The nearly edge-on starburst galaxy NGC 253 has been observed to exhibit extended halo emission in multiple bands, making it an ideal laboratory for studying the transfer of matter from the disk to the halo. We aim to determine how the cosmic-ray electrons (CREs) flow from the disk to the halo and understand what drives their propagation. By combining data from multiple observations, we generated improved total intensity images at 943 MHz with a resolution of 13 from the Australian SKA Pathfinder (ASKAP), and at 216 MHz with a resolution of 45 from the Murchison Widefield Array (MWA). The 1D advection and diffusion equations were solved, and the solutions were fitted to the observed synchrotron emission intensity and spectral-index profiles to constrain the propagation model and parameters. The ASKAP total intensity map has an rms noise of 16 μJy beam -1 $, reaching the classical confusion limit, and the MWA map has an rms noise of 1 mJy beam^-1. The sensitivities are significantly improved in comparison to previous observations at similar frequencies. In the ASKAP image, we identify a clear loop-like structure in the northwestern radio spur, extending vertically up to sim9,kpc above the disk, while the southeastern spur reaches heights of sim8,kpc. The synchrotron emission intensity profiles perpendicular to the disk can be fitted with exponential components in the central regions and with Gaussian components in the outer regions. This result implies that CREs in these two regions propagate differently. By jointly fitting the vertical synchrotron emission intensity profiles at 943 MHz and 216 MHz, together with the corresponding synchrotron spectral-index profiles, our results provide the clearest evidence to date that CREs are transported from the disk by advection in the central region and by diffusion elsewhere in NGC 253. The advection speed in the central region increases exponentially with height and reaches the escape speed to form a superwind of CREs at about 5.5 kpc. This superwind is associated with regions in the disk with active star formation and X-ray emission, indicating a bulk motion of baryons caused by the advection. The combined thermal, magnetic, cosmic-ray, and ram pressures exceed the gravitational pressure below $|z|łesssim5.5 kpc, and this overpressure condition accelerates the superwind. High-sensitivity low-frequency radio observations provide an important probe of the transport of CREs. With these observations, we have revealed a newly detailed view into the kinematic origin of the superwind from the center of NGC 253.

The nearly edge-on starburst galaxy NGC 253 exhibits extended multiwavelength halo emission, making it an ideal laboratory for studying disk-halo transport. We present improved ASKAP 943 MHz and MWA 216 MHz total-intensity images with resolutions of 13 and 45 arcsec and rms noise levels of 16 μJy beam^-1 and 1 mJy beam^-1, respectively. After subtracting the thermal emission, we fitted the vertical synchrotron emission intensity and spectral-index profiles with one-dimensional advection and diffusion models. The ASKAP image reveals a loop-like structure in the northwestern radio spur extending to ∼9 kpc above the disk, while the southeastern spur reaches ∼8 kpc. The vertical profiles are best fitted by exponential components in the central region and Gaussian components in the outer regions, indicating advection-dominated CRE transport in the center and diffusion elsewhere. In the central region, the advection speed increases exponentially with height and reaches the estimated escape speed at about 5.5 kpc. The spatial correspondence with star-forming and X-ray-emitting regions indicates that CRE advection traces the bulk motion of the magnetized outflow. Below ∼5.5 kpc, the combined thermal, magnetic, cosmic-ray, and ram pressures exceed the estimated gravitational pressure, consistent with acceleration of the galactic wind. These results demonstrate the power of sensitive low-frequency radio observations for probing CRE transport and galactic outflows.

