Astronomers analyzed new and archived multi-wavelength observations of the active galaxy NGC 5273. As a result, they detected so-called “aspect-change” events in the active galactic core of this galaxy. The discovery is reported in an article published November 7 on arXiv.org.
An AGN is a compact region at the center of a galaxy, brighter than the light of the surrounding galaxy. They are very energetic due to the presence of a black hole or star forming activity at the core of the galaxy.
Astronomers generally divide AGNs into two groups based on the characteristics of the emission lines. Type 1 AGNs exhibit both broad and narrow emission lines, while only narrow emission lines are present in type 2 AGNs. However, observations revealed that some AGNs transition between different spectral types; hence, they have been dubbed aspect-changing (CL) AGNs.
At a distance of about 53.8 million light-years, NGC 5273 is a Syefert galaxy hosting a variable low-luminosity AGN. The active galactic core of NGC 5273 is relatively weak compared to other AGNs. Previous observations of this galaxy revealed that it began to steadily increase in brightness in late 2021, peaking in 2022.
Now, a team of astronomers led by Jack MM Neustadt of The Ohio State University in Columbus, Ohio, reports the detection of new, changing AGN behavior in NGC 5273. The discovery is the result of a detailed analysis of a large set of infrared, optical, ultraviolet and X-ray data acquired by various spacecraft and ground-based telescopes.
The study conducted by the Neustadt team revealed that at least one appearance change event occurred in NGC 5273. The AGN changed from a Seyfert type 1.8/1.9 to a type 1 where broad optical and near-infrared emission lines appear in the spectrum, making the active galactic nucleus of NGC 5273, one of the few known AGNs to change aspect in the infrared.
The data show that the appearance-changing event in NGC 5273 coincides in time with an AGN eruption that occurred in 2014, and with evidence of historical variability prior to 2000. These results suggest that other eruptions in this galaxy may also have been temporary aspect change events from a Type 1.8/1.9 baseline to Type 1.
In general, the study found that the AGN of NGC 5273 varies by factors of 2 to 10 in the X-ray infrared flux, with short flares in 2002, 2014, 2016 and a long ongoing flare that started at the end of 2021.
Summarizing the results, the researchers concluded that the appearance-shifting events in NGC 5273 are likely due to changes in how the Broad Line Region (BLR) reprocesses continuum emission, as evidenced by the report of ‘Changing Eddington, Balmer’s decrement and near wide emergence. -infrared emission lines.
“Changes in wind due to changes in λEdd could therefore lead to changes in the BLR, although it is unclear how this would specifically affect the Balmer decrement or the outline of the NIR,” the authors explained. article.
JMM Neustadt et al, Once is an Instance, Twice is a Hobby: Multiple Optical and Near-Infrared Changing-Look Events in NGC 5273, arXiv (2022). DOI: 10.48550/arxiv.2211.03801
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Quote: Changing Look Events Observed in Galaxy NGC 5273 (November 17, 2022) Retrieved November 18, 2022 from https://phys.org/news/2022-11-changing-look-events-galaxy-ngc.html
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