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Charlie Conroy

Publications and source records attributed to Charlie Conroy.

At least 19 recordsLinked to original sources
arXiv2026

Modeling the Ages and Chemical Abundances of Elliptical Galaxies

Spectroscopic studies of elliptical galaxies show that their stellar population ages, mean metallicity, and $α$-enhancement traced by [Mg/Fe] all increase with galaxy stellar mass or velocity dispersion. We use one-zone galactic chemical evolution (GCE) models with a flexible star formation history (SFH) to model the age, [Mg/H], and [Mg/Fe] inferred from simple stellar population (SSP) fits to observed ellipticals at $z \sim 0$ and $z \sim 0.7$. We show that an SSP fit to the spectrum computed from a full GCE model gives ages and abundances close to the light-weighted, logarithmically averaged values of the composite stellar population, , <[Mg/H]>, and <[Mg/Fe]>. With supernova Mg and Fe yields fixed to values motivated by Milky Way stellar populations, we find that predicted <[Mg/H]>- and <[Mg/Fe]>- relations are surprisingly insensitive to SFH parameters: older galaxies have higher <[Mg/Fe]>, but the detailed form of the SFH has limited impact. The star formation efficiency and outflow efficiency affect the early and late evolution of <[Mg/H]>, respectively; explaining observed trends requires higher star formation efficiency and lower outflows in more massive galaxies. With core collapse supernova yields calibrated to the plateau [Mg/Fe]$_{\rm cc} \approx0.45$ observed in many Milky Way studies, our models underpredict the observed <[Mg/Fe]> ratios of ellipticals by 0.05-0.1 dex. Increasing the core collapse yield ratio to [Mg/Fe]$_{\rm cc} = 0.55$ improves the agreement, though the models still lie below the data. We discuss potential resolutions of this discrepancy, including the possibility that many ellipticals terminate their star formation with a self-enriching, terminating burst that reduces the light-weighted age and boosts <[Mg/Fe]>.

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arXiv2026

Which Milky Way Streams Make the Best Dark Matter Detectors?

The abundance and properties of low-mass dark matter subhalos can be inferred by measuring the density and velocity structure of stellar streams, testing physical models of dark matter. Which streams make the most promising dark matter detectors, and which subhalos would they encounter? We use the semi-analytic model galacticus to simulate the Milky Way's dark subhalos, including tidal stripping under the influence of the galactic disk. Deriving stream initial conditions that best match present-day observations, we forecast subhalo encounters for 24 globular cluster streams around the Milky Way. Over their lifetimes, the 10 most perturbed streams are predicted to each experience $\approx 2$-$12$ significant subhalo encounters with velocity kicks $v_\mathrm{kick} > 0.1$ km s$^{-1}$. Jet, AAU, GD-1, and Palomar 5 lead the list, with Jet encountering twice the subhalos of any other stream. The subhalos that encounter streams have been tidally stripped to $1$-$20\%$ of their peak mass and are twice as compact as previous works have assumed. A spectroscopic survey of streams with sub-km s$^{-1}$ precision could reveal the influence of dark subhalos below the threshold of galaxy formation. Predicting the abundance and scatter of low-mass subhalos that reach the inner galaxy remains a dominant uncertainty in connecting stellar streams to models of dark matter.

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arXiv2026

ENhanced Galactic Atmospheres With Arepo: Resolving the CGM at 200 pc with the ENGAWA Simulations

Simulating the small-scale features and dynamics of the circumgalactic medium (CGM) is computationally challenging due to its large volume, low densities, multiphase structure, and chaotic environmental effects. Traditional mass-based refinement schemes focus computational power on the high-density regions, thus alternative techniques are required to study the details of the CGM. In this paper, we introduce a new suite of four cosmological zoom-in simulations of Milky Way-like galaxies in which we include fixed-volume refinement throughout the CGM combined with the IllustrisTNG stellar and AGN feedback model down to redshift zero. Reaching spatial resolutions of 200 pc, we see enhancements in low ion column densities (H I and Mg II) and the number of cold clouds around galaxies, relieving some of the longstanding tensions between simulations and observations of the CGM. We additionally apply the COLT radiative transfer code in post-processing to account for stellar radiation, providing a more realistic gauge of ion populations. We find a reduction in the H I with minimal impact to the Mg II and O VI, tempering the impact of resolution while still providing results consistent with observations. In addition to the increase in the number of cold clouds in the CGM, we find that their intermediate temperature boundary regions are reduced in size as the resolution is increased, leading to smoother transitions to the ambient CGM temperature. This paper outlines initial results from this fixed-volume simulation suite which will serve as a basis for future explorations of CGM dynamics, gas accretion, and galaxy evolution.

