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List of largest galaxies

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A Hubble Space Telescope image of the supergiant elliptical galaxy ESO 306-17. Supergiant elliptical galaxies are some of the largest galaxies known.

This is a list of largest galaxies known, sorted by order of increasing major axis diameters. The unit of measurement used is the light-year (approximately 9.46×1012 kilometers).

Overview

Galaxies are vast collections of stars, planets, nebulae and others that are surrounded by an interstellar medium and held together by gravity. They do not have a definite boundary by nature, and are characterized with gradually decreasing stellar density as a function of increasing distance from its center. Because of this, measuring the sizes of galaxies can often be difficult and have a wide range of results depending on the sensitivity of the detection equipment and the methodology being used. Some galaxies emit more strongly in wavelengths outside the visible spectrum, depending on its stellar population, whose stars may emit more strongly in other wavelengths that are beyond the detection range. It is also important to consider the morphology of the galaxy when attempting to measure its size - an issue that has been raised by the Russian astrophysicist B.A. Vorontsov-Vel'Yaminov in 1961, which considers separate determination methods in measuring the sizes of spiral and elliptical galaxies.[1]

With the advent of large sky surveys in the second half of the 20th century, the need for a standard for accurate determination of galaxy sizes has been in greater demand due to its enormous implications in astrophysics, such as the accurate determination of the Hubble constant. Various standards have been adapted over the decades, with the methods being cited on this list discussed below.

Evolution and characteristics of large galaxies

Galaxies in the early universe tend to be very small and irregular, with their growth primarily driven by the environment and external forces that work on them.[2] Large galaxies have properties and evolutionary processes that make them distinct from their smaller counterparts, discussed below.

Type-cD galaxies

First described in 1964 by a paper by Thomas A. Matthews and others,[3], the cD class of galaxies are a subtype of the more general class of D galaxies, which are giant elliptical galaxies, except that they are much larger. They are popularly known as the supergiant elliptical galaxies and constitute the largest and most luminous galaxies known. These galaxies feature a central elliptical nucleus with an extensive, faint halo of stars extending to megaparsec scales.[2] The profile of their surface brightnesses as a function of their radius (or distance from their cores) falls off more slowly than their smaller counterparts.[4]

The formation of these cD galaxies remains an active area of research, but the leading model is that they are the result of the mergers of smaller galaxies in the environments of dense clusters, or even those outside of clusters with random overdensities. These processes are the mechanisms that drive the formation of fossil groups or fossil clusters, where a large, relatively isolated, supergiant elliptical resides in the middle of the cluster and are surrounded by an extensive cloud of X-rays as the residue of these galactic collisions. Another older model posits the phenomenon of cooling flow, where the heated gases in clusters collapses towards their centers as they cool, forming stars in the process, a phenomenon observed in clusters such as Perseus,[5] and more recently in the Phoenix Cluster.

Methodology and constraints for measurement

Defining the true extent of a galaxy has been a major challenge primarily due to their diffuse nature. Nevertheless, astronomers over the past decades made recent developments in order to properly define the extent of a galaxy quickly, especially with the advent of large-scale sky surveys that demand huge amounts of data. Discussed below are some of these methods, which are also being used by the NASA/IPAC Extragalactic Database (NED), all of which have their own advantages and disadvantages.

Isophotal diameters

The isophotal diameter is introduced as an objective way of measuring a galaxy's size based on its apparent surface brightness. Isophotes are curves in a diagram - such as a picture of a galaxy - that adjoins points of equal brightnesses, and are useful in defining the extent of the galaxy. Redman (1963) suggested that the diameters of galaxies should be defined at the 25.0 mag/arcsec2 isophote at the B-band (445 nm wavelength of light, in the blue part of the visible spectrum). This corresponds to at least 10% of the normal brightness of the night sky, and very near the limitations of blue filters at that time. This method was particularly used during the creation of the Uppsala General Catalogue using blue filters from the Palomar Observatory Sky Survey, which was later corrected in the Second Reference Catalogue of Bright Galaxies or RC2 Catalogue in 1963.

