arXiv subjects

Vincenzo R. D'Onofrio

Publications and source records attributed to Vincenzo R. D'Onofrio.

11 recordsLinked to original sources

arXiv2026

SQuIGGLE: Radio AGN Found Predominantly in Young, Gas-rich Post-starburst Galaxies at z ~ 0.7

The processes that rapidly quench massive galaxies and maintain their quiescence remain poorly understood. Substantial molecular gas reservoirs can survive this shutdown in post-starburst galaxies, raising the question of what prevents the remaining gas from efficiently forming stars. We present deep, subarcsecond VLA 6 GHz observations of 52 massive SQuIGGLE post-starburst galaxies at $z\sim0.7$ to test the prevalence and mechanical impact of radio activity during the gas-rich post-burst phase. We detect 6 GHz continuum emission in 18/52 galaxies ($\approx$35\%), spanning $\log(L_{1.4\,{\rm GHz}}/{\rm W\,Hz^{-1}})\simeq23.0$--$25.0$ and generally exceeding the contributions expected from ongoing star formation and the fading starburst, favoring an AGN origin. Ancillary data at other wavelengths provide little evidence for a population of luminous, radiatively efficient AGN, suggesting that these sources are instead dominated by comparatively weak, mechanically powered radio AGN. Radio activity is strongly concentrated within the first $\sim$200 Myr post-burst and is predominantly associated with galaxies retaining substantial gas reservoirs. Above a common radio luminosity threshold, the radio detection fraction is enhanced by a factor of $\approx$2.5 relative to the radio AGN candidate fraction in mass- and redshift-matched quiescent LEGA-C galaxies, primarily due to lower power sources. For efficient jet--ISM coupling, the inferred mechanical power could supply the approximate energy required to unbind the molecular gas on timescales comparable to its observed decline. Together, these results identify a population of radiatively inefficient AGN hosted predominantly by young, gas-rich post-starburst galaxies at $z\sim0.7$ and suggest that they may have a role in maintaining inefficient star formation.

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arXiv2026

SQuIGG$\vec{L}$E: Spatially resolved NIRSpec Pa$α$ reveals that the most CO-luminous, $z\sim0.7$ post-starburst galaxies exhibit falling---but still active---star formation behind optically thick dust

One of the fundamental uncertainties in the study of galaxies at the interface between star formation and quiescence--post-starburst galaxies--is their instantaneous star formation rate. While these galaxies appear quiescent in the rest UV-optical, many of the youngest systems are highly CO luminous, implying dense molecular gas, and potentially star formation. However, their instantaneous star formation rates have proved elusive, as measurements with rest-optical emission lines or UV-to-IR SED fitting yield order-of-magnitude uncertainty. Here, we present JWST/NIRSpec G395M/170LP integral field spectroscopy of the three most CO-luminous massive galaxies in the SQuIGG$\vec{L}$E survey, spatially resolving Pa$α$/Br$γ$/Br$β$ to map the dust-corrected star formation rate. We find that these galaxies host star formation rates of $27-80$ $M_\odot \ \mathrm{yr^{-1}}$, though $\sim30-40\%$ of the emission may arise from non-star-forming ionization (AGN or shocks), implied by high [FeII]/Pa$α$ in central spaxels. We also find effective $A_{\mathrm{Pa}α}\sim1$ and individual $\sim700$ pc spaxels with $A_{\mathrm{Paα}}\sim2$, implying significant dust obscuration of nebular regions that contribute little to the rest-optical lines. These galaxies are not consistent with total quiescence; the measured star formation rates place these galaxies on or above the main sequence. However, their star formation rates \textit{are} significantly lower ($\sim0.5-1$ dex) than the peak star formation rates inferred from spectrophotometric fitting. We propose that the CO luminous post-starburst phase represents the last gasp of star formation in galaxies on the rapid quenching pathway, and that dust-obscured star formation, outflows, and (speculatively) an uncertain CO-to-H2 conversion reconcile their gas exhaustion with observed timescales of fading.

