38 research outputs found
Semi-analytic forecasts for Roman -- the beginning of a new era of deep-wide galaxy surveys
The Nancy Grace Roman Space Telescope, NASA's next flagship observatory, will
redefine deep-field galaxy survey with a field of view two orders of magnitude
larger than Hubble and an angular resolution of matching quality. These future
deep-wide galaxy surveys necessitate new simulations to forecast their
scientific output and to optimise survey strategies. In this work, we present
five realizations of 2-deg^2 lightcones, containing a total of >25 million
simulated galaxies with -16 < MUV < -25 spanning z ~ 0 to 10. This dataset
enables a new set of experiments with the impacts of survey size on the derived
galaxy formation and cosmological constraints. The intrinsic and observable
galaxy properties are predicted using a well-established, physics-based
semi-analytic modelling approach. We provide forecasts for number density,
cosmic SFR, field-to-field variance, and angular two-point correlation
functions, and demonstrate how the future wide-field surveys will be able to
improve these measurements relative to current generation surveys. We also
present a comparison between these lightcones and others that have been
constructed with empirical models. The mock lightcones are designed to
facilitate the exploration of multi-instrument synergies and connecting with
current generation instruments and legacy surveys. In addition to Roman, we
also provide photometry for a number of other instruments on upcoming
facilities, including Euclid and Rubin, as well as the instruments that are
part of many legacy surveys. Full object catalogues and data tables for the
results presented in this work are made available through a web-based,
interactive portal https://www.simonsfoundation.org/semi-analytic-forecasts.Comment: 25 pages, 16 figures. Accepted for publication in MNRA
Extremely Red Galaxies at z = 5-9 with MIRI and NIRSpec:Dusty Galaxies or Obscured Active Galactic Nuclei?
We study a new population of extremely red objects (EROs) recently discovered by the James Webb Space Telescope (JWST) based on their NIRCam colors F277W − F444W > 1.5 mag. We find 37 EROs in the Cosmic Evolution Early Release Science Survey (CEERS) field with F444W < 28 mag and photometric redshifts between 5 < z < 7, with median z = 6.9 − 1.6 + 1.0 . Surprisingly, despite their red long-wavelength colors, these EROs have blue short-wavelength colors (F150W − F200W ∼ 0 mag) indicative of bimodal spectral energy distributions (SEDs) with a red, steep slope in the rest-frame optical, and a blue, flat slope in the rest-frame UV. Moreover, all these EROs are unresolved, point-like sources in all NIRCam bands. We analyze the SEDs of eight of them with MIRI and NIRSpec observations using stellar population models and active galactic nucleus (AGN) templates. We find that dusty galaxies or obscured AGNs provide similarly good SED fits but different stellar properties: massive and dusty, log M ⋆ / M ⊙ ∼ 10 and A V ≳ 3 mag, or low mass and obscured, log M ⋆ / M ⊙ ∼ 7.5 and A V ∼ 0 mag, hosting an obscured quasi-stellar object (QSO). SED modeling does not favor either scenario, but their unresolved sizes are more suggestive of AGNs. If any EROs are confirmed to have log M ⋆ / M ⊙ ≳ 10.5, it would increase the pre-JWST number density at z > 7 by up to a factor ∼60. Similarly, if they are QSOs with luminosities in the L bol > 1045-46 erg s−1 range, their number would exceed that of bright blue QSOs by more than three orders of magnitude. Additional photometry at mid-infrared wavelengths will reveal the true nature of the red continuum emission in these EROs and will place this puzzling population in the right context of galaxy evolution.</p
Cosmic Evolution Early Release Science (CEERS) survey: The colour evolution of galaxies in the distant Universe
The wavelength-coverage and sensitivity of JWST now enables us to probe the
rest-frame UV - optical spectral energy distributions (SEDs) of galaxies at
high-redshift (). From these SEDs it is, in principle, through SED fitting
possible to infer key physical properties, including stellar masses, star
formation rates, and dust attenuation. These in turn can be compared with the
predictions of galaxy formation simulations allowing us to validate and refine
the incorporated physics. However, the inference of physical properties,
particularly from photometry alone, can lead to large uncertainties and
potential biases. Instead, it is now possible, and common, for simulations to
be \emph{forward-modelled} to yield synthetic observations that can be compared
directly to real observations. In this work, we measure the JWST broadband
fluxes and colours of a robust sample of galaxies using the Cosmic
Evolution Early Release Science (CEERS) Survey. We then analyse predictions
from a variety of models using the same methodology and compare the
NIRCam/F277W magnitude distribution and NIRCam colours with observations. We
find that the predicted and observed magnitude distributions are similar, at
least at the distributions differ somewhat, though our
observed sample size is small and thus susceptible to statistical fluctuations.
