Star formation efficiency in the Barred Spiral Galaxy NGC 4303

TL;DR

This study measures star formation efficiency in NGC 4303, revealing higher activity in spiral arms than in the bar, and discusses how spatial resolution affects the applicability of the Kennicutt-Schmidt law.

Contribution

It provides high-resolution measurements of molecular gas and star formation in NGC 4303, highlighting differences between spiral arms and the bar, and examines resolution effects on the Kennicutt-Schmidt law.

Findings

Star formation efficiency is twice as high in spiral arms compared to the bar.

The Kennicutt-Schmidt law breaks down at 250 pc resolution.

Smoothing to 500 pc recovers the law with increased scatter.

Abstract

We present new $^{12}$CO(J=1-0) observations of the barred galaxy NGC 4303 using the Nobeyama 45m telescope (NRO45) and the Combined Array for Research in Millimeter-wave Astronomy (CARMA). The H$\alpha$ images of barred spiral galaxies often show active star formation in spiral arms, but less so in bars. We quantify the difference by measuring star formation rate and efficiency at a scale where local star formation is spatially resolved. Our CO map covers the central 2$\farcm$3 region of the galaxy; the combination of NRO45 and CARMA provides a high fidelity image, enabling accurate measurements of molecular gas surface density. We find that star formation rate and efficiency are twice as high in the spiral arms as in the bar. We discuss this difference in the context of the Kennicutt-Schimidt (KS) law, which indicates a constant star formation rate at a given gas surface density. The KS law breaks down at our native resolution ($\sim$ 250 pc), and substantial smoothing (to 500 pc) is necessary to reproduce the KS law, although with greater scatter.