XM Satellite Radio and Sirius Satellite Radio have agreed to merge, the two companies said Monday. The deal would consolidate the only two companies in the emerging business of subscription-only satellite radio, and is sure to face tough scrutiny from federal regulators. Investors and analysts have been speculating about a deal for months.The deal would consolidate the only two companies in the emerging business of subscription-only satellite radio, and is sure to face tough scrutiny from federal regulators. Investors and analysts have been speculating about a deal for months.