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A number of new $z>11$ galaxy candidates have recently been identified based on public James Webb Space Telescope (JWST) NIRCam observations. Spectroscopic confirmation of these candidates is necessary to robustly measure their redshift and put them in the context of our understanding of the buildup of galaxies in the early Universe. GLASS-z13 is one of these candidates, with a reported photometric redshift $z>11.9$. I present publicly available Atacama Large Millimeter/submillimeter Array (ALMA) band 6 Director's Discretionary Time observations (project 2021.A.00020.S; PI T. Bakx), taken to acquire a spectroscopic redshift for GLASS-z13 by searching for [OIII] line emission in the redshift range $z=11.9-13.5$. No [OIII] emission is detected in integrated spectra extracted within an aperture around GLASS-z13, nor when using an automated line finding algorithm (applying different uv-weighting strategies for the imaging). 1.2 mm continuum emission associated to GLASS-z13 is not detected either. If GLASS-z13 is at z$\approx$12-13, this implies a 3-$\sigma$ upper limit on the [OIII] and rest-frame $\sim$90 $\mu$m continuum emission of $\sim1\times10^8\,\rm{L}_\odot$ and 10.8 $\mu$Jy, respectively. The non-detection of [OIII] and continuum emission does not necessarily imply that GLASS-z13 is not at $z\approx12-13$. It can also be explained by a low metallicity ($\sim 0.2\,\rm{Z}_\odot$ or lower) and/or high-density (at least 100 $\rm{cm}^{-3}$) interstellar medium. This work demonstrates the synergy between ALMA and JWST to study the properties of the first galaxies, although JWST/NIRSpec spectroscopy will be necessary to confirm or reject the high photometric-redshift of GLASS-z13., Comment: Version accepted for publication in A&A

We present ALMA detections of the [CI] 1-0, CO J=3-2, and CO J=4-3 emission lines, as well as the ALMA band 4 continuum for a compact star-forming galaxy (cSFG) at z=2.225, 3D-HST GS30274. As is typical for cSFGs, this galaxy has a stellar mass of $1.89 \pm 0.47\,\times 10^{11}\,\rm{M}_\odot$, with a star formation rate of $214\pm44\,\rm{M}_\odot\,\rm{yr}^{-1}$ putting it on the star-forming `main-sequence', but with an H-band effective radius of 2.5 kpc, making it much smaller than the bulk of `main-sequence' star-forming galaxies. The intensity ratio of the line detections yield an ISM density (~ 6 $\times 10^{4}\,\rm{cm}^{-3}$) and a UV-radiation field ( ~2 $\times 10^4\,\rm{G}_0$), similar to the values in local starburst and ultra-luminous infrared galaxy environments. A starburst phase is consistent with the short depletion times ($t_{\rm H2, dep} \leq 140$ Myr) we find using three different proxies for the H2 mass ([CI], CO, dust mass). This depletion time is significantly shorter than in more extended SFGs with similar stellar masses and SFRs. Moreover, the gas fraction of 3D-HST GS30274 is smaller than typically found in extended galaxies. We measure the CO and [CI] kinematics and find a FWHM line width of ~$750 \pm 41 $ km s$^{-1}$. The CO and [CI] FWHM are consistent with a previously measured H$\alpha$ FWHM for this source. The line widths are consistent with gravitational motions, suggesting we are seeing a compact molecular gas reservoir. A previous merger event, as suggested by the asymmetric light profile, may be responsible for the compact distribution of gas and has triggered a central starburst event. This event gives rise to the starburst-like ISM properties and short depletion times. The centrally located and efficient star formation is quickly building up a dense core of stars, responsible for the compact distribution of stellar light in 3D-HST GS30274., Comment: Accepted for publication in A&A