OPINION

SHARON G. LEE, J., delivered the opinion of the Court, in which GARY R. WADE, C.J., JANICE M. HOLDER, CORNELIA A. CLARK, and WILLIAM C. KOCH, JR., JJ., joined.

We accepted a question of law certified by the United States District Court for the Middle District of Tennessee to determine whether the October 2009 Memorandum of Agreement between the United States Immigration and Customs Enforcement and the Metropolitan Government of Nashville and Davidson County, by and through the Davidson County Sheriff's Office, violates the Charter of Nashville and Davidson County or other state law. We conclude that the Memorandum of Agreement does not violate the Charter or any other state law cited by the plaintiffs.

We accepted this case pursuant to Tennessee Supreme Court Rule 23, which allows this Court to answer questions of Tennessee law certified by any federal court when "there are questions of law of this state which will be determinative of the cause and as to which it appears to the certifying court there is no controlling precedent in the decisions of the Supreme Court of Tennessee." Tenn. Sup. Ct. R. 23, § 1. As head of this state's judiciary and as part of our inherent judicial power under Article VI, section 1 of the Tennessee Constitution, we are authorized to answer certified questions of law. Seals v. H & F, Inc., 301 S.W.3d 237, 241 (Tenn.2010). Rather than requiring a federal court to make the law of this state or to abstain from deciding the case until the state courts resolve the point of law, answering certified questions from federal courts promotes judicial efficiency and comity and also protects this state's sovereignty. Haley v. Univ. of Tenn.-Knoxville, 188 S.W.3d 518, 521 (Tenn.2006). Under Rule 23, we only answer questions of law, not questions of fact or controversies as a whole. Seals, 301 S.W.3d at 241.

We address the question of whether the October 2009 Memorandum of Agreement between the United States Immigration and Customs Enforcement and the Metropolitan Government of Nashville and Davidson County, by and through the Davidson County Sheriff's Office, violates the Charter of Nashville and Davidson County or other state law. This issue of law arises out of litigation filed by the plaintiffs Daniel Renteria-Villegas, David Ernesto Gutierrez-Turcios, and Rosa Landaverde against the Metropolitan Government of Nashville and Davidson County ("Metro") and the United States Immigration and Customs Enforcement ("ICE").1 Plaintiffs Renteria-Villegas and Gutierrez-Turcios allege that Davidson County Sheriff's officers arrested and wrongfully interrogated and detained them while the officers investigated the plaintiffs' immigration status pursuant to the October 2009 Memorandum of Agreement ("MOA") entered into between the Davidson County Sheriff's Office ("DCSO") and ICE. Plaintiff Landaverde, a property owner and taxpayer in Davidson County, alleges that removal proceedings were instituted against her son after he was processed by Davidson County Sheriff's officers pursuant to the MOA. In addition to injunctive relief and damages, the plaintiffs seek declaratory relief regarding the validity of the MOA entered into between the DCSO and ICE under the Metropolitan Charter of Nashville and Davidson County (the "Charter").

According to the stipulated facts presented with the certified question, the MOA was entered into under the Immigration and Nationality Act, § 287(g), 8 U.S.C. § 1357(g) (2006). The MOA authorizes selected DCSO personnel to perform certain immigration officer duties after being trained and certified by ICE. Those duties include interrogating any person believed to be an alien as to his right to be or remain in the United States; processing any removable alien or those aliens who have been arrested for violating a federal, State, or local offense for immigration violations; serving arrest warrants for immigration violations; administering oaths, taking and considering evidence, and preparing affidavits and sworn statements for ICE supervisory review; preparing charging documents for signature of ICE supervisors; issuing immigration detainers for processing aliens in categories established by ICE supervisors; and detaining and transporting arrested aliens subject to removal to ICE-approved detention facilities. DCSO officers perform their duties subject to the limitations contained in the Standard Operating Procedure in Appendix D2 to the MOA; provide notification within twenty-four hours to an ICE supervisor of any detainees placed under authority; obtain authorization from an ICE supervisor or designee prior to initiating transfer of § 287(g) detainees into ICE custody; submit a plan to ensure that steps are taken to correct, modify, or prevent the recurrence of errors when informed by ICE of any error in the records; and make individualized custody recommendations to ICE.

