TY - JOUR

T1 - Energetic nuclear transients in luminous and ultraluminous infrared galaxies

AU - Reynolds, T. M.

AU - Mattila, S.

AU - Efstathiou, A.

AU - Kankare, E.

AU - Kool, E.

AU - Ryder, S.

AU - Pena-Monino, L.

AU - Perez-Torres, M. A.

PY - 2022/8/25

Y1 - 2022/8/25

N2 - Energetic nuclear outbursts have been discovered in luminous and ultraluminous infrared galaxies (U/LIRGs) at unexpectedly high rates. To investigate this population of transients, we performed a search in mid-IR data from the Wide-field Infrared Survey Explorer (WISE) satellite and its NEOWISE survey to detect and characterise luminous and smoothly evolving transients in a sample of 215 U/LIRGs. We report three new transients, all with Delta L > 10(43) erg s(-1), in addition to two previously known cases. Their host galaxies are all part of major galaxy mergers, and through radiative transfer model fitting we find that all have a significant contribution from an active galactic nucleus (AGN). We characterised the transients through measurements of their luminosities and resulting energetics, all of which are between 10(50.9) erg and 10(52.2) erg. The IR emission of the five transients was found to be consistent with re-radiation by the hot dust of emission at shorter wavelengths, presumably originating from an accretion event, onto the supermassive black hole. The corresponding transient rate of (1.6-4.6) x 10(-3) yr(-1) galaxy(-1) is over an order of magnitude higher than the rate of large amplitude flares shown by AGN in the optical. We suggest that the observed transients are part of a dust-obscured population of tidal disruption events (TDEs) that have remained out of the reach of optical surveys due to the obscuring dust. In one case, this is supported by our radio observations. We also discuss other plausible explanations. The observed rate of events is significantly higher than optical TDE rates, which can be expected in U/LIRG hosts undergoing a major galaxy merger with increased stellar densities in the nuclear regions. Continued searches for such transients and their multi-wavelength follow-up is required to constrain their rate and nature.

AB - Energetic nuclear outbursts have been discovered in luminous and ultraluminous infrared galaxies (U/LIRGs) at unexpectedly high rates. To investigate this population of transients, we performed a search in mid-IR data from the Wide-field Infrared Survey Explorer (WISE) satellite and its NEOWISE survey to detect and characterise luminous and smoothly evolving transients in a sample of 215 U/LIRGs. We report three new transients, all with Delta L > 10(43) erg s(-1), in addition to two previously known cases. Their host galaxies are all part of major galaxy mergers, and through radiative transfer model fitting we find that all have a significant contribution from an active galactic nucleus (AGN). We characterised the transients through measurements of their luminosities and resulting energetics, all of which are between 10(50.9) erg and 10(52.2) erg. The IR emission of the five transients was found to be consistent with re-radiation by the hot dust of emission at shorter wavelengths, presumably originating from an accretion event, onto the supermassive black hole. The corresponding transient rate of (1.6-4.6) x 10(-3) yr(-1) galaxy(-1) is over an order of magnitude higher than the rate of large amplitude flares shown by AGN in the optical. We suggest that the observed transients are part of a dust-obscured population of tidal disruption events (TDEs) that have remained out of the reach of optical surveys due to the obscuring dust. In one case, this is supported by our radio observations. We also discuss other plausible explanations. The observed rate of events is significantly higher than optical TDE rates, which can be expected in U/LIRG hosts undergoing a major galaxy merger with increased stellar densities in the nuclear regions. Continued searches for such transients and their multi-wavelength follow-up is required to constrain their rate and nature.

KW - black hole physics

KW - galaxies: starburst

KW - galaxies: nuclei

KW - infrared: general

KW - TIDAL DISRUPTION EVENT

KW - RADIATIVE-TRANSFER MODELS

KW - BLACK-HOLE MASS

KW - CIRRUS MODELS

KW - X-RAY

KW - SUPERNOVAE

KW - DISCOVERY

KW - CANDIDATE

KW - EVOLUTION

KW - CONTINUUM

U2 - 10.1051/0004-6361/202243289

DO - 10.1051/0004-6361/202243289

M3 - Journal article

VL - 664

JO - Astronomy & Astrophysics

JF - Astronomy & Astrophysics

SN - 0004-6361

M1 - A158

ER -