We present distances to ten supernova (SN) host galaxies determined via the red giant branch tip (TRGB) using JWST/NIRCAM and the F115W, F356W, and F444W bandpasses. Our analysis, including photometric catalog cleaning, adoption of disk light profiles, TRGB color slope estimation, and a novel technique for identifying the infrared TRGB, was conducted blinded. The new F115W TRGB distances agree well with our previously derived HST TRGB distances, differing by only 1 percent on average and 4 percent on a per-galaxy basis. The color-corrected F115W TRGB is therefore equally precise a method of distance measurement as, and offers unique advantages over, its color-insensitive, I-band counterpart. Using these distances, we update the absolute calibrations of eleven calibrator SNe, yielding 68.4 < H0 < 69.6 km/s/Mpc depending on which of four sets of SN magnitudes are used. We expand the sample of calibrator SNe to 24 by combining with HST TRGB distances. Doing so increases our H0 estimate based on the Carnegie Supernova Project II (CSP-II) by 0.8 km/s/Mpc (1.4 sigma) demonstrating that our JWST H0 based on 11 SNe is not significantly biased toward lower values. In contrast, the Pantheon+ calibration shifts higher by +2 km/s/Mpc (3.1 sigma), a significantly larger increase than seen in both the CSP and the Pantheon team's own SuperCal analysis. More JWST observations of the TRGB as well as independent analyses of low-redshift SNe are needed to continue unraveling the true nature of the Hubble Tension.

Galaxies build through infalling gas and galaxy mergers. Tracking the dynamical history of a galaxy from a single snapshot in time is notoriously difficult. Here we show that the dynamical history of a galaxy can be tracked using oxygen abundances as archaeological tracers. We derive the gas-phase oxygen abundances for 4,546 spaxels across the face-on spiral galaxy NGC 1365 at a spatial resolution of 175 pc, thus obtaining one of the most detailed chemical fossil records of a spiral galaxy outside our Milky Way. We apply IllustrisTNG cosmological simulations to analyse the chemical abundance distribution in a theoretical model for NGC 1365. In the model, the oxygen-abundance gradient of the main disk formed earliest, 11.9-12.5 billion years ago via mergers with several dwarf galaxies. A steep inner-bar gradient formed slowly over the last 12 billion years through enrichment from star formation triggered by the infall of gas into the nuclear regions. An extended ionized gas disk with flat oxygen abundances assembled more recently (5.9-8.6 billion years ago) through a minor merger. This work indicates that cosmological simulations and ultrahigh-spatial-resolution oxygen abundances can together provide an archaeological probe of the star-formation and merger histories of spiral galaxies.

Atomic hydrogen (H I) dominates the mass of the cold interstellar medium, undergoing thermal condensation to form molecular gas and fuel star formation. Kinematically colder H I components, identified via kinematic decomposition of H I 21 cm data cubes, serve as a crucial transition phase between diffuse warm neutral gas and molecular hydrogen (H-2). We analyse these colder H I components by decomposing H I 21 cm data cubes of seven nearby galaxies - Sextans A, NGC 6822, WLM, NGC 5068, NGC 7793, NGC 1566, and NGC 5236 - spanning metallicities (0.1 < Z/Z(circle dot)< 1.0) and physical scales (53-1134 pc). Using a velocity dispersion threshold of 6 km s(-1), we classify the kinematically distinct components into narrow (colder) and broad (warmer). Cross-correlation analysis between the narrow H I components and HI 21 or star formation rate (SFR) surface density at different spatial scales reveals that dwarf galaxies exhibit the strongest correlation at similar to 500-700 pc. The radially binned narrow H I fraction, fn = I-narrow (H l) / I-totalH I, in dwarf galaxies shows no clear trend with metallicity or SFR, while in spirals, f(n) is lower in inner regions with higher metallicity and SFR. We find that the data set resolution significantly impacts the results, with higher physical resolution data yielding a higher median f(n), < f(n)>, per galaxy. With this considered, dwarf galaxies consistently exhibit a larger f(n) than spiral galaxies. These findings highlight the critical role of cold H I in regulating star formation across different galactic environments and emphasize the need for high resolution H I observations to further unravel the connection between atomic-to-molecular gas conversion and galaxy evolution.

