What is the relation of Surya & Yama with Agni?

Question

Rig Veda Book 10, Hymn 21 is dedicated to Agni and mentions the following:

4 O Agni, what thou deemest wealth, Victorious and Immortal One! Bring thou to give us vigour,—at your glad carouse -splendid at sacrifices. Thou art waxing great.

5 Skilled in all lore is Agni, he whom erst Atharvan brought to life. He was Vivasvān's envoy, at your glad carouse-the weIl-loved friend of Yama, Thou art waxing great.

Are there any detailed stories about Agni & Surya or Yama in the scriptures that could justify these statements? I am not looking for their 'biological' relation but instances of their friendship or co-operation that can support the above statements.

Answer 1

I found the answer to the statement about Atharvan connection to agni (fire) but not the rest in Mahabharata Section CCXXI:

"The powerful fire thus gratified with penance, blazed forth intensely. But on beholding the Rishi (Atharvan), he again sought his watery refuse. At this extinction of the fire, the whole world was frightened, and sought the protection of Atharvan, and the gods and others began to worship him. Atharvan rummaged the whole sea in the presence of all those beings eager with expectation, and finding out the fire, himself began the work of creation.

Thus in olden times the fire was destroyed and called back to life by the adorable Atharvan. But now he invariably carries the oblations of all creatures. Living in the sea and travelling about various countries, he produced the various fires mentioned in the Vedas."