<table><caption>**Table 5**
(Continued)</caption><thead><tr><th>Region</th><th>V<sub>s</sub><sup>a</sup><br>(km s<sup>-1</sup>)</th><th>Mass Flow (120 K)<sup>b</sup><br>(10<sup>2</sup> M<sub>☉</sub> yr<sup>-1</sup>)</th><th>t<sub>cool</sub>(120 K)<sup>c</sup><br>(10<sup>2</sup> yr)</th><th>M(120 K)(H<sub>2</sub>)<sup>d</sup><br>(10<sup>5</sup> M<sub>☉</sub>)</th><th>Mass Flow (50 K)<sup>b</sup><br>(10<sup>2</sup> M<sub>☉</sub> yr<sup>-1</sup>)</th><th>t<sub>cool</sub>(50 K)<sup>c</sup><br>(10<sup>2</sup> yr)</th><th>M(50 K)(H<sub>2</sub>)<sup>d</sup><br>(10<sup>5</sup> M<sub>☉</sub>)</th></tr></thead><tbody><tr><td>127</td><td>4.0</td><td>227.58 (18.20)</td><td>2.19</td><td>49.88 (3.99)</td><td>215.19 (17.15)</td><td>6.38</td><td>137.35 (10.94)</td></tr><tr><td></td><td>20.5</td><td>0.19 (0.03)</td><td>4.87</td><td>0.09 (0.01)</td><td>0.18 (0.03)</td><td>6.63</td><td>0.12 (0.02)</td></tr><tr><td>128</td><td>4.5</td><td>127.92 (4.50)</td><td>2.29</td><td>29.23 (1.03)</td><td>125.74 (4.43)</td><td>5.91</td><td>74.30 (2.61)</td></tr><tr><td></td><td>17.0</td><td>0.46 (0.04)</td><td>4.85</td><td>0.22 (0.02)</td><td>0.46 (0.04)</td><td>6.61</td><td>0.31 (0.03)</td></tr><tr><td>129</td><td>4.5</td><td>254.67 (4.93)</td><td>2.29</td><td>58.20 (1.13)</td><td>250.26 (4.84)</td><td>5.91</td><td>147.87 (2.86)</td></tr><tr><td></td><td>19.0</td><td>0.92 (0.03)</td><td>4.91</td><td>0.45 (0.02)</td><td>0.92 (0.03)</td><td>6.66</td><td>0.61 (0.02)</td></tr><tr><td>130</td><td>5.0</td><td>137.62 (2.12)</td><td>2.32</td><td>31.96 (0.49)</td><td>136.58 (2.10)</td><td>5.99</td><td>81.79 (1.26)</td></tr><tr><td></td><td>19.5</td><td>1.11 (0.03)</td><td>4.92</td><td>0.55 (0.01)</td><td>1.11 (0.03)</td><td>6.49</td><td>0.72 (0.02)</td></tr><tr><td>131</td><td>5.0</td><td>124.45 (2.08)</td><td>2.32</td><td>28.90 (0.48)</td><td>123.54 (2.06)</td><td>5.99</td><td>73.98 (1.23)</td></tr><tr><td></td><td>20.0</td><td>0.84 (0.03)</td><td>4.95</td><td>0.42 (0.01)</td><td>0.84 (0.03)</td><td>6.65</td><td>0.56 (0.02)</td></tr><tr><td>132</td><td>4.5</td><td>272.62 (4.81)</td><td>2.29</td><td>62.30 (1.10)</td><td>266.63 (4.73)</td><td>5.91</td><td>157.54 (2.80)</td></tr><tr><td></td><td>19.0</td><td>1.01 (0.03)</td><td>4.91</td><td>0.50 (0.01)</td><td>1.06 (0.03)</td><td>6.59</td><td>0.70 (0.02)</td></tr><tr><td>133</td><td>5.0</td><td>122.38 (2.30)</td><td>2.32</td><td>28.42 (0.53)</td><td>121.49 (2.28)</td><td>5.99</td><td>72.75 (1.36)</td></tr><tr><td></td><td>19.0</td><td>0.90 (0.03)</td><td>4.91</td><td>0.44 (0.01)</td><td>0.90 (0.03)</td><td>6.66</td><td>0.60 (0.02)</td></tr><tr><td>134</td><td>5.0</td><td>123.74 (2.26)</td><td>2.32</td><td>28.74 (0.53)</td><td>122.85 (2.25)</td><td>5.99</td><td>73.57 (1.34)</td></tr><tr><td></td><td>19.5</td><td>0.83 (0.03)</td><td>4.92</td><td>0.41 (0.01)</td><td>0.83 (0.03)</td><td>6.49</td><td>0.54 (0.02)</td></tr><tr><td>135</td><td>4.5</td><td>266.75 (3.83)</td><td>2.29</td><td>60.96 (0.88)</td><td>262.14 (3.77)</td><td>5.91</td><td>154.89 (2.23)</td></tr><tr><td></td><td>20.0</td><td>0.54 (0.03)</td><td>4.95</td><td>0.27 (0.02)</td><td>0.54 (0.03)</td><td>6.65</td><td>0.36 (0.02)</td></tr><tr><td>136</td><td>5.5</td><td>7.46 (1.24)</td><td>2.30</td><td>1.72 (0.29)</td><td>7.42 (1.23)</td><td>5.42</td><td>4.03 (0.67)</td></tr><tr><td></td><td>33.5</td><td>3.57 (0.76)</td><td>10.86</td><td>3.88 (0.83)</td><td>2.20 (0.47)</td><td>33.27</td><td>7.33 (1.56)</td></tr><tr><td>137</td><td>5.5</td><td>9.39 (1.29)</td><td>2.30</td><td>2.16 (0.30)</td><td>9.35 (1.28)</td><td>5.42</td><td>5.07 (0.70)</td></tr><tr><td></td><td>33.5</td><td>3.44 (0.76)</td><td>10.86</td><td>3.74 (0.83)</td><td>1.80 (0.40)</td><td>32.25</td><td>5.81 (1.29)</td></tr><tr><td>138</td><td>5.0</td><td>23.98 (1.75)</td><td>2.32</td><td>5.57 (0.41)</td><td>23.81 (1.74)</td><td>5.99</td><td>14.26 (1.04)</td></tr><tr><td></td><td>33.5</td><td>3.74 (0.75)</td><td>10.86</td><td>4.06 (0.82)</td><td>2.31 (0.47)</td><td>33.27</td><td>7.69 (1.55)</td></tr><tr><td>139</td><td>5.5</td><td>22.96 (1.36)</td><td>2.30</td><td>5.29 (0.31)</td><td>22.86 (1.35)</td><td>5.42</td><td>12.39 (0.73)</td></tr><tr><td></td><td>33.0</td><td>2.61 (0.61)</td><td>8.49</td><td>2.21 (0.52)</td><td>1.70 (0.40)</td><td>32.25</td><td>5.48 (1.29)</td></tr><tr><td>140</td><td>4.5</td><td>137.20 (4.94)</td><td>2.29</td><td>31.35 (1.13)</td><td>134.86 (4.86)</td><td>5.91</td><td>79.68 (2.87)</td></tr><tr><td></td><td>16.5</td><td>0.51 (0.04)</td><td>4.89</td><td>0.25 (0.02)</td><td>0.51 (0.04)</td><td>6.57</td><td>0.34 (0.03)</td></tr><tr><td>141</td><td>4.5</td><td>221.42 (4.67)</td><td>2.29</td><td>50.60 (1.07)</td><td>217.55 (4.59)</td><td>5.91</td><td>128.54 (2.71)</td></tr><tr><td></td><td>17.5</td><td>0.95 (0.04)</td><td>4.93</td><td>0.47 (0.02)</td><td>0.95 (0.04)</td><td>6.58</td><td>0.62 (0.02)</td></tr><tr><td>142</td><td>5.0</td><td>150.29 (2.10)</td><td>2.32</td><td>34.90 (0.49)</td><td>149.19 (2.08)</td><td>5.99</td><td>89.34 (1.25)</td></tr><tr><td></td><td>20.5</td><td>1.01 (0.02)</td><td>4.87</td><td>0.49 (0.01)</td><td>1.01 (0.02)</td><td>6.63</td><td>0.67 (0.01)</td></tr><tr><td>143</td><td>5.0</td><td>138.33 (2.05)</td><td>2.32</td><td>32.12 (0.48)</td><td>137.34 (2.04)</td><td>5.99</td><td>82.25 (1.22)</td></tr><tr><td></td><td>20.5</td><td>1.00 (0.02)</td><td>4.87</td><td>0.49 (0.01)</td><td>1.00 (0.02)</td><td>6.63</td><td>0.66 (0.01)</td></tr><tr><td>144</td><td>4.0</td><td>893.29 (17.72)</td><td>2.19</td><td>195.78 (3.88)</td><td>241.53 (4.74)</td><td>5.91</td><td>142.71 (2.80)</td></tr><tr><td></td><td>17.0</td><td>0.85 (0.04)</td><td>4.85</td><td>0.41 (0.02)</td><td>0.71 (0.03)</td><td>6.64</td><td>0.47 (0.02)</td></tr><tr><td>145</td><td>4.0</td><td>851.21 (18.08)</td><td>2.19</td><td>186.56 (3.96)</td><td>799.40 (17.11)</td><td>6.38</td><td>510.24 (10.92)</td></tr><tr><td></td><td>15.5</td><td>0.81 (0.05)</td><td>4.71</td><td>0.38 (0.02)</td><td>0.87 (0.05)</td><td>6.43</td><td>0.56 (0.03)</td></tr><tr><td>146</td><td>4.0</td><td>555.47 (17.44)</td><td>2.19</td><td>121.74 (3.82)</td><td>525.26 (16.47)</td><td>6.38</td><td>335.26 (10.51)</td></tr><tr><td></td><td>22.5</td><td>0.35 (0.02)</td><td>4.80</td><td>0.17 (0.01)</td><td>0.35 (0.02)</td><td>6.48</td><td>0.22 (0.01)</td></tr><tr><td>147</td><td>5.5</td><td>10.11 (1.24)</td><td>2.30</td><td>2.33 (0.28)</td><td>10.07 (1.23)</td><td>5.42</td><td>5.46 (0.67)</td></tr><tr><td></td><td>33.5</td><td>3.46 (0.76)</td><td>10.86</td><td>3.76 (0.83)</td><td>1.81 (0.40)</td><td>32.25</td><td>5.84 (1.29)</td></tr><tr><td>148</td><td>5.5</td><td>8.69 (1.23)</td><td>2.30</td><td>2.00 (0.28)</td><td>8.65 (1.22)</td><td>5.42</td><td>4.69 (0.66)</td></tr><tr><td></td><td>33.5</td><td>3.49 (0.76)</td><td>10.86</td><td>3.79 (0.83)</td><td>2.15 (0.47)</td><td>33.27</td><td>7.16 (1.56)</td></tr><tr><td>149</td><td>5.5</td><td>11.41 (1.07)</td><td>2.30</td><td>2.63 (0.25)</td><td>11.36 (1.06)</td><td>5.42</td><td>6.16 (0.58)</td></tr><tr><td></td><td>33.0</td><td>2.70 (0.61)</td><td>8.49</td><td>2.29 (0.52)</td><td>1.76 (0.40)</td><td>32.25</td><td>5.66 (1.28)</td></tr><tr><td>150</td><td>5.5</td><td>16.06 (1.07)</td><td>2.30</td><td>3.70 (0.25)</td><td>16.00 (1.07)</td><td>5.42</td><td>8.67 (0.58)</td></tr><tr><td></td><td>33.0</td><td>2.50 (0.61)</td><td>8.49</td><td>2.12 (0.52)</td><td>1.61 (0.40)</td><td>32.25</td><td>5.21 (1.28)</td></tr><tr><td>151</td><td>5.5</td><td>29.61 (1.33)</td><td>2.30</td><td>6.82 (0.31)</td><td>29.47 (1.33)</td><td>5.42</td><td>15.98 (0.72)</td></tr><tr><td></td><td>33.5</td><td>3.42 (0.76)</td><td>10.86</td><td>3.71 (0.83)</td><td>2.11 (0.47)</td><td>33.27</td><td>7.03 (1.56)</td></tr><tr><td>152</td><td>4.0</td><td>619.91 (21.11)</td><td>2.19</td><td>135.86 (4.63)</td><td>205.95 (4.72)</td><td>5.91</td><td>121.69 (2.79)</td></tr><tr><td></td><td>7.5</td><td>8.91 (0.48)</td><td>2.78</td><td>2.48 (0.13)</td><td>1.21 (0.07)</td><td>6.33</td><td>0.76 (0.05)</td></tr><tr><td>153</td><td>5.0</td><td>160.69 (2.14)</td><td>2.32</td><td>37.32 (0.50)</td><td>159.48 (2.12)</td><td>5.99</td><td>95.50 (1.27)</td></tr><tr><td></td><td>20.5</td><td>1.03 (0.03)</td><td>4.87</td><td>0.50 (0.01)</td><td>1.03 (0.03)</td><td>6.63</td><td>0.68 (0.02)</td></tr><tr><td>154</td><td>5.0</td><td>159.68 (2.09)</td><td>2.32</td><td>37.08 (0.48)</td><td>158.51 (2.07)</td><td>5.99</td><td>94.92 (1.24)</td></tr><tr><td></td><td>22.5</td><td>0.81 (0.03)</td><td>4.80</td><td>0.39 (0.01)</td><td>0.81 (0.03)</td><td>6.48</td><td>0.53 (0.02)</td></tr><tr><td>155</td><td>4.0</td><td>691.00 (24.76)</td><td>2.19</td><td>151.44 (5.43)</td><td>580.99 (26.25)</td><td>6.38</td><td>370.84 (16.75)</td></tr><tr><td></td><td>7.0</td><td>11.58 (0.74)</td><td>2.63</td><td>3.05 (0.19)</td><td>17.23 (1.07)</td><td>4.83</td><td>8.32 (0.52)</td></tr><tr><td>156</td><td>4.0</td><td>559.37 (17.65)</td><td>2.19</td><td>122.59 (3.87)</td><td>525.44 (16.63)</td><td>6.38</td><td>335.38 (10.62)</td></tr><tr><td></td><td>17.5</td><td>0.36 (0.03)</td><td>4.93</td><td>0.18 (0.02)</td><td>0.38 (0.03)</td><td>6.61</td><td>0.25 (0.02)</td></tr><tr><td>157</td><td>5.0</td><td>54.06 (2.20)</td><td>2.32</td><td>12.55 (0.51)</td><td>52.68 (2.21)</td><td>5.99</td><td>31.55 (1.32)</td></tr><tr><td></td><td>35.0</td><td>4.57 (0.80)</td><td>12.43</td><td>5.68 (0.99)</td><td>2.46 (0.43)</td><td>32.34</td><td>7.95 (1.38)</td></tr><tr><td>158</td><td>4.0</td><td>84.83 (16.59)</td><td>2.19</td><td>18.59 (3.64)</td><td>75.06 (15.71)</td><td>6.38</td><td>47.91 (10.03)</td></tr></tbody></table>
<table><caption>**Table 5**
(Continued)</caption><thead><tr><th>Region</th><th>V<sub>s</sub><sup>a</sup><br>(km s<sup>-1</sup>)</th><th>Mass Flow (120 K)<sup>b</sup><br>(10<sup>2</sup> M<sub>☉</sub> yr<sup>-1</sup>)</th><th>t<sub>cool</sub>(120 K)<sup>c</sup><br>(10<sup>2</sup> yr)</th><th>M(120 K)(H<sub>2</sub>)<sup>d</sup><br>(10<sup>5</sup> M<sub>☉</sub>)</th><th>Mass Flow (50 K)<sup>b</sup><br>(10<sup>2</sup> M<sub>☉</sub> yr<sup>-1</sup>)</th><th>t<sub>cool</sub>(50 K)<sup>c</sup><br>(10<sup>2</sup> yr)</th><th>M(50 K)(H<sub>2</sub>)<sup>d</sup><br>(10<sup>5</sup> M<sub>☉</sub>)</th></tr></thead><tbody><tr><td></td><td>34.0</td><td>4.05 (0.78)</td><td>12.91</td><td>5.23 (1.00)</td><td>2.23 (0.43)</td><td>32.34</td><td>7.21 (1.38)</td></tr><tr><td rowspan="2">159</td><td>5.5</td><td>6.75 (1.23)</td><td>2.30</td><td>1.55 (0.28)</td><td>6.71 (1.23)</td><td>5.42</td><td>3.64 (0.66)</td></tr><tr><td>33.5</td><td>3.62 (0.76)</td><td>10.86</td><td>3.94 (0.83)</td><td>2.24 (0.47)</td><td>33.27</td><td>7.45 (1.56)</td></tr><tr><td rowspan="2">160</td><td>5.0</td><td>18.02 (2.04)</td><td>2.32</td><td>4.19 (0.47)</td><td>125.86 (15.42)</td><td>6.38</td><td>80.34 (9.85)</td></tr><tr><td>34.0</td><td>3.94 (0.77)</td><td>12.91</td><td>5.08 (1.00)</td><td>2.40 (0.44)</td><td>30.76</td><td>7.40 (1.34)</td></tr><tr><td rowspan="2">161</td><td>5.0</td><td>21.45 (2.21)</td><td>2.32</td><td>4.98 (0.51)</td><td>21.31 (2.20)</td><td>5.99</td><td>12.76 (1.32)</td></tr><tr><td>33.5</td><td>3.81 (0.75)</td><td>10.86</td><td>4.13 (0.82)</td><td>2.35 (0.47)</td><td>33.27</td><td>7.82 (1.55)</td></tr><tr><td rowspan="2">162</td><td>4.0</td><td>289.66 (13.97)</td><td>2.19</td><td>63.48 (3.06)</td><td>273.92 (13.19)</td><td>6.38</td><td>174.83 (8.42)</td></tr><tr><td>20.0</td><td>0.21 (0.03)</td><td>4.95</td><td>0.10 (0.01)</td><td>0.21 (0.03)</td><td>6.65</td><td>0.14 (0.02)</td></tr><tr><td rowspan="2">163</td><td>4.5</td><td>155.07 (5.08)</td><td>2.29</td><td>35.44 (1.16)</td><td>152.40 (4.98)</td><td>5.91</td><td>90.05 (2.94)</td></tr><tr><td>18.5</td><td>0.28 (0.03)</td><td>4.93</td><td>0.14 (0.02)</td><td>0.28 (0.03)</td><td>6.59</td><td>0.18 (0.02)</td></tr><tr><td rowspan="2">164</td><td>5.0</td><td>133.99 (2.13)</td><td>2.32</td><td>31.12 (0.49)</td><td>133.01 (2.11)</td><td>5.99</td><td>79.65 (1.26)</td></tr><tr><td>21.5</td><td>0.55 (0.02)</td><td>4.87</td><td>0.27 (0.01)</td><td>0.55 (0.02)</td><td>6.57</td><td>0.36 (0.02)</td></tr><tr><td rowspan="2">165</td><td>5.0</td><td>149.80 (2.11)</td><td>2.32</td><td>34.79 (0.49)</td><td>148.69 (2.10)</td><td>5.99</td><td>89.04 (1.25)</td></tr><tr><td>22.0</td><td>0.72 (0.02)</td><td>4.81</td><td>0.34 (0.01)</td><td>0.72 (0.02)</td><td>6.59</td><td>0.47 (0.02)</td></tr><tr><td rowspan="2">166</td><td>5.0</td><td>105.85 (2.22)</td><td>2.32</td><td>24.58 (0.52)</td><td>105.11 (2.21)</td><td>5.99</td><td>62.94 (1.32)</td></tr><tr><td>22.0</td><td>0.50 (0.02)</td><td>4.81</td><td>0.24 (0.01)</td><td>0.50 (0.02)</td><td>6.59</td><td>0.33 (0.02)</td></tr><tr><td rowspan="2">167</td><td>4.0</td><td>539.22 (16.38)</td><td>2.19</td><td>118.18 (3.59)</td><td>506.55 (15.43)</td><td>6.38</td><td>323.32 (9.85)</td></tr><tr><td>22.5</td><td>0.28 (0.01)</td><td>4.80</td><td>0.14 (0.01)</td><td>0.30 (0.01)</td><td>6.59</td><td>0.20 (0.01)</td></tr><tr><td rowspan="2">168</td><td>4.0</td><td>413.76 (18.24)</td><td>2.19</td><td>90.68 (4.00)</td><td>340.44 (19.59)</td><td>6.38</td><td>217.29 (12.50)</td></tr><tr><td>16.5</td><td>0.40 (0.05)</td><td>4.89</td><td>0.19 (0.02)</td><td>2.56 (0.32)</td><td>5.11</td><td>1.31 (0.16)</td></tr><tr><td rowspan="2">169</td><td>4.0</td><td>159.94 (13.95)</td><td>2.19</td><td>35.05 (3.06)</td><td>153.99 (13.08)</td><td>6.38</td><td>98.29 (8.35)</td></tr><tr><td>25.0</td><td>2.87 (0.53)</td><td>0.65</td><td>0.19 (0.03)</td><td>2.37 (0.44)</td><td>32.09</td><td>7.61 (1.40)</td></tr><tr><td rowspan="2">170</td><td>5.5</td><td>12.64 (1.33)</td><td>2.30</td><td>2.91 (0.31)</td><td>12.59 (1.33)</td><td>5.42</td><td>6.83 (0.72)</td></tr><tr><td>33.0</td><td>2.67 (0.61)</td><td>8.49</td><td>2.27 (0.52)</td><td>1.74 (0.40)</td><td>32.25</td><td>5.61 (1.29)</td></tr><tr><td rowspan="2">171</td><td>5.5</td><td>12.65 (1.23)</td><td>2.30</td><td>2.91 (0.28)</td><td>145.35 (15.10)</td><td>6.38</td><td>92.78 (9.64)</td></tr><tr><td>33.5</td><td>3.56 (0.76)</td><td>10.86</td><td>3.87 (0.83)</td><td>0.13 (0.02)</td><td>6.48</td><td>0.09 (0.01)</td></tr><tr><td rowspan="2">172</td><td>5.0</td><td>22.76 (2.08)</td><td>2.32</td><td>5.29 (0.48)</td><td>22.66 (2.06)</td><td>5.99</td><td>13.57 (1.23)</td></tr><tr><td>34.0</td><td>3.93 (0.77)</td><td>12.91</td><td>5.07 (1.00)</td><td>2.37 (0.46)</td><td>33.27</td><td>7.88 (1.55)</td></tr><tr><td rowspan="2">173</td><td>4.0</td><td>313.75 (13.96)</td><td>2.19</td><td>68.76 (3.06)</td><td>296.72 (13.17)</td><td>6.38</td><td>189.39 (8.41)</td></tr><tr><td>22.0</td><td>0.14 (0.02)</td><td>4.81</td><td>0.07 (0.01)</td><td>0.14 (0.02)</td><td>6.59</td><td>0.10 (0.02)</td></tr><tr><td rowspan="2">174</td><td>4.0</td><td>521.41 (17.02)</td><td>2.19</td><td>114.27 (3.73)</td><td>491.31 (16.02)</td><td>6.38</td><td>313.59 (10.23)</td></tr><tr><td>19.0</td><td>0.28 (0.03)</td><td>4.91</td><td>0.14 (0.01)</td><td>0.28 (0.03)</td><td>6.66</td><td>0.19 (0.02)</td></tr><tr><td rowspan="2">175</td><td>5.0</td><td>100.71 (2.11)</td><td>2.32</td><td>23.39 (0.49)</td><td>100.00 (2.10)</td><td>5.99</td><td>59.89 (1.26)</td></tr><tr><td>21.5</td><td>0.33 (0.02)</td><td>4.87</td><td>0.16 (0.01)</td><td>0.33 (0.02)</td><td>6.57</td><td>0.22 (0.02)</td></tr><tr><td rowspan="2">176</td><td>5.0</td><td>114.64 (2.11)</td><td>2.32</td><td>26.62 (0.49)</td><td>113.82 (2.10)</td><td>5.99</td><td>68.16 (1.26)</td></tr><tr><td>22.0</td><td>0.53 (0.02)</td><td>4.81</td><td>0.26 (0.01)</td><td>0.53 (0.02)</td><td>6.59</td><td>0.35 (0.02)</td></tr><tr><td rowspan="2">177</td><td>4.0</td><td>806.92 (16.58)</td><td>2.19</td><td>176.85 (3.63)</td><td>760.92 (15.62)</td><td>6.38</td><td>485.68 (9.97)</td></tr><tr><td>19.0</td><td>0.72 (0.03)</td><td>4.91</td><td>0.35 (0.02)</td><td>0.72 (0.03)</td><td>6.66</td><td>0.48 (0.02)</td></tr><tr><td rowspan="2">178</td><td>4.0</td><td>650.51 (16.49)</td><td>2.19</td><td>142.57 (3.61)</td><td>613.51 (15.53)</td><td>6.38</td><td>391.59 (9.91)</td></tr><tr><td>22.5</td><td>0.42 (0.02)</td><td>4.80</td><td>0.20 (0.01)</td><td>0.42 (0.02)</td><td>6.48</td><td>0.27 (0.02)</td></tr><tr><td rowspan="2">179</td><td>4.0</td><td>588.99 (17.49)</td><td>2.19</td><td>129.09 (3.83)</td><td>549.53 (16.52)</td><td>6.38</td><td>350.75 (10.55)</td></tr><tr><td>30.5</td><td>9.51 (0.76)</td><td>0.75</td><td>0.71 (0.06)</td><td>5.57 (0.45)</td><td>27.05</td><td>15.06 (1.21)</td></tr><tr><td rowspan="2">180</td><td>5.5</td><td>14.06 (1.06)</td><td>2.30</td><td>3.24 (0.25)</td><td>160.61 (13.12)</td><td>6.38</td><td>102.51 (8.37)</td></tr><tr><td>33.0</td><td>2.58 (0.61)</td><td>8.49</td><td>2.19 (0.52)</td><td>2.46 (0.43)</td><td>28.05</td><td>6.89 (1.22)</td></tr><tr><td rowspan="2">181</td><td>5.5</td><td>16.30 (1.29)</td><td>2.30</td><td>3.75 (0.30)</td><td>16.24 (1.28)</td><td>5.42</td><td>8.81 (0.70)</td></tr><tr><td>33.0</td><td>2.51 (0.61)</td><td>8.49</td><td>2.13 (0.52)</td><td>1.63 (0.40)</td><td>32.25</td><td>5.25 (1.29)</td></tr><tr><td rowspan="2">182</td><td>4.0</td><td>325.80 (16.45)</td><td>2.19</td><td>71.40 (3.61)</td><td>307.89 (15.49)</td><td>6.38</td><td>196.52 (9.89)</td></tr><tr><td>22.0</td><td>0.21 (0.02)</td><td>4.81</td><td>0.10 (0.01)</td><td>0.21 (0.02)</td><td>6.59</td><td>0.14 (0.02)</td></tr><tr><td rowspan="2">183</td><td>4.0</td><td>475.03 (16.13)</td><td>2.19</td><td>104.11 (3.54)</td><td>448.82 (15.20)</td><td>6.38</td><td>286.47 (9.70)</td></tr><tr><td>19.5</td><td>0.32 (0.03)</td><td>4.92</td><td>0.16 (0.01)</td><td>0.31 (0.03)</td><td>6.49</td><td>0.20 (0.02)</td></tr><tr><td rowspan="2">184</td><td>4.0</td><td>538.34 (17.94)</td><td>2.19</td><td>117.98 (3.93)</td><td>508.07 (16.87)</td><td>6.38</td><td>324.29 (10.77)</td></tr><tr><td>18.5</td><td>0.26 (0.03)</td><td>4.93</td><td>0.13 (0.02)</td><td>0.26 (0.03)</td><td>6.59</td><td>0.17 (0.02)</td></tr><tr><td rowspan="2">185</td><td>4.0</td><td>616.56 (16.83)</td><td>2.19</td><td>135.13 (3.69)</td><td>584.78 (15.90)</td><td>6.38</td><td>373.25 (10.15)</td></tr><tr><td>22.0</td><td>0.24 (0.02)</td><td>4.81</td><td>0.12 (0.01)</td><td>0.24 (0.02)</td><td>6.59</td><td>0.16 (0.01)</td></tr><tr><td rowspan="2">186</td><td>4.0</td><td>710.37 (16.79)</td><td>2.19</td><td>155.69 (3.68)</td><td>670.69 (15.80)</td><td>6.38</td><td>428.09 (10.09)</td></tr><tr><td>20.5</td><td>0.38 (0.02)</td><td>4.87</td><td>0.18 (0.01)</td><td>0.37 (0.02)</td><td>6.63</td><td>0.25 (0.02)</td></tr><tr><td rowspan="2">187</td><td>4.0</td><td>958.59 (16.74)</td><td>2.19</td><td>210.09 (3.67)</td><td>904.99 (15.77)</td><td>6.38</td><td>577.64 (10.06)</td></tr><tr><td>20.5</td><td>0.58 (0.03)</td><td>4.87</td><td>0.28 (0.01)</td><td>0.57 (0.03)</td><td>6.63</td><td>0.38 (0.02)</td></tr><tr><td rowspan="2">188</td><td>4.0</td><td>881.65 (18.94)</td><td>2.19</td><td>193.23 (4.15)</td><td>813.83 (18.26)</td><td>6.38</td><td>519.45 (11.65)</td></tr><tr><td>8.5</td><td>5.03 (0.26)</td><td>3.15</td><td>1.58 (0.08)</td><td>6.32 (0.32)</td><td>4.88</td><td>3.08 (0.16)</td></tr><tr><td rowspan="2">189</td><td>4.0</td><td>823.23 (16.43)</td><td>2.19</td><td>180.42 (3.60)</td><td>779.49 (15.52)</td><td>6.38</td><td>497.53 (9.91)</td></tr><tr><td>21.0</td><td>0.52 (0.02)</td><td>4.87</td><td>0.25 (0.01)</td><td>0.51 (0.02)</td><td>6.55</td><td>0.34 (0.02)</td></tr></tbody></table>
<table><caption>**Table 5**
