arXiv subjects

Christina W. Lindberg

Publications and source records attributed to Christina W. Lindberg.

12 recordsLinked to original sources

arXiv2026

Growth of Aromatic Hydrocarbon Dust Particles in the Extremely Metal-poor Galaxy Sextans A

The mid-infrared spectrum of star-forming, high metallicity galaxies is dominated by emission features from aromatic and aliphatic bonds in small carbonaceous dust grains, often referred to as polycyclic aromatic hydrocarbons (PAHs). In metal-poor galaxies, the abundance of PAHs relative to the total dust sharply declines, but the origin of this deficit is unknown. We present JWST observations that detect and resolve emission from PAHs in the 7% Solar metallicity galaxy Sextans A, representing the lowest metallicity detection of PAH emission to date. In contrast to higher metallicity galaxies, the clumps of PAH emission are compact (0.5-1.5$''$ or 3-10 pc), which explains why PAH emission evaded detection by lower resolution instruments. Ratios between the 3.3, 7.7, and 11.3 $μ$m PAH features indicate that the PAH grains in Sextans A are small and neutral, with no evidence of significant processing from radiation fields. These results favor inhibited grain growth over enhanced destruction as the origin of the low PAH abundance in Sextans A. The compact clumps of PAH emission are likely active sites of in-situ PAH growth within a dense, well-shielded phase of the interstellar medium. Our results show that PAHs can form and survive in extremely metal-poor environments common early in the evolution of the Universe.

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arXiv2026

Scylla: Observational Evidence for an Order of Magnitude in Dust Mass Opacity Evolution with ISM Density in the Large Magellanic Cloud

The emissivity of dust is known to vary greatly with radiative environment, density, grain chemistry, and geometry. Discrepancies between dust mass surface densities derived from far-infrared (FIR) emission and visible extinction persist across and within galaxies in the local Universe. Here, we use new extinction and emission measurements towards the LMC to show that this discrepancy is driven by the dust mass opacity evolving with the intrinsic density of the ISM, and that the ratio between FIR and optical dust mass opacity varies with gas surface density. These new findings imply that the dust mass opacity in the FIR could increase by nearly an order of magnitude (e.g., $κ_{160} = 0.3 - 6\ m^2\ kg^{-2}$) across over an order of magnitude of total hydrogen surface density $(Σ_H = 4 - 100 M_{\odot}\ pc^{-2})$, corroborating previous theoretical models for dust mass opacity evolution in the FIR, and providing new implications for emission-based dust mass estimates.

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arXiv2026

A Multiwavelength Inventory for the Local Group L-band Survey I: Atlas and Radial Profiles of Local Group Galaxies

Resolving atomic gas at $\lesssim100$ pc physical resolution is currently feasible only for the very nearest galaxies. We combine 120 pc resolution HI data using the Karl G. Jansky Very Large Array (VLA) from the first data release of the Local Group L-Band Survey (LGLBS) with uniformly processed infrared, ultraviolet, H$α$, and CO maps. We analyze the radial profiles of gas, stars, and recent star formation for six local galaxies: M31, M33, IC 10, IC 1613, NGC 6822, and WLM. Across the sample, atomic-gas disks are the most extended component, reaching $r_{\rm HI}=2.8$-$5.8$ kpc in the dwarfs and $13$-$26$ kpc in M33 and M31. Azimuthally averaged $Σ_{\rm HI}$ profiles are often flat or only slowly declining compared to the steeper decline of $Σ_{\star}$ and $Σ_\mathrm{SFR}$, with outer HI scale lengths of $l_{\rm HI}^{\rm outer}\approx1.0$-$8.5$ kpc. The mass-weighted HI surface densities on 120 pc scale generally exceed the azimuthally averaged values by 10-70%, showing that localized high-column-density atomic structures persist even where azimuthally averaged profiles appear smooth. Atomic-gas depletion times rise from $τ_{\rm dep}^{\rm atom}\approx0.8$-17 Gyr within the stellar half-mass radius to 10s-100 Gyr in the outer disks. Molecular depletion times are shorter. We provide a public release of these multi-wavelength data, which provide a valuable reference for the LGLBS targets and also form the basis for a companion paper that relates star formation, gas phases, and midplane pressure on 120 pc scales.

