Science Highlight: Spiral morphology in an intensely star-forming disk galaxy more than 12 billion years ago
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Spiral galaxies are thought to be fundamental objects, accounting for as much as 70% of the total number of galaxies in the local Universe. However, it is suggested that the proportion of spiral galaxies appears to decline rapidly as we look back through the history of the Universe. In a recent paper, Tsukui and Iguchi investigated the archival ALMA Band 7 data of BRI 1335-0417, an intensely star-forming galaxy at a redshift of 4.41, finding convincing evidence of spiral morphology which is located only 1.4 billion years after the Big Bang (see Figure on the left). As a result of the image decomposition into logarithmic spirals, a two-armed spiral with pitch angle of 27.6deg is identified as a dominant component. The [CII] kinematics show a symmetric velocity field and a steep velocity rise near the galaxy center, suggesting the presence of a rotating gas disk and a central compact object. These results may indicate that the spiral structure has formed in a very short period after the disk formation, providing important circumstantial evidence to identify the formation process of the galactic structures.
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