Exploring the Origin of Rejuvenating Gas from MaNGA Nearby Galaxies

arXiv:2510.25216 · astro-ph.GA · Submitted 2025-10-29 · Read on arXiv

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Introduction to the show: ident: Astrophysics Radio. Generated commentary on the latest astrophysics papers.

Vera: Next we'll be talking about the paper "Exploring the Origin of Rejuvenating Gas from MaNGA Nearby Galaxies".

Jocelyn: The paper was written by Ting-Xuan Li and Po-Feng Wu from Institute of Astrophysics, National Taiwan University and Taiwan.

Vera: Stay tuned as we take you through the paper and discuss its implications.

Jocelyn: We also have Subrahmanyan with us today — guest researcher.

Vera: Alright, let's get started.

Summary of Findings: Vera: Now, let's move to the summary of "Exploring the Origin of Rejuvenating Gas from MaNGA Nearby Galaxies," and what those observations reveal about where this fuel is truly coming from.

Jocelyn: The main finding is that for the majority of these rejuvenating galaxies, that gas isn't actually being pulled in from outside, which challenges a common assumption we often make.

Subrahmanyan: It seems like the initial hypothesis—that external accretion or a minor merger would be the driver—is largely incorrect for most local rejuvenation.

Vera: The evidence they’ve gathered is pretty compelling; they found that the gas metallicities are consistent with what we expect from standard star-forming galaxies, not from fresh, metal-poor infall.

Jocelyn: That’s a huge piece of the puzzle; if the gas were accreted, we would expect a noticeable dilution in metallicity that isn't happening.

Subrahmanyan: They also looked at the metallicity gradients and found they are not flattened, which strongly argues against radial inflows bringing fresh material to the center.

Vera: And it’s not just about the gas; they even checked the kinematics and found that gas velocities in those regions match their surroundings, so no clear sign of distinct components being pulled in.

Jocelyn: The HI gas fractions are also very high, which points toward a pre-existing reservoir within the galaxy rather than something new arriving.

Subrahmanyan: This suggests that the fuel is simply drawn from what’s already available in the galaxy, making this a process driven by internal mechanisms.

Vera: But they did find one specific case of MaNGA twelve thousand eighty-twelve thousand seven hundred five that’s definitely looking at external origin, which is an interesting exception to our rule.

Jocelyn: It's a great example where the low-metallicity and distinct kinematics are unambiguous evidence of something else is happening.

Subrahmanyan: This contrast between the general trend and that single case will be really important for understanding how these processes work in different galaxies.

Vera: We’re going to see if this pattern holds up across different galaxy types in the next segment, so let's look at how they are actually identifying these events.

Improvements and Methodology: Vera: The researchers also put forward some significant improvements to how we identify these rejuvenation events using "Exploring the Origin of Rejuvenating Gas from MaNGA Nearby Galaxies."

Jocelyn: They’ve shown that combining just two stellar absorption features, Dn four thousand and EW(H delta A), is a reliable way to select current rejuvenation.

Subrahmanyan: That’s such a powerful simplification of the problem; we usually need complex spectral fitting, but this uses the most prominent features.

Vera: It's perfect for finding these events across cosmic time, especially in huge spectroscopic surveys like those coming up in WEAVEStePS or PFS SSP.

Jocelyn: The selection criteria are rigorous—they used specific thresholds like Dn four thousand < one point four and EW(H delta A) < 3Å to isolate these spaxels.

Subrahmanyan: By focusing on those specific features, we’ are able to capture the subtle signatures of a short-lived star formation burst without getting lost in the noise from older stellar populations.

Vera: They found that using this method is very effective at catching current events, which is helpful because these secondary bursts don't last long.

Jocelyn: The authors meticulously screened the data too, removing interlopers and those who have AGN contamination to ensure the purity of our sample.

Subrahmanyin: This methodology allows us to isolate a "clean" population of rejuvenated regions that we can then use for statistical studies across different environments.

Vera: It’s important they are using this method consistently, and Jocelyn mentioned that the RJGs tend to be more massive and mostly late-types.

Jocelyn: We need to see how these specific types compare to the broader population in our next segment, but it sounds like the data is ready for a deeper comparison.

Conclusion: Vera: To wrap up our discussion on "Exploring the Origin of Rejuvenating Gas from MaNGA Nearby Galaxies," we’ve seen a lot of evidence pointing toward internal processes fueling these secondary bursts.

Jocelyn: We've concluded that for most local rejuvenation, the gas is simply being drawn from pre-existing reservoirs within the galaxies, rather than being pulled in from external space.

Subrahmanyin: The fact that the RJGs show high HI fractions and have similar metallicities to our control groups really supports this idea of a self-fueled revival.

