We study the distortions induced by peculiar velocities on the redshift–space correlation function of galaxies of different morphological types in the Pisces–Perseus redshift survey .
Redshift–space distortions affect early– and late–type galaxies in different ways .
In particular , at small separations , the dominant effect comes from virialized cluster cores , where ellipticals are the dominant population .
The net result is that a meaningful comparison of the clustering strength of different morphological types can be performed only in real space , i.e. , after projecting out the redshift distortions on the two–point correlation function \xi ( r _ { p } , \pi ) .
A power–law fit to the projected function w _ { p } ( r _ { p } ) on scales smaller than 10 h ^ { -1 } Mpc gives r _ { 0 } = 8.35 _ { -0.76 } ^ { +0.75 } h ^ { -1 } Mpc , \gamma = 2.05 _ { -0.08 } ^ { +0.10 } for the early–type population , and r _ { 0 } = 5.55 _ { -0.45 } ^ { +0.40 } h ^ { -1 } Mpc , \gamma = 1.73 _ { -0.08 } ^ { +0.07 } for spirals and irregulars .
These values are derived for a sample luminosity limited to M _ { Zw } \leq - 19.5 .
We detect a 25 % increase of r _ { 0 } with luminosity for all types combined , from M _ { Zw } = -19 to -20 .
In the framework of a simple stable–clustering model for the mean streaming of pairs , we estimate \sigma _ { 12 } ( 1 ) , the one–dimensional pairwise velocity dispersion between 0 and 1 h ^ { -1 } { Mpc } , to be 865 ^ { +250 } _ { -165 } { km } { s } ^ { -1 } for early–type galaxies and 345 ^ { +95 } _ { -65 } { km } { s } ^ { -1 } for late types .
This latter value should be a fair estimate of the pairwise dispersion for “ field ” galaxies ; it is stable with respect to the presence or absence of clusters in the sample , and is consistent with the values found for non–cluster galaxies and IRAS galaxies at similar separations .