It appears that the trailing $ for object references in publicly accessible system catalog views indicates an internal system catalog view. I say this because when looking at the source column for sys.objects, the source is not sys.objects$ but instead is a combination of the following three internal tables:
sysschobjssyssingleobjrefssyspalnames
When looking at the source columns for sys.objects$, they are the same sources as noted for sys.objects for the same columns, but there are plenty more columns in sys.objects$ (51 compared to 17 for sys.objects). Then, looking at the source columns for one of the base objects, syspalnames, the sources were finally that same object: sys.syspalnames.
While I can get the definition of sys.objects, I cannot get the definition of sys.objects$.
This pattern holds true for sys.configurations as well. Its definition points to sys.configurations$, yet the columns are all either expressions or have an actual source of sys.sysobjvalues. And the source for all columns in sys.sysobjvalues is itself: sys.sysobjvalues.
Below is the research output (some of it; not enough space here to put it all in).
I used the following query via a DAC connection. The final input parameter value of 1 is import as it enables the reporting of the "source" info.
USE [tempdb];
SELECT [name], [source_database], [source_schema], [source_table], [source_column],
[is_computed_column]
FROM sys.dm_exec_describe_first_result_set(N'SELECT * FROM sys.objects$', NULL, 1)
ORDER BY [column_ordinal] ASC;
The command-line was:
sqlcmd -A -E -Q "USE [tempdb]; SELECT [name], [source_database], [source_schema], [source_table], [source_column], [is_computed_column] FROM sys.dm_exec_describe_first_result_set(N'SELECT * FROM sys.objects$', NULL, 1) ORDER BY [column_ordinal] ASC;" -o InternalViews_SysObjects$.txt -W
sys.objects
name source_database source_schema source_table source_column is_computed_column
---- --------------- ------------- ------------ ------------- ------------------
name tempdb sys sysschobjs name 0
object_id tempdb sys sysschobjs id 0
principal_id tempdb sys syssingleobjrefs indepid 0
schema_id tempdb sys sysschobjs nsid 0
parent_object_id tempdb sys sysschobjs pid 0
type NULL NULL NULL NULL 1
type_desc mssqlsystemresource sys syspalnames name 0
create_date tempdb sys sysschobjs created 0
modify_date tempdb sys sysschobjs modified 0
is_ms_shipped NULL NULL NULL NULL 1
is_published NULL NULL NULL NULL 1
is_schema_published NULL NULL NULL NULL 1
depid tempdb sys syssingleobjrefs depid 0
class tempdb sys syssingleobjrefs class 0
depsubid tempdb sys syssingleobjrefs depsubid 0
class mssqlsystemresource sys syspalnames class 0
value mssqlsystemresource sys syspalnames value 0
sys.objects$
name source_database source_schema source_table source_column is_computed_column
---- --------------- ------------- ------------ ------------- ------------------
name tempdb sys sysschobjs name 0
object_id tempdb sys sysschobjs id 0
principal_id tempdb sys syssingleobjrefs indepid 0
schema_id tempdb sys sysschobjs nsid 0
parent_object_id tempdb sys sysschobjs pid 0
type tempdb sys sysschobjs type 0
type_desc mssqlsystemresource sys syspalnames name 0
property tempdb sys sysschobjs intprop 0
create_date tempdb sys sysschobjs created 0
modify_date tempdb sys sysschobjs modified 0
is_ms_shipped NULL NULL NULL NULL 1
is_auto_dropped NULL NULL NULL NULL 1
is_system_named NULL NULL NULL NULL 1
is_published NULL NULL NULL NULL 1
is_schema_published NULL NULL NULL NULL 1
is_cycling NULL NULL NULL NULL 1
lock_on_bulk_load NULL NULL NULL NULL 1
is_disabled NULL NULL NULL NULL 1
is_auto_executed NULL NULL NULL NULL 1
is_activation_enabled NULL NULL NULL NULL 1
has_opaque_metadata NULL NULL NULL NULL 1
is_not_for_replication NULL NULL NULL NULL 1
is_receive_enabled NULL NULL NULL NULL 1
is_cached NULL NULL NULL NULL 1
is_not_trusted NULL NULL NULL NULL 1
is_enqueue_enabled NULL NULL NULL NULL 1
with_check_option NULL NULL NULL NULL 1
is_retention_enabled NULL NULL NULL NULL 1
has_unchecked_assembly_data NULL NULL NULL NULL 1
update_referential_action NULL NULL NULL NULL 1
delete_referential_action NULL NULL NULL NULL 1
is_replicated NULL NULL NULL NULL 1
is_execution_replicated NULL NULL NULL NULL 1
has_replication_filter NULL NULL NULL NULL 1
is_repl_serializable_only NULL NULL NULL NULL 1
is_merge_published NULL NULL NULL NULL 1
skips_repl_constraints NULL NULL NULL NULL 1
is_sync_tran_subscribed NULL NULL NULL NULL 1
uses_ansi_nulls NULL NULL NULL NULL 1
null_on_null_input NULL NULL NULL NULL 1
uses_database_collation NULL NULL NULL NULL 1
is_tracked_by_cdc NULL NULL NULL NULL 1
large_value_types_out_of_row NULL NULL NULL NULL 1
lock_escalation_option NULL NULL NULL NULL 1
is_poison_message_handling_enabled NULL NULL NULL NULL 1
is_filetable NULL NULL NULL NULL 1
depid tempdb sys syssingleobjrefs depid 0
class tempdb sys syssingleobjrefs class 0
depsubid tempdb sys syssingleobjrefs depsubid 0
class mssqlsystemresource sys syspalnames class 0
value mssqlsystemresource sys syspalnames value 0
sys.syspalnames
name source_database source_schema source_table source_column is_computed_column
---- --------------- ------------- ------------ ------------- ------------------
class mssqlsystemresource sys syspalnames class 0
value mssqlsystemresource sys syspalnames value 0
name mssqlsystemresource sys syspalnames name 0