(Continued)</caption><thead><tr><th>Region</th><th>V<sub>s</sub><sup>a</sup><br>(km s<sup>-1</sup>)</th><th>Mass Flow (120 K)<sup>b</sup><br>(10<sup>2</sup> M<sub>☉</sub> yr<sup>-1</sup>)</th><th>t<sub>cool</sub>(120 K)<sup>c</sup><br>(10<sup>2</sup> yr)</th><th>M(120 K)(H<sub>2</sub>)<sup>d</sup><br>(10<sup>5</sup> M<sub>☉</sub>)</th><th>Mass Flow (50 K)<sup>b</sup><br>(10<sup>2</sup> M<sub>☉</sub> yr<sup>-1</sup>)</th><th>t<sub>cool</sub>(50 K)<sup>c</sup><br>(10<sup>2</sup> yr)</th><th>M(50 K)(H<sub>2</sub>)<sup>d</sup><br>(10<sup>5</sup> M<sub>☉</sub>)</th></tr></thead><tbody><tr><td>190</td><td>5.0</td><td>88.54 (2.19)</td><td>2.32</td><td>20.56 (0.51)</td><td>88.02 (2.17)</td><td>5.99</td><td>52.71 (1.30)</td></tr><tr><td></td><td>35.0</td><td>10.52 (0.85)</td><td>12.43</td><td>13.08 (1.05)</td><td>6.51 (0.52)</td><td>33.70</td><td>21.95 (1.76)</td></tr><tr><td>191</td><td>5.5</td><td>13.70 (1.33)</td><td>2.30</td><td>3.15 (0.31)</td><td>13.73 (1.32)</td><td>5.42</td><td>7.44 (0.72)</td></tr><tr><td></td><td>32.5</td><td>2.85 (0.67)</td><td>6.36</td><td>1.81 (0.42)</td><td>1.73 (0.41)</td><td>32.25</td><td>5.57 (1.32)</td></tr><tr><td>192</td><td>5.5</td><td>22.44 (1.25)</td><td>2.30</td><td>5.17 (0.29)</td><td>22.34 (1.24)</td><td>5.42</td><td>12.11 (0.67)</td></tr><tr><td></td><td>33.5</td><td>3.67 (0.76)</td><td>10.86</td><td>3.99 (0.82)</td><td>2.27 (0.47)</td><td>33.27</td><td>7.55 (1.56)</td></tr><tr><td>193</td><td>5.5</td><td>39.06 (1.21)</td><td>2.30</td><td>8.99 (0.28)</td><td>38.89 (1.20)</td><td>5.42</td><td>21.09 (0.65)</td></tr><tr><td></td><td>33.0</td><td>2.52 (0.61)</td><td>8.49</td><td>2.14 (0.52)</td><td>1.63 (0.40)</td><td>32.25</td><td>5.26 (1.28)</td></tr><tr><td>194</td><td>5.5</td><td>52.85 (1.23)</td><td>2.30</td><td>12.17 (0.28)</td><td>52.66 (1.23)</td><td>5.42</td><td>28.55 (0.67)</td></tr><tr><td></td><td>35.0</td><td>10.16 (0.81)</td><td>12.43</td><td>12.63 (1.00)</td><td>6.28 (0.50)</td><td>33.70</td><td>21.16 (1.67)</td></tr><tr><td>195</td><td>5.0</td><td>92.90 (2.27)</td><td>2.32</td><td>21.57 (0.53)</td><td>93.29 (2.24)</td><td>5.99</td><td>55.87 (1.34)</td></tr><tr><td></td><td>24.5</td><td>10.43 (0.52)</td><td>0.65</td><td>0.68 (0.03)</td><td>8.83 (0.44)</td><td>30.76</td><td>27.16 (1.35)</td></tr><tr><td>196</td><td>4.0</td><td>832.55 (18.77)</td><td>2.19</td><td>182.46 (4.11)</td><td>786.26 (17.63)</td><td>6.38</td><td>501.86 (11.25)</td></tr><tr><td></td><td>22.5</td><td>0.45 (0.02)</td><td>4.80</td><td>0.21 (0.01)</td><td>0.44 (0.02)</td><td>6.48</td><td>0.29 (0.01)</td></tr><tr><td>197</td><td>4.0</td><td>948.66 (20.14)</td><td>2.19</td><td>207.91 (4.42)</td><td>878.54 (19.37)</td><td>6.38</td><td>560.75 (12.37)</td></tr><tr><td></td><td>8.5</td><td>5.39 (0.27)</td><td>3.15</td><td>1.70 (0.09)</td><td>6.74 (0.34)</td><td>4.88</td><td>3.29 (0.17)</td></tr><tr><td>198</td><td>17.5</td><td>1.20 (0.04)</td><td>4.93</td><td>0.59 (0.02)</td><td>1.18 (0.04)</td><td>6.58</td><td>0.78 (0.02)</td></tr><tr><td></td><td>4.0</td><td>1000.00 (0.00)</td><td>2.19</td><td>219.16 (0.00)</td><td>1000.00 (0.00)</td><td>6.38</td><td>638.28 (0.00)</td></tr><tr><td>199</td><td>5.0</td><td>145.99 (2.28)</td><td>2.32</td><td>33.90 (0.53)</td><td>144.97 (2.26)</td><td>5.99</td><td>86.81 (1.35)</td></tr><tr><td></td><td>20.0</td><td>0.66 (0.03)</td><td>4.95</td><td>0.33 (0.01)</td><td>0.66 (0.03)</td><td>6.65</td><td>0.44 (0.02)</td></tr><tr><td>200</td><td>5.0</td><td>111.11 (2.11)</td><td>2.32</td><td>25.80 (0.49)</td><td>110.31 (2.09)</td><td>5.99</td><td>66.06 (1.25)</td></tr><tr><td></td><td>20.5</td><td>0.49 (0.03)</td><td>4.87</td><td>0.24 (0.01)</td><td>0.49 (0.03)</td><td>6.63</td><td>0.33 (0.02)</td></tr><tr><td>201</td><td>4.0</td><td>289.56 (33.40)</td><td>2.19</td><td>63.46 (7.32)</td><td>276.95 (31.31)</td><td>6.38</td><td>176.77 (19.99)</td></tr><tr><td></td><td>6.0</td><td>26.79 (1.75)</td><td>2.47</td><td>6.62 (0.43)</td><td>26.62 (1.73)</td><td>5.08</td><td>13.51 (0.88)</td></tr><tr><td>202</td><td>6.0</td><td>9.37 (0.84)</td><td>2.47</td><td>2.32 (0.21)</td><td>9.39 (0.84)</td><td>5.08</td><td>4.77 (0.42)</td></tr><tr><td></td><td>32.5</td><td>2.71 (0.66)</td><td>6.36</td><td>1.72 (0.42)</td><td>1.63 (0.41)</td><td>32.25</td><td>5.24 (1.31)</td></tr><tr><td>203</td><td>4.0</td><td>281.63 (18.31)</td><td>2.19</td><td>61.72 (4.01)</td><td>266.75 (17.27)</td><td>6.38</td><td>170.26 (11.03)</td></tr><tr><td></td><td>16.5</td><td>0.45 (0.04)</td><td>4.89</td><td>0.22 (0.02)</td><td>0.45 (0.04)</td><td>6.57</td><td>0.29 (0.03)</td></tr><tr><td>204</td><td>4.0</td><td>445.75 (16.88)</td><td>2.19</td><td>97.69 (3.70)</td><td>422.32 (15.94)</td><td>6.38</td><td>269.56 (10.18)</td></tr><tr><td></td><td>17.0</td><td>0.37 (0.04)</td><td>4.85</td><td>0.18 (0.02)</td><td>0.37 (0.04)</td><td>6.61</td><td>0.25 (0.02)</td></tr><tr><td>205</td><td>4.0</td><td>517.93 (19.03)</td><td>2.19</td><td>113.51 (4.17)</td><td>490.28 (17.93)</td><td>6.38</td><td>312.94 (11.44)</td></tr><tr><td></td><td>8.0</td><td>5.88 (0.33)</td><td>2.93</td><td>1.72 (0.10)</td><td>5.87 (0.33)</td><td>4.88</td><td>2.87 (0.16)</td></tr><tr><td>206</td><td>4.0</td><td>551.87 (21.63)</td><td>2.19</td><td>120.95 (4.74)</td><td>523.11 (20.41)</td><td>6.38</td><td>333.89 (13.03)</td></tr><tr><td></td><td>7.0</td><td>13.16 (0.59)</td><td>2.63</td><td>3.47 (0.16)</td><td>13.15 (0.59)</td><td>4.86</td><td>6.39 (0.29)</td></tr><tr><td>207</td><td>16.0</td><td>1.40 (0.04)</td><td>4.85</td><td>0.68 (0.02)</td><td>1.36 (0.04)</td><td>6.59</td><td>0.90 (0.03)</td></tr><tr><td></td><td>4.0</td><td>1000.00 (0.00)</td><td>2.19</td><td>219.16 (0.00)</td><td>1000.00 (0.00)</td><td>6.38</td><td>638.28 (0.00)</td></tr><tr><td>208</td><td>18.0</td><td>1.20 (0.03)</td><td>4.90</td><td>0.59 (0.02)</td><td>1.18 (0.03)</td><td>6.64</td><td>0.78 (0.02)</td></tr><tr><td></td><td>4.0</td><td>1000.00 (0.00)</td><td>2.19</td><td>219.16 (0.00)</td><td>1000.00 (0.00)</td><td>6.38</td><td>638.28 (0.00)</td></tr><tr><td>209</td><td>19.0</td><td>1.26 (0.03)</td><td>4.91</td><td>0.62 (0.01)</td><td>1.24 (0.03)</td><td>6.66</td><td>0.82 (0.02)</td></tr><tr><td></td><td>4.0</td><td>1000.00 (0.00)</td><td>2.19</td><td>219.16 (0.00)</td><td>1000.00 (0.00)</td><td>6.38</td><td>638.28 (0.00)</td></tr><tr><td>210</td><td>7.5</td><td>15.13 (0.37)</td><td>2.78</td><td>4.21 (0.10)</td><td>14.48 (0.37)</td><td>4.84</td><td>7.00 (0.18)</td></tr><tr><td></td><td>4.0</td><td>1000.00 (0.00)</td><td>2.19</td><td>219.16 (0.00)</td><td>1000.00 (0.00)</td><td>6.38</td><td>638.28 (0.00)</td></tr><tr><td>211</td><td>4.0</td><td>644.31 (25.70)</td><td>2.19</td><td>141.21 (5.63)</td><td>609.29 (24.19)</td><td>6.38</td><td>388.90 (15.44)</td></tr><tr><td></td><td>6.5</td><td>18.86 (0.90)</td><td>2.59</td><td>4.89 (0.23)</td><td>18.87 (0.89)</td><td>4.83</td><td>9.11 (0.43)</td></tr><tr><td>212</td><td>4.0</td><td>310.45 (25.13)</td><td>2.19</td><td>68.04 (5.51)</td><td>295.11 (23.51)</td><td>6.38</td><td>188.36 (15.00)</td></tr><tr><td></td><td>6.5</td><td>12.63 (0.89)</td><td>2.59</td><td>3.27 (0.23)</td><td>12.59 (0.88)</td><td>4.83</td><td>6.08 (0.43)</td></tr></tbody></table>

