High-Resolution Optical IFU Spectroscopy of the Complex Galaxy Merger II Zw 096

C. Riesco, E. Treister, G. Venturi, F. Bauer, G. Privon, C. Finlez, S. Zamora, D. Tubin, Y. Song, I. del Moral-Castro, C. Ricci, C. Ramos, N. Levenson, V. U, A. Medling, S. Aalto, G. D'Ago, V. Olivares, L. Barcos-Muñoz, F. Ricci, G. Olander, F. Muller-Sanchez, P. Tissera

First listed 2025-07-08 | Last updated 2025-07-08

Abstract

Luminous and Ultra-luminous IR galaxies ((U)LIRGs) are critical for investigating feedback mechanisms due to a combination of intense star formation (SF) episodes and active galactic nuclei (AGN), particularly in the context of complex galaxy interactions. We conduct a detailed analysis of the II ZW 096 merging system using the Multi-Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope (VLT), combining high-resolution Narrow Field Mode (NFM) and large-area Wide Field Mode (WFM) observations. We mapped the morphology, kinematics, and ionizing radiation of the system's gas by fitting atomic emission lines and the optical continuum. We identify three or more distinct galaxies within II ZW 096, revealing rotational patterns and complex interactions consistent with a collapsing small galaxy group. The kinematics and ionization structures suggest high star formation rates and shock-driven processes, which align with this proposed scenario. Focusing on the D1 compact region, which contributes 40-70% of the system's IR emission, and combining information from archival multi-wavelength observations, we find strong evidence of a heavily obscured AGN powering it. Our analysis of the internal structure, interactions, and merger state of II ZW 096 offers novel insights into the galaxy evolution processes in this dynamic and highly chaotic system

Short digest

Using VLT/MUSE in both NFM and WFM, this work resolves II Zw 096 into three or more interacting galaxies and maps ionized-gas morphology, kinematics, and excitation across the system. Velocity fields show rotation with strong deviations and widespread shocks, consistent with a collapsing small-group scenario and intense star formation. A compact D1 knot (≤175 pc) that contributes 40–70% of the IR luminosity shows strong multiwavelength evidence for a heavily obscured AGN. Multi-component fits to Hα+[N II] and continuum mapping clarify the internal structure and current merger stage.

Key figures to inspect

• Figure 2: Multiwavelength context and NFM footprints—use this to locate D0/D1 relative to A, B, and C, and to compare MIRI and ALMA CO detections that anchor the compact IR-bright regions.
• Figure 3: Hα flux maps (WFM+NFM)—trace where ionized emission peaks, check newly resolved knots near A and in overlap zones, and gauge how D1 sits within the broader SF/obscured energy distribution versus JWST/ALMA markers.
• Figure 4: Velocity fields—inspect rotation in A and B with strong edge deviations, and the absence of a clean gradient around D1, supporting complex, shock-affected kinematics expected for a collapsing group.
• Figure 1: Example spectra and line fits—see the need for two-component Hα+[N II] models (including a broad component at A’s center) and Balmer absorption in the tidal tail, diagnosing mixed kinematics and recent SF history.