Abstract
The time frame in which hydrogen reionization occurred is highly uncertain, but can be constrained by observations of Lyman-alpha (Ly
α
) emission from distant sources. Neutral hydrogen in ...the intergalactic medium (IGM) attenuates Ly
α
photons emitted by galaxies. As reionization progressed the IGM opacity decreased, increasing Ly
α
visibility. The galaxy Ly
α
luminosity function (LF) is thus a useful tool to constrain the timeline of reionization. In this work, we model the Ly
α
LF as a function of redshift,
z
= 5–10, and average IGM neutral hydrogen fraction,
x
¯
Hɪ
. We combine the Ly
α
luminosity probability distribution obtained from inhomogeneous reionization simulations with a model for the UV LF to model the Ly
α
LF. As the neutral fraction increases, the average number density of Ly
α
emitting galaxies decreases, and are less luminous, though for
x
¯
Hɪ
≲
0.4
there is only a small decrease in the Ly
α
LF. We use our model to infer the IGM neutral fraction at
z
= 6.6, 7.0, and 7.3 from observed Ly
α
LFs. We conclude that there is a significant increase in the neutral fraction with increasing redshift:
x
¯
Hɪ
(
z
=
6.6
)
=
0.08
−
0.05
+
0.08
,
x
¯
Hɪ
(
z
=
7.0
)
=
0.28
±
0.05
and
x
¯
Hɪ
(
z
=
7.3
)
=
0.83
−
0.07
+
0.06
. We predict trends in the Ly
α
luminosity density and Schechter parameters as a function of redshift and the neutral fraction. We find that the Ly
α
luminosity density decreases as the universe becomes more neutral. Furthermore, as the neutral fraction increases, the faint-end slope of the Ly
α
LF steepens, and the characteristic Ly
α
luminosity shifts to lower values; hence, we conclude that the evolving shape of the Ly
α
LF—not just its integral—is an important tool to study reionization.
Abstract
The selection of high-redshift galaxies often involves spectral energy distribution (SED) fitting to photometric data, an expectation for contamination levels, and measurement of sample ...completeness—all vetted through comparison to spectroscopic redshift measurements of a sub-sample. The first JWST data are now being taken over several extragalactic fields to different depths and across various areas, which will be ideal for the discovery and classification of galaxies out to distances previously uncharted. As spectroscopic redshift measurements for sources in this epoch will not be initially available to compare with the first photometric measurements of
z
> 8 galaxies, robust photometric redshifts are of the utmost importance. Galaxies at
z
> 8 are expected to have bluer rest-frame ultraviolet (UV) colors than typically used model SED templates, which could lead to catastrophic photometric redshift failures. We use a combination of BPASS and
Cloudy
models to create a supporting set of templates that match the predicted rest-UV colors of
z
> 8 simulated galaxies. We test these new templates by fitting simulated galaxies in a mock catalog, Yung et al., which mimic expected field depths and areas of the JWST Cosmic Evolution Early Release Science Survey (
m
5
σ
∼ 28.6 over ∼100 arcmin
2
). We use EAZY to highlight the improvements in redshift recovery with the inclusion of our new template set and suggest criteria for selecting galaxies at 8 <
z
< 10 with the JWST, providing an important test case for observers venturing into this new era of astronomy.