Vera: We also found no clear signs of gas flowing in from outside, and we didn't see any evidence of tidal interactions with neighboring galaxies either.

Jocelyn: The exceptional case of MaNGA twelve thousand eighty-twelve thousand seven hundred five is a striking piece that shows how things can happen when an external component does join the rejuvenation process.

Subrahmanyin: That specific case, where the low-metallicity gas has distinct kinematics, offers a perfect model of external triggering for future comparison.

Vera: It’s clear that this study provides a robust framework for understanding that these internal mechanisms are driving most local rejuvenation events.

Jocelyn: We are really excited to see how these findings help us interpret data from other major surveys down the line.

Subrahmanyin: This work is a huge step forward in seeing galaxy evolution through the lens of catching these processes in action at a definitive stage.

Conclusion: Vera: So, wrapping up our deep dive on "Exploring the Origin of Rejuvenating Gas from MaNGA Nearby Galaxies," it really hits you how much these gas reservoirs suggest ongoing fueling mechanisms are at play in galaxies.

Jocelyn: Exactly, Vera; it makes you rethink how static we thought the gas supply was in these nearby systems—it’s not just sitting there; it’s actively moving and rejuvenating the fuel for star formation.

Subrahmanyan: That's right, Jocelyn. From a theoretical standpoint, this implies that our models need to account for continuous, efficient transport of gas from different scales—not just one big burst event, but something more sustained over billions of years.

Vera: I agree with Subrahmanyan on the sustained aspect; looking at the data really shows these inflows are localized and complex, suggesting interactions or perhaps gravitational torques are doing the heavy lifting right in those nearby environments.

Jocelyn: Speaking of local environments, it prompts me to wonder how much of this rejuvenation is actually driven by satellite accretion versus something more internal, like bar instabilities stirring up the disk material?

Subrahmanyan: Well, while internal processes certainly contribute, Jocelyn's point about accretion is vital; if external structures are consistently funneling gas toward the disk plane, that fundamentally changes our timeline for quenching star formation.

Vera: And I think we need to keep combining these different observational views—the detailed kinematics from MaNGA with broader surveys—to truly disentangle those sources of fuel.

Jocelyn: It’s a reminder that the sky is always revealing more detail than we can capture in one single survey pass, isn't it?

Subrahmanyan: Absolutely; these findings on "Exploring the Origin of Rejuvenating Gas from MaNGA Nearby Galaxies" underscore that galaxy evolution is an ongoing process, not a series of discrete events.

Vera: It’s such an exciting area because it connects our immediate neighbors right out to the largest cosmic structures we can model.

Jocelyn: We're going to have to keep tracking these gas flows and how they impact the stellar populations in future surveys.

Subrahmanyan: For now, though, let’s take a breath from gas dynamics; next up, we've got a fascinating look at those old radio sources...

Ting-Xuan Li (李廷軒), Po-Feng Wu (吳柏鋒)

Institute of Astrophysics, National Taiwan University · National Taiwan University

astro-ph.GA

Submitted: 2025-10-29

Updated: 2026-08-25

Comments: Accepted for publication in ApJ. DOI: https://doi.org/10.3847/1538-4357/ae9093

Code: https://github.com/SwampThingPaul/NADA2

License: http://creativecommons.org/licenses/by/4.0/

Importance score: 85/100

The gist: This paper investigates the source of gas that triggers secondary star formation, a process known as "rejuvenation," in nearby galaxies using data from the MaNGA IFU survey.

Key concepts

Rejuvenating Gas
This gas fuels secondary bursts of star formation in galaxies. Researchers study its origin to determine if the supply comes from within the galaxy itself or if it is being drawn in from outside space.
Metallicity
Metallicity measures the abundance of elements heavier than hydrogen and helium found in galactic gas. The study uses consistent metallicities to argue that the fuel is internal, as opposed to fresh, metal-poor material from external sources.
MaNGA Nearby Galaxies
MaNGA is a survey that collected detailed spectroscopic data from nearby galaxies. This data allowed researchers to examine specific regions for gas kinematics and metallicity gradients, helping them track the source of the rejuvenating gas.

Terminology

Summary

This paper investigates the source of gas that triggers secondary star formation, a process known as rejuvenation, in nearby galaxies using data from the MaNGA IFU survey. Determining whether this gas is accreted from external sources or derived from a pre-existing internal reservoir is essential for understanding why some quiescent galaxies experience a revival of star formation activity.

Identification methodology

The researchers identify regions that have recently undergone rejuvenation by analyzing stellar absorption features. Specifically, they use the D n 4000 break and the equivalent width of H delta A to select spaxels that started the rejuvenation within the last about 200 Myr. This method allows them to isolate regions that are currently star-forming but possess a low star formation rate in the recent past, providing a clean sample of current rejuvenation events for statistical study.

