arXiv subjects

Julianne J. Dalcanton

Publications and source records attributed to Julianne J. Dalcanton.

At least 37 records · Page 2Linked to original sources

arXiv2025

The Mass of the Vela Pulsar Progenitor and the Age of the Vela-Puppis Complex

The association of the Vela Pulsar with the Vela Supernova Remnant has long supported the hypothesis that core-collapse supernovae yield neutron stars, but its surrounding stellar population now offers new insights into progenitor evolution. By age-dating stars within 150 pc of the Vela Pulsar, we infer properties of its progenitor. These stars belong to the Vela-Puppis complex, revealing the region's star formation history. While stellar population models with standard assumptions suggest a likely progenitor age and mass, these predictions are internally inconsistent with the observed population, indicating that something is missing in the standard modeling approach. With those assumptions, there is very weak support for a $\lesssim$10 Myr old population, moderate support for a 40 Myr old population, and strong support for an intermediate age population around 65-100 Myrs old. The $\lesssim$10 Myr signal hinges on two peculiar O stars, which are unlike any others in the Vela-Puppis complex and imply nearly three times more main sequence stars than are observed. The 40 Myr-old population is supported by 6 red supergiants (RSGs) and several Be stars; but this population is again marginally inconsistent with the observed distribution of main sequence stars. The red giant (RG) and MS distributions are consistent with a 65-100 Myr old population. We discuss several possible resolutions, emphasizing how binary evolution and/or very rapid rotation could resolve these discrepancies. Gaia parallaxes and {\it Stellar Ages} enable these results; {\it Stellar Ages} is a novel stellar population modeling algorithm that combines individual and population-level age inferences.

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arXiv2025

The Karl G. Jansky Very Large Array Local Group L-band Survey (LGLBS)

We present the Local Group L-Band Survey (LGLBS), a Karl G. Jansky Very Large Array (VLA) survey producing the highest quality 21-cm and 1-2 GHz radio continuum images to date for the six VLA-accessible, star-forming, Local Group galaxies. Leveraging the VLA's spectral multiplexing power, we simultaneously survey the 21-cm line at high 0.4 km/s velocity resolution, the 1-2 GHz polarized continuum, and four OH lines. For the massive spiral M31, the dwarf spiral M33, and the dwarf irregular galaxies NGC6822, IC10, IC1613, and the Wolf-Lundmark-Melotte Galaxy (WLM), we use all four VLA configurations and the Green Bank Telescope to reach angular resolutions of $< 5''$ ($10{-}20$~pc) for the 21-cm line with $<10^{20}$~cm$^{-2}$ column density sensitivity, and even sharper views ($< 2''$; $5{-}10$~pc) of the continuum. Targeting these nearby galaxies ($D\lesssim1$ Mpc) reveals a sharp, resolved view of the atomic gas, including 21-cm absorption, and continuum emission from supernova remnants and HII regions. These datasets can be used to test theories of the abundance and formation of cold clouds, the driving and dissipation of interstellar turbulence, and the impact of feedback from massive stars and supernovae. Here, we describe the survey design and execution, scientific motivation, data processing, and quality assurance. We provide a first look at and publicly release the wide-field 21-cm HI data products for M31, M33, and four dwarf irregular targets in the survey, which represent some of the highest physical resolution 21-cm observations of any external galaxies beyond the LMC and SMC.

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arXiv2025

A Low Metallicity Massive Contact Binary Star System Candidate in WLM identified by Hubble and James Webb Space Telescope imaging

We present archival HST and JWST ultraviolet through near infrared time series photometric observations of a massive minimal-contact binary candidate in the metal-poor galaxy WLM ($Z = 0.14 Z_{\odot}$). This discovery marks the lowest metallicity contact binary candidate observed to date. We determine the nature of the two stars in the binary by using the eclipsing binary modeling software (PHysics Of Eclipsing BinariEs; PHOEBE) to train a neural network to fit our observed panchromatic multi-epoch photometry. The best fit model consists of two hot MS stars ($T_1=29800^{+2300}_{-1700}$ K, $M_1=16^{+2}_{-3}~M_{\odot}$, and $T_2=18000^{+5000}_{-5000}$ K, $M_2=7^{+5}_{-3}~M_{\odot}$). We discuss plausible evolutionary paths for the system, and suggest the system is likely to be currently in a contact phase before ultimately ending in a merger. Future spectroscopy will help to further narrow down evolutionary pathways. This work showcases a novel use of data of JWST and HST imaging originally taken to characterize RR Lyrae. We expect time series imaging from LSST, BlackGEM, etc. to uncover similar types of objects in nearby galaxies.

