The k pairs with the smallest sums

Given two ascending arrays nums1 and nums2 and an integer k, return the k pairs (a, b) (one element from each array) with the smallest sums a + b, in nondecreasing order of sum.

nums1 = [1, 7, 11]
nums2 = [2, 4, 6]
k = 3   ->   [[1, 2], [1, 4], [1, 6]]

Aim for $O(k \log k)$ time and $O(k)$ memory.