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arXiv2026

The Blue Jay Survey: Deep JWST Spectroscopy for a Representative Sample of Galaxies at Cosmic Noon

We present the Blue Jay survey, a cycle 1 JWST program aimed at studying the stellar and gas content of galaxies at cosmic noon. The survey consists of deep spectroscopy for 153 targets observed over two pointings in the COSMOS field using the NIRSpec micro-shutter assembly (MSA). We employed the three medium-resolution gratings, G140M, G235M, and G395M, with exposure times of 13 hours, 3.2 hours, and 1.6 hours, respectively. We thus obtained full coverage of the 1 - 5 um range, corresponding to the entire rest-frame optical wavelength range, with a spectral resolution R~1000. Parallel observations provided deep multiband NIRCam imaging, which partially overlaps with the spectroscopic observations. The sample was carefully selected to provide a census of galaxies over the redshift range 1.7 < z < 3.5 without strong biases in color, star formation rate, or other properties. Since the standard A-B nod subtraction leads to flux self-subtraction for large galaxies, we constructed a master background from empty shutters and subtracted it from each of the science spectra. In order to obtain self-consistent fits of spectroscopic and photometric data, we measured multiband photometry using space-based observations from the exact area in the sky where the NIRSpec 1D spectrum is extracted. The spectra contain a wealth of emission and absorption lines, including hydrogen lines, helium lines, metal emission lines from ionized gas, metal stellar absorption lines, and resonant absorption lines. Spectroscopic redshifts are unambiguously measured for 93% of the sample. The Blue Jay dataset, which we publicly release, represents the ideal sample for studying the stellar populations, neutral gas, and ionized gas in cosmic noon galaxies, including star formation histories, quenching, outflows, metallicity, and dust attenuation.

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arXiv2026

A census of massive eclipsing binaries in the Whirlpool Galaxy

We present a census of massive eclipsing binary (EB) candidates in the Whirlpool Galaxy (M51), a face-on spiral galaxy at 7.5 Mpc with $Z\sim Z_\odot$. Using 34 epochs of red-optical Hubble Space Telescope (HST) photometry and a single epoch of broadband UV-optical photometry, we identify 173 massive EB candidates ($>5~{\rm M_\odot}$) with orbital periods $P_{\rm orb}$=1-30 days. The sample traces young stellar populations across the spiral arms of M51. Joint light-curve and spectral energy distribution fits for 136 systems yield binaries spanning $T_{\rm eff}=10{,}000$-$50{,}000$ K, $R=7$-$66~{\rm R_\odot}$, and masses of $5$-$120~{\rm M_\odot}$. We use detailed injection-recovery simulations to quantify the survey's completeness and infer intrinsic properties of the massive binary population. At the population level, we infer a close-binary fraction of $f_{\rm close}=27.4\pm7.1\%$ for $2\leq P_{\rm orb}/{\rm d}<20$ and $0.1\leq q\leq1$. Over the same period range, the intrinsic period distribution is consistent with being log-uniform, ${\rm d}N/{\rm d}\log P_{\rm orb}\propto P_{\rm orb}^π$ with $π=0.29\pm0.32$. These demographics broadly match those of massive-star populations in the Milky Way, LMC, and SMC, with tentative evidence for a lower close-binary fraction at lower metallicity. Across the $\sim0.2$-$1.1~Z_\odot$ range spanned by these galaxies, the overall similarities suggest that the formation of close massive binaries depends only weakly on metallicity. Our survey establishes EBs as a powerful tool for measuring massive-binary demographics beyond the Local Group and provides a rich panchromatic census of $\sim$100,000 luminous stars and variables in M51.

