The Local Group (original) (raw)

The Local Group of Galaxies

This is "our" group of galaxies. It was first recognized by Hubble, in the time of the first distance determinations and redshift measurements (see, e.g., his The Realm of the Nebulae).

Messier objects: The Andromeda GalaxyM31 and its satellitesM32 andM110, as well as the Triangulum GalaxyM33.

Other members (over 30 in all) include our Milky Way Galaxy, the Large and the Small Magellanic Cloud (LMC and SMC), which have been known before the invention of the telescope, as well as several smaller galaxies which were discovered more recently. These galaxies are spread in a volume of nearly 10 million light years diameter, centered somewhere between the Milky Way and M31. Membership is not certain for all these galaxies, and there are possible other candidate members.

Of the Local Group member galaxies, the Milky Way and M31 are by far the most massive, and therefore dominant members. Each of these two giant spirals has accumulated a system of satellite galaxies, where

the system of the Milky Way contains many (nearby) dwarf galaxies, spread all over the sky, namely Sag DEG, LMC, SMC, the recently discovered and widely disrupted Canis Major Dwarf, and the dwarf galaxies in Ursa Minor, Draco, Carina, Sextans (dwarf), Sculptor, Fornax, Leo I, Leo II, and perhaps the Phoenix Dwarf, and Leo A (which may alternatively belong to the NGC 3109 subgroup), as well as probably 11 to 13 known dwarf spheroidal galaxies discovered to 2010, and about 30 more discovered between 2015 and 2018.
the system of the Andromeda galaxy is seen from outside, and thus grouped around its main galaxy M31 in Andromeda, containing bright nearby M32 and M110 as well as fainter and more far-out NGCs 147 and 185, the very faint systems And I, And II, And III and possibly And IV (but for this one see remark below), And V, And VI (Pegasus dwarf), And VII (Cassiopeia dwarf), And VIII, And IX, and And X, as well as probably the newly discovered dwarf spheroidals And XI, And XII, And XIII, And XIV, as well as And XV to And XXXIII (And 33), and several tidal star streams, probable satellite remnants, notably the And Tidal Stream NW (And NW) and the And Tidal Stream SW (And SW).
The third-largest galaxy, the Triangulum spiral M33, may or may not be an outlying gravitationally bound companion of M31, but has itself probably the dwarf LGS 3 as a satellite. Also, IC 1613 may perhaps be a member of the M31 subgroup, as may be the doubtful members UGCA 86 and UGCA 92.
There is a third potential subgroup around irregular galaxy NGC 3109, which contains Sextans A, Sextans B, the Antlia Dwarf and perhaps Leo A (but that one may belong to the Milky Way subgroup).
The other members, mostly dwarf irregulars, cannot be assigned to one of these main subgroups, and float quite alone in the gravitational field of the giant group members. They tend to form a vast cloud, the Local Group Cloud. Only one dwarf galaxy, GR 8, seems to be so isolated that it doesn't belong to any of these substructures.

The substructures of the group are probably not stable. Observations and calculations suggest that the group is highly dynamic and has changed significantlyin the past: The galaxies around the large elliptical Maffei 1 have probably been once part of our galaxy group.

As this shows, the Local Group is not isolated, but in gravitional interaction, and member exchange, with the nearest surrounding groups, notably:

the Maffei 1 group, which besides the giant elliptical galaxy Maffei 1 also contains smaller Maffei 2, and is associated with nearby IC 342 and a number of smaller galaxies. Highly obscurred by dark dust near the Milky Way's equatorial plane.
the Sculptor Group or South Polar Group (with members situated around the South Galactic pole), dominated by NGC 253
the M81 group
the M83 group The next more distant galaxy groups, the NGC 4244 group and the CVn I Cloud (with M94and M64) are probably too remote to have interacted significantly with the Local Group in the past.

It is of interest that of the subgroups of the Local Group mentioned above, the NGC 3109 group tends to the general direction of the Maffei 1 group and the M81 group, while the Local Group Cloud tends to the general direction of the Sculptor Group.

