Optical rest-frame spectroscopic diagnostics are usually employed to distinguish between star formation and active galactic nucleus (AGN) powered emission. However, this method is biased against ...dusty sources, hampering a complete census of the AGN population across cosmic epochs. To mitigate this effect, it is crucial to observe at longer wavelengths in the rest-frame near-infrared (near-IR), which is less affected by dust attenuation and can thus provide a better description of the intrinsic properties of galaxies. AGN diagnostics in this regime have not been fully exploited so far, due to the scarcity of near-IR observations of both AGN and star-forming galaxies, especially at redshifts higher than 0.5. Using Cloudy photoionization models, we identified new AGN – star formation diagnostics based on the ratio of bright near-IR emission lines, namely SIII 9530 Å, CI 9850 Å, PII 1.188 μm, FeII 1.257 μm, and FeII 1.64 μm to Paschen lines (either Pa
γ
or Pa
β
), providing simple, analytical classification criteria. We applied these diagnostics to a sample of 64 star-forming galaxies and AGN at 0 ≤
z
≤ 1, and 65 sources at 1 ≤
z
≤ 3 recently observed with JWST-NIRSpec in CEERS. We find that the classification inferred from the near-IR is broadly consistent with the optical one based on the BPT and the SII/H
α
ratio. However, in the near-IR, we find ∼60% more AGN than in the optical (13 instead of eight), with five sources classified as “hidden” AGN, showing a larger AGN contribution at longer wavelengths, possibly due to the presence of optically thick dust. The diagnostics we present provide a promising tool to find and characterize AGN from
z
= 0 to
z
≃ 3 with low- and medium-resolution near-IR spectrographs in future surveys.
Abstract We analyze rest-frame ultraviolet to optical spectra of three z ≃ 7.47–7.75 galaxies whose Ly α emission lines were previously detected with Keck/MOSFIRE observations, using the JWST/NIRSpec ...observations from the Cosmic Evolution Early Release Science survey. From NIRSpec data, we confirm the systemic redshifts of these Ly α emitters, and emission-line ratio diagnostics indicate these galaxies were highly ionized and metal-poor. We investigate Ly α line properties, including the line flux, velocity offset, and spatial extent. For the one galaxy where we have both NIRSpec and MOSFIRE measurements, we find a significant offset in their flux measurements (∼1.3–5× greater in MOSFIRE) and a marginal difference in the velocity shifts. The simplest interpretation is that the Ly α emission is extended and not entirely encompassed by the NIRSpec slit. The cross-dispersion profiles in NIRSpec reveal that Ly α in one galaxy is significantly more extended than the nonresonant emission lines. We also compute the expected sizes of ionized bubbles that can be generated by the Ly α sources and discuss viable scenarios for the creation of sizable ionized bubbles (>1 physical Mpc). The source with the highest-ionization condition is possibly capable of ionizing its own bubble, while the other two do not appear to be capable of ionizing such a large region, but require additional sources of ionizing photons. Therefore, the fact that we detect Ly α from these galaxies suggests diverse scenarios for the escape of Ly α during the epoch of reionization. High-spectral-resolution spectra with JWST/NIRSpec will be extremely useful for constraining the physics of patchy reionization.
Abstract We present the Next Generation Deep Extragalactic Exploratory Public (NGDEEP) Survey, a deep slitless spectroscopic and imaging Cycle 1 JWST treasury survey designed to constrain feedback ...mechanisms in low-mass galaxies across cosmic time. NGDEEP targets the Hubble Ultra Deep Field (HUDF) with NIRISS slitless spectroscopy ( f lim , line , 5 σ ≈ 1.2 × 10 −18 erg s −1 cm −2 ) to measure metallicities and star formation rates (SFRs) for low-mass galaxies through the peak of the cosmic SFR density (0.5 < z < 4). In parallel, NGDEEP targets the HUDF-Par2 parallel field with NIRCam ( m lim , 5 σ = 30.6 − 30.9 ) to discover galaxies to z > 12, constraining the slope of the faint end of the rest-ultraviolet luminosity function. NGDEEP overlaps with the deepest HST Advanced Camera for Surveys optical imaging in the sky, F435W in the HUDF ( m lim , F 435 W = 29.6 ) and F814W in HUDF-Par2 ( m lim , F 814 W = 30 ), making this a premier HST+JWST deep field. As a treasury survey, NGDEEP data are public immediately, and we will rapidly release data products and catalogs in the spirit of previous deep-field initiatives. In this paper we present the NGDEEP survey design, summarize the science goals, and detail plans for the public release of NGDEEP reduced data products.
