Radio Galaxy Zoo Talk

How does passage through a foreground galaxy affect radio emissions from a background source?

  • JeanTate by JeanTate

    Over in the GZ forum, almost seven years' ago now, NGC3314 started a thread Wanted! Galaxy pairs which overlap but are not merging. Finding backlit disk galaxies - preferably backlit by pure ellipticals*! - is A GOOD THING because it can lead to all kinds of insights into dust and the ISM (interstellar medium) in general, because the foreground galaxy does interesting things to the light from the background one as it passes though.

    Of course, the same thing happens to light as it passes through the ISM in our own galaxy, and lots of astronomers study this too.

    Drop the frequency of the electromagnetic radiation a half dozen orders of magnitude or so; how does passage of ~1400 MHz light though the ISM affect it? From what I vaguely remember, there are dispersion and polarization effects, and there would surely also be line/band absorption if there were any lines or bands of astronomical significance in the frequency band.

    Is that right?

    Here's what I've been looking for, to provide a concrete example (it's from the ARG0002sqf - radio emission centered on an object which is not an SDSS PO? #overlap? thread; don't be put off by the title!):

    enter image description here

    This is, very likely, a z ~0.25 corejet radio source located behind (in the background of) a z=0.039 foreground spiral. But the 'radio light' had to pass through the spiral galaxy before it was detected here on Earth; how did its passage through the spiral galaxy affect it? In particular, how might its apparent morphology have been changed?

    *elliptical-elliptical overlaps are the 'ugly children'; apparently no (optical) astronomer thinks they are of any interest whatsoever (unless they happen to also be gravitational lenses)

    Posted