# UVI colour gradients of 0.4<z<1.4 star-forming main sequence galaxies in CANDELS: dust extinction and star formation profiles

## TL;DR

This study uses UV and optical colour profiles to analyze dust, gas, and star formation distributions in star-forming galaxies at redshifts 0.4 to 1.4, revealing mass-dependent gradients and the dominant role of dust.

## Contribution

It introduces a new UVI calibration method for radial colour profiles, enabling detailed analysis of dust and star formation distributions in high-redshift galaxies.

## Key findings

- Dust extinction profiles are shallower than stellar mass profiles.
- sSFR gradients are mostly flat, with central declines in massive galaxies.
- Dust content remains high in galaxy outskirts despite low stellar densities.

## Abstract

This paper uses radial colour profiles to infer the distributions of dust, gas and star formation in z=0.4-1.4 star-forming main sequence galaxies. We start with the standard UVJ-based method to estimate dust extinction and specific star formation rate (sSFR). By replacing J with I band, a new calibration method suitable for use with ACS+WFC3 data is created (i.e. UVI diagram). Using a multi-wavelength multi-aperture photometry catalogue based on CANDELS, UVI colour profiles of 1328 galaxies are stacked in stellar mass and redshift bins. The resulting colour gradients, covering a radial range of 0.2--2.0 effective radii, increase strongly with galaxy mass and with global $A_V$. Colour gradient directions are nearly parallel to the Calzetti extinction vector, indicating that dust plays a more important role than stellar population variations. With our calibration, the resulting $A_V$ profiles fall much more slowly than stellar mass profiles over the measured radial range. sSFR gradients are nearly flat without central quenching signatures, except for $M_*>10^{10.5} M_{\odot}$, where central declines of 20--25 per cent are observed. Both sets of profiles agree well with previous radial sSFR and (continuum) $A_V$ measurements. They are also consistent with the sSFR profiles and, if assuming a radially constant gas-to-dust ratio, gas profiles in recent hydrodynamic models. We finally discuss the striking findings that SFR scales with stellar mass density in the inner parts of galaxies, and that dust content is high in the outer parts despite low stellar-mass surface densities there.