a time domain survey on the Pan-STARRS telescopes, we construct light curves for each galaxy in up to four bands (griz) where available. We select objects with AGN-like variability by fitting each light curve with a damped random walk (DRW) model. After quality cuts and removing transient contaminants, we identify 1100 variability-selected AGN candidates (representing 2.4% of the available sample). We analyze their spectra to measure various emission lines and calculate black hole (BH) masses, finding general agreement with previously found mass scaling relations and nine potential intermediate-mass BH candidates. Furthermore, we reanalyze the light curves of our candidates to calculate the dampening timescaleτ_DRWassociated with the DRW and see a similar correlation between this value and the BH mass. Finally, we estimate the active fraction as a function of stellar mass and see evidence that the active fraction increases with host mass. 

Recent observations at low redshift have revealed that some post-starburst galaxies retain significant molecular gas reservoirs despite low ongoing star formation rates, challenging most theoretical predictions that rely on heating or expelling gas reservoirs to shut down star formation. To test whether this finding holds during the peak epoch of quenching, here we present Atacama Large Millimeter/submillimeter Array CO(2–1) observations of five spectroscopically confirmed massive post-starburst galaxies at z~ 1.4 from the HeavyMetal survey. While four galaxies are undetected in CO emission, we detect MH2 ∼ 10^9.7 M⊙ of molecular gas in one system. The detected system is a close pair of two massive (M_star = 10^11.1−11.2 M⊙) post-starburst galaxies with no clear tidal features, likely caught in the early stages of a major merger. These results suggest that mergers may be a key factor in retaining molecular gas while simultaneously suppressing star formation in quenched galaxies at high redshift, possibly by driving increased turbulence that decreases star formation efficiency. Our nondetected galaxies have postburst ages >200 Myr, consistent with results at z < 1; however, our gas-rich post-starburst pair is significantly older than typical gas-rich quenched systems at low redshift. Our results highlight the importance of major mergers in shaping the cold gas content of quiescent galaxies during the peak epoch of quenching. 

Tracking the cold molecular gas contents of galaxies is critical to understand the interplay between star formation and galaxy growth across cosmic time. Observations of the long-wavelength dust continuum, a proxy for the cold gas, are widely used in the high-redshift community because of their ease and efficiency. These measurements rely on the assumption of a molecular gas-to-dust mass ratio, typically taken to be δ_GDR ≈ 100 in massive, metal-rich systems. We present Atacama Large Millimeter/submillimeter Array observations of the 870μm dust continuum in a sample of five massive quiescent galaxies at z ∼ 1 with existing detections of CO(2–1). We find surprisingly weak dust emission, falling a factor of ≳0.4–0.8 dex below the typical correlation between CO and continuum luminosity. We interpret this dust deficiency as evidence for unusually high δ_GDR in these galaxies, which we calculate to range from 300 to at least 1200. Our results and other observations from the literature are generally compatible with predictions from the SIMBA cosmological simulation that dust is preferentially destroyed in quiescent galaxies. Ultimately, we conclude that the dust continuum is a highly unreliable tracer of the molecular gas in high-redshift quiescent galaxies. As a consequence, we may know much less about the cold gas contents of this population than previously thought. 

Abstract We present a detailed analysis of AT 2020nov, a tidal disruption event (TDE) in the center of its host galaxy, located at a redshift ofz= 0.083. AT 2020nov exhibits unique features, including double-peaked Balmer emission lines, a broad UV/optical flare, and a peak log luminosity in the extreme-ultraviolet (EUV) estimated at $\sim 45.66_{-0.33}^{+0.10}\mathrm{erg}{\mathrm{s}}^{-1}$ . A late-time X-ray flare was also observed, reaching an absorbed luminosity of 1.67 × 10⁴³erg s⁻¹approximately 300 days after the UV/optical peak. Multiwavelength coverage, spanning optical, UV, X-ray, and mid-infrared (MIR) bands, reveals a complex spectral energy distribution (SED) that includes MIR flaring indicative of dust echoes, suggesting a dust covering fraction consistent with typical TDEs. Spectral modeling indicates the presence of an extended, quiescent disk around the central supermassive black hole with a radius of $\sim 5.06_{-0.77}^{+0.59}\times 10^4{R}_{\mathrm{g}}$ . The multicomponent SED model, which includes a significant EUV component, suggests that the primary emission from the TDE is reprocessed by this extended disk, producing the observed optical and MIR features. The lack of strong active galactic nuclei signatures in the host galaxy, combined with the quiescent disk structure, highlights AT 2020nov as a rare example of a TDE occurring in a galaxy with a dormant but extended preexisting accretion structure. 

Abstract Shocked POstarburst Galaxies (SPOGs) exhibit both emission lines suggestive of shock-heated gas and poststarburst-like stellar absorption, resulting in a unique subset for galaxy evolution studies. We have observed 77 galaxies that fulfilled the SPOG criteria selection using the DeVeny Spectrograph on the Lowell Discovery Telescope. Our long-slit minor axis spectra detect Hαand [OIII] in some SPOGs out to 6 kpc above the galactic plane. We find extraplanar ionized gas in 31 targets of our sample overall. Using their internal and external kinematics, we argue that 22 galaxies host outflows with ionized gas masses ranging from 10²M_⊙to 10⁵M_⊙. The rest are likely extended diffuse ionized gas. A positive correlation exists between active galactic nuclei (AGN) luminosity and the extraplanar gas extent, velocity dispersion, and mass—suggesting that the AGN may indeed drive the outflows detected in AGN hosts. The low masses of the extraplanar gas suggest that these outflows are not depleting each galaxy’s gas reserves. The outflows, therefore, are not likely a significant quenching mechanism in these SPOGs.