arXiv subjects

Max J. B. Newman

Publications and source records attributed to Max J. B. Newman.

18 recordsLinked to original sources

arXiv2026

The JWST Resolved Stellar Populations Early Release Science Program. IX. The RR Lyrae Population in WLM with HST and JWST

RR Lyrae stars are a common, dependable Population II distance indicator, and provide an independent tracer of early star formation. Here, we utilize archival HST/ACS and JWST/NIRCam observations of the nearby dwarf star-forming galaxy WLM to study RR Lyrae in JWST filters. We independently identify RR Lyrae in HST and JWST imaging in order to evaluate JWST's efficacy at characterizing RR Lyrae in the near-IR. We use an MCMC template-fitting technique to obtain periods, amplitudes, and mean magnitudes from the RR Lyrae time-series data. The spatially overlapping HST and JWST observations allow us to directly compare the same sources observed with the instruments, and calibrate the NIRCam F090W and F150W RR Lyrae period-Wesenheit-metallicity (PWZ) relation to the Gaia-consistent HST PWZ. We additionally assess the epoch-to-epoch consistency of NIRCam photometry, and find evidence of burn-in. We conclude that the zero-point offset is negligible compared to the uncertainties from the template fitting. We conduct an MCMC fit of the PWZ with both HST and JWST data. Our results are three-fold. First, we find that we can reliably identify RR Lyrae in NIRCam data, but light-curve template fitting proves difficult on short-baseline observations. Second, the HST PWZ fit yields a distance modulus to WLM of $μ= 24.85\pm0.05$ ($0.93\pm0.02$ Mpc). This is closer than previous measurements, primarily attributed to consistency with the Gaia scale. Lastly, although the JWST PWZ fit has large uncertainties and a poorly-constrained slope, it represents a first-of-its-kind PWZ calibration in NIRCam filters.

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arXiv2026

A Quenched and Relatively Isolated Dwarf Galaxy in the Local Volume

An increasing number of discoveries of isolated and quenched dwarf galaxies are challenging the idea that the present-day local environment of low-mass systems is the main determinant of their quenching. We present new Hubble Space Telescope (HST) data of one such system, the dwarf galaxy Canes Venatici C (CVn C). CVn C is a low-mass (3.4(+4.2-2.6)*10^6 M_sun) galaxy with a Tip of the Red Giant Branch distance of 8.43(+0.47-0.32) Mpc determined from the resolved stars in the HST imaging, which we also use to derive CVn C's structural parameters. CVn C's distance places CVn C in the Local Volume and in an isolated environment with the most tidally influential L* galaxy > 5Rvir away. Additional constraints from the HST color-magnitude diagram, archival Far-Ultraviolet (FUV), and neutral hydrogen (HI) data show that CVn C is quenched, with no evidence of star formation in the last 100 Myr and no detectable gas (MHI < 1.5*10^6 M_sun). Circumstantial evidence suggests that CVn C may have quenched via past interactions with the L* galaxy NGC 4631 (L_K = 10^10.4 L_sun), and was possibly sent on an extreme backsplash orbit by the tidal dissolution of a subhalo group. However, other quenching mechanisms-such as stripping via the cosmic web-cannot be ruled out. CVn C adds to the growing number of quenched dwarf galaxies in under-dense environments, a population that will be critical to defining the mass and environment regimes in which different quenching mechanisms operate.

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arXiv2025

JWST Captures 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 like Spitzer. 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 the hard radiation fields within the galaxy. 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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arXiv2025

The Proper Motion of Draco II with HST using Multiple Reference Frames and Methodologies

We present proper motion (PM) measurements for Draco II, an ultra-faint dwarf satellite of the Milky Way. These PMs are measured using two epochs of Hubble Space Telescope Advanced Camera for Surveys (HST/ACS) imaging separated by a 7 year time baseline. Measuring PMs of low-luminosity systems is difficult due to the low number of member stars, requiring a precise inertial reference frame. We construct reference frames using three different sets of external sources: 1) stars with Gaia DR3 data, 2) stationary background galaxies, and 3) a combination of the two. We show that all three reference frames give consistent PM results. We find that for this sparse, low-luminosity regime including background galaxies into the reference frame improves our measurement by up to $\sim2\times$ versus using only Gaia astrometric data. Using 301 background galaxies as a reference frame, we find that Draco II's systemic PM is $(μ_α^*, μ_δ) = (1.043\pm0.029, 0.879\pm0.028)$ mas/yr, which is the most precise measurement of the three we present in this paper.

