User talk:SkyFlubbler/Archives/2023/April

List of largest nebulae

Could you take a look and maybe improve the list of largest nebulae? I am impressed with your work on the list of largest galaxies, so hopefully you could improve this as well. VY Canis Majoris (talk) 11:54, 11 March 2023 (UTC)

Unfortunately, I cannot do that. There is no extant database of nebulae that details their sizes, which can be accessed on a large scale. Measuring the sizes of nebulae is even problematic to begin with.

The reason I was able to revive the list of largest galaxies is because NED can be easily accessed for data from a huge amount of galaxies, and because I was able to make a search on how the physical diameters of galaxies are measured. These are two things which nebulae do not have yet. SIMBAD is the only database of a large enough scale on Milky Way objects, and they don't have data on gheir sizes.

Until that day comes, the list of largest nebulae would just end up in failure. It was a futile attempt without considering the long-term aspect of improving the list. I have been advocating repeatedly to delete that list, though it was unsuccessful. SkyFlubbler (talk) 15:03, 11 March 2023 (UTC)

Sad. If that's so, should we advocate for its deletion? There's also the issue of where NGC 2404's size came from. Speaking of the "where sizes came from" problem, I have seen this: https://ui.adsabs.harvard.edu/abs/1990IAUS..139..357B/abstract

It states that the diffuse light in Abell 2029 extends to a minor axis of 450 arcseconds, which is stated to be 500 kpc in the paper. Since IC 1101 has an axis ratio of 2:1, this means its major axis is 1 megaparsec in radius, or ~6.5 million light years in diameter. However, since cosmology was different at that time, if one uses the Virgo + GA + Shapley scaling relation of 1.716 kiloparsec per arcsecond, this would mean its minor axis is 772.2 kiloparsecs. This results in a major axis of 1.5444 megaparsecs. Converting this into light years and multyping that by 2, we get a diameter of ~10 million light years.

I know it sounds exaggerated and it may be superceded by the 1991 estimates, but the link may be the thing that resolves the question of where the purpoted size of 6 million light years came from. The Space Enthusiast (talk) 17:35, 11 March 2023 (UTC)

Regarding NGC 2404, I can't seem to find any source that states a specific size. But 940 light-years is not unreasonable for an H II region.

As for the IC 1101 paper, the paper concluded this size value under the three conditions that;

• The light profile is described by a two-parameter function (I believe is either Tully-Fischer or M-sigma).

• The ellipticity of the halo matches that of IC 1101

• The halo distribution is different from the other galaxies of Abell 2029.

Regarding the first one, here is another paper from 2005 that said:

Regardless of the radial trends, the amount of diffuse stellar mass has a low-scatter scaling relation with cluster's total mass in the simulation, out-performing the total stellar mass of cluster satellite galaxies. We conclude that there is no consistent evidence yet on whether or not diffuse light is a faithful radial tracer of the cluster matter distribution.

For the second condition, another paper here said this:

Dressler found that the measured velocity dispersion increased with central distance from IC 1101 implying that the mass-to-light (M/L)ratio of the envelope was increasing rapidly. His assessment of the physical implications of these measurements was that he identified the outermost high M/L component with the stripped stars from satellite galaxies orbiting in the cluster around IC1101. Today, we associate such diffuse light around central bright galaxies with the intracluster light (ICL), defined as the stellar component at the centres of groups and clusters which is not bound to individual galaxies.

As for the third condition, it has already been known for decades that the distribution of the ICM is expected to be different from the distribution of galaxies in clusters. This is a common phenomenon since the follow the dark matter trend, not the baryonic trend (which the individual galaxies follow). Plus, a cluster like A2029 which is the result of multiple past collisions is expected to have its galaxy distribution different from the halo. This however does not tell anything special regarding IC 1101.