Notes.

a Model Shock Velocity.

b Mass flow through the shock for gas above T = 120 K (or 50 K) to allow comparison with previous analysis.

c Cooling time for gas above T = 120 K (or 50 K).

d Total mass of gas shock heated above T = 120 K (or 50 K).

components (Figures 12(B), (D), and (F)). Overall there is a relatively flat kinetic energy deposition from the slow shocks from south to north, despite the decrease in overall shock velocities. There is also an indication that the fast-shock kinetic energy decreases from south to north.

What could cause these global differences in warm gas properties and energy deposition on such a large scale? The basic picture that has been presented is that of a collision

between the intruder galaxy NGC 7318b and a pre-existing, almost linear, tidal H I filament (Williams et al. 2002). We have argued in previous papers (Appleton et al. 2006; Guillard et al. 2009; Paper 1) that the warm H₂ can be understood in terms of the dissipation of mechanical energy through a turbulent cascade from a large-scale high-energy collision through supersonic turbulence to small scales and higher densities. Guillard et al. (2009) presented a model in which two phases in the pre-shock
<figure><img src="image_11.png" /><figcaption>**Figure 10.** The percentage of warm gas above a given temperature compared with that derived by extrapolating the power law down to 50 K (see text): (a) warm gas above 120 K; contour levels are 10%, 20%, 30%, 40%, 50%, and 60%; (b) for hotter gas with $T > 200$ K, with levels of 1%, 2.5%, 5%, 10%, 15%, and 20%. The plot shows that the warm gas fraction rises along the shock ridge as predicted by the models of Guillard et al. (2009). A smaller fraction is heated to higher temperatures near the shock center. Note also that the region to the east (left) also contains a higher fraction of warm gas in the region of the so-called “AGN bridge.”</figcaption></figure>

gas were present in the H I filament before compression by the intruder galaxy. Slightly overdense regions would be compressed by the high-speed shock from the intruder galaxy and would lead to molecular cloud formation on grains that would survive the compression. On the other hand, regions that were originally very underdense would be shock-heated to millions of degrees (generating X-ray emission as observed), and the grains would be destroyed (Guillard et al. 2009). This simple picture provides a working model of the system.

The large extent of the H₂ in the north-south direction is consistent with idea of NGC 7318b colliding with a long tidal filament. The collision, which is believed to be primarily toward the observer from behind the group, may have occurred first in the northern part of the filament, and the point of impact may have progressed along the filament in a southerly direction. The fact that the northern part of the H₂ filament is cooler and heated by lower velocity shocks implies that the energy has had more time to dissipate than in the south, where one might believe most of the current action is.