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arXiv2026

SQuIGG$\vec{L}$E: Ubiquitous Cool Gas Outflows with Large Mass-Loading Factors in $z\sim0.7$ Post-starburst Galaxies

While recent James Webb Space Telescope studies have highlighted cool gas outflows as an important mechanism for rapid quenching at $z\gtrsim2$, such space-based spectroscopic samples remain limited in size. In this work, we search for and characterize cool gas outflows traced by Fe II $λλ$2586,2600 and Mg II $λλ$2796,2803 absorption in post-starburst galaxies (PSBs) at $0.5<z<0.9$, which are accessible to ground-based spectroscopy. Utilizing the SQuIGG$\vec{L}$E survey containing over 1300 PSBs, we stack spectra in bins of stellar mass, (specific) star formation rate, burst mass, burst mass fraction, and time since quenching. We observe blueshifted line centroids indicative of outflows in all stacks except the one containing galaxies that quenched more than 260 Myr ago. Outflow velocities decline with increasing time since quenching, while showing little correlation with other galaxy properties. The inferred outflows have large mass loading factors of 1 -- 120, maximum velocities above the interstellar medium escape velocities of their host galaxies, and energy and momentum fluxes exceeding those expected from the current star formation. Our results suggest that cool gas outflows are ubiquitous in intermediate-redshift PSBs and are likely relic outflows launched by previous starburst or AGN activity. These outflows have the potential to quench star formation by transporting gas into the galactic halos, consistent with outflows playing an important role in rapid quenching from intermediate to high redshift.

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arXiv2026

Molecular Gas Excitation in z ~ 0.7 Gas-Rich Post-starburst Galaxies from SQuIGGLE

Many post-starburst galaxies at $z\sim0.7$ 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 post-burst phase. We present new Atacama Large Millimeter/submillimeter Array CO(5-4) observations of nine gas-rich post-starburst galaxies at $z\sim0.7$ from the Studying Quenching in Intermediate-z Galaxies: Gas, angu$\vec{L}$ar momentum, and Evolution (SQuIGG$\vec{L}$E) 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 8/9 targets and find that most have moderate CO excitation with $r_{52}\equiv L'_{\rm CO(5-4)}/L'_{\rm CO(2-1)}\approx0.1-0.3$. These systems show no clear trend between $r_{52}$ and either total or surface-density of star formation. Specifically, all objects have $Σ_{\mathrm{SFR}} \sim 0.01-1\ \text{M}_\odot\ \text{yr}^{-1}\ \text{kpc}^{-2}$, 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 $r_{52}\approx0.6$; its elevated excitation likely requires significant non-stellar heating, with a contribution from potentially obscured star formation. Together, most gas-rich SQuIGG$\vec{L}$E post-starbursts 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.

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arXiv2026

A Possible Protocluster of Galaxies Serendipitously Discovered in the Field of an Intermediate-Redshift Post-starburst Galaxy

We present the serendipitous discovery of an overdensity of submillimeter galaxies (SMGs) in the field of SDSSJ0909-0108, a massive z~0.7 post-starburst galaxy from the SQuIGGLE survey. ALMA observations at 870um and 2mm reveal six galaxies within a 35'' region with flux ratios consistent with emission from dust. Given the rarity of 870um sources and the small field-of-view of ALMA, we speculate that some of these sources are physically associated. None of the sources are at the same redshift as the post-starburst, and four do not have spectroscopic redshifts. We suggest that follow-up optical and/or ALMA observations be carried out to measure redshifts for the galaxies in this potential protocluster environment.

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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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arXiv2025

Unusually High Gas-to-Dust Ratios Observed in High-Redshift Quiescent Galaxies

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 GDR ~ 100 in massive, metal-rich systems. We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the 870um 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 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.

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arXiv2025

Meet the Neighbors: Gas Rich "Buddy Galaxies" are Common Around Recently Quenched Massive Galaxies in the SQuIGG$\vec{L}$E Survey

In this work, we characterize the environments of massive ($\log(M_\odot/M_\star)\sim11.2$) $z\sim0.7$ post-starburst galaxies (PSBs) by studying serendipitously-detected CO(2-1) emitters found in targeted observations of the SQuIGG$\vec{L}$E sample. We report $31\pm6\%$ of the galaxies from this survey host nearby gas-rich ``buddies'' with stellar masses $\geq 10^{10},M_\odot$ and molecular gas comparable to their central PSBs ($M_{H_{2}} \sim 10^{10} M_\odot$), but $\sim0.8$ dex lower stellar mass ($\sim 10^{10.4} M_\odot$). Based on their location in position-velocity space, each buddy is consistent with being bound to the haloes of their SQuIGG$\vec{L}$E host galaxies. We compare to the UniverseMachine model and find that SQuIGG$\vec{L}$E galaxies host a typical number of neighbors for their stellar mass, suggesting that PSBs live in environments typical of co-eval similarly-massive galaxies.