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arXiv2025

Tip of the Red Giant Branch Distances to NGC 1316, NGC 1380, NGC 1404, & NGC 4457: A Pilot Study of a Parallel Distance Ladder Using Type Ia Supernovae in Early-Type Host Galaxies

Though type-Ia supernovae (SNe Ia) are found in all types of galaxies, recent local Hubble constant measurements have disfavored using SNe Ia in early-type or quiescent galaxies, aiming instead for better consistency with SNe Ia in star-forming, late-type host galaxies calibrated by Cepheid distances. Here we investigate the feasibility of a parallel distance ladder using SNe Ia exclusively in quiescent, massive ($\log M_*/M_{\odot} \geq 10$) host galaxies, calibrated by tip of the red giant branch (TRGB) distances. We present TRGB measurements to four galaxies: three measured from the Hubble Space Telescope with the ACS F814W filter, and one measured from the JWST NIRCam F090W filter. Combined with literature measurements, we define a TRGB calibrator sample of five high-mass, early-type galaxies that hosted well-measured SNe Ia: NGC 1316 (SN 2006dd), NGC 1380 (SN 1992A), NGC 1404 (SN 2007on, SN 2011iv), NGC 4457 (SN 2020nvb), and NGC 4636 (SN 2020ue). We jointly standardize these calibrators with a fiducial sample of 124 Hubble-flow SNe Ia from the Zwicky Transient Facility that are matched in host-galaxy and light-curve properties. Our results with this homogenized subsample show a Hubble residual scatter of under 0.11 mag, lower than usually observed in cosmological samples of the full SN~Ia distribution. We obtain a measurement of the Hubble constant, $H_0 = 75.3 \pm 2.9$ km s$^{-1}$ Mpc$^{-1}$, including statistical and estimated systematic uncertainties, and discuss the potential to further improve the precision of this approach. As calibrator and supernova samples grow, we advocate that future cosmological applications of SNe Ia use subsamples matched in host-galaxy and supernova properties across redshift.

astro-ph.CO↗

arXiv2025

Leonessa: An Extremely Metal-poor Galaxy Undergoing Secular Chemical Evolution

Extremely metal-poor (XMP) galaxies are systems with gas-phase oxygen abundances below $\sim$5% Solar metallicity (12+log(O/H)$\le$7.35). These galaxies populate the metal-poor end of the mass-metallicity and luminosity-metallicity relations (MZR and LZR, respectively). Recent studies have found XMP galaxies in the nearby Universe to be outliers on the LZR, where they show enhanced luminosities relative to other galaxies of similar gas-phase oxygen abundance. Here, we present a study of the recently discovered XMP galaxy Leonessa and characterize the system's properties using new imaging from the Hubble Space Telescope and spectra from the Green Bank Telescope and Hobby-Eberly Telescope. We use these observations to measure a tip of the red giant branch (TRGB) distance (15.86$\pm$0.78 Mpc) to Leonessa, the HI gas mass, the gas-phase oxygen abundance, and N/O ratio. We find Leonessa is an isolated, gas rich (gas fraction $μ$=0.69), low-mass (log(M$_\star$/M$_\odot$)=6.12$\pm$0.08), XMP (12+log(O/H)=7.32$\pm$0.04), star-forming galaxy at a distance of 15.86$\pm$0.78 Mpc. Our measurements show that Leonessa agrees with the MZR, but disagrees with the LZR; we conclude the LZR offset is due to recent star formation enhancing the system's luminosity. To investigate possible chemical evolution pathways for nearby XMP galaxies we also compile a comparison sample of 150 dwarf galaxies (53 XMP systems) taken from the literature with gas-phase metallicity measurements based on the direct method. We find evidence for an anti-correlation between gas-phase oxygen abundance and HI gas-to-stellar mass ratios. We posit Leonessa is undergoing a chemical evolution pathway typical of field dwarf galaxies.

