"For we all come to Convergence to die." all who know of the ghastly planet know that phrase, without knowing how.
Convergence is a grave world, ruined by who knows what, whose most prevalent feature is the carrion sea; an ocean-sized grave-pit into which the corpses of a million battles are emptied, indiscriminately mingling congealing xenos bloods with that of the Imperium-- for the dead can't complain, can they?
Preserved by the cold from decaying with any sensible rapidity, some of the Imperium's most noble heroes lie shattered amid the very bodies of those they slew.
For such an insignificant world, Convergence possesses an insane level of planetary security, primarily a battery of laser trebuchet that dot the surface at regular intervals, along with orbital defence satellites and, most notably, a parasite moon people have referred to as an "infant hellstar". It is claimed that this defense is in place against the predations of the tyranid horde, though nobody has even managed to map the planet's local space to discern where it is in relation to the inexorable hive fleets.
Convergence: a Chapter homeworld?
So what did become of the mysterious Astartes, the so-called Fire Hawks we have associated with the undead apparition known as the legion of the Damned? The Index Astartes reads: "By a daring warp-exit maneuvre the craft burst out of warp-space, emerging... beyond even the psychic light of the Emperor". Now, navigators dead or not, you still need some realspace thing to focus on if you ever want to ecape from the warp; that was the one overlooked feature of the fateful Abyssal crusade, as you might recall. Not having any living psykers on board, and far out of the Astronomica's range, what drew the shattered legion? Convergence. The irresistible mental pull of that planet drew them out of the warp.
The mental pull of Dula Hazreb, the Carrion Christ and Primarch of the IInd legion was drawing them back home.
They knew their home and returned thence. Though one could argue that Convergence can draw any one it "wishes" to, one should keep in mind that only after these events did the Imperium even see and sense the ethereal flame of the damned legion. How would the Astartes have found Convergence if Hazreb was calling only his children home?
So these mysterious Space Marines exited the warp in Convergence local space, but they were changed. Cursed with undeath, abhorrent in the ignorant eyes of the wider Imperium. A legion of damned, so to speak, but was it the warp that transformed them, or Hazreb?
Again, as the Index Astartes states, the inflicted Astartes were left with no gene-seed, no means of initiation and no clear future, only to die when, as the book says, their malady finally overtakes them. Disrupting all premise of rank or unit, they chose to fight as equals, sharing this bond of undeath until the utter end. "Serving the Emperor beyond the point of death." That is the legion's motto. That would mean a damned legionnaire may never die until such time is fulfilled. And upon this premise, Astronomica is based.
Current state of affairs
You are an Inflicted Astartes, an outsider damned by the touch of the grave-world with no recollection of your previous life or Chapter, and no wish to probe. You were brought up from the distant sea of mouldering corpses for a reason, some reason, and to such an end you will pursue, for that is all you know.