Searcharxiv⌕ Search

arXiv subjects

Themiya Nanayakkara

Publications and source records attributed to Themiya Nanayakkara.

At least 37 records · Page 2Linked to original sources
arXiv2026

MSA-3D: Rotation Curves and Dark Matter Fractions at z~0.5-1.7 with JWST/NIRSpec

We present rotation curves and inner mass distributions for 30 star-forming galaxies at $0.5<z<1.7$, observed with JWST/NIRSpec as part of the MSA-3D Cycle 1 survey. Combining spatially resolved ionised-gas kinematics with JWST/NIRCam imaging, we constrain baryonic and dark matter contributions through forward dynamical modelling for galaxies extending down to stellar masses of $\sim10^{9}M_\odot$. For the 23 galaxies in our primary statistical sample, we find predominantly rotationally supported disks with intrinsic dispersions $σ_0\sim31$-65 km s$^{-1}$ and a wide range of dark matter fractions, $f_{DM}(R_e)\sim0.1$-0.9, with a median of 0.63 and substantial galaxy-to-galaxy scatter of $\sim0.2$ dex. These results are supported by a complementary consistency check using stellar mass maps and SFR-derived gas profiles. Among the 19 galaxies reaching $\gtrsim2R_e$, we identify six rising, six flat, and seven falling rotation curves. These classes define an observed ordering from rotationally dominated, dark-matter-rich disks ($V_{rot}/σ_0\approx4$, $f_{DM}\gtrsim0.7$) to more dispersion-supported systems with centrally concentrated baryonic mass distributions ($V_{rot}/σ_0\approx2$, $f_{DM}\lesssim0.55$). The stellar Tully-Fisher relation lies close to the local relation evolved under the adopted self-similar $Λ$CDM scaling. A simplified seeing-degradation test shifts the inferred normalisation by ~0.2 dex at fixed $V_c$, suggesting that spatial resolution contributes to, but does not fully explain, differences among high-redshift Tully-Fisher measurements. Overall, MSA-3D provides a high-resolution extension of previous surveys toward lower stellar masses, spanning $9.0 < \log(M_\star/M_\odot) < 11.2$, and reinforces that star-forming disks near $z\sim1$ span a broad range of dynamical states and inner mass distributions.

astro-ph.GA↗
arXiv2026

BLUEPRINT: Blue-dominant Lyman-$α$ emission as evidence of gas inflow in ultra-low-mass galaxies at z = 3

We report the detection of a clumpy, blue-dominated Ly$α$ emission at z = 3.066 located in the heart of a cosmic web filament in the MUSE eXtremely Deep Field (MXDF), spatially associated with the formation of two compact star-forming regions revealed by deep JWST/NIRCam imaging. Gas accretion in these regions is indicated by the blue-dominated Ly$α$ profiles, spectral signatures that are rarely observed. Radiative transfer simulations of the Ly$α$ profile using a clumpy multiphase model suggest a radial inflow of gas clumps with a velocity of 100 km/s. Embedded in this Ly$α$ structure, we find that the associated main galaxy dominates the stellar mass budget, while the two compact ultra-low-mass systems ($\log(M_\star/M_\odot) = 6.3\text{-}6.9$) have formed the bulk of their stellar mass in less than 7 Myr. These two components also have high specific star-formation rates, and elevated ionisation parameters, consistent with recent bursty star formation. This system provides compelling observational evidence that how gas accretion, most likely from the cosmic web, can induce starburst in ultra-low-mass galaxies.