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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.

astro-ph.SR↗

arXiv2025

The Remarkable Late-Time Flux Excess in Hubble Space Telescope Observations of the Type Iax Supernova 2012Z

Type Iax supernovae (SNe Iax) are thermonuclear explosions of white dwarfs, peculiar and underluminous compared to the normal type Ia supernovae. Observations of SNe Iax provide insight into the physics of white-dwarf explosions and suggest that some may not be terminal events. Late-time photometry ($\sim$1400 days post-peak) of the type Iax SN 2012Z, the only white dwarf supernova with a pre-explosion detection of a progenitor system, revealed a flux excess that may be explained by a gravitationally bound remnant driving a radioactively powered wind. We present further late-time Hubble Space Telescope photometry of SN 2012Z, $\sim$2500 days after the explosion, and find that the SN is still brighter than, but trending towards, the pre-explosion flux. Additionally, we observe that the excess F555W flux seen in previous data has grown more pronounced. The color of the excess flux disfavors a light echo or interaction with the circumstellar material. The decline rate of the excess flux is consistent with energy deposition from $^{55}$Fe, but the luminosity is higher than expected from models of the ejecta, further suggesting evidence for a bound remnant. Combining our data with future observations should allow for the detection of emission from the ejecta shock-heating of the companion helium star seen in the progenitor system.

astro-ph.HE↗

arXiv2025

LensWatch. II. Improved Photometry and Time-delay Constraints on the Strongly Lensed Type Ia Supernova 2022qmx ("SN Zwicky") with HST Template Observations

Strongly lensed supernovae (SNe) are a rare class of transient that can offer tight cosmological constraints that are complementary to methods from other astronomical events. We present a follow-up study of one recently-discovered strongly lensed SN, the quadruply-imaged Type Ia SN 2022qmx (aka, "SN Zwicky") at z = 0.3544. We measure updated, template-subtracted photometry for SN Zwicky and derive improved time delays and magnifications. This is possible because SNe are transient, fading away after reaching their peak brightness. Specifically, we measure point spread function (PSF) photometry for all four images of SN Zwicky in three Hubble Space Telescope WFC3/UVIS passbands (F475W, F625W, F814W) and one WFC3/IR passband (F160W), with template images taken $\sim 11$ months after the epoch in which the SN images appear. We find consistency to within $2σ$ between lens model predicted time delays ($\lesssim1$ day), and measured time delays with HST colors ($\lesssim2$ days), including the uncertainty from chromatic microlensing that may arise from stars in the lensing galaxy. The standardizable nature of SNe Ia allows us to estimate absolute magnifications for the four images, with images A and C being elevated in magnification compared to lens model predictions by about $6σ$ and $3σ$ respectively, confirming previous work. We show that millilensing or differential dust extinction is unable to explain these discrepancies and find evidence for the existence of microlensing in images A, C, and potentially D, that may contribute to the anomalous magnification.

astro-ph.HE↗

arXiv2025

The JWST Resolved Stellar Populations Early Release Science Program. VIII. The Spatially Resolved Star Formation History of WLM

