1998A&AS..128..545R

In this work we study the galaxy NGC 4736, using narrow band interference filters imaging centered at the emission lines [OII]_{λλ3727+3729}, Hβ, [OIII]_λ5007, Hα, [SII]_λ6716+6730 and [SIII]_λ9070 and nearby continua. We have obtained sizes, positions, emission line absolute fluxes, and continua intensities for 90 HII regions, mainly distributed in a ring-like structure of 3.2kpc in diameter. The Hα luminosities are in the range 37.3≤log(L_Hα)≤39.4erg/s. The HII regions size distribution presents a characteristic diameter D₀=115pc and verifies the relation log(L_Hα)∝D³. The temperature of the ionizing sources and the metallicity of the HII regions are respectively in the ranges 3.4x10⁴≲T_*≲4.0x10⁴K and 8.5≲12+log(O/H)≲9.3. The masses of the ionizing clusters are in the range 5x10³≲M_T/M_☉≲2x10⁵. The continua radial surface brightness distribution is better fitted by the superposition of a de Vaucouleurs', a thin and a thick exponential disk laws. The monochromatic colors show that outside the star forming ring the disk presents a younger stellar population than inside it.