Are the charts called Exhibit 7-3 and Exhibit-4 corporate yield curves? What are these graphs showing us?

Why do most municipal bonds pay lower interest than riskless Treasury bonds?

Exhibit 7.3 Yield Offered on General Obligation Municipal Bonds over Time 8 7 Percent han 4 3 1990 1995 2010 2015 2000 2005 Shaded areas indicate U.S. recessions. Exhibit 7.4 Risk Premiums of Junk Bonds versus Other Corporate Bonds over Time 18 16 14 12 10 Percentage points High-yield 8 wwhte men BBB AA 1998 2000 2002 2006 2008 2010 2004 Year Source: Federal Reserve