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Description
The morphological evolution of star-forming galaxies provides important clues to understand their physical properties, as well as the triggering and quenching mechanisms of star formation. We analyze the morphology of galaxies hosting star-forming events at low redshift (z<0.36). We aim at connecting morphology and star-formation properties of low-mass galaxies (median stellar mass ~10^8.5^M_{sun}_) beyond the local Universe. We use a sample of medium-band selected star-forming galaxies from the GOODS-North field. H images for the sample are created combining both spectral energy distribution fits and HST data. Using them, we mask the star forming regions to obtain an unbiased two-dimensional model of the light distribution of the host galaxies. For this purpose we use PHI, a new Bayesian photometric decomposition code. We applied it independently to 7 HST bands, from the ultraviolet to the near-infrared, assuming a Sersic surface brightness model. Star-forming galaxy hosts show low Sersic index (with median n~0.9), as well as small sizes (median Re~1.6kpc), and negligible change of the parameters with wavelength (except for the axis ratio, which grows with wavelength in 46% of the sample). Using a clustering algorithm, we find two different classes of star-forming galaxies: A more compact, redder, and high-n (class A) and a more extended, bluer and lower-n one (class B). This separation holds across all seven bands analyzed. In addition, we find evidence that the first class is more spheroidal-like (according to the distribution of observed axis ratios). We compute the color gradients of the host galaxies finding that 48% of the objects where the analysis could be performed show negative gradients, and only in 5% they are positive. The host component of low-mass star-forming galaxies at z<0.36 separates into two different classes, similar to what has been found for their higher mass counterparts. The results are consistent with an evolution from class B to class A. Several mechanisms from the literature, like minor and major mergers, and violent disk instability, can explain the physical process behind the likely transition between the classes.
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