In the future, interaction between the member galaxies and with the cosmic neighborhood will continue to change the Local Group. Some astronomers speculate that the two large spirals, our Milky Way and the Andromeda Galaxy, may perhaps collide and merge in some distant future, to form a giant elliptical (see a summary of a possible scenario). In addition, there is evidence that our nearest big cluster of galaxies, theVirgo Cluster, will probably stop our cosmological recession away from it, accelerate the Local Group toward itself so that it will finally fall and merge into this huge cluster of galaxies, see our Virgo Cluster & Local Group page.

A table of the currently known Local Group member galaxies follows. While the positions are known very acurately, the distances are only very vaguely known for some members, and the sources even disagree for the most prominent members such as M31 and M33. If interested, look at our compilation of distances from various sources. Please note that this table is currently under review, as new data (distances, discovery of new members) keep our knowledge in flow.

Local Group Member Galaxies

Galaxy RA Dec Type m_v dim RV Dist

WLM 00:02.0 -15:28 IB(s) IV-V 10.9 12 x 4 - 42 3400 IC 10 00:20.4 +59:18 KBm? 10.3 7.3 x 6.4 - 83 4200: Cet dw 00:26.1 -11:02 dSph/E4 14.4 2800 NGC 147 00:33.2 +48:31 dE5 pec 9.5 15.0 x 9.4 + 89 2400 And III 00:35.4 +36:31 dSph/E2 13.5p 4.5 x 3.0 2900: NGC 185 00:39.0 +84:20 dE3 pec 9.2 14.5 x 12.5 + 39 2300 M110 00:41.3 +41:41 E5 pec 8.5 19.5 x 12.5 - 1 2900
And VIII 00:42.3 +40:37 dSph pec 9.1 45 x 10 -250 2700: M 32 00:42.7 +40:52 E2 (cE2) 8.1 11.0 x 7.3 + 35 2900
M 31 00:42.7 +41:16 SA(s)b I-II 3.4 185.0 x 75.0 - 59 2900
And I 00:45.7 +38:00 dSph/E3 pec ? 13.2 2.5 x 2.5 2900: SMC 00:51.7 -73:14 SB(s)m pec 2.3 280 x 160 - 30 210
And IX 00:52.9 +43:12 dSph 16.2 5 2900: Scl dw 01:00.0 -33:42 dSph/E3 pec 10.5p +162 300: LGS 3 01:03.8 +21:53 Irr 15.4p 2 3000: IC 1613 01:05.1 +02:08 IAB(s)m V 9.2 20.0 x 18.5 -125 2900: And X 01:06.6 +44:48 dSph 16.1 7 2900: And V 01:10.3 +47:38 dSph 15.9 2900: And II 01:16.4 +33:27 dSph/E0 13.5 3.6 x 2.5 2900: M 33 01:33.9 +30:39 SA(s)cd II-III 5.7 67.0 x 41.5 + 3 3000
Phe dw 01:51.1 -44:27 Irr 13.1 4.9 x 4.1 1600: For dw 02:39.9 -34:32 dSph/E2 8.1 12.0 x 10.2 500 UGCA 92 04:32.0 +63:36 Irr ? S0 ? 13.8 2.0 x 1.0 + 66 4700 LMC 05:19.7 -68:57 SB(s)m 0.1 650 x 550 + 13 179
Car dw 06:14.6 -50:58 dSph/E3 20.9 23.5 x 15.5 360 CMa dw 07:15 -28 Irr 720 25 Leo A 09:59.4 +30:45 IBm V 12.9 5.1 x 3.1 2500 Sex B 10:00.0 +05:20 Ir+ IV-V 11.8 5.1 x 3.5 4700
NGC 3109 10:03.1 -26:09 Ir+ IV-V 10.4 16.0 x 2.9 +131 4500 Ant dw 10:04.1 -27:20 dSph/E3 14.8 2.0 x 1.5 4600
Leo I 10:08.5 +12:18 dE3 9.8 9.8 x 7.4 900 Sex A 10:11.1 -04:43 Ir+ V 11.9 5.9 x 5.0 5200
Sex dw 10:13.2 -01:37 dSph/E3 12. 320
Leo II 11:13.5 +22:10 dSph/E0 pec 12.6 12.0 x 11.0 750 GR 8 12:58.7 +14:13 Im V 14.5 1.2 x 1.1 +165 7900: UMi dw 15:08.8 +67:12 dSph/E4 10.9 41.0 x 26.0 240
Dra dw 17:20.1 +57:55 dSph/E0 pec 9.9 51.0 x 31.0 280
Milky Way 17:45.6 -28:56 SAB(s)bc I-II ? - 0 28 SagDEG 18:55 -30:30 dSph/E7 +168 88
SagDIG 19:30.1 -17:42 IB(s)m V 15.5 2.9 x 2.1 4200 NGC 6822 19:44.9 -14:49 IB(s)m IV-V 9.3 15.5 x 13.5 + 66 1800 Aqr dw 20:46.8 -12:51 Im V 13.9 2.3 x 1.2 3400 Tuc dw 22:41.7 -64:25 dSph/E5 15.7 2.9 x 1.2 3200 UKS2323-326 23:26.5 -32:23 Irr 13.9 1.5 x 1.2 4700 And VII 23:27.8 +50:35 dSph 2.5 x 2.0 2600 Peg dw 23:28.6 +14:45 Im V 13.2 5.0 x 2.7 3000: And VI 23:51.7 +24:36 dSph 11.2 3.5 x 3.5 2800

