1 Introduction

On the basis of luminosity alone, it is not possible to conclude whether or not star formation occurs in a burst. The FIR to blue luminosity ratio $L_{\rm fir}$/$L_{\rm B}$ provides a qualitative measure of the current star formation rate, and it may be strongly affected by extinction, while the gas emission in mm wavelengths is not affected by extinction.

It is well established that in luminous IR galaxies the star formation indicators, such as $L_{\rm fir}$/$L_{\rm B}$ or the flux density ratio at 60 and 100 microns f60/f100 are better correlated with the molecular hydrogen than with the atomic hydrogen content (e.g. Young et al. 1989). The ratio $L_{\rm fir}$/ $M_{\rm H_2}$, where $M_{\rm H_2}$denotes the molecular hydrogen mass, is usually interpreted as an indicator of efficiency of star formation (SFE) in galaxies. The SFE is independent of the Hubble type (Devereux & Young 1991; Young et al. 1996) but depends on the environment of a galaxy (Sanders et al. 1991; Combes et al. 1994; Young et al. 1996). This dependence is more pronounced in interacting galaxies rather than in isolated ones. For the IR-bright galaxies, there is a linear relation between $\element{H}_{2}$ and the dust content with SFE depending on the dust temperature of the warm component (Young et al. 1989). However, when longer wavelengths (mm range) were used in determining the dust content in IRAS-Mkn galaxies (Chini et al. 1992a), a strong correlation between $L_{\rm fir}$/ $M_{\rm gas}$ and temperature of the cold dust was found. According to Andreani et al. (1995), the cold dust emission is associated with both the molecular and atomic hydrogen phases.

The CO line area is used to estimate the $\element{H}_{2}$ gas mass of a galaxy. The line shape and line width of the CO emission involve information on distribution and kinematics of the gas (Krugel et al. 1990; Chini et al. 1992b).

Since molecular gas appears to play a critical role in the star formation process, it is of great importance to perform CO observations for galaxies, in particular for those with active starbursts.

Markarian galaxies exhibit a variety of activities, from starburst to nuclear, and this sample is one of the most suitable samples for investigation of the gas properties and the starburst phenomenon in galaxies. Using available HI, $\element{H}_{2}$, optical and radio continuum data, we have analyzed the gas kinematics and the star formation properties of 61 Mkn galaxies. How do the gas properties of galaxies with UV- and non-UV-excess compare?

The value of the Hubble constant equal to 75 $\mbox{km}~$s^-1 Mpc^-1 is adopted throughout this paper. Section 2 presents a sample of 61 Markarian galaxies detected in the CO(1-0) line. In Sect. 3, the gas-luminosity relations are discussed. The results obtained are discussed in the final section.