The northern part of the filament also contains a larger mass of warm gas, which radiates in the lower-J lines. This may be related to the structure of the initial target material before the collision of the intruder, implying a density gradient along that filament that is now reflected in an increase in cooler gas. Given the short cooling time of the molecular gas (typically 1000 yr—see Table 5), we might expect this material to continue to cool rapidly. It is interesting that the northern part of the filament contains the extragalactic star-forming region called “SQ-A.” SQ-A is the only region of the whole filament that contains significant quantities of H I. Also, unlike the rest of the filament (Konstantopoulos et al. 2014), this is one of the few regions where significant current star formation is occurring (star formation rate = $1.5 M_{\odot} yr^{-1}$; Xu et al. 2003). This may imply that this part of the filament may have cooled sufficiently for H I to re-form and scattered star formation to be initiated. Indeed, Gallagher et al. (2001) showed that SQ-A contains star clusters with a range of ages dating from the initial collision of NGC 7318a with the group (20 Myr ago) to much more recent activity. In fact recent observations support the earlier work (S. Gallagher 2017, private communication), which suggests that star formation

activity in the main filament, though currently quite weak, is very recent, and may be increasing in intensity with time.

Previous studies (Cluver et al. 2010; Iglesias-Páramo et al. 2012) suggest a higher level of star formation not just in SQ-A but also, to a lesser degree, in the southern part of the filament, near position 54 of Figure 1(b). Temperatures of the warm gas are a little higher there, but the study by Appleton et al. (2013; region D of that paper) shows that both H₂/PAH and [C II]/PAH ratios are inconsistent with photodissociation regions dominating the H₂ heating there. Indeed, although the H₂ is warmer in that region, the heating is not confined to the H II regions, but is more extensive, which suggests that the extra heating is not caused by star formation.

The structure of the main filament is quite different in the east-west direction, as we have shown. Perhaps surprising is the extent of the gas in the easterly direction, where it continues to the edge of our grid. Long-low observations with IRS extended further to the east than the short-low observations, and so we know that the warm H₂ continues eastward. In Paper 1 we suggested that the eastward extent of the emission was part of a “bridge” to NGC 7319 (see Figure 1(a)). However, such a bridge would have to be quite broad since we detect warm H₂ as far north as position 212 (estimated temperatures of $T_1 = 143$ K and $T_2 = 463$ K). This suggests that a large volume of gas is caught up in the shock heating.

It is worth considering the implications of the kinetic energy deposition in the warm gas. Both across and along the main H₂ filament (the main shock of Figure 1(a)), within each element the kinetic energy deposited every 500–1000 yr (the gas cooling time–see Table 5) is $10^{43.5–44.5}$ J per observational element (6.2 kpc$^2$). Summing over the whole observed region gives $6.3 \times 10^{46}$ J ($6.3 \times 10^{53}$ erg), and a total energy flow through the shocks in the warm gas of $4.4 \times 10^{36}$ W ($4.4 \times 10^{43}$ erg s$^{-1}$). The total H₂ line luminosity from the whole region (summing over the detected 0–0 S(0)–S(5) lines) is $1.3 \times 10^{35}$ W ($1.3 \times 10^{42}$ erg s$^{-1}$), and so the efficiency of conversion of kinetic energy in the shocks into warm H₂ line luminosity is ~3%.

## 7.1. Connection between Large-scale Gas Kinematics and Regions of Maximal Heating

An interesting question is whether the regions of maximal heating in the shocks (as measured by, for example, the distribution of warm H₂ gas fraction) bears any connection to the large-scale dynamics of the Quintet system. NGC 7318b is colliding with intergroup gas at about 1000 km s$^{-1}$; Guillard et al. (2009) proposed that, through a turbulent cascade, energy is being transferred to smaller scales and low velocities where a significant fraction of the energy escapes through rotational H₂ and far-IR fine-structure emission (Appleton et al. 2013).

The shock modeling refers to the microscale (parsec scale or smaller) shocks, which represent some of the smallest scales in a turbulent cascade. The large-scale kinematically broad lines measured in the ionized and diffuse molecular gas likely represent the largest velocities and scales in the turbulent cascade. In our picture of the turbulent cascade, we consider the broader lines as being composed of a multitude of narrow molecular shocks and turbulent eddies ($<30$ km s$^{-1}$) spread over the full range of observed large-scale stirring (caused by the larger scale collision of NGC 7318a).

If energy is indeed being fed down from large to small scales, then those regions of the gas that show large global
<figure><img src="image_12.png" /><figcaption>**Figure 11.** Sectional slices across the H₂ filament following the arrow in the inset image for: (A) warm H₂ fraction for *T* > 120 K, (B) power-law index of H₂ (see text), (C) warm (*T*₂, red line) and cooler (*T*₁, green line) temperature distributions derived from two-temperature fits, (D) mass of warm H₂ associated with the warm (*T*₂, red line) and fast shock (green line) components, showing similar distributions, (E) velocities of the fast (red line) and slower shocks (green line, velocities multiplied by 2 to show structure) needed to excite the H₂, (F) gas mass associated with the cooler *T*₁ component (green line), the fast shock component (red line), and the warm (*T* > 120 K) power-law mass (blue line), and (G) the kinetic energy in the warm (*T* > 120 K) H₂ component associated with the fast (green line) and slow (red line) shocks.</figcaption></figure>
<figure><img src="image_13.png" /><figcaption>**Figure 12.** Sectional slices (south to north) along the H₂ filament following the arrow in the inset image for: (A) warm H₂ fraction for *T* > 120 K, (B) power-law index of H₂ (see text), (C) warm (*T*₂, red line) and cooler (*T*₁, green line) temperature distributions derived from two-temperature fits, (D) mass of warm H₂ associated with the warm component (*T*₂, red line), (E) velocities of the fast (red line) and slower shocks (green line, velocities multiplied by 2 to show structure) needed to excite the H₂, (F) gas mass associated with the cooler *T*₁ component (red line), the fast shock component (green line), and the warm (*T* > 120 K) power-law mass (blue line), and (G) the kinetic energy in the warm (*T* > 120 K) H₂ component associated with the fast (green line) and slow (red line) shocks.</figcaption></figure>
<figure><img src="image_14.png" /><figcaption>**Figure 13.** The warm ($T > 120$ K) mass fraction (contours in steps of 10% starting at 10%) compared with the moment maps for the [C II] emission from Herschel: (a) [C II] integrated intensity (arbitrary units), (b) [C II] heliocentric mean velocity of the emission (km s⁻¹), (c) [C II] line width (FWHM) (km s⁻¹), and (d) compared with the F665N HST visible image. SQ-A, which contains recent star formation, is also shown. The largest warm H₂ gas fraction lies to the west of the main ridge of [C II] emission, but correlates well with the regions of maximum velocity dispersion. This suggests that the [C II] emission maps the leading edge of the main shock, and gas to the west is where the kinetic energy is being deposited, increasing the warm H₂ gas fraction in the post-shocked turbulent regions.</figcaption></figure>

velocity dispersions should correlate with the regions of maximal heating. Since the velocity resolution of the IRS was not sufficient to map the kinematics of the H₂, we turn to the [C II] emission as a tracer of the diffuse warm molecular gas. It is likely that the warm H₂ is the main collisional partner for the diffuse ionized carbon, leading to the excitation of the [C II] 158 µm transition in the shocked region (Appleton et al. 2013). We show in Figures 13(a)–(c) contours of the warm molecular fraction overplotted on moment maps (intensity, radial velocity map, and line width) for the [C II] emission over the areas that they overlap. Figure 13(d) shows the same contours on the optical image, for reference. From this figure, it is clear that the regions of highest warm fraction correlate most strongly with those regions with the largest ($>1000$ km s⁻¹) [C II] line width. This implies that the high level of heating of the warm H₂ is strongly correlated with more turbulent line

<figure><img src="image_15.png" /><figcaption>**Figure 14.** Red contours showing the CARMA CO (1–0) integrated emission (P. Guillard et al. 2017, in preparation) superimposed on the F665N HST image (see Guillard et al. 2016 for full discussion of CO emission). Blue contours show the integrated surface density of the 0–0 S(1) 17.08 µm emission covering most of the filament and NGC 7319 from Paper 1. Note that the clumps of CO emission define the main shock but also are scattered along the bridge to NGC 7319.</figcaption></figure>

widths (large-scale stirring), as expected from the model of Guillard et al. (2009). We note that the peak in the [C II] emission ridge is offset to the east (Figure 13(a)) from the region of most intense H₂ heating, suggesting that the [C II] emission peaks ahead of the region of maximum kinetic energy dissipation. This would be consistent with the idea that the main shock has a component of motion to the east. It is also consistent with Figure 11, which shows hotter gas, and faster shocks to the east of the main ridge of the peak in the warm gas fraction (Figures 11(D) and (E) compared with 11(A)). Given that the main disturbance driven into the intergalactic gas is a three-dimensional surface, the actual motions in the gas are likely to be quite complex and not easily interpreted without a realistic numerical simulation. None of the existing simulations mentioned in the introduction provides enough detail to explain all the facets of our observations.

## 7.2. *Excitation of Gas in the “Bridge”*

Most of the discussion so far has concentrated on the main north–south filament associated with the main shock of Figure 3. We turn now to discuss the emission to the east of the main shock, especially the “bridge” marked in Figure 3. The bridge has been previously detected in X-ray emission and diffuse Hα emission (Trinchieri et al. 2003; Xu et al. 2003), and in warm and cold molecular gas (Paper 1; Guillard et al. 2012). It was not detected in radio continuum emission, unlike the main shock.

