In the Bala Kanda of the Ramayana, during the wedding of Rama and Sita, both families share their respective family trees. Vashishta presents a long genealogy for Rama's family, the Ikshvaku dynasty, going all the way back to the gods including Surya, Brahma, and ultimately Vishnu. Then Sita's father Janaka presents his ancestry as follows:
Once there was an emperor Nimi, who was renowned in the triad of worlds by his own accomplishments, and who was uniquely seraphic-souled and a best one among all stalwart emperors. And his son was named as Mithi, and Janaka was Mithi's son, the first one to be designated as Janaka. And even from that Janaka it is Udaavasu who took birth. From Udaavasu it is noble souled Nandivardhana took birth, and Nandivardhana's son is named as Suketu, by his name. From Suketu the highly powerful and virtue-souled Devaraata is born, and from that kingly sage Devaraata, it is Brihadratha who took birth, thus we have heard. From Brihadratha it is the highly braving, courageous and valiant Mahaaviira has come, and the bold and truth-valiant Sudhriti from Mahaaviira. Form Sudhriti, the right-minded and highly generous Dhristaketu took birth, and from the kingly sage Dhristaketu it is highly renowned Haryashva is the son. Haryashva's son is Maru, and Maru's, son is Pratiindhaka, and the son of Pratiindhaka's is noble-souled king Kiirtiratha. The son of Kiirtiratha is remembered as Devamiidha, and the son of Devamiidha is Vibudha, and Vibudha's son is Mahiidraka. Mahiidraka's son is the great mighty king Kiirtiraata, and the son born to sagely king Kiirtiraata is Mahaaroma. From Mahaaroma it is the virtue-souled Swarnaroma, and from kingly sage Swarnaroma it is Hrasvaroma. Two sons are born to that knower of virtue and noble souled Hrasvaroma, I am the elder, and my younger brother is this brave Kushadhvaja.
So Janaka's lineage is presented up to "an emperor Nimi". But my question is, what is Janaka's ancestry beyond Nimi? Are there any scriptures that trace the ancestry of Janaka all the way back, just as Vashishta did for Rama? Was Janaka of the solar dynasty (Suryavansha) or some other dynasty?