Talk:List of largest galaxies

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Redirect, 3 June 2018, see discussion.
keep, 12 December 2014 (UTC), see discussion.

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Ranking[edit]

The ranking makes no sense, the ranks listed here only concern the entries list here, and not the ranking of all known galaxies. Therefore I am removing ranking -- 67.70.35.44 (talk) 05:54, 8 November 2014 (UTC)[reply]

deletion request[edit]

There is already the List of galaxies article. This could go there. Plus, the size of galaxies are too uncertain, so such list will always be misleading. I'm too lazy to go find the deletion template but here is my request Tetra quark (talk) 19:05, 29 December 2014 (UTC)[reply]

Finally following up on this after 4 years, after being reminded of these problems due to a number of recent edits here.

The numbers given in many wikipedia articles for galaxy sizes are often not traceable to primary sources, may use very out of date cosmological parameters, were not produced from a consistent set of measurements (some come from NED's "apparent size", some are x-ray gas extent, some are radio extent, etc.), and almost none of them are what would be typically used by an astronomer to quote a galaxy's physical size (the half light radius in the optical/near-IR). Those incorrect wikipedia numbers get turned into this list, where the various objects at the top of the list exhibit all of the above problems. We're better off deleting this page and slowly correcting the individual galaxy pages or even just removing infobox statements about galaxy physical size entirely, than attempting what would be a very long process of primary source searching. And even searching through the primary literature is not a good approach: a consistent catalog of sizes should come from a single survey with a known surface brightness depth. This list has spawned hundreds of blogposts and webpages talking about the sizes of galaxies, so references to secondary sources cannot be used to correct it either.

Our best choice is to just delete it, to prevent further misinformation. - Parejkoj (talk) 19:54, 1 June 2018 (UTC)[reply]

The article was nominated for AfD in 2014 (and the deletion rationale is similar), so PROD is not applicable. I have brought it to AfD instead. –LaundryPizza03 (d c̄) 02:59, 3 June 2018 (UTC)[reply]

Thanks LaundryPizza03: I'd completely forgotten about the old deletion request that I'd filed. Lets see if we can get any more discussion this time? - Parejkoj (talk) 03:40, 3 June 2018 (UTC)[reply]

Holmberg 15A[edit]

Shouldn't we add the galaxy, Holmberg 15A, on this list, especially since its infobox says that it is even larger than IC 1101?

Nope, 270*10^3 = 270*1000 = 270,000 Ioaxxere (talk) 23:55, 12 December 2016 (UTC)[reply]

Fixing the largest galaxy values[edit]

Per the discussion a few years ago about IC 1101's incorrect (or at least inconsistent) size, maybe its time to finally sort out this list of largest items. Doing so will require choosing a scale to use, finding appropriate references, and converting values from older references into sizes using modern cosmological values. I don't have time to do the finding, but I'd be happy to check refs or do conversions for folks who do. - Parejkoj (talk) 18:30, 12 December 2016 (UTC)[reply]

Either way the source given is a dead link, but here's a paper that states "over 600 kpc" or over 2 million light years (radius). Ioaxxere (talk) 23:54, 12 December 2016 (UTC)[reply]

I'm aware of Uson et al.'s number: my claim--see the gory details in Talk:IC 1101--is that the maximum measurable extent of the diffuse light is not a good value to use as the "size" of a galaxy. See that talk page for lots of discussion on this point, though I'm not sure a consensus was reached.

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A revived list[edit]

Now the list has finally been revived, I hope all the major issues that plagued the older list are solved here. Issues like "how do we define the size" and "where are the sources" are hopefully addressed as of now.

The list is not yet complete. Some tasks I think we should work on are:

Further define the methods being used, preferable an overview of its strong points and disadvantages in section Methodology and constraints for measurement.

Have a workspace so that we can add potential candidates. I have scanned 2,300 galaxies in NED so far (out of a total of 70,000+ retrievable by the algorithm; fortunately I've looked mostly on cD galaxies, which is a majority in this list).

Table organization, as if we need to include distance and redshift at all. I am thinking if we could add the major and minor angular diameters too, but as I can see it, it will not fit in the list.