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arXiv2026

Classical Cases of Non-solar Mixing Length in Low Mass Stars

The treatment of convection is one of the largest remaining uncertainties in models of low mass stars. The Mixing Length Theory (MLT) for super-adiabatic convection has come under particular scrutiny. Evidence is mounting that a single value of the mixing length parameter ($α_\mathrm{MLT}$) should not be applied universally across stellar model grids, although simulations and asteroseismic calibrations disagree on how it should vary with stellar parameters. A variable $α_\mathrm{MLT}$ causes critical systematic changes to the ages of low mass stars, the key age tracers for galactic and exoplanetary studies. In this work we use classical (non-seismic) geometric radii and specialized MIST isochrones with a variable $α_\mathrm{MLT}$ to measure mixing length in detached eclipsing binaries (DEBs) and interferometrically resolved stars, finding plenty of evidence for non-solar $α_\mathrm{MLT}$. In particular we find that standard evolutionary models overpredict the radii of metal-poor interferometric stars and that a sub-solar $α_\mathrm{MLT}$/$α_{\mathrm{MLT},\odot}\sim0.50-0.75$ can neatly explain this discrepancy, consistent with other empirical calibrations and in stark contrast to simulations. We infer low convective efficiency in cool, rapidly rotating lower main-sequence stars, consistent with the known phenomenon of magnetically-induced radius inflation. We also identify several slowly rotating DEBs whose measurements cannot be reproduced by standard isochrones, and we propose these systems as useful case studies of non-solar mixing length in stars outside of the Sun. However, we find no definitive population level correlations between $α_\mathrm{MLT}$ and stellar parameters among the DEBs, calling into question the existence of a ubiquitous mixing length calibration in low mass stars.

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arXiv2026

The Binary Populations of Stellar Streams are Set by Cluster Dynamics

We present a suite of direct N-body simulations of low mass ($<10^4~M_{\odot}$) globular cluster streams initialized with observationally-motivated binary demographics in order to understand the effect of in-cluster dynamical processing on the stream binary population. The models are initialized with a range of stellar densities and cluster orbits, and Poisson variation in the number of massive and short-lived stars. Wide binaries are disrupted on short timescales by internal tides and on long timescales by two-body encounters. Tides are most important prior to impulsive mass loss-driven cluster expansion. Close binaries ($P_{\rm orb}<10^2~\rm yr$) are most abundant at the stream center due to cluster mass segregation. The wide binary fraction and the degree of binary segregation in the resulting stream are sensitive to the initial cluster density and massive star fraction. In mock radial velocity surveys of the simulated streams, undetectable binaries have velocity amplitudes of $\sim$$0.5$-$1~\rm km~s^{-1}$, adding $\sim0.1~\rm km\ s^{-1}$ of velocity dispersion to the streams, and are dynamically depleted by $\sim10$-$60\%$ compared to the initial binary population. Custom N-body models of Milky Way streams with binaries will allow a holistic understanding of their dynamical structures in advance of upcoming multi-epoch spectroscopic surveys.

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arXiv2026

Hidden mass in early galaxies revealed by bottom-heavy initial mass functions

James Webb Space Telescope (JWST) observations have revealed that massive galaxies formed and evolved faster than predicted by galaxy formation models, with many having already assembled a large mass in stars approximately 12 billion years ago. However, masses of distant galaxies are uncertain, as they assume a distribution of stellar birth masses (the initial mass function (IMF)) similar to that in the Milky Way. Specifically, the contribution from low-mass stars, which make up the bulk of stellar mass, is not directly observed, but inferred based on an extrapolation of the Milky Way IMF. Here, we provide robust constraints on the low-mass IMF beyond the local Universe from full-spectrum models. Using ultra-deep spectra of nine massive quiescent galaxies at redshift $z$ $\approx0.7$ from the JWST Initial Mass Function of Early Red NIRSpec Objects program, extended to bluer wavelengths with deep Very Large Telescope Large Early Galaxy Astrophysics Census spectra, we find that the most massive galaxies have excess low-mass stars. Remarkably, our oldest galaxy (formation redshift $z_{\rm form} > 5$) has the most bottom-heavy IMF. This galaxy may be a descendant of JWST's 'impossibly early' galaxies, implying that the latter may have had similarly bottom-heavy IMFs increasing their masses by a factor of approximately $4\pm1$. Our findings may thus amplify the tension with galaxy formation models.

