Does this elliptical have strange colors? What are the unmarked emission lines?

by JeanTate

A couple of days' ago, zooite planetaryscience ('ps') wrote an interesting post in the Oddballs- Post your weird pics here! thread, over in the Galaxy Zoo forum; it's about this galaxy (SDSS J075056.73+285041.9; DR8 ObjId 1237657401335611678):

That's a DR8 image; here it is in DR10:

A bit of a discussion ensued, and is still going on. Rather than have it continue on a thread that's supposed to be about posting oddball images, not conducting investigations into them, I thought I'd start a thread here.

Please read ps' GZ forum post, and the several which follow from it, for all the details. Let's use this thread to find out whether "[y]ou don't usually see [...] that color in ellipticals (which it appears to be) and you don't see it in spirals, either." And also find out what the strange, strong, narrow emission lines are, in its SDSS spectrum.

Posted January 20, 2014 2:06 PM
by JeanTate in response to JeanTate's comment.

ps' last post, on this topic, ended with this (unfortunately it's a real bear to reproduce the formatting, and I'm not even going to try):

Galaxy comparison:

Galaxy Redshift (z) u-g g-r r-i i-z

2MASX J07505675+2850417 0.159908 2.00 1.17 0.37 0.44

2MASX J10373689-0041182 0.159200 2.06 1.16 0.51 0.38

2MASX J07495579+2840122 0.142201 2.11 1.19 0.48 0.32

It's hard to tell if the first galaxy - the one which kicked this exercise off - really does have unusual colors, just by looking at a table like this. And it'd be even more difficult if the table contained a hundred or so lines (rows), rather than just three.

How could we present such data so as to make the question easier to answer (or at least easier to tell)?

Posted January 20, 2014 2:15 PM
by planetaryscience in response to JeanTate's comment.

Well, first of all, the first galaxy has an obvious difference in the last 2 magnitudes: Compared to the 0.51 and 0.48 in r-i, it has a very small 37, more than 0.11 off, and then the last one (i-z) is larger than the 2nd largest by 0.08. This may not seem much, but only more data can tell that.

Meanwhile, I remembered a way to utilize NED to find more galaxies of the same redshift, but first I need to know: What should the upper and lower boundaries be?

I'll start with 0.155 to 0.165 and show you my results in the next post...

Posted January 20, 2014 3:43 PM
by JeanTate in response to planetaryscience's comment.

This may not seem much, but only more data can tell that.

Yes, that's certainly true! There's also the question of how significant those differences are, when the estimated errors - provided by SDSS - are taken into account (however, we can put off dealing with that until later).

I remembered a way to utilize NED to find more galaxies of the same redshift

SDSS provides a number of tools which make it pretty straight-forward to do this. Karen Masters provides an introduction to one - CasJobs - in this GZ blog post. If you - or any other zooite reading this - are interested, I could walk you through a simple example of how.

What should the upper and lower boundaries be?

I'll start with 0.155 to 0.165 and show you my results in the next post...

That's an excellent question! 😃 How do you think you could find out (other than by just guessing)?

Posted January 20, 2014 4:05 PM
by c_cld

Before use of casjobs have a look at DR7 from where the spectrum comes from as of mjd 52618

There is no strange emission line but a bad sky line!

The previous spectrum from mjd 52592 was presented in DR9-10, why not the last one which had a better S/N?

Posted January 20, 2014 4:44 PM
by JeanTate in response to C_cld's comment.

Thanks c_cld.

There are actually two different questions here; are the colors unusual? and what are the strange emission lines? They're related, of course (if the emission lines are real, then they should affect the broadband colors), but at this stage I myself would like to treat them separately, as if they're independent.

Addressing the spectrum question: the fact that they seem unrelated to any even half-way reasonable redshift system or set of skylines, and the fact that a nearby (on the sky) galaxy also has such lines (at completely different wavelengths!) would suggest that they're artifacts of some kind. And what you found seems to be consistent with that hypothesis ...

Posted January 20, 2014 4:52 PM
by c_cld

http://dr9.sdss3.org/advancedSearch

Survey PlateID MJD Fiber RA Dec Redshift zwarning r [S/N]2 Class

SDSS 1059 52592 568 117.73641 28.84499 0.1598 0 9.16 GALAXY
SDSS 1059 52618 580 117.73641 28.84499 0.1599 0 16.47 GALAXY

http://dr9.sdss3.org/spectrumDetail?plateid=1059&mjd=52592&fiber=568

http://dr9.sdss3.org/spectrumDetail?plateid=1059&mjd=52618&fiber=580

Posted January 20, 2014 4:58 PM
by c_cld

sample of red galaxy at redshift around 0.16

name ra dec
1237663782602670238 36.309 -1.086
1237673705576858015 111.213 40.561
1237651799624581279 152.535 -1.102
1237648721759830130 162.306 0.247
1237648720150462633 165.067 -0.868
1237648720156754092 179.479 -0.910
1237648704041451660 186.183 -0.346
1237648704041451668 186.209 -0.317
1237655494904840239 201.136 -2.247
1237655468063129962 230.929 1.039

copy/paste list in http://skyserver.sdss3.org/dr10/en/tools/chart/list.aspx

Posted January 20, 2014 5:58 PM
by c_cld in response to JeanTate's comment.

The other galaxy SDSS J074955.83+284011.9 (DR8 ObjId 1237657118404575239) was a spectrum target on the same day 52292 and the same plate 1059 as the first galaxy 2MASX J07505675+2850417. The two show bad peaks: the explanation could come from what said Bill once on weird features/artifacts in spectra.

http://www.galaxyzooforum.org/index.php?topic=279434.msg644292 #msg644292

Posted January 20, 2014 8:48 PM
by c_cld in response to JeanTate's comment.

Same color space

name ra dec
1237656494580170971 7.99864629 14.19987008
1237649954403844246 20.35607876 14.82474831
1237673704503705920 113.18700861 40.07514341
1237657401335611678 117.73641179 28.84497537
1237651251484098717 126.58184142 48.93281299
1237658299525824608 139.66223087 5.46772341
1237658492264448247 145.68255048 7.47948072
1237661069787660482 155.77595617 13.34371992
1237661137424482402 157.67640788 38.51528237
1237671128053579937 178.42119776 3.10457277
1237651754010607726 180.63567087 2.49353283
1237658800432349282 203.81699731 52.30952159
1237664854180626566 214.55893438 34.56508194
1237661872413671630 215.7903598 40.26892066
1237665351318044768 218.48819274 27.6841046
1237655464852914305 228.81491857 54.20892814
1237655349427306668 236.13836837 51.42998303
1237651538723471395 236.2991235 56.42841149

copy/paste list in http://skyserver.sdss3.org/dr10/en/tools/chart/list.aspx

Posted January 20, 2014 10:01 PM