astro-ph.GA↗
arXiv2026

Spatially resolved gas-phase metallicity at z~2-3 with JWST/NIRISS

Spatially resolved gas-phase metallicity maps are a crucial element in understanding the chemical evolution of galaxies. We present spatially resolved metallicity maps obtained from NIRISS/WFSS observations. This is the first such work presenting multiple individual galaxies. We investigate the source of ionisation, metallicity and its relation to star-formation in a spatially-resolved sense for a sample of eight galaxies -- four from JWST-PASSAGE and four from GLASS-JWST ERS. All but one galaxy are in the redshift range $1.9 \leq z \leq 2$, the outlier being at $z = 3.1$. Our sample covers a range of $8.0 <$ \logM $< 9.5$ in stellar mass, $0.2 <$ $\log{\rm{(SFR}}$/\Msunpyr) $< 1.1$ in star-formation rate (SFR) and $7.8 <$ \logOH $< 9.0$ in global metallicity. As a solution to the challenge of SF-AGN demarcation in absence of resolved \halpha, we present a new SF-demarcation line in the \textit{OHNO} parameter space based on MAPPINGS v5.1 publicly available \hii region model grids. We present the mass-metallicity gradient relation for our sample, which showed no clear trend with stellar mass, perhaps hinting at the fact that the high-$z$ galaxies have not yet started their accretion dominated phase. By interpreting the correlation between spatially resolved metallicity and SFR maps as a proxy for effective timescales of metal-transport in galaxies, we find a weak trend such that this timescale increases with stellar mass, implying a more effective feedback in lower mass galaxies.

astro-ph.GA↗
arXiv2026

A stellar dynamical mass measurement of an inactive black hole at redshift 2

Supermassive black holes and their host galaxies grow together over time, producing correlations between the black hole mass and various galaxy properties. Determining the evolution of these correlations requires precise measurements of the masses of distant black holes. We observe the gravitationally lensed quiescent galaxy MRG-M0138, at redshift 1.95, using JWST integral field spectroscopy to spatially resolve the kinematics of stars within the black hole's sphere of influence. By using a foreground lens model and fitting stellar dynamical models, we determine the mass of its inactive black hole, $M_{\bullet}=6.0^{+2.1}_{-1.7}\times10^9$ solar masses. Comparing this measurement to local galaxies, we find that $M_{\bullet}$ is higher than expected given the galaxy's bulge mass, but consistent with the correlation with stellar velocity dispersion.

astro-ph.GA↗
arXiv2026

Early Results from GLASS-JWST. XXVI. Spatially Resolved Star Formation and Balmer Decrements at $1.1<z<2.3$ from NIRISS Slitless Spectroscopy

Using JWST/NIRISS slitless spectroscopy, we present spatially resolved Balmer decrement measurements for 79 galaxies at $1.1 < z < 2.3$, which are gravitationally lensed by the foreground cluster Abell 2744. By stacking $\mathrm{H}α$ and $\mathrm{H}β$ emission maps in bins of stellar mass and redshift, we derive radial profiles of nebular dust attenuation and dust-corrected star formation rate (SFR). We find tentative evidence that the radial gradients of dust attenuation toward $\mathrm{H}α$ ($\rm A(\mathrm{H}α)$) vary with both redshift and stellar mass. At lower redshifts ($z = 1.10$--$1.53$), low-mass galaxies ($\rm 7.0<log(M_*/M_\odot)\leq8.5$) exhibit steeper $\rm A(Hα)$ gradients than higher-mass galaxies ($\rm 9.5<log(M_*/M_\odot)\leq11.0$), while the latter maintain detectable dust attenuation out to larger galactocentric radii. Galaxies at higher redshifts ($z = 1.76$--$2.29$) show lower attenuation levels. At fixed galactocentric radius, galaxies in the low-redshift bin generally exhibit higher dust attenuation than those at high redshifts, consistent with an increase in dust content toward later cosmic times. Dust-corrected SFR profiles in massive systems at lower redshifts are more spatially extended than those at higher redshifts, consistent with inside-out disk growth at $z\lesssim1.5$. These results suggest possible differences in attenuation properties across stellar mass and redshift bins, and demonstrate the power of gravitational lensing to probe internal structures in faint galaxies at sub-kiloparsec resolution.