Possible further members:

UGCA 86 03:59.9 +67:08 Irr ? S0 ? 13.5 0.8 x 0.7 +262 6200 IC 5152 22:06.1 -51:17 IAB(s)m IV 10.6 4.9 x 3.0 + 30 5800

Willman 1 10:49.4 +51:03 dSph? GC ? 15.3 1.75 147 UMa I 10:34.9 +51:55 dSph 330 UMa II 08:51.5 +63:08 dSph 14.3 815 Vir Stream 12:24 -01.1 dSph 30 x 10 30 CVn I 13:28.1 +33:33 dSph 13.9 8.4 x 5.0 730 Boo dw 14:00.0 +14:30 dSph 13.6 13.0 x 8.7 200 Leo T 09:34.9 +17:03 dSph/dIrr 16.0 1.4 x 1.4 1370 Com dw 12:27.0 +23:54 dSph 14.5 5.0 x 2.5 143 CVn II 12:57.2 +34:19 dSph 15.1 3.0 x 2.1 490 Her dw 16:31.0 +12:48 dSph 14.7 8.0 x 6.0 460 Leo IV 11:32.9 -00:32 dSph 15.9 3.3 x 2.5 520

Segue 2 02:19:16.0 +20:10:31 dSph 15.2 6.8 115 Boo II 13:58:08.0 +12:50:54 dSph Leo V 11:31:09.6 +02:13:12 dSph Boo III 13:57:07.4 +26:46:30 dSph Psc I dSph? Psc II 22:58.5 -05:57 dSph

And XI 00:46.3 +33:48 dSph 0.5 2900: And XII 00:47.4 +34:22 dSph 0.55 2900: And XIII 00:51.8 +33:00 dSph 0.5 2900: And XIV 00:51.6 +29:41 dSph 2900: And XV 01:14.3 +38:07 dSph And XVI 00:59.5 +32:23 dSph And XVII 00:37.1 +44:19 dSph 16.0 1.1 x 0.9 2590 And XVIII 00:02.2 +45:05 dSph/Sm And XIX 00:19.5 +35:03 dSph And XX 00:07.5 +35:08 dSph And XXI 23:54.8 +42:28 dSph And XXII 01:27.7 +28:05 dSph And XXIII 01:29.4 +38:43 dIrr
And XXIV 01:18.5 +46:22 dSph And XXV 00:30.1 +46:51 dSph And XXVI 00:23.6 +47:55 dSph And XXVII 00:37.5 +45:23 dSph And XXVIII 22:32.7 +31:13 dSph And XXIX 23:58.9 +30:45 dIrr 2900: And XXX 00:36.6 +49:39 dSph And XXXI 22:58.3 +41:17 dSph And XXXII 00:36.0 +51:34 dSph And XXXIII 03:01.4 +40:59 dSph And NW St. 00:20.0 +46:00 And SW St. 00:30.0 +37:30