However, not every study chooses to apply this standard. Holmberg (1958) utilizes ~26.5 mag/arcsec2 value (later known as the Holmberg isophote),[6] and even other studies point to standards with higher magnitudes (fainter brightnesses), making this measure less well-defined. Further discoveries of low surface brightness galaxies and very high redshift galaxies also puts constraints in using isophotal diameters; this has been a problem issued in a 1987 paper by Cornell et al, finding out that the use of the isophotal diameters give rise to overestimations in the measurements of small UGC galaxies, with overestimations more pronounced on low-surface brightness galaxies. Corrections have been introduced by the advent of the Third Reference Catalogue of Bright Galaxies or RC3 in 1991.[7]

Petrosian magnitude

First described by V. Petrosian in 1976,[8] a modified version of this method has been utilized by the Sloan Digital Sky Survey (SDSS).[9] This method employs a mathematical model on a galaxy whose radius is determined by the azimuthally (horizontal) averaged profile of its brightness flux. In particular, the SDSS employed the Petrosian magnitude in the R-band (658 nm, in the red part of the visible spectrum) to ensure that the brightness flux of a galaxy would be captured as much as possible while counteracting the effects of background noise. For a galaxy whose brightness profile is exponential, it is expected to capture all of its brightness flux, and 80% for galaxies that follow a profile under de Vaucouleurs's law.

Petrosian magnitudes have the advantage that it is redshift and distance independent, allowing the measurement of the galaxy's apparent size since the Petrosian radius is defined in terms of the galaxy's overall luminous flux.

A critique of an earlier version of this method has been issued by IPAC,[10] with the method causing a magnitude of error (upwards to 10%) of the values than using isophotal diameter. The use of Petrosian magnitudes also have the disadvantage of missing most of the light outside the Petrosian aperture, which is defined relative to the galaxy's overall brightness profile, especially for elliptical galaxies, with higher signal-to-noise ratios on higher distances and redshifts.[11] A correction for this method has been issued by Graham et al in 2005,[12] based on the assumption that galaxies follow Sersic's law.

Half-light radius and its variations

The half-light radius is a measure that is based on the galaxy's overall brightness flux. This is the radius upon which half, or 50%, of the total brightness flux of the galaxy was emitted. In this method it is necessary to capture the overall brightness flux of a galaxy, with a method employed by Bershady in 2000 suggesting to measure twice the size where the brightness flux of an arbitrarily chosen radius, defined as the local flux, divided by the overall average flux equals to 0.2.[13] Using half-light radius allows a rough estimate of a galaxy's size, but is not particularly helpful in determining its morphology.[14]

Variations of this method exist. In particular, in the ESO-Uppsala Catalogue of Galaxies values of 50%, 70%, and 90% of the total blue light (the light detected through a B-band specific filter) had been used to calculate a galaxy's diameter.[15]

Near-infrared method

This method has been used by 2MASS as an adaptation from the previously used methods of isophotal measurement. Since 2MASS operates in the near infrared, which has the advantage of being able to recognize dimmer, cooler, and older stars, it has a different form of approach compared to other methods that normally use B-filter. The detail of the method used by 2MASS has been described thoroughly in a document by Jarrett et al, with the survey measuring several parameters.[16]

The standard aperture ellipse (area of detection) is defined by the infrared isophote at the Ks band (roughly 2.2 μm wavelength) of 20 mag/arcsec2. Gathering the overall luminous flux of the galaxy has been employed by at least four methods: the first being a circular aperture extending 7 arcseconds from the center, an isophote at 20 mag/arcsec2, a "total" aperture defined by the radial light distribution that covers the supposed extent of the galaxy, and the Kron aperture (defined as 2.5 times the first-moment radius, an integration of the flux of the "total" aperture).[16]

List

This is a dynamic list and may never be able to satisfy particular standards for completeness. You can help by adding missing items with reliable sources.

Listed below are galaxies with diameters greater than 500,000 light-years. Due to different techniques, each figure listed on the galaxies has varying degrees of confidence in them. The reference to those sizes plus further additional details can be accessed by clicking the link for NED on the right-hand side of the table.