astro-ph.GA↗
arXiv2026

MSA-3D: Connecting the Chemical and Kinematic Structures of Galaxies at $z \sim 1$

We investigate the connection between ionized gas kinematics and gas-phase metallicity gradients in 21 star-forming galaxies at $0.5 < z < 1.7$ from the MSA-3D survey, using spatially resolved JWST/NIRSpec slit-stepping observations. Galaxy kinematics are characterized by the ratio of rotational velocity to intrinsic velocity dispersion, $v/σ$, measured at $1.5\,R_e$, where $R_e$ is the effective radius. We find that dynamically hotter disks exhibit systematically flatter metallicity gradients, with a moderate anti-correlation between metallicity gradient and $v/σ$ (Pearson $r=-0.43$, $p=0.05$) and a linear fit yields a slope of $\sim 0.005$ dex per dex in $v/σ$, weaker than the dependence on stellar mass. A significantly stronger anti-correlation is observed with $R_e/σ$, interpreted as a proxy for the radial mixing timescale ($r=-0.59$, $p=0.005$), indicating that cumulative radial mixing more directly regulates chemical stratification. The metallicity gradients in our sample are uniformly shallow, indicating that efficient turbulent mixing in kinematically settled disks regulates the chemical structure of typical star-forming galaxies at $z\sim1$.

astro-ph.GA↗
arXiv2026

A Census of Double-Peaked Lyman-alpha Emitters in MAGPI: Classification, Global Characteristics, and Spatially Resolved Properties

Double-peaked Ly$α$ profiles provide critical insights into gas kinematics and the distribution of neutral hydrogen (HI) from the interstellar to the intergalactic medium (ISM to IGM), and serve as valuable diagnostics of ionising Lyman continuum (LyC) photon escape. We present a study of the global and spatially resolved properties of double-peaked Ly$α$ emitters (LAEs) based on VLT/MUSE data from the MAGPI survey. From a parent sample of 417 LAEs at z = 2.9 - 6.6 in the first 35 fields, we identify 108 double-peaked LAEs using an automated peak classification technique. We measure a double-peak fraction of $\sim37\%$ at $z < 4$, decreasing to $\sim14\%$ at $z > 4$, likely due to enhanced IGM attenuation. Approximately $17\%$ of the double-peaked LAEs are blue-dominated, possibly tracing gas inflows, though backscattering remains a viable alternative for sources without systemic redshift. The blue-to-total flux ratio exhibits a luminosity dependence: fainter lines generally show higher blue flux. We find a narrowing of the red peak at $z > 4$, despite the presence of the blue peak, indicating intrinsic galaxy evolution rather than IGM attenuation. Several LAEs exhibit residual flux in the absorption trough, with normalised trough flux anticorrelating with peak separation, reflecting variations in HI column density. We further investigate spatially resolved properties of ten red-dominated LAEs with extended Ly$α$ halos. Despite azimuthal variations, both the blue-to-total flux ratio and normalised trough flux density increase with radius, while peak separation decreases. The red peak asymmetry shows only minor radial changes. These trends are consistent with variations in shell outflow velocity and HI column density across the halos. Based on peak separation, red peak asymmetry, and residual trough flux, we identify five LAEs as strong LyC-leaker candidates.

astro-ph.GA↗
arXiv2026

Resolved Maps of Gas and Dust in a Massive Quiescent Galaxy at z=2 from INQUEST-JWST: Evidence of Accretion and Rejuvenation

