I have a authors list and its sorted in the alphabetical order. The query for it is here

$user_args = array(
    'orderby' => 'display_name',
    'order' => 'ASC',
    array( 'who' => 'authors' ),
    'has_published_posts' => array('post'),
    'number'    => 4,
);

$authors = new WP_User_Query( $user_args );

I need to change this list of authors to sort by ones with most recent posts first. How can that be done?