Ask yourself if you could have done the work without the assistance, direct or indirect, of the head.
I do assume a minimal interaction between members of the lab/group and at least between you and the head. If you pursued a research out of black I don't really know how to answer. It wouldn't be a normal situation.
Did you rise the funds for your salary or are you a permanent researcher with at least a fixed allowance? This allows more freedom.
Opposite if the founds are coming from the head's applications, considered how hard s/he may have worked to secure that. Likely, details aside, your activity and results correlate at least with the scientific content of those successful applications.
What about consumables and equipment? What about the presence of a group and how that impacted or even just motivated your work?
What is supposed to be the role of the head on your activity? Merely an administrator of resources? And at which level?
Consider that the simple fact that you conducted an independent research can be seen as positive, as for lot of researchers struggle with lack of autonomy.
For instance, deserving finances and time machine to a certain research can be see as a factual collaboration. As a group or lab head I would not let those be used to something that I would not consider really worth of investigation. At the end in a perfect environment your current doubt should not have even emerged, as it should be clear a priori what are the freedom of single researchers (which ideally should be almost unlimited within the field but it cannot be unless you have your own allowance) and expectations.
I do realised that there could be (there are) concerns about considering all the above as a scientific contribution, but it is also true that almost every action (or absence of) of the head of a lab in biology, chemistry, and other hardware disciplines, not only influences the outcomes of research, but often permits the research to be conducted at first.
Depending on the type of lab and economical situation, I would personally be glad to have the head as a coauthor.
A specific answer might depends on a lot of variables, which not surprisingly are even personal and based on the atmosphere at the working place rather than scientific or economic. But it is customary for a head to be in most if not all the papers produced by his/her group. Different is the case when papers are outcomes of his/her lab, and this distinction is contingent to each situation.
Finally, and less general, personally and depending on career stage, I would simply go to him/her and look for an opinion. I wouldn't be surprise of an answer like "go solo, you are young and it will makes a nice display" or "I did nothing*,go ahead just thank me for discussions". It is a real possibility, too.
What I would not do, is to submit without the other members of the group knowing. It would be at least strange if we do not profit of discussions with other scientists/researchers we have around every days, even more considering we are travelling to conferences overseas to discuss with others. As such, I would go through the above step (discussion with the head) anyway, and I will get a direct opinion or I could infere his/her expectations.
*even if s/he obtained the funds.