IC 1101

Coordinates: Sky map 15h 10m 56.1s, +05° 44′ 41″
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IC 1101
IC 1101 in Abell 2029 (hst 06228 03 wfpc2 f702w pc).jpg
June 1995 image of IC 1101 taken by the Hubble Space Telescope
Observation data (J2000 epoch)
Right ascension15h 10m 56.1s[1]
Declination+05° 44′ 41″[1]
Helio radial velocity22,419 km/s (13,931 mi/s)[1]
Distance354.0 ± 24.8 Mpc (1,154.6 ± 80.9 million ly)h−1
Group or clusterAbell 2029
Apparent magnitude (V)13.22[1]
TypecD; S0-[1]
Size123.65 to 169.61 kpc (403,300 to 553,200 ly)
(D25 B-band and total K-band isophotes)[3][4][a]
Apparent size (V)1'.2 × 0'.6[1]
Other designations
UGC 9752,[1] PGC 54167,[1] A2029-BCG[1]

IC 1101 is a class S0 supergiant (cD) lenticular galaxy at the center of the Abell 2029 galaxy cluster. It has an isophotal diameter at about 123.65 to 169.61 kiloparsecs (400,000 to 550,000 ly). It possesses a diffuse core which is the largest known core of any galaxy to date,[5] and also hosts a supermassive black hole that is one of the largest black holes known.[5] The galaxy is located at 354.0 megaparsecs (1.15 billion light-years) from Earth. The galaxy was discovered on 19 June 1790, by the British astronomer William Herschel.[6]



IC 1101 imaged by the Sloan Digital Sky Survey

The galaxy is classified as a supergiant elliptical (E) to lenticular (S0)[7] and is the brightest galaxy in A2029 (hence its other designation A2029-BCG; BCG meaning brightest cluster galaxy).[8][9] The galaxy's morphological type is debated due to it possibly being shaped like a flat disc but only visible from Earth at its broadest dimensions. A morphology of S0- (Hubble stage -2; see Hubble stage for details) has been given by the Third Reference Catalogue of Bright Galaxies (RC3) in 1991.[3]

Components and Structure[edit]

Like most large galaxies, IC 1101 is populated by a number of metal-rich stars, some of which are seven billion years older than the Sun, making it appear golden yellow in color. It has a bright radio source at the center, which is likely associated with an ultramassive black hole in the mass range of 40–100 billion M measured using core dynamical models,[5] or alternatively at 50-70 billion M using gas accretion rate and growth modelling,[10] which would make IC 1101's black hole one of the most massive known to date. The estimates of the mass of IC 1101's black hole are near the upper bound of cosmological limits,[10] and is referred to as an "overmassive" black hole.[5]

IC 1101's Mass to light ratio has been described as being anomalously high. The galaxy also has a unique velocity dispersion profile, which indicates a massive Dark Matter halo. It accretes roughly 450 solar masses per year. In spite of lying the center of a large inflow of gas, the galaxy lacks optical nuclear emission at its center as well as signs of recent star formation.[11] There is also no evidence of dust lanes in the core.[12]

A 2017 paper suggests that IC 1101 has the largest core size of any galaxy, with a core radius of around 4.2 ± 0.1 kpc (13.70 ± 0.33 thousand ly) by fitting a model to a Hubble Space Telescope (HST) image of the galaxy. This makes its core larger than the one observed in A2261-BCG, which is 3.2 kpc (10 thousand ly). The diffuse and depleted core is also roughly an order of magnitude larger than the cores of other large elliptical galaxies, such as NGC 4889 and NGC 1600. However, estimates of the absolute magnitude of IC 1101's spheroid are very faint for such a large core, thus indicating a large stellar mass deficit estimated at 4.9×1011 MSun and a large luminosity deficit estimated at 1.1×1011 LIt has been theorized that when the supermassive black holes coalesce, they eject stars, sending them on radial orbits. Thus, the massive core is believed to have formed due to black holes scouring the galactic core. This, along with the stellar mass deficit at the core and the somewhat bluer color of IC 1101's halo suggests that IC 1101 underwent a large number of major galaxy mergers,[13] with the number of major mergers likely being around ~10, or 10-20.[5] However, when examining large and diffuse galactic cores, caution must be taken, as various estimates may differ between the computer models used. As an example, Holmberg 15A was originally claimed to have the largest galactic core of any galaxy but other studies proved otherwise, either not finding a core or estimating a smaller size for it.[12]

IC 1101's major axis is oriented in the northeast to southwest direction. Its components, the spheroid and its intermediate scale are well-aligned, but its halo is twisted from the galaxy's other components. Its isophotes are predominantly somewhat boxy, although its ellipticity increases farther and farther away from its center. Closer to the core, the ellipticity increases, suggesting a nuclear disc. The nuclear component might be due to an unresolved double nucleus, produced by a low intensity Active Galactic Nucleus (AGN) as well as the remnant stellar nuclei of an accreted satellite that had been tidally disrupted by the central Supermassive Black Hole. The elliptical galaxies NGC 44386B, NGC 5419, VCC 128 contain two point-sources, producing high ellipticities. The NRAO VLA sky-survey detected a radio source near IC 1101, suggesting a possible AGN. Another, weaker radio source has also been detected nearby. Thus, a double AGN cannot be ruled out.[12]

