arXiv subjects

Laura Congreve Hunter

Publications and source records attributed to Laura Congreve Hunter.

9 recordsLinked to original sources

arXiv2026

Radial Stellar Age Gradients in 42 Local Volume Dwarf Galaxies

We present radial stellar age gradients measured from star formation histories (SFHs) fit to resolved color-magnitude diagrams (CMDs) of 42 Local Volume dwarfs (6$\lesssim$Log M$_{\star}$/M$_{\odot}$$\lesssim$9), spatially divided into elliptical annuli. Ages in each annulus are quantified using $τ_{90}$ and $τ_{50}$, the lookback times to form 90% and 50% of the cumulative stellar mass. We find that radial age gradients are uncorrelated with environment, but gradients in $τ_{90}$ are significantly correlated ($p$-values$\lesssim$0.001) with lifetime galaxy-wide "global" SFHs, in agreement with two independent cosmological zoom-in simulations. For radial gradients of $τ_{50}$, simulation predictions differ. We demonstrate that given our large (N=42) and diverse observational sample, the strength of an observed correlation with global SFH is an actionable parameter to discriminate between different simulations with differing stellar feedback prescriptions. Overall, our results support predictions that dwarfs form inside-out like their more massive counterparts, with a combination of feedback-driven outward radial stellar migration and increasing birth radii for young stellar populations yielding present-day stellar age gradients ranging from outside-in to flat. In addition, the lack of a correlation between $τ_{50}$ gradients and global SFH argues against recent star formation in radially outflowing gas. We also discuss the impact of differences between our observational sample and samples available in the latest simulations, highlighting areas for future investigation.

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arXiv2026

Deep Imaging of Grus II and Horologium II: Structure and Extent of Two Ultra-Faint Milky Way Satellites

We present deep, wide-field Magellan/Megacam imaging of the ultra-faint Milky Way (MW) satellites Grus II (Gru II) and Horologium II (Hor II), with the aim of deriving improved constraints on their distances, luminosities, and structural parameters, while also searching for possible signs of tidal disturbance. Our photometry reaches approximately 3 magnitudes deeper than the discovery data, enabling robust measurements of these quantities. Both systems exhibit color-magnitude diagrams consistent with old ($\sim$12.5 Gyr), very metal-poor stellar populations. We find Gru II to be at a distance of $52.3 \pm 1.9$ kpc, with a half-light radius of $6.8 \pm 0.5$ arcmin (103 $\pm$ 9 pc), ellipticity $ε= 0.25 \pm 0.07$, and absolute magnitude $M_V = -4.07 \pm 0.50$ mag. Hor II is further away at a distance of $72.4^{+5.9}_{-5.5}$ kpc and more compact, with $r_h = 2.1 \pm 0.2$ arcmin (44$^{+6}_{-5}$ pc), $ε= 0.32^{+0.20}_{-0.16}$, and $M_V = -2.10 \pm 0.44$ mag. Both galaxies lie within the typical size-luminosity locus of MW ultra-faint dwarfs. Gru II shows an asymmetric morphology including multi-directional clumpy features, some of which may be suggestive of tidal disturbance. We further identify and spectroscopically confirm a new distant member just outside $3r_h$ in Gru II, providing independent evidence for member stars at large projected radii. In contrast, Hor II appears regular, with no significant extended structure detected to the surface-brightness limits of our data.

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arXiv2026

ID-MAGE II: The Star Forming Satellites of Low-Mass Hosts

We present results from our ongoing campaign to follow up the satellite candidates from the Identifying Dwarfs of MC Analog GalaxiEs (ID-MAGE) survey. Previously, we published a list of 355 unresolved satellite candidates identified around 36~nearby LMC- and SMC-mass hosts (D$=$4$-$10~Mpc). We present the velocities of 83 satellite candidates from new Green Bank Telescope \hi\ observations, optical long-slit spectra, and the Dark Energy Survey Instrument Data Release 1. Based on their velocities, we identify six candidates as probable satellite galaxies ($6.5\times10^5\leq M_\star/M_\odot\leq1.5\times10^7$) and 77 as background galaxies. Our results underscore the ability of spectroscopic follow-up to effectively separate satellites from background galaxies. Using the refined sample, we update our previously derived estimates for the average satellite population per host and find 1.7$\pm$0.7 (1.0$\pm$0.3) satellites per LMC-mass (SMC-mass) host. Our current satellite sample includes 25 galaxies confirmed by distances or velocities. This set includes the complete satellite populations of three hosts (UGC~04422: zero satellites, UGC~08201: zero satellites, NGC~3432: four satellites), which we compare to simulations and known satellite systems from the literature. Our sample is nearly complete for the most massive satellites (M$_\star > 10^7~M_\odot$). We find these massive satellites have a quenched fraction of 10--25\%, placing them between the $<$5\% quenched fraction of isolated galaxies and the 40--70\% quenched fraction of MW-analog satellites with $10^7~M_\odot < $ M$_\star < 10^8~M_\odot$. This demonstrates the impact that low-mass galaxies have on the evolution of their satellites.