Likewise, the predicted and observed colour evolution show broad agreement, at
least at . There is however some disagreement between the observed and
modelled strength of the strong line contribution. In particular all the models
fails to reproduce the F410M-F444W colour at , though, again, the sample
size is small here.Comment: 11 pages, 10 figures, submitted to MNRA
Near-infrared emission line diagnostics for AGN from the local Universe to redshift 3
Optical rest-frame spectroscopic diagnostics are usually employed to
distinguish between star formation and 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 AGNs and star-forming galaxies, especially at redshifts higher than 0.5.
Using Cloudy photoionization models, we identify new AGN - star formation
diagnostics based on the ratio of bright near-infrared emission lines, namely
[SIII] 9530 Angstrom, [CI] 9850 Angstrom, [PII] 1.188 , [FeII] , and [FeII] to Paschen lines (either Pa or
Pa), providing simple, analytical classification criteria. We apply
these diagnostics to a sample of 64 star-forming galaxies and AGNs 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-infrared is broadly
consistent with the optical one based on the BPT and the [SII]/H ratio.
However, in the near-infrared, we find more AGNs than in the
optical (13 instead of 8), with 5 sources classified as 'hidden' AGNs, 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 AGNs from z=0 to z=3 with low and medium-resolution
near-IR spectrographs in future surveys.Comment: Paper accepted for publication in A&A on 05/09/2023. Three public
Github repositories include: (1) a table with emission line measurements for
the paper sample : https://github.com/Anthony96/Line_measurements_nearIR ,
Cloudy emission line predictions for star-forming galaxies and AGN models :
https://github.com/Anthony96/star-forming_models ,
https://github.com/Anthony96/AGN_model
Unveiling the distant Universe: Characterizing Galaxies in the first epoch of COSMOS-Web
We report the identification of 15 galaxy candidates at using the
initial COSMOS-Web JWST observations over 77 arcmin through four NIRCam
filters (F115W, F150W, F277W, F444W) with an overlap with MIRI (F770W) of 8.7
arcmin. We fit the sample using several publicly-available SED fitting and
photometric redshift codes and determine their redshifts between and
(), UV-magnitudes between M =
21.2 and 19.5 (with M) and rest-frame
UV slopes (). These galaxies are, on average, more
luminous than most candidates discovered by JWST so far in the
literature, while exhibiting similar blue colors in their rest-frame UV. The
rest-frame UV slopes derived from SED-fitting are blue ([2.0,
2.7]) without reaching extremely blue values as reported in other recent
studies at these redshifts. The blue color is consistent with models that
suggest the underlying stellar population is not yet fully enriched in metals
like similarly luminous galaxies in the lower redshift Universe. The derived
stellar masses with MM are not in tension with the standard
CDM model and our measurement of the volume density of such UV
luminous galaxies aligns well with previously measured values presented in the
literature at . Our sample of galaxies, although compact, are
significantly resolved.Comment: Submitted to Ap
Evidence for a Shallow Evolution in the Volume Densities of Massive Galaxies at to from CEERS
We analyze the evolution of massive (log [] )
galaxies at 4--8 selected from the JWST Cosmic Evolution Early Release
Science (CEERS) survey. We infer the physical properties of all galaxies in the
CEERS NIRCam imaging through spectral energy distribution (SED) fitting with
dense basis to select a sample of high redshift massive galaxies. Where
available we include constraints from additional CEERS observing modes,
including 18 sources with MIRI photometric coverage, and 28 sources with
spectroscopic confirmations from NIRSpec or NIRCam wide-field slitless
spectroscopy. We sample the recovered posteriors in stellar mass from SED
fitting to infer the volume densities of massive galaxies across cosmic time,
taking into consideration the potential for sample contamination by active
galactic nuclei (AGN). We find that the evolving abundance of massive galaxies
tracks expectations based on a constant baryon conversion efficiency in dark
matter halos for 1--4. At higher redshifts, we observe an excess
abundance of massive galaxies relative to this simple model. These higher
abundances can be explained by modest changes to star formation physics and/or
the efficiencies with which star formation occurs in massive dark matter halos,
and are not in tension with modern cosmology.Comment: 20 pages, 10 figure
CEERS Epoch 1 NIRCam Imaging: Reduction Methods and Simulations Enabling Early JWST Science Results
