JWST reveals star formationãcrossã spiralãrm in M33

Abstract

Young stellar objects (YSOs)ãre the gold standard for tracing star formation in galaxies but have been unobservable beyond the Milky Wayãnd Magellanic Clouds. But thatãll changed when the JWST was launched, which we use to identify YSOs in the Local Group galaxy M33, marking the first time that individual YSOs have been identifiedãt these large distances. We present Mid-Infrared Instrument (MIRI) imaging mosaicsãt 5.6ãnd 21 μm that co v erã significant portion of one of M33's spiralãrms that has existing panchromatic imaging from the Hubble Space Telescopeãnd deep Atacama Large Millimeter/submillimeter Array CO measurements. Using these MIRIãnd Hubble Space Telescope images, we identify point sources using the new DOLPHOT MIRI module. We identify 793 candidate YSOs from cuts based on colour, proximity to giant molecular clouds (GMCs),ãnd visual inspection. Similar to Milky Way GMCs, we find that higher mass GMCs contain more YSOsãnd YSO emission, which further show YSOs identify star formation better than most tracers that cannot capture this relationshipãt cloud scales. We find evidence of enhanced star formation efficiency in the southern spiralãrm by comparing the YSOs to the molecular gas mass.