paper

Revisiting the Dragonfly Galaxy I. High-resolution ALMA and VLA Observations of the Radio Hotspots in a Hyper-luminous Infrared Galaxy at

arXiv:2305.03979 · doi:10.1093/mnras/stad1428

Abstract

Radio-loud active galactic nuclei (RLAGNs) are rare among AGN populations. Lacking high-resolution and high-frequency observations, their structure and evolution stages are not well understood at high redshifts. In this work, we report ALMA 237 GHz continuum observation at resolution and VLA 44 GHz continuum observation at resolution of the radio continuum emission from a high-redshift radio and hyper-luminous infrared galaxy at . The new observations confirm the South-East (SE) and North-West (NW) hotspots identified by previous low-resolution VLA observations at 4.7 and 8.2 GHz and identify a radio core undetected in all previous observations. The SE hotspot has a higher flux density than the NW one does by a factor of 6, suggesting that there can be a Doppler boosting effect in the SE one. In this scenario, we estimate the advance speed of the jet head, ranging from 0.1c -- 0.3c, which yields a mildly relativistic case. The projected linear distance between the two hotspots is kpc, yielding a linear size ( kpc) of a Compact-Steep-Spectrum (CSS) source. Combined with new \black{high-frequency ( GHz) and archived low-frequency observations ( GHz)}, we find that injection spectra of both NW and SE hotspots can be fitted with a continuous injection (CI) model. Based on the CI model, the synchrotron ages of NW and SE hotspots have an order of yr, consistent with the order of magnitude yr observed in CSS sources associated with radio AGNs at an early evolution stage. The CI model also favors the scenario in which the double hotspots have experienced a quiescent phase, suggesting that this RLAGN may have transient or intermittent activities.

arXiv commentAccepted for publication in MNRAS

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