I teach economics at an Indian University and recently came across some good publicly available lecture slides by another professor (US R1 University). I would like to share the slides with my students (with slight modifications). To be clear, I do not want to use the slides during my lectures but only provide the slides as reference material (of course, with due credit to the original creator).
I have emailed the professor requesting permission to reuse their slides, but I haven't heard from them. The slides themselves do not carry any copyright notice, but are available on the professor's personal website.
Assuming the prof does not respond, is it appropriate/ethical to distribute the slides, and simply mention/link the original source? Ideally, I would have liked to add a note saying "Slides used with permission from Prof. X", but if Prof. X hasn't explicitly given permission, can I still add the note?