Using KCWI to Explore the Chemical Inhomogeneities and Evolution of J1044+0353

Abstract

J1044+0353 is considered a local analog of the young galaxies that ionized the intergalactic medium at high redshift due to its low mass, low metallicity, high specific star formation rate, and strong high-ionization emission lines. We use integral field spectroscopy to trace the propagation of the starburst across this small galaxy using Balmer emission- and absorption-line equivalent widths and find a poststarburst population (∼15–20 Myr) roughly 1 kpc east of the much younger, compact starburst (∼3–4 Myr). Using the direct electron temperature method to map the O/H abundance ratio, we find similar metallicities (1–3σ) between the starburst and poststarburst regions but with a significant dispersion of about 0.3 dex within the latter. We also map the Doppler shift and width of the strong emission lines. Over scales several times the size of the galaxy, we discover a velocity gradient parallel to the galaxy’s minor axis. The steepest gradients (∼30 km s−1 kpc−1) appear to emanate from the oldest stellar association. We identify the velocity gradient as an outflow viewed edge on based on the increased line width and skew in a biconical region. We discuss how this outflow and the gas inflow necessary to trigger the starburst affect the chemical evolution of J1044+0353. We conclude that the stellar associations driving the galactic outflow are spatially offset from the youngest association, and a chemical evolution model with a metal-enriched wind requires a more realistic inflow rate than a homogeneous chemical evolution model.

Resolving the Mechanical and Radiative Feedback in J1044+0353 with Keck Cosmic Web Imager Spectral Mapping

“…Most local dwarf galaxies are very diffuse, inactive systems (Weisz et al 2012;Guo et al 2016), so the high specific SFR in J1044+0353 indicates that some mechanism recently drove gas inward. The low gas-phase metallicity across J1044+0353, relative to the mass −metallicity relation, provides indirect evidence for this recent gas inflow (Peng et al 2023). Notes.…”

“…In known LyC leakers, the intensity of He II relative to Hβ appears to be driven by metallicity rather than f esc (Marques-Chaves et al 2022). J1044+0353 has a gasphase oxygen abundance of 12 log O H 7.45 ( ) + = (Peng et al 2023) but lacks the strong nitrogen enhancement seen in GN-z11 (Senchyna et al 2023). Massive stars of similar metallicity are expected to have a harder ionizing spectrum on empirical grounds; see Figures 2-4 of Sander (2022), for example.…”

“…The compact starburst is offcenter in J1044+0353. In a preliminary analysis of our KCWI data cube (Peng et al 2023), we mapped the star formation history (SFH) across the surrounding galaxy and discovered a poststarburst population roughly 1.3 kpc east of the starburst. Whereas the interstellar absorption lines in the FUV spectrum had indicated a very weak outflow (Xu et al 2022), the global gas kinematics revealed a large, bipolar outflow (Peng et al 2023).…”

“…In a preliminary analysis of our KCWI data cube (Peng et al 2023), we mapped the star formation history (SFH) across the surrounding galaxy and discovered a poststarburst population roughly 1.3 kpc east of the starburst. Whereas the interstellar absorption lines in the FUV spectrum had indicated a very weak outflow (Xu et al 2022), the global gas kinematics revealed a large, bipolar outflow (Peng et al 2023). Initially, it came as a surprise that the apex of this galactic wind was outside the FUV spectral aperture, well separated from the compact starburst circled in Figure 1.…”

“…Throughout this paper, we correct for internal reddening using A V = 0.20 ± 0.10, measured (from the Balmer decrement) in the starburst region (Peng et al 2023), and an SMC extinction curve (Gordon et al 2003). We correct fluxes for Galactic extinction (Fitzpatrick 1999) using the dust map of Schlafly & Finkbeiner (2011), which we accessed via the IRSA interface.…”