The JWST Resolved Stellar Populations Early Release Science Program. I. NIRCam Flux Calibration

Research Notes of the AAS · 2022 · 64 citations

• Computer Science
• Physics
• Astronomy

Abstract We use globular cluster data from the Resolved Stellar Populations Early Release Science (ERS) program to validate the flux calibration for the Near Infrared Camera (NIRCam) on the James Webb Space Telescope. We find a significant flux offset between the eight short wavelength detectors, ranging from 1% to 23% (∼0.01–0.2 mag) that affects all NIRCam imaging observations. We deliver improved zero-points for the ERS filters and show that alternate zero-points derived by the community also improve the calibration significantly. We also find that the detector offsets appear to be time variable by up to at least 0.1 mag.

Star Formation Histories of Ultra-faint Dwarf Galaxies: Environmental Differences between Magellanic and Non-Magellanic Satellites?

The Astrophysical Journal Letters · 2021 · 39 citations

• Physics
• Astrophysics
• Astronomy

We present the color-magnitude diagrams and star formation histories (SFHs) of seven ultra-faint dwarf galaxies: Horologium 1, Hydra 2, Phoenix 2, Reticulum 2, Sagittarius 2, Triangulum 2, and Tucana 2, derived from high-precision Hubble Space Telescope photometry. We find that the SFH of each galaxy is consistent with them having created at least 80% of the stellar mass by z ~ 6. For all galaxies, we find quenching times older than 11.5 Gyr ago, compatible with the scenario in which reionization suppresses the star formation of small dark matter halos. However, our analysis also reveals some differences in the SFHs of candidate Magellanic Cloud satellites, i.e., galaxies that are likely satellites of the Large Magellanic Cloud and that entered the Milky Way potential only recently. Indeed, Magellanic satellites show quenching times about 600 Myr more recent with respect to those of other Milky Way satellites, on average, even though the respective timings are still compatible within the errors. This finding is consistent with theoretical models that suggest that satellites' SFHs may depend on their host environment at early times, although we caution that within the error bars all galaxies in our sample are consistent with being quenched at a single epoch.

The Orbital Histories of Magellanic Satellites Using Gaia DR2 Proper Motions

The Astrophysical Journal · 2020 · 137 citations

• Physics
• Astronomy
• Astrophysics

With the release of Gaia DR2, it is now possible to measure the proper motions (PMs) of the lowest-mass, ultrafaint satellite galaxies in the Milky Way's (MW) halo for the first time. Many of these faint satellites are posited to have been accreted as satellites of the Magellanic Clouds (MCs). Using their six-dimensional phase-space information, we calculate the orbital histories of 13 ultrafaint satellites and five classical dwarf spheroidals in a combined MW+LMC+SMC potential to determine which galaxies are dynamically associated with the MCs. These 18 galaxies are separated into four classes: (i) long-Term Magellanic satellites that have been bound to the MCs for at least the last two consecutive orbits around the MCs (Carina 2, Carina 3, Horologium 1, Hydrus 1); (ii) Magellanic satellites that were recently captured by the MCs < 1 Gyr ago (Reticulum 2, Phoenix 2); (iii) MW satellites that have interacted with the MCs (Sculptor 1, Tucana 3, Segue 1); and (iv) MW satellites (Aquarius 2, Canes Venatici 2, Crater 2, Draco 1, Draco 2, Hydra 2, Carina, Fornax, Ursa Minor). Results are reported for a range of MW and LMC masses. Contrary to previous work, we find no dynamical association between Carina, Fornax, and the MCs. Finally, we determine that the addition of the SMC's gravitational potential affects the longevity of satellites as members of the Magellanic system (long-Term versus recently captured), but it does not change the total number of Magellanic satellites.