KKs 3 02:24.7 -73:31 dSph 14.5 7000 Eri II 03:44.3 -43:32 dSph Ret II 03:35.7 -54:03 dSph Tuc II 22:51.9 -58:34 dSph Eri III 02:22.8 -52:17 dSph? Hor I 02:55.5 -54:07 dSph? Phe II 23:40.0 -54:24 dSph? Pic (I) dSph? Gru I dSph Tri II 02:13.3 +36:11 dSph Hya II dSph Peg III dSph Hor II dSph Dra II dSph Sgr II dSph Ind II dSph? Tuc IV dSph Col I dSph Gru II dSph Ret III dSph Tuc III dSph Tuc V dSph Cet II dSph? Crt II dSph Aqr II dSph Vir dw dSph? Cet III dSph? Ant 2 09:35.6 -36:48 dSph: 420 Car II dSph? Car III dSph? GC?

Below we list some nearby but probably non-member field galaxies (which are also not members of one of the neighboring groups listed above), in the same format as above:

Nearby Non-Member (?) Galaxies

Galaxy RA Dec Type m_v dim RV Dist

NGC 55 00:14.9 -39:11 Sc/SB(s)m 8.8 32.4 x 5.6 +129 7000 NGC 404 01:09.4 +35:43 E0 10.1 4.4 x 4.1 +178 8000: Cam A 04:25.3 +72:48 Irr 14.8 3.7 x 2.1 6500:: NGC 1569 04:30.8 +64:51 Irp+ III-IV: 11.2v 2.9 x 1.5 + 87 7500:: NGC 1560 04:32.8 +71:53 Sd 11.5v 9.8 x 2.0 +151 7500:: Argo dw 07:05.3 -58:31 Irr 14.2 3.5 x 1.7 +554 12000: UGC 9128 14:15.9 +23:03 Irp+ 14.4 1.7 x 1.3 +154

And NE 00:52.0 +44:06 Ir? 2900: Segue 1 10:07.1 +12:48 prob. GC 14.7 4.5 55.1 Ind I 21:08.8 -51:10 GC DES 1 00:34.0 -49:02 GC

Key:

RA, Dec:

Right Ascension and Declination for epoch 2000.0

Type:

Classification type from Tom Polakis' article, or elsewhere

m_v

Apparent visual brightness in Magnitudes. A "p" indicates that only photographic magnitudes are available and given.

dim

Angular dimension in arc minutes

RV:

Radial velocity wrt galactic center in km/sec

Dist:

Distance in 1000 light years (kly)

A colon following a number indicates this value is uncertain.

