SHARP: Beyond JWST -- Revealing the galaxy birth and growth with the resolution of the ELT

A deep understanding of the life-cycle of galaxies, particularly those of high mass, requires clarifying the mechanisms that regulate star formation (SF) and its abrupt shutdown (quenching), often capable of stopping SF rates of hundreds of solar masses per year. What initially triggers quenching, and what sustains the quiescent state thereafter, especially given the frequent presence of large gas reservoirs or even massive gas inflows, are unsolved key issues. Ultimately, the crucial connection between the galaxy life-cycle and the surrounding Intergalactic (IGM) and Circumgalactic (CGM) Medium remains largely unclear. Addressing these issues requires studying star formation, chemical enrichment, and quenching homogeneously up to high redshift. The upcoming AO-assisted Extremely Large Telescope (ELT), will deliver sharper and deeper data than the JWST. SHARP is a concept study for a near-IR (0.95-2.45 mu) spectrograph designed to fully exploit the capabilities of ELT. Designed for multi-object slit spectroscopy and multi-Integral Field spectroscopy, SHARP points to achieve angular resolutions (~30 mas) far superior to NIRSpec at JWST(100 mas) to decipher and reconstruct the life-cycle oa galaxies.

💡 Research Summary

The paper presents SHARP, a concept study for a near‑infrared (0.95–2.45 µm) spectrograph to be mounted on the Extremely Large Telescope (ELT). Leveraging the ELT’s 39‑m aperture and the MCAO system MORFEO, SHARP aims to deliver an angular resolution of ~30 mas (≈250 pc at z≈2), a factor of three better than JWST/NIRSpec and significantly finer than existing ELT instruments such as HARMONI or MICADO. The instrument comprises two complementary modules: NEXUS, a multi‑object slit spectrograph capable of deploying ~30 configurable slits over a 1.2′×1.2′ AO‑corrected field with 35 mas pixels, and VESPER, a modular multi‑integral‑field unit consisting of 12 probes (each 1.7″×1.5″) sliced at 31 mas. This design enables simultaneous spectroscopy of dozens of high‑z galaxies and their environments, a capability lacking in current facilities.

The scientific motivation centers on unresolved issues in massive galaxy evolution: extraordinarily high star‑formation rates (hundreds of solar masses per year), rapid metal enrichment to solar or super‑solar levels within <1 Gyr, and abrupt quenching despite the presence of large gas reservoirs or inflows. By resolving structures on the scale of giant molecular clouds (150–250 pc), SHARP can directly measure star‑formation efficiencies, metallicity gradients, and kinematics, and trace gas inflows/outflows in both the galaxies and their surrounding IGM/CGM. The paper illustrates this with the case study of GLASS‑180009 (z≈2.66), an old, massive, quiescent galaxy that still shows a neutral gas inflow. Using NEXUS and VESPER, SHARP would map the galaxy’s stellar population, internal dynamics, and the properties of neighboring galaxies within a ~150 kpc overdensity, thereby probing the origin of the inflow (cosmic filaments, nearby companions, or IGM) and the mechanisms that maintain quiescence.

SHARP is positioned as complementary to other ELT instruments: MOSAIC offers wider surveys but lower resolution (≈0.2″) and a shorter wavelength limit (λ<1.8 µm); ANDES provides ultra‑high spectral resolution (R≈100 000) for single objects; JWST/NIRSpec delivers broader wavelength coverage but insufficient spatial resolution. SHARP fills the niche of high‑resolution, multiplexed, near‑IR spectroscopy over a moderately wide field, enabling synergistic studies with JWST imaging, ALMA molecular gas maps, and future large‑scale surveys.

Technical challenges include the limited wavelength range (missing key rest‑frame optical lines at z>3), dependence on MCAO performance, and the complexity of configuring slits and IFU probes for crowded high‑z fields. Data reduction will also be demanding due to the large volume of high‑resolution spectra.

In summary, SHARP promises to revolutionize our understanding of massive galaxy formation, chemical enrichment, and quenching by delivering unprecedented spatially resolved spectroscopy of multiple objects simultaneously at ELT diffraction‑limited resolution. Its successful implementation would provide the missing observational link between galaxy interiors and their circumgalactic environments, thereby tightening the constraints on theoretical models of galaxy evolution.