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Latest articles for The Astrophysical Journal

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  • Truncated Star Formation and Ram Pressure Stripping in the Coma Cluster
    We use 45 galaxies from the Mapping Nearby Galaxies at Apache Point Observatory survey to study the physical drivers of star formation quenching in the Coma Cluster. We measure specific star formation rate (sSFR) radial profiles for the Coma sample as well as a control sample of noncluster field galaxies. We find that compared to the control sample, galaxies within the Coma Cluster have sSFR profiles that fall off more steeply with galactocentric radius. We then apply a toy model based on slow-then-rapid quenching via ram pressure stripping. We find that this model is able to reproduce the difference in sSFR profiles between field and Coma galaxies. These results demonstrate that ram pressure stripping plays a significant role in quenching star formation in the nearest massive galaxy cluster.

  • DIISC-V: Variations in Hα-to-FUV Star Formation Rate Ratios Across Star-forming Regions in Nearby Galaxies
    We present the variations in far-ultraviolet (FUV) and Hα star formation rates (SFR), SFRUV and SFRHα, respectively, at subkiloparsec scales in 11 galaxies as part of the Deciphering the Interplay between the Interstellar Medium, Stars, and the Circumgalactic medium survey. Using archival GALEX FUV imagery and Hα+[N ii] narrowband images obtained with the Vatican Advanced Technology Telescope, we detect a total of 1335 (FUV-selected) and 1474 (Hα-selected) regions of recent high-mass star formation, respectively. We find the Hα-to-FUV SFR ratios tend to be lower primarily for FUV-selected regions, where SFRHα generally underestimates the SFR by an average factor of 2–3, for SFR < 10−4M⊙ yr−1. In contrast, the SFRs are generally observed to be consistent for Hα-selected regions. This discrepancy arises from morphological differences between the two indicators. Extended FUV morphologies and larger areas covered by FUV-only regions, along with decreasing overlap between FUV clumps and compact H ii regions with R/R25 suggest that stochastic sampling of the initial mass function may be more pronounced in the outer regions of galaxies. Our observed Hα-to-FUV SFR ratios are also consistent with stochastic star formation model predictions. However, using larger apertures that include diffuse FUV emission results in an offset of 1 dex between SFRHα and SFRUV, suggesting that the observed low Hα-to-FUV SFR ratios in galaxies are likely caused by diffuse FUV emission, which can contribute ∼60%–90% to the total FUV flux.

  • Submillimeterwave Spectroscopy of and Interstellar Search for Nitrosomethane: CH3NO
    New measurements of nitrosomethane (CH3NO), a formamide isomer, were done up to 660 GHz. The molecule exhibits internal rotation motion from the CH3 group, and therefore the analysis with a dedicated rho-axis method code, RAM36, was used. A total of 2035 lines for vt = 0 and 1 states of A and E symmetries were fitted with an rms deviation of 41.1 kHz, with the maximum quantum numbers values J = 30 and Ka = 15. Using these new data, CH3NO was searched in the cold dark cloud Taurus Molecular Cloud 1 as well as the high mass star-forming regions Sgr B2(N) and NGC 6334I. CH3NO was not observed in any of the sources, 3σ column density upper limits were determined, and we discuss the implications for the chemistry of CH3NO in the interstellar medium. The accurate spectroscopic prediction of its spectra provided in this work will allow astronomers to continue the search of CH3NO in other interstellar sources.

  • Asteroseismology of Metal-poor Red Giants Observed by TESS
    Galactic archeology has long been limited by a lack of precise masses and ages for metal-poor stars in the Milky Way’s thick disk. However, with TESS providing a growing number of photometric observations, it is possible to calculate masses and ages for more solar-like oscillators than ever using asteroseismology. We have used the pySYD pipeline to determine global asteroseismic parameters, and calculated the masses and ages of 506 metal-poor ([M/H] < −0.5) red giants observed by TESS. Our findings appear to show metallicity-dependent mass loss on the upper red giant branch and identify a set of “young” high-α stars that have been detected in other studies. We also find that 32.6% of the metal-poor stars appear to be binary interaction products, and four stars with stellar ages that could be from the Gaia-Enceladus/Sausage system. In combination with existing ages from Kepler/K2, these data can be compared to galactic evolution models to better determine the formation history of the Galaxy.

  • A MARVEL-ous Study of How Well Galaxy Shapes Reflect Dark Matter Halo Shapes in Cold Dark Matter Simulations
    We present a 3D shape analysis of both dark matter (DM) and stellar matter (SM) in simulated dwarf galaxies to determine whether stellar shape traces DM shape. Using 80 central and satellite dwarf galaxies from three simulation suites (“Marvelous Massive Dwarfs,” “Marvelous Dwarfs,” and the “DC Justice League”) spanning stellar masses of 106–1010 M⊙, we measure 3D shapes through the moment of inertia tensor at twice the effective radius to derive axis ratios (C/A and B/A) and triaxiality. We find that stellar shape does follow DM halo shape for our dwarf galaxies. However, the presence of a stellar disk in more massive dwarfs (M* ≳ 107.5 M⊙) pulls the distribution of stellar C/A ratios to lower values, while in lower-mass galaxies the gravitational potential remains predominantly shaped by DM. Similarly, stellar triaxiality generally tracks DM triaxiality, with this relationship being particularly strong for nondisky galaxies and weaker in disky systems. These correlations are reinforced by strong alignment between the SM and DM axes, particularly in disk galaxies. Further, we find no detectable difference in either SM or DM shapes when comparing two different supernova feedback implementations, demonstrating that shape measurements are robust to different implementations of baryonic feedback in dwarf galaxies. We also observe that a dwarf galaxy’s shape is largely unperturbed by recent mergers. This comprehensive study demonstrates that stellar shape measurements can serve as a reliable tool for inferring DM shapes in dwarf galaxies.