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arXiv2025

Delayed and Displaced: The Impact of Binary Interactions on Core-collapse SN Feedback

Core-collapse supernova feedback models in hydrodynamical simulations typically assume that all stars evolve as single stars. However, the majority of massive stars are formed in binaries and multiple systems, where interactions with a companion can affect stars' subsequent evolution and kinematics. We assess the impact of binary interactions on the timing and spatial distribution of core-collapse supernovae, using `cogsworth` simulations to evolve binary star populations, and their subsequent galactic orbits, within state-of-the-art hydrodynamical zoom-in galaxy simulations. We show that binary interactions: (a) displace supernovae, with ~13% of all supernovae occurring more than 0.1 kpc from their parent cluster; and (b) produce delayed supernovae, such that ~25% of all supernovae occur after the final supernova from a single star population. Delays are largest for low-mass merger products, which can explode more than 200 Myr after a star formation event. We characterize our results as a function of: (1) initial binary population distributions, (2) binary physics parameters and evolutionary pathways, (3) birth cluster dissolution assumptions, and (4) galaxy models (which vary metallicity, star formation history, gravitational potential and simulation codes), and show that the overall timing and spatial distributions of supernovae are surprisingly insensitive to most of these variations. We provide metallicity-dependent analytic fits that can be substituted for single-star subgrid feedback prescriptions in hydrodynamical simulations, and discuss some of the possible implications for binary-driven feedback in galaxies, which may become particularly important at high redshift.

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arXiv2025

Discovery of a Weak CN Spectral Absorption Feature in Red Supergiant Stars in the Andromeda (M31) and Triangulum (M33) Galaxies

Using Keck DEIMOS spectra of stars in the Andromeda (M31) and Triangulum (M33) galaxies, selected from the large multi-band (near ultraviolet, visible light, and near infrared) Hubble Space Telescope surveys PHAT and PHATTER, respectively, we have identified a subset of stars that contain a previously unnoticed weak spectral absorption feature around 8000 Angstrom (0.8 micron). This absorption feature appears to be associated with the cyanogen (CN) molecule. Strong CN spectral absorption is a standard feature of carbon stars, which are thought to be intermediate mass (2-3 ~ M_sun) stars with C/O > 1 in the thermally-pulsating asymptotic giant branch phase of stellar evolution. However, the stars that are the focus of this paper are characterized by a weak version of this CN spectral absorption feature in a spectrum that is otherwise dominated by normal O-rich spectral absorption lines such as TiO and/or the Ca near infrared triplet. We have dubbed these stars "weak CN" stars. We present an automated method for identifying weak CN stars in M31 and M33, and examine their photometric properties in relation to model isochrones and stellar tracks. We find that weak CN stars tend to be fairly localized in color-magnitude space, and appear to be red supergiant stars with masses ranging from 5-10 M_sun, overall lifetimes of about 40-50 Myr, and currently in the core He burning phase of stellar evolution.

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arXiv2025

Relationships between PAHs, Small Dust Grains, H$_2$, and HI in Local Group Dwarf Galaxies NGC 6822 and WLM Using JWST, ALMA, and the VLA

