Galaxy formation and evolution

Abstract:

Lyα emission is one of a few observable features of galaxies that can trace the neutral hydrogen content in the Universe during the Epoch of Reionization (EoR). To accomplish this, we need an efficient way to survey for Lyα emitters (LAEs) at redshifts beyond 7, requiring unbiased emission-line observations that are both sufficiently deep and wide to cover enough volume to detect them. Here we present results from PASSAGE—a pure-parallel JWST/NIRISS slitless spectroscopic survey to detect LAEs deep into the EoR, without the bias of photometric preselection. We identify four LAEs at 7.5 ≤ z ≤ 9.5 in four surveyed pointings and estimate the luminosity function (LF). We find that the LF does show a marked decrease compared to post-reionization measurements, but the change is a factor of ≲10, which is less than expected from theoretical calculations and simulations, as well as observational expectations from the pre-JWST literature. Modeling of the intergalactic medium and expected Lyα profiles implies that these galaxies reside in ionized bubbles of ⪆2 physical Mpc. We also report that in the four fields we detect {3, 1, 0, 0} LAEs, which could indicate strong field-to-field variation in the LAE distribution, consistent with a patchy H i distribution at z ∼ 8. We compare the recovered LAE number counts with expectations from simulations and discuss the potential implications for reionization and its morphology.

Abstract:

Early-type galaxies (ETGs) are known to harbour dense spheroids of stars with scarce star formation (SF). Approximately a quarter of these galaxies have rich molecular gas reservoirs yet do not form stars efficiently. These gas-rich ETGs have properties similar to those of bulges at the centres of spiral galaxies. We use spatially resolved observations (∼100 pc resolution) of warm ionized-gas emission lines (Hβ, [O iii], [N ii], H, and [S ii]) from the imaging Fourier transform spectrograph SITELLE at the Canada-France-Hawaii Telescope and cold molecular gas [12CO(2-1) or 12CO(3-2)] from the Atacama Large Millimeter/submillimeter Array to study the SF properties of eight ETGs and bulges. We use the ionized-gas emission lines to classify the ionization mechanisms and demonstrate a complete absence of regions dominated by SF ionization in these ETGs and bulges, despite abundant cold molecular gas. The ionization classifications also show that our ETGs and bulges are dominated by old stellar populations. We use the molecular gas surface densities and H -derived SF rates (in spiral galaxies outside of the bulges) or upper limits (in ETGs and bulges) to constrain the depletion times (inverse of the SF efficiencies), suggesting again suppressed SF in our ETGs and bulges. Finally, we use the molecular gas velocity fields to measure the gas kinematics, and show that bulge dynamics, particularly the strong shear due to the deep and steep gravitational potential wells, is an important SF regulation mechanism for at least half of our sample galaxies.

Abstract:

Early-type galaxies (ETGs) are known to harbour dense spheroids of stars with scarce star formation (SF). Approximately a quarter of these galaxies have rich molecular gas reservoirs yet do not form stars efficiently. These gas-rich ETGs have properties similar to those of bulges at the centres of spiral galaxies. We use spatially resolved observations (∼100 pc resolution) of warm ionized-gas emission lines (Hβ, [O iii], [N ii], H, and [S ii]) from the imaging Fourier transform spectrograph SITELLE at the Canada-France-Hawaii Telescope and cold molecular gas [12CO(2-1) or 12CO(3-2)] from the Atacama Large Millimeter/submillimeter Array to study the SF properties of eight ETGs and bulges. We use the ionized-gas emission lines to classify the ionization mechanisms and demonstrate a complete absence of regions dominated by SF ionization in these ETGs and bulges, despite abundant cold molecular gas. The ionization classifications also show that our ETGs and bulges are dominated by old stellar populations. We use the molecular gas surface densities and H -derived SF rates (in spiral galaxies outside of the bulges) or upper limits (in ETGs and bulges) to constrain the depletion times (inverse of the SF efficiencies), suggesting again suppressed SF in our ETGs and bulges. Finally, we use the molecular gas velocity fields to measure the gas kinematics, and show that bulge dynamics, particularly the strong shear due to the deep and steep gravitational potential wells, is an important SF regulation mechanism for at least half of our sample galaxies.

Abstract:

Early-type galaxies (ETGs) are known to harbour dense spheroids of stars with scarce star formation (SF). Approximately a quarter of these galaxies have rich molecular gas reservoirs yet do not form stars efficiently. These gas-rich ETGs have properties similar to those of bulges at the centres of spiral galaxies. We use spatially resolved observations ( pc resolution) of warm ionized-gas emission lines (H , [O iii], [N ii], H , and [S ii]) from the imaging Fourier transform spectrograph SITELLE at the Canada–France–Hawaii Telescope and cold molecular gas [12CO(2–1) or 12CO(3–2)] from the Atacama Large Millimeter/submillimeter Array to study the SF properties of eight ETGs and bulges. We use the ionized-gas emission lines to classify the ionization mechanisms and demonstrate a complete absence of regions dominated by SF ionization in these ETGs and bulges, despite abundant cold molecular gas. The ionization classifications also show that our ETGs and bulges are dominated by old stellar populations. We use the molecular gas surface densities and H -derived SF rates (in spiral galaxies outside of the bulges) or upper limits (in ETGs and bulges) to constrain the depletion times (inverse of the SF efficiencies), suggesting again suppressed SF in our ETGs and bulges. Finally, we use the molecular gas velocity fields to measure the gas kinematics, and show that bulge dynamics, particularly the strong shear due to the deep and steep gravitational potential wells, is an important SF regulation mechanism for at least half of our sample galaxies.