Abstract We present measurements of the rest-frame UV spectral slope, β , for a sample of 36 faint star-forming galaxies at z ∼ 9–16 discovered in one of the deepest JWST NIRCam surveys to date, the ...Next Generation Deep Extragalactic Exploratory Public Survey. We use robust photometric measurements for UV-faint galaxies (down to M UV ∼ −16), originally published in Leung et al., and measure values of the UV spectral slope via photometric power-law fitting to both the observed photometry and stellar population models obtained through spectral energy distribution (SED) fitting with Bagpipes . We obtain a median and 68% confidence interval for β from photometric power-law fitting of β PL = − 2.7 − 0.5 + 0.5 and from SED fitting, β SED = − 2.3 − 0.1 + 0.2 for the full sample. We show that when only two to three photometric detections are available, SED fitting has a lower scatter and reduced biases than photometric power-law fitting. We quantify this bias and find that after correction the median β SED , corr = − 2.5 − 0.2 + 0.2 . We measure physical properties for our galaxies with Bagpipes and find that our faint ( M UV = − 18.1 − 0.9 + 0.7 ) sample is low in mass ( log M * / M ⊙ = 7.7 − 0.5 + 0.5 ), fairly dust-poor ( A v = 0.1 − 0.1 + 0.2 mag), and modestly young ( log age = 7.8 − 0.8 + 0.2 yr) with a median star formation rate of log ( SFR ) = − 0.3 − 0.4 + 0.4 M ⊙ yr − 1 . We find no strong evidence for ultrablue UV spectral slopes ( β ∼ −3) within our sample, as would be expected for exotically metal-poor ( Z / Z ⊙ < 10 −3 ) stellar populations with very high Lyman continuum escape fractions. Our observations are consistent with model predictions that galaxies of these stellar masses at z ∼ 9–16 should have only modestly low metallicities ( Z / Z ⊙ ∼ 0.1–0.2).
Abstract
We investigate the impact of field-to-field variation, deriving from cosmic variance, in measured Ly
α
emitter (LAE) luminosity functions (LFs) and this variation’s impact on inferences of ...the neutral fraction of the intergalactic medium (IGM) during reionization. We post-process a
z
= 7 IGM simulation to populate the dark matter halos with LAEs. These LAEs have realistic UV magnitudes, Ly
α
fluxes, and Ly
α
line profiles. We calculate the attenuation of Ly
α
emission in universes with varying IGM neutral fraction,
x
¯
H
I
. In a
x
¯
H
I
= 0.3 simulation, we perform 100 realizations of a mock 2 deg
2
survey with a redshift window Δ
z
= 0.5 and flux limit
f
Ly
α
> 1 × 10
−17
erg s
−1
cm
−2
; such a survey is typical in depth and volume of the largest LAE surveys conducted today. For each realization, we compute the LAE LF and use it to recover the input
x
¯
H
I
. Comparing the inferred values of
x
¯
H
I
across the ensemble of the surveys, we find that cosmic variance, deriving from large-scale structure and variation in the neutral gas along the sightline, imposes a floor in the uncertainty of
Δ
x
¯
H
I
∼
0.2
when
x
¯
H
I
= 0.3. We explore mitigation strategies to decrease this uncertainty, such as increasing the volume, decreasing the flux limit, or probing the volume with many independent fields. Increasing the area and/or depth of the survey does not mitigate the uncertainty, but composing a survey with many independent fields is effective. This finding highlights the best strategy for LAE surveys aiming at constraining the
x
¯
H
I
of the universe during reionization.
Abstract
We present the data release and data reduction process for the Epoch 1 NIRCam observations for the Cosmic Evolution Early Release Science Survey (CEERS). These data consist of NIRCam imaging ...in six broadband filters (F115W, F150W, F200W, F277W, F356W and F444W) and one medium-band filter (F410M) over four pointings, obtained in parallel with primary CEERS MIRI observations. We reduced the NIRCam imaging with the JWST Calibration Pipeline, with custom modifications and reduction steps designed to address additional features and challenges with the data. Here we provide a detailed description of each step in our reduction and a discussion of future expected improvements. Our reduction process includes corrections for known prelaunch issues such as 1/
f
noise, as well as in-flight issues including snowballs, wisps, and astrometric alignment. Many of our custom reduction processes were first developed with prelaunch simulated NIRCam imaging over the full 10 CEERS NIRCam pointings. We present a description of the creation and reduction of this simulated data set in the Appendix. We provide mosaics of the real images in a public release, as well as our reduction scripts with detailed explanations to allow users to reproduce our final data products. These represent one of the first official public data sets released from the Directors Discretionary Early Release Science (DD-ERS) program.
