A possibility to observe synchronous emission of distant galaxies' ionized hydrogen by extended disks is discussed in this work. It is shown that the most preferred wavelength range from the viewpoint of observation success rate is decameter range on low frequency limit allowing for such observations: 3 MHz. It is shown that high brightness temperature of noise in this frequency range forces to consider only a possibility of interferometer observations. This mode allows to detect a signal from extended ionized galactic disks located within the Local Group. The work also provides an assessment of the capacity to measure the parameters of these disks by means of raying them with radiation from pulsars and measuring dispersion of signal.
Keywords: HII and HI regiones, synchrotron radiation, radio emission galaxies, brightness and noise temperature, radiointerferometry, decameters interferometer