Abstract
We present JWST NIRSpec spectroscopy for 11 galaxy candidates with photometric redshifts of
z
≃ 9 − 13 and
M
UV
∈ −21, −18 newly identified in NIRCam images in the Cosmic Evolution Early ...Release Science Survey. We confirm emission line redshifts for 7 galaxies at
z
= 7.762–8.998 using spectra at ∼1–5
μ
m either with the NIRSpec prism or its three medium-resolution (
R
∼ 1000) gratings. For
z
≃ 9 photometric candidates, we achieve a high confirmation rate of ≃90%, which validates the classical dropout selection from NIRCam photometry. No robust emission lines are identified in three galaxy candidates at
z
> 10, where the strong O
iii
and H
β
lines would be redshifted beyond the wavelength range observed by NIRSpec, and the Ly
α
continuum break is not detected with the sensitivity of the current data. Compared with Hubble Space Telescope-selected bright galaxies (
M
UV
≃ −22) that are similarly spectroscopically confirmed at
z
≃ 8 − 9, these NIRCam-selected galaxies are characterized by lower star formation rates (SFRs; SFR ≃ 4
M
⊙
yr
−1
) and lower stellar masses (≃10
8
M
⊙
), but with higher specific SFR (≃40 Gyr
−1
), higher O
iii
+H
β
equivalent widths (≃1100 Å), and elevated production efficiency of ionizing photons (
log
(
ξ
ion
/
Hz
erg
−
1
)
≃
25.8
) induced by young stellar populations (<10 Myr) accounting for ≃20% of the galaxy mass, highlighting the key contribution of faint galaxies to cosmic reionization. Taking advantage of the homogeneous selection and sensitivity, we also investigate metallicity and ISM conditions with empirical calibrations using the O
iii
5008
/H
β
ratio. We find that galaxies at
z
≃ 8 − 9 have higher SFRs and lower metallicities than galaxies at similar stellar masses at
z
≃ 2 − 6, which is generally consistent with the current galaxy formation and evolution models.
Abstract
We report on the discovery of two low-luminosity, broad-line active galactic nuclei (AGNs) at
z
> 5 identified using JWST NIRSpec spectroscopy from the Cosmic Evolution Early Release Science ...(CEERS) survey. We detect broad H
α
emission in the spectra of both sources, with FWHM of 2060 ± 290 km s
−1
and 1800 ± 200 km s
−1
, resulting in virial black hole (BH) masses that are 1–2 dex below those of existing samples of luminous quasars at
z
> 5. The first source, CEERS 2782 at
z
= 5.242, is 2–3 dex fainter than known quasars at similar redshifts and was previously identified as a candidate low-luminosity AGN based on its morphology and rest-frame optical spectral energy distribution (SED). We measure a BH mass of
M
BH
= (1.3 ± 0.4) × 10
7
M
⊙
, confirming that this AGN is powered by the least massive BH known in the Universe at the end of cosmic reionization. The second source, CEERS 746 at
z
= 5.624, is inferred to be a heavily obscured, broad-line AGN caught in a transition phase between a dust-obscured starburst and an unobscured quasar. We estimate its BH mass to be in the range of
M
BH
≃ (0.9–4.7) × 10
7
M
⊙
, depending on the level of dust obscuration assumed. We perform SED fitting to derive host stellar masses,
M
⋆
, allowing us to place constraints on the BH–galaxy mass relationship in the lowest mass range yet probed in the early Universe. The
M
BH
/
M
⋆
ratio for CEERS 2782, in particular, is consistent with or higher than the empirical relationship seen in massive galaxies at
z
= 0. We examine the narrow emission line ratios of both sources and find that their location on the BPT and OHNO diagrams is consistent with model predictions for moderately low metallicity AGNs with
Z
/
Z
⊙
≃ 0.2–0.4. The spectroscopic identification of low-luminosity, broad-line AGNs at
z
> 5 with
M
BH
≃ 10
7
M
⊙
demonstrates the capability of JWST to push BH masses closer to the range predicted for the BH seed population and provides a unique opportunity to study the early stages of BH–galaxy assembly.
