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Statistics with Hubble type

Statistics with Hubble type - assigned as follows Type E...

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Statistics with Hubble type The number of galaxies of various Hubble types in a magnitude-limited sample is typified by these numbers from the RSA catalog: Ordinar y Barred E+E/S0 173 SB0+SB0/Sba 48 S0+S0/a 142 SBa+SBab 42 Sa+Sab 123 SBb+SBbc 96 Sb+Sbc 187 SBc 77 Sc 293 SBcd+SBd 8 Scd+Sd 26 SBm+IBm 9 Sm+Im 13 ... ... S 16 ... ... Special 18 ... ... Totals 991 ... 285 Types Sd,Sm are underrepresented in this flux-limited compilation because they are intrinsically fainter than the earlier spiral classes Sa-Sc. Some ellipticals (the sequence continuing into dwarfs) have similar problems. Only the types S0-Sc are probably fairly represented - these are giant galaxies and can be seen at large distances. If we regard Hubble type as mapping a continuous structural variable, the number of galaxies tells us about the bin widths of the Hubble classes in this variable. Correlations with Hubble type may be examined in detail by using de Vaucouleurs' type index T,
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Unformatted text preview: assigned as follows: Type E E/S0 S0 Sa Sb Sc Sd Im T -4 -2 0 1 3 5 7 10 A further luminosity-class index L (ranging 1-5) is defined for spirals and irregulars. The joint distribution of these for galaxies in the RC2 is given by de Vaucouleurs 1977 ( Evolution of Galaxies and Stellar Populations , p. 43). Many useful quantities correlate with T, as shown in his Fig. 2. Later-type galaxies are fainter in the mean- the scatter is quite large. Note that corrections for internal extinction needed to be made. As well as total optical luminosity and H I content, optical spectra and therefore color indices that relate to SFR history change with Hubble type. Some well-known examples are the UBV system indices U-B,B-V . These three passbands are centered near 3500, 4300, and 5800 Angstroms with passband widths 600-1400 Angstroms. Fig. 6 from de Vaucouleurs 1977 shows their variation (integrated across the whole galaxy) with T....
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