Galaxy Science with ORCAS: Faint Star-Forming Clumps to AB$\leq$31 mag and r$_e$$\geq$ 0.01"

TL;DR

The ORCAS mission concept aims to enable ultra-high-resolution imaging of faint star-forming regions and individual stars at cosmological distances, significantly advancing galaxy formation and stellar population studies with ground-based telescopes.

Contribution

This paper introduces the potential of ORCAS combined with Keck to achieve unprecedented resolution and sensitivity for faint galaxy and star studies, including detecting and analyzing star-forming clumps and individual stars at high redshifts.

Findings

ORCAS+Keck can reach AB<31 mag with 0.01-0.02" resolution.

Detects ~5 million faint star-forming clumps per square degree.

Enables study of galaxy assembly and first stars at high redshift.

Abstract

The NASA concept mission ORCAS (Orbiting Configurable Artificial Star) aims to provide near diffraction-limited angular resolution at visible and near-infrared wavelengths using laser signals from space-based cubesats as Adaptive Optics beacons for ground-based 8-30 meter telescopes, in particular the 10 meter Keck Telescopes. When built as designed, ORCAS+Keck would deliver images of ~0.01-0.02" FWHM at 0.5-1.2 micron wavelength that reach AB<31 mag for point sources in a few hours over a 5x5" FOV that includes IFU capabilities. We summarize the potential of high-resolution faint galaxy science with ORCAS. We show that the ability to detect optical-near-IR point sources with r_e>0.01" FWHM to AB<31 mag will yield about 5.0x10^6 faint star-forming (SF) clumps per square degree, or ~0.4 per arcsec^2. From recent HST lensing data, the typical intrinsic (unlensed) sizes of SF clumps at z~1-7 will be r_e ~1-80 m.a.s. to AB<31 mag, with intrinsic (unmagnified) fluxes as faint as AB<35-36 mag when searching with ORCAS around the critical curves of lensing clusters imaged with HST and JWST. About half of these SF clumps will have sizes below the ORCAS diffraction limit, and the other half will be slightly resolved, but still mostly above the ORCAS surface brightness (SB) limits. ORCAS will address how galaxies assemble from smaller clumps to stable disks by measuring ages, metallicities, and gradients of clumps within galaxies. ORCAS can monitor caustic transits of individual stars in SF clumps at z>1-2 that have been detected with HST, and those that may be detected with JWST at z>6 at extreme magnifications (mu>10^3-10^5) for the first stars and their stellar mass black hole accretion disks. ORCAS provides a unique opportunity to obtain a statistical census of individual stars at cosmological distances, leveraging the largest telescopes only available on the ground.