Galaxies with diameters 500 kly or greater
Galaxy name/designation Major axis diameter (in light-years) Minor axis diameter (in light years) Redshift Comoving distance
(in millions of light-years) 		Apparent visible magnitude Morphology Estimation
method 		Link for object
ESO 539-13 NED03 (ESO 539-G 013 NED03)[a] 1,128,000 1,128,000 0.0540 709.7 16 E 27.0 B-mag arcsec-2 NED
ESO 383-76 (ESO 383-G 076) 1,125,000 562,600 0.0386 528.7 13.01 cD5; E5; BrClG 90% total B-light NED
ESO 306-17 (ESO 306-G 017) 992,800 655,200 0.0358 482.4 13.33 cD3; E3 90% total B-light NED
ESO 350-15 (ESO 350-G 015) 967,900 484,000 0.05 655.2 14.2 cD3; E3 90% total B-light NED
ESO 409-25 (ESO 409-G 025) 953,700 591,300 0.0619 816.0 13.9 cD; E4; BrClG 90% total B-light NED
ESO 253-27 (ESO 253-G 027) 791,300 538,100 0.0516 695.0 14.88 cD3; E3 90% total B-light NED
ESO 541-13 (ESO 541-G 013) 780,100 608,500 0.057 750.2 13.8 cD; E3 pec 90% total B-light NED
NGC 623 746,000 567,000 0.03 390.4 13.88 cD; E 27.0 B-mag arcsec-2 NED
ESO 197-1 NED 03 (ESO 197-G 001 NED 03)[a] 745,900 372,900 0.056 742.0 15.71 E 27.0 B-mag arcsec-2 NED
ESO 488-15 (ESO 488-G 015) 743,800 580,200 0.0422 568.5 14.72 E 90% total B-light NED
ESO 291-9 (ESO 291-G 009) 737,800 427,900 0.0564 744.6 14.64 cD4; SA0-;BrClG 90% total B-light NED
IC 5353 709,600 574,700 0.0275 354.9 14.05 cD; S0- 26.0 B-mag arcsec-2 NED
ESO 198-1 (ESO 198-G 001) 688,200 523,000 0.0643 854.9 14.36 cD4; E4 27.0 B-mag arcsec-2 NED
ESO 205-21 (ESO 205-G 021) 675,200 425,400 0.033 446.2 13.9 SAB0- pec; E/S0 90% total B-light NED
ESO 417-1 (ESO 417-G 001) 657,900 302,600 0.0217 283.8 15.59 SA00 pec 90% total B-light NED
ESO 11-4 (ESO 011-G 004) 656,700 452,900 0.0575 770.1 15.38 cD4; E4 pec 90% total B-light NED
NGC 1759 652,100 587,000 0.0542 727.0 14.08 cD; E 27.0 B-mag arcsec-2 NED
ESO 351-21 (ESO 351-G 021) 616,700 542,700 0.0571 754.1 15.21 SA0- 90% total B-light NED
NGC 1668 612,600 404,300 0.0335 449.1 13.73 SA0-; D/cD 90% total B-light NED
IC 5358 611,700 281,400 0.029 372.8 13.58 cD4; E4 pec 27.0 B-mag arcsec-2 NED
IC 1633 609,400 469,200 0.0242 316.4 12.48 cD; E1 27.0 B-mag arcsec-2 NED
ESO 552-20 (ESO 552-G 020) 608,600 353,000 0.0314 420.1 13.32 cD; E 90% total B-light NED
ESO 444-46 (ESO 444- G 046) 598,200 341,000 0.047 640.9 15.23 cD4; E4; BrClG 27.0 B-mag arcsec-2 NED
ESO 349-10 (ESO 349-G 010) 595,900 369,500 0.049 644.8 13.0 cD4; E4; BrClG 90% total B-light NED
ESO 118-6 (ESO 118-G 006) 590,700 336,700 0.0485 648.7 15.23 cD4; E4 26.0 B-mag arcsec-2 NED
WISEA J000150.28+010154.9 576,100 368,700 0.0861 1,138 16.0 E0 2MASS K-band total mag NED
ESO 539-11 (ESO 539-G 011) 569,100 335,800 0.0529 693.7 14.9 S0 90% total B-light NED
ESO 33-3 (ESO 033-G 003) 564,000 344,000 0.0255 343.4 13.7 E4 90% total B-light NED
ESO 307-13 (ESO 307-G 013) 563,600 377,600 0.0466 628.2 13.5 cD3; E3; BrClG 90% total B-light NED
ESO 482-21 (ESO 482-G 021) 560,800 319,700 0.0552 734.8 15.24 S0 90% total B-light NED
ESO 86-62 (ESO 086-G 062) 558,900 346,500 0.0366 493.5 13.55 cD4; E4 90% total B-light NED
WISEA J005939.38-181807.5 558,700 424,600 0.091 1,206 16.01 SB(s)a pec 2MASS K-band total mag NED
PKS 2225-309 554,800 133,100 0.058 764.8 14.0 cD3; E3; BrClG 25.0 B-mag arcsec-2 NED
WISEA J005700.34-004930.8 553,700 476,200 0.049 638.6 16.0 S0 25.0 mag arcsec-2 NED
ESO 488-27 (ESO 488-G 027) 548,400 449,700 0.0396 798.8 13.99 cD; E1 27.0 B-mag arcsec-2 NED
ESO 195-1 (ESO 195-G 001) 546,600 486,500 0.05 658.5 14.96 S0 90% total B-light NED
ESO 488-13 (ESO 488-G 013) 536,100 337,800 0.045 611.5 15.1 SA(r)0+ 27.0 B-mag arcsec-2 NED
ESO 146-28 (ESO 146-G 028) 533,400 368,000 0.0412 545.7 13.9 cD3; E3 27.0 B-mag arcsec-2 NED
ESO 161-8 (ESO 161-G 008) 532,600 266,300 0.0486 655.2 13.8 cD5; E5; BrClG 90% total B-light NED
ESO 306-4 (ESO 306-G 004) 519,900 260,000 0.0314 423.4 14.71 cD4; E4 pec 90% total B-light NED
2MASX J12571157-1724344 517,600 393,400 0.0475 650.7 13.1 cD4; E4 2MASS K-band total mag NED
ESO 424-1 (ESO 424-G 001) 511,800 373,600 0.0594 798.8 15.20 cD4; E4 pec 90% total B-light NED
WISEA J222418.56-551451.7 507,200 365,200 0.079 1,051 15.83 cD3; E3 2MASS K-band total mag NED
WISEA J214529.50-513625.1 506,000 182,200 0.0538 712.3 15.48 cD5; E5 pec 25.0 B-mag arcsec-2 NED
ESO 349-1 (ESO 349-G 001) 505,600 374,200 0.0574 757.0 14.52 cD1; E1 27.0 B-mag arcsec-2 NED
NGC 77 504,300 489,100 0.063 831.0 15.67 SA0- 90% total B-light NED
NGC 7012 502,100 306,300 0.0293 384.5 13.65 cD4; E4 pec 90% total B-light NED

