A Most Curious Object

AndyC3339 asked:
“Simbad says there two galaxies in a merger @GStark
2MASX J23034121+0102362 – Low Surface Brightness Galaxy
NVSS J230341+010238 – Radio Source
RA,Dec = 345.9210, 1.0434
Legacy Survey Sky Browser

I agree, this is a curious object so let’s look, shall we?

First set zoom=15 cont=1.6 brtnss=1.1 and look at this area:
You can see that many objects are collecting into several streams
1: A group of small clumps from just below and to the right of the Blue Star - out as far as the red pair
2: Larger clumps immediately below the BS
3: More large clumps join on the left side.
4: As the three streams approach the large dense galaxy, they interact, warp & cross paths

With zoom=15or16 and cont=0.8 brtnss=0.7
focus on the galaxy itself

The diffuse streams just spread out and go directly in without orbiting that I can see
The thick stream goes across the top, behind everything and then down and across the front just behind the blue stream. It then makes a couple of tighter orbits leaving a fog of trails until now here we see a group of starburst cluster to the left of the large orange overlay and the starforming spearhead of clusters on the upper right side.
(keep this tab open - we’ll need it below)

Rather than a merger this is a starburst spiral-2 galaxy colliding with a debris field from a merger in the past - possibly the one that created this galaxy or maybe a merger that spun off a series of clusters like this one:
ra 272.702713
dec 67.042745

from GalaxyZoo

That’s all interesting enough… but the curious bit is the artifact seen in most views in the close up tab.

Switch to DR10
Do you se the green scratch-like artifact under the core that stretches from the right side, over the center orange blob and out left to a tiny tan overlay above and to the left of the orange pair

It is there from DR10 to DR5, in DECaLS DR7 it is not green but with Cont=1.1& Brt=1.0 the trace is there. HSC DR2 is the hardest but set C=1.3 and B=0.8 and click back and forth - DR10, DECals, DR10, HSC, DR10 and you’ll see that trace is there on each of them.

What the heck is it?


Hi there,

I have a no-fun explanation…

With the LS-DR9 or DR10 layer on, click on the map and follow the “Single exposures” link to get cutouts from all the images that got stacked together,
Legacy Survey Sky Browser
and then scroll through and you’ll see that giant cosmic ray in one of the exposures (239319).

Each LS DRs uses all available data up to that point, so it would appear in all LS DRs.

And then I think that HSC-DR2 just coincidentally also has a cosmic ray nearby. It’s harder to find and eliminate cosmic rays against a bright background (eg a galaxy), so that’s why they are seen more frequently in galaxies.



Great answer. I knew there had to be a rational explanation and comic rays were high on my list, it just surprised me to see it so widely.