We present the latest results from the Chicago-Carnegie Hubble Program to measure the Hubble constant, using data from the James Webb Space Telescope (JWST). The overall program aims to calibrate three independent methods: (1) tip of the red giant branch (TRGB) stars, (2) J -region asymptotic giant branch (JAGB) stars, and (3) Cepheids. To date, our program includes 10 nearby galaxies, hosting 11 Type Ia supernovae (SNe Ia) suitable for measuring the Hubble constant ( H _0 ). It also includes the galaxy NGC 4258, whose geometric distance provides the zero-point calibration. In this paper, we discuss our results from the TRGB and JAGB methods. Our current best (highest-precision) estimate is H _0 = 70.39 ± 1.22 (stat) ± 1.33 (sys) ± 0.70 ( σ _SN ), based on the TRGB method alone, with a total of 24 SN Ia calibrators from both Hubble Space Telescope and JWST data. Based on our new JWST data only, and tying into SNe Ia, we find values of H _0 = 68.81 ± 1.79 (stat) ± 1.32 (sys) for the TRGB, and H _0 = 67.80 ± 2.17 (stat) ± 1.64 (sys) km s ^−1 Mpc ^−1 for the JAGB method. The distances measured using the TRGB and the JAGB methods agree, on average, at a level better than 1%, and with the SHoES Cepheid distances at just over the 1% level. Our results are consistent with the current standard Lambda cold dark matter (ΛCDM) model, without the need for the inclusion of additional new physics. Future JWST data will be required to increase the precision and accuracy of the local distance scale.

In the I -band color–magnitude diagrams of resolved nearby galaxies, the reddest asymptotic giant branch ( AGB ) stars form a previously unremarked-upon, but nevertheless distinct and easily identified population of high-luminosity stars. Hereafter we refer to this population as being comprised of I-band AGB ( IAGB ) stars. Identifying these stars in the Large Magellanic Cloud (LMC), the Small Magellanic Cloud (SMC) and in NGC 4258 (for all three of which there are published geometric distances) we find that the marginalized luminosity functions are each well approximated by single-peaked Gaussians, having 1 σ dispersions of ±0.22 mag, ±0.25 mag and ±0.24 mag, respectively. The zero points for the modal I -band absolute magnitudes of IAGB stars are found to be M _I = −4.49 ± 0.003 mag (stat) in the LMC (4204 stars), M _I = −4.67 ± 0.008 mag (stat), for the SMC sample (916 stars), and M _I = −4.78 ± 0.030 mag (stat) for NGC 4258 (62 stars). A global average over these three independent calibrations of the IAGB zero-point (weighted inversely by squares of their systematic errors) gives 〈 M _I 〉 = −4.65 ± 0.119 mag (stat) ± 0.025 (sys). In Paper II we will show the results of applying the IAGB Method to 92 galaxies additional galaxies resolved by Hubble Space Telescope, reaching out to distances just short of 10 Mpc.

Hubble Space Telescope observations of 92 galaxies that have a strong showing of I -band asymptotic giant branch (IAGB) stars in their color–magnitude diagrams (CMDs) are used to measure the relative offset between the mean apparent I -band magnitudes of the IAGB population and the corresponding apparent I -band magnitudes of the TRGB as measured in the same frames (and CMDs) of those individual galaxies. This first exploratory, large-sample comparison is independent of any extinction (foreground or internal) that may be shared by these two populations. The marginalized luminosity functions used to determine the modal value of the IAGB population are well fit by a single, symmetric Gaussian. The difference in the two apparent magnitudes (in the sense IAGB minus TRGB) is −0.589 mag, with a combined standard deviation of ±0.119 mag. Adopting M _I = −4.05 mag for the TRGB stars, the modal absolute magnitude of the IAGB is then calculated to be M _I (IAGB) = −4.64 ± 0.12 mag. The ensemble dispersion quoted above gives a standard error on the mean of ±0.012 mag (based on the full sample of 92 galaxies). Independently, the three geometry-based zero-points for I -band AGB stars are found (in Paper I) to be M _I = −4.49 ± 0.003 mag in the LMC (4204 stars), M _I = −4.67 ± 0.008 mag for the SMC (916 stars), and M _I = −4.78 ± 0.030 mag for NGC 4258 (62 stars), leading to a global zero-point (weighted) average of < M _I > = −4.64 ± 0.15 mag (stat). The scatter found in the anchors is comparable to the scatter in the field sample discussed here, but the calibration sample is small. The application of this method to galaxies well outside of the Local Group shows that these standard candles can readily be found and measured out to at least 9 Mpc, using already available archival data.

