Two different spectra for the same galaxy in DR9

For the left-most galaxy in this image, two different spectra are shown by SkyServer in DR9. No problems in DR13.

Load page http://skyserver.sdss.org/dr9/en/tools/explore/obj.asp?id=1237655108360667248
Click on the spectrum shown in the page. The spectrum will be displayed with z=0.03058.
Click on 'Navigate'
Click on the spectrum shown in the right bottom of the page. The spectrum displayed
looks different than the previous one and has z=0.05756.

The RA and DEC have the same values in both spectra. Fiber, MJD, z and Class values differ.

The problem is not seen in DR13.

Posted June 15, 2017 10:44 AM

It was observed spectroscopically twice, which is not unusual, and both spectra are accessible from DR13: link.

What's a little unusual is there are two quite different redshift measurements (z=0.058 and z=0.031) and neither has a warning flag set. Just from eyeballing the spectrum I'd say most likely these are overlapping systems and the spectrum contains significant contributions from both.

I don't know if Dr. Keel is still interested in overlaps, but if he is perhaps a mod should ping him.

Posted June 15, 2017 4:28 PM

by Budgieye moderator

Interesting. The emission peaks are correctly labelled at 0.05, and the absorption peaks correctly identified at 0.03. My guess, and perhaps this will give Dr Keel a good laugh, is that the light from the most distant orange galaxy at 0.05 passed through the dust of the nearer galaxy at 0.03 and some of the light was absorbed with chararacteristic of 0.03

enter image description here

http://skyservice.pha.jhu.edu/DR9/ImgCutout/getjpeg.aspx?ra=126.0721377&dec=41.95955726&scale=0.2&width=200&height=200&opt=G

http://skyserver.sdss.org/dr9/en/tools/explore/obj.asp?id=1237655108360667248

enter image description here

http://skyserver.sdss.org/dr9/en/get/specById.asp?id=856866766851172352

enter image description here

http://skyserver.sdss.org/dr9/en/get/specById.asp?id=856871752536451072

Posted June 15, 2017 6:08 PM

by Budgieye moderator

4 spectra on "All Spectra" in SDSS dr13, though I think 2 are just relabelled.

http://skyserver.sdss.org/dr13/en/tools/explore/Summary.aspx?id=1237655108360667248

http://skyserver.sdss.org/dr13/en/tools/explore/allSpec.aspx?id=1237655108360667248&spec=856871752536451072&apid=&fieldId=0x112d08c380490000&ra=126.072137694887&dec=41.9595572555374&plateId=856809905007388672

Posted June 15, 2017 6:56 PM

by NGC3314 scientist

Nice find! The spectrum does show two sets of lines, visual most obvious in the sodium Na D features and H-alpha+[N II]. Fo extra fun, H-alpha and [N II] in the background galaxy are seen at nearly enough the same wavelengths as [S II] from the foreground to confuse the line IDs on the top spectrum shown by Budgieye. The DR13 interactive spectrum display is http://dr12.sdss.org/spectrumDetail?plateid=761&mjd=54524&fiber=225

This system was not in the original Galaxy Zoo overlap catalog; this piece of the sky, IIRC, was only covered later, so it was found in the continuation after the DR8 images were released and went into in our "live" update kept going after that. This is the first time I've seen the redshift for the background system, so it's been gleefully added to the working table. Still no redshift value for the third galaxy to the south as of DR13.

Posted June 15, 2017 7:12 PM

by Budgieye moderator

Thank you, Dr Keel. Congratulations on your find karthikeyan.d 😃

I have put this in The Index 2.3 Overlapping galaxies https://talk.galaxyzoo.org/#/boards/BGZ0000001/discussions/DGZ0000wrb?page=2

Posted June 15, 2017 7:33 PM

by ElisabethB moderator