More data of and remarks on Local Group Galaxies

Galaxy R SG Diam Mass Other names/Remarks

WLM () LGC 8 ? UGCA 444, DDO 221 IC 10 LGC UGC 192 Cet dw LGC
NGC 147 M31 UGC 326, DDO 3 And III M31 PGC 2121 NGC 185 M31 UGC 396 M 110 M31 17 10000 NGC 205 And VIII M31 33 M 32 M31 8 3000 NGC 221 M 31 M31 195 400000 NGC 224 And I M31 PGC 2666 SMC MW 25 6000 NGC 292, Nubecula Minor And IX M31 Scl dw MW ESO 351- G 030, PCG 3589 LGS 3 () M31/33 Psc dw, PCG 3792 IC 1613 M31/LC UGC 668, DDO 8 And X M31 And V M31
And II M31 Psc II, PGC 4601 M 33 M31/33 60 25000 NGC 598 Phe dw (I) MW/LGC ESO 245- G 007, PGC 6830 For dw MW ESO 356- G 004, PGC 10093 UGCA 92 (I) M31? EGB 0427+63, PGC 15439 LMC MW 30 20000 ESO 056- G 115, PGC 17223, Nubecula Major Car dw MW ESO 206- G 220, ESO 206- GA020, PGC 19441 CMa dw () MW Leo A M/3109 Leo III, UGC 5364, DDO 69 Sex B (I) N3109 UGC 5373, DDO 70 NGC 3109 (I) N3109 UGCA 194, DDO 236 Ant dw (I) N3109 5 PGC 29194
Leo I MW UGC 5470, DDO 74, Harrington-Wilson 1, Regulus Galaxy Sex A N3109 UGCA 205, DDO 75 Sex dw MW
Leo II MW Leo B, UGC 6253, DDO 93, Harrington-Wilson 2 GR 8 (?) GR8 UGC 8091, DDO 155, VV 558 UMi dw MW UGC 9749, DDO 199 Dra dw MW UGC 10822, DDO 208 Milky Way MW 100 750000
SagDEG () MW Sgr dShp, Sgr I dw SagDIG (*) LGC Sgr dw, ESO 594- G 004, UKS 1927-177, PGC 63287, Kowal's Object NGC 6822 LGC IC 4895, DDO 209, Barnard's Galaxy Aqr dw LGC DDO 210, PGC 65367 Tuc dw LGC PCG 69519 UKS2323-326 LGC UGCA 438 And VII M31 Cas dSph, Cas dw Peg dw LGC UGC 12613, DDO 216, Peg DIG And VI M31 Peg dSph, Peg II

Possible members:

UGCA 86 (?) M31/L? PGC 14241
Willman 1 MW SDSSJ1049+5103 IC 5152 (?) LGC? ESO 237- G 027

UMa I MW discovered 2005, SDSS (Willman et.al.) UMa II MW discovered 2006, SDSS (Zucker et.al.) Virgo Stream MW discovered 2005, SDSS (Duffau et.al.) CVn dw MW discovered 2006, SDSS (Zucker et.al.) Boo dw MW discovered 2006, SDSS (Belokurov et.al.) Leo T MW discovered 2007, SDSS (Irwin et.al.) Com dw MW discovered 2006, SDSS (Belokurov et.al.) CVn II MW discovered 2006, SDSS (Belokurov et.al.) Her dw MW discovered 2006, SDSS (Belokurov et.al.) Leo IV MW discovered 2006, SDSS (Belokurov et.al.)

Segue 2 MW discovered 2007 Bootes II MW discovered 2007 Leo V MW discovered 2007 Bootes III MW discovered 2009 Pisces I MW discovered 2009, SDSS (Watkins et.al.) Pisces II MW discovered 2010

And XI M31 discovered 2006, CFHT (Martin et.al.) And XII M31 discovered 2006, CFHT (Martin et.al.) And XIII M31 Psc III, discovered 2006, CFHT (Martin et.al.) And XIV M31 Psc IV, discovered 2007, KPNO (Majewski et.al.) And XV M31 discovered 2007, CFHT And XVI M31 discovered 2007, CFHT And XVII M31 discovered 2007, INT (Irwin et.al.) And XVIII M31 discovered 2008 And XIX M31 discovered 2008 And XX M31 discovered 2008 And XXI M31 discovered 2009 And XXII M31 discovered 2009 And XXIII M31 discovered 2011 And XXIV M31 discovered 2011 And XXV M31 discovered 2011 And XXVI M31 discovered 2011 And XXVII M31 discovered 2011 And XXVIII M31 discovered 2011 And XXIX M31 discovered 2011 And XXX M31 Cas II, discovered 2012 And XXXI M31 Lac I, discovered 2013 And XXXII M31 Cas III, discovered 2013 And XXXIII M31 Per I, discovered 2013 And NE Stream M31 discovered 2009; Tidal Stream And SW Stream M31 discovered 2009; Tidal Stream

