Physical properties of star-forming clumps in nearby galaxies from CLAUDS and HSC-SSP

Giant Star-forming Clumps (GSFCs) are kpc-scale regions of enhanced star-formation with stellar masses of 10 6 to 10 10,M that are commonly observed in high-redshift (z 1) galaxies but their formation and role in galaxy evolution remain unclear. We applied a Faster R-CNN object detection framework (FRCNN) to identify star-forming clumps in astrophysical imaging data from a mass-complete sample of about 210,000 low-redshift galaxies (z 0.32), located in the HSC-SSP Wide and Deep fields observed by the Hyper Suprime-Cam Subaru Strategic Survey (HSC-SSP) and CFHT Large Area U-band Deep Survey (CLAUDS). We present a population of about 710,000 detected clumps for which we measured the (u)grizy-photometry and derived the physical properties (stellar mass, age, dust extinction and star-formation rate) for each clump by fitting the photometric data to stellar population models. We estimate that the clump Stellar Mass Function (cSMF) for young clumps (<100, Myr) follows a power law with an exponent of α=1.98 plus or minus0.02 down to a completeness limit of about10 8,M which is consistent with an in situ formation through violent disk instabilities (VDI). The clumps show elevated star-formation rates and negative gradients in their ages and stellar masses as a function of galactocentric distance. These gradients are steeper than those measured for the intra-clump regions of the host galaxies and are robust against uncertainties introduced by different modelling assumptions. For nearby galaxies we argue that the observed low-redshift clumps are likely analogues of high-redshift GSFCs and that the inward migration of star-forming clumps directly contributes to the central bulge formation of the host galaxy.