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Abstract: We present deep HST-ACS images and Keck spectroscopy of MC2 1635+119, a QSOhosted by a galaxy previously classified as an undisturbed elliptical. Our newimages reveal dramatic shell structure indicative of a merger event in therelatively recent past. The brightest shells in the central regions of the hostare distributed alternately in radius, with at least two distinct shells on oneside of the nucleus and three on the other, out to a distance of ~13 kpc. Thelight within the five shells comprises ~6% of the total galaxy light. Lowersurface brightness ripples or tails and other debris extend out to a distanceof ~65 kpc. A simple N-body model for a merger reproduces the inner shellstructure and gives an estimate for the age of the merger between ~30 Myr and~1.7 Gyr, depending on a range of reasonable assumptions. While the inner shellstructure is suggestive of a minor merger, the total light contribution fromthe shells and extended structures are more indicative of a major merger. Thespectrum of the host galaxy is dominated by a population of intermediate age~1.4 Gyr, indicating a strong starburst episode that may have occurred at thetime of the merger event. We speculate that the current QSO activity may havebeen triggered in the recent past by either a minor merger, or by debris froman older ~Gyr major merger that is currently ``raining- back into thecentral regions of the merger remnant.

Author: Gabriela Canalizo, Nicola Bennert, Bruno Jungwiert, Alan Stockton, Francois Schweizer, Mark Lacy, Chien Peng

Source: https://arxiv.org/

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