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arXiv2026

Scylla VI: Parsec-Scale Dust Extinction Maps in the SMC and LMC

We present a novel methodology for mapping dust extinction in nearby galaxies at parsec-scale resolution. We apply it to HST 68 fields within the Small and Large Magellanic Clouds (23 fields in the SMC and 45 fields in the LMC) using multi-band HST photometry from the Scylla and METAL surveys. Our technique leverages \textit{kriging}, a geostatistical interpolation method built on the principles of Gaussian Process regression, combined with Gaussian mixture modeling to statistically isolate background stellar sources and account for line-of-sight depth effects. 3D dust simulations demonstrate the method's capability to recover column densities to an accuracy of $A_V \approx 0.1$ mag in fields with at least 1000 sources. The resulting $4^{\prime\prime}$ resolution ($\sim1$-pc) dust maps reveal detailed structure and strong spatial correlation with ancillary ISM tracers, especially in star-forming regions like 30 Doradus. Global extinction of total column densities follows log-normal profiles in both galaxies, with the SMC exhibiting slightly higher mean extinction ($e^μ=0.47$ mag) than the broader LMC ($e^μ=0.43$ mag), likely due to significant line-of-sight depths. We find systematic offsets between dust mass surface densities ($Σ_{D}$) derived from extinction versus FIR emission in both galaxies, with $Σ_{D, FIR}/Σ_{D, A_V}$ ratios ranging from $0.6-1.8$. This work provides the highest-resolution dust extinction maps in SMC and LMC to date, which offer a vital independent benchmark for constraining dust emissivity, $\text{CO}$-dark gas fractions, and the multi-scale structure of the ISM in low-metallicity environments.

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arXiv2026

Scylla at APOGEE: The Impact of Starbursts on the Chemical Evolution of the Magellanic Clouds

Owing to their proximity to the Milky Way, the Large and Small Magellanic Clouds (L/SMC) uniquely probe the evolution of low-mass galaxies undergoing mutual interactions. In this work, we investigate the connection between the star formation histories (SFHs) of the L/SMC measured from HST imaging in the Scylla survey and APOGEE chemical abundances. We model the chemical evolution of the L/SMC in the [Mg/Fe]-[Fe/H] plane within a robust statistical framework to predict chemical abundance signatures resulting directly from starbursts in Scylla SFHs. Both the L/SMC rapidly enrich to high metallicity ([Fe/H] $\gtrsim$ $-1$) within 3 Gyr, followed by slower chemical evolution regulated by sequential starbursts, where the SMC may require higher Fe yields from Type Ia supernovae than the LMC. We also model the [Mg/Fe]-[Fe/H] plane to infer starburst properties across distinct spatial regions in the L/SMC. We identify dominant starbursts in the L/SMC with broadly similar timing, though the SMC may host an earlier burst, and larger burst strength in the LMC. The global starburst properties are nearly uniform across the LMC disk, whereas the dominant SMC population experiences a stronger and later-onset burst in its eastern wing compared to the main body. We also find evidence for a chemically distinct secondary population in the SMC that preferentially traces the foreground and may originate from the LMC. We discuss the implications of these results for the evolutionary history of the L/SMC and for starbursts in interacting low-mass galaxy pairs.

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arXiv2025

Scylla V: Constraints on the spatial and temporal distribution of bursts and the interaction history of the Magellanic Clouds from their resolved stellar populations

We measure the star formation histories (SFHs) from the Scylla survey in approximately 98,000 pc^2 and 75,000 pc^2 of the SMC and LMC, respectively, using deep Hubble Space Telescope imaging (80% complete to more than 1 mag below the ancient main-sequence turnoff, 25.1 and 26.0 mag in F475W and F814W) from 74 pointings. We group the fields into eight sub-regions in the SMC and seven in the LMC. We use the birth rate parameter to identify bursts of star formation and measure their properties in each sub-region. Our methodology provides a standardized framework for burst identification and reveals both broad and fine burst characteristics. We identify global and local bursts, defined as those occurring in at least half or less than half of a galaxy's sub-regions, respectively. In the SMC we find two global (about 5 and 1.5 Gyr ago) and one local burst (about 3 Gyr ago). In the LMC we find one global burst (about 3 Gyr ago). Comparing these findings with dynamical models of the LMC and SMC orbital histories, we find that when models predict a shared dynamical trigger for bursts across both galaxies, the burst begins earlier in the SMC with a greater enhancement in star formation rate than in the LMC. Finally, using age-metallicity relations (AMRs) and cumulative SFHs, we report that the Wing/Bridge region in the SMC resembles the southwestern LMC both chemically and in stellar mass assembly over the last about 7 Gyr, possibly due to stellar material stripped from the LMC during their last interaction.

