Constraints on the Cosmic-Ray Ionization Rate in the $z\sim 2.3$ Lensed Galaxies SMM J2135$-$0102 and SDP 17b from Observations of OH${}^{+}$ and H${}_2$O${}^{+}$

Abstract

Cosmic rays are predominantly accelerated in shocks associated with star formation such as supernova remnants and stellar wind bubbles, so the cosmic-ray flux and thus cosmic-ray ionization rate, ${\zeta }_{\mathrm{H}}$, should correlate with the star-formation rate in a galaxy. Submillimeter bright galaxies (SMGs) are some of the most prolific star forming galaxies in the Universe, and gravitationally lensed SMGs provide bright continuum sources suitable for absorption line studies. Abundances of OH${}^{+}$ and H${}_2$O${}^{+}$ are useful for inferring ${\zeta }_{\mathrm{H}}$ when combined with chemical models, and have been used for this purpose within the Milky Way. At redshifts $z\gtrsim 2$ transitions out of the ground rotational states of OH${}^{+}$ and H${}_2$O${}^{+}$ are observable with ALMA, and we present observations of both molecules in absorption toward the lensed SMGs SMM J2135$-$0102 and SDP 17b. These detections enable an exploration of ${\zeta }_{\mathrm{H}}$ in galaxies with extreme star formation and high supernova rates, both of which should significantly enhance cosmic-ray production. The observed OH${}^{+}$ and H${}_2$O${}^{+}$ absorption is thought to arise in massive, extended halos of cool, diffuse gas that surround these galaxies. Using a chemical model designed to focus on the reaction network important to both species, we infer cosmic-ray ionization rates of ${\zeta }_{\mathrm{H}}\sim 10^{-16}$-$10^{-14}$ s${}^{-1}$ in these extended gaseous halos. As our estimates come from gas that is far away from the sites of cosmic-ray acceleration, they imply that cosmic-ray ionization rates in the compact regions where star formation occurs in these galaxies are orders of magnitude higher.

16 pages, 5 figures, 3 tables, accepted for publication in ApJ

References in corpus (14)

• Cosmic Star Formation History
• Intense Star Formation within Resolved Compact Regions in a Galaxy at z=2.3
• Herschel Survey of Galactic OH+, H2O+, and H3O+: Probing the Molecular Hydrogen Fraction and Cosmic-Ray Ionization Rate
• The Herschel-ATLAS: a sample of 500μm-selected lensed galaxies over 600 square degrees
• Molecular gas in the Herschel-selected strongly lensed submillimeter galaxies at z~2-4 as probed by multi-J CO lines
• Large turbulent reservoirs of cold molecular gas around high-redshift starburst galaxies
• Chemical probes of turbulence in the diffuse medium: the TDR model
• The Ionization Fraction of Barnard 68: Implications for Star and Planet Formation
• Submillimeter H2O and H2O+ emission in lensed ultra- and hyper-luminous infrared galaxies at z ~ 2-4
• Infrared H3+ and CO Studies of the Galactic Core: GCIRS 3 and GCIRS 1W
• The interstellar medium in high-redshift submillimeter galaxies as probed by infrared spectroscopy
• OH+ and H2O+ absorption toward PKS1830-211
• Outflowing OH${}^{+}$ in Markarian 231: the ionization rate of the molecular gas
• The ionization rates of galactic nuclei and disks from Herschel/HIFI observations of water and its associated ions

Cited by in corpus (26)

• High-redshift star formation in the ALMA era
• Impact of low-energy cosmic rays on star formation
• Turbulent Gas in Lensed Planck-selected Starbursts at redshifts 1-3.5
• ALMACAL VI: Molecular gas mass density across cosmic time via a blind search for intervening molecular absorbers
• Giant star-forming clumps?
• The EDIBLES survey IV. Cosmic ray ionization rates in diffuse clouds from near-ultraviolet observations of interstellar OH${}^{+}$
• Close-up view of a luminous star-forming galaxy at z=2.95
• Stellar versus Galactic: The intensity of cosmic rays at the evolving Earth and young exoplanets around Sun-like stars
• Cold Clouds as Cosmic-Ray Detectors
• The GADOT Galaxy Survey: Dense Gas and Feedback in Herschel-Selected Starburst Galaxies at Redshifts 2 to 6
• Chaotic cold accretion in giant elliptical galaxies heated by AGN cosmic rays
• Rise of the Titans: Gas Excitation and Feedback in a Binary Hyper-Luminous Dusty Starburst Galaxy at z~6
• The cosmic ray ionisation and $\gamma$-ray budgets of star-forming galaxies
• Molecular Outflows in z > 6 QSO Hosts Driven by Star Formation
• SUNRISE: The rich molecular inventory of high-redshift dusty galaxies revealed by broadband spectral line surveys
• Where infall meets outflows: turbulent dissipation probed by CH${}^{+}$ and Ly$\alpha$ in the starburst/AGN galaxy group SMM J02399$-$0136 at z$\sim$2.8
• HD molecules at high redshift: cosmic-ray ionization rate in the diffuse interstellar medium
• A new analytic approach to infer the cosmic-ray ionization rate in hot molecular cores from HCO${}^{+}$, N${}_2$H${}^{+}$, and CO observations
• Cosmic-ray-induced H${}_2$ line emission: Astrochemical modeling and implications for JWST observations
• HYACINTH: HYdrogen And Carbon chemistry in the INTerstellar medium in Hydro simulations
• Molecular ionization rates and ultracompact dark matter minihalos
• Neutral outflows in high-z QSOs
• Energetic particles and high-energy processes in cosmological filaments and their astronomical implications
• Branching ratio for $\text{O}+{\text{H}}_3^{+}$ forming ${\text{OH}}^{+}+{\text{H}}_2$ and ${\text{H}}_2{\text{O}}^{+}+\text{H}$
• Do Unusually Cold Starburst Galaxies Exist? A Case Study
• Resolved Neutral Outflow from a Lensed Dusty Star Forming Galaxy at z=2.09