The matter is just easy to resolve, we dismiss this measurement because this is not how you define the size of a galaxy. The diameters of galaxies are defined by the D25 isophote, or any other related isophotal measurement, and not the size of the halo - the one used by large-scale surveys for decades. SkyFlubbler (talk)

Thanks for that eloquent answer. Since you are an Astronomy student, I would assume you know a magnitude more than I do, but if D25 is the standard for galaxy size, then why do even astronomers refer to IC 1101 as being among the largest galaxies known, if not the largest known, based on a non-standard measurement? Also, do you think there needs to be more high resolution surveys regarding galaxies, so their sizes can be affected less by noise? I also remember seeing Abell 1413's BCG envelope being estimated at 3.5 Mpc radius, but is this spurious?

I am honestly sorry if I appear overly curious. There's a lot more small talk that is better done on Discord than here.

It's not actually wrong to claim that IC 1101 is still one of the largest galaxies known, even using the D25 measurements (There are only 200+ entries in the list of largest galaxies out of the 2,500 I have looked into, so IC 1101 belongs to the top ~8%). But to claim that it is the largest known is an entirely different matter. This is probably due to the fact that the mainstream media has been reporting IC 1101 to be the largest known, while not looking at the methodology used. And it just gets echoed and repeated over time.

With the current resources that we have, I am confident that we are secure enough to at least make a decent comparison list of galaxy sizes. That being said, new surveys are welcome, but they also must be careful and clear regarding the methods they use to measure the physical sizes of galaxies. They should use a method made by surveys of the past, or if they want to introduce a new one, justify why the new one is preferable vs the D25 isophote. We have to make sure that when we quote the size of galaxies, the authors are at least aware of the concept of the D25 and such, and not make an assumption based on what they like (such as using halo stars for the Milky Way giving it a bloated 175,000 light-year diameter).

Regarding the Abell 1413-BCG, yes I am aware of this and I am actually keeping a close eye on it. Many papers including one from the 1960's already claim it as the largest galaxy in an Abell cluster. For all intents and purposes there is no question that this galaxy is larger than IC 1101 by a long shot, in every standards possible. That being said this size of 3.5 Mpc should be taken with a grain of salt, since one may confuse this to the ICL which is not actually a part of the galaxy. The largest reliable diameter available is the R25 isophote of the SDSS, giving it the 804,000 light-year diameter listed at the list of largest galaxies. Note that we do not have a measurement of this in the R90 light radius, which can be much larger. This galaxy is in the northern sky and is beyond the scope of ESO-Uppsala which used this standard.

That being said, if I am asked, I can say with at least 90% certainty that Abell 1413-BCG might possibly be the actual largest galaxy known. This is just a gut feeling, as we don't have the numbers. And one should just not boldly claim without the numbers. SkyFlubbler (talk) 07:16, 12 March 2023 (UTC)

To be honest, because of this, I am actually quite terrified at Abell 1413's BCG. That many papers assign a ridiculously large radius is a testament to its size. I may not be surprised if certain components of the galaxy are more superlative than IC 1101, but who knows...

Also, what is the galaxy of SC1325-31-G1? In Schombert et al. 1987, it is listed as having a larger logR Compared to Abell 1413 BCG.--The Space Enthusiast (talk) 05:19, 14 March 2023 (UTC)

There is no entry in NED with "SC1325-31-G1" or any variation of that. Could you please link the Schombert paper? SkyFlubbler (talk) 16:59, 14 March 2023 (UTC)

Looking at clues based on the designation, 13h 25m and -31d, points me to Abell 3558. I assume that the galaxy is ESO 444-46 which has the designation SGC 132508-3114.2. It is already at the list of largest galaxies and is about 205.9 kpc in diameter, which is smaller than Abell 1413 BCG at 237.67 kpc. There we go. SkyFlubbler (talk) 17:18, 14 March 2023 (UTC)

https://articles.adsabs.harvard.edu/pdf/1988ApJ...328..475S (harvard.edu) here you go. Look for it on the 2nd page. The Space Enthusiast (talk) 17:33, 14 March 2023 (UTC)

Yep, judging from the footnote in there where they used UK/SERC Southern Sky Survey it seems that this galaxy is ESO 444-46, which is already on the list. We cannot use this paper though, as the author arbitrarily made the cutoff to 30 V-mag/arcsec², which is fainter than the D₂₅ standard and might be confused to the intracluster light. SkyFlubbler (talk) 17:52, 14 March 2023 (UTC)