Abstract
We present JWST/NIRSpec prism spectroscopy of seven galaxies selected from Cosmic Evolution Early Release Science (CEERS) survey NIRCam imaging with photometric redshifts
z
phot
> 8. We ...measure emission line redshifts of
z
= 7.65 and 8.64 for two galaxies. For two other sources without securely detected emission lines we measure
z
=
9.77
−
0.29
+
0.37
and
10.01
−
0.19
+
0.14
by fitting model spectral templates to the prism data, from which we detect continuum breaks consistent with Ly
α
opacity from a mostly neutral intergalactic medium. The presence of strong breaks and the absence of strong emission lines give high confidence that these two galaxies have redshifts
z
> 9.6, but the redshift values derived from the breaks alone have large uncertainties given the low spectral resolution and relatively low S/N of the CEERS NIRSpec prism data. The two
z
∼ 10 sources observed are relatively luminous (
M
UV
< −20), with blue continua (−2.3 ≲
β
≲ −1.9) and low dust attenuation (
A
V
≃
0.15
−
0.1
+
0.3
); and at least one of them has a high stellar mass for a galaxy at that redshift (
log
(
M
⋆
/
M
⊙
)
≃
9.3
−
0.3
+
0.2
). Considered together with spectroscopic observations of other CEERS NIRCam-selected high-
z
galaxy candidates in the literature, we find a high rate of redshift confirmation and low rate of confirmed interlopers (8%). Ten out of 35
z
> 8 candidates with CEERS NIRSpec spectroscopy do not have secure redshifts, but the absence of emission lines in their spectra is consistent with redshifts
z
> 9.6. We find that
z
> 8 photometric redshifts are generally in agreement (within their uncertainties) with the spectroscopic values, but also that the photometric redshifts tend to be slightly overestimated (〈Δ
z
〉 = 0.45 ± 0.11), suggesting that current templates do not fully describe the spectra of very-high-
z
sources. Overall, the spectroscopy solidifies photometric redshift evidence for a high spatial density of bright galaxies at
z
> 8 compared to theoretical model predictions, and further disfavors an accelerated decline in the integrated UV luminosity density at
z
> 8.
Genome editing in plants typically relies on T-DNA plasmids that are mobilized by
Agrobacterium
-mediated transformation to deliver the CRISPR/Cas machinery. Here, we introduce a series of ...CRISPR/Cas9 T-DNA vectors for minimal settings, such as teaching labs. Gene-specific targeting sequences can be inserted as annealed short oligonucleotides in a single straightforward cloning step. Fluorescent markers expressed in mature seeds enable reliable selection of transgenic or transgene-free individuals using a combination of inexpensive LED lamps and colored-glass alternative filters. Testing these tools on the
Arabidopsis
GROWTH-REGULATING FACTOR (GRF) genes, we were able to create a collection of predicted null mutations in all nine family members with little effort. We then explored the effects of simultaneously targeting two, four and eight GRF genes on the rate of induced mutations at each target locus. In our hands, multiplexing was associated with pronounced disparities: while mutation rates at some loci remained consistently high, mutation rates at other loci dropped dramatically with increasing number of single guide RNA species, thereby preventing a systematic mutagenesis of the family.
We investigate the impact of field-to-field variation, deriving from cosmic
variance, in measured Lyman-$\alpha$ emitter (LAE) luminosity functions (LFs)
and this variation's impact on inferences of ...the neutral fraction of the
intergalactic medium (IGM) during reionization. We post-process a z=7 IGM
simulation to populate the dark matter halos with LAEs. These LAEs have
realistic UV magnitudes, Ly$\alpha$ fluxes, and Ly$\alpha$ line profiles. We
calculate the attenuation of Ly$\alpha$ emission in universes with varying IGM
neutral fraction, $\bar{\rm{x}}_{\rm{HI}}$. In a $\bar{\rm{x}}_{\rm{HI}}=0.3$
simulation, we perform 100 realizations of a mock 2 square degree survey with a
redshift window $\Delta z = 0.5$ and flux limit
$\rm{f}_{Ly\alpha}>1\times10^{-17}\:\rm{ergs}\:\: \rm{s}^{-1} \: \rm{cm}^{-2}$;
such a survey is typical in depth and volume of the largest LAE surveys
conducted today. For each realization, we compute the LAE LF and use it to
recover the input $\bar{\rm{x}}_{\rm{HI}}$. Comparing the inferred values of
$\bar{\rm{x}}_{\rm{HI}}$ across the ensemble of the surveys, we find that
cosmic variance, deriving from large-scale structure and variation in the
neutral gas along the sightline, imposes a floor in the uncertainty of $\Delta
\bar{\rm{x}}_{\rm{HI}} \sim 0.2$ when $\bar{\rm{x}}_{\rm{HI}}$ $=0.3$. We
explore mitigation strategies to decrease this uncertainty, such as increasing
the volume, decreasing the flux limit, or probing the volume with many
independent fields. Increasing the area and/or depth of the survey does not
mitigate the uncertainty, but composing a survey with many independent fields
is effective. This finding highlights the best strategy for LAE surveys aiming
at constraining $\bar{\rm{x}}_{\rm{HI}}$ of the universe during reionization.