Like most BCGs, IC 1101 has a massive and diffuse stellar halo and has excessive halo light. The halo extends throughout a large part of Abell 2029 and can be easily traced out to several hundred kiloparsecs from the galaxy center.[14] The galaxy's halo, rising ellipticity at larger radii from the center and its intermediate scale profile seem to be the reasons why IC 1101 is classified as a lenticular galaxy In RC3.[12]


IC 1101 is considered a large galaxy characterized by an extensive, diffuse halo. Defining the size of a galaxy varies according to the method used in the astronomical literature. Photographic plates of blue light from the galaxy (sampling stars excluding the diffuse halo) yield an effective radius (the radius within which half the light is emitted) of 65 ± 12 kpc (212 ± 39 thousand ly)[11] based on an earlier distance measurement. The galaxy has a very large halo of much lower intensity "diffuse light" extending to a radius of 600 kpc (2 million ly).[14][verification needed] The authors of the study identifying the halo conclude that IC 1101 is "possibly one of the largest and most luminous galaxies in the universe". This view has been stated in several other papers as well,[10][14] though this figure was based on an earlier assumed distance of 262 megaparsecs (855 million light-years).

More recent measurements, using the 25.0 magnitude/arcsec2 standard (commonly known as D25, a method recommended by R.O. Redman in 1936)[15][b] has been utilized by the RC3 in the B-band, with a measured major axis (log 2a+1) of 1.08 (equivalent to 72.10 arcseconds),[3] translating to a diameter of 123.65 kiloparsecs (403,000 ly).[1] Another calculation by the Two Micron All-Sky Survey using the "total" aperture at the K-band yield a much larger size of 169.61 kiloparsecs (553,000 ly).[4] Both measurements are based on the currently-accepted distance to IC 1101. This would make it one of the largest and most luminous galaxies known, though there are other galaxies with larger isophotal diameter measurements (such as NGC 623, Abell 1413 BCG, and ESO 306-17).


The distance to IC 1101 has also been uncertain, with different methods across different wavelengths producing varying results. An earlier distance calculation from 1980 using the galaxy's photometric property yield a distance of 262.0 Mpc (855 million ly) and a redshift of z = 0.077, based on a Hubble constant value H0 of 60 km/s/Mpc.[16] The RC3 catalogue gave a nearly similar value of z=0.078, based on optical emission lines,[3] a value conformed to as recently as 2017 based on luminosity, stellar mass, and velocity dispersion functions,[2] all yielding distances of 354.0 megaparsecs (1.2 billion light-years) based on the modern value of the Hubble constant H0 = 67.8 km/s/Mpc; the currently accepted values. Lower redshifts have been calculated for other wavelengths such as the photometric redshift measurement by the Two Micron All-Sky Survey (2MASS) in 2014, which gave a value of z = 0.045,[17] translating to a distance of 197.1 megaparsecs (643 million light-years). A measurement made in 2005 by the Arecibo Observatory using the 21-cm hydrogen emission line yields a redshift of z = 0.021,[18] and hence a distance of 97.67 ± 6.84 megaparsecs (318.6 ± 22.3 million light-years).


Massive galaxies are thought to build up hierarchically, when smaller systems merge, forming larger and larger systems. Due to their high luminosities and distinct properties, BCGs likely experienced numerous galactic interactions and mergers.[12] The lack of other bright and luminous galaxies other than IC 1101 at the center of the Abell 2029 galaxy cluster suggests that they were absorbed and consumed ("Chewed-Up") by the nascent IC 1101. Since the halo is somewhat flattened, the halo might have assumed the distribution of the bright luminous galaxies as they were consumed.[13] The depleted core and other characteristics of IC 1101 such as the halo component suggests that the galaxy underwent numerous galactic mergers and interactions. The smoothness of the halo suggests that it formed early in the history if the cluster.[9][13][12] Using some methods to estimate the possible number of major mergers that IC 1101 has been involved in results in an unrealistically large number of major galactic mergers, about 76 or even greater. Further examination reduces the number of major mergers to ~10-20, or less than 10. As Supermassive Balack holes merged at the center of IC 1101, they ejected stars, resulting in a large stellar mass deficit and a large luminosity deficit at the center, with the final mass of the Supermassive black hole at 40–100 billion M. The somewhat offset core of IC 1101 with respect to its isophotes also supports this.[12] Now, the Abell 2029 galaxy cluster is among the most relaxed clusters in the universe.[12]

See also[edit]


  1. ^ The diameters given at NED were based on a redshift-independent distance measurement. The diameters given here were based on NED's provided scale "Virgo + GA + Shapley" multiplied with the given angular diameter values of the estimation methods being stated.
  2. ^ Date mistakenly stated as 1963.