Quiescent galaxies in the distant universe exhibit a range of gas content that may indicate a variety of quenching processes are at play. Mapping the distribution and kinematics of the gas can illuminate its origins, but nearly all such observations have been unresolved. We present JWST/NIRSpec IFU observations of MRG-M0138, a gravitationally lensed, massive quiescent galaxy at $z\sim2$ observed as part of the INQUEST-JWST survey. We use Na I D absorption, which we detect in excess of the stellar absorption over most of the galaxy, to trace the kinematics and spatial distribution of the neutral gas in 219 spatial bins. The gas exhibits clear rotation that is kinematically aligned with the stellar disk. Both the gas and dust have a complex spatial structure, including an off-nuclear clump, a dust lane, and patches in the outer disk. The non-equilibrium distribution suggests that the gas was accreted. Analysis of the galaxy's star formation history supports this interpretation by indicating a rejuvenation event 500 Myrs ago. We identify two plausibly associated galaxies and suggest that tidal interactions are a likely source of the accreted gas. Our results indicate that some of the variation in gas content among early quiescent galaxies is not related to differences in gas consumption timescales. The detection of a gas clump at a projected distance of $\sim90$ pc from the known supermassive black hole illustrates a mechanism to fuel the episodic AGN feedback that may maintain quiescence.

astro-ph.GA↗
arXiv2026

The GLASS-JWST Early Release Science Program. V. H$α$ luminosity functions at $z\sim1.3$ and $z\sim2.0$

We present H$α$ luminosity function (LF) measurements at redshifts $z\sim1.3$ and $z\sim2.0$ using JWST NIRISS grism data from the GLASS-JWST survey. Based on emission lines spectroscopically identified in the F115W, F150W and F200W filters, we select 99 H$α$ emitters. Through detailed effective volume and completeness analysis for each source, we construct the H$α$ LF in two redshift bins. Thanks to the sensitivity of NIRISS WFSS and gravitational lensing magnification, our sample reaches intrinsic H$α$ luminosities $\sim$10 times deeper than previous grism surveys, down to $L_{\rm Hα}\sim10^{40.5}~\rm erg~s^{-1}$ at $z\sim1.3$ and $L_{\rm Hα}\sim10^{40.9}~\rm erg~s^{-1}$ at $z\sim2.0$ with completeness larger than 0.8, corresponding to star formation rates of 0.4 and 1.0 $M_{\odot}~\rm yr^{-1}$, respectively. We robustly constrain the faint-end slope of the H$α$ luminosity function to be $-1.50^{+0.14}_{-0.08}$ at $z\sim1.3$ and $-1.60^{+0.17}_{-0.09}$ at $z\sim2.0$ after considering the cosmic variance of $\sim 20\%$, consistent with previous estimations. The emission-line samples presented here will enable further detailed studies of galaxy properties including metallicities. We find a negligible contribution from bright active galactic nuclei in our sample. We estimate integrated cosmic star formation rate densities of $0.097^{+0.015}_{-0.016}~M_{\odot}~\rm yr^{-1}~Mpc^{-3}$ at $z\sim1.3$ and $0.129^{+0.025}_{-0.030}~M_{\odot}~\rm yr^{-1}~Mpc^{-3}$ at $z\sim2.0$. The methodology presented here can be readily applicable to other JWST slitless spectroscopic datasets and future wide-field slitless surveys, including those from Euclid, Roman, and the Chinese Space Station Telescope.

astro-ph.GA↗
arXiv2026

Discovery of Ancient Globular Cluster Candidates in the Relic, a Quiescent Galaxy at $z=2.5$

Globular clusters (GCs) are some of the oldest bound structures in the Universe, holding clues to the earliest epochs of star formation and galaxy assembly. However, accurate age measurements of ancient clusters are challenging due to the age-metallicity degeneracy. Here, we report the discovery of 36 compact stellar systems within the 'Relic', a massive, quiescent galaxy at $z=2.53$. The Relic resides in an overdensity behind the Abell~2744 cluster, with a prominent tidal tail extending towards two low-mass companions. Using deep data from the UNCOVER/MegaScience JWST Surveys, we find that clusters formed in age intervals ranging from 8~Myr up to $\sim2$~Gyr, suggesting a rich formation history starting at $z\sim10$. While the cluster-based star formation history is broadly consistent with the high past star formation rates derived from the diffuse host galaxy light, one potential discrepancy is a tentative $\sim2-3\times$ higher rate in the cluster population for the past Gyr. Taken together with the spatial distribution and low inferred metallicities of these young-to-intermediate age clusters, we may be seeing direct evidence for the accretion of star clusters in addition to their early in situ formation. The cluster masses are high, $\sim10^6-10^7~M_{\odot}$, which may explain why we are able to detect them around this likely post-merger galaxy. Overall, the Relic clusters are consistent with being precursors of the most-massive present-day GCs. This unique laboratory enables the first connection between long-lived, high-redshift clusters and local stellar populations, offering insights into the early stages of GC evolution and the broader processes of galaxy assembly.

