In Star Trek: The Next Generation and its contemporaneously set sequels (Star Trek: Deep Space Nine and Star Trek: Voyager), impulse engines are used for moving spacecraft at sublight speeds, whereas the warp drive is used for travelling at light or faster-than-light speeds. Warp drive speeds are measured in "warp factor", an irregular numeric scale with values known to range from 1 (light speed) up to but not including 10 (infinite speed).
My question is whether it has been definitely established that it is possible in the TNG era to use the warp drive to travel at sublight speeds, which would correspond to a warp factor of less than 1. In particular, I am looking for the following types of evidence, in descending order of priority:
- An unambiguous depiction in the primary canon (i.e., the TV shows and feature films) of sublight warp travel.
- A statement in paracanonical works such as the Star Trek: The Next Generation Technical Manual or the Star Trek: Deep Space Nine Technical Manual that warp drives can operate at sublight speeds.
- An unambiguous depiction in official but non-canonical works (e.g., novels, comics, computer games) of sublight warp travel.
As discussed in the answers to this more open-ended question, I am aware that some Trek shows set before the TNG era occasionally referenced ships travelling at warp factors less than 1. However, these shows used a different warp factor scale and depicted a more primitive warp technology. My question is specifically about TNG, DS9, and Voyager, and about the warp technology and the warp factor scale in use in that era. I'm looking for actual depictions of sublight warp travel in this era, or in-universe statements in this era that such travel is possible. I'm not interested in extrapolations from what we know about ENT- or TOS-era warp.