We present 0.7-3.3 pc resolution mid-infrared (MIR) JWST images at 7.7 $μ$m (F770W) and 21 $μ$m (F2100W) covering the main star-forming regions of two of the closest star-forming low-metallicity dwarf galaxies, NGC6822 and Wolf-Lundmark-Melotte (WLM). The images of NGC6822 reveal filaments, edge-brightened bubbles, diffuse emission, and a plethora of point sources. By contrast, most of the MIR emission in WLM is point-like, with a small amount of extended emission. Compared to solar metallicity galaxies, the ratio of 7.7 $μ$m intensity ($I_ν^{F770W}$), tracing polycyclic aromatic hydrocarbons (PAHs), to 21 $μ$m intensity ($I_ν^{F2100W}$), tracing small, warm dust grain emission, is suppressed in these low-metallicity dwarfs. Using ALMA CO(2-1) observations, we find that detected CO intensity versus $I_ν^{F770W}$ at ~2 pc resolution in dwarfs follows a similar relationship to that at solar metallicity and lower resolution, while the CO versus $I_ν^{F2100W}$ relationship in dwarfs lies significantly below that derived from solar metallicity galaxies at lower resolution, suggesting more pronounced destruction of CO molecules at low metallicity. Finally, adding in Local Group L-Band Survey VLA 21 cm HI observations, we find that $I_ν^{F2100W}$ and $I_ν^{F770W}$ vs. total gas ratios are suppressed in NGC6822 and WLM compared to solar metallicity galaxies. In agreement with dust models, the level of suppression appears to be at least partly accounted for by the reduced galaxy-averaged dust-to-gas and PAH-to-dust mass ratios in the dwarfs. Remaining differences are likely due to spatial variations in dust model parameters, which should be an exciting direction for future work in local dwarf galaxies.

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arXiv2025

An Investigation of Disk Thickness in M51 from H-alpha, Pa-alpha, and Mid-Infrared Power Spectra

Power spectra (PS) of high-resolution images of M51 (NGC 5194) taken with the Hubble Space Telescope and the James Webb Space Telescope have been examined for evidence of disk thickness in the form of a change in slope between large scales, which map two-dimensional correlated structures, and small scales, which map three-dimensional correlated structures. Such a slope change is observed here in H-alpha, and possibly Pa-alpha, using average PS of azimuthal intensity scans that avoid bright peaks. The physical scale of the slope change occurs at ~120 pc and ~170 pc for these two transitions, respectively. A radial dependence in the shape of the H-alpha PS also suggests that the length scale drops from ~180 pc at 5 kpc, to ~90 pc at 2 kpc, to ~25 pc in the central ~kpc. We interpret these lengths as comparable to the thicknesses of the star-forming disk traced by HII regions. The corresponding emission measure is ~100 times larger than what is expected from the diffuse ionized gas. PS of JWST Mid-IR Instrument (MIRI) images in 8 passbands have more gradual changes in slope, making it difficult to determine a specific value of the thickness for this emission.

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arXiv2025

Strikingly high fraction of fast rotators in Magellanic Cloud star clusters

There has been growing evidence that the rich star clusters in the Magellanic Clouds contain significant fractions of rapidly rotating stars. In this work, we aim to constrain these fractions by studying the colour-magnitude diagrams of four star clusters, selected among those with the most striking signatures of fast rotators. Using isochrones derived from PARSEC v2.0 stellar tracks, we generate distinct stellar populations, each covering a limited interval of initial rotation rates $ω_\mathrm{i}$, referred to as 'Partial Models' (PMs). Using optimization algorithms and Monte Carlo Markov Chains, PMs are combined to create the final best-fitting model. In our analysis, we adopt two key assumptions: a uniform age and an isotropic distribution of stellar spin axes within each cluster. The solutions are allowed to explore the entire range of $ω_\mathrm{i}$, and different values of age, metallicity, distance and foreground extinction. We find that the rotational velocity distributions in all four clusters reveal a high fraction of stars with $ω_\mathrm{i}$ close to the break-up value, in all cases. Specifically, the fraction of stars with $ω_\mathrm{i}>0.7$ exceeds $80\%$ in the clusters NGC 419 of the Small Magellanic Cloud (SMC) and NGC 1831 and NGC 1866 of the Large Magellanic Cloud (LMC). For NGC 2203 of the LMC, this fraction is smaller, although it still exceeds $50\%$, confirming that also this cluster is mainly populated by fast-rotating stars.

