TiNy Titans HI: Discovering Satellites via HI Gas in an Isolated, Compact Group of Dwarf Galaxies

Sabrina Stierwalt; Nicholas Luber; Zelie Goldberg Little; George C. Privon; Gurtina Besla; Kelsey E. Johnson; Nitya Kallivayalil; David R. Patton; Mary Putman; David Simpson Heil

arXiv · 2512.09174

TiNy Titans HI: Discovering Satellites via HI Gas in an Isolated, Compact Group of Dwarf Galaxies

Sabrina Stierwalt·Nicholas Luber·Zelie Goldberg Little·George C. Privon·Gurtina Besla·Kelsey E. Johnson·Nitya Kallivayalil·David R. Patton·Mary Putman·David Simpson Heil

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Abstract

We report on the HI content of an isolated, compact group of 6 dwarf galaxies at a distance of 145 Mpc. The distribution and kinematics of the HI, including multiple gaseous bridges, indicate the group is a gravitationally bound system. The HI maps further reveal two newly discovered dwarf satellites easily identified by their gas but only barely visible in optical images. The four dwarf group members previously identified in SDSS have 9.06 < log(Mstar/Msun) < 9.43 and 9.42 < log(MHI/Msun) < 9.73. The two newly discovered dwarf satellites have log(Mstar/Msun) = 6.10 with log(MHI/Msun) = 8.71 and log(Mstar/Msun) = 7.07 with log(MHI/Msun) = 9.18. New Gemini optical spectra link the HI detections and their optical counterparts. The group's 3D velocity dispersion (188 km/s), mass-to-light ratio (M_L/B ~44), dynamical-to-baryonic mass ratio (Mdyn/Mbary ~ 21), size (69 kpc), and gas fraction (0.56) are all consistent with the compact dwarf groups in the TNG50 simulation. The group has a top-heavy satellite mass function that is inconsistent with predictions for LMC-sized hosts and may instead be two or more groups coming together. A Voronoi tessellation reveals the group resides in a tendril outside the intersection of two filaments. These intermediate density environments within large scale structure provide the conditions needed for groups of star forming, gas-rich dwarf galaxies to form and eventually merge. Our results further show that it is possible to uncover fainter dwarf satellites around dwarf galaxy hosts via HI maps.

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Sabrina Stierwalt, Nicholas Luber, Zelie Goldberg Little, George C. Privon, Gurtina Besla, Kelsey E. Johnson, Nitya Kallivayalil, David R. Patton, Mary Putman, David Simpson Heil. 2025-12-09. TiNy Titans HI: Discovering Satellites via HI Gas in an Isolated, Compact Group of Dwarf Galaxies. https://arxiv.org/abs/2512.09174

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