With this script you can see the objects that belong to the filegroup.

use

GO

SELECT

fg.data_space_id, fg.name,

ObjectName = OBJECT_NAME(p.object_id), p.index_id

,df.name, df.physical_name, [Size] = df.size*8/1024

FROM sys.filegroups fg

LEFT JOIN sys.database_files df

ON fg.data_space_id = df.data_space_id

LEFT JOIN sys.partitions p

ON fg.data_space_id = p.partition_number

WHERE (p.object_id>4096 or p.object_id IS NULL)