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arXiv2025

The Local Ultraviolet to Infrared Treasury II. Refining Star Formation Histories of Ten Metal-Poor Dwarf Galaxies with Simultaneous UV-Optical Two-CMD Fitting

We present the star formation histories (SFHs) of ten metal-poor (<12% Zsun), star-forming dwarf galaxies from the Local Ultraviolet to Infrared Treasury (LUVIT) survey. The derived SFHs exhibit significant variability, consistent with the irregular star formation expected for dwarf galaxies. Using synthetic near ultraviolet (UV) and optical CMDs with various yet targeted configurations for dust and input SFHs, we quantitatively demonstrate that simultaneous modeling of the UV and optical CMDs ("UVopt" case) improves the precision of SFH measurements in recent time bins up to ~1 Gyr, compared to the classical single optical CMD modeling ("Opt-only" case). The UVopt case reduces uncertainties relative to the Opt-only case by ~4-8% over the past 10 Myr, ~8-20% over 100 Myr, and ~8-14% over 1 Gyr, across various dust configurations and input SFHs. Additionally, we demonstrate discrepancies in stellar models for blue core helium-burning (BHeB) stars at the low metallicity regime. This discrepancy can artificially inflate star formation rate (SFR) estimates in younger age bins by misinterpreting the evolved BHeB stars as reddened upper main-sequence (MS) stars. Incorporating UV data improves BHeB-MS separation and mitigates the limitations of current low metallicity stellar models. Comparisons of the UVopt SFHs with Ha and FUV-based SFRs reconfirm that Ha is an unreliable tracer over its nominal 10 Myr timescale for low-SFR galaxies, while FUV provides a more reliable tracer but yields SFR_FUV values up to twice those of CMD-based _100Myr. Our findings underscore the importance of UV data in refining recent SFHs in low-metallicity environments.

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arXiv2025

Stellar Ages: A Code to Infer Properties of Stellar Populations

We present a novel statistical algorithm, Stellar Ages, which currently infers the age, metallicity, and extinction posterior distributions of stellar populations from their magnitudes. While this paper focuses on these parameters, the framework is readily adaptable to include additional properties, such as rotation, in future work. Historical age-dating techniques either model individual stars or populations of stars, often sacrificing population context or precision for individual estimates. Stellar Ages does both, combining the strengths of these approaches to provide precise individual ages for stars while leveraging population-level constraints. We verify the algorithm's capabilities by determining the age of synthetic stellar populations and actual stellar populations surrounding a nearby supernova, SN 2004dj. In addition to inferring an age, we infer a progenitor mass consistent with direct observations of the precursor star. The median age inferred from the brightest nearby stars is $\log_{10}$(Age/yr) = $7.19^{+0.10}_{-0.13}$, and its corresponding progenitor mass is $13.95^{+3.33}_{-1.96}$ $\text{M}_{\odot}$.

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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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arXiv2025

A Catalog of Stellar and Dust Properties for 500,000 Stars in the Southwest Bar of the Small Magellanic Cloud

We present a catalog of individual stellar and dust extinction properties along close to 500,000 sight lines in the southwest bar of the Small Magellanic Cloud (SMC). The catalog is based on multiband Hubble Space Telescope photometric data spanning near-ultraviolet to near-infrared wavelengths from the Small Magellanic Cloud Investigation of Dust and Gas Evolution survey (SMIDGE) covering a 100 x 200 pc area. We use the probabilistic technique of the Bayesian Extinction And Stellar Tool (BEAST) to model the spectral energy distributions of individual stars in SMIDGE and include the effects of observational uncertainties in the data. We compare BEAST-derived dust extinction properties with tracers of the interstellar medium, such as the emission from the 12CO (2-1) transition (I(CO)), the dust mass surface density (Σdust) from far-IR emission, the H I column density (N(HI)) from the 21cm transition, and the mass fraction of polycyclic aromatic hydrocarbons (PAHs; qPAH, derived from IR emission). We find that the dust extinction (A(V )) in the SMIDGE field is strongly correlated with Σdust and I(CO), and less so with N(HI) and qPAH, and suggest potential explanations. Our extinction measurements are also sensitive to the presence of the 2175 Å bump in the extinction curve toward UV bright stars. While most do not show evidence for the bump, we identify ~200 lines of sight that are 2175 Å bump candidates. Furthermore, we find distinct structures in the dust extinction-distance distributions that provide insights into the 3D geometry of the SMC.