Evidence for internal gas origins

By comparing rejuvenating galaxies (RJGs) to controlled star-forming and quiescent samples, the study concludes that for most RJGs, the rejuvenating gas is originally in the galaxy rather than accreted gas. The authors provide four specific pieces of evidence to support this:

  1. Gas metallicities consistent with the mass-metallicity relation of SF galaxies;

  2. Metallicity gradients that are not flattened, which argues against radial inflows;

  3. Gas velocities in rejuvenating regions consistent with their surroundings; and

  4. High HI gas fractions comparable to SF galaxies, suggesting a pre-existing reservoir.

Environmental and kinematic factors

The study also examines whether external triggers, such as gravitational interactions, drive these events. The results show no evidence that the rejuvenating events are triggered by tidal interactions with neighbors, as RJGs do not experience stronger tidal forces or reside in higher-density environments than quiescent galaxies. Consequently, the authors suggest that internal processes appear to dominate the majority of local rejuvenation events.

The case of MaNGA 12080-12705

While internal gas is the primary driver, the paper presents a single unambiguous case of rejuvenation triggered by gas accretion. The galaxy MaNGA 12080-12705, an old and massive galaxy, hosts a low-metallicity, kinematically distinct star-forming region that provides evidence of an external origin. This specific component is characterized by:

  • Gas metallicities that are significantly lower than the* - Z relation;

  • A velocity profile indicating it is a distinct kinematic component; and

  • An intense, localized star formation rate approximately 20 times higher than typical star-forming galaxies of similar mass.

Improvements for AI systems

1. Optimized Feature Engineering for Transient Evolutionary State Detection

  • Improvement: Replace computationally expensive full-spectral fitting architectures with a lightweight, high-precision feature selection layer specifically targeting the D n4000 and EW(H delta A) absorption indices.

  • Capability: The improved AI can rapidly scan massive spectroscopic datasets (e.g., DESI, PFS) to identify galaxies in rejuvenation states—specifically those undergoing secondary star formation within a narrow about 200 Myr window—distinguishing them from steady-state star-forming galaxies with significantly lower computational overhead and higher temporal resolution.

2. Multimodal Anomaly Detection for External Accretion Identification

  • Improvement: Implement a multimodal fusion architecture that cross-references spectroscopic gas-phase metallicity (* - Z relation), kinematic velocity maps, and morphological data to detect localized deviations.

  • Capability: The system can automatically flag rare external origin events (such as MaNGA 12080-12705) by identifying spaxels that exhibit a simultaneous triple-anomaly: low metallicity relative to the mass-metallicity relation, kinematically distinct velocities from the host galaxy's rotation, and localized star formation. This enables the automated discovery of minor mergers and gas accretion in large-scale surveys.

3. Spatio-Temporal Classification of Galaxy Evolutionary Trajectories

  • Improvement: Transition from static classification models (e.g., Star-forming vs. Quiescent) to a dynamic, state-based transition model using the D n4000 - EW(H delta A) parameter space as a latent variable for evolutionary phase.

  • Capability: The AI can predict the probability of a galaxy being in a temporary quiescent state versus a permanent one, and identify rejuvenating galaxies as a distinct transitional class, allowing for more accurate statistical modeling of galaxy evolution across different cosmic epochs.

Abstract

This study investigates the origin of secondary star formation, i.e., rejuvenation in nearby galaxies. From the MaNGA IFU survey, we use stellar absorption features, D n 4000 and EW(H δ A), to identify regions that started the rejuvenation within the last about 200 Myr and use gas-phase metallicity as a primary tracer for accretion of pristine gas, in order to verify the mechanism that triggers the rejuvenation. We compare the metallicity and the velocity of rejuvenating regions with typical star-forming regions. We also compare metallicity gradients, environments, 1 gas fractions, and visual morphologies of galaxies hosting rejuvenating regions to controlled star-forming and quiescent galaxy samples. Overall, we do not find the rejuvenating regions or their hosts show anomalies in metallicity, kinematics, and visual morphology to the controlled comparison samples. These observations suggest that local rejuvenation is likely fueled by gas already residing within the host rather than accreted from outside, and reflect the short life time of small scale dense gas clouds. On the contrary, if the rejuvenation is fueled by gas accretion, the chemical and mixing timescale should be much shorter than about100 Myr so that no chemical and kinematical anomalies are measured. Meanwhile, we report a clear case of a massive quiescent galaxy brought back to star-forming by accreting gas. Our method of identifying rejuvenation is simple and effective, and can be applied to large spectroscopic surveys to investigate the origin of rejuvenation across cosmic time.

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