狭义的投资银行其业务主要是什么？

我想要具体的 这些都太笼统了！

An individual or institution which acts as an underwriter or agent for corporations and municipalities issuing securities. Most also maintain broker/dealer operations, maintain markets for previously issued securities, and offer advisory services to investors. investment banks also have a large role in facilitating mergers and acquisitions, private equity placements and corporate restructuring. Unlike traditional banks, investment banks do not accept deposits from and provide loans to individuals. also called investment banker.

大意就是说帮助其他机构买卖金融产品的、并且不接收存款也不办理个人贷款的、帮助机构进行并购的机构或个人。