We measure radial stellar age gradients in the relatively isolated gas-rich dwarf irregular WLM, combining JWST NIRCam and NIRISS imaging with six archival Hubble fields over semi-major axis equivalent distances of 0$\lesssim$R$_{SMA}$$\lesssim$4 kpc ($\lesssim$3R$_{hl}$). Fitting lifetime star formation histories (SFHs) to resolved color-magnitude diagrams (CMDs), radial age gradients are quantified using $τ_{90}$ and $τ_{50}$, the lookback times to form 90\% and 50\% of the cumulative stellar mass. We find that globally, the outskirts of WLM are older on average, with ($δ$$τ_{90}$, $δ$$τ_{50}$)/$δ$R$_{SMA}=$(0.82$^{+0.10}_{-0.10}$, 1.60$^{+0.23}_{-0.22}$) Gyr/kpc (stat.), in good agreement with simulations. However, we also detect an azimuthal dependence of radial stellar age gradients, finding that stars on the leading edge of WLM (relative to its proper motion) are both younger and have a flatter age gradient compared to the trailing edge. This difference persists over 0.6$\lesssim$R$_{SMA}$$\lesssim$3.2 kpc ($\sim$0.5$-$2.5R$_{hl}$) and lookback times up to $\sim$8 Gyr, and is robust to assumed stellar evolutionary model. Our results are consistent with star formation triggered by ram pressure stripping from a circumgalactic and/or intergalactic medium, suggested by recent HI observations. If confirmed, processes typifying dense environments, such as ram pressure stripping, may be more relevant to the evolution of isolated galaxies than previously thought.

astro-ph.GA↗

arXiv2024

The Ancient Star Formation History of the Extremely Low-Mass Galaxy Leo P: An Emerging Trend of a Post-Reionization Pause in Star Formation

Isolated, low-mass galaxies provide the opportunity to assess the impact of reionization on their star formation histories (SFHs) without the ambiguity of environmental processes associated with massive host galaxies. There are very few isolated, low-mass galaxies that are close enough to determine their SFHs from resolved star photometry reaching below the oldest main sequence turnoff. JWST has increased the volume for which this is possible, and here we report on JWST observations of the low-mass, isolated galaxy Leo P. From NIRCam imaging in F090W, F150W, and F277W, we derive a SFH which shows early star formation followed by a pause subsequent to the epoch of reionization which is then later followed by a re-ignition of star formation. This is very similar to the SFHs from previous studies of other dwarf galaxies in the ``transition zone'' between quenched very low-mass galaxies and the more massive galaxies which show no evidence of the impact of reionization on their SFHs; this pattern is rarely produced in simulations of SFHs. The lifetime SFH reveals that Leo P's stellar mass at the epoch of reionization was in the range that is normally associated with being totally quenched. The extended pause in star formation from z~5-1 has important implications for the contribution of low-mass galaxies to the UV photon budget at intermediate redshifts. We also demonstrate that, due to higher sensitivity and angular resolution, observing in two NIRCam short wavelength filters is superior to observing in a combination of a short and a long wavelength filter.

astro-ph.GA↗

arXiv2024

An Empirical Calibration of the Tip of the Red Giant Branch Distance Method in the Near Infrared. II. JWST NIRCam Wide Filters

The tip of the red giant (TRGB) is a standardizable candle and is identifiable as the discontinuity at the bright extreme of the red giant branch (RGB) stars in color-magnitude diagram (CMD) space. The TRGB-based distance method has been calibrated and used to measured distances to galaxies out to $D\leq20$ Mpc with the $I$-band equivalent Hubble Space Telescope ($HST$) $F814W$ filter, and as an important rung in the distance ladder to measure the Hubble constant, $H_0$. In the infrared (IR), the TRGB apparent magnitude ranges from $1-2$ magnitudes brighter than in the optical, and now with the IR James Webb Space Telescope ($JWST$) observatory the feasible distance range of the TRGB method can be extended to $\sim50$ Mpc. However, in the IR the TRGB luminosity depends to varying degrees on stellar metallicity and age. In this study we standardize the TRGB luminosity using stellar colors as a proxy for metallicity/age to derive color-based corrections for the $JWST$ Near-Infrared Camera (NIRCam) short wavelength (SW) filters $F090W$, $F115W$, $F150W$ and the long wavelength (LW) filters $F277W$, $F356W,$ and $F444W$. We provide recommended filter combinations for distance measurements depending on the requisite precision. For science requiring high precision ($\leq1\%$ in distance) and robustness we recommend measuring the TRGB in $F090W$ vs $F090W-F150W$ or $F115W$ vs. $F115W-F277W$ with the caveat that even with $JWST$ long integration times will be necessary at further distances. If lower precision ($>1.5\%$ in distance) can be tolerated, or if shorter integration times are desirable, we recommend measuring the TRGB in either $F115W$ or $F150W$ paired with $F356W$. We do not recommend $F444W$ for precision TRGB measurements due to its lower angular resolution.

