2.5. Summary of the Low Redshift Budget
Our estimates of the baryon budget at low redshift, expressed as fractions of the critical Einstein-de Sitter value, are listed in lines 1 to 7 in Table 3. We rewrite the Hubble constant from equation (1) as H_{0} = 70h_{70} km s^{-1} Mpc^{-1} to center it on a more likely value. The central values in the table are computed from the central values of the parameters entering the estimate. An upper bound is obtained by systematically choosing each parameter at the end of its reasonable-looking range that maximizes the contribution to the mean mass density, and likewise for the lower bound.
Line 7a is an estimate of the X-ray-detected plasma around groups (eq. [29]), line 7b is an estimate of the cooler component detected by resonance Lyman absorption in the trace HI fraction (eq. [31]), and the sum is an estimate of the plasma associated with groups of galaxies. Both entries are quite uncertain, and may well have missed a substantial amount of cool plasma. Consistent with this, the entry in line 7' from the scaling from the plasma mass in clusters of galaxies (eq. [32]) is larger. We suspect line 7' is more reliable than the sum of lines 7a and 7b. In the sums over the budget we use line 7' for the maximum and central values, and lines 7a and 7b instead of 7' for the minimum.
Component | Central | Maximum | Minimum | Grade ^{a} |
Observed at z 0 | ||||
1. Stars in spheroids | 0.0026 h_{70}^{-1} | 0.0043 h_{70}^{-1} | 0.0014 h_{70}^{-1} | A |
2. Stars in disks | 0.00086 h_{70}^{-1} | 0.00129 h_{70}^{-1} | 0.00051 h_{70}^{-1} | A- |
3. Stars in irregulars | 0.000069 h_{70}^{-1} | 0.000116 h_{70}^{-1} | 0.000033 h_{70}^{-1} | B |
4. Neutral atomic gas | 0.00033 h_{70}^{-1} | 0.00041 h_{70}^{-1} | 0.00025 h_{70}^{-1} | A |
5. Molecular gas | 0.00030 h_{70}^{-1} | 0.00037 h_{70}^{-1} | 0.00023 h_{70}^{-1} | A- |
6. Plasma in clusters | 0.0026 h_{70}^{-1.5} | 0.0044 h_{70}^{-1.5} | 0.0014 h_{70}^{-1.5} | A |
7a. Warm plasma in groups | 0.0056 h_{70}^{-1.5} | 0.0115 h_{70}^{-1.5} | 0.0029 h_{70}^{-1.5} | B |
7b. Cool plasma | 0.002 h_{70}^{-1} | 0.003 h_{70}^{-1} | 0.0007 h_{70}^{-1} | C |
7'. Plasma in groups | 0.014 h_{70}^{-1} | 0.030 h_{70}^{-1} | 0.0072 h_{70}^{-1} | B |
8. Sum (at h = 70 and z 0) | 0.021 | 0.041 | 0.007 | ... |
Gas components at z 3 | ||||
9. Damped absorbers | 0.0015 h_{70}^{-1} | 0.0027 h_{70}^{-1} | 0.0007 h_{70}^{-1} | A- |
10. Lyman- forest clouds | 0.04 h_{70}^{-1.5} | 0.05 h_{70}^{-1.5} | 0.01 h_{70}^{-1.5} | B |
11. Intercloud gas (HeII) | ... | 0.01 h_{70}^{-1.5} | 0.0001 h_{70}^{-1} | B |
Abundances of: | ||||
12. Deuterium | 0.04 h_{70}^{-2} | 0.054 h_{70}^{-2} | 0.013 h_{70}^{-2} | A |
13. Helium | 0.010 h_{70}^{-2} | 0.027 h_{70}^{-2} | ... | A |
14. Nucleosynthesis | 0.020 h_{70}^{-2} | 0.027 h_{70}^{-2} | 0.013 h_{70}^{-2} | ... |
^{a} Confidence of evaluation, from A (robust) to C (highly uncertain). |
The true values for each line are not likely to be close to the maximum in all entries, or close to the minima in all entries, but we retain the whole range in quoting the sums in each column in line 8 because the sums are dominated by a few entries.
At h_{70} = 1 our estimate of the baryons in stars and remnants is = 0.0035^{+0.0025}_{-0.0014} times the critical density. This star mass is only about 17% of our sum over all detected baryons. In our budget, in the 2.2µm K band, 26% of the light is from disk and irregular galaxies, in agreement with the fraction of the star mass. (We use < B - K > = 4.27 for ellipticals and bulges, and 2.78 for disks and irregulars). In the B band, 61% of the mean luminosity density is from disks and irregular galaxies. This component represents only about 25% of the star mass and only about 4% of our estimated sum of all observed baryons.