Overview
The MIRI EGS Galaxy and AGN survey (MEGA; PID: 3794; PI: A. Kirkpatrick) is a 67 hour JWST MIRI imaging program covering 70 sq. arcmin of the Extended Groth Strip (EGS) field. MEGA has 25 MIRI pointing taken in March 2024, using the F770W, F1000W, F1500W, and F2100W filters. For further information, see Reduction Paper. MEGA was designed to coincide with the ERS CEERS NIRCam observations (CEERS; PID: 1345; PI: Steven Finkelstein), which covers six filters F115W, F150W, F200W, F277W, F356W, F410W, and F444W. In addition to CEERS MEGA builds upon the wealth of observation in the EGS field. These observations also overlap with the Hubble Space Telescope (HST) imaging F125W, F160W, F606W, and F814W, and the Chandra X-ray observations. 68.9% of MEGA MIRI observations have CEERS NIRCam coverage, as shown in this figure.
Co-evolution of Black Holes and Stars
Previous studies measurements of black hole growth and obscured star formation at z>0.5 galaxies has been limited to the brightest of galaxies. An accurate measurement of obscured and unobscured star formation within individual galaxies is vital to understanding the buildup of mass over time. The more complete sampling of the IR SED enabled by MEGA will allow multiple detection methods including with CIGALE (Yang2023)and machine learning (Hamblin et al. 2025, in prep). With our rich data set, we are creating new luminosity functions to measure the unobscured and obscured SFR densities, and we are calculating new black hole accretion rate densities (Backhaus et al. 2025, in prep). MEGA will enable an in-depth look at how the SFR and black hole accretion rate (BHAR) densities co-evolve, using the same population of galaxies for each calculation. This allows for a unique, direct comparison between the various densities.
Finding AGN
JWST MIRI's coverage allows us to find obscured and low-luminosity AGN, as the mid-IR is largely insensitive to obscuration. We are selecting AGN in MEGA program by utilizing the existing 3-5 µm coverage from CEERS to observe stellar minimum in addition to the MEGA MIRI coverage to observe dust emission longwards of 6 µm (Kirkpatrick et al. 2025, in prep). Preliminary results show that at least 10% of MEGA galaxies are classified as low-luminosity AGN at cosmic noon.Additionally, our longer wavelength coverage is enabling the search for hot dust in little red dots, to confirm their AGN nature (Roynane et al.,2025, Kocevski et al.,2025)
Morphology
MEGA observations allow us to reveal crucial gap by measuring the distribution of obscured star formation in M* galaxies during the heyday of mass assembly. By combining HST, NIRCam, and MIRI we are creating obscured SFR density , unobscured SFR density , and stellar mass density profiles for resolved galaxies. We are measuring the dust/star distributions as a function of M*, revealing any mismatch between dust and stellar morphology for moderately massed galaxies. Preliminary results indicate that galaxy morphology in the observed-frame mid-IR is significantly different from morphology in the near-IR, revealing more massive bulges and more merger signatures (Troiani et al., 2025, in prep). Please participate in the galaxy classification at this Zooniverse link.
