Sonar sensors topic shows in gazebo topics not in ros topics

[raomin]

Hi, first, I'm new to ROS so it's probably a noob mistake...
I added a libhector_gazebo_ros_sonar to my robot description as follow:

<xacro:property name="SONAR_HEIGHT" value="0.35" />

  <xacro:include filename="$(find hector_sensors_description)/urdf/sonar_sensor.urdf.xacro" />
  <property name="M_PI" value="3.1415926535897931" />
  <xacro:sonar_sensor name="sonar_sensor_zero" parent="link_chassis" ros_topic="sonar" update_rate="5" min_range="0.01" max_range="10" field_of_view="${30*M_PI/180}" ray_count="3">
    <origin xyz="0.0 0.0 ${SONAR_HEIGHT}" rpy="0 0 1.309"/>
  </xacro:sonar_sensor>

When I spawn my robot in the gazebo empty world, I can see a topic for the sonar in gazebo and it publishes proper values:

$ gz topic -l
...
/gazebo/default/lawnbot/link_chassis/sonar_sensor_zero/scan
...

However, in rostopics the sonar topic is missing.

$ rostopic list
/clock
/cmd_vel
/gazebo/link_states
/gazebo/model_states
/gazebo/parameter_descriptions
/gazebo/parameter_updates
/gazebo/set_link_state
/gazebo/set_model_state
/lb/laser/scan
/odom
/rosout
/rosout_agg
/tf

and I see no error in the ros master logs...

SUMMARY
========

PARAMETERS
 * /gazebo/enable_ros_network: True
 * /rosdistro: melodic
 * /rosversion: 1.14.3
 * /use_sim_time: True

NODES
  /
    gazebo (gazebo_ros/gzserver)
    gazebo_gui (gazebo_ros/gzclient)

auto-starting new master
process[master]: started with pid [14442]
ROS_MASTER_URI=http://localhost:11311

setting /run_id to 1bea7888-5626-11e9-8d05-34e6d75a3654
process[rosout-1]: started with pid [14453]
started core service [/rosout]
process[gazebo-2]: started with pid [14456]
process[gazebo_gui-3]: started with pid [14461]
[ INFO] [1554305730.366763778]: Finished loading Gazebo ROS API Plugin.
[ INFO] [1554305730.367947499]: waitForService: Service [/gazebo/set_physics_properties] has not been advertised, waiting...
[ INFO] [1554305730.419426726]: Finished loading Gazebo ROS API Plugin.
[ INFO] [1554305730.420407117]: waitForService: Service [/gazebo_gui/set_physics_properties] has not been advertised, waiting...
[ INFO] [1554305734.825188343, 0.022000000]: waitForService: Service [/gazebo/set_physics_properties] is now available.
[ INFO] [1554305734.842592068, 0.039000000]: Physics dynamic reconfigure ready.
[Err] [REST.cc:205] Error in REST request

libcurl: (51) SSL: no alternative certificate subject name matches target host name 'api.ignitionfuel.org'
[ INFO] [1554305790.480759050, 55.426000000]: Laser Plugin: Using the 'robotNamespace' param: '/'
[ INFO] [1554305790.480839712, 55.426000000]: Starting Laser Plugin (ns = /)
[ INFO] [1554305790.481919458, 55.426000000]: Laser Plugin (ns = /)  <tf_prefix_>, set to ""
[ INFO] [1554305790.505892471, 55.426000000]: Starting plugin DiffDrive(ns = //)
[ WARN] [1554305790.505995793, 55.426000000]: DiffDrive(ns = //): missing <rosDebugLevel> default is na
[ INFO] [1554305790.506670621, 55.426000000]: DiffDrive(ns = //): <tf_prefix> =
[ WARN] [1554305790.506788343, 55.426000000]: DiffDrive(ns = //): missing <publishWheelTF> default is false
[ WARN] [1554305790.506810463, 55.426000000]: DiffDrive(ns = //): missing <publishOdomTF> default is true
[ WARN] [1554305790.506834367, 55.426000000]: DiffDrive(ns = //): missing <publishWheelJointState> default is false
[ WARN] [1554305790.506950087, 55.426000000]: DiffDrive(ns = //): missing <wheelAcceleration> default is 0
[ WARN] [1554305790.506975768, 55.426000000]: DiffDrive(ns = //): missing <wheelTorque> default is 5
[ WARN] [1554305790.507071666, 55.426000000]: DiffDrive(ns = //): missing <odometrySource> default is 1
[ WARN] [1554305790.507146784, 55.426000000]: GazeboRosDiffDrive Plugin (ns = ) missing <publishTf>, defaults to 1
[ INFO] [1554305790.507751222, 55.426000000]: DiffDrive(ns = //): Try to subscribe to cmd_vel
[ INFO] [1554305790.509423395, 55.426000000]: DiffDrive(ns = //): Subscribe to cmd_vel
[ INFO] [1554305790.509951925, 55.426000000]: DiffDrive(ns = //): Advertise odom on odom

What am I missing...?