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arXiv2024

The Local Group L-Band Survey: The First Measurements of Localized Cold Neutral Medium Properties in the Low-Metallicity Dwarf Galaxy NGC 6822

Measuring the properties of the cold neutral medium (CNM) in low-metallicity galaxies provides insight into heating and cooling mechanisms in early Universe-like environments. We report detections of two localized atomic neutral hydrogen (HI) absorption features in NGC 6822, a low-metallicity (0.2 Z$_{\odot}$) dwarf galaxy in the Local Group. These are the first unambiguous CNM detections in a low-metallicity dwarf galaxy outside the Magellanic Clouds. The Local Group L-Band Survey (LGLBS) enabled these detections due to its high spatial (15 pc for HI emission) and spectral (0.4 \kms) resolution. We introduce LGLBS and describe a custom pipeline to search for HI absorption at high angular resolution and extract associated HI emission. A detailed Gaussian decomposition and radiative transfer analysis of the NGC 6822 detections reveals five CNM components, with key properties: a mean spin temperature of 32$\pm$6 K, a mean CNM column density of 3.1$\times$10$^{20}$ cm$^{-2}$, and CNM mass fractions of 0.33 and 0.12 for the two sightlines. Stacking non-detections does not reveal low-level signals below our median optical depth sensitivity of 0.05. One detection intercepts a star-forming region, with the HI absorption profile encompassing the CO (2$-$1) emission, indicating coincident molecular gas and a depression in high-resolution HI emission. We also analyze a nearby sightline with deep, narrow HI self-absorption dips, where the background warm neutral medium is attenuated by intervening CNM. The association of CNM, CO, and H$α$ emissions suggests a close link between the colder, denser HI phase and star formation in NGC 6822.

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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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arXiv2024

Introducing the DREAMS Project: DaRk mattEr and Astrophysics with Machine learning and Simulations

We introduce the DREAMS project, an innovative approach to understanding the astrophysical implications of alternative dark matter models and their effects on galaxy formation and evolution. The DREAMS project will ultimately comprise thousands of cosmological hydrodynamic simulations that simultaneously vary over dark matter physics, astrophysics, and cosmology in modeling a range of systems -- from galaxy clusters to ultra-faint satellites. Such extensive simulation suites can provide adequate training sets for machine-learning-based analyses. This paper introduces two new cosmological hydrodynamical suites of Warm Dark Matter, each comprised of 1024 simulations generated using the Arepo code. One suite consists of uniform-box simulations covering a $(25~h^{-1}~{\rm M}_\odot)^3$ volume, while the other consists of Milky Way zoom-ins with sufficient resolution to capture the properties of classical satellites. For each simulation, the Warm Dark Matter particle mass is varied along with the initial density field and several parameters controlling the strength of baryonic feedback within the IllustrisTNG model. We provide two examples, separately utilizing emulators and Convolutional Neural Networks, to demonstrate how such simulation suites can be used to disentangle the effects of dark matter and baryonic physics on galactic properties. The DREAMS project can be extended further to include different dark matter models, galaxy formation physics, and astrophysical targets. In this way, it will provide an unparalleled opportunity to characterize uncertainties on predictions for small-scale observables, leading to robust predictions for testing the particle physics nature of dark matter on these scales.

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arXiv2024

The JWST Resolved Stellar Populations Early Release Science Program V. DOLPHOT Stellar Photometry for NIRCam and NIRISS

