I see some plants like chimney grows behind my sunflowers that you can see in picture:
location:western foothills of Iran
What are these and should I remove these from garden?
They look like small Asparagus spears. The triangular leaves (like scales) on the stem and the slightly swollen tips of the stems are the characteristics that helped that identification. An image search for "Asparagus+spears" will provide lots of other photos for comparison.
Wikipedia says that they're native to your region (Iran), and that it even gets its name from a Persian word, so it could be either a cultivated or a wild specimen. If you let them grow taller, the foliage will look feathery (image courtesy of Wikipedia):
Harvest when they are a thickness of a pencil. Once the asparagus starts shooting up thiner stocks, just let them go for the rest of the season with out harvesting any more. When they become dorment, you can dig the rhizomes up to spread them out by replanting them further apart or relocate them to a different part of the garden.
The asparagus might of been hibernating until it got the right nutrients or water indirectly by how you take care of your sunflower. It looks like it was a mature rhizome because durring the first few years the asparagus will only fern out and shoot up very thin spears.