We present results of an analysis of the local ( z \sim 0 ) morphology-environment relation for 911 bright ( M _ { B } < -19 ) galaxies , based on matching classical RC3 morphologies with the SDSS-based group catalog of Yang et al. , which includes halo mass estimates .
This allows us to study how the relative fractions of spirals , lenticulars , and ellipticals depend on halo mass over a range of 10 ^ { 11.7 } – 10 ^ { 14.8 } h ^ { -1 } M _ { \odot } , from isolated single-galaxy halos to massive groups and low-mass clusters .
We pay particular attention to how morphology relates to central vs. satellite status ( where “ central ” galaxies are the most massive within their halo ) .
The fraction of galaxies which are elliptical is a strong function of stellar mass ; it is also a strong function of halo mass , but only for central galaxies .
We interpret this as evidence for a scenario where elliptical galaxies are always formed , probably via mergers , as central galaxies within their halos , with satellite ellipticals being previously central galaxies accreted onto a larger halo .
The overall fraction of galaxies which are S0 increases strongly with halo mass , from \sim 10 % to \sim 70 % .
Here , too , we find striking differences between the central and satellite populations . 20 \pm 2 % of central galaxies with stellar masses M _ { * } > 10 ^ { 10.5 } M _ { \odot } are S0 regardless of halo mass , but satellite S0 galaxies are only found in massive ( > 10 ^ { 13 } h ^ { -1 } M _ { \odot } ) halos , where they are 69 \pm 4 % of the M _ { * } > 10 ^ { 10.5 } M _ { \odot } satellite population .
This suggests two channels for forming S0 galaxies : one which operates for central galaxies , and another which transforms lower mass ( M _ { * } \lesssim 10 ^ { 11 } M _ { \odot } ) accreted spirals into satellite S0 galaxies in massive halos .
Analysis of finer morphological structure ( bars and rings in disk galaxies ) shows some trends with stellar mass , but none with halo mass ; this is consistent with other recent studies which indicate that bars are not strongly influenced by galaxy environment .
Radio sources in high-mass central galaxies are common , similarly so for elliptical and S0 galaxies , with a frequency that increases with the halo mass .
Emission-line AGN ( mostly LINERs ) are more common in S0s , but show no strong trends with environment .