astro-ph.CO↗

arXiv2024

An Empirical Calibration of the Tip of the Red Giant Branch Distance Method in the Near Infrared. I. HST WFC3/IR F110W and F160W Filters

The Tip of the Red Giant Branch (TRGB)-based distance method in the I band is one of the most efficient and precise techniques for measuring distances to nearby galaxies (D <= 15 Mpc). The TRGB in the near infrared (NIR) is 1 to 2 magnitudes brighter relative to the I band, and has the potential to expand the range over which distance measurements to nearby galaxies are feasible. Using Hubble Space Telescope (HST) imaging of 12 fields in 8 nearby galaxies, we determine color-based corrections and zero points of the TRGB in the Wide Field Camera 3 IR (WFC3/IR) F110W and F160W filters. First, we measure TRGB distances in the I band equivalent Advanced Camera System (ACS) F814W filter from resolved stellar populations with the HST. The TRGB in the ACS F814W filter is used for our distance anchor and to place the WFC3/IR magnitudes on an absolute scale. We then determine the color dependence (a proxy for metallicity/age) and zero point of the NIR TRGB from photometry of WFC3/IR fields which overlap with the ACS fields. The new calibration is accurate to ~1% in distance, relative to the F814W TRGB. Validating the accuracy of the calibrations, we find that the distance modulus for each field using the NIR TRGB calibration agrees with the distance modulus of the same fields as determined from the F814W TRGB. This is a JWST preparatory program and the work done here will directly inform our approach to calibrating the TRGB in JWST NIRCam and NIRISS photometric filters.

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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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arXiv2024

The JWST Resolved Stellar Populations Early Release Science Program VI. Identifying Evolved Stars in Nearby Galaxies

We present an investigation of evolved stars in the nearby star-forming galaxy WLM, using NIRCam imaging from the JWST resolved stellar populations early-release science (ERS) program. We find that various combinations of the F090W, F150W, F250M, and F430M filters can effectively isolate red supergiants (RSGs) and thermally-pulsing asymptotic giant branch (TP-AGB) stars from one another, while also providing a reasonable separation of the primary TP-AGB subtypes: carbon-rich C-type stars and oxygen-rich M-type stars. The classification scheme we present here agrees very well with the well-established Hubble Space Telescope (HST) medium-band filter technique. The ratio of C to M-type stars (C/M) is 0.8$\pm$0.1 for both the new JWST and the HST classifications, which is within one sigma of empirical predictions from optical narrow-band CN and TiO filters. The evolved star colors show good agreement with the predictions from the PARSEC$+$COLIBRI stellar evolutionary models, and the models indicate a strong metallicity dependence that makes stellar identification even more effective at higher metallicity. However, the models also indicate that evolved star identification with NIRCam may be more difficult at lower metallicies. We test every combination of NIRCam filters using the models and present additional filters that are also useful for evolved star studies. We also find that $\approx$90\% of the dusty evolved stars are carbon-rich, suggesting that carbonaceous dust dominates the present-day dust production in WLM, similar to the findings in the Magellanic Clouds. These results demonstrate the usefulness of NIRCam in identifying and classifying dust-producing stars without the need for mid-infrared data.

astro-ph.GA↗

arXiv2023

The JWST Resolved Stellar Populations Early Release Science Program IV: The Star Formation History of the Local Group Galaxy WLM