This is the second of two papers exploring the effects of metallicity on the multi-wavelength properties of Cepheids in terms of their multi-wavelength period-luminosity (PL) relations, impacting their use as extragalactic distance indicators, underpinning one of the most popular paths to estimating of the expansion rate of the Universe, Ho. In Paper I (Madore Freedman 2024) we presented five tests for the influence of metallicity on galactic and extragalactic Cepheid PL relations, spanning nearly 2 dex in metallicity, and inspecting PL relations from the optical (BVI), through the near-infrared (JHK) and into mid-infrared (at 3.4 and 4.5 microns). And,in no case were any statistically significant results forthcoming. Here we interrogate published spectral energy distributions constructed from theoretical (static) stellar atmospheres, cov- ering the surface gravity and temperature ranges attributed to classical (supergiant, F and K spectral type) Cepheid variables, and explore the differential effects of changing the atmospheric metallicity, down by 2 dex from solar (a factor of 100 below the average Milky Way value) and then up from solar by 0.5 dex (i.e., factor of 3x above the Milky Way value). The theoretical models clearly show that metallicity systematically impacts each of the bandpasses differentially: the level of this effect is largest in the ultraviolet (where line blanketing is most intense), reversing sign in the optical (due to flux redistribution from the UV), and then asymptotically falling back to zero from the red to the far infrared. The discovered effects of metallicity are systematic, but they are small; and as such they do not contradict the findings of Paper I, but they do explain why the problem has been so hard to resolve given the low level of precision of the photometry for all but the very nearest and apparently brightest Cepheids.

We apply population synthesis techniques to analyze TYPHOON long slit spectra of the starburst barred spiral galaxy M83. The analysis covers a central square of 5 arcmin side length. We determine the spatial distribution of dust through the analysis of reddening and extinction, together with star formation rates, ages, and metallicities of young and old stellar populations. For the first time, a spatial one-to-one comparison of metallicities derived from full-spectral fitting techniques with those obtained from individual young stellar probes has been carried out. The comparison with blue supergiant stars, young massive star clusters, and super star clusters shows a high degree of concordance when wavelength coverage in the B-band is available. The metallicity of the young population is supersolar and does not show a radial metallicity gradient along the investigated part of the disk, in agreement with our chemical evolution model. However, a notable decrease in metallicity is observed in a tightly confined region at the galaxy center, coinciding with circumnuclear orbits. We attribute this to matter infall either from the circumgalactic medium or a dwarf galaxy interloper or, alternatively, to AGN-interrupted chemical evolution. We confirm the presence of a dust cavity with a diameter of 260 pc close to the galaxy center. Dust absorption and molecular CO emission are spatially well correlated. We find an anticorrelation between R_V, the ratio of dust attenuation to reddening, and the emission strength of molecular species present in photo-dissociation regions. We confirm our results by using alternative fitting algorithms and stellar libraries.

The J-region asymptotic giant branch (JAGB) method is a new standard candle based on the constant luminosities of carbon-rich AGB stars in the J band. The JAGB method is independent of the Cepheid and tip of the red giant branch (TRGB) distance indicators. Therefore, we can leverage it to both cross-check Cepheid and TRGB distances for systematic errors and use it to measure an independent local H _0 . The JAGB method also boasts a number of advantages in measuring distances relative to the TRGB and Cepheids, several of which are especially amplified when combined with JWST’s revolutionary resolving power. First, JAGB stars are 1 mag brighter in the near-IR (NIR) than the TRGB and can be discovered from single-epoch NIR photometry, unlike Cepheids, which require congruent optical imaging in at least 12 epochs. Thus, JAGB stars can be used to measure significantly farther distances than both the TRGB stars and Cepheids using the same amount of observing time. Dust extinction is also reduced in NIR observations and JAGB stars are ubiquitous in all galaxies with intermediate-age populations. We present a novel algorithm that identifies the optimal location in a galaxy for applying the JAGB method, so as to minimize the effects from crowding. We then deploy this algorithm in JWST NIRCam imaging of seven SN Ia host galaxies, to measure their JAGB distances, undertaking a completely blind analysis. In our Chicago–Carnegie Hubble Program H _0 results paper, by W. L. Freedman et al., we apply the JAGB distances measured in this paper to the Carnegie Supernova Program type Ia supernova sample, measuring a Hubble constant of H _0 = 67.80 ±2.17 (stat) ± 1.64 (sys) km s ^−1 Mpc ^−1 .