KKs 3 discovered 2014 Eri II MW discovered 2015 Ret II MW discovered 2015 Tuc II MW discovered 2015 Eri III MW discovered 2015 Hor I MW discovered 2015 Phe II MW discovered 2015 Pic (I) MW discovered 2015 Gru I MW discovered 2015 Tri II MW Laevens 2, discovered 2015 Hya II MW discovered 2015 Peg III MW discovered 2015 Hor II MW discovered 2015 Dra II MW discovered 2015 Sgr II MW discovered 2015 Ind II MW discovered 2015 Tuc IV MW discovered 2015 Col I MW discovered 2015 Gru II MW discovered 2015 Ret III MW discovered 2015 Tuc III MW discovered 2015 Tuc V MW discovered 2015 Cet II MW discovered 2015 Crt II MW discovered 2016 Aqr II MW discovered 2016 Vir dw MW discovered 2016 Cet III MW discovered 2017 Ant 2 MW discovered 2018, Gaia (Torrealba et.al.) Car II MW discovered 2018 Car III MW discovered 2018

Key:

Remarks: (*), (?) and (I); see below

SG:

Subgroup (after Mateo 1999). MW=Milky Way subgroup, M31: M31 subgroup, M31/33: M33 subgroup (probably part of M31 subgroup), LGC: Local Group Cloud (vast cloud of dwarf irregulars), N3109: NGC 3109 subgroup (not counted to Local Group by Van den Bergh), GR8: GR8 group (LG membership in doubt), M/N3109: Either MW or NGC 3109 group

Diam:

Diameter in 1000 light years (kly)

Mass:

Mass in million solar masses

Remarks (*):

"WLM" is "Wolf-Lundmark-Melotte"
"LGS" stands for "Local Group (suspected)" (LGS 3)
CMa dw (the Canis Major Dwarf) may be former host galaxy ofM79 and 3 other globulars
"SagDEG" is the "Sagittarius Dwarf Elliptical Galaxy" (discovered 1994, containing M54)
"SagDIG" is the "Sagittarius Dwarf Irregular Galaxy" Galaxies marked with "(?)" may be non-members as they are not in the list of Irwin et.al. 1997 (this list has 35 Local Group members), in particular:
UGCA 86 may be a member of the Maffei 1 group
GR8 and IC 5152 are listed as nearby non-member galaxies in Irwin's list. They may be lonely nearby non-members near the edges of the group.
The Aquarius Dwarf is also listed by Irwin as non-member, but Van den Bergh (2000) reports its membership has now be confirmed.
Leo A was also listed in Irwin's list of non-members, but recent distant re-determination confirmed its membership. Galaxies marked with "(I)" are newly taken into the list from Irwin's list: Besides the newly discovered Antlia dwarf, these are the Phoenix dwarf, UGCA 92, Sextans B, and NGC 3109.

More Data on the Probable Nearby Non-Members listed above:

Galaxy Other names/Remarks

NGC 55 ESO 293- G 050 NGC 404 UGC 718 Cam A
NGC 1569 UGC 3056 NGC 1560 UGC 3060 Argo dw PGC 20125 UGC 9128 DDO 187

Segue 1 discovered 2007; prob. Globular Cluster Ind I Globular Cluster Kim 2, discovered 2015 (DES) DES 1 Globular Cluster, discovered 2015 (DES) And NE Stellar structure in M31 halo

Various sources have listed other, former Local Group candidates which however have not been confirmed:

"Galaxy" listed Rem

1010-27 McGraw = Ant dw ? DDO 187 (UGC 9128) McGraw Nearby probable non-member galaxy, see above SDIG KKT Member of the Sculptor Group of Galaxies LGS 2 Irwin diffuse reflection nebulosity And IV vdB Background galaxy, or open cluster in M31 Sex C (A 1003) LGAA globular cluster Palomar 3 UMa dw (A 1127) dV,LGAA globular cluster Palomar 4 Ser dw (A 1513) dV globular cluster Palomar 5 Cap dw (A 2144) McGraw globular cluster Palomar 12 Snickers Radio observations of 1975 indicated this nearby galaxy candidate NGC 6946 Hubble Nearby non-member galaxy IC 342 Hubble Member of the Maffei 1 or IC 342 Group of Galaxies Maffei 1 Maffei Member of the Maffei 1 or IC 342 Group of Galaxies Maffei 2 Maffei Member of the Maffei 1 or IC 342 Group of Galaxies 2318-42 Irwin

