def make_catalog_sources(catalog_roi_model, source_names):
    """Construct and return dictionary of sources that are a subset of sources
    in catalog_roi_model.

    Parameters
    ----------

    catalog_roi_model : dict or `fermipy.roi_model.ROIModel`
        Input set of sources

    source_names : list
        Names of sourcs to extract

    Returns dict mapping source_name to `fermipy.roi_model.Source` object
    """
    sources = {}
    for source_name in source_names:
        sources[source_name] = catalog_roi_model[source_name]
    return sources