MIGHTEE HI observations of low surface brightness and ultra-diffuse galaxies in the XMM-LSS field

Abstract

Untargeted neutral hydrogen (HI) surveys are well suited to identifying low surface brightness galaxies (LSBGs) that are gas rich, and they offer a complementary view to optically selected populations. We examined the LSBG population as identified via stellar and gaseous content using the MIGHTEE HI XMM-LSS early science data and the publicly available catalogs of optically identified LSBGs. There is currently little overlap between these datasets, with only three galaxies commonly detected. We performed surface brightness photometry of selected MIGHTEE HI detections to find 29 LSBGs, and 26 of these meet the size requirement (R_eff > 1.5 kpc) to be ultra-diffuse galaxies (UDGs). Furthermore, we extracted HI spectra at the location of all optically identified galaxies, placing upper limits on the HI-to-stellar mass ratio in these systems. While the HI-identified population overall tends toward bluer colors, the HI-identified and the optically selected samples mostly overlap in mean effective surface brightness, effective radii, and color. Although it is not straightforward to discern why the HI-identified LSBGs were missed in optical searches, this work highlights the utility of HI surveys in finding these faint systems. The HI-identified LSBGs are gas rich compared to the general HI-selected population. Furthermore, three out of four HI-selected UDGs with available kinematics show no systematic offset from the baryonic Tully-Fisher relation, although we are biased away from sources with low rotational velocities due to the low spectral resolution of the data. This work demonstrates the utility of HI observations for finding and characterizing the low surface brightness Universe.

Figures (10)

• Figure 1: Region of XMM-LSS covered in the MIGHTEE ES data. From left-to-right (decreasing right ascension), the three fields are XMM-LSS-14, XMM-LSS-13, and XMM-LSS-12. The solid lines indicate the full width half maximum of the MeerKAT primary beam, and the dashed lines represent the 30% response level. The MIGHTEE H i detections are shown as circles, shaded based on their H i mass. Also included are the LSBGs of G18 (blue squares) and the UDGs and UPGs of L23 (green pentagons) that fall within the considered footprint.
• Figure 2: The three cross-matched optical and H i sources. H i contours at [2.5, 5, 7, 10] $\times 10^{20}$ atoms cm$^{-2}$ overlaid on $g$ band images.
• Figure 3: Optically detected LSBG, G327 (blue circle), near two H i-detected galaxies. Red H i contours are MGTH_J021719.4- 052851 and green contours are MGTH_J021714.5-052922. The levels are [2.5, 5, 10] $\times 10^{20}$ atoms cm$^{-2}$ for both.
• Figure 4: Comparison of apparent (non-extinction corrected) $g$ band magnitudes derived through aperture and surface brightness photometry. Upper: Magnitudes derived through surface brightness photometry (y-axis) plotted against those derived from aperture photometry (x-axis). Lower: Differences between the two magnitudes plotted against the apparenet magnitude from aperture photometry.
• Figure 5: Colors of the optically and H i-selected galaxies. Upper: g-i color vs. $M_{HI}$/$M_{*}$. Downward arrows indicate upper limits. Symbols highlighted in black indicate the cross-matched galaxies that are plotted twice. The vertical dotted line at 0.64 indicates the cut between "red" and "blue" used in G18. The dashed horizontal line indicates a $M_{HI}$/$M_{*}$ value of one. Lower: Histogram of the color distribution of both the MIGHTEE-detected (blue) and optically detected galaxies (pink).