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arXiv · 2507.04703

Deep neutral hydrogen observations of the early-type galaxy NGC 2768: collided by a newly discovered satellite galaxy?

Nai-Ping Yu·Ming Zhu·Jin-Long Xu·Chuan-Peng Zhang·Xiao-Lan Liu·Peng Jiang
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Abstract

We present the results of a deep neutral hydrogen (Hi) observation of the early-type galaxy NGC 2768 using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Leveraging the high sensitivity of FAST, we discover an extended gas envelope around NGC 2768. The total Hi mass is measured to be 8.1 x 10^8 M_sun , representing a magnitude increase compared to previous Westerbork Synthesis Radio Telescope (WSRT) studies. Position-velocity (PV) diagram indicates the envelope mainly involves two components: an Hi disk of NGC 2768 and a newly discovered satellite galaxy without detectable counterparts in currently deep optical surveys. The center of the gas disk is mis-aligned with the optical disk of NGC 2768, with more gas redshifted, indicating it has been disturbed. Our study indicates NGC 2768 is currently undergoing a transition from a spiral galaxy to an S0. Previous deep WSRT observations reveal two dense clumps (named as Clumps A and Clump B throughout this paper) in the center of the envelope. We find Clump A corresponds to the densest part of the disk, while Clump B might be a newly discovered satellite galaxy which probably collided NGC 2768 about 0.38 Gyr ago. We also find tidal interactions between Clump B and PGC 2599651, NGC 2768 and UGC 4808. Based on these new findings, we finally analyze hierarchical accretion history of NGC 2768.

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Nai-Ping Yu, Ming Zhu, Jin-Long Xu, Chuan-Peng Zhang, Xiao-Lan Liu, Peng Jiang. 2025-07-07. Deep neutral hydrogen observations of the early-type galaxy NGC 2768: collided by a newly discovered satellite galaxy?. https://doi.org/10.3847/1538-4357%2Fade30b

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