Galaxies and Galaxy Formation

Figure-1-1-4-1.pngThe most distant known radio blazar has been discovered in the VLASS, J0410-0139 at z = 7. Broadband VLA radio observations show that this source is a highly time variable, GHz-peaked spectrum radio AGN, characteristic of blazars, a conclusion supported by X-ray observations. ALMA and the Northern Extended Millimeter Array (NOEMA) observations of the [CII] 158mm emission provide a very accurate redshift of 6.9964, and a star formation rate of 50 M⊙ yr-1. The [CII] dynamics imply a host galaxy mass of 4.6x109 M⊙. The black hole mass to host galaxy mass ratio is 0.16, which is larger than is seen for the relationship in nearby galaxies, suggesting earlier growth of the supermassive black hole relative to the host galaxy.

Left: ALMA and NOEMA observations of the [CII] 158mm emission and mm continuum from the most distant known radio Blazar at z = 7, identified in the VLASS. Right: the radio spectrum and time variability verifying the blazar nature of the source (Banados et al. 2024), including variability and a GHz-peaked spectrum.

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The [CII] Resolved ISm in STar-forming galaxies with ALMA (CRISTAL) large program with ALMA observed the gas ([CII]), dust, and stellar distribution (with Hubble Space Telescope, or HST), in a sample of z = 4 to 6 galaxies. The derived gas distributions range in size from 0.5 to 3.5 kpc, with an average value of 1.9 kpc, and the gas appears to be more extended than the dust emission and the stars by factors of 2.9 and 1.5, respectively. The [CII] emission can be explained by photodissociation regions driven by star formation, plus a possible contribution from more diffuse neutral atomic gas. The effect of mergers further inflates the [C II] spatial distributions.

Right: ALMA [CII] 158mm observations of z = 4 to 6 galaxies in the CRISTAL large program (contours), with the HST images (Ikeda et al. 2024).

Figure-1-1-4-3.pngA gravitationally lensed z = 8.3 galaxy was observed with ALMA and the JWST, resolving the three primary star forming regions in the galaxy on sub-kiloparsec scales, in a possibly merging galaxy system. This gas-rich galaxy shows comparable star formation efficiency to cosmic noon galaxies (z ~ 2), and the emission line ratios of the galaxy indicate an evolved interstellar medium, again similar to z ∼ 2 star-forming galaxies, with possible evidence for ionization from an active galactic nucleus. Comparison of the thermal dust emission with the rest frame UV and optical emission, shows major dust obscuration of the dominant star forming regions, such that the UV only reveals a trace amount of the star formation activity in the galaxy.

Left: Images of the z = 8.3 lensed galaxy MACS0416-Y1: (a) ALMA 353 GHz dust continuum emission; (b) JWST near-IR F277W image with the three stellar components of the galaxy labeled, with ALMA contours; (c) JWST RGB image of rest-frame UV; (d) JWST rest frame optical image (Harshan et al. 2024).

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The VLA Sky Survey (VLASS), VLA Low-band Ionosphere and Transient Experiment (VLITE), and ALMA, working with the JWST and other telescopes, have identified the highest redshift, heavily obscured, radio-loud (RL) active galactic nucleus (AGN) to date at z = 7.7 in the Cosmic Evolution Survey (COSMOS) field. The AGN is seen only at radio through (possibly) mid-IR wavelengths, implying extreme obscuration, with NH > 1043 cm-2. A massive stellar host galaxy is seen, with a stellar mass of ~ 1012 M⊙. The AGN bolometric luminosity for the growing supermassive black hole is of order 1047 erg/s. This source represents the farthest-known highly obscured radio loud AGN.

Right: Images of the z = 7.7 AGN galaxy with the JWST, ALMA, and the VLA, and the UV to meter wavelength spectrum. This is the most distant radio loud AGN identified to date (Lambrides et al. 2024).  

 

Figure-1-1-4-5.pngPerhaps the most exciting result from the JWST has been the robust detection of galaxies well into the epoch of reionization, at z = 10 to 15, corresponding to the very first generation of star formation in the Universe, within a few hundred Myr of the Big Bang. ALMA provides crucial follow-up observations, through the study of the interstellar medium in these first galaxies, with observations of the rest-frame far infrared fine structure lines. The new record holder for the most distant ALMA galaxy detection is [OIII] 88mm line emission from JADES-GS-z14-0. The ALMA detection yields a spectroscopic redshift of z = 14.1793±0.0007, improving the precision on the JWST redshift by a factor of 180! The star forming galaxy is at the lower end the local L[OIII]88 – star formation rate relation. No dust continuum emission from GS-z14 is detected, implying an upper limit on the dust-to-stellar mass ratio of 0.002, consistent with dust production from supernovae. GS-z14 is surprisingly metal-enriched (Z ∼ 0.05 − 0.2Zo). The detection of a bright oxygen line in GS-z14 thus reinforces the notion that galaxies in the early Universe undergo rapid evolution and InterStellar Medium (ISM) enrichment through active star formation, just 300 Myr after the Big Bang.

Right: The ALMA [OIII] 88mm detection of a z = 14.18 galaxy. Left shows the [OIII] contours on the JWST near-IR image. Right shows the ALMA spectrum (Schouws et al. 2024 arXiv:2409.20549).

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