Numerical simulations predict that some poor groups of galaxies have merged by the present epoch into giant ellipticals ( cf .
Barnes 1989 ) .
To identify the possible remnants of such mergers , we have compiled a sample of nearby , isolated ellipticals ( Colbert , Mulchaey , & Zabludoff 1998 ) .
ASCA observations of the first galaxy studied , NGC 1132 , reveal an X-ray halo that extends out to at least \approx 250 kpc h _ { 100 } ^ { -1 } .
The temperature ( \sim 1 keV ) , metallicity ( \sim 0.25 solar ) and luminosity ( \sim 2.5 \times 10 ^ { 42 } h _ { 100 } ^ { -2 } erg s ^ { -1 } ) of NGC 1132 ’ s X-ray halo are comparable to those of poor group halos .
The total mass inferred from the X-ray emission , \sim 1.9 ^ { +0.8 } _ { -0.6 } \times 10 ^ { 13 } h _ { 100 } ^ { -1 } M _ { \odot } , is also like that of an X-ray detected group .
Optical imaging uncovers a dwarf galaxy population clustered about NGC 1132 that is consistent in number density and in projected radial distribution with that of an X-ray group .
The similarities of NGC 1132 to poor groups in both the X-ray band and at the faint end of the galaxy luminosity function , combined with the deficit of luminous galaxies in the NGC 1132 field , are compatible with the merged group picture .
Another possibility is that the NGC 1132 system is a ‘ failed ’ group ( i.e . , a local overdensity in which other bright galaxies never formed ) .