That is all for now. Comment below if you have any issues with the new list, and I'll do my best to answer it all. Thanks. SkyFlubbler (talk) 14:32, 11 July 2022 (UTC)[reply]

With the discussion at IC 1101’s talk page, is it possible to calculate its size at a distance of 1.093 Billion light years away? The Space Enthusiast (talk) 04:41, 25 July 2022 (UTC)[reply]

The quoted size for IC 1101 at NED uses a distance of 262 Mpc, which is different from the 334.8 Mpc using optical redshift values. Unfortunately, we have no scale to use for this one, since NED uses a scale based on the distance of 97 Mpc (they prefer this value over the optical).

I will not change IC 1101's size here for consistency purposes, as I have used the same method for it with most of the galaxies in this list. One can manually compute using the 338.4 Mpc distance, find the value of the scale, and multiply it to the physical diameter value in 2MASS. Either way, IC 1101 is just an entry for the comparison table, not the main one, so it will not be a superr important, total game changer galaxy for this list. SkyFlubbler (talk) 06:06, 25 July 2022 (UTC)[reply]

Links to pages[edit]

I would suggest to add links to the galaxies that have pages on Wikipedia. VY Canis Majoris (talk) 18:07, 17 July 2022 (UTC)[reply]

The list was still pretty much at the development stage, so I think I will add them by tomorrow morning. I will also simplify the names of the galaxies here, as I just haphazardly placed their names from NED here just for technical reasons to avoid duplication. SkyFlubbler (talk) 18:17, 17 July 2022 (UTC)[reply]

Moved the intro[edit]

I decided to move the very long introduction and much of the details away towards the main Galaxy article, which I think is better suited for it. It would hopefully give viewers some context on galaxy size. Also, people came here for the list, not for the absurdly long details.

As of here, we can just make a simple overview, and recommend the section Galaxy#Physical diameters for details about the methods used here. SkyFlubbler (talk) 18:37, 3 September 2022 (UTC)[reply]

A list of spurious candidates[edit]

I will be having a workpage here: Talk:List of largest galaxies/Spurious candidates in order to have entries of spurious or unwanted NED entries to prevent them from being included in the list. I will constantly add more as soon as I find them. Thanks. SkyFlubbler (talk) 19:14, 9 November 2022 (UTC)[reply]

WP:OWN[edit]

Almost all of the edits on this page are by SkyFlubbler and he is acting like he is owning the list (based on when he undid one of my edits where he said that I had to ‘ask him what to do’). So is this SkyFlubbler owning the page or does no one really want to edit it? SpaceImplorerExplorerImplorer (talk) 11:57, 17 November 2022 (UTC)[reply]

There are edit summaries where I undid some of your edits. For this particular edit. I undid it awhile back because the quoted distance is wrong (730 Mpc when it's supposed to be 763.7); and uses a LEDA catalogue entry even though it has an Abell-based entry (Abell 2218 G1) and is quoted as unlisted morphology even though NED provides it as cD; E. I guess it was a wrong move to just remove it altogether, my bad. My line of thinking at the time is to add it later, which I did here. It is the same object but in a more pleasing catalogue entry. SkyFlubbler (talk) 12:27, 17 November 2022 (UTC)[reply]

Sizes by methods[edit]

Is it possible to configure the table to show which galaxies are the largest by a specific method, such as the largest galaxy by R90, D25, D27, etc?--The Space Enthusiast (talk) 03:08, 28 March 2023 (UTC)[reply]

Regarding the use of sizes.[edit]

To make this clear, due to SpaceImplorerExplorerImplorer's recent edits.

When you see something in NED in the lines of:

Physical diameters are derived using a scale of ### kpc/arcsec based on Average NED-D Metric Distance of (### +/- ###) Mpc.

Then completely ignore the diameters given.

The phrase "based on Average NED-D Metric Distance" means that the diameter is calculated based on an average taken on one or more independent distance estimates. Most of these estimates are quite old and can vary a lot (an extreme example is UGC 568 which is caused by an erroneous supernova measurement that gave 2.5 Gpc.

