What is a spiral tracer and what are its characteristics?

[blumfeld0]

Spiral Tracer??

Hello. Has anyone ever heard of a spiral tracer? and what characteristics they have??
any good link on the topic would also be appreciated
thank you

 

[SpaceTiger]

I'm not familiar with it as any special terminology, I think it just refers to something that traces spiral arms, such as neutral hydrogen gas or stars.