Hi a_colombo,
You could create personalized links and add the embedded data field of the email address etc. at the beginning of the survey flow. After you add an authenticator connected to the exact same list you have used to create the personlized links with. This way you can make sure that the person is automatically authenticated.
Since you want to make sure that you do not know, WHO has given WHICH answer in your poll you then add a "end of survey" element in the survey flow and customize the option to NOT record personal information.
When the survey data comes in you then have your answers in Data & analysis. If you are missing certain amount of responses you can then go into the contact list which is connected to the authenticator and filter for statistics as to who has not given an answer.
Please make sure you test the set up before you go into the field.
Hope this helps