Amorphous looking interaction

1 Like

Wow! #interesting-things:beautiful-or-unusual-objects


Wow!!! That is the most amazing intriguing site so far. Im new to all this and do not know much at all about it. I find it all very interesting and i cant stop working towards learning all i can!



A really complicated pair of mergers / Ram Pressure Stripping story?

1 Like

IMO mostly mergers and tidal interactions. Possibly RPS influences as well but if galaxies are interacting it is very often hard to see the RPS effects versus interaction and merger effects (if they are large enough like here)

1 Like

Look at the star formation going on in the trails. The upper one is far closer to jellyfish tendrils than merger trail, and I’ve never seen a tidal trail with star formation like that. It looks to me like the gasses from the upper merger have been blown into the lower which, combined with the merger action, has driven radical amounts and patterns of star formation.

Lower galaxy:

Upper galaxy:

1 Like

Interactions/mergers can induce star formation - there’s no need for ram pressure to be invoked. They’re not in a particularly dense area, so i’d be surprised if they were indeed jellyfish.

1 Like

“Interactions/mergers can induce star formation”

Of course they can, it is the streamers of star formation that I haven’t seen in mergers…

Streamers aren’t two-body phenomena

Up top you can see the tidal tails on both sides but then there are the bits hanging below.

Yes, I know that RPS is mostly found in the hot intracluster medium clusters have but I don’t think that is a definitive habitat.

There are strong gas currents, AFAIK, in intergalactic space most everywhere except the voids.

1 Like

Strong yes but not strong enough to cause jellyfish fragments/RPS. Equally you can’t have strong currents everywhere because, by definition, a current is an area of higher than usual velocity/pressure. To me this is just an interaction. Tidal tails might not look like this but a (pre-)merger interaction could.

Separating jellyfish from interactions can be difficult but it’s usually safe to say that if something is interacting, its disturbed shape is more likely due to that interaction. This is particularly true for these 2 where both are undergoing extremely unusual deformation (i.e. non linear/no specific direction is apparent).

1 Like

I’ve never heard of a jellyfish occuring in a sparsely populated medium.

If a flyby occurs (which appears to have happened here), it shouldnt be a huge surprise to see vaguely linear trails of star formation in the direction of motion of one of the galaxies. Could either be interaction-induced, or they could be areas of existing star formation in one galaxy that got pulled away by the other, hence the trails.

Occam’s razor - ram pressure stripping is a wild thing to jump to when considering the sparse medium and active interaction occuring.


I only realised a few days ago that the “razor” in Occam’s razor was not referring to some literal razor (that cut down explanations or something mad) but a “razor” as in a philosophical principle. Perhaps slightly ironically the simplest answer (the one I jumped straight to) for the meaning of razor was not the correct one :slight_smile:

On the explanation side of things, 100% agreed. Flybys and pre-merger interactions will cause material to be stripped and it doesn’t seem right to be RPS.

1 Like

Ram pressure exists wherever a fluid flows against an object (a gas is a fluid in this sense)

It doesn’t matter whether the gas is flowing into the object or the object is moving through the gas

The same resistive pressure occurs either way if everything else is the same.

Intra-Cluster Medium (ICM) is the darling of RPS researchers because it is so hot and dense which makes the effect more efficient and extreme. It is also easy to find clusters and groups (and their RPS)

Gas flows - both hot and cold, weak and strong - are found throughout the cosmos

we conclude that gas disks of galaxies in high density environments are heavily truncated or even completely stripped, but also the gas disks of galaxies in low density environments are disturbed by the flow and back-falling material
A&A 433, 875-895 (2005)
Ram pressure stripping of disk galaxies
From high to low density environments
E. Roediger and G. Hensler

Consider these signs of RPS in relation to this image:
From: Ram Pressure Stripping | COSMOS

Clear indicators that ram pressure stripping is at work:

1. The disk of dust and gas appears bowed. This indicates that the galaxy is having trouble holding onto the loosely bound dust and gas in the outer regions of the disk against the pressure of the ‘wind’.

2. The stellar disk (blue) appears to extend well beyond the star forming disk of dust and gas. This observation suggests that the loosely bound dust and gas in the outer regions of the disk has been stripped from the galaxy after the formation of these stars.

3. Streamers of dust and gas can be seen trailing behind the motion of the galaxy, obscuring and reddening the stars behind (top of the galaxy in the image). At the same time, the ‘wind’ has pushed the dust and gas that would normally be found ahead of the motion of the galaxy up into the galaxy itself. This has revealed bright blue stars along the leading edge of the galaxy

1 Like

Interesting note: “Seeming right” is not a per-requisite for being right :rofl:

1 Like

Are we all sure that the bottom object IS a merger?

I see pressure from the gas flow that is producing the tendrils above:
A) pushing the edge-on (which would be face-on to the pressure) down - leaving the short trail above it
B) the wavy disk, rich in star formation - a sign of the turbulent flow
C) more tendrils and starforming streamers hanging down

1 Like

The paper you cite seems to define a low density environment as “cluster outskirts”, not areas of space with no obvious clusters. Find a paper that suggests that you could get RPS to this extent in such an area and I might get on board, but i’m sticking with the more likely explanation of interaction-induced star formation.

1 Like

No, it is not a prerequisite for being right. It is a qualifier I add in to what I post so that I don’t seem overly assertive. Equally, whatever one posts is always just an opinion, i.e. what something seems to be to someone.

1 Like

While I would love another opinion, I would be shocked if this is not eventually a merger.

1 Like

That was meant to be funny… Sorry if it didn’t seem to be so

1 Like

Sorry that’s my bad - my reply sounded far more defensive than it was meant to be :slight_smile:

1 Like

I don’t think it has ever been that RPS happens only in clusters, it is just that they are much more common/easier to find and that they are stronger/more energetic/just all around better in the ICM
so everyone studies clusters

The first census of RPS Candidates found ~80 field galaxies - Table 4, pg 16
Look at the makeup of the third group in this paper: the end of Section 2.1 and 2.2. PM2GC

B. M. Poggianti, G. Fasano 2016

Overall, the morphology and kinematics of this gas show that WLM (galaxy) is undergoing ram-pressure stripping, despite being 930 and 830 kpc from the MilkyWay and M31, respectively.
This finding indicates the presence of an intergalactic, gaseous reservoir far from large galaxies whose evolutionary role in galaxies, both large and small, may not be fully appreciated.
Evidence of ram-pressure stripping of WLM, a dwarf galaxy far
away from any large host galaxy
Yanbin Yang, Roger Ianjamasimanana, et al 2022

We have then extracted from the cluster control sample
and the field those galaxies that indeed are undisturbed
and do not show any sign of environmental effects
(RPS, tidal interaction, mergers, gas accretion…)
on their spatially resolved SF distribution, for a total
of 17 cluster members and 15 field galaxies

Enhanced star formation in both disks and ram pressure stripped tails of GASP jellyfish galaxies
Benedetta Vulcani,1 Bianca M. Poggianti, et al 2018