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22. the Nearest Galaxies - the Local Group

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22. The Nearest Galaxies - the Local Group The following table summarizes the basic properties of the nearest galaxies. As of this writing, the Local Group of galaxies consists of about 40 members. More members are likely, however, as increasingly more sensitive surveys probe the sky for nearby faint dwarfs. Therefore, this table should not be regarded as a complete census of our galaxian neighborhood, especially at the faint end. Dynamical masses have been calculated for most of the Local Group systems. These estimates are based on either the gas rotation velocities or the stellar velocity dispersions in the galaxies (see Endnote 16). They range from close to a trillion (1012) solar masses for M31 and the Milky W ay, to less than a few million Suns for the faintest dwarf ellipticals. The corresponding mass-to-light ratios are greatest for the faintest dwarfs, indicating that they harbor the highest proportions of dark matter. Table E6: Selected Galaxies of the Local Group (in order of decreasing luminosity [increasing absolute magnitude, M(B)]) Name Type RA(hr:min) Dec (°: ) Distance m(B) M(B) (1) (2) (3) (4) (light-yrs)(5) (mags)(6) (mags)(7) M31 SbI-II 00:42.73 +41:16.1 2.5 x 106 4.4 -21.6 Galaxy SBbcI-II? 17:45.67 -20:00.5 2.7 x 104 -20.5? M33 ScII-III 01:33.85 +30:39.6 2.7 x 106 6.3 -19.1 LMC SBmIII 05:23.57 -69:45.4 1.6 x 105 0.6 -18.4 SMC ImIV-V 00:52.73 -72:49.7 1.9 x 105 2.8 -17.0 NGC 205 S0/E5p 00:40.37 +41:41.4 2.7 x 106 8.7 -16.0 M32 E2 00:42.70 +40:51.9 2.6 x 106 9.1 -15.8 NGC 3109 SmIV 10:03.12 -26:09.5 4.1 x 106 10.4 -15.2 IC10 Im 00:20.42 +59:17.5 2.7 x 106 12.9 -15.2 NGC 6822 ImIV-V 19:44.93 -14:48.1 1.6 x 106 9.8 -14.8 NGC 147 dE5/dSph 00:33.20 +48:30.5 2.4 x 106 10.3 -14.8 NGC 185 dE3p/dSph 00:38.97 +48:20.2 2.0 x 106 10.0 -14.7 IC 5152 SdmIV-V 22:02.70 -51:17.7 5.2 x 106 11.5 -14.5 IC 1613 ImV 01:04.90 +02:08.0 2.3 x 106 10.2 -14.2 Sextans A ImV 10:11.10 -04:42.5 4.7 x 106 11.7 -14.2 W LM ImIV-V 00:01.97 -15:27.8 3.0 x 106 11.0 -13.9 Sagittarius dIm/dSph 18:55.05 -30:28.7 7.8 x 104 4.1 -12.8 Fornax dE3/dSph 02:39.98 -34:27.0 4.5 x 105 8.2 -12.6 Pegasus dIm/dSph 23:28.57 +14:44.8 3.1 x 106 12.6 -12.3 SagDIG dIm 19:29.98 -17:40.7 3.5 x 106 13.9 -12.1 Leo A dIm 09:59.40 +30:44.7 2.2 x 106 12.9 -11.3 GR8 dIm 12:58.67 +14:13.0 5.2 x 106 14.8 -11.2 And I dE3/dSph 00:45.72 +38:00.4 2.6 x 106 13.5 -11.2 Leo I dE3/dSph 10:08.45 +12:18.5 8.1 x 105 10.9 -11.1 And II dE2/dSph 01:16.45 +33:25.7 1.7 x 106 13.3 -10.5 Sculptor dE3/dSph 01:00.15 -33:42.5 2.6 x 105 8.5 -10.4 LGS 3 dIm/dSph 01:03.88 +21:53.1 2.6 x 106 15.0 -9.9 DDO 210 dIm/dSph 20:46.77 -12:51.0 2.6 x 106 14.9 -9.9 And III dE5/dSph 00:35.28 +36:30.5 2.5 x 106 14.8 -9.7 Leo II dE0/dSph 11:13.48 +22:09.2 6.7 x 105 12.6 -9.0 Tucana dE/dSph 22:41.83 -64:25.2 2.9 x 106 15.7 -8.9 Carina dE4/dSph 06:41.62 -50:58.0 3.3 x 105 11.5 -8.6 Draco dE3/dSph 17:20.32 +57:54.8 2.7 x 105 11.8 -7.8 UrsaMinor dE5/dSph 15:09.18 +67:12.9 2.1 x 105 11.6 -7.6 Notes to table: (1) Name of galaxy. (2) Galaxy classification, based mostly on the Hubble-Sandage system. Dwarf ellipticals are designated —dE,“ while dwarf irregulars are designated dIm. The dwarf spheroidal classification preferred by many investigators of the Local Group is designated —dSph.