We are guided in our interpretation of the Charter by the principles of statutory construction. Jordan v. Knox Cnty., 213 S.W.3d 751, 763 (Tenn.2007). We must give full effect to the intent and purpose of the drafters, see Waldschmidt v. Reassure Am. Life Ins. Co., 271 S.W.3d 173, 176 (Tenn.2008), without unduly broadening or restricting the Charter. Seals, 301 S.W.3d at 242. We must look to the language of the Charter, and if the language is "clear and unambiguous, ... we must simply enforce it as written." Waldschmidt, 271 S.W.3d at 176. However, if the language is ambiguous, then we may refer to the broader statutory scheme, the history of the Charter, and other sources to discern its meaning. See Colonial Pipeline Co. v. Morgan, 263 S.W.3d 827, 836 (Tenn.2008).

When the Charter was adopted in 1962, it consolidated the functions of the DC SO and the Nashville Police Department. The stated purpose of the constitutional amendment authorizing consolidation was to "eliminate duplication and overlapping of duties and services" to realize "economic savings to taxpayers." Metro. Gov't of Nashville & Davidson Cnty. v. Poe, 215 Tenn. 53, 383 S.W.2d 265, 277 (1964). It is not likely that the Charter framers envisioned that decades later, a sheriff would be performing immigration functions for the federal authorities and, accordingly, there are no Charter provisions that directly address the DCSO's authority to perform these duties.

Consistent with its purpose of consolidation, the Charter delineated the separate duties of the Sheriff and Police Chief. Charter section 16.05 provides that the Sheriff shall have such duties prescribed by Tennessee Code Annotated section 8-8-201 or by any other provisions of general law. Pursuant to section 8-8-201 (2011), the Sheriff has broad general powers, including the power to enforce the ordinances of the municipality, Tenn.Code Ann. § 8-8-201(34), and "such other duties as are, or may be, imposed by law or custom." Tenn.Code Ann. § 8-8-201(36)(b)(2). Section 8-8-201(36)(b)(1) references over 100 code sections which also set forth the Sheriff's duties. Tennessee Code Annotated section 38-3-102 (2010) is among the code sections listed, and it provides

Contrary to section 38-3-102, however, section 16.05 of the Charter expressly provides that within the area of the metropolitan government, the Sheriff shall not be the "principal conservator of the peace." This function is assigned to the Metropolitan Chief of Police. As between the Sheriff and the Police Chief, Charter section 16.05 gives the Sheriff custody and control of the metropolitan jail, and designates the Police Chief as the "principal conservator of the peace." Charter section 2.01 provides that when any power is vested by the Charter in a specific officer, that officer shall be deemed to have exclusive jurisdiction within the particular field.

The Charter marks the boundary between the duties of the Sheriff and the Police Chief. There is no dispute, however, between the Sheriff and the Police Chief as to who can perform the duties required by the MOA. The question is whether the Sheriff can perform these duties when the Police Chief does not do so and Metro has specifically directed the Sheriff to perform the duties. By resolution, Metro authorized and directed the Sheriff to perform "such immigration officer functions, in coordination with ICE, as specified in the [MOA]."3 The Sheriff, acting at the direction of Metro, entered into the MOA with ICE.4

While the Charter makes the Police Chief the "principal conservator of the peace," it does not expressly prohibit the Sheriff from engaging in all activities that could conceivably be considered "law enforcement." Nothing in section 16.05 indicates that the Police Chief is the only conservator of the peace. The role of principal conservator of the peace, assigned to the sheriff by section 38-3-102, is shared with other officials based on the following language from section 38-3-103:

This statute, giving more than one governmental official the title and authority of conservator of the peace, was in effect when the Charter was drafted,5 and the drafters' use of similar language in the Charter reflects an awareness of the statute. The language of the Charter clearly contemplates that the principal conservator of the peace is not the only conservator of the peace.