The period–luminosity (PL) relation is usually derived using time-averaged magnitudes, which require multiple-epoch observations to determine periods and adequately sample the light curves. Although single-epoch observations are more practical and require significantly less observational effort, they inherently introduce greater photometric scatter, leading to an increased dispersion in the derived PL relations. In this paper, we explore, in detail, a method that transforms single random-phase data to their mean-light values, using information obtained in other bands for the same Cepheid. This approach enables the accurate reconstruction of mean-light PL relations for wavelengths observed with space-based facilities, for instance, where the number of epochs per star makes simple averaging or template fitting less than optimal, with the latter requiring very high-precision periods for predictive phasing. While applying this technique across multiple bands, from optical to mid-IR, we focus particularly on widely separated bands covering the mid-IR to the optical. We showcase this method using the J band (as being observed by JWST) as the random-phase component. Our results show that this correction reduces the scatter of the PL relation in the J band by a factor of approximately 0.7×, equivalent to increasing the number of random-phase observations by a factor of 10, needed to obtain the same increase in precision as delivered here.

Understanding the effects of metallicity on the multiwavelength properties of Cepheids is of continuing importance for their effective use as extragalactic distance indicators and an accurate measure of the Hubble constant, H _0 . Quantifying the magnitude, and even the sign, of a metallicity effect, at one or more wavelengths, has been and continues to be challenging, and has not yet converged. Here we present the results of a multipronged investigation looking for empirical evidence of correlations linking the metallicities of Cepheids to the zero-point of the their multiwavelength period–luminosity relations. The empirical evidence leads to a self-consistent conclusion based on six tests, across many galaxies and in up to nine different bandpasses, from the optical to the mid-infrared. The major result is that for classical Cepheids, in none of the cases examined is there a metallicity effect, of any statistical significance, detected at any of the wavelengths examined. However, theoretical models of stellar atmospheres clearly show that metallicity will impact each of the bandpasses differently: the level of this effect is largest in the ultraviolet (where line blanketing is most intense), reversing sign in the optical (due to flux redistribution from the UV), and then asymptotically falling back to zero from the red to the far infrared. Close examination of these models reveals infrared regions in Cepheid spectral energy distributions that allow for the simultaneous correction for extinction and metallicity differences by the judicious combination of infrared filters alone, one centered at 1.2 μ m and the other at 3.6 μ m. Both of these bands can be simultaneously observed in single exposures using the dual-channel imager NIRCam on JWST.

We present a catalog of clouds identified from the (CO)-C-12 (1-0) data of M83, which was observed using the Atacama Large Millimeter/submillimeter Array with a spatial resolution of similar to 46 pc and a mass sensitivity of similar to 10(4)M(circle dot) (3 sigma). The almost full-disk coverage and high sensitivity of the data allowed us to sample 5724 molecular clouds with a median mass of similar to 1.9 x 10(5)M(circle dot), which is comparable to the most frequently sampled mass of giant molecular clouds by surveys in the Milky Way (MW). About 60% of the total CO luminosity in M83's disk arises from clouds more massive than 10(6)M(circle dot). Such massive clouds comprise 16% of the total clouds in number and tend to concentrate toward the arm, bar, and center, while smaller clouds are more prevalent in interarm regions. Most >10(6)M(circle dot) clouds have peak brightness temperatures T-peak above 2 K with the current resolution. Comparing the observed cloud properties with the scaling relations determined by P. M. Solomon et al. (1987, hereafter S87), T-peak > 2 K clouds follow the relations, but T-peak < 2 K clouds, which are dominant in number, deviate significantly. Without considering the effect of beam dilution, the deviations would suggest modestly high virial parameters (median alpha(vir) similar to 2.7) and low surface mass densities (median Sigma similar to 22 M-circle dot pc(-2)) for the entire cloud samples, which are similar to values found for the MW clouds by T. S. Rice et al. (2016) and M.-A Miville-Desch & ecirc;nes et al. (2017). However, once beam dilution is taken into account, the observed alpha(vir) and Sigma for a majority of the clouds (mostly T-peak <2 K) can be potentially explained with intrinsic Sigma of similar to 100 M-circle dot pc(-2) and alpha(vir) of similar to 1, which are similar to the clouds of S87.

