Lensed quasar or maybe voorwerps?


I posted this before from the SDSS, but this image in DR9 is clearer. The DR9 photometric z shift puts the small satellite objects behind the central galaxy (but within the error range of the measurement) so I am not sure what this is. Could it be a PAIR of highly red-shifted voorwerps? The VLASS image is very strong.

This is the VLASS (different scale)

Screenshot 2021-09-13 at 14.32.01

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I suspect the central galaxy is a radio galaxy (or a similar variety of radio loud AGN), which would explain the strong VLASS detection. Tricky to be sure of what the two satellite objects are. They seem slightly thick for a lensing effect, and they don’t have the right morphology for voorwerpjes. One possibility is that they are part of a background galaxy and unrelated to the foreground object. At this resolution its incredibly difficult to give an accurate answer.

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The central object is 4C 00.83 The ‘4C’ indicates that it is a bright radio source. HSC has an even better view of it

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All we need now is a Hubble image! :grin:

It’s apparent that the central galaxy has an AGN. The environment around the nucleus contains a lot of gas that emits in radio wavelengths when the jets from the AGN strike it and excite it. This is the same physical mechanism that produces voorwerps, isn’t it? So that is what makes me think that these two “satellite” glowing regions may be voorwerps. They appear at roughly the right orientation to the radio emissions to be associated with the jets.

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Oh I agree, its theoretically possible, but the issue for me is the morphology. I’ve never seen a voorwerp that a) is this shape and b) is this colour. They’re at the right angle vs the nucleus, but they dont quite look right :confused:

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I agree with tombickle, usually voorwerps are a different color, larger, and have lower surface brightness.

Not necessarily larger. This is a reasonably distant galaxy, bear in mind. But certainly different morphology.

The point is, this is a distant galaxy that is red-shifted (z~0.5). If you red-shift a green oxygen emission line to that extent, what colour do you expect it to appear? (answer: orange-yellow)

Judging by the configuration of Hanny’s Voorwerp, a voorwerp near this galaxy should be about the size that these blobs are. But you won’t see any structure in these features because of the distance and limited resolution. In response to Tom, the shape and morphology would be dictated by the distribution of material surrounding the galaxy, so I am not sure what shape one might ‘expect’ to see?

I agree with you though, these do seem to be remarkably bright, but I still think it is worth the speculation.

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You are correct that the shape is dependent on the distribution of material surrounding the galaxy, but I wouldnt expect to see a voorwerp be so and thick and round regardless. The most known voorwerpjes have a wispy quality to them. Given that its 5 billion light years away, they would also have to be abnormally bright voorwerpjes.

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So, potentially a good find then. :grin:

Potentially. Its not likely to catch the eye of a professional for followup due to the uncertainty surrounding it, but if it is a voorwerp (which is a huge if, as it stands), it could be a pretty cool one.

My money’s on background galaxy though.

Regarding red-shifting an emission line:

Hanny’s Voorwerp (Legacy Survey Sky Browser) is, I guess, the [OIII] emission line, at ~500 nm (cyan). It shows up blue in this rendering because that’s in the SDSS g filter.

If you take a narrow line (that is, a region that is emitting all its energy in a small wavelength range) and red-shift it, it’ll stay the same color in these color renderings, until it hits the edge of the filter. If the filters overlap (Filter Response Curves — speclite v0.14dev391), you would briefly get an intermediate color (for a small range of redshifts), but it’ll then be entirely within the next broad-band filter, and (in this case) appear pure green, until it hits the next filter edge.

Amusingly, if this is at z=0.5, then the [OIII] emission line is actually in the gap in between the DECam r filter and the DECam z filter, so we wouldn’t see it at all. (It would be in the SDSS i band, so would appear pure red in the viewer’s g,r,i renderings.)

If I look at the single exposures, I think I can see these satellite objects in all filters, so I don’t think they’re dominated by emission lines.



Yeah, Hanny’s Voorwerp is bright in the SDSS g band due to unusually strong [OIII] 4959, 5007 emission lines

Nice explanation, thanks. Any idea what these objects are then? It seems too much of a coincidence that they would be chance alignments of satellite galaxies, but anything is possible I suppose.

I have no idea :slight_smile: My guess would be chance aligned background or satellite galaxies. But certainly a lucky configuration!

I should do the lottery this week!

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So, anyone looking for voorwerps in here should be looking for monochromatic features, then.

That’s worth knowing! Good pointer.