Special Talk

• Special Talks

  Speaker: Jared Bull (JHU)
  Title: Uncovering the Space Weather of the Cold, Planetary-mass, Ross 458C
  Abstract: Ross 458C is a planetary-mass T8.0 spectral type brown dwarf (~700 K). Prior studies suggest that its near-IR spectrum is best described by cloudy models, contrasting theoretical predictions of cloud-free atmospheres in late-T dwarfs. More recent theory predicts that sulfide cloud formation can explain these features. Ross 458C has also shown variability in the WFC3/G141 filter in HST (Manjavacas et al. 2019), with inhomogeneous cloud cover as a possible cause. However, the limited wavelength coverage of prior work has prevented investigation of present variability mechanisms and the presence of clouds. We present JWST NIRSpec PRISM time-resolved spectroscopy of Ross 458C, capturing at least one full rotation from 0.6-5.3 microns. We compare the observed variability to the predictions in Morley et al. (2014) to constrain the presence of clouds. We find wavelength-dependent complexity and periodicity in the variability, indicating multiple mechanisms and pressure-dependent atmospheric structure. Comparison with earlier time-series observations in overlapping wavelengths also shows that this variability is stable over the long term, unlike L/T transition objects, which evolve rapidly. These results help inform our understanding of atmospheres and cloud formation in colder brown dwarf and giant planet populations.

  Speaker: Ryan Rickards Vaught (STScI)
  Title: Hunting for Ionization Sources and Chemical Secrets in I Zw 18 with JWST and Keck
  Abstract: Blue compact dwarfs (BCDs) are intensely star-forming dwarf galaxies that serve as nearby analogs of low-mass, low-metallicity, reionization era galaxies. Predicted by scaling relations these reionization era galaxies may host elusive Intermediate Mass Black Holes (IMBH). BCDs offer a new pathway to potentially detect IMBHs. Recently, models suggest that mid-infrared [Ne V] emission in BCDs could signal an IMBH, yet distinguishing IMBHs from signatures [Ne V] produced metal-poor stellar evolution or other exotic sources remains a major challenge. I Zw 18, one of the lowest metallicity (2-3%Z_sun) BCDs known, exhibits intense He II and [NeV] emission that cannot be explained by stellar sources alone. In this talk, I will present Keck-KCWI and JWST-MIRI/MRS integral field observations of I Zw 18 that have enabled 10’s of pc scale resolved maps of high-ionization lines ([Ne V], [O IV], He II). These observations allow us to critically test the latest low-metallicity IMBH models in an environment strikingly similar to the first galaxies. Additionally, towards understanding chemical evolution in the early universe, using JWST’s ability to resolve [O IV] emission we uncovered a hidden layer of complexity in I Zw 18’s chemical structure. Our maps reveal 60 pc-scale inhomogeneities that emerge when metallicities are derived using accurate gas conditions. The results presented here highlight how JWST is transforming our ability to probe chemical and ionization properties in extreme environments. They also focus attention to the need for HWO in understanding the underlying sources within these extreme environments.