So, does this mean that the ICL of That galaxy is larger than A1413's? The Space Enthusiast (talk) 18:08, 14 March 2023 (UTC)

Also, there's this (https://ui.adsabs.harvard.edu/abs/1986ApJS...60..603S/abstract) which says the name of the galaxy I asked about earlier is SC 1325.1-3111, with the last number being slightly different, but is this any different? The Space Enthusiast (talk) 05:04, 15 March 2023 (UTC)

I have to warn about the term "ICL of that galaxy." ICL or the intracluster light is part of the galaxy cluster, not the galaxy itself. Abell 3558 might have a more extensive ICL than Abell 1413, in part because it was the center of the Shapley Supercluster, but that's it. It does not say anything specifically about ESO 444-46 or Abell 1413 BCG per se. I hope I emphasize this well.

Regarding the other designation SC 1325.1-3111, yes, this is possible. They might have used the B1950.0 instead of the modern J2000.0 epoch, but they are just close enough that it was not really a big deal. For the location at 13h 25m 00s and -31d 11m 00s, the only large galaxy in this region is ESO 444-46 and the smaller Abell 3558 members, which means that it is likely that they are pertaining to this galaxy. SkyFlubbler (talk) 05:23, 15 March 2023 (UTC)

Thanks. Should we start the rework of the Abell 1413 article? The Space Enthusiast (talk) 05:30, 15 March 2023 (UTC)

Wait...Why did you use R90 for ESO 383-76 instead of D25? The Space Enthusiast (talk) 04:08, 16 March 2023 (UTC)

R90 is a variant of the half-light radius, which uses 90% instead of the usual 50%. This is produced by the ESO-Uppsala catalogue and is still a valid way of measuring galaxies. That's why this was used for ESO 383-76. SkyFlubbler (talk) 05:22, 16 March 2023 (UTC)

But why was not D25 used on the list? The Space Enthusiast (talk) 05:59, 16 March 2023 (UTC)

The R90 size is the largest one there is, and this is also the figure that you will see if you searched for ESO 383-76 using the modern NED interface. SkyFlubbler (talk) 06:51, 16 March 2023 (UTC)

OK. What are the references that claim Abell 1413 BCG is one of the largest galaxies known? The Space Enthusiast (talk) 18:17, 16 March 2023 (UTC)

Just a question. Where did you get the 7 million light year halo diameter (You said it here:https://www.reddit.com/r/spaceporn/comments/wl31kb/comment/iju369j/) of Abell 1413 BCG? I am assuming that it is implied in https://ui.adsabs.harvard.edu/abs/2003AJ....126..675D/abstract, but is there any more data to it? Is it even plausible that A1413's ICL extends out to 24 arcminutes? Finally, I found this:https://ui.adsabs.harvard.edu/abs/2012A%26A...548A..18C/references where it is stated that Abell 1413 BCG's halo is much smaller than initially presumed.

I am honestly sorry if I am once again overly curious. Ever since you mentioned that Abell 1413's BCG has been stated repeatedly to be among the largest of all cD galaxies, I accepted that it extends much farther than IC 1101 and likely even ESO 383-76 and began plans on an article for it. The Space Enthusiast (talk) 04:00, 17 March 2023 (UTC)

Is it possible for you to help me find more Abell 1413 BCG references? I have compiled some of them here: https://en.wikipedia.org/wiki/User:The_Space_Enthusiast/MCG%2B4-28-97 The Space Enthusiast (talk) 16:17, 20 March 2023 (UTC)

No need to compile those. Just search for the cluster in the NASA/IPAC Extragalactic Database. There are 351 references there. SkyFlubbler (talk) 03:10, 21 March 2023 (UTC)

It appears that Juan M. Uson and Stephen M. Boughn has a project on Abell 1413, saying in another paper that the ICL extends for more than 1 Megaparsec, but where could I find t? It seems to be hidden. The Space Enthusiast (talk) 18:33, 22 March 2023 (UTC)

Hello? The Space Enthusiast (talk) 17:30, 31 March 2023 (UTC)