Boasting a 6.5 m mirror in space, JWST can increase by several times the number of supernovae (SNe) to which a redshift-independent distance has been measured with a precision distance indicator (e.g., tip of the red giant branch (TRGB) or Cepheids); the limited number of such SN calibrators currently dominates the uncertainty budget in distance ladder Hubble constant (H 0) experiments. JWST/NIRCAM imaging of the Virgo Cluster galaxy NGC 4536 is used here to preview JWST program GO-1995, which aims to measure H 0 using three stellar distance indicators (Cepheids, TRGB, and J-branch asymptotic giant branch/carbon stars). Each population of distance indicator was here successfully detected-with sufficiently large number statistics, well-measured fluxes, and characteristic distributions consistent with ingoing expectations-so as to confirm that we can acquire distances from each method precise to about 0.05 mag (statistical uncertainty only). We leverage overlapping Hubble Space Telescope imaging to identify TRGB stars, crossmatch them with the JWST photometry, and present a preliminary constraint on the slope of the TRGB's F115W versus (F115W - F444W) relation equal to -0.99 +/- 0.16 mag mag-1. This slope is consistent with prior slope measurements in the similar Two Micron All-Sky Survey J band, as well as with predictions from the BaSTI isochrone suite. We use the new TRGB slope estimate to flatten the 2D TRGB feature and measure a (blinded) TRGB distance relative to a set of fiducial TRGB colors, intended to represent the absolute fiducial calibrations expected from geometric anchors such as NGC 4258 and the Magellanic Clouds. In doing so, we empirically demonstrate that the TRGB can be used as a standardizable candle at the IR wavelengths accessible with JWST.

We present a novel technique for mapping single-phase observations of Cepheids in any given band into their time-averaged values, using strong priors on the known interrelations of the multiwavelength widths of Cepheid period–luminosity (PL) relations, combined with the physical ordering of individual Cepheids within and across the instability strip, as a function of temperature (or radius). The method is empirically calibrated and tested using high-precision published multiwavelength observations of Cepheids in the LMC. The example, given herein, takes a single-epoch B -band PL relation and transforms those random-phase observations to within ±0.05–0.06 mag of their time-averaged values. For high-precision single-phase data points, this method can transform single-phase magnitudes into mean magnitudes (without additional observations), bringing the statistical error budget for the PL relation at that wavelength down to the systematic floor. This technique is of particular importance for use with space-based facilities (e.g., Hubble Space Telescope or JWST) where limits on the availability of telescope time preclude dense phase coverage, often resulting in only single-epoch observations being available.

The J-region Asymptotic Giant Branch (JAGB) method is a standard candle that leverages the constant luminosities of color-selected, carbon-rich AGB stars, measured in the near-infrared at 1.2 μ m. The Chicago-Carnegie Hubble Program has obtained JWST imaging of the SN Ia host galaxies NGC 7250, NGC 4536, and NGC 3972. With these observations, the JAGB method can be studied for the first time using JWST. Lee et al. demonstrated the JAGB magnitude is optimally measured in the outer disks of galaxies, because in the inner regions the JAGB magnitude can vary significantly due to a confluence of reddening, blending, and crowding effects. However, determining where the “outer disk” lies can be subjective. Therefore, we introduce a novel method for systematically selecting the outer disk. In a given galaxy, the JAGB magnitude is first separately measured in concentric regions, and the “outer disk” is then defined as the first radial bin where the JAGB magnitude stabilizes to a few hundredths of a magnitude. After successfully employing this method in our JWST galaxy sample, we find the JAGB stars are well segregated from other stellar populations in color–magnitude space, and have observed dispersions about their individual F115W modes of σ _N7250 = 0.32 mag, σ _N4536 = 0.34 mag, and σ _N3972 = 0.35 mag. These measured dispersions are similar to the scatter measured for the JAGB stars in the LMC using 2MASS data ( σ = 0.33 mag). In conclusion, the JAGB stars as observed with JWST clearly demonstrate their considerable power both as high-precision extragalactic distance indicators and as SN Ia supernova calibrators.