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arXiv2026

Identifying Dwarfs of MC Analog GalaxiEs (ID-MAGE): The Search for Satellites Around Low-Mass Hosts

We present results from ID-MAGE (Identifying Dwarfs of MC Analog GalaxiEs), a survey aimed at identifying and characterizing unresolved satellite galaxies around 36~nearby LMC- and SMC-mass hosts (D$=$4$-$10~Mpc). We use archival DESI Legacy Survey imaging data and perform an extensive search for dwarf satellites, extending out to a radius of 150~kpc ($\sim$$R_{vir}$). We identify 355 candidate satellite galaxies, including 264 new discoveries. Extensive tests with injected galaxies demonstrate that the survey is complete down to $M_V\sim-$9.0 (assuming the distance of the host) and $μ_{0,V}\sim$26 mag arcsec$^{-2}$ (assuming a n$=$1 Sérsic profile). We perform consistent photometry, via Sérsic profile fitting, on all candidates and have initiated a comprehensive follow-up campaign to confirm and characterize candidates. Through a systematic visual inspection campaign, we classify the top candidates as high-likelihood satellites. On average, we find 4.0$\pm$1.4 high-likelihood candidate satellites per LMC-mass host and 2.1$\pm$0.6 per SMC-mass host which is within the range predicted by cosmological models. We use this sample to establish upper and lower estimates on the satellite luminosity function of LMC/SMC-mass galaxies. ID-MAGE nearly triples the number of low-mass galaxies surveyed for satellites with well-characterized completeness limits, providing a unique dataset to explore small-scale structure and dwarf galaxy evolution around low-mass hosts in diverse environments.

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arXiv2025

SEAMLESS Survey: Four Faint Dwarf Galaxies Tracing Low-Mass Galaxy Evolution Across Environments

We report on four Local Volume dwarf galaxies identified through our ongoing SEmi-Automated Machine LEarning Search for Semi-resolved galaxies (SEAMLESS): Hydrus A, LEDA 486718, Cetus B, and Sculptor 26, with the discovery of Hydrus A reported here for the first time. These four galaxies span a wide range of environments and evolutionary states. Hydrus A (MV = -9.39+/-0.20, D = 3.38-0.30+0.32 Mpc) and LEDA 486718 (MV = -11.62+/-0.08, D = 4.80+/-0.17 Mpc) are among the most isolated dwarfs known within 5 Mpc, while Cetus B (MV = -8.26+/-0.17, D = 3.32-0.23+0.25 Mpc) and Sculptor 26 (MV = -11.25+/-0.10, D =3.21+/-0.13 Mpc) lie < 2 Rvir of NGC 253. Hydrus A shows properties consistent with quenching driven by cosmic reionization, cosmic-web interactions, or internal feedback. LEDA 486718 is an isolated star forming dwarf. Cetus B appears quenched and morphologically disturbed, making it a low-mass satellite or backsplash candidate, while Sculptor 26 is red and seemingly gas-poor but displays signs of recent activity, consistent with a transitional evolutionary state. Together, these systems demonstrate the power of SEAMLESS for building a census of faint galaxies beyond the Local Group.

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arXiv2025

Searching for Stellar-Feedback-Driven Outflow Signatures: A Deep Dive into NGC 3741

Stellar feedback drives winds and outflows critical to the baryon cycles of low-mass galaxies whose shallow gravitational potential wells make them particularly susceptible to mass and metal loss through outflows. However, spatially resolved observations of stellar-feedback-driven outflows are limited due to their low-surface brightness and transient nature. We present the pilot of a larger multi-wavelength study searching for and quantifying stellar-feedback-driven winds and outflows on both spatially and globally resolved scales for a sample of 40 nearby low-mass galaxies. We search for outflow signatures in the star-forming dwarf galaxy NGC 3741 using new optical imaging and spectroscopy from the WIYN 3.5m telescope in conjunction with VLA 21cm observations and local star formation histories derived from resolved HST photometry. With this extensive dataset, we compare the neutral and ionized gas morphologies and kinematics, calculate mass-loading factors, and investigate spatial variations in the star formation history of NGC 3741. Though the galaxy is experiencing a burst in star formation, we find little evidence of strong outflows and calculate very low mass-loading factors. We suggest that, though star formation activity has increased dramatically in the central region of the galaxy over the last 40 Myr, the star formation rate is not high enough to produce a sufficient amount of high mass stars responsible for fueling outflows. Future analysis of the larger sample will allow us to explore how stellar feedback impacts mass loss on local scales, providing a deeper understanding of the interplay between stellar feedback and the interstellar medium in low-mass galaxies.

