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Home , Hydra (constellation), Shapley Supercluster, Supercluster, Velocity dispersion

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The Shapley : the Largest Matter Concentration in the Local

Dominique Proust1 Hernán Quintana 2 Eleazar R. Carrasco 3 Andreas Reisenegger 2 14h Eric Slezak 4 Hernán Muriel 5 Rolando Dünner 2 Laerte Sodré Jr. 6 Michael J. Drinkwater 7 Quentin A. Parker 8 Cinthia J. Ragone 5 13h

1 GEPI – Observatoire de Paris-Meudon, France 2 Pontificia Universidad Católica de Chile, Santiago, Chile 10 000 20 000 30 000 40 000 50 000 60 000 3 Observatory, La Serena, Chile 4 Observatoire de la Côte d’Azur, France Figure 1: Cone diagram (right ascen- 5 Observatorio Astronómico, Córdoba, sion) of the observed in the area of the and CONICET, Buenos-Aires, Argentina (SSC) up to a recession velocity of 6 IAG-USP, São Paulo, Brazil 60000 km/s. 7 University of Queensland, Australia 8 Macquarie University and AAO, Aus- 1987). This meant that an enormous Figure 1 shows the ‘cone diagram’ of tralia amount of matter attracted our these galaxies. Velocity is plotted versus and the surrounding galaxies; it took the right ascension, ranging between 12h30m generic name of . In this and 14h30m. Each cluster of galaxies is Since the 1980s, we have known that direction, there is already the Hydra- characterised by an apparent elongated the of galaxies is moving supercluster, whose galaxies structure along the line of sight, due to at a velocity of 366 ± 125 km/s in the have on average a recession velocity of the inside the cluster. direction of Centaurus. In this region, 4 000 km/s. However, in spite of its wealth Note the presence of the foreground the well-known Shapley supercluster of of galaxies, this huge complex has only a Hydra-Centaurus supercluster. It is con- galaxies (SSC) consists of many clus- negligible gravitational effect on the Lo- nected by a bridge of galaxies to the ters and groups of galaxies in the red- cal Group. This is why we undertook a Shapley supercluster itself, whose 5 701 shift range 0.04 < z < 0.055. An interna- dynamical analysis of the SSC by study- galaxies have a mean recession veloc- tional collaboration has highlighted ing galaxies as faint as magnitude ity of 15 400 km/s. Many structures con- this greatest matter concentration in the mb = 18.0, beyond the Hydra-Centaurus nect the SSC to other , local Universe, less than 500 million complex, in an area of the sky extending underlining the filamentary distribution light years from us. The SSC may be over 30˚ × 12˚. of the matter in the Local Universe. The able to account for half of the sought longest one appears to extend out to for ‘Great Attractor’. The galaxies were selected from photo- 48 000 km/s, joining structures evidenced graphic plates of ESO, then digitised on by Einasto et al. (2001). The analysis the MAMA at Paris Observatory. The of the SSC made by Ragone et al. (2006) The supercluster of galaxies Shapley 8 observations were carried out with the based on simulations, shows that it is (SSC), located in the north of the constel- 2.5-m Du Pont telescope at Las Cam- composed of 122 galaxy systems; 60 are lation of Centaurus (a 13h25m, d –30˚), panas with the spectrograph 2D-frutti, new and 44 belong to the supercluster was observed in 1930 by Harlow Shapley; the ESO 3.60-m telescope with the (Figure 2). The galaxies contained in the he then noticed an oval cloud of galaxies OPTOPUS and MEFOS spectrographs, SSC represent an average matter over- in Centaurus which appears to be one of and the 1.8-m UKST telescope at the density of 5.4 ± 0.2, definitely larger than the richest currently detected, having Anglo-Australian Observatory with the nearby superclusters such as Horolo- dimensions of approximately 2.8˚ by 0.8˚. spectrographs FLAIR and 6dF. By sup- gium- whose density excess is In the 1980s, this structure interested plementing the observations with ve- only 2.4. The SSC extends more than astronomers particularly because they locities from the NASA extragalactic 120 million light years, its volume being discovered that the Local Group, formed database (NED), 10 529 velocity measure- equivalent to that of a sphere of 80 mil- by about thirty galaxies surrounding us, ments were gathered, corresponding lion light years in radius: it is the largest moved with respect to the cosmic micro- to 8 632 galaxies. In the central part of matter concentration in the Local Uni- wave background frame of reference the supercluster, 92 % of the galaxies verse, less than 500 million light years at the velocity of 366 ± 125 km/s in the could be measured, and on the whole from us. direction of Centaurus (Dressler et al. 61 % of the objects were observed.

30 The Messenger 124 – June 2006 Figure 2: Distribution on Clusters of galaxies related with X-ray 0 9 000 km/s < v < 13 000 km/s sources are located at the centre of the –2 the sky of the 44 clus- ters and galaxies in the SSC, indicating the presence of gas 8 velocity range of the at very high temperature, more than ten 57 A3 SSC. Upper panel: million degrees. They were analysed clusters with velocities 25 – 6a between 9 000 and by Bardelli et al. (1996), deriving a mass 6 73 3 14 –1 7 A1 13 000 km/s. Lower M = 3.1 × 10 h Msun within a radius AS panel: clusters between –1 of 2h Mpc (h = Ho/100 km/s/Mpc). 13000 and 18000 km/s.

0) 14 -3 0 Using our catalogue, we determined the 00 336 (2 –3 4 7 8 3 δ 74 C1 luminosity and the mass of the super- 745 1 S 5 57 AS57 A3 AS 72 A3 A35 cluster using various models such as the A3 2

determination of the mass by X-ray A354

properties, the analysis of the velocity 35 fields of each and the – spherical collapse model. We obtained a total luminosity of about 1.4 × 1014 h–2

times that of the for a total mass of 0

–4 h m h m m m h m m 16 –1 14 20 14 00 40 20 13 00 40 the supercluster Mt = 5 × 10 h Msun. α (2000) Although very high, this mass would rep-

resent only half of that required to at- 0 13 000 km/s < v < 18 000 km/s tract the Local Group (Hoffman et al. –2 2001) in the direction of the supercluster. In addition to this, at least an identical amount of matter in the same direction 25 b – 6 must be present in order to account for 7 73 A1 57 the particular motion of our Galaxy. A3 5 16 -302 59 528 5 A355 31 42 A3 3 A3 4 2 5- 0) 1 31 2. 31 35323530 5 0 SC 00 278 A A 12 2 29 5 2 J (2 –3 6 1313 35 3556 RX References δ 5C A 3 SC A A356S A355 A 0 44 5 54 3 5 A 18 A356 3 a Dressler A. et al. 1987, ApJ 313, L37 2 A S7 74 68 1 42 A 6 59 3 5 74 AS A373 7 Einasto M. et al. 2001, AJ 122, 2222 66 A3 AS AS 3564 AS 29 35 A

35 A S7 Hoffman Y. et al. 2001, arXiv:astro-ph/0102190 A – 3 Proust D. et al. 2006, AA 447, 133 33 5 S7 35 21 A A 7 Ragone C. J. et al. 2006, AA 445, 819 AS 0

–4 14h20m 14h00m 40m 20m 13h00m 40m α (2000) Photo: H. H. Heyer, ESO

The VLT and its Auxiliary Telescopes at Sunset.

The Messenger 124 – June 2006 31