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arXiv2026

Calibrating Eruptive Mass Loss in Red Supergiants with Local Group Data

We calibrate a physically motivated, super-Eddington eruptive mass-loss prescription for red supergiants (RSGs) using Local Group stellar populations. Building on MESA models that add eruptive mass loss with a free scaling parameter $ξ$, we generate stellar evolution tracks and isochrones, and synthesize mock populations at metallicities of $Z/Z_\odot=0.2,\ 0.4$, and $1.0$. We compare model luminosity functions to observations of RSGs in the SMC, LMC, and M31, restricting to $3.5<\log T_{\rm eff}/K<3.75$ and $\log(L/L_\odot)>4.5$. By-eye fits to the observations yield values of $ξ_\mathrm{SMC}=0.0-0.05$, $ξ_\mathrm{LMC}=0.1$, and $ξ_\mathrm{M31}=0.35$, implying a positive, linear trend between the strength of eruptive mass-loss and metallicity. This calibrated eruptive mass loss prevents stars with initial masses $\gtrsim 20~M_\odot$ from evolving to become red supergiants, with implications for the mass spectrum of core-collapse progenitors, compact remnants, early supernova interaction signatures, and the spectral energy distributions of unresolved galaxies.

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arXiv2026

Probing neutral outflows in z ~ 2 galaxies using JWST observations of Ca II H and K absorption lines

Using deep JWST/NIRSpec spectra from the Blue Jay survey, we perform the first systematic investigation of neutral gas content in massive galaxies at Cosmic Noon based on the Ca II H, K absorption lines. We analyze a sample of 9 galaxies at 1.8 < z < 2.8 with stellar masses > 10.6, for which we detect neutral gas absorption both in Ca II and in Na I. After removing the stellar continuum using the best-fit model obtained with Prospector, we fit the excess absorption due to neutral gas in the Ca II H, K doublet and in the Na I D doublet, together with nearby emission lines produced by ionized gas. We measure covering fractions between 0.2 and 0.9 from the Ca II H and K lines, which are spectrally well resolved in the NIRSpec R ~ 1000 observations, unlike the absorption lines in the Na I D doublet. We measure the velocity shift, velocity dispersion, and column density separately for Ca II and Na I. About half of the galaxies present blueshifted Ca II, indicative of an outflow of neutral gas, consistent with previous results based on Na I. The velocity shift and the column density measured from Ca II are correlated with those measured from Na I, implying that these absorption lines trace gas in similar physical conditions. However, the column densities are not in a 1:1 relation, meaning that the relative amount of Ca II and Na I atoms along the line of sight varies with the gas column density. After discussing possible reasons for this behavior, we derive an empirical relation between the column density of Ca II and the column density of Na I and, in a more indirect way, of neutral hydrogen H I. This calibration offers a new way to estimate the outflow mass and the mass outflow rate for the neutral phase from current and future JWST observations of massive galaxies at Cosmic Noon and beyond

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arXiv2026

A Path to an All-Sky Survey with Roman

A deep, space-based, all-sky near-infrared survey carried out with the Nancy Grace Roman Space Telescope would constitute a foundational astronomical infrastructure for decades to come. In this white paper, we present a concrete and feasible path to imaging the entire sky at $\sim0.1''$ resolution, beginning with high-impact fields in Cycle 1 and scaling to ultra-wide coverage within the nominal mission. This first-epoch survey will reach $\mathrm{H}\sim25.5$ AB mag (5$σ$) and maximize synergies with contemporaneous observatories, while preserving substantial time for other ambitious Roman programs. We outline representative scheduling scenarios and an example Cycle 1 program that triples early Roman-LSST overlap and delivers high-value community data products such as LSST forced photometry, joint \textit{Gaia}-Roman astrometry, and catalogs of Galactic substructure, stong lenses, and other rare systems. The Cycle 1 program will lay the foundation for an eventual all-sky survey, while also delivering high-impact early science. We invite broad community participation in shaping and carrying out both the initial program and the long-term vision of an all-sky Roman survey.

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arXiv2026

JWST Confirmation of a Runaway Supermassive Black Hole via its Supersonic Bow Shock