Abstract
We present a comprehensive analysis of the evolution of the morphological and structural properties of a large sample of galaxies at
z
= 3–9 using early James Webb Space Telescope (JWST) ...CEERS NIRCam observations. Our sample consists of 850 galaxies at
z
> 3 detected in both Hubble Space Telescope (HST)/WFC3 and CEERS JWST/NIRCam images, enabling a comparison of HST and JWST morphologies. We conduct a set of visual classifications, with each galaxy in the sample classified three times. We also measure quantitative morphologies across all NIRCam filters. We find that galaxies at
z
> 3 have a wide diversity of morphologies. Galaxies with disks make up 60% of galaxies at
z
= 3, and this fraction drops to ∼30% at
z
= 6–9, while galaxies with spheroids make up ∼30%–40% across the redshift range, and pure spheroids with no evidence for disks or irregular features make up ∼20%. The fraction of galaxies with irregular features is roughly constant at all redshifts (∼40%–50%), while those that are purely irregular increases from ∼12% to ∼20% at
z
> 4.5. We note that these are apparent fractions, as many observational effects impact the visibility of morphological features at high redshift. On average, Spheroid-only galaxies have a higher Sérsic index, smaller size, and higher axis ratio than disk or irregular galaxies. Across all redshifts, smaller spheroid and disk galaxies tend to be rounder. Overall, these trends suggest that galaxies with established disks and spheroids exist across the full redshift range of this study, and further work with large samples at higher redshift is needed to quantify when these features first formed.
The Host of Blue Compact Galaxies AMORIN, Ricardo O
Publications of the Astronomical Society of the Pacific,
04/2010, Volume:
122, Issue:
890
Journal Article
Abstract
We present rest-frame optical emission-line flux ratio measurements for five
z
> 5 galaxies observed by the James Webb Space Telescope Near-Infared Spectrograph (NIRSpec) in the SMACS 0723 ...Early Release Observations. We add several quality-control and post-processing steps to the NIRSpec pipeline reduction products in order to ensure reliable
relative
flux calibration of emission lines that are closely separated in wavelength, despite the uncertain
absolute
spectrophotometry of the current version of the reductions. Compared to
z
∼ 3 galaxies in the literature, the
z
> 5 galaxies have similar O
iii
λ
5008/H
β
ratios, similar O
iii
λ
4364/H
γ
ratios, and higher (∼0.5 dex) Ne
III
λ
3870/O
II
λ
3728 ratios. We compare the observations to MAPPINGS V photoionization models and find that the measured Ne
III
λ
3870/O
II
λ
3728, O
iii
λ
4364/H
γ
, and O
iii
λ
5008/H
β
emission-line ratios are consistent with an interstellar medium (ISM) that has very high ionization (
log
(
Q
)
≃
8
−
9
, units of cm s
−1
), low metallicity (
Z
/
Z
⊙
≲ 0.2), and very high pressure (
log
(
P
/
k
)
≃
8
−
9
, units of cm
−3
). The combination of O
iii
λ
4364/H
γ
and O
iii
λ
(4960 + 5008)/H
β
line ratios indicate very high electron temperatures of
4.1
<
log
(
T
e
/
K
)
<
4.4
, further implying metallicities of
Z
/
Z
⊙
≲ 0.2 with the application of low-redshift calibrations for “
T
e
-based” metallicities. These observations represent a tantalizing new view of the physical conditions of the ISM in galaxies at cosmic dawn.
Abstract
Far-ultraviolet (FUV; ∼1200–2000 Å) spectra are fundamental to our understanding of star-forming galaxies, providing a unique window on massive stellar populations, chemical evolution, ...feedback processes, and reionization. The launch of the James Webb Space Telescope will soon usher in a new era, pushing the UV spectroscopic frontier to higher redshifts than ever before; however, its success hinges on a comprehensive understanding of the massive star populations and gas conditions that power the observed UV spectral features. This requires a level of detail that is only possible with a combination of ample wavelength coverage, signal-to-noise, spectral-resolution, and sample diversity that has not yet been achieved by any FUV spectral database. We present the Cosmic Origins Spectrograph Legacy Spectroscopic Survey (CLASSY) treasury and its first high-level science product, the CLASSY atlas. CLASSY builds on the Hubble Space Telescope (HST) archive to construct the first high-quality (S/N
1500 Å
≳ 5/resel), high-resolution (
R
∼ 15,000) FUV spectral database of 45 nearby (0.002 <
z
< 0.182) star-forming galaxies. The CLASSY atlas, available to the public via the CLASSY website, is the result of optimally extracting and coadding 170 archival+new spectra from 312 orbits of HST observations. The CLASSY sample covers a broad range of properties including stellar mass (6.2 < log
M
⋆
(
M
⊙
) < 10.1), star formation rate (−2.0 < log SFR (
M
⊙
yr
−1
) < +1.6), direct gas-phase metallicity (7.0 < 12+log(O/H) < 8.8), ionization (0.5 < O
32
< 38.0), reddening (0.02 <
E
(
B
−
V
) < 0.67), and nebular density (10 <
n
e
(cm
−3
) < 1120). CLASSY is biased to UV-bright star-forming galaxies, resulting in a sample that is consistent with the
z
∼ 0 mass–metallicity relationship, but is offset to higher star formation rates by roughly 2 dex, similar to
z
≳ 2 galaxies. This unique set of properties makes the CLASSY atlas the benchmark training set for star-forming galaxies across cosmic time.
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