A B S T R A C TWe investigate the evolution of the metallicity of the intergalactic medium (IGM) with particular emphasis on its spatial distribution. We propose that metal enrichment occurs as a two-step process. First, supernova (SN) explosions eject metals into relatively small regions confined to the surroundings of star-forming galaxies. From a comprehensive treatment of blowout we show that SN by themselves fail by more than one order of magnitude to distribute the products of stellar nucleosynthesis over volumes large enough to pollute the whole IGM to the metallicity levels observed. Thus, an additional (but as yet unknown) physical mechanism must be invoked to mix the metals on scales comparable to the mean distance between the galaxies that are most efficient pollutants. From this simple hypothesis we derive a number of testable predictions for the evolution of the IGM metallicity. Specifically, we find that: (i) the fraction of metals ejected over the starformation history of the Universe is about 50 per cent at z 0; that is, approximately half of the metals today are found in the IGM; (ii) if the ejected metals were homogeneously mixed with the baryons in the Universe, the average IGM metallicity would be kZl V ej Z aV b . 1a25Z ( at z 3X However, due to spatial inhomogeneities, the mean of the distribution of metallicities in the diffusive zones has a wide (more than 2 orders of magnitude) spread around this value; (iii) if metals become more uniformly distributed at z & 1Y as assumed, at z 0 the metallicity of the IGM is narrowly confined within the range Z < 0X1^0X03Z ( X Finally, we point out that our results can account for the observed metal content of the intracluster medium.

Using idealized 1-D Eulerian hydrodynamic simulations, we contrast the behavior of isolated supernovae with the superbubbles driven by multiple, collocated supernovae. Continuous energy injection via successive supernovae going off within the hot/dilute bubble maintains a strong termination shock. This strong shock keeps the superbubble over-pressured and drives the outer shock well after it becomes radiative. Isolated supernovae, in contrast, with no further energy injection, become radiative quite early ( ∼ < 0.1 Myr, 10s of pc), and stall at scales ∼ < 100 pc. We show that isolated supernovae lose almost all of their mechanical energy by a Myr, but superbubbles can retain up to ∼ 40% of the input energy in form of mechanical energy over the lifetime of the star cluster (few 10s of Myr). These conclusions hold even in the presence of realistic magnetic fields and thermal conduction. We also compare various recipes for implementing supernova feedback in numerical simulations. For various feedback prescriptions we derive the spatial scale below which the energy needs to be deposited for it to couple to the interstellar medium (ISM). We show that a steady thermal wind within the superbubble appears only for a large number ( ∼ > 10 4 ) of supernovae. For smaller clusters we expect multiple internal shocks instead of a smooth, dense thermalized wind.

HD molecules can be an important cooling agent of the primordial gas behind the shock waves originated through mergings of the dark matter haloes at epochs when first luminous objects were to form. We study the necessary conditions for the HD cooling to switch on in the low temperature range $T<200$ K. We show that these conditions are fulfiled in merging haloes with the total (dark matter and baryon) mass in excess of $M_{\rm cr}\sim 10^7[(1+z)/20]^{-2}\msun$. Haloes with masses $M>M_{\rm cr}$ may be the sites of low-mass star formation.Comment: 9 pages, 7 figures, corrected version, accepted in MNRA

This paper describes outstanding issues in astrophysics and cosmology that can be solved by astronomical observations in a broad spectral range from far infrared to millimeter wavelengths. The discussed problems related to the formation of stars and planets, galaxies and the interstellar medium, studies of black holes and the development of the cosmological model can be addressed by the planned space observatory Millimetron (the "Spectr-M" project) equipped with a cooled 10-m mirror. Millimetron can operate both as a single-dish telescope and as a part of a space-ground interferometer with very long baseline.

Using hydrodynamic simulations, we study the mass loss due to supernova-driven outflows from Milky Way type disk galaxies, paying particular attention to the effect of the extended hot halo gas. We find that the total mass loss at inner radii scales roughly linearly with total mass of stars formed, and that the mass loading factor at the virial radius can be several times its value at inner radii because of the swept up hot halo gas. The temperature distribution of the outflowing material in the inner region (∼10 kpc) is bimodal in nature, peaking at 10 5 K and 10 6.5 K, responsible for optical and X-ray emission, respectively. The contribution of cold/warm gas with temperature 10 5.5 K to the outflow rate within 10 kpc is ≈ 0.3-0.5. The warm mass loading factor, η 3e5 (T 3 × 10 5 K) is related to the mass loading factor at the virial radius (η v ) as η v ≈ 25 η 3e5 SFR/M ⊙ yr −1 −0.15 for a baryon fraction of 0.1 and a starburst period of 50 Myr. We also discuss the effect of multiple bursts that are separated by both short and long periods. The outflow speed at the virial radius is close to the sound speed in the hot halo, 200 km s −1 . We identify two 'sequences' of outflowing cold gas at small scales: a fast (≈ 500 km s −1 ) sequence, driven by the unshocked free-wind; and a slow sequence (≈ ±100 km s −1 ) at the conical interface of the superwind and the hot halo.