Why are these topics appearing?

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This is a basic question. I've "installed" all the bits for a Turtlebot3 on my ubuntu running in vmware.

I have run roscore.

I have explicitly run a single script which creates a single new topic, cmd_vel.

But when I list rostopic list is see a long list of topics (see below).

It is clear that those topic come from the Turtlebot3 installed code. But my question is what ended up "invoking it"? As the only thing I've run are roscore and my little script, lots of other code must be in play to declare those topics.

Can someone please clarify?

Here's the list:

/camera/depth/camera_info
/camera/depth/image_raw
/camera/depth/points
/camera/parameter_descriptions
/camera/parameter_updates
/camera/rgb/camera_info
/camera/rgb/image_raw
/camera/rgb/image_raw/compressed
/camera/rgb/image_raw/compressed/parameter_descriptions
/camera/rgb/image_raw/compressed/parameter_updates
/camera/rgb/image_raw/compressedDepth
/camera/rgb/image_raw/compressedDepth/parameter_descriptions
/camera/rgb/image_raw/compressedDepth/parameter_updates
/camera/rgb/image_raw/theora
/camera/rgb/image_raw/theora/parameter_descriptions
/camera/rgb/image_raw/theora/parameter_updates
/clock
/cmd_vel
/joint_states
/mobile_base/commands/motor_power
/mobile_base/commands/reset_odometry
/mobile_base/commands/velocity
/mobile_base/events/bumper
/mobile_base/events/cliff
/mobile_base/sensors/imu_data
/odom
/rosout
/rosout_agg
/tf