Context : The recent star formation history in the solar vicinity is not yet well constrained , and the real nature of the so-called Gould Belt is still unclear .

Aims : We present a study of the large-scale spatial distribution of 6482 ROSAT All-Sky Survey ( RASS ) X-ray sources in approximately 5000 deg ^ { 2 } in the general direction of Orion .
We examine the astrophysical properties of a sub-sample of \sim 100 optical counterparts , using optical spectroscopy .
This sub-sample is then used to investigate the space density of the RASS young star candidates by comparing X-ray number counts with Galactic model predictions .

Methods : The young star candidates were selected from the RASS using X-ray criteria .
We characterize the observed sub-sample in terms of spectral type , lithium content , radial and rotational velocities , as well as iron abundance .
A population synthesis model is then applied to analyze the stellar content of the RASS in the studied area .

Results : We find that stars associated with the Orion star-forming region , as expected , do show a high lithium content .
As in previous RASS studies , a population of late-type stars with lithium equivalent widths larger than Pleiades stars of the same spectral type ( hence younger than \sim 70 - 100 Myr ) is found widely spread over the studied area .
Two new young stellar aggregates , namely “ X-ray Clump 0534+22 ” ( age \sim 2 - 10 Myr ) and “ X-ray Clump 0430 - 08 ” ( age \sim 2 - 20 Myr ) , are also identified .

Conclusions : The spectroscopic follow-up and comparison with Galactic model predictions reveal that the X-ray selected stellar population in the general direction of Orion is characterized by three distinct components , namely the clustered , the young dispersed , and the widespread field populations .
The clustered population is mainly associated with regions of recent or ongoing star formation and correlates spatially with molecular clouds .
The dispersed young population follows a broad lane apparently coinciding spatially with the Gould Belt , while the widespread population consists primarily of active field stars older than 100 Myr .
We expect the still “ bi-dimensional ” picture emerging from this study to grow in depth as soon as the distance and the kinematics of the studied sources will become available from the future Gaia mission .