The Sarmatians are new to me. I’m not up on my Kazakhstan history. I have a couple of coins, though.
Technically, they weren’t Kazakhs but an Iranian speaking group.
These are among the “Scythian” cultures that roamed north of Iran, east of the thracians/nordics, south of the slavic and finno-ugric peoples and west of the tocharians/Tibetan plateau
In my opinion they were a continuation of the Alans or Alanni - Alan is a variation of “Aryan” meaning Iranian/Nort-Indian (NOT Nordic :)) and their linguistic (and genetic) descendents are the Ossetians.
They, along with most of the IraniC peoples were chased or murdered by Turkic groups in central Asia and what is now Ukraine and then some were assimilated by the various Slavic groups OR they migrated to Iran, northern India.
As an aside, the “Tocharians” - Tok Aryans - who were an Indo-European speaking people living in what is now Zinjiang province of western China, were chased out in circa 200 BC by the XIongnu (the Huns) and they moved to Bactria, then Afghanistan before finally settling in western India and becoming the ancestors of the Rajasthani peoples.