We present measurements of the rest-frame UV spectral slope, $\beta$, for a
sample of 36 faint star-forming galaxies at z ~ 9-16 discovered in one of the
deepest JWST NIRCam surveys to date, the Next ...Generation Deep Extragalactic
Exploratory Public (NGDEEP) Survey. We use robust photometric measurements for
UV-faint galaxies (down to $M_{UV}$ ~ -16), originally published in Leung+23,
and measure values of the UV spectral slope via photometric power-law fitting
to both the observed photometry and to stellar population models obtained
through spectral energy distribution (SED) fitting with Bagpipes. We obtain a
median and 68% confidence interval for $\beta$ from photometric power-law
fitting of $\beta_{PL} = -2.7^{+0.5}_{-0.5}$ and from SED-fitting, $\beta_{SED}
= -2.3^{+0.2}_{-0.1}$ for the full sample. We show that when only 2-3
photometric detections are available, SED-fitting has a lower scatter and
reduced biases than photometric power-law fitting. We quantify this bias and
find that after correction, the median $\beta_{SED,corr} = -2.5^{+0.2}_{-0.2}$.
We measure physical properties for our galaxies with Bagpipes and find that our
faint ($M_{UV} = -18.1^{+0.7}_{-0.9}$) sample is low mass
(${log}M_{\ast}/M_\odot = 7.7^{+0.5}_{-0.5}$), fairly dust-poor ($A_{v} =
0.1^{+0.2}_{-0.1}$ mag), and modestly young (${logage} = 7.8^{+0.2}_{-0.8}$
yr) with a median star formation rate of $\mathrm{log(SFR)} =
-0.3^{+0.4}_{-0.4} M_\odot{/yr}$. We find no strong evidence for ultra-blue UV
spectral slopes ($\beta$ ~ -3) within our sample, as would be expected for
exotically metal-poor ($Z/Z_{\odot}$ < 10$^{-3}$) stellar populations with very
high LyC escape fractions. Our observations are consistent with model
predictions that galaxies of these stellar masses at z~9-16 should have only
modestly low metallicities ($Z/Z_{\odot}$ ~ 0.1--0.2).
The selection of high-redshift galaxies often involves spectral energy distribution (SED) fitting to photometric data, an expectation for contamination levels, and measurement of sample completeness ...-- all vetted through comparison to spectroscopic redshift measurements of a sub-sample. The first JWST data is now being taken over several extragalactic fields, to different depths and across various areas, which will be ideal for the discovery and classification of galaxies out to distances previously uncharted. As spectroscopic redshift measurements for sources in this epoch will not be initially available to compare with the first photometric measurements of z > 8 galaxies, robust photometric redshifts are of the utmost importance. Galaxies at z > 8 are expected to have bluer rest-frame ultraviolet (UV) colors than typically-used model SED templates, which could lead to catastrophic photometric redshift failures. We use a combination of BPASS and Cloudy models to create a supporting set of templates that match the predicted rest-UV colors of z > 8 the simulated galaxies in a mock catalog (Yung et al. 2022), which mimics expected field depths and areas of the Cosmic Evolution Early Release Science Survey (CEERS: m\(_{5\sigma}\) ~ 28.6 over ~100 arcmin\(^2\); Finkelstein et al. 2022a, Bagley et al. 2022). We use EAZY to highlight the improvements in redshift recovery with the inclusion of our new template set and suggest criteria for selecting galaxies at 8 < z < 10 with JWST, providing an important test case for observers venturing into this new era of astronomy.
PDF
