Abstract
The Reionization Era Bright Emission Line Survey (REBELS) is a cycle-7 ALMA Large Program (LP) that is identifying and performing a first characterization of many of the most luminous ...star-forming galaxies known in the
z
> 6.5 universe. REBELS is providing this probe by systematically scanning 40 of the brightest UV-selected galaxies identified over a 7 deg
2
area for bright C
ii
158
μ
m
and O
iii
88
μ
m
lines and dust-continuum emission. Selection of the 40 REBELS targets was done by combining our own and other photometric selections, each of which is subject to extensive vetting using three completely independent sets of photometry and template-fitting codes. Building on the observational strategy deployed in two pilot programs, we are increasing the number of massive interstellar medium (ISM) reservoirs known at
z
> 6.5 by ∼4–5× to >30. In this manuscript, we motivate the observational strategy deployed in the REBELS program and present initial results. Based on the first-year observations, 18 highly significant ≥ 7
σ
C
ii
158
μ
m
lines have already been discovered, the bulk of which (13/18) also show ≥3.3
σ
dust-continuum emission. These newly discovered lines more than triple the number of bright ISM-cooling lines known in the
z
> 6.5 universe, such that the number of ALMA-derived redshifts at
z
> 6.5 rival Ly
α
discoveries. An analysis of the completeness of our search results versus star formation rate (SFR) suggests an ∼79% efficiency in scanning for C
ii
158
μ
m
when the SFR
UV+IR
is >28
M
⊙
yr
−1
. These new LP results further demonstrate ALMA’s efficiency as a “redshift machine,” particularly in the Epoch of Reionization.
ABSTRACT
We study the ionizing photon production efficiency at the end of the Epoch of Reionization (z ∼ 5.4 − 6.6) for a sample of 30 Ly α emitters. This is a crucial quantity to infer the ionizing ...photon budget of the universe. These objects were selected to have reliable spectroscopic redshifts, assigned based on the profile of their Ly α emission line, detected in the MUSE deep fields. We exploit medium-band observations from the JWST Extragalactic Medium-band Survey (JEMS) to find the flux excess corresponding to the redshifted Hα emission line. We estimate the ultraviolet (UV) luminosity by fitting the full JEMS photometry, along with several HST photometric points, with Prospector. We find a median UV continuum slope of $\beta = -2.09^{+0.23}_{-0.21}$, indicating young stellar populations with little-to-no dust attenuation. Supported by this, we derive ξion,0 with no dust attenuation and find a median value of log$\frac{\xi _{ion,0}}{\text{Hz erg}^{-1}} = 25.44^{+0.21}_{-0.15}$. If we perform dust attenuation corrections and assume a Calzetti attenuation law, our values are lowered by ∼0.1 dex. Our results suggest Ly α emitters at the Epoch of Reionization have slightly enhanced ξion,0 compared to previous estimations from literature, in particular, when compared to the non-Ly α emitting population. This initial study provides a promising outlook on the characterization of ionizing photon production in the early universe. In the future, a more extensive study will be performed on the entire data set provided by the JWST Advanced Deep Extragalactic Survey (JADES). Thus, for the first time, allowing us to place constraints on the wider galaxy populations driving reionization.
ABSTRACT
We use deep imaging from the JWST Advanced Deep Extragalactic Survey (JADES) to study the evolution of the ionizing photon production efficiency, ξion. We estimate ξion for a sample of 677 ...galaxies at z ∼ 4–9 using NIRCam (Near-Infrared Camera) photometry. Specifically, combinations of the medium and wide bands F335M–F356W and F410M–F444W to constrain emission lines that trace ξion: Hα and O iii. Additionally, we use the spectral energy distribution fitting code prospector to fit all available photometry and infer galaxy properties. The flux measurements obtained via photometry are consistent with FRESCO (First Reionisation Epoch Spectroscopic Complete Survey) and NIRSpec-derived fluxes. Moreover, the emission-line-inferred measurements are consistent with the prospector estimates. We also confirm the observed ξion trend with redshift and MUV, and find: log ξion(z, MUV) = (0.05 ± 0.02)z + (0.11 ± 0.02)MUV + (27.33 ± 0.37). We use prospector to investigate correlations of ξion with other galaxy properties. We see a clear correlation between ξion and burstiness in the star formation history of galaxies, given by the ratio of recent to older star formation, where burstiness is more prevalent at lower stellar masses. We also convolve our ξion relations with luminosity functions from the literature, and constant escape fractions of 10 per cent and 20 per cent, to place constraints on the cosmic ionizing photon budget. By combining our results, we find that if our sample is representative of the faint low-mass galaxy population, galaxies with bursty star formation are efficient enough in producing ionizing photons and could be responsible for the reionization of the Universe.
