An elliptical with a nucleus waaaay off-center: anyone seen this kind of object before?
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JeanTate
SDSS J111143.60+404914.7, a.k.a. MCG +07-23-031, PGC 034049, GALEXASC J111143.85+404914.2, 2MASX J11114358+4049142, and a bazillion other names (including FIRST J111143.6+404916) is the nucleus of an elliptical galaxy ... or is it? Here's an SDSS image, centered on it:
It's clearly waaay off-center of the brighter yellow patch, though it may be rather nearer the center of the bigger, fainter yellow patch (I haven't checked). The SDSS spectrum has a couple of unusual features, to my inexpert eye, H-alpha absorption for example, and a label "broadband" but I can see no broadened lines, emission or otherwise (and [NII] is strong, [OIII] absent, etc):
Have you come across a galaxy like this before?
By the way, A1001 pointed to this, over in RGZ Talk (Discussion thread link); yes, it's a radio source (that's what its name beginning with FIRST means), and an IR one, and a UV one, ...
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zoob1172
1237661966887616697 is one photometric object. The target is a RS. What's special about this one?
There are 77 objects at z=0.07 just in the field limit of DECaLS. 7 of those are .078s.
1237678808533958664
A search of "disturbed" yielded 10,034 hits. Maybe there are a few in there?
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Ghost_Sheep_SWR
in response to JeanTate's comment.
Can't remember such an extreme example.
Does 'lopsidedness' apply? Got two papers but one focuses on spirals and the other on spirals and irregulars (WHISP).
Secondly this is probably induced by interaction with at least one of the smaller galaxies around:
SDSS J111144.93+404846.2 zsp 0.07739 +/- 0.00002
Spectrum looks quite the same except for [NII]?
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JeanTate
in response to zoob1172's comment.
The target is a RS.
"RS"?
What's special about this one?
As I said, the nucleus seems way off-center, with respect to the rest of the galaxy.
1237678808533958664
Here's an SDSS cutout image:
In this, the nuclei are hidden within the "bulges" (the luminosity distribution looks pretty smooth, though even a semi-quantitative analysis would test this better), but the outer envelope(s) are distorted/disturbed. This sort of thing is pretty common, in images of ellipticals in/near the centers of rich cluster, in my experience. SDSS J111143.60+404914.7 is, to me, unusual in having a very sharply defined nucleus that is very obviously way off-center.
A search of "disturbed" yielded 10,034 hits. Maybe there are a few in there?
Maybe. I wonder how many are what we'd classify as disturbed spirals however (such objects are very common).
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JeanTate
in response to Ghost_Sheep_SWR's comment.
Secondly this is probably induced by interaction with at least one of the smaller galaxies around:
Possibly. But "interaction with at least one of the smaller galaxies around" is very common, yet offset, sharply defined nuclei seem rare; why?
Spectrum looks quite the same except for [NII]?
The second one lacks [SII] and [OII] emission.
I vaguely remember a post by Bill Keel, back in the GZ forum, explaining that, among the prominent forbidden lines (emission, by definition), [OIII] fades first when a starburst/AGN switches off, along with H-beta (in emission); then [NII] (H-alpha in emission disappears before this), then [SII] and [OII] (I'm ignoring the high ionization forbidden lines you often see in QSO spectra). If so, then we're seeing two fading AGNs at two slightly different ages. Pity there are no voorwerpjie echos ... 😦
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ElisabethB
moderator
What if this was not an elliptical to begin with, but it a seriously disturbed lenticular. (Sorry, if this has been mentioned before, I only skimmed the thread) ;D
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mlpeck
in response to JeanTate's comment.
By the way, A1001 pointed to this, over in RGZ Talk (Discussion thread
link); yes, it's a radio source (that's what its name beginning with
FIRST means), and an IR one, and a UV one, ...Also X-ray: Crawford et al. 1999.
It might be my imagination but there appear to be 2 nearly merged nuclei, or maybe it's just one bisected by dust. If it's two that would point to a recent (cosmologically speaking) merger.
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CeciliaB
in response to JeanTate's comment.
You write that SDSS J111143.60+404914.7 is unusual in having a very sharply defined nucleus.
But to me the nucleus seems to have another small, oblong object just above it, which one can't see in other nuclei in the neighbourhood.
Could this galaxy in fact have a double nucleus as a result of an earlier merger. That would explain the strange shape of the galaxy and the off-center nucleus.
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JeanTate
@mlpeck, @CeciliaB the SDSS spectrum is a legacy one, meaning (among other things) that the entrance fiber is 3" in diameter. Here's a zoomed in image with a grid, and without:
If the nucleus is somehow split or double, it almost certainly lies within the SDSS spectroscopic fiber (assuming that fiber is not waaay off the photocenter). A detailed analysis may reveal something else, but from the interactive spectrum, I can see just one hint of a possible second source with a slightly different redshift: the H-alpha profile. Of course, two redshift systems are not necessarily going to be seen in every binary/split nucleus ...
@ElisabethB yes that's entirely possible I guess.
I'm going to play with DS9 and maybe do a couple of GALFITs; at least I should be able to get a somewhat semi-quantitative idea of the luminosity profile ...
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mlpeck
This looks somewhat similar:
and the SDSS spectrum looks similar too:
This is in the first MaNGA release: mangaid 1-24145 and it was interesting enough to get its own paper. Lin et al. 2017, "SDSS IV MaNGA: Discovery of an Hα Blob Associated with a Dry Galaxy Pair—Ejected Gas or a “Dark” Galaxy Candidate?"
The southern nucleus in the MaNGA cube is blue shifted by about 300 km/sec relative to the central one. The galaxy to the south is NGC 6338.
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Ghost_Sheep_SWR
in response to JeanTate's comment.