We present the first star formation history (SFH) and age-metallicity relation (AMR) derived from resolved stellar populations imaged with the JWST NIRCam instrument. The target is the Local Group star-forming galaxy WLM at 970 kpc. The depth of the color-magnitude diagram (CMD) reaches below the oldest main sequence turn-off with a SNR=10 at M_F090W=+4.6 mag; this is the deepest CMD for any galaxy that is not a satellite of the Milky Way. We use Hubble Space Telescope (HST) optical imaging that overlaps with the NIRCam observations to directly evaluate the SFHs derived based on data from the two great observatories. The JWST and HST-based SFHs are in excellent agreement. We use the metallicity distribution function measured from stellar spectra to confirm the trends in the AMRs based on the JWST data. Together, these results confirm the efficacy of recovering a SFH and AMR with the NIRCam F090W-F150W filter combination and provide validation of the sensitivity and accuracy of stellar evolution libraries in the near-infrared relative to the optical for SFH recovery work. From the JWST data, WLM shows an early onset to star formation, followed by an extended pause post-reionization before star formation re-ignites, which is qualitatively similar to what has been observed in the isolated galaxies Leo~A and Aquarius. Quantitatively, 15% of the stellar mass formed in the first Gyr, while only 10% formed over the next ~5 Gyr; the stellar mass then rapidly doubled in ~2.5 Gyr, followed by constant star formation over the last ~5 Gyr.

astro-ph.GA↗

arXiv2023

The JWST Resolved Stellar Populations Early Release Science Program III: Photometric Star-Galaxy Separations for NIRCam

We present criteria for separately classifying stars and unresolved background galaxies in photometric catalogs generated with the point spread function (PSF) fitting photometry software DOLPHOT from images taken of Draco II, WLM, and M92 with the Near Infrared Camera (NIRCam) on JWST. Photometric quality metrics from DOLPHOT in one or two filters can recover a pure sample of stars. Conversely, colors formed between short-wavelength (SW) and long-wavelength (LW) filters can be used to effectively identify pure samples of galaxies. Our results highlight that the existing DOLPHOT output parameters can be used to reliably classify stars in our NIRCam data without the need to resort to external tools or more complex heuristics.

astro-ph.IM↗

arXiv2023

The JWST Resolved Stellar Populations Early Release Science Program II. Survey Overview

We present the JWST Resolved Stellar Populations Early Release Science (ERS) science program. We obtained 27.5 hours of NIRCam and NIRISS imaging of three targets in the Local Group (Milky Way globular cluster M92, ultra-faint dwarf galaxy Draco II, star-forming dwarf galaxy WLM), which span factors of $\sim10^5$ in luminosity, $\sim10^4$ in distance, and $\sim10^5$ in surface brightness. We describe the survey strategy, scientific and technical goals, implementation details, present select NIRCam color-magnitude diagrams (CMDs), and validate the NIRCam exposure time calculator (ETC). Our CMDs are among the deepest in existence for each class of target. They touch the theoretical hydrogen burning limit in M92 ($<0.08$ $M_{\odot}$; SNR $\sim5$ at $m_{F090W}\sim28.2$; $M_{F090W}\sim+13.6$), include the lowest-mass stars observed outside the Milky Way in Draco II (0.09 $M_{\odot}$; SNR $=10$ at $m_{F090W}\sim29$; $M_{F090W}\sim+12.1$), and reach $\sim1.5$ magnitudes below the oldest main sequence turnoff in WLM (SNR $=10$ at $m_{F090W}\sim29.5$; $M_{F090W}\sim+4.6$). The PARSEC stellar models provide a good qualitative match to the NIRCam CMDs, though are $\sim0.05$ mag too blue compared to M92 F090W$-$F150W data. The NIRCam ETC (v2.0) matches the SNRs based on photon noise from DOLPHOT stellar photometry in uncrowded fields, but the ETC may not be accurate in more crowded fields, similar to what is known for HST. We release beta versions of DOLPHOT NIRCam and NIRISS modules to the community. Results from this ERS program will establish JWST as the premier instrument for resolved stellar populations studies for decades to come.

astro-ph.GA↗