Listed below are some notable galaxies under 500,000 light-years in diameter, for the purpose of comparison. All links to NED are available, except for the Milky Way, which is linked to the relevant paper detailing its size.

Notable galaxies with diameters 500kly or less
Galaxy name/designation Major axis diameter (in light-years) Minor axis diameter (in light years) Redshift Comoving distance
(in millions of light-years) 		Apparent visible magnitude Morphology Estimation
method 		Link for object
A2261-BCG 494,900 485,000 0.223 2,989 19.2 cD; E 2MASS K-band total mag NED
Hercules A 426,700 264,500 0.155 2,096 17.7 E; WLRG; NLRG 2MASS K-band total mag NED
IC 1101 409,700 262,200 0.0215 295.8 14.73 cD; S0- 2MASS K-band total mag NED
NGC 1399 365,000 339,000 0.0047 59.36 10.6 cD; E1 pec 90% total B-light NED
NeVe 1 308,200 221,900 0.028 407.4 8.94(K)[b] cD; E 2MASS K-band total mag NED
Alcyoneus (galaxy) 225,400[c] 144,200 0.247 3,310 19.6 E 25.0 r-mag arcsec-2 {NED
Milky Way 169,600–199,000 169,600–199,000 ~ ~[d] -5.0 Sb; Sbc; SB(rs)bc Gaia stellar disk estimate H. Rix and J. Bovy
Andromeda Galaxy 152,300 152,300 -0.001[e] 2.446 0.17 SA(s)b 25.0 mag/arcsec2 NED
Malin 1 103,200 110,100 0.0827 1,122 17.6(g) S; LSB SDSS r-band 25.0 mag/arcsec2 NED
NGC 262 33,240 25,930 0.0150 187.5 13.2(r) SA(s)0/a; Sy2 2MASS K-band total mag NED

