Content
This site contains videos and downloadable tables of cooling rates presented in the following paper:Abstract
Radiative cooling is central to a wide range of astrophysical problems. Despite its importance, cooling rates are generally computed using very restrictive assumptions. We investigate the effects of photo-ionization of heavy elements by the meta-galactic UV/X-ray background and of variations in relative abundances on the cooling rates of optically thin gas in ionization equilibrium. We find that photo-ionization by the meta-galactic background radiation reduces the cooling rates by up to an order of magnitude for gas densities and temperatures typical of the shock-heated intergalactic medium and proto-galaxies. In addition, photo-ionization changes the relative contributions of different elements to the cooling rates. We conclude that photo-ionization by the ionizing background and heavy elements both need to be taken into account in order for the cooling rates to be correct to order of magnitude. Moreover, if the rates need to be known to better than a factor of a few, then departures of the relative abundances from solar need to be taken into account. We propose a method to compute cooling rates on an element-by-element basis by interpolating pre-computed tables that take photo-ionization into account. We provide such tables for a popular model of the evolving UV/X-ray background radiation, computed using the photo-ionization package CLOUDY.
Movies showing how various factors impact cooling rates
The first thing we show is how the cooling rates depend on density at a fixed redshift. For this example we take redshift 3 and solar metallicity. As the density decreases, the contribution from hydrogen is suppressed at low densities as it becomes ionized. As density decreases further, helium, and then heavier elements become ionized until finally inverse Compton cooling off the cosmic microwave background (CMB) dominates.
| Density dependence, z = 3 |
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| Click title for downloadable (.avi) version. Click square in the lower right hand corner for full screen. |
Next we show how the cooling rates depend on redshift. There are two redshift-dependent parameters in our calculations. One of them is the Haardt and Madau (2001) UV/X-ray radiation background from quasars and galaxies which peaks at a redshift of about 2. The other is Compton cooling off the CMB which decreases with decreasing redshift.
We show the redshift dependence for a proper hydrogen density of 0.0001 cm-3 and solar metallicity.
| Redshift dependence, nH = 0.0001 cm-3 |
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| Click title for downloadable (.avi) version. Click square in the lower right hand corner for full screen. |
Below we also show the redshift dependence at a constant overdensity of 10 for solar metallicity.
| Redshift dependence, &delta = 10 |
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| Click title for downloadable (.avi) version. Click square in the lower right hand corner for full screen. |
To show the importance of the composition of the gas, we evolve the metallicity from [Z] = -3.0 to 1.0 for a proper hydrogen density of 0.0001 cm-3 at z = 3.
| Metallicity dependence, z = 3, nH = 10-4cm-3 |
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| Click title for downloadable (.avi) version. Click square in the lower right hand corner for full screen. |
Downloadable Tables
Cooling rates computed using CLOUDY version 07.02 for the Haardt and Madau (2001) UV/X-ray background from quasars and galaxies
Click here to download the complete set of low resolution tables (36MB, 61MB unpacked).
Click here to download the complete set of high resolution tables (133MB, 232MB unpacked).
Click here to download only the redshift z = 0 low resolution table (0.7MB, 1.2MB unpacked).
Click here to download only the redshift z = 0 high resolution table (2.7MB, 4.6MB unpacked).
Click here to download only the collisional ionization equilibrium table in text file format (106KB).
Click here for a set of sample idl computation routines (5.5KB, 68KB unpacked).
WB note - Tables and routines altered to include reference and slightly better documentation. Cosmetic changes only (2010/04/23)