We report sub-parsec-scale observations of the 321 GHz H2O emission line in the radio galaxy NGC 1052. The H2O line emitter size is constrained in <0.6 mas distributed on the continuum core component. The brightness temperature exceeding 106 K and the intensity variation indicate certain evidence for maser emission. The maser spectrum consists of redshifted and blueshifted velocity components spanning ∼400 km s−1, separated by a local minimum around the systemic velocity of the galaxy. The spatial distribution of maser components shows a velocity gradient along the jet direction, implying that the population-inverted gas is driven by the jets interacting with the molecular torus. We identified a significant change of the maser spectra between two sessions separated by 14 days. The maser profile showed a radial velocity drift of 127 ± 13 km s−1 yr−1 implying inward gravitational acceleration at 5000 Schwarzschild radii. The results demonstrate the feasibility of future very long baseline interferometry observations to resolve the jet–torus interacting region.
The Atacama Large Millimeter/submillimeter Array (ALMA) serendipitously detected H2O $J_{K_{\rm a}, K_{\rm c}} = 10_{2,9}$–93, 6 emission at 321 GHz in NGC 1052. This is the first submillimeter maser detection in a radio galaxy and the most luminous 321 GHz H2O maser known to-date with the isotropic luminosity of $1090\, L_{\odot }$. The line profile consists of a broad velocity component with FWHM = 208 ± 12 km s−1 straddling the systemic velocity and a narrow component with FWHM = 44 ± 3 km s−1 blueshifted by 160 km s−1. The profile is significantly different from the known 22 GHz 61, 6–52, 3 maser which shows a broad profile redshifted by 193 km s−1. The submillimeter maser is spatially unresolved with a synthesized beam of ${0{^{\prime \prime}_{.}}68} \times {0{^{\prime \prime}_{.}}56}$ and coincides with the continuum core position within 12 pc. These results indicate amplification of the continuum emission through high-temperature (>1000 K) and dense [n(H2O) > 104 cm−3] molecular gas in front of the core.
more » « less- NSF-PAR ID:
- 10398523
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Publications of the Astronomical Society of Japan
- Volume:
- 75
- Issue:
- 2
- ISSN:
- 0004-6264
- Format(s):
- Medium: X Size: p. L1-L5
- Size(s):
- ["p. L1-L5"]
- Sponsoring Org:
- National Science Foundation
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