SDSS-IV MaNGA: Distinct Structural Growth and Star Formation in Low and High Surface Brightness Disks

Abstract

We analyze a clean sample of 1,118 late-type, face-on galaxies without AGN contamination from the MaNGA survey. Their photometric structures are quantified via two-component (bulge+disk) decompositions on deep $g$-band images from the DESI Legacy Survey. Using a disk central surface brightness of $μ_{\rm 0,d,cor}$(g) = 22 $\pm$ 0.3 mag arcsec$^{-2}$ (corrected for inclination and cosmic dimming) as the classification threshold, we identify 159 low surface brightness (LSB) galaxies, 388 LSB candidates, and 571 high surface brightness (HSB) galaxies. LSB galaxies are predominantly low-mass ($M_\ast < 3 \times 10^{10}$ M$_\odot$), exhibiting 29\% larger effective radii, 15\% lower star formation rates (SFRs), and 12\% reduced gas-phase metallicities than HSB counterparts at comparable masses. These differences cause systematic offsets from standard scaling relations. Despite comparable gas content, LSB galaxies host older stellar populations, longer gas depletion times, and less efficient star formation. Spatially resolved analyses further reveal that LSB galaxies display centrally suppressed $Σ_{\rm SFR}$, flatter SFR gradients, and rising specific SFR profiles toward their outskirts. Together with steeper negative metallicity gradients, these trends suggest ongoing gas accretion fueling outer-disk star formation. Consistently, the outer regions of LSB galaxies exhibit stronger H$δ_A$ absorption and lower D$_n$4000 indices, indicating fading A-star populations. Moreover, LSB galaxies show lower $Σ_{\ast}$ across all $R/R_e$ and more centrally depleted stellar mass profiles on an absolute radial scale, compared with HSB and large-size star-forming galaxies. Collectively, LSB galaxies represent a distinct population with slow evolution, inefficient star formation, and continued susceptibility to late-time gas accretion and peripheral star formation.

Figures (19)

• Figure 1: The two-component decomposition results for galaxies 11760-12701 (a bulge-dominated galaxy with spiral arms, upper eight panels) and 11867-12701 (a disk-dominated galaxy with weak spiral arms, lower eight panels). The first and third rows display decomposition results for a Sérsic bulge combined with an exponential disk, while the second and fourth rows show results for a Sérsic bulge combined with a Sérsic disk. The first column presents fitting results for the surface brightness radial profile and corresponding residuals, where black open circles represent the median $g$-band surface brightness obtained from elliptical isophotal fitting of the galaxies; red and blue dotted lines are the fitting results for the bulge and disk components, respectively, and the black dotted line indicates the fitting result for the total surface brightness of the bulge and disk. All model lines are convolved with the PSF, and the maximum error of the observed data points (red error bar) is labeled in the lower right corner of each panel. The residuals $\Delta\mu_g$ (black dots) are calculated as the difference between the measured surface brightness (black open circles) and the total surface brightness fitting curve (black dotted line). To guide the eye, the horizontal red line indicates a 0 mag arcsec$^{-2}$ difference between fit and data, while the $\Delta$rms of the deviation between fit and data is given in the lower right corner. The second column presents $g$-band images from the DESI Survey. The third column shows model images with annotations of $R_e$ and Sérsic index $n$ for each component (bulge and disk). The fourth column displays residual images, with the sum of residuals for each image labeled in the lower left corner, and its unit is nanomaggy.
• Figure 2: Histogram distributions of the fitted parameters for the bulge (red dashed) and disk (blue solid) components of the sample in the $g$-band: (a) apparent magnitude ($m$); (b) half-light radius ($R_e$) in arcsec; (c) Sérsic index $n$; (d) axial ratio ($b/a$).
• Figure 3: The histogram distribution of the corrected central surface brightness of the disk component in the $g$-band $\mu_{\rm 0,d,cor}(g)$ for the selected face-on late-type galaxies (1,118 in total). The entire sample is divided into three categories: the region where $\mu_{\rm 0,d,cor}(g) \geq$22.3 mag arcsec$^{-2}$ represents LSB galaxies (159, indicated by the blue region), the region with 21.7$< \mu_{\rm 0,d,cor}(g) <$22.3 mag arcsec$^{-2}$ denotes LSB candidates (388, represented by the black region), and the region where $\mu_{\rm 0,d,cor}(g) \leq$21.7 mag arcsec$^{-2}$ as HSB galaxies (571, shown in the red region).
• Figure 4: The relationship between stellar mass and SFR, 12+log(O/H) and size. The first row presents a scatter plot, while the second row displays a number density contour. Blue circles and contour represent LSB galaxies, hollow triangles and gray contour denote LSB candidates, while red stars and contour indicate HSB galaxies. In the left panel, the black dashed line depicts the SFMS derived from MaNGA data Belfiore_2018. The black dashed line in the median panel illustrates the mass-metallicity relationship for star-forming galaxies presented by Tremonti_2004. In the right panel, the black dashed lines represent the mass-size relation for late-type galaxies based on SDSS data Shen_2003. In the second row, the blue, gray, and red solid lines represent the quantile regression lines for LSB galaxies, LSB candidates, and HSB galaxies at $q$ = 0.5, respectively. Meanwhile, in the legend of each graph, we also present the $r$ and the $p$ value for each sample provided by Spearman rank correlation.
• Figure 5: The residuals of key galaxy parameters (SFR: $\Delta$log(SFR); gas-phase metallicity: $\Delta$12+log(O/H); effective radius: $\Delta$log($R_e$))-calculated relative to correlations from reference galaxy samples-along with D$_n$4000 values, plotted against the corrected disk central surface brightness ($\mu_{\rm 0,d,cor}$(g)) across three stellar mass ranges. The first, second and third columns correspond to galaxies with $M_\ast \leq 10^{9.5}$ M$_\odot$, $10^{9.5} <$$M_\ast < 10^{10}$ M$_\odot$, and $M_\ast \geq 10^{10}$ M$_\odot$, respectively. Gray points (in distinct shapes) denote individual galaxies in this study: circles for LSB galaxies, triangles for LSB candidates, and stars for HSB galaxies. Larger colored symbols (blue circles for LSB galaxies, green triangles for LSB candidates, red stars for HSB galaxies) represent the weighted averages of each sample. Error bars indicate median measurement uncertainties, while gray dashed lines mark central disk surface brightness boundaries separating HSB, LSB candidates, and LSB galaxies (from left to right). The Pearson correlation coefficients ($r$) and $p$-values for all galaxies in each mass range are displayed in the upper left corner of each panel.