Galaxy Zoo Talk

AGNs

  • magslis by magslis

    The tutorial says that AGNs are very bright, compact, star-like but I was wondering if that's always the case. Could this object: Image AGZ0005ngr have an AGN? the centre is quite blindingly bright, esp. compared to the rest of the galaxy - or is the otherwise bright galaxy being outshone here? There doesn't seem to be much information on the system 😕 and the picture isn't very sharp but it's just about possible to make out some small irregularities on the outer edges of the arms which would indicate a history of merger. Or am I just looking too hard:-)
    I also seem to recall examples of galaxies with AGNs that don't have a bright centre at all - will post them here if I manage to find them in my collections.

    Posted

  • magslis by magslis

    Here is a example of one without a bright centre:
    AGZ0001I0H
    or is it because these are optical light images and there's so much dust in the way that the centre looks dimmer?

    Posted

  • JeanTate by JeanTate in response to magslis's comment.

    If you click on the "Galaxy Zoo examine" link, and then on the "View on SkyServer" one, you'll get a DR10 image of the object. DR10 images are nearly always sharper than the ones we get to classify in Galaxy Zoo. Like this:

    enter image description here

    Yes, AGZ0005ngr does have a bright center, doesn't it? Unfortunately, without a spectrum, you really can't tell if there's an AGN there or not ... it might be a particularly compact, bright bulge; it might be a supernova; it might be a foreground star; it might be an overlap; ... (all of these exist, among SDSS images of galaxies) ... it might even be a strong gravitational lens (I doubt it, and no such has been seen in any SDSS GZ image, but ...).

    I also seem to recall examples of galaxies with AGNs that don't have a bright centre at all

    Indeed, and they're more common than you might otherwise imagine! 😮 For example, an AGN can be 'hidden' by being viewed through the whole of a spiral galaxy's disk, even the dust lane (in an Eos, edge-on spiral), or even just by dusty clouds in an inner arm.

    AGZ0001i0h (lowercase letters) does have a spectrum, and the SDSS automated pipeline calls it STARFORMING. My guess is that this refers as much to the blue-white blob just to the SW (lower-right) of the nucleus/bulge as the bulge itself.

    Happy (continuing) hunting! 😃

    Posted

  • magslis by magslis

    Thank you for responding. I've read somewhere that there is something called 'low-luminosity AGNs' and that's what got me thinking that perhaps it isn't always an obviously star-like nucleus.

    I use "examine", SkyServer, NED and SIMBAD (by the way, the second object shows up as AGN there) and they help with the quality of image and additional data but there's still some educated guesswork involved, isn't there?

    Thank you again.

    Thank you again.

    Posted