Search for: All records

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. 

We present GBT-EDGE, a new CO(1-0) survey using the Green Bank Telescope to map 62 nearby (10-140 Mpc) galaxies spanning the star-forming main sequence (SFMS), green valley, and red sequence. The galaxy sample is selected from the CALIFA survey with integral field spectroscopy (IFS), which provides a representative census of local galactic environments. Combining the CO dataset with CALIFA's optical IFS measurements, we derive molecular gas masses, star formation rates (SFR), metallicities, and stellar mass densities to measure star formation efficiency (SFE) and investigate the physical drivers of galaxy quenching. We obtain a median molecular gas depletion time of $$2.10^{+2.35}_{-1.31}$$, $$6.90^{+17.00}_{-3.67}$$, and $$127.7^{+201.6}_{-113.4}$$ Gyr for our sample of main sequence, green valley, and red galaxies, respectively, assuming a Galactic CO-to-H2 conversion factor. By applying various conversion factor prescriptions, we also confirm a systematic decrease of SFE with galaxy's offset below the SFMS, regardless of the adopted prescription. This suggests that the low SFR in some quenched galaxies is primarily driven by suppressed SFE rather than an absence of molecular gas. Our results provide evidence that galaxies below the main sequence can retain substantial molecular gas reservoirs comparable to star-forming galaxies, but they exhibit longer depletion times and form stars inefficiently, possibly due to the combined effects of low gas density and morphological quenching mechanisms. 

We report the discovery of an extended emission-line region (EELR) in MUSE observations of Markarian 950, a nearby (z = 0.01628) poststarburst (PSB) galaxy that hosted the tidal disruption event (TDE) iPTF 16fnl. The EELR requires a nonstellar ionizing continuum with a luminosity erg s‑1, inconsistent with the current weak state (L IR,AGN < 2.5 × 1042 erg s‑1) of the galactic nucleus. The ionized gas has low velocity (∼–50 km s‑1) and low turbulence (σ gas ≲ 50 km s‑1) and is kinematically decoupled from the stellar motions, indicating that the gas kinematics is not active galactic nucleus (AGN) driven. Markarian 950 is the third PSB galaxy to host a weak nuclear ionizing source as well as an EELR and a TDE. The overall properties of these three galaxies, including the kinematics and accretion history, are unusual but strikingly similar. We estimate that the incidence of EELRs in PSB-TDE hosts is a factor of ∼10 × higher than in other PSB galaxies. This suggests that a gas-rich postmerger environment is a key ingredient in driving elevated TDE rates. Based on the current observations, we cannot rule out that the EELRs may be powered through an elevated TDE rate in these galaxies. If the EELRs are not TDE powered, the presence of intermittent AGN activity, and in particular the fading of the AGN, may be associated with an increased TDE rate and/or an increased rate of detecting TDEs. 

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.” 

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. 

Abstract Outflows are one of the most spectacular mechanisms through which active galactic nuclei (AGN) impact their host galaxy, though the role of AGN-driven outflows in global star formation regulation across the galaxy population is unclear. NGC 1266 is an excellent case study for investigating outflows and star formation quenching because it is a nearby (D ∼ 30 Mpc) AGN host galaxy with an outflow driving shocks through the interstellar medium (ISM) and has recently quenched its star formation outside the nucleus. While previous works have studied the molecular outflow from its CO emission, to fully characterize the impact the outflow has on the ISM observations probing the dense, cold gas are necessary. Our Atacama Large Millimeter/submillimeter Array Cycle 0 observations do not detect a molecular outflow in¹³CO(2–1) and yield a lower limit of¹²CO/¹³CO ≥ 250, suggesting a highly optically thin CO outflow with low¹³CO abundance. In contrast, we detect substantial HCN(1–0) emission in the outflow, with an HCN(1–0)/¹²CO(1–0) ratio of 0.09, consistent with global measurements of many star-forming galaxies and luminous infrared galaxies. We conclude that the CO emission traces a diffuse component of the molecular gas with a low optical depth, whereas the HCN(1–0) traces dense clumps of gas entrained in the outflow. We measure an upper limit molecular outflow rate of <85M_⊙yr^–1. Assuming the ongoing nuclear star formation and outflow continue at the same rates, NGC 1266 will deplete its gas reservoir in 450 Myr or longer, indicating that relatively low-level AGN feedback is capable of gradually expelling the molecular gas reservoir after a rapid quenching event. 

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.