View Full Version : What do you think this is?

Jean Tate
2012-Nov-23, 01:08 AM

Its name is SDSS J075137.19+325447.3 (http://skyserver.sdss3.org/dr9/en/tools/explore/obj.asp?id=1237674365918970282), and its location (RA, Dec) is in its name.

(If someone knows how to post it as an image, please do so, and please explain how to do it).

I posted this in the Galaxy Zoo forum Oddballs- Post your weird pics here! (http://www.galaxyzooforum.org/index.php?topic=1434.0) thread, here (http://www.galaxyzooforum.org/index.php?topic=1434.msg620831#msg620831).

2012-Nov-23, 01:38 AM
Galaxy merger, with two active nucleus?

2012-Nov-23, 04:37 AM
That's a superposition - there are two distinct redshift systems in the spectrum. The strong emission lines at higher redshift z=0.356 would account for the green color of one of the knots (since green in the SDSS color images actually gets mapped from the r filter in the deep red). The line ratios suggest that this is a starburst object. The lower-redshift galaxy, contributing absorption lines roughly at z=0.21 to the combined spectrum, looks more like a normal elliptical.

Rats. If the gas-rich galaxy were in front, I could add this to the GZ catalog of backlit galaxies to study dust.

Jean Tate
2012-Nov-24, 12:29 AM
Thanks ngc3314!

Another zooite (zutopian) copied my original post into the GZ forum thread Weirdest Spectra (http://www.galaxyzooforum.org/index.php?topic=279434.0) (here (http://www.galaxyzooforum.org/index.php?topic=279434.msg620835#msg620835)). As is clear from the ensuring discussion, the conclusion that there are two distinct redshift systems in that spectrum is one the zooites who participated in that discussion also reached (presumably independently).

Two things strike me:

1) if the background galaxy is a starburst object, it must be an incredibly furious (and large) one, mustn't it? At a stage when the starburst has barely begun too (otherwise it'd be so choked with dust it'd look more like Arp 220, and at that distance be invisible to the SDSS camera). If so, are there any starbursts, closer than z = 0.355, of comparable intrinsic luminosity? And does the apparent lack of massive amounts of choking dust in the higher-z object imply low metallicity, of the kind found in Green Peas (and if so, is this - perhaps - a super-giant Pea)?

2) Why does the foreground ETG (elliptical) seem split? The shape of the outer parts - at the edges of the yellow - seems nice and round, suggesting that it's just one object. Is the vertical brown line a dust lane in the foreground ETG (making it, perhaps, a lenticular)? Or is it - somehow - something caused by the far-in-the-background intense starburst object?

I'll keep an eye out for z < 0.2 gas-rich objects back-lit by a z > 0.3 ETGs ;) :D