tokens: the cooling time depends on the gas density, it is expected to vary according to location. This is clearly visible in the top panel of Fig. 16 , where the spherically averaged temperature profiles of galaxies only models are plotted. Here, the temperature in the inner part of the H ii region is lower than the gas temperature immediately behind the I-front, 11 and the spread is large (see the difference in the spread in the temperaturedensity relation inside H ii regions shown in Figs 13 and 17 ). Figure 16. Spherically averaged temperature profiles of galaxies only models (top panel) GAL_0.5R (blue dotted line), GAL_R (black solid), GAL_2R (red dashed), and galaxiesQSO models (bottom panel) GAL_0.5RQSO_UVXsec (blue dotted), GAL_RQSO_UVXsec (black solid), GAL_2RQSO_UVXsec (red dashed). The shaded regions indicate the 1 scatter around the mean. Figure 17. Temperaturedensity diagram for galaxies only models GAL_0.5R, GAL_R, GAL_2R and galaxiesQSO models GAL_0.5RQSO_UVXsec, GAL_RQSO_UVXsec, GAL_2RQSO_UVXsec. The red (blue) colour indicates the H ii (H i ) regions defined as cells with (0.5). The contours are overlaid as a guide. To emphasize the temperaturedensity relation both in H ii and H i regions, two different y -axis scales are used. On the other hand, the thermal structure in the neutral regions is nearly identical in all galaxies only models, as, similarly to Section 4.1 , hydrodynamical processes, and not UV photons, are responsible for controlling the temperature in the neutral gas. 4.3.2 Heating by galaxies and a QSO Fig. 15 shows that as the QSO increases the extent of the fully ionized region, the radius at which the gas is heated to 10 4 K is larger than in the corresponding galaxies only models. However, both the average profiles (Fig. 16 ) and the overall temperaturedensity relations (Fig. 17 ) are similar to those of the corresponding galaxies only models. This indicates that a QSO plays a small role in controlling the thermal state in the inner parts of the H ii region, where the pre-existing galaxies have ionized the IGM before the QSO activity. On the other hand, the top panels in Fig. 17 show that galaxiesQSO models reach temperatures that are typically higher than those in the corresponding galaxies only models. The differences become less evident with increasing ionizing emissivity from the galaxies (from left to right in the three rightmost panels). The reason for this is that when both the H ii and He iii I-fronts from the QSO are larger than the pre-existing H ii region due to galaxies, the gas experiences the highest heating. However, when only the H ii I-front from the QSO is larger than the pre-existing H ii region (but the QSO He iii I-front is still inside it), the portion of the gas newly heated up by H i photoionization of a QSO has not yet undergone QSO-driven He ii photoionization. This lack of He ii photoionization by the QSO results in a slightly lower temperature. This non-linear heating process, which
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