Charles Goldberg

We explore the accretion rates of supermassive black holes (SMBHs) in late-stage galaxy mergers by observing three ultraluminous infrared galaxies (ULIRGs), IRAS 14378-3651, IRAS 17208-0014 and IRAS 23365+3604, using the JWST/MIRI Medium Resolution Spectrometer and JWST/NIRSpec integral field unit. In all three cases, we fail to detect [Ne vi] λ7.65 μm, a robust active galactic nuclei (AGN) tracer lying in a low-opacity interstellar window, nor do we detect any other lines that might indicate AGNs. The only detected high-excitation emission line, [Mg iv] (λ4.488 μm), arises from shocks associated with supernovae. Our new, deep flux limits on AGN tracers in the near- and mid-infrared indicate that the nuclear obscuration of any purported AGNs in our sample is isotropic, i.e., the far-infrared luminosities of these galaxies are unlikely to be driven by escaping AGN power. This allows us to show that the Eddington ratios of their SMBHs are low. We then assemble an unbiased sample of 19 ULIRGs (from the IRAS Bright Galaxy Sample with L(TIR) ≥ 10¹² L _⊙) in late-stage mergers and show that their dynamically measured black hole masses are consistent with the values from scaling from their stellar masses. On this basis, we show that the Eddington ratios of any AGNs in 15 of these galaxies are also very low, ≲10%. This indicates that any black holes are in a relatively quiescent state. That is, high levels of accretion are found in only a minority of late-merger-phase ULIRGs.

The Galileo mission first detected CO2 on Europa over 25 years ago [1, 2], and it remains the only known carbon-bearing species on the satellite. Since this discovery, the origin and physical state of the CO2 have been important questions key to understanding any potential relationship between the CO2 and Europa’s subsurface chemistry. Specifically, the source of the CO2 could be endogenic (possibly from the subsurface ocean), exogenic, or radiolytically produced from endogenic or exogenic carbon-bearing surface materials. In addition, pure CO2 ice is highly unstable at Europa’s surface temperatures, so the CO2 must be trapped within other, so-far-unidentified surface materials [1,2,3]. Recently, a single Cycle 1 JWST NIRSPec observation of Europa’s leading hemisphere provided new detail of Europa’s CO2 by 1) resolving the 2.7 μm ν1+ν3 combination band for the first time, 2) revealing that the ν3 fundamental asymmetric stretch band near 4.26 μm exhibits a double-peaked minimum, and 3) finding an association with the large-scale chaos region Tara Regio [4,5]. This observation provided new clues to uncovering the still-unknown trapping mechanism(s) and host material(s) of the CO2, and suggested that the CO2 may have an endogenic origin. However, the observation was limited to the leading hemisphere, which limited the ability to investigate relationships to the widespread geologic terrain and radiation patterns across Europa’s variegated surface. We present our analysis of the first full surface observations of Europa’s CO2 with JWST NIRSpec. We investigate how the CO2 band strengths and positions correspond to Europa’s geology, compositional components, and surface bombardment patterns. We find that all three CO2 features are widespread (Figure 1) and that the CO2 is enhanced in chaos regions on the leading, sub-Jovian, and anti-Jovian hemispheres (Figure 2). Conversely, the CO2 is depleted on the trailing hemisphere, which may be related to particle bombardment from Jupiter’s magnetosphere. We will discuss how these global JWST observations constrain the origin of Europa’s CO2, as well as its physical state, correlation with other species, and relationship to radiolytic processes.Figure 1: The total band area of the ν3 asymmetric stretch feature across Europa’s surface, with regions of disrupted surface terrain outlined in black [6]. The CO2 correlates with the disrupted terrain on all but the trailing hemisphere, where CO2 appears substantially depleted and could reflect the effects of particle bombardment from Jupiter’s magnetosphere. The correlation with the disrupted terrain on the rest of the surface suggests that the CO2 reflects an endogenic carbon source.Figure 2: Example spectra of the 2.7 μm ν1+v3 fundamental band and double-peaked ν3 fundamental asymmetric stretch bands of disrupted surface terrain on each of Europa’s hemispheres. While all of the CO2 signatures are widespread, their depths and shapes vary across the surface, providing clues to the mechanisms underlying the stability of the CO2.[1] McCord, T. B., Hansen, G. B., Clark, R. N., et al. 1998, J. Geophys. Res., 103, 8603, doi: 10.1029/98JE00788[2] Carlson, R. W., Calvin, W. M., Dalton, J. B., et al. 2009, in Europa, ed. R. T. Pappalardo, W. B. McKinnon, & K. K. Khurana, 283[3] Hibbitts, C. A., & Szanyi, J. 2007, Icarus, 191, 371, doi: 10.1016/j.icarus.2007.04.012[4] Trumbo, S. K., & Brown, M. E. 2023, Science, 381, 1308, doi: 10.1126/science.adg4155[5] Villanueva, G. L., Hammel, H. B., Milam, S. N., et al. 2023, Science, 381, 1305, doi: 10.1126/science.adg4270[6] Leonard, E. J., Patthoff, A. D, Senske, D. A. 2024, USGS, 18, 3513, doi: 10.3133/sim3513

The late-stage galaxy merger and prototypical ultraluminous infrared galaxy (ULIRG) Arp 220 is probed using the JWST Mid Infrared Instrument medium-resolution spectrometer to search for multiple diagnostic active galactic nuclei (AGN) emission lines in the low-interstellar-opacity spectral ranges of 5.3–7.9 μm and 12.9–16.0 μm. We detect none of the characteristic high-excitation AGN emission lines. The most diagnostic nondetections are of the [Ne vi] λ 7.652 μm and [Ne v] λ 14.32 μm lines, for which the combined upper limit is ∼10–20 times fainter than the equivalent limit from Spitzer data. We also use X-ray measurements of the reflected Fe Kα line to suggest a relatively low X-ray luminosity. These results suggest that the high obscuration observed along the line of sight to the nuclei of Arp 220 is isotropic and keeps any high-excitation emission from a putative AGN from escaping. An implication is that the observed mid-infrared output of the nuclei is essentially their bolometric luminosity, i.e., no significant additional energy escapes. We utilize this result to show that any embedded AGNs are accreting at no more than ∼5% of the Eddington rate, lower than many theoretical predictions for this stage of ULIRG evolution.

We analyze jet features found in the coma of comet 21P/Giacobini–Zinner (21P/GZ) during its 2018 perihelion passage using narrowband CN photometric imaging in order to determine the comet’s rotational period, and we constrain the CN gas outflow velocity and rotational state through the analysis of azimuthally enhanced morphological features. We find that 21P/GZ has a period of either 7.39 ± 0.01 hr or 10.66 ± 0.01 hr. We measure a lower limit to the outflow velocity for the northern jet of 730 ± 30 m s⁻¹ and for the southern jet of 740 ± 30 m s⁻¹. We analyze the morphologies of the jet features and determine that the northern jet possesses a corkscrew pattern, and we utilize that knowledge to determine a rotational pole position at an R.A. of 169 − 23 + 28 deg and a decl. of 73 − 11 + 5 deg, with an undetermined sense of rotation.