What you do instead is this:

Go to Scale (Virgo + GA + Shapley) in NED.
Take the value of ### kpc/arcsec.
Multiply the number with the Apparent Major Axis (2a) [arcsec] and the Apparent minor axis (2b) [arcsec] on the corresponding method that has the largest value. The result is the corrected diameter based on redshift.
When you place the entry of the galaxy in the list, add {{efn|name=Lambda}} immediately before the galaxy's name. That is what this note is for, to note that the listed diameter is different from the one in NED because it was corrected based on redshift.

I hope that makes sense if one should place entries here again. Thanks. SkyFlubbler (talk) 07:13, 16 April 2023 (UTC)[reply]

Proposed changes[edit]

Some concerns I want to rase:

I feel like we should use units of kiloparsecs for sizes for the list. This was the standard for extragalactic distance scales, and plus it is in line with the raw data we get from NED. This is not a big change and we can just change the parameters slightly so it will show it.

Second, I want to change the "{{efn|name=Lambda}}" into something much more subtle as it would be overused as a note. Maybe having a distinctive color for the entry galaxy will give an indication that it was changed towards the diameter based on redshift, instead of just a note.

Third, in order to be transparent, we should also include other diameter methods, however this will be exhilarating and will take a very long time to do. So this is just optional, nevertheless I still mention it here in case anyone also advocates for this.

Thoughts? SkyFlubbler (talk) 15:27, 24 April 2023 (UTC)[reply]

I don’t really see the point of changing the sizes to kiloparsecs, instead we could use a format like ly (kpc). SpaceImplorerExplorerImplorer (talk) 12:46, 26 April 2023 (UTC)[reply]

Then explain why instead of leaving a disagreement without any proper explanation. Regards—ZaperaWiki44^{(✉/Contribs)} 21:29, 27 April 2023 (UTC)[reply]

I am now thinking something like kpc (ly); kiloparsecs have been used most of the time in scientific articles, outside of them light-years have been used a lot as well (not by experts). SpaceImplorerExplorerImplorer (talk) 05:20, 28 April 2023 (UTC)[reply]

I keep hearing that professional astronomers recommend the use of parsecs (including prefixes) and don't really use light-years. I hope there's some formal recommendation out there that we could cite for this list. VY Canis Majoris (talk) 05:05, 27 April 2023 (UTC)[reply]

It does make sense: the vast majority of reliable scientific papers has been used parsec (including prefixes) as the standard unit for very large distances and sizes (in galactic scales) for decades. For that matter, we should use megaparsecs for the List of largest cosmic structures for the similar reason. Regards—ZaperaWiki44^{(✉/Contribs)} 21:15, 27 April 2023 (UTC)[reply]

Cutoff point[edit]

Another concern about this list:

I realized that the list is becoming way too lengthly as it has over a hundred of listed galaxies larger than 500,000 light-years (150 kiloparsecs) cutoff point. Not to mention, more galaxies above the said "minimum" major axis diameter are being reguliarly added in the list. This will end up going to the point that there will be an even more unnessessary substantial number of galaxies that are not even close to the largest galaxy diameter estimates quoted in the list (not even by any margin of error if some galaxies do have), in the view of the fact that there are many dozens of galaxies above already closer to the largest listed diameters.

As such, I propose that we should move the cutoff point to perhaps 700,000 light-years (200 kiloparsecs) as I think it would more reasonnable and would make the list less longer (and maybe keep only highly notable galaxies and/or that are not household names or exceptional in some way below the proposed cutoff point). Regards—ZaperaWiki44^{(✉/Contribs)} 21:58, 29 April 2023 (UTC)[reply]

I have a gut feeling to retain Abell 1413 BCG however, as it is quite notable due to being known as a very large galaxy, as stated in Oemler 1976, Morgan and Lesh 1965, Feldemeier 2002, and Schombert 1988. The first paper stated states that this galaxy's profile could be traced out to 24 arcminutes, which would correspond to an absurdly large size (stated as 3.5 megaparsecs in radius, but I might have misinterpreted the text. The paper also uses a 50 km/s per megaparsec Hubble constant, which inflates distances. I am very cautious in rewriting its article though, as my revisions usually become very long and a similar scenario to IC 1101 might happen with this galaxy's page, which I don't want. Nussun05, if you remember, I talked about this galaxy on Discord. Other galaxiesmay warrant a stay, such as ESO 444-46.-- The Space Enthusiast (talk) 01:26, 1 May 2023 (UTC)[reply]