  1. ^ a b c d e f g h i j k l "NED results for object IC 1101". NASA/IPAC Extragalactic Database. Retrieved 28 August 2022.
  2. ^ a b "Reference Lookup | NASA/IPAC Extragalactic Database". ned.ipac.caltech.edu. Retrieved 9 December 2022.
  3. ^ a b c d De Vaucouleurs, Gerard; De Vaucouleurs, Antoinette; Corwin, Herold G.; Buta, Ronald J.; Paturel, Georges; Fouque, Pascal (1991). Third Reference Catalogue of Bright Galaxies. Bibcode:1991rc3..book.....D.
  4. ^ a b "NASA/IPAC Extragalactic Database". Archived from the original on 15 August 2022. Retrieved 26 August 2022.
  5. ^ a b c d e Dullo, Bililign T.; Graham, Alister W.; Knapen, Johan H. (October 2017). "A remarkably large depleted core in the Abell 2029 BCG IC 1101". Monthly Notices of the Royal Astronomical Society. 471 (2): 2321–2333. arXiv:1707.02277. Bibcode:2017MNRAS.471.2321D. doi:10.1093/mnras/stx1635. S2CID 119000593.
  6. ^ "William Herschel's astronomical discoveries". MacTutor. University of St Andrews, Scotland. Retrieved 4 April 2020.
  7. ^ "IC 1101". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 21 December 2014.
  8. ^ Lewis, Aaron D.; Buote, David A.; Stocke, John T. (March 2003). "Chandra Observations of A2029: The Dark Matter Profile Down to below 0.01rvir in an Unusually Relaxed Cluster". The Astrophysical Journal. 586 (1): 135–142. arXiv:astro-ph/0209205. Bibcode:2003ApJ...586..135L. doi:10.1086/367556. S2CID 119439086.
  9. ^ a b Uson, Juan M.; Boughn, Stephen P.; Kuhn, Jeffrey R. (October 1990). "The central galaxy in Abell 2029 - an old supergiant". Science. 250 (4980): 539–540. Bibcode:1990Sci...250..539U. doi:10.1126/science.250.4980.539. PMID 17751483. S2CID 23362384.
  10. ^ a b c Brockamp, M.; Baumgardt, H.; Britzen, S.; Zensus, A. (January 2016). "Unveiling Gargantua: A new search strategy for the most massive central cluster black holes". Astronomy & Astrophysics. 585. A153. arXiv:1509.04782. Bibcode:2016A&A...585A.153B. doi:10.1051/0004-6361/201526873. S2CID 54641547.
  11. ^ a b Fisher, David; Illingworth, Garth; Franx, Marijn (January 1995). "Kinematics of 13 brightest cluster galaxies". The Astrophysical Journal. 438 (2): 539–562. Bibcode:1995ApJ...438..539F. doi:10.1086/175100.
  12. ^ a b c d e f g h Dullo, Bililign T. (December 2019). "The Most Massive Galaxies with Large Depleted Cores: Structural Parameter Relations and Black Hole Masses". The Astrophysical Journal. 886 (2): 80. arXiv:1910.10240. Bibcode:2019ApJ...886...80D. doi:10.3847/1538-4357/ab4d4f. S2CID 204838306. Retrieved 12 March 2022.
  13. ^ a b c Dressler, A. (August 1979). "The dynamics and structure of the cD galaxy in Abell 2029". Astrophysical Journal. 231: 659-670. doi:10.1086/157229. Retrieved 17 January 2023.
  14. ^ a b c Uson, Juan M.; Boughn, Stephen P.; Kuhn, Jeffrey R. (March 1991). "Diffuse light in dense clusters of galaxies. I. R-band observations of Abell 2029". The Astrophysical Journal. 369: 46–53. Bibcode:1991ApJ...369...46U. doi:10.1086/169737.
  15. ^ "Dimensions of Galaxies". ned.ipac.caltech.edu. Retrieved 9 December 2022.
  16. ^ Hoessel, J. G.; Gunn, J. E.; Thuan, T. X. (1980). "The photometry properties of brightest cluster galaxies. I. Absolute magnitudes in 116 nearby Abell clusters". The Astrophysical Journal. 241: 486. Bibcode:1980ApJ...241..486H. doi:10.1086/158363.
  17. ^ Bilicki, Maciej; Jarrett, Thomas H.; Peacock, John A.; Cluver, Michelle E.; Steward, Louise (2014). "Two Micron All Sky Survey Photometric Redshift Catalog: A Comprehensive Three-dimensional Census of the Whole Sky". The Astrophysical Journal Supplement Series. 210 (1): 9. arXiv:1311.5246. Bibcode:2014ApJS..210....9B. doi:10.1088/0067-0049/210/1/9. S2CID 118733998.
  18. ^ Springob, Christopher M.; Haynes, Martha P.; Giovanelli, Riccardo; Kent, Brian R. (2005). "A Digital Archive of H I 21 Centimeter Line Spectra of Optically Targeted Galaxies". The Astrophysical Journal Supplement Series. 160 (1): 149. arXiv:astro-ph/0505025. Bibcode:2005ApJS..160..149S. doi:10.1086/431550. S2CID 14911447.

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