astro-ph.GA↗

arXiv2025

The NGC3109 Satellite System: The First Systematic Resolved Search for Dwarf Galaxies Around a SMC-mass Host

We report the results of the deepest search to date for dwarf galaxies around NGC3109, a barred spiral galaxy with a mass similar to that of the Small Magellanic Cloud (SMC), using a semi-automated search method. Using the Dark Energy Camera (DECam), we survey a region covering a projected distance of $\sim$70 kpc of NGC 3109 ($D$ = 1.3 Mpc, $R_\mathrm{vir}\sim$ 90 kpc, $M\sim10^8M_\ast$) as part of the MADCASH and DELVE-DEEP programs. Through our resolved and newly designed semi-resolved searches, we successfully recover the known satellites Antlia and Antlia B. We identified a promising candidate, which was later confirmed to be a background dwarf through deep follow-up observations. Our detection limits are well defined, with the sample $\sim 80\%$ complete down to $M_V\sim-$8.0 , and includes detections of dwarf galaxies as faint as $M_V\sim-$6.0. This is the first comprehensive study of a satellite system through resolved star around an SMC mass host. Our results show that NGC 3109 has more bright ($M_V\sim-$9.0) satellites than the mean predictions from cold dark matter (CDM) models, but well within the host-to-host scatter. A larger sample of LMC/SMC-mass hosts is needed to test whether or not the observations are consistent with current model expectations.

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arXiv2023

Timescale of Stellar Feedback-Driven Turbulence in the ISM: A Deep Dive into UGC 4305

Understanding the interplay of stellar feedback and turbulence in the interstellar medium (ISM) is essential to modeling the evolution of galaxies. To determine the timescales over which stellar feedback drives turbulence in the ISM, we performed a spatially resolved, multi-wavelength study of the nearby star-forming dwarf galaxy UGC 4305 (aka Holmberg II). As indicators of turbulence on local scales (400 pc), we utilized ionized gas velocity dispersion derived from IFU H$α$ observations and atomic gas velocity dispersion and energy surface densities derived from HI synthesis observations with the Very Large Array. These indicators of turbulence were tested against star formation histories over the past 560 Myr derived from Color-Magnitude Diagrams (CMD) using Spearman's rank correlation coefficient. The strongest correlation identified at the 400 pc scale is between measures of HI turbulence and star formation 70-140 Myr ago. We repeated our analysis of UGC 4305's current turbulence and past star formation activity on multiple physical scales ($\sim$560, and 800 pc) to determine if there are indications of changes in the correlation timescale with changes to the physical scale. No notable correlations were found at larger physical scales emphasizing the importance of analyzing star formation driven turbulence as a local phenomenon.

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arXiv2022

Determining the Timescale over Which Stellar Feedback Drives Turbulence in the ISM: A Study of four Nearby Dwarf Irregular Galaxies

Stellar feedback is fundamental to the modeling of galaxy evolution as it drives turbulence and outflows in galaxies. Understanding the timescales involved are critical for constraining the impact of stellar feedback on the interstellar medium (ISM). We analyzed the resolved star formation histories along with the spatial distribution and kinematics of the atomic and ionized gas of four nearby star-forming dwarf galaxies (NGC 4068, NGC 4163, NGC 6789, UGC 9128) to determine the timescales over which stellar feedback drives turbulence. The four galaxies are within 5 Mpc and have a range of properties including current star formation rates of 0.0005 to 0.01 M$_{\odot}$ yr$^{-1}$, log(M$_*$/M$_{\odot}$) between 7.2 and 8.2, and log(M$_{HI}$/M$_\odot$) between 7.2 and 8.3. Their Color-Magnitude Diagram (CMD) derived star formation histories over the past 500 Myrs were compared to their atomic and ionized gas velocity dispersion and HI energy surface densities as indicators of turbulence. The Spearman's rank correlation coefficient was used to identify any correlations between their current turbulence and their past star formation activity on local scales ($\sim$400 pc). The strongest correlation found was between the HI turbulence measures and the star formation rate 100-200 Myrs ago. This suggests a coupling between the star formation activity and atomic gas on this timescale. No strong correlation between the ionized gas velocity dispersion and the star formation activity between 5-500 Myrs ago was found. The sample and analysis are the foundation of a larger program aimed at understanding the timescales over which stellar feedback drives turbulence.

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