I have considered the BCG of Abell 1413 to be one of the largest (if not the largest) galaxy known. With trying to measure angular diameter myself to the fainter visible parts of it in the DESI Legacy survey DR10, I got to some ridiculous size of 4–6 million light-years (1.23-1.84 Mpc) assuming the angular diameter I measured myself (>11 arcmin) (I have recalculated the angular diameter and get to something from 7.5–9 arcminutes with a physical diameter of ~4-5 Mly but some of these measurements might have noise and light of other galaxies being mistaken for an actual part of Abell 1413 BCG). The 3.5 Mpc diameter does though seem to be unreliable as you mentioned. SpaceImplorerExplorerImplorer (talk) 06:59, 1 May 2023 (UTC)[reply]

Yes. The 3.5 megaparsec radius was cited here, on the 7th page. :https://ui.adsabs.harvard.edu/abs/1976ApJ...209..693O The Space Enthusiast (talk) 16:46, 1 May 2023 (UTC)[reply]

You can also use the residual images of Legacy Survey DR10. You can measure the halo by that measurement. The Space Enthusiast (talk) 19:06, 3 May 2023 (UTC)[reply]

I have traced out the very dim portions of the halo and intracluster light. The extent of the intracluster light is indeed crazy, with a radius of more than 15 arcminutes! I might be too loose on considering what the intracluster light is, however. The Space Enthusiast (talk) 22:20, 23 May 2023 (UTC)[reply]

While it is true that 154 kpc (500 kly) galaxies are some of the largest in the universe (hence the name of the page), the list is indeed extremely long. I was thinking on putting a limit like that in the past but for now I think that the limit should remain what it is. SpaceImplorerExplorerImplorer (talk) 06:52, 1 May 2023 (UTC)[reply]

The more generous cutoff point for me might be at 200 kpc (650 kly), which includes NGC 6872. A substantially large part of the list is below this size and it is indeed becoming excessively long. A more stricter cutoff point would be 750 kly which includes 3C 295 and will cut the list by as much as 30% of its current size. That being said, in either cases if we took this as the cutoff point then we have to remove IC 1101 from the main list, instead backing it towards the consolation "Notable galaxies" used as comparison. SkyFlubbler (talk) 12:29, 1 May 2023 (UTC)[reply]

To further emphasize this possible change, may I propose that we should not edit the article or not add any more candidates first in order to determine the cutoff point based on the sample of the list that we have as of the moment. Thanks! SkyFlubbler (talk) 16:10, 3 May 2023 (UTC)[reply]

I would be cutting the list now. The new cutoff point is at 700,000 light-years (214.61 kiloparsecs). Any objections or suggestions are appreciated. SkyFlubbler (talk) 13:20, 7 May 2023 (UTC)[reply]

Yet another concern about the list...[edit]

On a now-deleted Youtube video, SpaceImplorerExplorerImplorer said that ESO 383-76 should not have its massive size because only the R90 diameter was used. He also says that this was cherrypicked and used instead of the D25 diameter which is much smaller. Should we base the list on just one specific method, like D25?--The Space Enthusiast (talk) 17:34, 1 May 2023 (UTC)[reply]

R90 is a method that can be used, that was probably old and I was just assuming that it was cherrypicking. Like with Abell 1413 BCG, I attempted to measure the diameter of that galaxy with the DESI Legacy Survey and got to a similar major axis diameter. SpaceImplorerExplorerImplorer (talk) 17:42, 1 May 2023 (UTC)[reply]

Thanks for the clarification. If only we had an R90 estimate for MCG+4-28-97 and IC 1101... The Space Enthusiast (talk) 19:55, 1 May 2023 (UTC)[reply]

