Cooling flow

About: Cooling flow is a research topic. Over the lifetime, 1452 publications have been published within this topic receiving 72353 citations.

Cooling Functions for Low-Density Astrophysical Plasmas

Abstract: The cooling functions for a plasma slab are investigated under equilibrium and nonequilibrium conditions, over a range of 10 4 -10 85 K and for a range of abundances Radiative transfer and diffuse field are calculated in the isobaric nonequilibrium models using a one-dimensional cooling flow model, and the plasma is not assumed to be optically thin to all radiation Limiting cases of the plasma diffuse field coupling are calculated, and the resulting cooling functions are presented Some functions are terminated before reaching 10 4 K when the internal photoionization halts the cooling The functions represent a self-consistent set of curves covering a wide grid of temperature and metallicities using recently published atomic data and processes

How do galaxies get their gas

Abstract: Not the way one might have thought. In hydrodynamic simulations of galaxy formation, some gas follows the traditionally envisioned route, shock heating to the halo virial temperature before cooling to the much lower temperature of the neutral ISM. But most gas enters galaxies without ever heating close to the virial temperature, gaining thermal energy from weak shocks and adiabatic compression, and radiating it just as quickly. This “cold mode” accretion is channeled along filaments, while the conventional, “hot mode” accretion is quasi-spherical. Cold mode accretion dominates high redshift growth by a substantial factor, while at z < 1 the overall accretion rate declines and hot mode accretion has greater relative importance. The decline of the cosmic star formation rate at low z is driven largely by geometry, as the typical cross section of filaments begins to exceed that of the galaxies at their intersections.

Cooling Flows in Clusters of Galaxies

Abstract: The cooling time in the dense gas within 50 – 300 kpc of the central galaxy in most clusters is found from X-ray images to be less than about 1010 yr. The weight of the overlying gas then causes a net inflow which is called a cooling flow. X-ray spectra confirm that the gas is cooling and loses at least 90 per cent of its thermal energy. The rate at which the gas cools ranges from ~ 10 – 500 M⊙ yr−1 . The soft X-ray absorption now discovered in cooling flows suggests that the cooled gas accumulates as very cold, small, gas clouds. Any large-scale star formation must be biased to low mass objects, except in the centres of some flows where some massive star may form, possibly from larger clouds assembled from cloud collisions and aggregation.

Galaxies in a simulated ΛCDM Universe – I. Cold mode and hot cores

Abstract: We study the formation of galaxies in a large volume (50 h −1 Mpc, 2 × 288 3 particles) cosmological simulation, evolved using the entropy and energy-conserving smoothed particle hydrodynamics (SPH) code GADGET-2. Most of the baryonic mass in galaxies of all masses is originally acquired through filamentary ‘cold mode’ accretion of gas that was never shock heated to its halo virial temperature, confirming the key feature of our earlier results obtained with a different SPH code. Atmospheres of hot, virialized gas develop in haloes above 2–3 × 10 11 M � , a transition mass that is nearly constant from z = 3 to 0. Cold accretion persists in haloes above the transition mass, especially at z ≥ 2. It dominates the growth of galaxies in low-mass haloes at all times, and it is the main driver of the cosmic star formation history. Our results suggest that the cooling of shock-heated virialized gas, which has been the focus of many analytic models of galaxy growth spanning more than three decades, might be a relatively minor element of galaxy formation. At high redshifts, satellite galaxies have gas accretion rates similar to central galaxies of the same baryonic mass, but at z < 1t he accretion rates of low-mass satellites are well below those of comparable central galaxies. Relative to our earlier simulations, the GADGET-2 simulations predict much lower rates of ‘hot mode’ accretion from the virialized gas component. Hot accretion rates compete with cold accretion rates near the transition mass, but only at z ≤ 1. Hot accretion is inefficient in haloes

Galaxies in a simulated $\Lambda$CDM Universe I: cold mode and hot cores

Abstract: We study the formation of galaxies in a (50 Mpc/h)^3 cosmological simulation (2x288^3 particles), evolved using the entropy conserving SPH code Gadget-2. Most of the baryonic mass in galaxies of all masses is originally acquired through filamentary "cold mode" accretion of gas that was never shock heated to its halo virial temperature, confirming the key feature of our earlier results obtained with a different SPH code (Keres et al. 2005). Atmospheres of hot, virialized gas develop in halos above ~2.5e11 Msun, a transition mass that is nearly constant from z=3 to z=0. Cold accretion persists in halos above the transition mass, especially at z>=2. It dominates the growth of galaxies in low mass halos at all times, and it is the main driver of the cosmic star formation history. Satellite galaxies have accretion rates similar to central galaxies of the same baryonic mass at high redshifts, but they have less accretion than comparable central galaxies at low redshift. Relative to our earlier results, the Gadget-2 simulations predict much lower rates of "hot mode" accretion from the virialized gas component of massive halos. At z<=1, typical hot accretion rates in halos above 5e12 Msun are below 1 Msun/yr, even though our simulation does not include AGN heating or other forms of "preventive" feedback. The inner density profiles of hot gas in these halos are shallow, with long associated cooling times. The cooling recipes typically used in semi-analytic models can overestimate the accretion rates in these halos by orders of magnitude, so such models may overemphasize the role of preventive feedback in producing observed galaxy masses and colors. A fraction of the massive halos develop cuspy profiles and significant cooling rates between z=1 and z=0, a redshift trend similar to the observed trend in the frequency of cooling flow clusters.