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 (Yang et
al. in prep). 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 pre-launch 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 pre-launch simulated NIRCam imaging over the full 10 CEERS
NIRCam pointings. We present a description of the creation and reduction of
this simulated dataset 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 datasets released from the Directors
Discretionary Early Release Science (DD-ERS) program.Comment: 27 pages, 14 figures, submitted to ApJ. Accompanying CEERS public
Data Release 0.5 available at ceers.github.io/releases.htm
CEERS Key Paper VII: Emission Line Ratios from NIRSpec and NIRCam Wide-Field Slitless Spectroscopy at z>2
We use James Webb Space Telescope Near-Infrared Camera Wide Field Slitless
Spectroscopy (NIRCam WFSS) and Near-Infrared spectrograph (NIRSpec) in the
Cosmic Evolution Early Release survey (CEERS) to measure rest-frame optical
emission-line 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 Ha, [OIII]/Hb, and
[NeIII]/[OII] emission lines in terms of redshift by comparing to lower
redshift SDSS and CLEAR samples. We find a significant (>3) correlation
between [OIII]/Hb with redshift, while [NeIII]/[OII] has a marginal (2)
correlation with redshift. We compare [OIII]/Hb and [NeIII]/[OII] to stellar
mass and Hb SFR. We find that both emission-line ratios have a correlation with
Hb SFR and an anti-correlation 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 IllustriousTNG predictions and find that they
effectively describe the highest [OIII]/Hb ratios observed in our sample,
without the need to invoke MAPPINGS models with significant shock ionizionation
components.Comment: 16 pages, 11 figure
CEERS Spectroscopic Confirmation of NIRCam-Selected z > 8 Galaxy Candidates with JWST/NIRSpec: Initial Characterization of their Properties
We present JWST NIRSpec spectroscopy for 11 galaxy candidates with
photometric redshifts of and newly
identified in NIRCam images in the Cosmic Evolution Early Release Science
(CEERS) Survey. We confirm emission line redshifts for 7 galaxies at
using spectra at m either with the NIRSpec prism or
its three medium resolution gratings. For 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 , where the strong [OIII] and
H lines would be redshifted beyond the wavelength range observed by
NIRSpec, and the Lyman- continuum break is not detected with the
current sensitivity. Compared with HST-selected bright galaxies
() that are similarly spectroscopically confirmed at
, these NIRCam-selected galaxies are characterized by lower star
formation rates (SFR~yr) and lower stellar masses
(), but with higher [OIII]+H equivalent widths
(1100), and elevated production efficiency of ionizing photons
() induced by young stellar
populations (~Myrs) accounting for 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 [OIII]/H ratio. We find that galaxies at have higher SFRs
and lower metallicities than galaxies at similar stellar masses at ,
which is generally consistent with the current galaxy formation and evolution
models.Comment: 21 pages, 11 figures, 2 tables. Submitted to ApJL Focus Issu
Spectroscopic confirmation of CEERS NIRCam-selected galaxies at
We present JWST/NIRSpec prism spectroscopy of seven galaxies selected from
the Cosmic Evolution Early Release Science Survey (CEERS) NIRCam imaging with
photometric redshifts z_phot>8. We measure emission line redshifts of z=7.65
and 8.64 for two galaxies, and z=9.77(+0.37,-0.29) and 10.01(+0.14,-0.19) for
two others via the detection of continuum breaks consistent with Lyman-alpha
opacity from a mostly neutral intergalactic medium. The presence (absense) of
strong breaks (strong emission lines) give high confidence that these two
galaxies are at z>9.6, but the break-derived redshifts have large uncertainties
given the low spectral resolution and relatively low signal-to-noise of the
CEERS NIRSpec prism data. The two z~10 sources are relatively luminous
(M_UV<-20), with blue continua (-2.3<beta<-1.9) and low dust attenuation
(A_V=0.15(+0.3,-0.1)); and at least one of them has high stellar mass for a
galaxy at that redshift (log(M_*/M_sol)=9.3(+0.2,-0.3)). 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 (8.3%). Ten out of 34 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
uncertainties) with the spectroscopic values. However, the photometric
redshifts tend to be slightly overestimated (average Delta(z)=0.50+/-0.12),
suggesting that current templates do not fully describe the spectra of very
high-z sources. Overall, our results solidifies photometric evidence for a high
space 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.Comment: Submitted to ApJL. 24 pages, 9 figures, 7 tables. File with Table 6
included in source .tar fil