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arXiv2025

SQuIGG$\vec{L}$E: Buried star formation cannot explain the rapidly fading CO(2-1) luminosity in massive, $z\sim0.7$ post-starburst galaxies

Observational and theoretical studies have long held that rapid gas consumption in starbursts is responsible for the formation of quiescent galaxies. 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 ALMA CO(2-1) observations of 50 massive ($\log(M_\star/M_\odot)\sim11.2$) post-starburst galaxies from the SQuIGG$\vec{L}$E sample at $z\sim0.7$. We detect a large fraction (27/50) of the galaxies in CO(2-1). Furthermore, we find that the CO luminosity correlates with the age of the recent starburst, suggesting a gas-removal timescale of $\lesssim140$ Myr, an order of magnitude shorter than is implied by their rest optical star formation rates. We perform new spectral energy distribution fits incorporating mid- and far-IR photometry to test whether dust-obscured star formation can explain this trend. We find that while allowing for buried star formation can raise star formation rates by $\sim0.5$ 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 SQuIGG$\vec{L}$E galaxies will soon rejuvenate.

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arXiv2025

Quenching Through Tidal Gas Removal: Molecular Gas and Star Formation in Tidal Tails of z ~ 0.7 Post-Starburst Galaxies

The active suppression of star formation in galaxies is critical in preventing the growth of overly massive systems and explaining the formation of present-day elliptical galaxies. We present a high-resolution, spatially-resolved multiwavelength study of two z ~ 0.7 massive post-starburst galaxies, SDSS J1448+1010 and SDSS J2258+2313, from the SQuIGGLE survey (Studying Quenching in Intermediate-z Galaxies: Gas, anguLar momentum, and Evolution), providing new insights into the role of mergers in driving quenching. ALMA CO(2-1) observations show that both galaxies removed ~50% of their molecular gas into extended tidal tails, spanning up to 65 kpc, following recent mergers. HST WFC3 imaging and grism spectroscopy show that while SDSS J1448+1010 exhibits Halpha emission in its northern tidal tail consistent with ongoing star formation, SDSS J2258+2313 lacks detectable star-forming activity outside the central galaxy. VLA 6 GHz continuum data reveal compact radio emission in SDSS J2258+2313, while SDSS J1448+1010 hosts small radio jets indicative of AGN activity. Both galaxies retain substantial molecular gas reservoirs in their central regions that appear more turbulent than 'normal' star-forming galaxies, likely contributing to the observed low star formation rates in the hosts. Despite similarities in their cold gas content and tidal features the galaxies are distinct from each other in their star formation, gas-star alignment, and radio morphology, highlighting the complexity of tidal gas removal as a quenching mechanism at intermediate redshifts.

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arXiv2025

Cold gas in a post-starburst pair at z ~ 1.4: major mergers as a pathway to quenching in the HeavyMetal survey

Recent observations at low redshift have revealed that some post-starburst galaxies retain significant molecular gas reservoirs despite low ongoing star formation rates, challenging theoretical predictions for galaxy quenching. To test whether this finding holds during the peak epoch of quenching, here we present ALMA CO(2-1) observations of five spectroscopically confirmed post-starburst galaxies at z ~ 1.4 from the HeavyMetal survey. While four galaxies are undetected in CO emission, we detect M_H2 ~ 10^9.7 Msun of molecular gas in one system. The detected system is a close pair of massive (M* = 10^(11.1-11.2) Msun) 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. Unlike previous studies at z < 1, we find no correlation between molecular gas mass and time since quenching. This may be explained by the fact that -- despite having similar UVJ colors -- all galaxies in our sample have post-burst ages 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.

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