In a given population, let's say a Hive city, how many psykers will be present?

Like a lot of things, it depends a fair amount on local conditions. More important hive worlds will have more imperial bureaucracy, and as a consequence, more psykers- astropaths and savants and the like. If the planet has a large Imperial Guard, Imperial Navy, or Inquisition presence, there will be more psykers present who are associated with those organizations. If the planet is heavily involved in interstellar trade, there will likely be even more, given the vital role that astropaths and navigators play in space travel. Even an isolated world will still experience some incidence of psykers just through people being born who carry the genetic markers that allow them to become psykers. The exact percentage of people this occurs in is not given, to my knowledge, but it would seem reasonable to suggest that it likely varies based on how tied to the immaterium a location is. On most worlds, these individuals will be gathered up and sent off to Terra on the Black Ships as soon as they begin to demonstrate their abilities, but some will to go unnoticed, especially if the law is loosely enforced, or there are more pressing dangers.

where do psykers go, having been taken by the local agencies, awaiting the arrival of the black ships?

signoftheserpent said:

I believe they are held in special void-shielded facilities.

I cant remember where i read it, but i seem to remember reading somewhere that the estimate is about one psyker per million Imperial citizens, and when identified they are kept in prisons with psy dampeners and whatever other tech it takes to control their powers. the second part was in a novel called scourge the heretic.

Do Sanctioned Psykers have their own quarters/hab facilities? How much independence do they get (relative to other characters of course, as this is 40k).

That would, as with most things, depend on the case we're looking at.

Obviously, the Adeptus Astra Telepathica releases the psykers after sanctioning from Terra. It further appears that at least some are conscripted into the Imperial Guard and some wind up in the retinue of nobles, merchant houses, planetary governments and other power players. The most probable course would be that the local branches of the AAT simply sell the psykers not meant for service in the Adepta to those judged stable enough to hold a psyker's leash. This would probably result in the psykers being treated as valuable tools - usually afforded a certain measure of luxury so they don't want to escape (because even when a psyker is caught after escaping, they'll usually inflict a lot of collateral damage on his way out and an Inquisitor might want to have a few pointed words with their former owner).
The actual measure of freedom afforded to individual wyrds would thus entirely depend on their employer and the surrounding culture, with puritan cultures retaining as few psykers as possible (almost only astropaths) and treating them as necessary abominations while more relaxed ones would view them as skilled artisans of their craft - though at least those not used to their actual presence will always fear and shun them.

In various fluff out there, proportion of psykers seems to vary by world. Certainly Titan has a very high proportion of Psykers, but that's a special case

Worlds where there are nearby warp storms will have a higher proportion of psykers and general mutation. There's also some possibility that a world just has a higher genetic disposition to psykers... possibly as an evolutionary effect of not having tithed their entire population of psykers. If they're allowed to stay on world and have kids, their kids might be psykers, etc. There's certainly support in fluff for at least some in the Inquisition believing psyker is genetic, and the presence of Navigators confirms at least some forms of psykerness are genetic (but that may be gene engineered).

As far as how they are treated? Well, that's your call, but I'd say that varies by who/where. Some fluff treats astropaths as being barely more than servitors, being permanently wired into an astropathic relay(not unlike what you see in Minority Report). Others treat them almost in the same way as a navigator, elite specialists. It seems it varies by the individuals potential (At least according to RT). There's not even agreement in fluff of what constitutes an astropathic message. Some indicate it's pure vision, some just feelings, some that it's precise messages. In short,it's done in a way that leaves you a ton of wiggle room.

At the end, remember that those psykers who are not deemed strong enough to be trained will get executed outright or sent to power the Astronomicon which burns out 1000s a day. That should inform you of how low the lot of a psyker may be. Then again, many Inquisitors are psykers, so they aren't held back from reaching high level. Likewise, Navigators are also treated well, but there's little info on how the houses might treat weaklings Suffice to say that most psykers probably have poor prospects though. The short of it is that most psykers probably would have no more than the slightest of abilities... maybe a telekine that's particularly "lucky" at dice games or a precognitive that's particularly "lucky" at card games.