Abstract We use James Webb Space Telescope Near-Infrared Camera Wide Field Slitless Spectroscopy (NIRCam WFSS) and the Near-Infrared spectrograph (NIRSpec) in the Cosmic Evolution Early Release ...survey to measure rest-frame optical emission-line ratios of 155 galaxies at z > 2. The blind NIRCam grism observations include a sample of galaxies with bright emission lines that were not observed on the NIRSpec masks. We study the changes of the H α , O III /H β , and Ne III /O II emission lines in terms of redshift by comparing to lower-redshift SDSS, CLEAR, and MOSDEF samples. We find a significant (>3 σ ) correlation between O III /H β with redshift, while Ne III /O II has a marginal (2 σ ) correlation with redshift. We compare O III /H β and Ne III /O II to stellar mass and H β SFR. We find that both emission-line ratios have a correlation with H β SFR and an anticorrelation with stellar mass across the redshifts 0 < z < 9. Comparison with MAPPINGS V models indicates that these trends are consistent with lower metallicity and higher ionization in low-mass and high-SFR galaxies. We additionally compare to IllustrisTNG predictions and find that they effectively describe the highest O III /H β ratios observed in our sample, without the need to invoke MAPPINGS models with significant shock ionization components.
Abstract We present a sample of 88 candidate z ∼ 8.5–14.5 galaxies selected from the completed NIRCam imaging from the Cosmic Evolution Early Release Science survey. These data cover ∼90 arcmin 2 (10 ...NIRCam pointings) in six broadband imaging filters and one medium-band imaging filter. With this sample we confirm at higher confidence early JWST conclusions that bright galaxies in this epoch are more abundant than predicted by most theoretical models. We construct the rest-frame ultraviolet luminosity functions at z ∼ 9, 11, and 14 and show that the space density of bright ( M UV = −20) galaxies changes only modestly from z ∼ 14 to z ∼ 9, compared to a steeper increase from z ∼ 8 to z ∼ 4. While our candidates are photometrically selected, spectroscopic follow-up has now confirmed 13 of them, with only one significant interloper, implying that the fidelity of this sample is high. Successfully explaining the evidence for a flatter evolution in the number densities of UV-bright z > 10 galaxies may thus require changes to the dominant physical processes regulating star formation. While our results indicate that significant variations of dust attenuation with redshift are unlikely to be the dominant factor at these high redshifts, they are consistent with predictions from models that naturally have enhanced star formation efficiency and/or stochasticity. An evolving stellar initial mass function could also bring model predictions into better agreement with our results. Deep spectroscopic follow-up of a large sample of early galaxies can distinguish between these competing scenarios.
Abstract
The Cosmic Evolution Early Release Science program observed the Extended Groth Strip (EGS) with the Mid-Infrared Instrument (MIRI) on the James Webb Space Telescope (JWST) in 2022. In this ...paper, we discuss the four MIRI pointings that observed with longer-wavelength filters, including F770W, F1000W, F1280W, F1500W, F1800W, and F2100W. We compare the MIRI galaxies with the Spitzer/MIPS 24
μ
m population in the EGS field. We find that MIRI can observe an order of magnitude deeper than MIPS in significantly shorter integration times, attributable to JWST's much larger aperture and MIRI’s improved sensitivity. MIRI is exceptionally good at finding faint (
L
IR
< 10
10
L
⊙
) galaxies at
z
∼ 1–2. We find that a significant portion of MIRI galaxies are “mid-IR weak”—they have strong near-IR emission and relatively weaker mid-IR emission, and most of the star formation is unobscured. We present new IR templates that capture how the mid-to-near-IR emission changes with increasing infrared luminosity. We present two color–color diagrams to separate mid-IR weak galaxies and active galactic nuclei (AGN) from dusty star-forming galaxies and find that these color diagrams are most effective when used in conjunction with each other. We present the first number counts of 10
μ
m sources and find that there are ≲10 IR AGN per MIRI pointing, possibly due to the difficulty of distinguishing AGN from intrinsically mid-IR weak galaxies (due to low metallicities or dust content). We conclude that MIRI is most effective at observing moderate-luminosity (
L
IR
= 10
9
–10
10
L
⊙
) galaxies at
z
= 1–2, and that photometry alone is not effective at identifying AGN within this faint population.
Abstract
We report the discovery of a candidate galaxy with a photo-
z
of
z
∼ 12 in the first epoch of the James Webb Space Telescope (JWST) Cosmic Evolution Early Release Science Survey. Following ...conservative selection criteria, we identify a source with a robust
z
phot
=
11.8
−
0.2
+
0.3
(1
σ
uncertainty) with
m
F200W
= 27.3 and ≳7
σ
detections in five filters. The source is not detected at
λ
< 1.4
μ
m in deep imaging from both Hubble Space Telescope (HST) and JWST and has faint ∼3
σ
detections in JWST F150W and HST F160W, which signal a Ly
α
break near the red edge of both filters, implying
z
∼ 12. This object (Maisie’s Galaxy) exhibits F115W − F200W > 1.9 mag (2
σ
lower limit) with a blue continuum slope, resulting in 99.6% of the photo-
z
probability distribution function favoring
z
> 11. All data-quality images show no artifacts at the candidate’s position, and independent analyses consistently find a strong preference for
z
> 11. Its colors are inconsistent with Galactic stars, and it is resolved (
r
h
= 340 ± 14 pc). Maisie’s Galaxy has log
M
*
/
M
⊙
∼ 8.5 and is highly star-forming (log sSFR ∼ −8.2 yr
−1
), with a blue rest-UV color (
β
∼ −2.5) indicating little dust, though not extremely low metallicity. While the presence of this source is in tension with most predictions, it agrees with empirical extrapolations assuming UV luminosity functions that smoothly decline with increasing redshift. Should follow-up spectroscopy validate this redshift, our universe was already aglow with galaxies less than 400 Myr after the Big Bang.
