Abstract
We report the study of the spatial distribution of the anion C
6
H
−
and its comparison with abundant neutral species such as C
6
H and HC
3
N, and with the cation NNH
+
. We achieved the spatial distribution of an anion in space for the first time. The neutrals and the anion follow practically the same spatial distribution at all velocities. However, we found some differences between cations, neutrals, and C
6
H
−
for some velocities that are more likely related to their different formation and destruction processes. The spatial size of the anion source can be fitted as an ellipse with half major axis of 80″ and 40″. We conclude that the spatial size derived previously in TMC-1 for the anion C
10
H
−
, whose lines are only clearly detected in IRC+10216, is not compatible with the results of our study. Moreover, we consider that the column density of this large anion, if it is really present in TMC-1, has to be reduced by a factor of ∼20–30 at least. Although we cannot definitively exclude the presence of C
10
H
−
, we conclude that the possibility that C
9
N
−
might be the carrier of the lines observed in IRC+10216 seriously has to be taken into account based on our data.