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Motivated by recent observation of Lanzetta et al. that most luminousgalaxies at low redshifts produce $\lya$ absorption at impact parameter $l\lsim160 \kpch$, we propose that these absorbers are clouds confined by the pressureof ambient hot gas in galactic haloes. We determine the properties of this hotgas and of the absorption systems on the basis of observational and theoreticalconstraints. The absorbing clouds need to be replenished on about one orbitaltime ($\sim 10^9$ yrs) in the galactic halo. The pressure and temperature ofthe gas at radius $r\sim 100\kpc$ are $P=(10-100){\rm cm^{-3} K}$,$T=10^{(5.5-6.5)}{\rm K}$. The model requires that about 10 per cent of the gasin low-redshift galactic haloes is in the hot phase. Such gas in galactichaloes emits x-ray with bolometric luminosity of the order $10^{37-40}{\rmerg\,s^{-1}}$. The plausibility for such gas to exist in current models ofgalaxy formation is discussed.Comment: 14 pages,1 figure,uuencoded,compressed,ps file,accepted by MNRA

Lyman absorption at low redshifts and hot gas in galactic haloes