Question: In what region did the Sika deer that are now found on the Tibradden Mountain originate?

Context paragraphs:
Tibradden Mountain: Tibradden Mountain (Irish: "Sliabh Thigh Bródáin" , meaning "mountain of the house of Bródáin" ) is a mountain in County Dublin in Ireland.  Other former names for the mountain include "Garrycastle" and "Kilmainham Begg" (a reference to Kilmainham Priory which once owned the lands around the mountain).  It is 467 m high and is the 561st highest mountain in Ireland.  It forms part of the group of hills in the Dublin Mountains which comprises Two Rock, Three Rock, Kilmashogue and Tibradden Mountains.  The views from the summit encompass Dublin to the north, Two Rock to the east and the Wicklow Mountains to the south and west.  The geological composition is mainly granite and the southern slopes are strewn with granite boulders.  The summit area is a habitat for heather, furze, gorse and bilberry as well as Sika deer, foxes and badgers.  The forestry plantation on the slopes – known as the Pine Forest – contains Scots pine, Japanese larch, European larch, Sitka spruce, oak and beech.  The mountain is also a site of archaeological interest with a prehistoric burial site close to the summit.

Vietnamese sika deer: The Vietnamese sika deer ("Cervus nippon pseudaxis") is one of the many subspecies of the sika deer.  It is one of the smaller subspecies, due to the tropical environment they live in.  They were previously found in northern Vietnam and possibly southwestern China, but have now become extinct in the wild.  There are plans for reintroducing this subspecies in the future.

Shanxi sika deer: The Shanxi sika deer ("Cervus nippon grassianus") is a possibly extinct subspecies of the sika deer.  It is also one of its largest, being 105–110 cm tall at the shoulders and weighing 100 kg.  The color is tawny or grayish dark, and is brown on the back of the leg.  The spots are nearly invisible.  It is previously found in two populations in the upland forests of Lüliang Mountains in western Shanxi, while its range might be much larger in historical times, encompassing the entire loess plateau.  There has been no sightings of the subspecies for decades and it is now believed to be extinct, though no actual investigations have been done.  Although pure bred individuals remain in farms as a breed, there is not enough suitable habitat nor government effort for reintroduction to take place.

North China sika deer: The North China sika deer or Mandarin sika deer ("Cervus nippon mandarinus") is one of the many subspecies of sika deer.  It is a large subspecies with some of the most prominent spots of all subspecies, which is permanent throughout the year.  It previously inhabited lowland forests of North China Plain and Northeast China Plain.  Because of intensive habitat alterations the subspecies was endangered centuries ago, surviving only in remote areas of northeastern China and the Qing Imperial Hunting Grounds.  Though no surveys have been conducted on the subspecies' status, there have been no sightings for many decades and it is reasonable to presume that it is extinct in the wild.  Although it is fairly common in zoos and purebred North China sika deer is a valuable breed in the Asian antler farming industry, the lack of suitable habitats and government efforts makes reintroduction impossible.

Sika deer: The sika deer ("Cervus nippon") also known as the spotted deer or the Japanese deer, is a species of deer native to much of East Asia, and introduced to various other parts of the world.  Previously found from northern Vietnam in the south to the Russian Far East in the north, it is now uncommon in these areas, excluding Japan, where the species is overabundant.

Yezo sika deer: The Yezo sika deer ("Cervus nippon yesoensis)" is one of the many subspecies of the sika deer.  The sika that inhabit the island of Hokkaido are indigenous, although it is not known whether they originated there or migrated from the main island of Japan.  Is it thought they may have traveled across the strait between the islands.  The indigenous Ainu people of Hokkaido have hunted them for centuries and relied on them as a major food source.

Kilmashogue: Kilmashogue or Kilmashoge (Irish: "Sliabh Chill Mochióg" , meaning "Mountain of the Church of Saint Mochióg" ) is a mountain in Dún Laoghaire–Rathdown county in Ireland.  It is 408 m high and forms part of the group of hills in the Dublin Mountains which comprises Two Rock, Three Rock, Kilmashogue and Tibradden Mountains.  The forest plantation on its northern slope, which is composed mainly of Sitka spruce, Scots pine and beech, is a habitat for Sika deer, hares, rabbits and foxes.  A number of prehistoric monuments can be found on the slopes of the mountain.

Sichuan sika deer: The Sichuan sika deer ("Cervus nippon sichuanicus") is one of the many subspecies of sika deer.  It was discovered in 1978 and was proven to be a distinct subspecies.  It is found in the mountains of northern Sichuan and southern Gansu, which holds the largest population of Sika Deer in China.  There are currently 500 individuals left in the wild, and the numbers currently seems to be stable.

Manchurian sika deer: The Manchurian sika deer or Dybowski's sika deer ("Cervus nippon mantchuricus" or "Cervus nippon dybowskii" ) is a subspecies of deer, the largest of the 14 subspecies of sika deer.

Formosan sika deer: The Formosan sika deer, (), is a subspecies of sika deer endemic to the island of Taiwan.  Formosan sika, like most of the terrestrial fauna and flora of Taiwan, arrived on the island during Pleistocene glacial periods when lower sea levels connected Taiwan to the Asian mainland.

Supporting paragraphs: Tibradden Mountain Sika deer
Answer: East Asia