Boasting a 6.5m mirror in space, JWST can increase by several times the number of supernovae (SNe) to which a redshift-independent distance has been measured with a precision distance indicator (e.g., TRGB or Cepheids); the limited number of such SN calibrators currently dominates the uncertainty budget in distance ladder Hubble constant (H0) experiments. JWST/NIRCAM imaging of the Virgo Cluster galaxy NGC4536 is used here to preview JWST program GO-1995, which aims to measure H0 using three stellar distance indicators (Cepheids, TRGB, JAGB/carbon stars). Each population of distance indicator was here successfully detected -- with sufficiently large number statistics, well-measured fluxes, and characteristic distributions consistent with ingoing expectations -- so as to confirm that we can acquire distances from each method precise to about 0.05mag (statistical uncertainty only). We leverage overlapping HST imaging to identify TRGB stars, cross-match them with the JWST photometry, and present a preliminary constraint on the slope of the TRGB's F115W-(F115W}-F444W) relation equal to -0.99 +/- 0.16 mag/mag. This slope is consistent with prior slope measurements in the similar 2MASS J-band, as well as with predictions from the BASTI isochrone suite. We use the new TRGB slope estimate to flatten the two-dimensional TRGB feature and measure a (blinded) TRGB distance relative to a set of fiducial TRGB colors, intended to represent the absolute fiducial calibrations expected from geometric anchors such as NGC4258 and the Magellanic Clouds. In doing so, we empirically demonstrate that the TRGB can be used as a standardizable candle at the IR wavelengths accessible with JWST.

Most star formation in the local Universe occurs in spiral galaxies, but their origin remains an unanswered question. Various theories have been proposed to explain the development of spiral arms, each predicting different spatial distributions of the interstellar medium. This study maps the star formation rate (SFR) and gas-phase metallicity of nine spiral galaxies with the TYPHOON survey to test two dominating theories: density wave theory and dynamic spiral theory. We discuss the environmental effects on our galaxies, considering reported environments and merging events. Taking advantage of the large field of view covering the entire optical disk, we quantify the fluctuation of SFR and metallicity relative to the azimuthal distance from the spiral arms. We find higher SFR and metallicity in the trailing edge of NGC 1365 (by 0.117 dex and 0.068 dex, respectively) and NGC 1566 (by 0.119 dex and 0.037 dex, respectively), which is in line with density wave theory. NGC 2442 shows a different result with higher metallicity (0.093 dex) in the leading edge, possibly attributed to an ongoing merging. The other six spiral galaxies show no statistically significant offset in SFR or metallicity, consistent with dynamic spiral theory. We also compare the behaviour of metallicity inside and outside the co-rotation radius (CR) of NGC 1365 and NGC 1566. We find comparable metallicity fluctuations near and beyond the CR of NGC 1365, indicating gravitational perturbation. NGC 1566 shows the greatest fluctuation near the CR, in line with the analytic spiral arms. Our work highlights that a combination of mechanisms explains the origin of spiral features in the local Universe.

Using an updated and significantly augmented sample of Cepheid and tip of the red giant branch (TRGB) distances to 28 nearby spiral and irregular galaxies, covering a wide range of metallicities, we have searched for evidence of a correlation of the zero-point of the Cepheid period–luminosity relation with H ii region (gas-phase) metallicities. Our analysis, for the 21 galaxies closer than 12.5 Mpc, results in the following conclusions: (1) The zero-points of the Cepheid and TRGB distance scales are in remarkably good agreement, with the mean offset in the zero-points of the most nearby distance-selected sample being close to zero, Δ μ _o (Cepheid—TRGB) = −0.026 ± 0.015 mag (for an I -band TRGB zero-point of M _I = −4.05 mag); however, for the more distant sample, there is a larger offset between the two distance scales, amounting to −0.073 ± 0.057 mag 〈Δ μ _o 〉 (Cepheids—TRGB) = −0.026 ± 0.015 mag, for an I -band TRGB zero-point of M _I = −4.05 mag. (2) The individual differences, about that mean, have a measured scatter of ±0.068 mag. (3) We find no statistically significant evidence for a metallicity dependence in the Cepheid distance scale using the reddening-free W ( V , VI ) period–luminosity relation: Δ μ _o ( Cepheid − TRGB ) = − 0.022( ± 0.015) × ([O/H] − 8.50) − 0.003(±0.007).