According to the MOA, the purpose of the collaboration between ICE and the Sheriff is to "enhance the safety and security of communities by focusing resources on identifying and processing for removal criminal aliens who pose a threat to public safety or danger to the community." In other words, the goal of the MOA and its delegation of authority to the Sheriff is to preserve the public peace through enforcement of federal immigration law. Since collaborative programs such as the one at issue were rare in 1962 when the Charter was adopted, it is understandable that the Charter is silent regarding the power of the city or its agencies to enter into a contract such as the MOA. However, Section 18.17 of the Charter anticipates cooperative endeavors between metropolitan officials and outside authorities, as follows:

The language of this section encompasses and sanctions the contract in this case, which constitutes a cooperative law enforcement effort between the Sheriff and ICE.

The plaintiffs assert that the outcome of this case is controlled by our holding in Poe, in which, shortly after adoption of the Charter in 1964, we addressed the division of law enforcement duties between the Sheriff and the Metropolitan Police Department. In Poe, a declaratory judgment was sought concerning the relationship of the Sheriff's office to the Metropolitan Government in matters of duties, functions, budgeting, purchasing, and personnel policies. 383 S.W.2d at 267. Addressing the issue of whether the "criminal law enforcement powers and authority in the area of the Metropolitan Government [are] vested in the Metropolitan Chief of Police exclusively," id., we held as follows:

Id. at 275 (footnote added).

Although we stated in Poe that the intent of the Charter was to take away from the sheriff the responsibility for the preservation of the public peace, necessarily, given the express language of the Charter, our holding can only be viewed as divesting the Sheriff of his authority as principal conservator of the peace. As specifically stated at Section 16.05 of the Charter, "the sheriff shall not be the principal conservator of peace. The function as principal conservator of peace is hereby transferred and assigned to the metropolitan police chief." (emphasis added). The express language of the Charter only divested the Sheriff of his authority as principal conservator of the peace, and it is only to that extent that his role as conservator of the peace was transferred to the Police Chief. Our holding in Poe is, consequently, so restricted. Accordingly, our ruling in Poe does not prohibit a construction of the Charter which allows the Sheriff to perform the federal immigration officer duties set forth in the MOA, when directed to do so by Metro and in the absence of action by the Police Chief.

The plaintiffs also argue that the MOA violates Tennessee Code Annotated section 50-1-101(b), which provides in pertinent part that "[i]f a memorandum of understanding with the United States department of homeland security is executed pursuant to subsection (a), municipal and county law enforcement officers shall be designated from local law enforcement agencies who, ... shall be trained pursuant to the memorandum of understanding." The plaintiffs contend that section 50-1-101(b) directs power, authority, and duties to local law enforcement officers and that the language of this section falls within the Charter's exclusive vestment of law enforcement authority in the Police Chief. We respectfully disagree. As we have explained, the Charter does not prohibit the Sheriff from engaging in all law enforcement functions.

The plaintiffs additionally contend that the MOA violates section 1.16.050 of the Metro Code of Ordinances, which provides in pertinent part that "[t]he sheriff shall permit the interrogation of prisoners by authorized personnel of the police department." Metro. Gov't of Nashville & Davidson Cnty., Tenn., Code of Ordinances (2012). The plaintiffs argue that this section indicates that the Police Department, not the DCSO, shall conduct interrogations of prisoners and that the MOA violates this section to the extent the MOA authorizes the DCSO to interrogate suspected aliens. We respectfully disagree. The language of this section merely requires that the DCSO allow the Police Department to interrogate prisoners in the Sheriff's custody; it does not prohibit the DCSO from also interrogating those prisoners. The plaintiffs do not cite to any other state or municipal law that the MOA allegedly violates, and we are aware of none.

We conclude that the October 2009 Memorandum of Agreement between the United States Immigration and Customs Enforcement and the Metropolitan Government of Nashville and Davidson County, by and through the Davidson County Sheriff's Office, does not violate the Charter of Nashville and Davidson County or any other state law cited by the plaintiffs. The Sheriff of Davidson County has authority under the Charter to perform the duties enumerated in the Agreement. Costs of this appeal are taxed equally to the plaintiffs, Daniel Renteria-Villegas, David Ernesto Gutierrez-Turcios, and Rosa Landaverde, for which execution may issue, if necessary.