Galaxies and Galaxy Formation

ALMA [OIII] image of a z = 11.1 galaxy pair at 0.8” resolution at 280 GHz (red contours), plus the JWST near-IR images (Witstok et al. 2025, arXiv:2507.22888).

The era of high resolution (sub-kiloparsec) studies of the most distant galaxies is upon us, with the advent of the near-IR capabilities of the JWST to study the stars and ionized gas, working with ALMA and the VLA probing the cooler gas, dust, and non-thermal continuum. These studies have been pushed to within 500 Myr of the Big Bang, or z > 10, where observations show a much higher abundance of galaxies than expected so early in the Universe. Recent JWST and ALMA observations at z = 11.1 have shed new light on the earliest galaxy formation process through study of a lower luminosity, relatively ‘normal’ galaxy pair. [OIII] emission has been detected with ALMA in this system, but the non-detection of dust continuum emission sets an upper limit to the star formation rate of 6 M⊙ yr-1. The system resembles a low-z metal poor dwarf galaxy, although the presence of oxygen indicates an even earlier epoch of star formation in this forming galaxy.

Figure: ALMA [OIII] image of a z = 11.1 galaxy pair at 0.8” resolution at 280 GHz (red contours), plus the JWST near-IR images (Witstok et al. 2025, arXiv:2507.22888).

ALMA + JWST images of the stars and [CII] 158um line emission from a z = 7.9 merging galaxy cluster (Fudamoto et al. arXiv:2510.11770), elucidating the details of massive galaxy formation in the early Universe.

A further serious challenge to models of very early galaxy formation has come to the fore based on the JWST discovery of galaxies with large stellar masses, ~ 1010 M⊙, within a few hundred Myr of the Big Bang, thereby requiring an unnaturally efficient conversion of gas into stars. Again, ALMA has been a key tool in addressing this puzzle. ALMA and JWST have recently observed a protocluster of five galaxies at z=7.9, all within a 10 kpc region. The observations reveal a dynamic cycle of merger induced gas stripping, which drives gas cycling among the group galaxies, and efficient star formation. The new observations represent the first comprehensive evidence of a massive galaxy forming through gas-rich, multiple-galaxy mergers enhanced by the dense protocluster environment, just 650 Myrs after the Big Bang. The results suggest that the protocluster core is indeed one of the main drivers of efficient massive galaxy formation and rapid evolution in the early Universe.

Figure: ALMA + JWST images of the stars and [CII] 158um line emission from a z = 7.9 merging galaxy cluster (Fudamoto et al. arXiv:2510.11770), elucidating the details of massive galaxy formation in the early Universe.

Left: ALMA observations of the dust continuum and [CII] 158 um emission from a z = 5.85 massive galaxy pair at 70mas resolution (contours), plus the JWST near-IR images (Akins et al. arXiv:2508.06607). Right: the velocity fields of the galaxies measured with the [CII] line, plus best-fit rotation curves.

ALMA is also critical for obtaining sub-kpc information on gas dynamics and galaxy rotation curves and dynamical masses in the early Universe. Recent observations of the dust and [CII] 158um line emission at 0.4 kpc resolution of an interacting pair of galaxies at z ~ 6 show clear signatures of rotation in the gas dynamics, as well as strong tidal interactions. The dynamical masses of the galaxies are 10.6 and 2.0 x1010 M⊙, or five times larger than the stellar masses derived from JWST observations.

Figure: Left: ALMA observations of the dust continuum and [CII] 158 um emission from a z = 5.85 massive galaxy pair at 70mas resolution (contours), plus the JWST near-IR images (Akins et al. arXiv:2508.06607). Right: the velocity fields of the galaxies measured with the [CII] line, plus best-fit rotation curves.

Left: Chandra image of the X-ray emitting hot gas plus the HST image of the stars in a z = 0.5 brightest cluster galaxy and cooling flow cluster. Center: the JVLA L band image at 1” resolution, and the VLBA 5 GHz image at 1.4mas x 4.3mas resolution. Right: the HST image of the stars and the JVLA image at 1.4 GHz of the parent galaxy (Ubertosi et al. 2025, ApJ 989, 128).

The VLA and VLBA remain crucial for the study of AGN in massive galaxies, and the role of jets in gas heating on tens of kpc scales. Recent VLA + VLBA observations of a massive, ‘cooling flow’ cluster at z = 0.5 reveal both a young powerful radio jet AGN on 30pc scales, plus radio emission associated with a 10kpc scale starburst in the host galaxy with a star formation rate of 150 M⊙ yr-1. This system, CHIPS 1911+4455, represents a transitional phase in cluster evolution, where the AGN in the central galaxy has just begun to respond to the inflow of cooling cluster gas, and star formation is still very active in the evolving giant elliptical galaxy.

Figure: Left: Chandra image of the X-ray emitting hot gas plus the HST image of the stars in a z = 0.5 brightest cluster galaxy and cooling flow cluster. Center: the JVLA L band image at 1” resolution, and the VLBA 5 GHz image at 1.4mas x 4.3mas resolution. Right: the HST image of the stars and the JVLA image at 1.4 GHz of the parent galaxy (Ubertosi et al. 2025, ApJ 989, 128).

Left: ALMA image CO 2-1 velocity field at 75mas (7pc) resolution of the barred lenticular galaxy NGC1574, which hosts a supermassive black hole. Center: the velocity field along the major axis, plus the best fit model including a SMBH. Right: separating the mass contributions from the galaxy and the SMBH, indicating a black hole mass of 6.2x107 M⊙ (Zhang et al. arXiv:2507.10662).

ALMA has also been used to map the velocity fields of molecular gas at parsec-scale resolution in nearby galaxies, to isolate the dynamical sphere of influence of the supermassive black hole (SMBH). Imaging of the CO 2-1 emission at 75mas resolution (7pc) from the nearby barred lenticular galaxy NGC 1574, are the first to spatially resolve the SMBH’s sphere of influence, resulting in an unambiguous detection of the Keplerian velocity increase due to the SMBH at the center of the galaxy, with an implied black hole mass of 6x107 M⊙. The black hole mass is slightly below that expected from the bulge mass–black hole mass relationship in the nearby Universe.

Figure: Left: ALMA image CO 2-1 velocity field at 75mas (7pc) resolution of the barred lenticular galaxy NGC1574, which hosts a supermassive black hole. Center: the velocity field along the major axis, plus the best fit model including a SMBH. Right: separating the mass contributions from the galaxy and the SMBH, indicating a black hole mass of 6.2x107 M⊙ (Zhang et al. arXiv:2507.10662).

Connect with NRAO

The NSF National Radio Astronomy Observatory and NSF Green Bank Observatory are facilities of the U.S. National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Founded in 1956, the NSF NRAO provides state-of-the-art radio telescope facilities for use by the international scientific community. NSF NRAO telescopes are open to all astronomers regardless of institutional or national affiliation. Observing time on NSF NRAO telescopes is available on a competitive basis to qualified scientists after evaluation of research proposals on the basis of scientific merit, the capability of the instruments to do the work, and the availability of the telescope during the requested time. NSF NRAO also provides both formal and informal programs in education and public outreach for teachers, students, the general public, and the media.

The U.S. National Science Foundation (U.S. NSF) is an independent federal agency created by Congress in 1950 "to promote the progress of science; to advance the national health, prosperity, and welfare; to secure the national defense..."

AUI collaborates with the scientific community and research sponsors to plan, build, and operate cutting-edge facilities. We cultivate excellence, deliver value, enhance education, and engage the public.