What are Infrared-Faint Radio Sources?

• by enno.middelberg scientist, translator

  Several participants have classified sources as Infrared-Faint Radio Sources, or IFRS. When using this classification one has to be careful about the infrared faintness: a very faint radio source (say, one or two contours) is very likely to have no infrared counterpart, simply because it is either intrinsically faint or very far away. In fact, we cannot tell if it is an IFRS or not, because all we know is that the IR is fainter than what could be detected with the IR telescope at the time.

  When a bright radio source has no IR counterpart, then it is much more likely to be an unusual, infrared-faint object, because for it to fall below the sensitivity limit of the IR telescope its IR emission needs to be really, really faint.

  And that's the point of IFRS: these sources have much fainter IR than radio emission (a ratio of at least 500 is commonly adopted).

  Let's suppose a typical, non-IFRS galaxy has a radio emission which is 50 times brighter than the IR. If such a source is close to us, both the radio and IR emission are detected in our images. If such a source is farther away, at some point the IR becomes too faint to be detected, while we can still detect the radio emission. Does this make the source an IFRS? Of course not, it's still a normal galaxy.

  Therefore I'd argue that not every one/two-contour radio source without IR counterpart should be tagged #ifrs.

  Enno

  Posted December 19, 2013 8:19 AM

• by 42jkb scientist, admin

  Agreed. There will be a blog post on this topic by Ray.

  Posted December 19, 2013 11:07 AM