Active galactic nuclei are primarily powered by a supermassive black hole lying at the center of a host galaxy that is accreting matter from its vicinity. The radiation from the central source ionizes the inner dense gas, the so-called broad-line region. Using the Gemini Near-Infrared Spectrograph on the Gemini North telescope, one half of the International Gemini Observatory, operated by NSF’s NOIRLab, astronomers have detected two near-infrared emission lines associated with the broad-line region of the Seyfert 1 galaxy III Zw 002.
“The Paschen-alpha (hydrogen) line originates in the inner region of the broad line region, and the O I (neutral oxygen) line originates in the outskirts of the broad line region, a region that has never been observed before,” said Denimara Dias dos Santos, a Ph.D. student at the Instituto Nacional de Pesquisas Espaciais.
“These are the first double-peaked profiles to be found in the near-infrared, and they emerged unexpectedly during observations with the Gemini Near-Infrared Spectrograph (GNIRS).”
“In 2003, observations of III Zw 002 in the visible revealed evidence of an accretion disk, and a 2012 study found similar results.”
In 2021, Rodriguez-Ardila and colleagues set out to supplement these findings with observations in the near-infrared using GNIRS, which is capable of observing the entire near-infrared spectrum (800-2500 nm) all in one go.
Because GNIRS is capable of making simultaneous observations across multiple bands of light, the team was able to capture a single clean, consistently calibrated spectrum in which multiple double-peaked profiles were revealed.
“We didn’t know previously that III Zw 002 had this double peaked profile, but when we reduced the data we saw the double peak very clearly,” Rodriguez-Ardila said.
“In fact, we reduced the data many times thinking it could be a mistake, but every time we saw the same exciting result.”
The observations not only confirm the theorized…
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