Extended far-ultraviolet emission in distant dwarf galaxies

Abstract

Blue Compact Dwarfs (BCDs) are low-luminosity (M${}_K>-21$ mag), metal-poor ($\frac{1}{50}$ $\le Z/Z_{\odot }\le \frac{1}{2}$), centrally concentrated galaxies with bright clumps of star-formation. Cosmological surface brightness dimming and small size limit their detection at high redshifts, making their formation process difficult to observe. Observations of BCDs are needed at intermediate redshifts, where they are still young enough to show their formative stages, particularly in the outer regions where cosmic gas accretion should drive evolution. Here, we report the discovery of excess far-ultraviolet (FUV) emission in the outer regions of 11 BCDs in the GOODS-South field at redshifts between 0.1 and 0.24, corresponding to look back times of 1.3 - 2.8 Gyr in standard cosmology. These observations were made by the Ultra-Violet Imaging Telescope (UVIT) on AstroSat. For ten BCDs, the radial profiles of intrinsic FUV emission, corrected for the instrument point spread function, have larger scale-lengths than their optical counterparts observed with the Hubble Space Telescope. Such shallow FUV profiles suggest extended star-formation in cosmically accreting disks. Clumpy structure in the FUV also suggests the outer FUV disks are gravitationally unstable. Dynamical friction on the clumps drives them inward at an average rate exceeding $10^6{M}_{\odot }$Gyr${}^{-1}$.

23 pages, 7 Figures, 5 Tables. Published on 20th July, 2022, by Nature

References in corpus (9)

• 3D-HST WFC3-selected Photometric Catalogs in the Five CANDELS/3D-HST Fields: Photometry, Photometric Redshifts and Stellar Masses
• A Search for Extended Ultraviolet Disk (XUV-disk) Galaxies in the Local Universe
• The Outer Disks of Early-Type Galaxies. I. Surface-Brightness Profiles of Barred Galaxies
• Clumpy Galaxies in GOODS and GEMS: Massive Analogs of Local Dwarf Irregulars
• Abundant molecular gas and inefficient star formation in intracluster regions: Ram pressure stripped tail of the Norma galaxy ESO137-001
• The Hawk-I UDS and GOODS Survey (HUGS): Survey design and deep K-band number counts
• AstroSat detection of Lyman continuum emission from a z=1.42 galaxy
• CO map and steep Kennicutt-Schmidt relation in the extended UV disk of M63
• The Effect of Surface Brightness Dimming in the Selection of High-z Galaxies