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arXiv2025

Scylla IV: Intrinsic Stellar Properties and Line-of-Sight Dust Extinction Measurements Towards 1.5 Million Stars in the SMC and LMC

By analyzing the spectral energy distributions (SEDs) of resolved stars in nearby galaxies, we can constrain their stellar properties and line-of-sight dust extinction. From the Scylla survey, we obtain ultraviolet to near-infrared photometry from Wide Field Camera 3 onboard the {\it Hubble Space Telescope} for more than 1.5 million stars in the SMC and LMC. We use the Bayesian Extinction and Stellar Tool (BEAST) to analyze the multi-band SEDs of these sources and characterize their initial masses, ages, metallicities, distances, and line-of-sight extinction properties (e.g.~$A_V$, $R_V$). We apply quality cuts and perform validation simulations to construct a catalog of over 550,000 stars with high-reliability SED fits, which we use to analyze the stellar content and extinction properties of the SMC and LMC. We detect stars with masses as low as 0.6 $M_{\odot}$. BEAST stellar age distributions show a jump in observed stars around 6 Gyrs ago, which agrees with star-formation histories. Extinctions ($A_V$) in both galaxies follow a log-normal distribution. We compare $A_V$ with ancillary gas and dust tracers like $HI$, $H_α$, and far infrared (FIR) dust emission and find positive correlations on a field-by-field basis. We convert observed $A_V$ to predicted dust surface densities using the Draine et. al. (2014) model and find $A_V$-based dust surface densities are a factor of $\sim$2.5 lower than observed FIR-based dust surface densities, a correction factor similar to other studies.

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arXiv2025

The Local Ultraviolet to Infrared Treasury I. Survey Overview of the Broadband Imaging

The Local Ultraviolet to Infrared Treasury (LUVIT) is a Hubble Space Telescope program that combines newly acquired data in the near ultraviolet (NUV), optical, and near infrared (NIR) with archival optical and NIR imaging to produce multiband panchromatic resolved stellar catalogs for 23 pointings in 22 low-mass, star-forming galaxies ranging in distance from the outskirts of the Local Group to ~3.8 Mpc. We describe the survey design, detail the LUVIT broadband filter observations and the archival datasets included in the LUVIT reductions, and summarize the simultaneous multiband data reduction steps. The spatial distributions and color-magnitude diagrams (CMDs) from the resulting stellar catalogs are presented for each target, from the NUV to the NIR. We demonstrate in which regions of the CMDs stars with NUV and optical, optical and NIR, and NUV through NIR detections reside. For each target, we use the results from artificial star tests to measure representative completeness, bias, and total photometric uncertainty as a function of magnitude in each broadband filter. We also assess which LUVIT targets have significant spatial variation in the fraction of stars recovered at a given magnitude. The panchromatic LUVIT stellar catalogs will provide a rich legacy dataset for a host of resolved stellar population studies.

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arXiv2024

Scylla I: A pure-parallel, multi-wavelength imaging survey of the ULLYSES fields in the LMC and SMC

Scylla is a deep Hubble Space Telescope survey of the stellar populations, interstellar medium and star formation in the LMC and SMC. As a pure-parallel complement to the Ultraviolet Legacy Library of Young Stars as Essential Standards (ULLYSES) survey, Scylla obtained 342 orbits of ultraviolet (UV) through near-infrared (IR) imaging of the LMC and SMC with Wide Field Camera 3. In this paper, we describe the science objectives, observing strategy, data reduction procedure, and initial results from our photometric analysis of 96 observed fields. Although our observations were constrained by ULYSSES primary exposures, we imaged all fields in at least two filters (F475W and F814W), and 64% of fields in at least three and as many as seven WFC3 filters spanning the UV to IR. Overall, we reach average 50% completeness of $m_{\rm F225W}=26.0$, $m_{\rm F275W}=26.2$, $m_{\rm F336W}=26.9$, $m_{\rm F475W}=27.8$, $m_{\rm F814W}=25.5$, $m_{\rm F110W}=24.7$, and $m_{\rm F160W}=24.0$ Vega magnitudes in our photometric catalogs, which is faintward of the ancient main sequence turnoff in all filters. The primary science goals of Scylla include characterizing the structure and properties of dust in the MCs, as well as their spatially-resolved star formation and chemical enrichment histories. Our images and photometric catalogs, which represent the widest-area coverage of MCs with HST photometry to date, are available as a high-level science product at the Barbara A. Mikulski Archive for Space Telescopes.

