A Multi-Wavelength Study of Comet C/2022 E3 (ZTF): Complementary ALMA and JWST Investigations of Water and Methanol in Cometary Comae

TL;DR

This work presents the first contemporaneous JWST and ALMA spectroscopic study of a comet, C/2022 E3 (ZTF), focusing on H2O and CH3OH to probe chemical inventories and inheritance from the protosolar disk. Using SUBLIME radiative-transfer modeling for H2O and CH3OH and LTE fits with a Haser framework, the authors derive $T_{rot}$, column densities, and production rates, finding general agreement between JWST and ALMA within uncertainties. A statistically significant anti-Sunward enhancement of $T_{rot}$ is detected, while H2O cooling with radius is explained by non-LTE effects at a kinetic temperature of ~85 K; CH3OH yields a combined production rate of about $4.26 imes 10^{26}$ s−1 and CH3OH/H2O abundance near 1.4%. The study demonstrates the power of simultaneous multi-wavelength observations to build robust molecular inventories and informs inheritance tests by comparing independent datasets across facilities.

Abstract

Long-period comets, which are often considered to be representative of material in the protoplanetary disk that formed the Solar System, are ideal to investigate the question of chemical inheritance in astronomy. Determining the chemistry of comets, both individually and as a population, has become of great importance in comparative studies against sources representative of evolutionary precursors to planetary systems. Contemporaneous observations of long-period comet C/2022 E3 (ZTF) were obtained with the JWST and the Atacama Large Millimeter/submillimeter Array (ALMA) in early 2023 March. This work focuses on \ce{CH3OH} measurements from both ALMA and JWST as well as \ce{H2O} measurements from JWST. Radiative transfer modeling of \ce{CH3OH} and \ce{H2O} was performed to investigate spatial variations in rotational temperature, column density, and production rates, as well as a comparison of derived values between the two telescopes. Most of the spatial distributions of the modeled values are centrally peaked, and the modeled values from JWST are all within the error bars of the average values from ALMA. C/2022 E3 (ZTF) also displays an enhancement in modeled rotational temperature in the anti-Sunward direction that is shown to be statistically significant. Based on non-LTE radiative transfer modeling, the declining \ce{H2O} rotational temperatures as a function of nucleocentric distance observed by JWST can be explained primarily as a result of rotational line cooling. The values derived in this work are in general agreement with single-dish millimeter-wave observations.

Figures (14)

• Figure 1: ALMA spectrum of CH3OH extracted from the center of the methanol emission peak. The best-fit LTE model is overlaid in red, providing a modeled rotational temperature ($\mathrm{T_{rot}}$) of 56.11 ± 0.77 K and a methanol column density (N[CH3OH]) of (9.70 ± 0.04)$\times$1017 m-2. Dashed lines depict the thresholds for 1$\sigma$ (0.0169 K) and 3$\sigma$ (0.0507 K).The potential HNCO line is highlighted in green.
• Figure 2: Modeled excitation temperature maps for the wavelength and frequency regions discussed in Figures \ref{['fig_Jspec']} and \ref{['fig_Aspec']}. The rows split the JWST maps by observation: (top) G235H-F170LP and (bottom) G395H-F290LP, while the columns group the maps by molecule: (left) predominantly H2O, (center) H2O, specifically the spectral region covered by both observations, and (right) CH3OH. The maps are masked to only show values at 3$\sigma$ or greater confidence. Maps modeled from the JWST spectra are labeled with a letter corresponding to the region in Figure \ref{['fig_Jspec']}. The bottom-right map was modeled from the ALMA rotational spectrum (Figure \ref{['fig_Aspec']}). Arrows in the bottom-right corner indicate the direction of the Sun ($\odot$) and comet velocity ($\vec{\mathrm{v}}$). The ALMA synthesized beam is shown in the bottom-left corner.
• Figure 3: Maps depicting modeled gas production rates for the wavelength regions in Figure \ref{['fig_Jspec']} that contain H2O ro-vibrational emission. The rows split the maps by observation: (top) G235H-F170LP and (bottom) G395H-F290LP, while the columns group the maps by molecule: (left) predominantly H2O and (right) H2O, specifically the spectral region covered by both observations. The maps are masked to only show values at 3$\sigma$ or greater confidence. Maps are labeled with a letter corresponding to the wavelength region. The top two maps are from the first observation and the bottom two are from the second observation, taken 3 hours later. Arrows in the bottom-right corner indicate the direction of the Sun ($\odot$) and comet velocity ($\vec{\mathrm{v}}$).
• Figure 4: CH3OH (top) column density maps and (bottom) projected density maps modeled from (left) the CH3OH ro-vibrational emission peak in JWST region [d] (Figure \ref{['fig_Jspec']}) and (right) the rotational emission ladder from the ALMA observations (Figure \ref{['fig_Aspec']}). The maps are masked to only show values at 3$\sigma$ or greater confidence. Arrows in the bottom-right corner indicate the direction of the Sun ($\odot$) and comet velocity ($\vec{\mathrm{v}}$). The ALMA synthesized beam is shown in the bottom-left corner.
• Figure 5: Spectrally integrated intensity map of the CH3OH emission lines from a combined ALMA image of the seven March observations. The overlaid contours show the integrated intensity starting at approximately three times the RMS noise, 15 mJy, and incrementing by the same value per level. Arrows in the bottom-right corner indicate the direction of the Sun ($\odot$) and comet velocity ($\vec{\mathrm{v}}$). The ALMA synthesized beam is shown in the bottom-left corner.