We present JWST/NIRSpec IFU observations of a candidate runaway supermassive black hole at the tip of a 62 kpc-long linear feature at z=0.96. The JWST data show a sharp kinematic discontinuity at the tip, with a radial velocity change of $\approx 600$ km/s across 0.1'' (1 kpc). The velocity gradient, together with the projected post-shock flow velocity of $\approx 300$ km/s, is well described by a simple shock-compression model of a supersonic object, with a velocity of $v_{BH} = 954^{+110}_{-126}$ km/s and an inclination $i=29^{+6}_{-3}$ deg. The previously puzzling kinematics along the linear feature, with the observed radial velocity decreasing from $\approx 300$ km/s near the tip to $\approx 100$ km/s closer to the former host galaxy, are naturally explained as gradual downstream mixing of shocked gas with the circumgalactic medium through turbulent entrainment. The bow shock interpretation is further supported by the morphology of the gas at the tip of the wake and an analysis of the [OIII]/H$α$, [NII]/H$α$, [SII]/H$α$, and [SIII]/[SII] line ratios. The line ratios are consistent with fast radiative shocks and rapid cooling, with best-fit shock velocities that are in agreement with expectations from the black hole velocity and the shock geometry. Energy conservation over the lifetime of the wake suggests a SMBH mass of $M_{BH} \gtrsim 10^7$ M$_{\odot}$. These results confirm that the wake is powered by a supersonic runaway supermassive black hole, a long-predicted consequence of gravitational-wave recoil or multi-body ejection from galactic nuclei.

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arXiv2025

MESA Isochrones and Stellar Tracks (MIST) III. The White Dwarf Cooling Sequence

We present a substantial update to the MESA Isochrones and Stellar Tracks (MIST) library, extending the MIST model grids and isochrones down the white dwarf (WD) cooling sequence with realistic physics for WD cooling timescales. This work provides a large grid of MESA models for carbon-oxygen core WDs with hydrogen atmospheres (spectral type DA/DC), descended from full prior stellar evolution calculations. The model tracks, isochrones, and WD cooling timescale contours are available on the MIST project website and at https://doi.org/10.5281/zenodo.15242046. Our WD models provide a very large, publicly available grid with detailed physics for WD cooling timescales: realistic interior and envelope compositions, with element diffusion and heavy-element sedimentation, nuclear burning at the base of the WD hydrogen envelope, core crystallization, and C/O phase separation. As a large grid of open-source stellar evolution models, these WD models provide both out-of-the-box model tracks for comparison with observations and a framework for building further WD models to investigate variations in WD physics.

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arXiv2025

How Early Could the Milky Way's Disk Form?

We investigate early, $z > 3$, galaxy formation in a cosmological zoom-in simulation of a close, early-forming Milky Way (MW) analog extracted from TNG50 simulation and resimulated with detailed modeling of cold interstellar medium (ISM) formation, coupled with on-the-fly UV radiative transfer, turbulence-regulated star formation, and stellar feedback. In our enhanced-physics simulation, the galaxy develops a bistable ISM structure (warm, with $T \sim 10^4$ K, and cold, with $T < 100$ K) and exhibits significantly more efficient, early, and bursty star formation than in TNG. Notably, the stellar disk of this MW progenitor forms extremely early, around $z\sim6-7$, and exhibits chemo-kinematic properties consistent with the low-metallicity population of the MW stars. The disk forms rapidly, on a timescale of $\sim$0.2 Gyr which is significantly shorter than the timescale implied by the observable chemo-kinematic signatures of disk spinup, $\sim$0.7 Gyr, due to the scatter in the age--metallicity relation. The rotational support of the gas disk and the location of the galaxy on the main sequence are consistent with early disk galaxies observed by JWST and ALMA at $z\sim4-7$, suggesting that some of these galaxies could be progenitors of MW-like systems. Remarkably, the variation of the global star formation rate (SFR) before disk formation is similar to the observed SFR scatter at these early times. Our findings underscore the critical role of modeling a turbulent cold ISM and turbulence-regulated star formation and feedback in driving early SFR variability, while at the same time enabling early disk formation, without destroying it with overly efficient stellar feedback.

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arXiv2025

From UV-bright Galaxies to Early Disks: the Importance of Turbulent Star Formation in the Early Universe

