The topic of Skanda and Subrahmanya is intriguing.
Subrahmanya or Murugan is not mentioned in the Vedas.
Skanda is referred to in The Sama Veda thus.
iti dve esā skandasya samhitā, etām prayuñjan skandam prīnati
The Vamśa Brāhmana is a minor treatise associated with the Sāma Veda. It is concerned with the deities, the Samhitās or their musical renderings of specific hymns among them, and the long line of sages through which the Sāma Veda has come down. The introductory part of Vamśa Brāhmana entitled Sāmatarpana enumerates the list of deities, to whom water-libations are to be offered. Amongst them figure the twin-gods Skanda-Viśākhau, (p. 217, Vamśa Brāhmana).
The Atharva Pariśistas are a collection/compilation delating with elaborate ritualistic and procedures details of important Atharva rites as related to many deities. The 20th section in this text is titled Skandayāga or Dhūrtakalpa, ‘dhūrta’ (literally, ‘rogue’) being a synonym of Skanda.
This vrata is to be observed on the sixth day after new moon in the months of Phālguna (February-March), Āsādha (June-July) and Kārtika (October-November). The worship of Skanda on the occasion follows the usual routine of invocation (āvāhana), invitation (āhvāna), his entry, offering of pādya to wash his feet, worship with flowers, followed by the cordialities (upacāras), naivedya, offerings in fire, worship and consecration of the thread (pratisara), and tying the same, and allowing the god to leave the place (visarjana).
Skanda is called by his other names including Viśākha in the course of the varied worship. In one context (20.6.4) his diverse parentage as the son of Agni, Krttikās, Paśupati, Rudra and Indra is mentioned.
āgneyam krttikāputiamaindram kecidadhīyate /
kecitpāśupatam raudram yo śi so śi namo stu te // iti //
Importantly in 20.2.9, in the context of inviting Skanda to be present for the worship, Skanda is referred to as a ‘brother of Viśākha’.
bhrātra viśakhena ca viśvarūpa
imam balim sānucaram jusasva
Valmiki in his Rāmāyana, compares Rāmā and Laksmana to Skanda-Kumāra, the twin sons of Agni, in youthful charm and prowess (Kumārāviva Pāvakī)..
While Skanda is extolled in the Vedas no mention is made of Subrahmanya.
However Skanda Purana refers thus.
As narrated here, Śiva listens to the troubles of the gods created by the demons against them, and the necessity for Śiva procreating a son soon to overcome their problems. According to their wishes, Śiva took up a beautiful form with six faces and looked at Pārvatī lovingly. At that time, a dazzling lustre similar to numerous suns arose from the eye in his forehead. This was so, because Śiva is greatly self-controlled that his semen can have only an upward movement. Hence he is called Ūrdhva-retas.
The six-faced lustre spread out in the whole world. People, not being able to put up with it, ran in all directions. At Śiva’s suggestion, the Fire and Wind gods carry the lustre to a forest of reeds near Ganges, who united it with a lotus that was in a pond nearby. There a charming child with six faces and twelve arms was born. In the next moment the infant was transformed into a normal but extremely beautiful child (26.16-17).
Again, when at the bidding of Visnu, the six Krttikās came near, the child again became sextuple in order to allow each of them to feed it with millk (tāsām anugrahārthāya sodhā mūrtir abhūt ksanāt). In another context it is said that when Pārvatī embraced the children, they all converged into one form.
In this account there is the emission of the lustre of Śiva through his eye(s) in his forehead. We also have the appearance of Kumāra as a baby in six forms or their merger into a single personality as needed in the context. Hence both the meanings of the root skand, namely, ’emitting’ and ‘merging into one’ are applicable here.
II.v. In yet another context the Skanda Purāna (35.11) applies the third meaning of skand as ‘drying’ or ‘scorching’ (śosana). Does he not attack and scorch the power of his enemies in the three worlds and win over them?
ākramya ca yato śkandaddhikramena jagattrayam
tena skando yamākhyātah sutaste girisambhave..
So Subrahmanya seems to be different as Skanda is associated with Vishaka as his brother whereas Ganesha is treated as the Brother of Subrahmaya.
Skanda Poorvaja , Ganesha is elder to Skanda.
There is a cause for a little confusion here.
Ganesha is referred in the Vedas with Ganesha Upanishad and I have published the text..
But no reference to Subrahmanya in the Vedic texts.
Yet there is another legend that Skanda is the son of Agni, born of Vadavagni, the northern Fire.
Vadavagni is a form of Agni (fire) that is mentioned in the Hindu scriptures. It is believed that it is the escape of this fire from under the ocean which will finally consume the current cycle of creation and prepare the universe for the next cycle of creation.
Hindu Puranas states that Vadavagni was born in the lineage of Sage Bhrigu. The sons of Kartavirya Arjuna in order to finish off the lineage of the Sage Bhrigu started killing descendents of Bhrigu including children. A wise woman of the lineage, who was pregnant, in order to save her child moved the unborn child from her womb to her thighs. When the child was born it was called Aurva.
Later when the sons of Kartavirya came to know about the child they came to kill it. When they held it up they became blind due to the rays that emitted from the child’s body. The child’s anger did not subside and it gave rise to a flame which had the power to eat up the whole world. Sages then put the flame under the ocean. This is the story of Vadavagni.
Vadavagni is located beneath the ocean and has the face of a horse. Hindu Scriptures suggest that mists and clouds are formed due to the activity of the Vadavagni under the sea. It also prevents the sea from consuming the land.
Just before Pralaya, Vadavagni will burst forth as volcanoes from under the sea and escape. Subsequently the seas will consume the land. .
Considering these points and the fact that the Rig Veda was composed in the Arctic, Satyavrata Manu medtiated in the Mascarene Plateau, the land mass of the present India was near the Arctic in the distant past(please read my post on this), Shiva is found in Australia and Antarctica, The place where Soora Samhara, where Soorapadman was killed by Subrahmanya,Thiruchendur in the southern most tip of India , Murugan Shiva worship is widespread in the far-eastern countries,, it is probable that Shiva and Subrahmanya have more of Southern connection and they moved to Arctic later, as I have postulated earlier.
I shall be checking this with Geology and post my views..
Citation and references