regularly-arranged colored dots in the image
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jstoke
how do we explain the red, orange, green, and yellow spots at the upper left?
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KWillett
scientist, admin, translator
Objects in a straight line with a varying color (like these) are almost always the result of something moving. Since the other stars are well-aligned, it might be an asteroid that was moving across the field at the time of exposure?
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vrooje
admin, scientist
This may sound odd, but I've spent a lot of time looking at these images and I believe I recognize that collection of spots. The central image here is very big and relatively nearby for Hubble, so it's zoomed pretty far out. Those spots, on the other hand, will show up at some point as their own object/objects and will be much more zoomed-in. There's a kind of 3x3 diagonal grid, each row very similar but stacked on top of one another. I'd bet on it being an artifact, but I don't recognize what kind. I haven't seen this all over the fields, so I don't think it's a persistent chip artifact, but a transient chip artifact might explain the grid as part of a dither pattern.
I'm not even sure it could be an asteroid because to see an asteroid in the rainbow formation we're used to from SDSS the different bands need to be taken in relatively short order, and I don't know that was the case with this CANDELS field. And I also don't know how that would make a 3x3 instead of just a row. (It's hard to see the grid in this image, but it's there.)
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zutopian
Maybe those spots are cosmic rays? Or maybe just background noise pixels?
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KWillett
scientist, admin, translator
You've been looking at HST raw images for too long, @vrooje. 😉
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vrooje
admin, scientist
Yep! You know you've been staring at the same data for too long when you think, "I recognize this galaxy," know where to look to verify it, and turn out to be right. 😃
@zutopian, I think they're some kind of artifact, but probably neither a cosmic ray nor noise. This image is zoomed way out so it's a bit hard to see, but they actually take up a reasonable footprint of Hubble pixels and have pretty jagged edges, so they're not simple noise. There are certainly cosmic rays in the raw images, but the reduction process removes them pretty faithfully and I wouldn't expect to see a stray set in this pattern.
Separate point: totally agree with @JeanTate that this is an #overlap -- in fact, it seems to be a double and maybe even a triple overlap (the reddish blob at 5:00 on the edge of the disk).
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KWillett
scientist, admin, translator
Absolutely. Hope this one is in @NGC3314 's catalog.
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zutopian
in response to vrooje's comment.
Thanks for your reply.
I think, that the #artifact looks similiar to this one.:
http://talk.galaxyzoo.org/#/boards/BGZ0000004/discussions/DGZ1002ctyPosted
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KWillett
scientist, admin, translator
I agree, @zutopian - nice catch. Any ideas for a hashtag to name this particular artifact?
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zutopian
in response to KWillett's comment.
I suggest #UFO. 😃
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vrooje
admin, scientist
I agree too, and it's in a completely different field! So perhaps it is a chip effect, then, but I also don't have a great name for it...
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zutopian
Concerning the other image AGZ0000360 .:
The corresponding SDSS image shows 2 small/distant galaxies.
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zutopian
Here is a GZ image, which shows the same galaxies, but it is centered on one of the small galaxies.: AGZ0000pzj
The artifact is outside of that image.Posted
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zutopian
Here is an image of another spiral and there is the same artifact.:
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c_cld
in response to zutopian's comment.
No artifact in this AGZ0000pjd when compared to CFHTLS cutout: visible dash in left side of spiral
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