Bursty star formation at early times can explain the surprising abundance of early UV-bright galaxies revealed by JWST but can also be a reason for the delayed formation of galactic disks in high-resolution cosmological simulations. We investigate this interplay in a cosmological simulation of an early-forming Milky Way analog with detailed modeling of the cold turbulent interstellar medium (ISM), star formation, and feedback. We find that the modeling of locally variable star formation efficiency (SFE) coupled with the ISM turbulence on the scales of star-forming regions is important for producing both early bursty evolution and early formation and survival of galactic disks. Such a model introduces a qualitatively new channel of the global star formation rate (SFR) burstiness caused by chaotic fluctuations in the average SFE due to changes in the ISM turbulence, which, in our simulation, dominates the short-term SFR variability. The average SFE stays low, close to $\sim 1\%$ per freefall time, and its variation decreases when the gas disk forms, leading to only mild effects of stellar feedback on the early disk, enabling its survival. By rerunning our simulation with fixed SFE values, we explicitly show that low SFEs lead to smoother SFR histories and disk survival, while high SFEs lead to bursty SFRs and hinder disk formation. The model with variable SFE switches between these two regimes at the moment of disk formation. These trends are missing in more commonly used star formation prescriptions with fixed SFE; in particular, the prescriptions tying star formation to molecular gas should be interpreted with caution because the two are decoupled at early times, as we also show in this paper.

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arXiv2025

Mapping the Distant and Metal-Poor Milky Way with SDSS-V

The fifth-generation Sloan Digital Sky Survey (SDSS-V) is conducting the first all-sky low-resolution spectroscopic survey of the Milky Way's stellar halo. We describe the stellar parameter pipeline for the SDSS-V halo survey, which simultaneously models spectra, broadband photometry, and parallaxes to derive stellar parameters, metallicities, alpha abundances, and distances. The resulting BOSS-MINESweeper catalog is validated across a wide range of stellar parameters and metallicities using star clusters and a comparison to high-resolution spectroscopic surveys. We demonstrate several scientific capabilities of this dataset: identifying the most chemically peculiar stars in our Galaxy, discovering and mapping distant halo substructures, and measuring the all--sky dynamics of the Milky Way on the largest scales. The BOSS-MINESweeper catalog for SDSS DR19 is publicly available and will be updated for future data releases.

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arXiv2025

Invisible Accretion: Ionized Envelopes of TNG50 HVCs can Sustain Star Formation

Galactic high-velocity clouds (HVCs) are known to be complex, multiphase systems consisting of neutral and/or ionized gas moving at high velocities relative to the rotation of the disk. In this work, we investigate Milky Way-like galaxies from the TNG50 simulation to characterize the properties, morphology, and accretion rates of the warm and hot ionized material comoving with neutral HVCs visible in HI. We find that the ionized gas forms an envelope around the neutral material, and in most cases (73% of the HVCs) it is prolate in morphology. We also find that the ionized mass is ~6 times greater than the neutral mass, which leads to significantly more accretion possible from the ionized gas ($\dot{M}_\mathrm{ion}$) than the neutral gas ($\dot{M}_\mathrm{neut}$), consistent with estimates made from observations of our own Galaxy. We investigate the accretion rates from both phases of HVCs around 47 Milky Way-like galaxies and find that $\dot{M}_\mathrm{ion}$ scales with $\dot{M}_\mathrm{neut}$, and both scale with the star formation rate of the galaxy. Finally, we find that, on average, $\dot{M}_\mathrm{ion}$ could account for 81% of the galactic star formation rate (assuming the material can sufficiently cool and condense), while $\dot{M}_\mathrm{neut}$ can only balance 11%. Thus, the diffuse, ionized, high-velocity circumgalactic medium plays a defining role in the evolution and growth of galaxies at low redshift.

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arXiv2025

Rising from the Ashes II: The Bar-driven Abundance Bimodality of the Milky Way

The Milky Way hosts at least two modes in its present day distribution of Fe and alpha-elements. The exact cause of this bimodality is disputed, but one class of explanations involves the merger between the Milky Way and a relatively massive satellite (Gaia-Sausage-Enceladus) at z~2. However, reproducing this bimodality in simulations is not straightforward, with conflicting results on the prevalence, morphology, and mechanism behind multimodality. We present a case study of a galaxy in the Illustris TNG50 simulation which undergoes sequential phases of starburst, brief quiescence, and then rejuvenation. This scenario results in a pronounced abundance bimodality after a post-processing adjustment of the [alpha/Fe] of old stars designed to mimic a higher star formation efficiency in dense gas. The high- and low-alpha sequences are separated in time by the brief quiescent period, which is not associated with a merger but by the formation of a bar followed by AGN activity. This galaxy indicates a novel scenario in which the alpha-bimodality in the Milky Way is caused by the formation of the bar via AGN-induced quenching. In addition to a stellar age gap in the Milky Way, we predict that abundance bimodalities should be more common in barred as opposed to unbarred galaxies.

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