“ Peculiar morphologies are flagged with a —p.“ (3) Right Ascension (celestial longitude) in units of hours (hrs) and minutes (min), precessed to the 2000.0 epoch. (4) Declination (celestial latitude) in units of degrees (°) and arcminutes ( ), precessed to the 2000.0 epoch. (5) Distance from the Sun in units of light-years, determined mostly from observations of Cepheid and RR Lyrae variable stars. (6) Apparent magnitude at B-band (440 nm wavelength). (7) Absolute magnitude at B-band, based on apparent magnitude m(B) and the distance (see Technical Notes 2 and 3). References for table: Mateo, M. 1998, —Dwarf Galaxies of the Local Group,“ Annual Review of Astronomy and Astrophysics, Vol. 36, p. 435 Sandage, A. and Tammann, G. A. 1981, A Revised Shapley-Ames Catalog of Bright Galaxies, Carnegie Institution of W ashington Publication 635, W ashington, D.C. 23. Nearby Giant Galaxies In the following table, 30 giant spiral (S), lenticular (S0), and elliptical galaxies (E) in the Local Group and other neighboring groups are listed. These galaxies have been selected for their apparent brightness in the sky (with m(B) < 10 mags) and high absolute luminosity (with M(B) < -19 mags and corresponding B-band luminosity exceeding 3 billion Suns [see Endnote 3]). Table E7: Selected Giant Galaxies (in order of increasing distance from the Sun) Name(s) Type RA (hr:min) Size (Å ) vel (km/s) A(B) (mags) (1) Comment Dec (o:Å ) m(B) (mags) Dist. (Mpc) M(B) (mags) (2) (3) (4) (5) (6) Galaxy SBbc(rs)I-II 17:45.67 0.0 -20.5? —MilkyW ay“ -20:00.5 0.008 NGC 224 SbI-II 00:42.73 190 x 60 -10 1.7 (M31) —Andromeda +41:16.1 4.4 0.77* -21.7 NGC 598 Sc(s)II-III 01:33.85 70.8 x 41.7 670 0.6 (M33) —Pinwheel“ +30:39.6 6.3 0.85* -19.0 NGC 55 ,c 00:15.13 32.4 x 5.6 115 0.9 (edge-on) -39:13.2 8.2 2.1 -19.3 NGC 3031 Sb(r)I-II 09:55.57 26.9 x 14.1 124 0.8 (M81) +69:04.1 7.9 3.6* -20.8 NGC 2403 Sc(s)III 07:36.90 21.9 x 12.3 2999 0.6 +65:35.9 8.9 3.2* -19.2 .GC 253 Sc(s) 00:47.60 27.5 x 6.8 504 0.7 (starburst) -25:17.4 8.1 2.8 -19.8 NGC 4736 RSab(rs) 12:50.90 11.2 x 9.1 345 0.5 (M94) +41:07.17 8.9 4.6 -19.9 NGC 6946 Sc(s)II 20:34.85 11.5 x 9.8 336 1.5 +60:09.4 9.7 4.5 -20.1 NGC 5236 SBc(s)II 13:37.00 12.9 x 11.5 275 0.4 (M83) -29:52.0 8.5 4.6 -20.2 NGC 5128 S0+S pec 13:25.48 25.7 x 20.0 251 1.27 (Cen A) (AGN) -43:01.0 7.9 4.6 -21.7 NGC 4826 Sab(s)II 12:56.75 10.0 x 5.4 350 0.7 (M64) +21:41.0 9.4 4.7 -19.7 NGC 4945 Sc 13:05.43 20.0 x 3.8 275 1.3 (edge-on) -49:28.0 9.6 4.7 -20.0 NGC 2903 Sc(s)I-II 09:32.17 12.6 x 6.0 472 0.6 +21:29.9 9.5 6.3 -20.1 NGC 4258 Sb(s)II 12:18.95 18.6 x 7.2 520 0.9 (M106) (AGN) +47:18.4 8.9 6.7 -21.2 NGC 5055 SbcII-III 13:15.83 12.6 x 7.2 550 0.5 (M63) —Sunflower“ +42:01.7 9.3 7.3 -20.5 NGC 5194 Sbc(s)I-II 13:29.88 11.2 x 6.9 541 0.4 (M51) —W hirlpool“ +47:11.9 8.6 7.3 -20.7 NGC 5457 Sc(s)I 14:03.22 28.8 x 26.9 372 0.3 (M101) —Pinwheel“ +54:21.0 8.2 7.4* -21.5 NGC 3627 Sb(s)II.2 11:20.25 9.1 x 4.2 593 0.8 (M66) —Black Eye“ +12:59.1 9.7 8.0 -20.6 NGC 4631 Sc 12:42.08 15.5 x 2.7 606 0.9 (edge-on) +32:32.4 9.8 8.0 -20.6 NGC 3521 Sb(s)II-III 11:05.82 11.0 x 5.1 627 0.8 -00:02.0 9.6 8.7 -20.8 NGC 6744 Sbc(r)II 19:09.77 20.0 x 12.9 663 0.6 -63:51.3 9.2 8.7 -21.1 NGC 1291 SBa 03:17.32 9.8 x 8.1 738 0.2 -41:06.5 9.4 10.0 -20.8 NGC 628 Sc(s)I 01:36.70 10.5 x 9.5 861 0.3 (M74) +15:47.2 9.8 11.5 -20.9 NGC 4594 Sa/Sb 12:40:00 8.7 x 3.5 