Galaxy Zoo Talk

Possible AGN ?

  • suelaine by suelaine

    The brilliant white centre in this either disc or elliptical, might it be an AGN?

    Posted

  • planetaryscience by planetaryscience

    that particular thing is an artifact caused by the center being so bright that the images make it dimmer. #ukidssring

    Posted

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

    It's a disk galaxy - it has pointy ends! - and yes, the extremely bright center means it's almost certainly an AGN.

    Posted

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

    Well, astronomy is full of surprises! 😄

    Here's this galaxy as seen by SDSS:

    enter image description here

    Very bright nucleus/bulge, no surprise there. However, look at the spectrum!

    enter image description here

    It'd be very cool if an astronomer (a SCIENTIST) could weigh in, but I think this shows a quite 'dead and red' stellar population - without even the slightest hint of an AGN - and very little dust either. If so, how come the bulge is so bright?

    Posted

  • planetaryscience by planetaryscience

    Well, there's a small OIII spike in its different emission lines, and the hydrogen emission line appears to support the red-and-dead elliptical. It appears to be that the center just has a dense cluster of stars.

    Posted

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

    Well, there's a small OIII spike in its different emission lines

    It certainly looks like that in the png version I copy/pasted; however, if you use the interactive spectrum, you'll see that there's no [OIII] emission

    It appears to be that the center just has a dense cluster of stars.

    Yes. I wonder how easy it would be to estimate the surface brightness, and compare that with the core of a big globular cluster (like Omega Cen)?

    Posted

  • planetaryscience by planetaryscience

    S = m + 2.5 * log10 A.

    m: 14.43

    14.43 + 2.5 = 16.93

    A= ~2.5 arcseconds

    0.39794

    16.93 * 0.39794 = surface brightness of +6.7

    Posted

  • planetaryscience by planetaryscience

    Omega Centauri's surface brightness:

    S = m + 2.5 * log10 A

    m: 3.9

    3.9 + 2.5 = 7.4

    A= 2178 arcseconds

    3.33806

    7.4 * 3.33806 = surface brightness of +24.7

    That means that this galaxy has a surface brightness of almost 4x as much as Omega Centauri.

    Posted

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

    Good start, planetaryscience! 😃

    m: 14.43

    A= ~2.5 arcseconds

    Where did you get these values from, may I ask?

    Also, A is an area, so it will have units of square arcsecs (or similar), not arcsecs.

    16.93 * 0.39794 =

    The default precedence order for operators in an equation like "S = m + 2.5 * log10 A" is multiplication then addition, so you first need to calculate "log10 A", then "2.5 * log10 A", and finally "m + 2.5 * log10 A".

    Posted

  • planetaryscience by planetaryscience

    I got the magnitude value from finding the average of the different values from SDSS (ugriz)

    I got the area from visually measuring the galaxy.

    Here is the corrected calculation:

    S = m + 2.5 * log10 A

    A= 135 arcsecs (15 x 9)

    2.13033

    4.63033

    surface brightness= 19.06033


    Omega Centauri:

    A= 4743684 😮

    6.67611

    9.17611

    surface brightness= 16.57611

    Posted