Dwarf galaxies with the highest concentration are not thicker than ordinary dwarf galaxies

• Published in: arXiv.org
• Main Authors: Chen, Lijun, Hong-Xin, Zhang, Lin, Zesen, Chen, Guangwen, Tao, Bojun, Liang, Zhixiong, Lin, Zheyu, Xu, Kong
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 10.09.2023
• Subjects: Acquisitions & mergers; Astronomical models; Axial stress; Broadband; Comparative studies; Dwarf galaxies; Physics - Astrophysics of Galaxies; Red shift; Star & galaxy formation; Star formation; Stellar mass
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2309.05052

The formation mechanism of high-concentration dwarf galaxies is still a mystery. We perform a comparative study of the intrinsic shape of nearby low-mass galaxies with different stellar concentration. The intrinsic shape is parameterized by the intermediate-to-major axis ratios B/A and the minor-to-major axis ratios C/A of triaxial ellipsoidal models. Our galaxies (\(10^{7.5} M_\odot\) < \(M_\star\) < \(10^{10.0} M_\odot\)) are selected to have spectroscopic redshift from SDSS or GAMA, and have broadband optical images from the HSC-SSP Wide layer survey. The deep HSC-SSP images allow to measure the apparent axis ratios \(q\) at galactic radii beyond the central star-forming area of our galaxies. We infer the intrinsic axis ratios based on the \(q\) distributions. We find that 1) our galaxies have typical intrinsic shape similarly close to be oblate (\(\mu_{B/A}\) \(\sim\) 0.9--1), regardless of the concentration, stellar mass, star formation activity, and local environment (being central or satellite); 2) galaxies with the highest concentration tend to have intrinsic thickness similar to or (in virtually all cases) slightly thinner (i.e. smaller mean \(\mu_{C/A}\) or equivalently lower triaxiality) than ordinary galaxies, regardless of other properties explored here. This appears to be in contrast with the expectation of the classic merger scenario for high-concentration galaxies. Given the lack of a complete understanding of dwarf-dwarf merger, we cannot draw a definite conclusion about the relevance of mergers in the formation of high-concentration dwarfs. Other mechanisms such as halo spin may also play important roles in the formation of high-concentration dwarf galaxies.