Mid-infrared Outbursts in Nearby Galaxies (MIRONG). II. Optical Spectroscopic Follow-up
Abstract
Infrared echo has proven to be an effective means to discover transient accretion events of supermassive black holes (SMBHs), such as tidal disruption events (TDEs) and changing-look active galactic nuclei (AGNs), in dusty circumnuclear environments. To explore the dusty populations of SMBH transient events, we have constructed a large sample of mid-infrared outbursts in nearby galaxies (MIRONG) and performed multiwavelength observations. Here we present the results of multiepoch spectroscopic follow-up observations of a subsample of 54 objects spanning a timescale of 4 yr. Emission-line variability was detected in 22 of them with either emergence or enhancement of broad Balmer emission lines in comparison with pre-outburst spectra. Coronal lines, He iiλ4686, and Bowen line N iiiλ4640 appeared in the spectra of nine, seven, and two sources, respectively. These results suggest that MIRONG is a mixed bag of different transient sources. We have tentatively classified them into different subclass according to their spectral evolution and light curves. Two sources have been in a steady high broad Hα flux up to the latest observation and might be turn-on AGNs. Broad lines faded out in the remaining sources, indicating a transient ionizing source ignited by TDE or sporadic gas accretion. Thirty-one sources do not show noticeable spectral change with respect to their pre-outburst spectra. They have a statistically redder MIR color and lower MIR luminosity of the outbursts, which are consistent with heavily obscured events.
Additional Information
© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2021 August 31; revised 2021 October 13; accepted 2021 October 25; published 2022 January 14. We thank the referee for helpful comments and suggestions, which led to the improvement of the paper. This work is supported by the B-type Strategic Priority Program of the Chinese Academy of Sciences (grant No. XDB41000000), Chinese Science Foundation (NSFC-11833007, 12073025, 12103048, 11421303, 11822301), China Manned Spaced Project (CMS-CSST-2021-B11), and the Fundamental Research Funds for the Central Universities. This research uses data obtained through the Telescope Access Program (TAP). Observations obtained with the Hale Telescope at Palomar Observatory were obtained as part of an agreement between the National Astronomical Observatories, Chinese Academy of Sciences, and the California Institute of Technology.Attached Files
Published - Wang_2022_ApJS_258_21.pdf
Accepted Version - 2111.12729.pdf
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Additional details
- Eprint ID
- 112956
- Resolver ID
- CaltechAUTHORS:20220118-993886000
- XDB41000000
- Chinese Academy of Sciences
- 11833007
- National Natural Science Foundation of China
- 12073025
- National Natural Science Foundation of China
- 12103048
- National Natural Science Foundation of China
- 11421303
- National Natural Science Foundation of China
- 11822301
- National Natural Science Foundation of China
- CMS-CSST-2021-B11
- China Manned Spaced Project
- Fundamental Research Funds for the Central Universities
- National Astronomical Observatories, Chinese Academy of Sciences (NAOC)
- Caltech Optical Observatories
- Created
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2022-01-19Created from EPrint's datestamp field
- Updated
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2022-01-19Created from EPrint's last_modified field