It depends.

OK, firstly remember that technically every human (except Nulls) are 'psychic' in that they have a Warp presence.

Those with sufficient mutation will be some way along the line to the next stage of human evolution; the psyker.

This will vary from world to world depending on local conditions, the relative strength of the local veil between Realspace and the Empyrean, the genetic strains of the planet itself, etc.

You'll need to pick a percentage for each world i guess (and the 'speed of plot' should decide this...need a world full of psykers? Percentage could be up around 80%!).

Personally i'd work on somewhere around 5% being average for a typical world, so a Hive world of 100 billion poeple will have 5 billion psykers. Even if you drop the number to 1%, you're still looking at 1 billion psykers.

Presumably a fair few of these will be Astropaths (who represent 90% of the Astra Telepathica). The rest will be a mix of sanctioned psykers (the remaining 10% of the official psyker population) and unsanctioned psykers.

You could rationalise it and say that the vast majority of 'psykers' (with the mutant gene) never actually manifest anything like psykers powers i suppose...and that only say 1 in a billion ever get to be something like an Alpha-grade psyker, but even then you're looking at 5 Alpha psykers on the aforementioned Hive world!

This is the problem with 40k - put numbers to things and they start to look a bit...unexpected...

where do psykers go, having been taken by the local agencies, awaiting the arrival of the black ships?

It's one of the main responsibilities of a planetary governor to ensure the the local psyker population is kept under control. How the governor does this will vary from world to world but its worth remembering that he will also have a tithe quota for psykers to be submitted to Holy Terra for feeding the Golden Throne and for recruitment into the Imperial interplanetary communicatons system (the Astropaths).

In bad years, there may simply be a mass cull of local psykers (akin to the general population culls committed by the Adeptus Arbites on Hive worlds).

For those psykers 'rounded up' they will typically be held in some form of 'interrment camps'. Since the Black Ships will arrive to take the psykers to Holy Terra, these may actually be seen as a blessing - those with 'the mark' (a psyker) being held in some sort of preparation temple complex to await transportation to meet the God-Emperor in person. Perhaps the families of these individuals will be rewarded with recognition or status for having a 'blessed one' from their lineage.

Of course, others may actually be the worse sort of interrment camp or prison, but i've always struggled to see how such institutions would possibly work given the nature of the inmates! Perhaps the guards are all powerful sanctioned psykers too?!

If shown to be dangerous, but worth retaining, perhaps the psyker will be handed over to the Adeptus Arbites for containment in the local stasis cells of the Arbites Blockhouse. More likely though, these dangerous individuals will simply be culled.

Psykers can be interred for years, possibly even their whole lives, awaiting the arrival of a Black Ship - unless you have millions of these ships touring the Imperium constantly bringing the psyker tithe to Holy Terra...which if you think about it, actually HAS to happen to maintain the Golden Throne and the supply of Astropaths.

an issue i see as being important is how many psykers actually make it to terra. The IoM spans three quarters of the galaxy and is said to contain over a million worlds. Given these factors, and likley maltreatment of those 'mutants', not only how many would there be, but what is the rate of attrition amongst this population. Almost certainly, some die of old age or maltreatment or disease waiting for black ships, where they are then mixed with psykers from other worlds with other diseases and maladies to spread around, then how long is the circuit between a place like Malfi to terra. A long ways, with many ways to die along the way. Another point i would like to make is that in all the books ive read, few psykers seem to have ever been to terra. Most seem to have been taken in and trained by an Inquistor. The only real exception i can think of is Inquistor Jaq Draco from the Inquisition war trilogy, but if anyone knows any other signifcant psykers that have made the 'pilgrimage', please let me know i am interested.