Searching for Stellar-Feedback-Driven Outflow Signatures: A Deep Dive into NGC 3741

TL;DR

This study investigates whether stellar feedback drives outflows in a low-mass dwarf, using a multi-wavelength dataset (SparsePak IFU Hα spectroscopy, pODI imaging, archival HI data, and HST-derived SFHs) for NGC 3741. By comparing ionized and neutral gas kinematics, fitting nebular lines, and deriving local and global mass-loading factors, the authors find no strong wind signatures and very low mass-loading factors, with wind speeds well below the galaxy's escape velocity $V_{esc} \approx 330$ km s^-1. The central starburst over the past ~40 Myr appears insufficient to produce the high-mass-star population required to launch significant outflows, suggesting most feedback energy does not expel gas from this dwarf. The work demonstrates a robust local-scale approach and lays the groundwork for applying the method to a larger 40-galaxy sample to map how feedback couples to the ISM in dwarfs and informs models of the baryon cycle.

Abstract

Stellar feedback drives winds and outflows critical to the baryon cycles of low-mass galaxies whose shallow gravitational potential wells make them particularly susceptible to mass and metal loss through outflows. However, spatially resolved observations of stellar-feedback-driven outflows are limited due to their low-surface brightness and transient nature. We present the pilot of a larger multi-wavelength study searching for and quantifying stellar-feedback-driven winds and outflows on both spatially and globally resolved scales for a sample of 40 nearby low-mass galaxies. We search for outflow signatures in the star-forming dwarf galaxy NGC 3741 using new optical imaging and spectroscopy from the WIYN 3.5m telescope in conjunction with VLA 21cm observations and local star formation histories derived from resolved HST photometry. With this extensive dataset, we compare the neutral and ionized gas morphologies and kinematics, calculate mass-loading factors, and investigate spatial variations in the star formation history of NGC 3741. Though the galaxy is experiencing a burst in star formation, we find little evidence of strong outflows and calculate very low mass-loading factors. We suggest that, though star formation activity has increased dramatically in the central region of the galaxy over the last 40 Myr, the star formation rate is not high enough to produce a sufficient amount of high mass stars responsible for fueling outflows. Future analysis of the larger sample will allow us to explore how stellar feedback impacts mass loss on local scales, providing a deeper understanding of the interplay between stellar feedback and the interstellar medium in low-mass galaxies.

Figures (9)

• Figure 1: Example CMD (left) for a 400$\times$400 pc box and the corresponding derived SFH (right) with $\leq15$ Myr time resolution in the $t<70$ Myr time bins. See Section \ref{['subsec:HSTdata']} for specific time binning. Random uncertainties are represented with red shading.
• Figure 2: Optical $r$-band (top) and deep H$\alpha$ pODI imaging of NGC 3741. The H$\alpha$ emission is concentrated in a central group of star forming regions with diffuse clouds of emission extending out from the central region. The stellar component shows a bright concentration coincident with the central H ii regions with some faint extensions of stellar material to the north and south.
• Figure 3: Top panel: Integral H ii region luminosity function derived from the selected regions of H$\alpha$. The vertical dashed line denotes the completeness limit for the galaxy. The luminosity function is steep with a power-law index of -1.39 $\pm$ 0.16. Bottom panel: Histogram showing the distribution of the H ii emission region luminosities from which the luminosity function was derived.
• Figure 4: The top panel shows from left to right the H i column density contours at levels [1.5, 5, 15, 25, 35, and 45] $\times 10^{20}$ cm$^{-2}$ overlaid on the optical pODI $r$-band image, the H i velocity field of the galaxy, and the H i velocity dispersion map of the galaxy. The bottom panel shows a zoomed in FOV on the central most region of the galaxy. From left to right this panel shows the H$\alpha$ pODI image with the H i column density contours overlaid in red and the H$\alpha$ contours overlaid in white and black at levels of [0.2, 0.5, 1, 2, and 4] $\times 10^{-17}$ erg s$^{-1}$ cm$^{-2}$, the H i velocity field, and the H i velocity dispersion with the same H$\alpha$ contours overlaid. The ovals in the bottom left of each panel represents the beam size.
• Figure 5: Top row from left to right: optical-continuum subtracted H$\alpha$ image with selected emission regions overlaid, same narrowband image with SparsePak pointing overlaid, and H$\alpha$ flux map. Bottom row from left to right: H$\alpha$ velocity field, H$\alpha$ velocity dispersion, and H$\alpha$$-$ H i gas velocity differences (H i velocity field is shown separately in Figure \ref{['HImoments']}). The filled circles correspond to the SparsePak pointing fiber locations from where we recover flux.