Can't find the split / double nucleus in other images. I suspect it is an SDSS optical artifact that can also be seen in other nearby galaxies and stars: green on one side and reddish / purple on the other side. Direction of the colouring is also consistent with the nearby sources. Can be seen in the field image here:
https://dr12.sdss.org/fields/runCamcolField?run=3840&camcol=3&field=89
SDSS DR13 and other optical images PanSTARRS DR1 y/i/g and MzLS+BASS DR4 (DECaLS web viewer) for comparison.
http://skyserver.sdss.org/dr13/en/tools/explore/Summary.aspx?id=1237661966887616697
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A1001
SIMBAD HAS A CLEAR VIEW IMAGE OF MCG+07-23-031 SDSS J111143.60+404914.7
SHOWS LARGE OFF CENTER PART OF GALAXY.Posted
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CeciliaB
in response to Ghost_Sheep_SWR's comment.
I'm not at all sure that SDSS J111143.60+404914.7 has a double nucleus. But I don't think that other galaxies in the area have a similar appearance to their nuclei. They may be green/red on the sides, but their nuclei don't look split or divided.
I also very much doubt that the special shape of the nucleus of our main object would come out in full detail in the somewhat 'crude' images you get from Pan-STARRS and DECaLS.
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JeanTate
in response to CeciliaB's comment.
I also very much doubt that the special shape of the nucleus of our main object would come out in full detail in the somewhat 'crude' images you get from Pan-STARRS and DECaLS.
I agree. And I'm somewhat surprised ... the average (in some sense) resolution of SDSS r-band images (data actually) is 1.4" (if I'm remembering what I read somewhere). What seems to be presented in the PS1 web interface is some sort of combined image (data), so while an individual component image may have better resolution (down to 0.7"?), the combo likely is ~comparable to SDSS.
DECaLS is a bit of a mystery however; doesn't the web interface give you a JPG version of an individual FITS dataset? And isn't the average resolution considerably better than 1.4"?
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Ghost_Sheep_SWR
in response to CeciliaB's comment.
In response to CeciliaB:
Yes you may be right about other sources not having the same 'split' appearance, but I suspect it is caused by the colouring artifact nonetheless. I'll check the FITS files to make sure 😃 oh too much fun too little time. If only I could spend all my time on Zooniverse. Also new asteroid project XP
In response to JeanTate:
I'm not sure what method is used in DECaLS for the images, but the image itself is not from DECaLS. It is a combination of two Northern hemisphere surveys that is viewable in the DECals web viewer (like SDSS can also be viewed in the viewer).
More info on those surveys here: https://talk.galaxyzoo.org/?_ga=1.244656832.476670387.1443719759#/boards/BGZ0000002/discussions/DGZ0002jf1?page=1&comment_id=594b56ef61ec36007e000e87
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A1001
my computer does not make copies of SIMBAD images. it shows north SDSS J111143.60+404914.7 extending to east galaxies NED says is a galaxy LO95] 1108+410B SDSS J111142.44+404925.3 & SDSS J111142.31+404915.6. it also extends to south to SDSS J111144.93+404846.2
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mlpeck
I think Ghost_Sheep_SWR is right that this is an imaging artifact. I downloaded the fits files (you can get them here) and it turns out there's a single hot pixel in the r band image only. You might be able to see it in these monochrome jpegs if you zoom in enough:
This doesn't really change my opinion that this is a "dry" merger that happened recently enough to still show visible disturbance.
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Ghost_Sheep_SWR
in response to mlpeck's comment.
Ah yes I can see it too in Aladin, thanks for checking. Not a colour artifact as I thought but a single hot pixel in r band.
What is a dry merger btw?
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JeanTate
in response to Ghost_Sheep_SWR's comment.
What is a dry merger btw?
One that involves no fireworks 😉
More prosaically, a merger which involves two (or more?) galaxies, each of which has ~zero 'cold gas' ... as spirals (usually) have (lots of) 'cold gas' (i.e. the interstellar medium component which includes 'high density', 'low temperature', mostly unionized gas+dust), a spiral-spiral merger is (usually, very) 'wet'. And an elliptical-elliptical merger is (almost always?) dry, because neither galaxy has much (if any) 'cold gas'. Sorta, kinda ...
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Ghost_Sheep_SWR
in response to JeanTate's comment.
aaah yes...ok I guess..... 😛 Cool name for a cocktail anyway...
So a bit like ellipticals have almost no 'ISM material' in general so there won't be any starburst areas and similar things? I think I get it thanks.
On this galaxy, which (GZ) scientist / scientists might be interested in this off-centered nucleus galaxy and perhaps follow-up?
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JeanTate
in response to Ghost_Sheep_SWR's comment.
I'm not sure what method is used in DECaLS for the images, but the image itself is not from DECaLS. It is a combination of two Northern hemisphere surveys that is viewable in the DECals web viewer (like SDSS can also be viewed in the viewer).
From the Legacy Surveys page, I see there are three separate surveys, using three different telescopes, cameras, etc.
Sadly, the descriptions of each are somewhat, um, misaligned - seconds and mag depth on one but not others; seeing on two, but not the third; that sort of thing - but it's clear that the BASS and MzLS have seeing that's no better than SDSS' (and BASS' is worse), on average.
The Bok telescope used by BASS is comparable to the Apache Point one used for SDSS (2.3m vs 2.5m); both the DECaLS and MzLS ones are much bigger (4m). Assuming comparably good cameras (and I think the DEC one(s) may be better), DECaLS images should be deeper than ordinary SDSS ones (DECaLS integration times are comparable or greater than the SDSS 57s), though the Stripe 82 SDSS images should be quite a bit deeper.
So thanks; mystery (for me) solved.
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