Notes

  1. ^ a b Part of a galaxy group. Listed name refers to the NED identifier.
  2. ^ Magnitude at the K-band; invisible in naked eye.
  3. ^ Major axis refers to the visible stellar axis of the host galaxy. Radio lobes are 15 million light-years across, though not considered a part of the main galaxy.
  4. ^ Earth resides within the Milky Way, so the distance to it is zero. The distance towards its center (Sagittarius A*) is 8.34 ± 0.14 kiloparsecs (27,200 ± 456.6 ly).
  5. ^ Negative sign indicates blueshift

Further reading

Evolution of Galaxies in Clusters

See also

References

  1. ^ Vorontsov-Vel'Yaminov, B. A. (1961). "The Comparision of Galaxy Diameters". Soviet Astronomy. 4: 735. Bibcode:1961SvA.....4..735V.
  2. ^ a b "Discoveries - Highlights | Tracing the Growth of Galaxies". 6 February 2017.
  3. ^ Matthews, Thomas A.; Morgan, William W.; Schmidt, Maarten (1964). "A Discussion of Galaxies Indentified with Radio Sources". The Astrophysical Journal. 140: 35. Bibcode:1964ApJ...140...35M. doi:10.1086/147890.
  4. ^ Tonry, John L. (1987). "Properties of CD galaxies". Structure and Dynamics of Elliptical Galaxies. 127: 89. Bibcode:1987IAUS..127...89T. doi:10.1007/978-94-009-3971-4_7. ISBN 978-90-277-2586-8. S2CID 117980521.
  5. ^ Fabian, A. C.; Nulsen, P. E. J. (1977). "Subsonic accretion of cooling gas in clusters of galaxies". Monthly Notices of the Royal Astronomical Society. 180 (3): 479. Bibcode:1977MNRAS.180..479F. doi:10.1093/mnras/180.3.479.
  6. ^ http://astro.vaporia.com/start/holmbergradius.html
  7. ^ "RC3 - Third Reference Catalog of Bright Galaxies".
  8. ^ Petrosian, V. (1976). "Surface Brightness and Evolution of Galaxies". The Astrophysical Journal. 210: L53. Bibcode:1976ApJ...209L...1P. doi:10.1086/182301.
  9. ^ "SkyServer: Algorithms".
  10. ^ "Circular and Fixed Elliptical Apertures: The Petrosian and Isophotal Photometry".
  11. ^ "About NED | NASA/IPAC Extragalactic Database". ned.ipac.caltech.edu.
  12. ^ Graham, Alister W.; Driver, Simon P.; Petrosian, Vahé; Conselice, Christopher J.; Bershady, Matthew A.; Crawford, Steven M.; Goto, Tomotsugu (2005). "Total Galaxy Magnitudes and Effective Radii from Petrosian Magnitudes and Radii". The Astronomical Journal. 130 (4): 1535–1544. arXiv:astro-ph/0504287. Bibcode:2005AJ....130.1535G. doi:10.1086/444475. S2CID 11517686.
  13. ^ Conselice, Christopher J.; Bershady, Matthew A.; Jangren, Anna (2000). "The Asymmetry of Galaxies: Physical Morphology for Nearby and High-Redshift Galaxies". The Astrophysical Journal. 529 (2): 886–910. arXiv:astro-ph/9907399. Bibcode:2000ApJ...529..886C. doi:10.1086/308300. S2CID 118962524.
  14. ^ https://www.aanda.org/articles/aa/full/2001/14/aa10027/node4.html
  15. ^ Lauberts, Andris; Valentijn, Edwin A. (1989). The surface photometry catalogue of the ESO-Uppsala galaxies. Bibcode:1989spce.book.....L.
  16. ^ a b Jarrett, T. H.; Chester, T.; Cutri, R.; Schneider, S. E.; Huchra, J. P. (2003). "The 2MASS Large Galaxy Atlas". The Astronomical Journal. 125 (2): 525–554. Bibcode:2003AJ....125..525J. doi:10.1086/345794. S2CID 117784410.
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