As the primary fuel for star formation, molecular gas plays a key role in
galaxy evolution. A number of techniques have been used for deriving the mass
of molecular reservoirs in the early Universe ...(e.g., CII158$\mu$m, CI, dust
continuum), but the standard approach of CO-based estimates has been limited to
a small number of galaxies due to the intrinsic faintness of the line. We
present Jansky Very Large Array (JVLA) observations of the $z\sim8.31$ galaxy
MACS0416_Y1, targeting CO(2-1) and rest-frame radio continuum emission, which
result in upper limits on both quantities. Adding our continuum limit to the
published far-infrared (FIR) spectral energy distribution (SED), we find a
small non-thermal contribution to the FIR emission, a low dust mass
($\rm\log_{10}(M_D/M_{\odot})\sim5$), and an abnormally high dust temperature
($\rm T_D\gtrsim90K$) that may indicate a recent starburst. Assuming a low
metallicity ($Z/Z_{\odot}\sim0.25$), we find evidence for $M_{\rm
H_2,CO}\lesssim10^{10}$M$_{\odot}$, in agreement with previous CII
investigations ($M_{\rm H_2,CII}\sim10^{9.6}$M$_{\odot}$). Upcoming JWST
observations of this source will result in a precise determination of $Z$,
enabling better constraints and an unprecedented view of the gaseous reservoir
in this primordial starburst galaxy.
As the primary fuel for star formation, molecular gas plays a key role in galaxy evolution. A number of techniques have been used for deriving the mass of molecular reservoirs in the early Universe ...(e.g., CII158\(\mu\)m, CI, dust continuum), but the standard approach of CO-based estimates has been limited to a small number of galaxies due to the intrinsic faintness of the line. We present Jansky Very Large Array (JVLA) observations of the \(z\sim8.31\) galaxy MACS0416_Y1, targeting CO(2-1) and rest-frame radio continuum emission, which result in upper limits on both quantities. Adding our continuum limit to the published far-infrared (FIR) spectral energy distribution (SED), we find a small non-thermal contribution to the FIR emission, a low dust mass (\(\rm\log_{10}(M_D/M_{\odot})\sim5\)), and an abnormally high dust temperature (\(\rm T_D\gtrsim90K\)) that may indicate a recent starburst. Assuming a low metallicity (\(Z/Z_{\odot}\sim0.25\)), we find evidence for \(M_{\rm H_2,CO}\lesssim10^{10}\)M\(_{\odot}\), in agreement with previous CII investigations (\(M_{\rm H_2,CII}\sim10^{9.6}\)M\(_{\odot}\)). Upcoming JWST observations of this source will result in a precise determination of \(Z\), enabling better constraints and an unprecedented view of the gaseous reservoir in this primordial starburst galaxy.
Massive, starbursting galaxies in the early Universe represent some of the most extreme objects in the study of galaxy evolution. One such source is HFLS3 (z~6.34), which was originally identified as ...an extreme starburst galaxy with mild gravitational magnification (\(\mu\)~2.2). Here, we present new observations of HFLS3 with the JWST/NIRSpec IFU in both low (PRISM/CLEAR; R~100) and high spectral resolution (G395H/290LP; R~2700), with high spatial resolution (~0.1") and sensitivity. Thanks to the combination of the NIRSpec data and a new lensing model with accurate spectroscopic redshifts, we find that the 3"x3" field is crowded, with a lensed arc (C, \(z=6.3425\pm0.0002\)), two galaxies to the south (S1 and S2, \(z=6.3592\pm0.0001\)), two galaxies to the west (W1, \(z=6.3550\pm0.0001\); W2, \(z=6.3628\pm0.0001\)), and two low-redshift interlopers (G1, \(z=3.4806\pm0.0001\); G2, \(z=2.00\pm0.01\)). We present spectral fits and morpho-kinematic maps for each bright emission line from the R2700 data for all sources except G2. From a line ratio analysis, the galaxies in component C are likely powered by star formation, while we cannot rule out or confirm the presence of AGN in the other high-redshift sources. We perform gravitational lens modelling, finding evidence for a two-source composition of the lensed central object and a comparable magnification factor (\(\mu\)=2.1-2.4) to previous work. The projected distances and velocity offsets of each galaxy suggest that they will merge within the next ~1Gyr. Finally, we examine the dust extinction-corrected SFR(Ha) of each z>6 source, finding that the total star formation (\(510\pm140\)Msol/yr, magnification-corrected) is distributed across the six z~6.34-6.36 objects over a region of diameter ~11kpc. Altogether, this suggests that HFLS3 is not a single starburst galaxy, but instead is a merging system of star-forming galaxies in the Epoch of Reionisation.
One of the surprising early findings with JWST has been the discovery of a
strong "roll-over" or a softening of the absorption edge of Ly$\alpha$ in a
large number of galaxies at ($z\gtrsim 6$), in ...addition to systematic offsets
from photometric redshift estimates and fundamental galaxy scaling relations.
