Ionized gas components in low surface brightness galaxy AGC 111629

TL;DR

This study uses integral field spectroscopy with the Palomar PCWI to dissect the ionized gas components of the edge-on low surface brightness galaxy AGC 111629. The authors identify an irregular Hα morphology with an extraplanar arch, a central peanut-shaped [O III] structure potentially linked to AGN activity, and a southern-disk superbubble, all embedded in a rotating disk with a dynamical mass of roughly 4×10^10 M⊙. Gas-phase metallicity derived from [N II]/Hα shows a low central abundance and overall flat radial trends, suggesting the influence of feedback from AGN and supernovae, as well as a past minor-merger with a satellite (AGC 748815). The results imply that violent processes and accretion histories shape the ISM and chemical evolution of LSBGs differently from more massive, higher-surface-brightness systems, with implications for dwarf-galaxy evolution and AGN activity in low-mass hosts.

Abstract

We present integral field spectroscopy of ionized gas components in AGC 111629, an edge-on low surface brightness galaxy (LSBG) with a stellar mass of 5.7$\times$10$^{8}$ M$_{\odot}$. AGC 111629 displays an irregular H$α$ morphology and an arch-like structure in the extraplanar region, which is absent in continuous stellar image. The irregular H$α$ morphology may be related to a past merger event with its satellite galaxy AGC 748815. A peanut-shaped structure at the center in the integrated [OIII]$λ$5007 map, with a position angle that differs from that of the main stellar disk. This structure exhibits a higher [OIII]$λ$5007/H$β$ flux ratio, a larger equivalent width (EW) of [OIII]$λ$5007, and a lower H$α$/H$β$ flux radio ($<$ 2.86). Some spaxels associated with the peanut-shaped structure fall within the composite region of the BPT diagram based on [NII]$λ$6583. These features may be associated with the central AGN. Additionally, a sub-peak in the southern disk is clearly visible in the [OIII]$λ$5007 map. An extended region ($\sim$ 2 kpc) with an extremely low value of H$α$/H$β$ flux ratio is observed near this sub-peak. We interpret the sub-peak as a superbubble likely driven by supernova explosions in the southern disk. We derive the gas-phase metallicity, 12+log(O/H), using the [NII]$λ$6583/H$α$ diagnostic and find that AGC 111629 exhibits low central metallicity. This may result from feedback associated with AGN activity and supernova explosions.

Figures (12)

• Figure 1: Integrated H$\alpha$ contours at [3, 8, 18, 36] $\times$$\sigma$ (where $\sigma$ = 8.3 $\times$ 10$^{-19}$ erg s$^{-1}$ cm$^{-2}$) overlaid on the images of the same integrated H$\alpha$ line emission image in (a), the H$\alpha$ line emission velocity field (moment 1) in (b), and the velocity dispersion (moment 2) in (c). The images in (b) and (c) are generated by those spaxels above 3$\sigma_{ch}$, where $\sigma_{ch}$ is the mean channel noise ($\sigma_{ch}$ = 6.0 $\times$ 10$^{-19}$ erg s$^{-1}$ cm$^{-2}$$\rm \AA^{-1}$) of AGC 111629. Three peaks of H$\alpha$ are marked by "1", "2", and "3". We mark the major axis and minor axis with black lines in panel (b) with 25 degree PA. The red line parallels to major axis and at 8.0$"$ offset from the perpendicular disk center. The black cross represents the center of integrated H$\alpha$ image fitted by GALFIT S$\acute{e}$rsic profile. The oval in the lower left corner represents the spatial resolution 2.5$"$$\times$ 1.1$"$.
• Figure 2: Integrated H$\alpha$ emission contours (white lines) at [3, 8, 18, 36] $\times$$\sigma$ (where $\sigma$ = 8.3 $\times$ 10$^{-19}$ erg s$^{-1}$ cm$^{-2}$) overlaid on DESI g-band image of AGC 111629. The point source near AGC 111629 is identified as a star in SDSS. The red square is the same region of Figure \ref{['Ha']}.
• Figure 3: The red line is the HI spectrum from ALFALFA, and the blue dots represent the integrated H$\alpha$ spectrum of AGC 111629 among the 3$\sigma$ contour region in Figure \ref{['Ha']}(a). The blue solid line is the Gaussian fitting of the integrated H$\alpha$ spectrum. The grey dashed line is the systemic velocity of the Gaussian fitting center 6457 km s$^{-1}$ which is consistent with the center of HI spectrum 6454 km s$^{-1}$
• Figure 4: Left panel:The H$\alpha$ PVD along the major axis of AGC 111629. H$\alpha$ is shown in gray with blue contours. Right panel: The H$\alpha$ PVD along the minor axis of AGC 111629. The red line marks the arch-like structure position in Figure \ref{['Ha']}(b). 1$"$ corresponds to 0.43 kpc.
• Figure 5: The upper panels: Integrated [@series O III O III O III]$\lambda$5007 contours at [3, 15, 40, 80, 105] $\times$$\sigma$ (where $\sigma$ = 6.2 $\times$ 10$^{-19}$ erg s$^{-1}$ cm$^{-2}$) overlaid on the images of the same integrated [@series O III O III O III]$\lambda$5007 line emission image in the left, the [@series O III O III O III]$\lambda$5007 emission line velocity field (moment 1) in the middle, and the velocity dispersion (moment 2) in the right. The lower panels: Integrated H$\beta$ contours at [3, 7, 15, 25] $\times$$\sigma$ (where $\sigma$ = 6.0 $\times$ 10$^{-19}$ erg s$^{-1}$ cm$^{-2}$) overlaid on the images of the same integrated H$\beta$ line emission image in the left, the H$\beta$ emission line velocity field (moment 1) in the middle, and the velocity dispersion (moment 2) in the right. The images in velocity fields (moment 1) and the velocity dispersions (moment 2) are generated by those spaxels above 3$\sigma_{ch}$, where $\sigma_{ch}$ is the mean channel noise ($\sigma_{ch}$ = 5.4 $\times$ 10$^{-19}$ erg s$^{-1}$ cm$^{-2}$$\rm \AA^{-1}$). The black cross represents the same the center of integrated H$\alpha$ image with Figure \ref{['Ha']}. The black line is the major axis of H$\alpha$ image with PA = 25 degree. The PA of the white dashed line is 46 degree. The oval in the lower left corner represents the spatial resolution 2.5$"$$\times$ 1.3$"$.