The parentheses at the end of javascript object

Question

 var ajaxCall = new function () {
    var baseUrl = 'Home/',

    getCategory = function (callBack) {
        $.getJSON(baseUrl + "GetCategories", function (data) {
            callBack(data);
        });
    }
    getSubCategory = function (callBack) {
        $.getJSON(baseUrl + "GetSubCategories", function (data) {

        });

    }
    return {
        getCategory: getCategory,
        getSubCategory: getSubCategory
    };

}();

This is a part of our front end code. I know that we are creating an object with functions and this renders flexibility. I wonder two things: 1. the new keyword - why not just leave it like var ajaxCall = function(){}; ?? 2. The () at the end of this code snippet, we do we need that?

ANY comments to newbie here is welcome. Thanks.