Abstract
We present an investigation into the first 500 Myr of galaxy evolution from the Cosmic Evolution Early Release Science (CEERS) survey. CEERS, one of 13 JWST ERS programs, targets galaxy ...formation from
z
∼ 0.5 to >10 using several imaging and spectroscopic modes. We make use of the first epoch of CEERS NIRCam imaging, spanning 35.5 arcmin
2
, to search for candidate galaxies at
z
> 9. Following a detailed data reduction process implementing several custom steps to produce high-quality reduced images, we perform multiband photometry across seven NIRCam broad- and medium-band (and six Hubble broadband) filters focusing on robust colors and accurate total fluxes. We measure photometric redshifts and devise a robust set of selection criteria to identify a sample of 26 galaxy candidates at
z
∼ 9–16. These objects are compact with a median half-light radius of ∼0.5 kpc. We present an early estimate of the
z
∼ 11 rest-frame ultraviolet (UV) luminosity function, finding that the number density of galaxies at
M
UV
∼ −20 appears to evolve very little from
z
∼ 9 to 11. We also find that the abundance (surface density arcmin
−2
) of our candidates exceeds nearly all theoretical predictions. We explore potential implications, including that at
z
> 10, star formation may be dominated by top-heavy initial mass functions, which would result in an increased ratio of UV light per unit halo mass, though a complete lack of dust attenuation and/or changing star formation physics may also play a role. While spectroscopic confirmation of these sources is urgently required, our results suggest that the deeper views to come with JWST should yield prolific samples of ultrahigh-redshift galaxies with which to further explore these conclusions.
Abstract
The new capabilities that JWST offers in the near- and mid-infrared (IR) are used to investigate in unprecedented detail the nature of optical/near-IR-faint, mid-IR-bright sources, with ...HST-dark galaxies among them. We gather JWST data from the CEERS survey in the Extended Groth Strip, jointly with HST data, and analyze spatially resolved optical-to-mid-IR spectral energy distributions to estimate photometric redshifts in two dimensions and stellar population properties on a pixel-by-pixel basis for red galaxies detected by NIRCam. We select 138 galaxies with F150W − F356W > 1.5 mag and F356W < 27.5 mag. The nature of these sources is threefold: (1) 71% are dusty star-forming galaxies (SFGs) at 2 <
z
< 6 with
9
<
log
M
⋆
/
M
⊙
<
11
and a variety of specific SFRs (<1 to >100 Gyr
−1
); (2) 18% are quiescent/dormant (i.e., subject to reignition/rejuvenation) galaxies (QGs) at 3 <
z
< 5, with
log
M
⋆
/
M
⊙
∼
10
and poststarburst mass-weighted ages (0.5–1.0 Gyr); and (3) 11% are strong young starbursts with indications of high equivalent width emission lines (typically, O
iii
+H
β
) at 6 <
z
< 7 (XELG-
z
6) and
log
M
⋆
/
M
⊙
∼
9.5
. The sample is dominated by disk-like galaxies with remarkable compactness for XELG-
z
6 (effective radii smaller than 0.4 kpc). Large attenuations in SFGs, 2 <
A
(
V
) < 5 mag, are found within 1.5 times the effective radius, approximately 2 kpc, while QGs present
A
(
V
) ∼ 0.2 mag. Our SED-fitting technique reproduces the expected dust emission luminosities of IR-bright and submillimeter galaxies. This study implies high levels of star formation activity between
z
∼ 20 and
z
∼ 10, where virtually 100% of our galaxies had already formed 10
8
M
⊙
, 60% had assembled 10
9
M
⊙
, and 10% up to 10
10
M
⊙
(in situ or ex situ).
Abstract
We present the results of a systematic search for Ly
α
emitters (LAEs) at
6
≲
z
≲
7.6
using the
HST
WFC3 Infrared Spectroscopic Parallel (WISP) Survey. Our total volume over this redshift ...range is
∼
8
×
10
5
Mpc
3
, comparable to many of the narrowband surveys despite their larger area coverage. We find two LAEs at
z
= 6.38 and 6.44 with line luminosities of
L
Ly
α
∼
4.7
×
10
43
erg s
−1
, putting them among the brightest LAEs discovered at these redshifts. Taking advantage of the broad spectral coverage of WISP, we are able to rule out almost all lower-redshift contaminants. The WISP LAEs have a high number density of
7.7
×
10
−
6
Mpc
−3
. We argue that the LAEs reside in megaparsec-scale ionized bubbles that allow the Ly
α
photons to redshift out of resonance before encountering the neutral intergalactic medium. We discuss possible ionizing sources and conclude that the observed LAEs alone are not sufficient to ionize the bubbles.
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