Thursday

We developed an ultra-long wavelength (or ultra-low frequency) radio sky model that is valid down to ~1 MHz. We take into account the free-free absorption by Galactic ISM. This absorption becomes obvious at ~ 10 MHz and would significantly change the sky morphology, and make the global radio spectrum turn over at ~ 3MHz. We find that at ultra-long wavelength the Galactic plane is darker than high Galactic latitude regions, in contrast to the sky at higher frequencies, and there are huge shadows of the spiral arms on the sky map. Currently the radio sky below 10 MHz is still largely unknown, our model would be useful for designing the future ultra-long wavelength observations, for example the upcoming lunar-orbit or lunar-surface based array.