astro-ph.GA↗
arXiv2026

On the unique evolutionary mechanisms of massive quiescent galaxies in the epoch of reionisation

We investigate the evolutionary histories of a population of high mass, high redshift, quiescent galaxies in the cosmohydrodynamical simulation Thesan, studying the characteristic properties of their haloes and environments over the epoch of reionisation. Thesan employs a modified version of the Arepo moving-mesh code utilised in IllustrisTNG, which incorporates on-the-fly radiative transfer to couple haloes and galaxies with the evolving radiation field. Thesan exhibits nine massive quiescent galaxies at $z=5.5$, in a $(95.5 \text{cMpc})^3$ volume, with no counterpart in IllustrisTNG. A numerical issue in the simulation reduces AGN feedback efficiency by a factor of 25 while enhancing accretion rates, creating a regime of suppressed feedback. We find their stellar mass assembles rapidly through smooth halo accretion in dense environments, particularly from massive neighbouring structures, while their early-forming haloes develop fast-growing potential wells hosting massive black holes. This suppressed feedback allows prolonged black hole growth before eventual kinetic-mode quenching, providing insight into galaxy evolution under weakened AGN regulation. We find that megaparsec-scale overdensities and halo masses continue growing after quenching, suggesting these galaxies will reside in some of the largest haloes and densest regions of space by $z=6$. With massive quiescent galaxies found in JWST data, the identification of such galaxies in Thesan enables isolation of halo and environmental conditions most conducive to their evolution under this suppressed feedback regime, guiding future deep surveys and N-body simulation studies of analogous systems.

astro-ph.GA↗
arXiv2026

Taking a Break at Cosmic Noon: Continuum-selected Low-mass Galaxies Require Long Burst Cycles

While bursty star formation in low-mass galaxies has been observed in local populations and reproduced in simulations, the dormant phase of the burst cycle has not been well studied beyond the local Universe due to observational limitations. We present a unique sample of 43 JWST PRISM spectra of low-mass galaxies ($M_\star < 10^{9.5}\,M_\odot$) at cosmic noon ($1<z<3$), uniformly selected on F200W magnitude and precise photometric redshifts enabled by 20-band JWST photometry from the UNCOVER and MegaScience surveys. The spectra reveal numerous strong Balmer breaks, which are negatively correlated with the galaxies' H$α$ equivalent width. By comparing these observations to synthetic samples of spectra generated using a simple parametrization of bursty star formation histories, we show that star formation in low-mass galaxies at cosmic noon is likely dominated by burst cycles with long timescales ($\gtrsim 100$ Myr) and large deviations below the star-forming main sequence ($\gtrsim 0.8$ dex). Our results suggest that galaxies in this population--at least those within our detection limits--should not be classified solely by their current star formation rates, but instead viewed as a unified population undergoing dynamic movement above and below the star-forming main sequence. The derived constraints demonstrate that long-timescale fluctuations are important for this class of galaxies, indicating that galaxy-scale gas cycles--rather than molecular-cloud-scale stochasticity--are the primary regulators of star formation variability in low-mass galaxies at cosmic noon.

astro-ph.GA↗
arXiv2026

Everything Every Band All at Once II: The Relationship Between Optical Size and Stellar Mass Over Eight Billion Years of Cosmic History

