1 Introduction

Circumnuclear rings of star formation have been shown to occur in barred spiral galaxies since the early 1980s (e.g. Benedict 1980) and they have been studied in great detail in many galaxies since this pioneering work (e.g. Knapen 1996; Knapen et al. 1999). They are thought to be a result of a funneling of material to the central regions of the galaxies by a bar potential. Indeed, hydrodynamical simulations of galaxies have shown that gaseous material is shocked at the leading edge of a bar and diverted towards the centre of the galaxy (Roberts et al. 1979). The material can then accumulate at the inner Lindblad resonance (ILR) until it reaches a critical density at which star formation can be induced.

The spiral galaxy, Messier 74 (NGC 628), is classed as a non-barred spiral galaxy (its Hubble classification is SAc - de Vaucouleurs et al. 1991). However, a circumnuclear ring of star formation does exist in the central regions of M 74. This has been observed in ¹²CO J=1-0 sub-mm imaging (Wakker & Adler 1995) and 2.3 $\mu$m CO absorption spectroscopy (James & Seigar 1999). Is it therefore possible that a bar-like structure exists in the centre of M 74, but is shrouded in dust? One way to answer this question is to observe M 74 at near-infrared wavelengths. The first demonstration that bars are more common in the near-infrared was performed by Hackwell & Schweizer(1983). Since then, this method has proved successful for uncovering bars in spiral galaxies in many cases (e.g. Seigar & James 1998; Eskridge et al. 2000). In this paper we present I, J and K band images of M 74, the longest wavelength images available, in order to uncover a bar in its centre.

This paper is arranged as follows: Sect. 2 describes the observations; Sect. 3 is a discussion of the results presented in this paper; in Sect. 4 we summarise our main results.