Sources:

dV:

G. De Vaucouleurs 1975, Nearby Groups of Galaxies, ch. 4, The Local Group. Published in "Galaxies and the Universe," ed. by A. Sandage, M. Sandage and J. Kristian.

Hubble

E.P. Hubble 1936, The Realm of the Nebulae, Yale University Press. Local group table on p. 126.

KKT:

Kraan-Korteweg & Tammann, 1979. Astronomische Nachrichten 300, p. 181

LGAA:

Le Grand Atlas de L'Astronomie, Encyclopedia Universalis, 1986. German edition: "Der große JRO Atlas der Astronomie"

McGraw:

McGraw-Hill Dictionary of Astronomy, by Sybil P. Parker (ed), p. 242

Maffei:

P. Maffei 1968, PASP 80, p. 618

vdB:

S. van den Bergh 1972, Search for Faint Companions to M31.ApJ. 171, p. L31-L33.
Andromeda IV is probably not an independent Local Group galaxy, but either a large open cluster in M31 (Jones, 1993), or a more remote background galaxy (Ferguson et.al., 2000)

As our Milky Way obscures parts of the sky, there is still a steady flow of new discoveries of galaxies, in low galactic latitudes (i.e., near the equatorial plane of our galaxy, where the obscuring dust is most dense). Also, some of the galaxies are of extreme low surface brightness, and it was only recently possible to detect them. Therefore, it must be expected that more Local Group members exist, obscurred by dust, or extremely faint, and are still waiting for their detection somewhen in the future.

Jeff Bondono has compiled a comprehensive listof Local Group member and member candidate galaxies.

References

Annette M.N. Ferguson, J.S. Gallagher, and Rosemary F.G. Wyse, 2000. On the Nature of Andromeda IV. Astronomical Journal, Vol. 120, No. 2, pp. 821-832 (08/2000) [ADS: 2000AJ....120..821F]
Joseph H. Jones, 1993. CCD photometry of Andromeda IV - Dwarf irregular galaxy or M31 open cluster? Astronomical Journal, vol. 105, no. 3, pp. 933-7 (03/1993) [ADS: 1993AJ....105..933J]
Mario Mateo, 1998. Dwarf Galaxies of the Local Group. Annual Review of Astronomy and Astrophysics, Volume 36, 1998, pp. 435-506 [ADS: 1998ARA&A..36..435M]. Available online [framed version] - table of Local Group galaxies (NED Level 5)
Sidney van den Bergh, 1972. Search for Faint Companions to M31. Astrophysical Journal, Vol. 171, pp. L31-L33 [ADS: 1972ApJ...171L..31V]
Sidney van den Bergh, 1994. The Outer Fringes of the Local Group. Astronomical Journal 107, No. 4, pp. 1328-1332 (April 1994) [ADS: 1994AJ....107.1328V]
Sidney van den Bergh, 2000. Updated Information on the Local Group. Publications of the Astronomical Society of the Pacific, Vol. 112, No. 770, pp. 529-536 (April 2000) [ADS: 2000PASP..112..529V]
Tom Polakis has published an interesting article for observers of local group galaxies, Observing the Local Group, in the_Deep Sky_ magazine (#36), which was reprinted in David Eicher's book Galaxies and the Universe. (was also available online but disappeared)
Paul W. Hodge, Galaxies. Harvard University Press, 1986. In particular Chapter 7: The Local Group.
Edwin P. Hubble, The Realm of the Nebulae, Yale University Press, 1936 (in particular, pp. 124, 145)

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