Structure of the Galactic gas at high latitudes: Observations

Details Structure of the Galactic gas at high latitudes: Observations Structure of the Galactic gas at high latitudes: Observations

Nov 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999astl...25..712g&link_type=abstract

Astronomy Letters, Volume 25, Issue 11, November 1999, pp.712-717

Astronomy and Astrophysics

Astronomy

1

Scientific paper

The angular structure of the interstellar neutral-hydrogen emission at 21 cm is studied at declinations of +5, +16, +25.7, +39, and +50 deg in the range of right ascensions 10^h to 16^h (at Galactic latitudes from +45 deg to +90 deg) using the RATAN-600 radio telescope with a mean beamwidth of 2.0x20 arcmin. The frequency resolution is 30 kHz (6.3 km/s), and the rms noise fluctuations are 0.1 K. The large-scale structure of the gas at high latitudes is eliminated by means of a high-pass filter. The angular-frequency spectrum of the interstellar neutral-hydrogen emission is calculated in each spectral channel by using the standard FFT software and smoothed over 1^h in right ascension. The Galactic-latitude dependence of the mean parameters for the distribution of HI line emission over the sky (the HI column density and the dispersion of fluctuations in antenna temperature) is found to generally correspond to the gas distribution as a plane layer. In the region 11^h < alpha < 13^h and 27 deg < delta < 39 deg, the gas column density is lower than 1.5 x 1019 cm^{-2}, i.e., below the instrumental sensitivity level. The power spectrum of the angular fluctuations in the region studied in the range of angular periods 10 arcmin to 6 deg is a power-law spectrum with an exponent from 3 to 0.7; in general, as the HI column density decreases, the fluctuation spectrum of the interstellar-gas emission becomes flatter.

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