Discovery of Hydrogen Radio Recombination Lines at z = 0.89 toward PKS 1830-211
Journal article, 2023
We report the detection of stimulated hydrogen radio recombination line (RRL) emission from ionized gas in a z = 0.89 galaxy using 580-1670 MHz observations from the MeerKAT Absorption Line Survey. The RRL emission originates in a galaxy that intercepts and strongly lenses the radio blazar PKS 1830−211 (z = 2.5). This is the second detection of RRLs outside of the local Universe and the first clearly associated with hydrogen. We detect effective H144α (and H163α) transitions at observed frequencies of 1156 (798) MHz by stacking 17 (27) RRLs with 21σ (14σ) significance. The RRL emission contains two main velocity components and is coincident in velocity with H i 21 cm and OH 18 cm absorption. We use the RRL spectral line energy distribution and a Bayesian analysis to constrain the density (n e ) and the volume-averaged path length (ℓ) of the ionized gas. We determine log ( n e ) = 2.0 − 0.7 + 1.0 cm−3 and log ( ℓ ) = − 0.7 − 1.1 + 1.1 pc toward the northeast (NE) lensed image, likely tracing the diffuse thermal phase of the ionized ISM in a thin disk. Toward the southwest (SW) lensed image, we determine log ( n e ) = 3.2 − 1.0 + 0.4 cm−3 and log ( ℓ ) = − 2.7 − 0.2 + 1.8 pc, tracing gas that is more reminiscent of H scii regions. We estimate a star formation (surface density) rate of ΣSFR ∼ 0.6 M ⊙ yr−1 kpc−2 or SFR ∼ 50 M ⊙ yr−1, consistent with a star-forming main-sequence galaxy of M ⋆ ∼ 1011 M ⊙. The discovery presented here opens up the possibility of studying ionized gas at high redshifts using RRL observations from current and future (e.g., SKA and ngVLA) radio facilities.
Author
K.L. Emig
National Radio Astronomy Observatory
Neeraj Gupta
Inter-University Centre for Astronomy and Astrophysics
P. Salas
Green Bank Observatory
Sebastien Muller
Chalmers, Space, Earth and Environment, Onsala Space Observatory
S. Balashev
Russian Academy of Sciences
National Research University Higher School of Economics
Françoise Combes
Paris Observatory
E. Momjian
National Radio Astronomy Observatory Socorro
Y. Song
National Radio Astronomy Observatory
University of Virginia
P. Jagannathan
National Radio Astronomy Observatory Socorro
Partha P. Deka
Inter-University Centre for Astronomy and Astrophysics
G. I.G. Józsa
Rhodes University
Max Planck Society
H. R. Klockner
Max Planck Society
Abhisek Mohapatra
Inter-University Centre for Astronomy and Astrophysics
P. Noterdaeme
Institut d 'Astrophysique de Paris
University of Chile (UCH)
Patrick Petitjean
Institut d 'Astrophysique de Paris
R. Srianand
Inter-University Centre for Astronomy and Astrophysics
Jonah D. Wagenveld
Max Planck Society
Astrophysical Journal
0004-637X (ISSN) 1538-4357 (eISSN)
Vol. 944 1 93Subject Categories
Astronomy, Astrophysics and Cosmology
Atom and Molecular Physics and Optics
Fusion, Plasma and Space Physics
DOI
10.3847/1538-4357/acb49d