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arXiv2024

Scylla II. The Spatially Resolved Star Formation History of the Large Magellanic Cloud Reveals an Inverted Radial Age Gradient

The proximity of the Magellanic Clouds provides the opportunity to study interacting dwarf galaxies near a massive host, and spatial trends in their stellar population properties in particular, with a unique level of detail. The Scylla pure parallel program has obtained deep (80% complete to >1 mag below the ancient main sequence turnoff), homogeneous two-filter Hubble Space Telescope (HST) imaging sampling the inner star-forming disk of the Large Magellanic Cloud (LMC), the perfect complement to shallower, contiguous ground-based surveys. We harness this imaging together with extant archival data and fit lifetime star formation histories (SFHs) to resolved color-magnitude diagrams (CMDs) of 111 individual fields, using three different stellar evolutionary libraries. We validate per-field recovered distances and extinctions as well as the combined global LMC age-metallicity relation and SFH against independent estimates. We find that the present-day radial age gradient reverses from an inside-out gradient in the inner disk to an outside-in gradient beyond $\sim$2 disk scalelengths, supported by ground-based measurements. The gradients become relatively flatter at earlier lookback times, while the location of the inversion remains constant over an order of magnitude in lookback time, from $\sim$1$-$10 Gyr. This suggests at least one mechanism that predates the recent intense LMC-SMC interaction. We compare observed radial age trends to other late-type galaxies at fixed stellar mass and discuss similarities and differences in the context of potential drivers, implying strong radial migration in the LMC.

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arXiv2024

Scylla III. The Outside-In Radial Age Gradient in the Small Magellanic Cloud and the Star Formation Histories of the Main Body, Wing and Outer Regions

The proximity of the Large and Small Magellanic Clouds (LMC and SMC) provides the opportunity to study the impact of dwarf-dwarf interactions on their mass assembly with a unique level of detail. To this end, we analyze two-filter broadband imaging of 83 Hubble Space Telescope (HST) pointings covering 0.203 deg$^2$ towards the SMC, extending out to $\sim$3.5 kpc in projection from its optical center. Lifetime star formation histories (SFHs) fit to each pointing independently reveal an outside-in age gradient such that fields in the SMC outskirts are older on average. We measure radial gradients of the lookback time to form 90%, 75% and 50% of the cumulative stellar mass for the first time, finding $δ$($τ_{90}$, $τ_{75}$, $τ_{50}$)/$δ$R = (0.61$^{+0.08}_{-0.07}$, 0.65$^{+0.09}_{-0.08}$, 0.82$^{+0.12}_{-0.16}$) Gyr/kpc assuming PARSEC evolutionary models and a commonly used elliptical geometry of the SMC, although our results are robust to these assumptions. The wing of the SMC deviates from this trend, forming 25\% of its cumulative mass over the most recent 3 Gyr due to a best-fit star formation rate that remains approximately constant. Our results are consistent with chemodynamical evidence of a tidally stripped SMC component in the foreground, and imply contributions to the observed SFH from multiple previous LMC-SMC interactions. We also compare our SMC SFH with results from a companion study of the LMC, finding that while the two galaxies present different internal, spatially resolved SFH trends, both the LMC and SMC have similar near-constant lifetime SFHs when viewed globally.

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arXiv2024

The Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER). VI. The High-Mass Stellar Initial Mass Function of M33

We measure the high-mass stellar initial mass function (IMF) from resolved stars in M33 young stellar clusters. Leveraging \textit{Hubble Space Telescope's} high resolving power, we fully model the IMF probabilistically. We first model the optical CMD of each cluster to constrain its power-law slope $Γ$, marginalized over other cluster parameters in the fit (e.g., cluster age, mass, and radius). We then probabilistically model the distribution of MF slopes for a highly strict cluster sample of 9 clusters more massive than log(Mass/M$_{\odot}$)=3.6; above this mass, all clusters have well-populated main sequences of massive stars and should have accurate recovery of their MF slopes, based on extensive tests with artificial clusters. We find the ensemble IMF is best described by a mean high-mass slope of $\overlineΓ = 1.49\pm0.18$, with an intrinsic scatter of $σ^{2}_Γ = 0.02^{+0.16}_{0.00}$, consistent with a universal IMF. We find no dependence of the IMF on environmental impacts such as the local star formation rate or galactocentric radius within M33, which serves as a proxy for metallicity. This $\overlineΓ$ measurement is consistent with similar measurements in M31, despite M33 having a much higher star formation rate intensity. While this measurement is formally consistent with the canonical Kroupa ($Γ= 1.30$) IMF, as well as the Salpeter ($Γ= 1.35)$) value, it is the second Local Group cluster sample to show evidence for a somewhat steeper high-mass IMF slope. We explore the impacts a steeper IMF slope has on a number of astronomical sub-fields.

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