As shown in Figure 13(c), by comparison with normal galaxies, even the bridge region has excessively large [C II] line widths of ~500 km s⁻¹, which may explain why so much of the H₂ is excited over such a large area. The bridge structure has its own distinct [C II] kinematics, as can be seen in Figure 13(b), where even in this limited coverage of the full bridge, a strong velocity gradient is seen of 300 km s⁻¹ over a
linear scale of ~15 kpc, with the highest velocities seen closer to NGC 7319. The IRAM 30 m CO (1–0) and (2–1) observations of the bridge region by Guillard et al. (2012) show that this region contains multiple broad CO-emitting components with gas at velocities intermediate between those in the extreme north of the group and those in the south (this can been seen also in the [C II] velocity field of Figure 13(b)). Figure 14 shows new, higher resolution observations of some brighter CO condensations within the bridge made with the CARMA interferometer superimposed on the 0–0 S(1) Spitzer map. These data (which will be discussed in much more detail in a companion paper: P. Guillard et al. 2017, in preparation) imply a coherent string of multiphase gas emission extending from the Seyfert nucleus of NGC 7319 into the intragroup medium. This raises the possibility that there is an atomic and molecular outflow associated with the nucleus of NGC 7319. A full discussion of this possibility is beyond the scope of the present paper, since both the warm H₂ diagnostics and the [C II] emission do not extend far enough to explore a possible jet-heating scenario.

We have already shown in Section 7 that, as one progresses further east from the main shock, the excitation of the cooler component of the warm H₂ gas remains high. Figures 11(F) and (G) show that in the region of the bridge (positions 106–108) the dominant heating is from slower shocks associated with cooler ($T = 150$ K) gas, which contains a significant mass of H₂. As Figure 11(A) shows, this is also a region with a much lower warm H₂ fraction based on the power-law analysis, suggesting that the balance has shifted to a large reservoir of cooler, but still excited gas in the bridge. We might speculate that the source of heating of this 150 K gas is kinetic energy injected into the medium by an AGN outflow from NGC 7319. This process is evidently less efficient at heating the gas than the collisionally driven shock from NGC 7318b. More work will be needed to explore this possibility in a future paper (Guillard et al. 2016).

## 8. Conclusions

We have analyzed the two-dimensional excitation distribution of warm molecular hydrogen based on 212 individually extracted mid-IR spectra from Spitzer IRS observations of the Stephan's Quintet intergalactic filament. The analysis was conducted on those regions with common IRS short-low and long-low spectral coverage to allow detailed fitting of the molecular excitation. Our main conclusions are as follows.

1. Using simple linear fits to the H₂ excitation diagrams, we have mapped for the first time the temperature and mass distribution of warm H₂ across the intergalactic gas in Stephan's Quintet. The mapped region extends over an area of at least 35 × 55 kpc², and includes the area dominated by shocked gas ahead of the intruder galaxy NGC 7318b. The warmest gas (600–1000 K) is found in the center and to the south of the main filament, with an extension of warm gas extending toward the Seyfert galaxy NGC 7319. The extragalactic star-forming region called “SQ-A,” at the northern tip of the main filament, contains the coolest of the warm H₂. A total of 1.1 × 10⁹ M☉ of warm ($T > 120$ K) H₂ is detected across the entire mapped region, with the largest contribution coming from the cooler ($T \sim 120–150$ K) extended regions on either

side of the narrow, highly shocked region, and from SQ-A.

2. We also fit the H₂ excitation diagrams with a power-law distribution of H₂ column density with temperature $dN_{H2} \propto T^{-n} dT$. The power-law indices range from $n = 5$ in the north (lower excitation) to lower values (higher excitation) of $n = 4.2–4.3$ in the southern filament. Except in the north, the measured power-law indices are much lower than those seen in normal galaxies, reflecting the high excitation likely resulting from shock heating. The distribution of the lowest power-law values defines a curved band lying to the east and ahead of the intruder galaxy NGC 7318b, as expected if the galaxy is driving a large-scale disturbance into the group-wide gas. The power-law method can self-consistently predict the mass of cold gas at each point in the map. This analysis shows that along the crest of the main filament, where shocks are expected to be the most intense, the warm gas ($T > 120$ K) fraction is between 60% and 100%.

3. We have found that the warm H₂ fraction correlates strongly with the large-scale kinematics of the gas (as measured by the [C II] emission). Where the FWHM of the velocity field is >800 km s⁻¹, the warm H₂ is heated the most strongly. This provides compelling evidence that large-scale turbulent stirring of the diffuse gas caused by the collision of NGC 7318b with the group is able to influence and heat gas on the small scales and at the low velocities needed to excite the rotational H₂ lines.

4. We modeled the H₂ excitation with a molecular shock modeling code (Lesaffre et al. 2013) that computes, along with other common fine-structure lines, the populations of 150 rotation–vibration H₂ levels in parallel to the MHD equations. Although the models are not unique, the best results were achieved with shocks propagating in a molecular medium containing gas with two different pre-shock densities. A system of slow magnetic C-shocks (4–5 km s⁻¹) and faster mainly J-shocks (up to 25 km s⁻¹) was required to explain the observed emission. The models support the idea that the high-speed disturbance caused by the intruder (at 1000 km s⁻¹) has been degraded into millions of slower molecular shocks through the effects of supersonic turbulence.

5. Our results provide a picture of the dissipation of kinetic energy through compressive turbulence (shocks) both along the length of the main filament (north–south) and across it, mainly east–west. Gas temperatures rise, the power-law index flattens, and the velocity of the shocks needed to excite the gas increases as we move from north to south along the main filament. Similar phenomena are seen across the shock in the east–west direction, where the hottest, most intense shocks are seen at the peak of the H₂ surface density, with a slow drop-off on either side. However, although brighter at the peak, the estimated total surface density in warm H₂ actually decreases with this increasing temperature. This may reflect the density structure in the initial pre-shock material that was overrun by the main disturbance from the intruding galaxy, or it may be a result of molecules being increasingly dissociated in the most excited region of the structure.

6. Our analysis shows that the H₂ gas continues to be warm and excited far to the east of the main filament, in the region of the bridge that connects to NGC 7319. Some
<figure><img src="image_16.png" /><figcaption>**Figure 15.** Selected IRS spectra from the spectral grid of Figure 1(b) with main detected lines identified. Spectra from: (a) a near bright H II region in the foreground galaxy NGC 7320, position P7. Note that features of the foreground and background groups are mainly separated; (b) average of four spectra centered on the high-excitation region in the south (P34, 35, 44, 45); (c) behind the main shock (P75); (d) on the main shock-south (P77); (e) the nucleus of NGC 7318b (average P100, 101, 113, 114); (f) main shock-central (P104); (g) AGN bridge region (P121); (h) near the nucleus of NGC 7318a (P123); (i) AGN bridge region (P134).</figcaption></figure>

of this may be related to a known collimated radio jet. Our [C II] observations show an extension of diffuse gas toward the nucleus of this galaxy associated with a kinematically shifting component, but the observations do not extend far enough to conclusively associate this with an outflow. However, our CO (1–0) map from CARMA covers a larger area and shows a string of dense H₂ clumps extending from NGC 7319 in a similar region to the bridge, suggesting a connection with the center of NGC 7319. If the AGN in NGC 7319 is somehow exciting warm molecular hydrogen in that direction, it must have a broad effect, since the warm H₂ gas is extended on a large scale and is generally cooler than the intragroup gas associated with the main filament.

The observations of shock-heated gas in Stephan's Quintet emphasize the wealth of information that can be obtained from rest-frame mid-IR molecular lines, and may point the way toward future studies of turbulent gas at higher redshift with the *James Webb Space Telescope*, *SPICA*, and other possible future facilities. Systems with similar or more powerful rotational H₂ lines were discovered toward the end of the *Spitzer* cryogenic mission. These include a wide range of environments from

nearby shock-excited systems and groups (Appleton et al. 2006; Peterson et al. 2012; Cluver et al. 2013; Alatalo et al. 2014), low-redshift radio galaxies (Ogle et al. 2007, 2010, 2014; Nesvadba et al. 2010; Guillard et al. 2012b; Lanz et al. 2015), and central cluster galaxies (Egami et al. 2006; Donahue et al. 2011). It is interesting that the most powerful H₂ emission found to date has been from the Spiderweb protocluster at z = 2.15 (Ogle et al. 2012), and from stacked IRS spectra of z ~ 2 galaxies (Fiolet et al. 2010). Although the emission mechanism for the high-z gas is not yet clear, the IRS points the way toward potentially important discoveries in the future (Appleton et al. 2009; Guillard et al. 2015).