While the size-mass relation provides insight into the structural evolution of galaxies, the data available and methods employed have hindered our ability to study a detailed and comprehensive description of this key relation across cosmic history. The first paper in this series presents a morphology catalog based on 20 band JWST data in the field of Abell 2744. In this paper we utilize this catalog to measure the size-mass relation from $0.5 10$, we discuss three distinct phases: Rapid growth at $z>5$, growth that mimics dark matter halos at $5< z <1$ and a late plateau at $0.5 1$. Our results imply that quiescent galaxies are smaller than their star-forming counterparts only at around $\log M_*/M_\odot = 10$; the two populations have similar sizes at lower and higher masses.

astro-ph.GA↗
arXiv2026

Evidence for Shallow Nebular Attenuation Curves and Patchy Dust Geometry at z~2 with Pa-beta/H-alpha Measurements from JWST-MegaScience Medium Band Photometry

We constrain the nebular attenuation curve and investigate dust geometry in star-forming galaxies at cosmic noon using photometric medium-band emission line measurements. We measure H-alpha emission line fluxes for a sample of 209 star-forming galaxies at 1.2<z<2.4 in MegaScience/UNCOVER with stellar masses spanning $7.85<\log_{10}(M_*/M_\odot)<11.0$. For 66 of these galaxies, we also measure a Pa-beta flux. We find that the Pa-beta/H-alpha line ratio increases strongly with stellar mass and star-formation rate (SFR) across our full mass range, indicating that more massive galaxies are dustier. We compare our results with a mass-, SFR-, and redshift-matched sample of galaxies from the MOSDEF survey with spectroscopic measurements of H-alpha/H-beta, finding that a shallow Reddy et al. (2025) nebular attenuation curve is more consistent with our observations than the typically assumed Cardelli et al. (1989) attenuation curve, especially for massive galaxies. This shallow attenuation curve could be explained by low dust covering fractions in star-forming regions. Through comparison to other studies, we show that assuming this shallower attenuation curve can increase the inferred A_Halpha,neb by up to 1 magnitude at high masses. We observe no trend between A_Halpha,neb and axis ratio, indicating that nebular attenuation is likely localized to small clumps. Altogether, our results strongly suggest that dust geometry is patchy and non-uniform, especially in massive galaxies. Our results highlight the ability of JWST medium bands to probe emission lines for large samples of galaxies, and statistically constrain dust properties in upcoming large programs.

astro-ph.GA↗
arXiv2026

REBELS-IFU: Spatially Resolved Ionizing Photon Production Efficiencies of 12 Bright Galaxies in the Epoch of Reionization

Measuring the ionizing photon production efficiency $ξ_{\mathrm{ion,0}}$ -- the ratio of ionizing photon output rate $Q_{\rm H^0}$ to UV continuum luminosity $L_{\rm UV}$ -- in galaxies at $z > 6$ is crucial for constraining their contribution to cosmic reionization. We present integrated and spatially resolved measurements of $ξ_{\mathrm{ion,0}}$ for 12 exceptionally bright ($M_\mathrm{UV} \sim -22$ mag) star-forming galaxies at $z \sim 7$ from the REBELS survey. These measurements are based on JWST NIRSpec/IFU PRISM spectroscopy, probing the rest-frame UV and optical regime. Notably, in 8 of the 12 galaxies, the spectral coverage includes H$α$, enabling self-consistent dust attenuation estimates in both the ionized gas and stellar continuum via the Balmer decrement and rest-UV slope, respectively. We find global $\logξ_{\mathrm{ion,0}}$ values ranging from $25.19\pm0.11$ to $25.61\pm0.11$, with a weighted mean of $25.44\pm0.15$, consistent with the canonical value of $\sim25.3$. Using a sample of 25 star-forming clumps within these galaxies, we explore local variations in LyC production efficiency, finding a broader range, from $24.52\pm0.21$ to $26.18\pm0.61$. We identify strong correlations between $ξ_{\mathrm{ion,0}}$ and specific star formation rate, star formation surface density, H$β$ equivalent width, and stellar mass. Clumps with the highest $ξ_{\mathrm{ion,0}}$ exhibit $\mathrm{EW}_0(\mathrm{H}β) \ge 150$ Angstrom, consistent with young stellar ages. From previous Ly$α$ measurements in three galaxies, we estimate a typical Ly$α$ escape fraction of $f_{\rm esc, Lyα} \sim 2\%$, suggesting similar or lower escape fractions for LyC photons. Combining this with our H$α$ measurements, we infer ionized bubble sizes $\sim 1$ pMpc, aligned with expectations from Ly$α$-detected systems and reionization models.