We present NIRCam and NIRISS modules for DOLPHOT, a widely-used crowded field stellar photometry package. We describe details of the modules including pixel masking, astrometric alignment, star finding, photometry, catalog creation, and artificial star tests (ASTs). We tested these modules using NIRCam and NIRISS images of M92 (a Milky Way globular cluster), Draco II (an ultra-faint dwarf galaxy), and WLM (a star-forming dwarf galaxy). DOLPHOT's photometry is highly precise and the color-magnitude diagrams are deeper and have better definition than anticipated during original program design in 2017. The primary systematic uncertainties in DOLPHOT's photometry arise from mismatches in the model and observed point spread functions (PSFs) and aperture corrections, each contributing $\lesssim0.01$ mag to the photometric error budget. Version 1.2 of WebbPSF models, which include charge diffusion and interpixel capacitance effects, significantly reduced PSF-related uncertainties. We also observed minor ($\lesssim0.05$ mag) chip-to-chip variations in NIRCam's zero points, which will be addressed by the JWST flux calibration program. Globular cluster observations are crucial for photometric calibration. Temporal variations in the photometry are generally $\lesssim0.01$ mag, although rare large misalignment events can introduce errors up to 0.08 mag. We provide recommended DOLPHOT parameters, guidelines for photometric reduction, and advice for improved observing strategies. Our ERS DOLPHOT data products are available on MAST, complemented by comprehensive online documentation and tutorials for using DOLPHOT with JWST imaging data.

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arXiv2023

Orbital Torus Imaging: Acceleration, density, and dark matter in the Galactic disk measured with element abundance gradients

Under the assumption of a simple and time-invariant gravitational potential, many Galactic dynamics techniques infer the Milky Way's mass and dark matter distribution from stellar kinematic observations. These methods typically rely on parameterized potential models of the Galaxy and must take into account non-trivial survey selection effects, because they make use of the density of stars in phase space. Large-scale spectroscopic surveys now supply information beyond kinematics in the form of precise stellar label measurements (especially element abundances). These element abundances are known to correlate with orbital actions or other dynamical invariants. Here, we use the Orbital Torus Imaging (OTI) framework that uses abundance gradients in phase space to map orbits. In many cases these gradients can be measured without detailed knowledge of the selection function. We use stellar surface abundances from the APOGEE survey combined with kinematic data from the Gaia mission. Our method reveals the vertical ($z$-direction) orbit structure in the Galaxy and enables empirical measurements of the vertical acceleration field and orbital frequencies in the disk. From these measurements, we infer the total surface mass density, $Σ$, and midplane volume density, $ρ_0$, as a function of Galactocentric radius and height. Around the Sun, we find $Σ_{\odot}(z=1.1$ kpc)$=72^{+6}_{-9}$M$_{\odot}$pc$^{-2}$ and $ρ_{\odot}(z=0)=0.081^{+0.015}_{-0.009}$ M$_{\odot}$pc$^{-3}$ using the most constraining abundance ratio, [Mg/Fe]. This corresponds to a dark matter contribution in surface density of $Σ_{\odot,\mathrm{DM}}(z=1.1$ kpc)$=24\pm4$ M$_{\odot}$pc$^{-2}$, and in total volume mass density of $ρ_{\odot,\mathrm{DM}}(z=0)=0.011\pm0.002$ M$_{\odot}$pc$^{-3}$. Moreover, using these mass density values we estimate the scale length of the low-$α$ disc to be $h_R=2.24\pm0.06$kpc.

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arXiv2023

JWST Reveals Star Formation Across a Spiral Arm in M33

Young stellar objects (YSOs) are the gold standard for tracing star formation in galaxies but have been unobservable beyond the Milky Way and Magellanic Clouds. But that all changed when the James Webb Space Telescope was launched, which we use to identify YSOs in the Local Group galaxy M33, marking the first time that individual YSOs have been identified at these large distances. We present MIRI imaging mosaics at 5.6 and 21 microns that cover a significant portion of one of M33's spiral arms that has existing panchromatic imaging from the Hubble Space Telescope and deep ALMA CO measurements. Using these MIRI and Hubble Space Telescope images, we identify point sources using the new DOLPHOT MIRI module. We identify 793 candidate YSOs from cuts based on colour, proximity to giant molecular clouds (GMCs), and visual inspection. Similar to Milky Way GMCs, we find that higher mass GMCs contain more YSOs and YSO emission, which further shows YSOs identify star formation better than most tracers that cannot capture this relationship at cloud scales. We find evidence of enhanced star formation efficiency in the southern spiral arm by comparing the YSOs to the molecular gas mass.

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