10.6.4 Completeness

We compare the completeness in different globular clusters with the expected HST completeness, after removing the duplicated sources. No other filtering was applied to the data. The HST magnitudes were converted to the G magnitudes using the relations of Jordi et al. (2010). The zero point of this transformation was adjusted for each cluster using a subset of bright stars in common, in order to avoid variations due to metallicity and interstellar extinction

Figures 10.50, 10.51, and 10.52 present the luminosity function (in HST and Gaia data) for three globulars at different level of crowding. In NGC 6656 the completeness is better than 80% down to G =17 and then drops to 0 at G =18; in NGC 6366 the completeness is around 90% even at 20.5. For NGC 5139 it is about 100% at G =14; 80% near G =15, drops around G =16, down to 0 at G =17.

Figure 10.50: Completeness for NGC 6656.
Figure 10.51: Same as Figure 10.50, for NGC 5139.
Figure 10.52: Same as Figure 10.50, for NGC 6366.

We computed the ratio of number of sources in different magnitude bins, in the inner (inside 0.5 arcmin) and outer (0.5 to 2.2 arcmin) regions of each GC. An example is shown for NGC 6121 (M4) in Figure 10.53. The result for all GCs is presented in Table 10.6. The content of this Table is also presented Figure 10.54, where the double dependence on magnitude and local density can be clearly seen. The completeness of the Gaia DR2 Catalogue is, overall, higher than it was in Gaia DR1.

Figure 10.53: Completeness level with respect to HST data in the inner (within 0.5 arcmin) and outer region of the cluster (from Arenou et al. 2018).
Figure 10.54: Completeness levels in different regions of 26 globular clusters with different local density, showing the influence of crowding on the completeness (from Arenou et al. 2018).
Table 10.6: Completeness level (in percentage with respect to HST fields) in various magnitude ranges, in the inner and outer regions of 26 globular clusters (inner: within 0.5 arcmin; outer: 0.5 to 2.2 arcmin)
name region G
11 – 13 12 – 14 13 – 15 14 – 16 15 – 17 16 – 18 17 – 19 18 – 20 19 – 21 20 – 22
LYN07 inner 56 33 18 5 1
LYN07 outer 54 50 35 24 9 2
NGC0104 inner 23 2 0 0 0 0 0 0 0 0
NGC0104 outer 85 55 43 21 7 1 0 0 0 0
NGC0288 inner 60 40 15 1
NGC0288 outer 100 85 79 70 54 28 6
NGC1261 inner 77 55 37 10 1 0 0
NGC1261 outer 100 96 89 62 30 11 2
NGC1851 inner 40 29 14 3 0 0 0 0
NGC1851 outer 100 86 61 34 14 5 1
NGC2298 inner 86 67 30 10 3 0
NGC2298 outer 97 90 83 62 36 10
NGC4147 inner 52 29 12 3 1
NGC4147 outer 94 78 63 27 7
NGC5053 inner 78 44 13
NGC5053 outer 100 94 82 46 13
NGC5139 inner 1 1 0 0 0 0 0 0
NGC5139 outer 43 11 5 2 1 0 0 0 0 0
NGC5272 inner 69 44 27 6 0 0 0 0
NGC5272 outer 100 99 86 75 45 17 6 1 0
NGC5286 inner 52 33 13 4 0 0 0 0
NGC5286 outer 86 83 69 51 25 6 1 0
NGC5466 inner 69 31 7
NGC5466 outer 100 99 100 86 48 12
NGC5927 inner 52 37 24 2 0 0 0
NGC5927 outer 81 75 75 60 28 6 1 0
NGC5986 inner 59 34 14 2 0 0 0
NGC5986 outer 90 88 81 61 34 10 2 0
NGC6121 inner 66 54 38 20 5 0 0
NGC6121 outer 95 92 85 79 66 48 25 7 0
NGC6205 inner 68 42 15 1 0 0 0 0
NGC6205 outer 89 92 92 80 56 25 7 2 0 0
NGC6366 inner 69 55 32 9
NGC6366 outer 91 90 81 79 69 42 11
NGC6397 inner 62 49 28 11 2 0 0 0
NGC6397 outer 95 89 82 72 56 33 12 2 0
NGC6656 inner 53 38 11 1 0 0 0 0
NGC6656 outer 75 75 69 61 41 10 1 0 0 0
NGC6752 inner 62 37 18 6 1 0 0 0 0
NGC6752 outer 98 94 78 57 32 13 3 0 0
NGC6779 inner 63 43 16 2 0 0
NGC6779 outer 94 87 82 76 56 30 13 2
NGC6809 inner 48 20 4 0 0
NGC6809 outer 100 96 84 66 37 11 1 0
NGC6838 inner 67 54 31 8 1
NGC6838 outer 91 89 72 80 74 56 28 5
NGC7099 inner 47 34 11 2 0 0 0
NGC7099 outer 94 80 66 38 17 5 1
PAL01 inner 73 39
PAL01 outer 67 21
PAL02 inner 84 62 24 7
PAL02 outer 92 89 47 14