astro-ph.GA↗
arXiv2026

MAMMOTH-LyC: Investigating the Role of Galaxy Mergers in a Strong Lyman Continuum Leaker at $z=2.39$

The MAMMOTH-LyC survey is a cycle 30 Hubble Space Telescope (HST) medium program obtaining 18-orbit-deep WFC3/UVIS F225W imaging in two massive galaxy protocluster fields at $z\sim2.2$. We introduce this survey by reporting the discovery of J1244-LyC1, a strong Lyman continuum (LyC) leaker at $z = 2.39$, exhibiting clear merger signatures. J1244-LyC1 has a highly significant ($10σ$) LyC detection, corresponding to an absolute escape fraction of $f_{\mathrm{esc}} \! =\!36\%\pm4\%$ ($1σ$). The LyC emission is spatially resolved into multiple peaks that coincide with the system's disturbed morphology, confirming genuine multi-site LyC leakage. With a stellar mass of $10^{10.2}{M_\odot}$, J1244-LyC1 is both the first confirmed high-redshift LyC-leaking merger and the most massive LyC emitter known to date. We interpret J1244-LyC1 as a merger-driven starburst system in which tidal interactions have disrupted the interstellar medium, creating multiple low-column-density pathways that facilitate LyC escape. This discovery provides the first direct evidence of spatially resolved LyC escape in a merging system, offering new insight into the potential role of major mergers in driving the cosmic reionization.

astro-ph.GA↗
arXiv2026

It's More Complicated Than You Think: A Forward Model to Infer the Recent Star Formation History, Bursty or Not, of Galaxy Populations

Observations of the early Universe (z > 4) with the James Webb Space Telescope reveal galaxy populations with a wide range of intrinsic luminosities and colors. Bursty star formation histories (SFHs), characterized by short-term fluctuations in the star formation rate (SFR), may explain this diversity, but constraining burst timescales and amplitudes in individual galaxies is challenging due to degeneracies and sensitivity limits. We introduce a population-level simulation-based inference framework that recovers the power and timescales of SFR fluctuations by forward-modeling galaxy populations and distributions of rest-UV to rest-optical spectral features sensitive to star formation timescales. We adopt a stochastic SFH model based on a power spectral density formalism spanning 1 Myr-10 Gyr. Using simulated samples of N=500 galaxies at z~4 with typical JWST/NIRSpec uncertainties, we demonstrate that: (i) the power of SFR fluctuations can be measured with sufficient precision to distinguish between simulations (e.g., FIRE-2-like vs. Illustris-like populations at >99% confidence for timescales < 100 Myr); (ii) simultaneously modeling stochastic fluctuations and the recent (t_L < 500 Myr) average SFH slope is essential, as secular trends otherwise mimic burstiness in common diagnostics; (iii) frequent, intense bursts impose an outshining limit, and bias inference toward underestimating burstiness due to the obscuration of long-timescale power; and (iv) the power of SFR fluctuations can be inferred to 95% confidence across all timescales in both smooth and bursty populations. This framework establishes a novel and robust method for placing quantitative constraints on the feedback physics regulating star formation using large, uniformly selected spectroscopic samples.

astro-ph.GA↗