We cannot use D₂₅ for all galaxies because only a tiny fraction of them have their diameters available using this method. Most entries on this list have only the 2MASS measurements available, and some using half-light radius and its variants including R₉₀. Plus, not all D₂₅ measurements are the same, for example ESO-Uppsala uses the 445 nm wavelength while SDSS uses 658 nm filters. SkyFlubbler (talk) 07:24, 2 May 2023 (UTC)[reply]

Thank you SkyFlubbler. The Space Enthusiast (talk) 14:19, 2 May 2023 (UTC)[reply]

HyperLEDA Database[edit]

I have been thinking for quite some time to also include this database as a potential source. It also contains many diameter estimates with cited sources in them as well. Problem is that it has lots of diameter estimates and I don't know yet how to reconcile the estimations with the list. We can subdivide each galaxy by the largest estimates from NED and this one.

I will try to recreate the list to also include the estimations from here, in the manner similar to the list of largest stars. The project would be at the workpage. Thanks! SkyFlubbler (talk) 06:01, 6 June 2023 (UTC)[reply]

Thanks. I think we should check the Siena Galaxy Atlas as well. While using the Legacy Survey Sky Browser, one can overlay bright objects from both HyperLeda and the Siena Galaxy Atlas. The angular diameters provided by the Siena Galaxy Atlas are of interest for me because IC 1101 has a quoted angular diameter of roughly 4.8 arcminutes, while Abell 1413-BCG's angular diameter is given as 2.2 arcminutes. I may be wrong, but when calculating their sizes, IC 1101 is actually somewhat larger than Abell 1413 BCG, despite the latter having a shallower and much larger profile. I presume that this is due to IC 1101's curvier profile, but I am not a professional astronomer so please do give your opinions on this. The Space Enthusiast (talk) 01:35, 7 June 2023 (UTC)[reply]

Anyone? The Space Enthusiast (talk) 15:11, 7 June 2023 (UTC)[reply]

4.8 arcminutes seems so way off. RC3 and 2MASS provides angular sizes closer to 1.5 to 1.8 arcminutes. SkyFlubbler (talk) 20:05, 10 June 2023 (UTC)[reply]

Okay. Maybe it is a different reference lvel? The Space Enthusiast (talk) 20:33, 10 June 2023 (UTC)[reply]

I am once again reviving this discussion due to the recent edits by InTheAstronomy32 regarding PGC 088678. Most of the references citing uses "external surface photometry" which has no clear isophotal level, but this measurement seems to have been warranted in a recent 2021 paper by Lacki et al.

For now I would rather hold that particular galaxy as tentative, because NED cites a much smaller diameter, but we really need to reach consensus if we should start using the Lyon-Meudon database (HyperLEDA) for this purpose. SkyFlubbler (talk) 15:05, 6 May 2024 (UTC)[reply]

On second thought, after a further investigation into this, I think I found the discrepancy of what happened.

The supposed size given by InTheAstronomy32 of 3.13 million light-years might be due to a misinterpretation of the numbers at LEDA. The cited log_D25 value of 0.94 ± 0.05 was interpreted as-is as the exponent in arcminutes, which is supposed to be in 0.1 arcminute units (that is why log(0.1 arcmin) is cited). This gives an D25 diameter value offset by a factor of 10: 8.709 arcmin instead of the actual value of 0.8709 arcmin.

Using the distance in NED of 389.5 Mpc, the latter gives a value of 986.8 kpc or 3.21 million light-years, while the latter is a measly 98.68 kpc or 321,000 light-years, which is much closer to the diameter cited at NED at 136.89 kpc or 446,000 light years. SkyFlubbler (talk) 21:31, 6 May 2024 (UTC)[reply]

More?[edit]

sould we add more galaxies? using the wayback machine i saw this list used to have so much more galaxies. sould we add them back? APerosn53248 (talk) 08:29, 2 February 2024 (UTC)[reply]

This list uses isophotal diameters (mostly from NED) only. The ones on the old list included galactic haloes, which can be misleading. SpaceImplorerExplorerImplorer 14:50, 16 March 2024 (UTC)[reply]