This has been interpreted as damped Ly$\alpha$ absorption (DLA) wings from high
column densities of neutral atomic hydrogen (HI), signifying major gas
accretion events in the formation of these galaxies. To explore this new
phenomenon systematically, we assemble the JWST/NIRSpec PRImordial gas Mass
AssembLy (PRIMAL) legacy survey of 494 galaxies at $z=5.5-13.4$. We
characterize this benchmark sample in full and spectroscopically derive the
galaxy redshifts, metallicities, star-formation rates, and ultraviolet slopes.
We define a new diagnostic, the Ly$\alpha$ damping parameter $D_{\rm Ly\alpha}$
to measure and quantify the Ly$\alpha$ emission strength, HI fraction in the
IGM, or local HI column density for each source. The JWST-PRIMAL survey is
based on the spectroscopic DAWN JWST Archive (DJA-Spec). All the software,
reduced spectra, and spectroscopically derived quantities and catalogs are made
publicly available in dedicated repositories. The fraction of strong galaxy
DLAs are found to be in the range $65-95\%$ at $z>5.5$. The fraction of strong
Ly$\alpha$ emitters (LAEs) is found to increase with decreasing redshift, in
qualitative agreement with previous observational results, and are
predominantly associated with low-metallicity and UV faint galaxies. By
contrast, strong DLAs are observed in galaxies with a variety of intrinsic
physical properties. Our results indicate that strong DLAs likely reflect a
particular early assembly phase of reionization-era galaxies, at which point
they are largely dominated by pristine HI gas accretion. abridged
We study galaxies in JADES Deep to study the evolution of the ionising photon production efficiency, \(\xi_{\rm{ion}}\), observed to increase with redshift. We estimate \(\xi_{\rm{ion}}\) for a ...sample of 677 galaxies at \(z \sim 4 - 9\) using NIRCam photometry. Specifically, combinations of the medium and wide bands F335M-F356W and F410M-F444W to constrain emission lines that trace \(\xi_{\rm{ion}}\): H\(\alpha\) and OIII. Additionally, we use the spectral energy distribution fitting code \texttt{Prospector} to fit all available photometry and infer galaxy properties. The flux measurements obtained via photometry are consistent with FRESCO and NIRSpec-derived fluxes. Moreover, the emission-line-inferred measurements are in tight agreement with the \texttt{Prospector} estimates. We also confirm the observed \(\xi_{\rm{ion}}\) trend with redshift and M\(_{\rm{UV}}\), and find: \(\log \xi_{\rm{ion}} (z,\text{M}_{\rm{UV}}) = (0.05 \pm 0.02)z + (0.11 \pm 0.02) \text{M}_{\rm{UV}} + (27.33 \pm 0.37)\). We use \texttt{Prospector} to investigate correlations of \(\xi_{\rm{ion}}\) with other galaxy properties. We see a clear correlation between \(\xi_{\rm{ion}}\) and burstiness in the star formation history of galaxies, given by the ratio of recent to older star formation, where burstiness is more prevalent at lower stellar masses. We also convolve our \(\xi_{\rm{ion}}\) relations with luminosity functions from the literature, and constant escape fractions of 10 and 20\%, to place constraints on the cosmic ionising photon budget. By combining our results, we find that if our sample is representative of the faint low-mass galaxy population, galaxies with bursty star formation are efficient enough in producing ionising photons and could be responsible for the reionisation of the Universe.
We analyse the chemical properties of three z~8 galaxies behind the galaxy cluster SMACS J0723.3-7327, observed as part of the Early Release Observations programme of the James Webb Space Telescope ...(JWST). Exploiting O III4363 auroral line detections in NIRSpec spectra, we robustly apply the direct Te method for the very first time at such high redshift, measuring metallicities ranging from extremely metal poor (12+log(O/H)~7) to about one-third solar. We also discuss the excitation properties of these sources, and compare them with local strong-line metallicity calibrations. We find that none of the considered diagnostics match simultaneously the observed relations between metallicity and strong-line ratios for the three sources, implying that a proper re-assessment of the calibrations may be needed at these redshifts. On the mass-metallicity plane, the two galaxies at z~7.6 (log(M*/M_sun) = 8.1, 8.7) have metallicities that are consistent with the extrapolation of the mass-metallicity relation at z~2-3, while the least massive galaxy at z~8.5 (log(M*/M_sun) = 7.8) shows instead a significantly lower metallicity . The three galaxies show different level of offset relative to the Fundamental Metallicity Relation, with two of them (at z~7.6) being marginally consistent, while the z~8.5 source deviating significantly, being probably far from the smooth equilibrium between gas flows, star formation and metal enrichment in place at later epochs.
