H${}_3^{+}$ absorption and emission in local U/LIRGs with JWST/NIRSpec: Evidence for high H${}_2$ ionization rates

Abstract

We study the 3.4-4.4$\mu$m fundamental rovibrational band of H3+, a key tracer of the ionization of the molecular interstellar medium (ISM), in a sample of 12 local (d< 400 Mpc) ultra/luminous infrared galaxies (U/LIRGs) observed with JWST/NIRSpec. The P, Q, and R branches of the band are detected in 13 out of 20 analyzed regions within these U/LIRGs, which increases the number of extragalactic H3+ detections by a factor of 6. For the first time in the ISM, the H3+ band is observed in emission in 3 of these regions. In the remaining 10 regions, the band is seen in absorption. The absorptions are produced toward the 3.4-4.4$\mu$m hot dust continuum rather than toward the stellar continuum, indicating that they likely originate in clouds associated with the dust continuum source. The H3+ band is undetected in Seyfert-like U/LIRGs where the mildly obscured X-ray radiation from the AGN might limit the abundance of this molecule. For the detections, the H3+ abundances, N(H3+)/N_H = (0.5-5.5)x10^-7, imply relatively high ionization rates between 3x10^-16 and >4x10^-15 s^-1, which are likely associated with high-energy cosmic rays. In half of the targets the absorptions are blue-shifted by 50-180 km/s, which are lower than the molecular outflow velocities measured using other tracers such as OH 119$\mu$m or rotational CO lines. This suggests that H3+ traces gas close to the outflow launching sites before it has been fully accelerated. We used nonlocal thermodynamic equilibrium models to investigate the physical conditions of these clouds. In 7 out of 10 objects, the H3+ excitation is consistent with inelastic collisions with H2 in warm translucent molecular clouds (T_kin ~ 250-500 K and n(H2) ~ 10^(2-3) cm^-3). In three objects, dominant infrared pumping excitation is required to explain the absorptions from the (3,0) and (2,1) levels of H3+ detected for the first time in the ISM.

Accepted for publication in A&A Letters. 6 pages, 5 figures. Appendix: 5 pages, 4 figures

References in corpus (31)

• The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope I. Overview of the instrument and its capabilities
• JWST MIRI flight performance: The Medium-Resolution Spectrometer
• The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope III. Integral-field spectroscopy
• Photodissociation and X-Ray Dominated Regions
• Molecular outflows in local ULIRGs: energetics from multi-transition OH analysis
• Molecular outflows in local galaxies: Method comparison and a role of intermittent AGN driving
• Absorption Line Survey of H3+ toward the Galactic Center Sources II. Eight Infrared Sources within 30 pc of the Galactic Center
• A hard X-ray view of Luminous and Ultra-luminous Infrared Galaxies in GOALS: I - AGN obscuration along the merger sequence
• The Central 300 pc of the Galaxy probed by infrared spectra of H${}_3^{+}$ and CO: part I. Predominance of warm and diffuse gas and high H${}_2$ ionization rate
• A high angular resolution view of the PAH emission in Seyfert galaxies using JWST/MRS data
• GOALS-JWST: Mid-Infrared Spectroscopy of the Nucleus of NGC 7469
• CON-quest: Searching for the most obscured galaxy nuclei
• Low-power jet-ISM interaction in NGC 7319 revealed by JWST/MIRI MRS
• A 33 GHz Survey of Local Major Mergers: Estimating the Sizes of the Energetically Dominant Regions from High Resolution Measurements of the Radio Continuum
• Far-Ultraviolet & X-ray Observations of VV 114: Feedback in a Local Analog to Lyman Break Galaxies
• Infrared H3+ and CO Studies of the Galactic Core: GCIRS 3 and GCIRS 1W
• Polycyclic Aromatic Hydrocarbons in Seyfert and star-forming galaxies
• Physics of ULIRGs with MUSE and ALMA: PUMA IV. No tight relation between cold molecular outflow rates and AGN luminosities
• The Interstellar Medium of IRAS 08572+3915 NW: H3+ and Warm High Velocity CO
• Are local ULIRGs powered by AGN? The sub-kpc view of the 220 GHz continuum. PUMA II
• Warm molecular gas temperature distribution in six local infrared bright Seyfert galaxies
• OH+ in astrophysical media: state-to-state formation rates, Einstein coefficients and inelastic collision rates with He
• GOALS-JWST: Resolving the Circumnuclear Gas Dynamics in NGC 7469 in the Mid-Infrared
• A comparison of the morphological properties between local and z~1 infrared luminous galaxies. Are local and high-z (U)LIRGs different?
• Physics of ULIRGs with MUSE and ALMA: The PUMA project I. Properties of the survey and first MUSE data results
• The Obscured Nucleus and Shocked Environment of VV 114E Revealed by JWST/MIRI Spectroscopy
• GOALS-JWST: Gas Dynamics and Excitation in NGC7469 revealed by NIRSpec
• GOALS-JWST: Pulling Back the Curtain on the AGN and Star Formation in VV 114
• Infrared and X-Ray Evidence of an AGN in the NGC 3256 Southern Nucleus
• GOALS-JWST: Unveiling Dusty Compact Sources in the Merging Galaxy IIZw096
• The Opaque Heart of the Galaxy IC 860: Analogous Protostellar, Kinematics, Morphology, and Chemistry

Cited by in corpus (5)

• PDRs4All XV: CH radical and H${}_3^{+}$ molecular ion in the irradiated protoplanetary disk d203-506
• The Rich JWST Spectrum of the Western Nucleus of Arp 220: Shocked Hot Core Chemistry Dominates the Inner Disk
• Inelastic H + H${}_3^{+}$ Collision rates and their impact in the determination of the excitation temperature of H${}_3^{+}$
• Abundant hydrocarbons in a buried galactic nucleus with signs of carbonaceous grain and polycyclic aromatic hydrocarbon processing
• H3+ in irradiated protoplanetary disks: Linking far-ultraviolet radiation and water vapor