AGN versus Star-formation: A MUSE Analysis of NGC 1365

TL;DR

This work investigates how AGN- and star-formation feedback shape the gas and star formation in a nearby galaxy, using high-resolution MUSE IFU data complemented by JWST and Chandra observations to map ionization and kinematics across ~40 kpc. The authors perform Bayesian spectral fitting with BADASS on archival data to produce robust emission-line flux and velocity maps, applying stringent quality masks. They identify a region of unexpectedly high ionization in the star-forming arms and argue that shock heating contributes significantly, helping to disentangle the relative roles of AGN- and SF-driven feedback on the host gas. The study demonstrates the power of resolved, multiwavelength diagnostics for constraining feedback processes and informs broader galaxy evolution models.

Abstract

Active galactic nuclei (AGN) and star formation feedback may heat and remove gas from galaxies in a process that quenches ongoing star formation and shapes the evolution of galaxies. Potential impacts from these processes can be seen in the complex and interconnected signatures of AGN and star formation activity throughout a galaxy. Here, we analyze archival integral field unit (IFU) data for the nearby Seyfert galaxy, NGC 1365, as observed with the Multi Unit Spectroscopic Explorer (MUSE) instrument on the Very Large Telescope (VLT). Our analysis probes the ionization and kinematic properties of NGC 1365 at high spatial resolution over unprecedentedly large physical scales (approximately 40 kpc), allowing us to trace the effects of feedback throughout nearly an entire galaxy. We use these optical IFU data in conjunction with observations from the James Webb Space Telescope (JWST) and Chandra X-ray Observatory to analyze and compare maps of emission line flux, ionization state, star formation, and gas kinematics. In doing so, we identify a region of BPT-identified unexpectedly high ionization relative to surrounding areas in the star forming arms, and work to identify its source, finding that shock heating may play a significant role. Results from this analysis allow us to place constraints on the relative impact of AGN and star formation processes on the star forming gas in NGC 1365, as well as begin to inform our understanding on the global impacts of feedback in galaxy populations as a whole.

Figures (2)

• Figure 1: Flux maps of the primary emission lines used in this work, computed from the maximum likelihood BADASS models. All are masked as specified for each line flux, requiring a 3$\sigma$ detection, an SNR greater than 8, percent residual error $< 20$%, and a velocity offset $< 400$ km s$^{-1}$. These masks are used throughout the work, and combined when a figure references more than one emission line. On the left, moving from top to bottom, we show the the fluxes for H$\alpha\lambda6563$, [S2]$\lambda$6718, H$\beta\lambda4861$, and on the right from top to bottom, we show the flux for [N2]$\lambda$6585, [O1]$\lambda$6302, [O3]$\lambda$5007.
• Figure 2: SFR surface density map for NGC 1365 as calculated from JWST and optical H$\alpha$ data in Section \ref{['subsec:UV_IR_SFR']}. We present the SFR surface density in M$_\odot$ yr$^{-1}$ kpc$^{-1}$, and limit the plotted value at 1 M$_\odot$ yr$^{-1}$ kpc$^{-1}$ to show the structure in the spiral arms. As can be seen, the majority of star formation is concentrated within the nucleus, though there are regions of scattered heightened star formation in the lower left spiral arms.