873 0.9 (M104) —Sombrero“ -11:37.4 9.3 11.3 -21.9 NGC 4472 E1/S0 12:29.78 10.2 x 8.3 822 0.0 (M49) +07:59.8 9.3 14.7 -21.5 NGC 4486 E0 12:30.83 8.3 x 6.6 1136 0.0 (M87) —Virgo A“ +12:23.6 9.6 14.7 -21.2 NGC 4649 S0 12:43.67 7.4 x 6.0 1142 0.0 (M60) +11:33.1 9.8 14.7 -21.0 NGC 1068 Sb(rs)II 02:42.68 7.1 x 6.0 1234 0.5 (M77) (AGN) -00:00.9 9.5 16.7 -22.0 NGC 1316 Sa pec 03:22.70 12.0 x 8.5 1713 0.3 —Fornax A“ -37:12.5 9.6 22.3 -22.4 Notes to table: (1) Name(s) of galaxy in the New General Catalogue (NGC) and Messier (M) listings.
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    Title: Resolving acceleration to very high energies along the Jet of Centaurus A Author: The H.E.S.S. Collaboration Correspondence to: [email protected] The full author list with affiliations can be found at the end of this paper Summary: The nearby radio galaxy Centaurus A belongs to a class of Active Galaxies that are very luminous at radio wavelengths. The majority of these galaxies show collimated relativistic outflows known as jets, that extend over hundreds of thousands of parsecs for the most powerful sources. Accretion of matter onto the central super-massive black hole is be- lieved to fuel these jets and power their emission 1, with the radio emission being related to the synchrotron radiation of relativistic electrons in magnetic fields. The origin of the extended X-ray emission seen in the kiloparsec-scale jets from these sources is still a mat- ter of debate, although Centaurus A’s X-ray emission has been suggested to originate in electron synchrotron processes 2–4. The other possible explanation is inverse Compton scat- tering with CMB soft photons 5–7. Synchrotron radiation needs ultra-relativistic electrons (∼ 50 TeV), and given their short cooling times, requires some continuous re-acceleration mechanism to be active 8. Inverse Compton scattering, on the other hand, does not require very energetic electrons, but requires jets that stay highly relativistic on large scales (≥1 Mpc) and that remain well-aligned with the line of sight. Some recent evidence disfavours 9–12 arXiv:2007.04823v1 [astro-ph.HE] 9 Jul 2020 inverse Compton-CMB models , although other evidence seems to be compatible with them 13, 14.
  • Astronomy Magazine Special Issue

    Astronomy Magazine Special Issue

    γ ι ζ γ δ α κ β κ ε γ β ρ ε ζ υ α φ ψ ω χ α π χ φ γ ω ο ι δ κ α ξ υ λ τ μ β α σ θ ε β σ δ γ ψ λ ω σ η ν θ Aι must-have for all stargazers η δ μ NEW EDITION! ζ λ β ε η κ NGC 6664 NGC 6539 ε τ μ NGC 6712 α υ δ ζ M26 ν NGC 6649 ψ Struve 2325 ζ ξ ATLAS χ α NGC 6604 ξ ο ν ν SCUTUM M16 of the γ SERP β NGC 6605 γ V450 ξ η υ η NGC 6645 M17 φ θ M18 ζ ρ ρ1 π Barnard 92 ο χ σ M25 M24 STARS M23 ν β κ All-in-one introduction ALL NEW MAPS WITH: to the night sky 42,000 more stars (87,000 plotted down to magnitude 8.5) AND 150+ more deep-sky objects (more than 1,200 total) The Eagle Nebula (M16) combines a dark nebula and a star cluster. In 100+ this intense region of star formation, “pillars” form at the boundaries spectacular between hot and cold gas. You’ll find this object on Map 14, a celestial portion of which lies above. photos PLUS: How to observe star clusters, nebulae, and galaxies AS2-CV0610.indd 1 6/10/10 4:17 PM NEW EDITION! AtlAs Tour the night sky of the The staff of Astronomy magazine decided to This atlas presents produce its first star atlas in 2006.