One question that is raised by the current observations is that of the dominance of molecular hydrogen cooling versus IR fine-structure lines. For example, in the pioneering work of Santoro & Shull (2006), these authors describe how the initial formation of the first galaxy-sized clumps of gas is dominated by cooling from mid- and far-IR rest-frame fine-structure lines (principally [Si II] 34.8 µm, [C II] 157.7 µm and [O I] 63.2/145.5 µm), once the metallicity increases above a critical value (typically Z > 10⁻³ solar). In such a case, the initial collapse of the first clouds would radiate mainly in the metal fine-structure lines, with the mid-IR H₂ lines playing a minor role in the cooling. However, once the collapse is initiated,
<figure><img src="image_17.png" /><figcaption>**Figure 16.** Selected IRS spectra from the spectral grid of Figure 1(b) with main detected lines identified. Spectra from: (a) the main shock-north (P142); (b) the main shock further north (P165); (c) the main shock and beginning of SQ-A complex, including rising PAH features indicating some heating from star formation (P187); (d) in the northern stellar loop from NGC 7318a (P192)—note very faint H₂ lines; (e) SQ-A region (P209) and stronger PAHs.</figcaption></figure>

many complex processes, including shocks and turbulence, could rapidly change the conditions in the gas. Our purely molecular models of Stephan's Quintet's shock (Guillard et al. 2009; Lesaffre et al. 2013, and the current paper) predict comparable H₂ and [C II] line luminosities, as observed (Appleton et al. 2013), even in regions of much higher metallicity than those expected in primordial clouds. A lesson from the Stephan's Quintet system is that the collision of NGC 7318b with a mainly H I tidal arm has resulted in an

almost total transformation of the H I into H₂ in 10–20 Myr (see Guillard et al. 2009). We have also shown here that most of the kinetic energy is bound up in the coolest gas heated by low-velocity (V ~ 4–5 km s⁻¹) shocks. If low-velocity shocks form at the end-point of a turbulent cascade in gas accreting within dark-matter halos, the H₂ lines may again become important in the cooling of the gas, perhaps forming H₂-bright hotspots. Models investigating conditions in shocked gas with low metallicity are being investigated with this in mind
<figure><img src="image_18.png" /><figcaption>**Figure 17.** (A) The difference between the model-derived and the observed H₂ line ratios (R) as a function of lower temperature to determine T<sub>l</sub>. The black solid, red dotted, and blue dashed curves represent different cases. For the case of the black curve we adopt the value of T<sub>l</sub> = 50 K. The red and blue curves occur in warm regions, where the temperature of all H₂ molecules is high enough to be traced completely by the mid-IR rotational lines. In such cases we adopt the value of T<sub>l</sub> at the temperature where we have the minimum deviation. For instance for the red and blue curves we adopt T<sub>l</sub> = 120 and 198 K, respectively, given by our power-law model. (B) The spatial distribution of the extrapolation methods of cases I–III displayed as a schematic diagram covering the mapped area shown in Figure 1(b) (see text). Case III is where the 0–0 S(0) is not detected but the higher-<i>J</i> levels are, implying high temperatures.</figcaption></figure>

(Guillard et al. 2016), and may help to motivate future far-IR
attempts to detect rest-frame H₂ emission at redshifts at or
beyond the era of reionization.

This paper is dedicated to the work of James Houck of
Cornell University (1940–2015), who was the PI of the *Spitzer*
IRS instrument. Without his vision and dedication to building a
superb instrument, the work described in this paper would
never been possible. This work is based, in part, on
observations (and archival observations) made with the *Spitzer*
*Space Telescope*, which is operated by the Jet Propulsion
Laboratory, California Institute of Technology under a contract
with NASA. The work is also based, in part, on observations
made with *Herschel*, a European Space Agency Cornerstone
Mission with significant participation by NASA. Partial
support for the *Herschel* work was provided by NASA through
an award issued by JPL/Caltech. U.L. acknowledges support
by the research projects AYA2011-24728 and AYA2014-
53506-P financed by the Spanish Ministerio de Economía y
Competividad and by FEDER (Fondo Europeo de Desarrollo
Regional) and the Junta de Andalucía (Spain) grants FQM108.

Appendix A

IRS Spectra of Various Extraction Regions Shown in
Figure 1

IRS spectra of various extraction regions shown in Figure 1
are provided in Figures 15 and 16. The properties derived
from these and the full set of spectra are presented in
Tables 2–5.

Appendix B

Extrapolating the Mass of Gas to Low Gas Temperatures
Using the Power-law Method

The power-law analysis described earlier can also make a
prediction about the total molecular mass below 100 K (the
practical limit for exciting the lowest 0–0 S(0) H₂ rotational
line), since we can extrapolate the mass of gas below which the
rotational H₂ emission is excited (see Togi & Smith 2016 for

more details). This assumes that the same power law derived
for warmer gas can be extrapolated to lower temperatures.
Increasing the number of extremely cold H₂ molecules below a
certain temperature will cause a change in the total molecular
gas mass, but will result in an insignificant change in the mid-
IR H₂ rotational-line flux. We define the sensitive temperature,
T<sub>s</sub>, below which H₂ molecules are too cold to cause substantial
changes in the mid-IR rotational-line H₂ excitation diagram. In
our analysis three different cases emerge in determining T<sub>s</sub>,
depending on the individual spectral region explored.

1. Case I. We found that for some positions in the filament, as we decrease the lower temperature T<sub>l</sub>, the ratio (R) of the difference between the observed and the model fits decreases continuously, and below a certain temperature (T<sub>s</sub>) the deviation becomes insignificant and minor change in the model fit occurs. The parameter, R, is defined as

$$
R = \sum_{i=1}^{m} \left( \frac{f_{i,\text{mod}} - f_{i,\text{obs}}}{\sigma_{f_{i,\text{obs}}}} \right)^2, \quad (\text{B1})
$$

where $f = \ln\left(\frac{N_u / g_u}{(N_u / g_u) S_{(1)}}\right)$, $f_{i,\text{mod}}$ and $f_{i,\text{obs}}$ are the modeled and observed flux ratios for the $i$th line with uncertainty $\sigma_{f_{i,\text{obs}}}$, and the summation is over all the independent line flux ratios. The black solid curve in Figure 17(A) demonstrates this case. In such a scenario we extrapolate our power-law model to 50 K to calculate the total molecular gas mass. The molecular gas mass calculated by extrapolating our model to 50 K correlates with the molecular gas mass derived using the Galactic CO conversion factor, $\alpha_{\text{CO,Gal}}$ (Togi & Smith 2016)

2. Case IIa. As we decrease the lower temperature, T<sub>l</sub>, the value of R decreases, but below a certain temperature it starts increasing and at low temperatures shows no significant change. The red dotted curve in Figure 17(A) demonstrates this case in region 76. The value of R decreases until the lower temperature of about 120 K but
increases in the range 50–120 K and remains almost constant below 50 K. In such a case we adopt the corresponding temperature for $T_t$, here 120 K, where the deviation is found to be minimum. The presence of excess warm molecular gas due to shocks could be the reason for high $T_t$, and the complete molecular gas in these regions is traced by the mid-IR $H_2$ rotational lines.

Case Iib. The blue dashed curve is a similar case but the minimum deviation occurs at very high $T_t$. This was observed in region 103 (see Figure 1(b)), the central shocked region of the Quintet, where the model yields the best-fit value of $T_t = 198$ K. The molecular gas in this central shocked region of the Quintet is heated to a temperature of ~200 K.

3. Case III. In some regions the S(0) line is undetected but there are detections of high-$J$ lines of $H_2$. The S(1) and higher-$J$ lines of $H_2$ correspond to energy levels $J \ge 3$. High-$J$ levels require high temperatures for excitation, which result in high $T_s$. In such cases we extrapolate our power-law model to 80 K to calculate the total molecular gas mass. Several ultraluminous infrared galaxies, which are local mergers, with warm dust color temperatures have nondetections of S(0) but detection with good signal-to-noise ratio for high-$J$ rotational lines (Higdon et al. 2006; Stierwalt et al. 2014). In these galaxies we need to extrapolate our power-law model to 80 K to recover the total molecular gas mass in order to be consistent with their dynamical mass estimates (Togi & Smith 2016).

We show in Figure 17(B) a schematic map of the distribution of the various cases over the mapped area. The squares of case I (38%) are dark and occupy mainly the cooler northern part of the mapped region, and the median value of warm mass fraction is only 4%. Cases II (54%, green squares) and Case III (8%, red) occupy the regions where the stronger shocks dominate and have median warm mass fractions of 39% and 27% respectively.

Although we detect $H_2$ in almost every position observed, there are areas near the western and southern borders of the maps where no warm $H_2$ is detected, even though it lies within the mapping region. We note that there is potentially another possible scenario, where no rotational $H_2$ lines are detected at all because the gas has too low a temperature to be detected in the mid-IR. Although this is theoretically possible, we assume instead the simpler explanation that there is no molecular gas at these undetected positions. This is probably justifiable, given that both single-dish and interferometric observations confine the CO-emitting gas to similar regions to the warm $H_2$ distribution. Furthermore, the C$^+$ emission (Figure 3), which could potential map CO-dark molecular gas (Wolfire et al. 2010), also seems to follow the same spatial distribution as the warm $H_2$ emission, and so large quantities of intergalactic “dark” molecules are not strongly favored by the current observations.

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