33 research outputs found
Low Metallicity Galaxies from the Dark Energy Survey
We present a new selection of 358 blue compact dwarf galaxies (BCDs) from
5,000 square degrees in the Dark Energy Survey (DES), and the spectroscopic
follow-up of a subsample of 68 objects. For the subsample of 34 objects with
deep spectra, we measure the metallicity via the direct T method using the
auroral [\oiii] 4363 emission line. These BCDs have average oxygen
abundance of 12+log(O/H)= 7.8, stellar masses between 10 to 10
M and specific SFR between 10 to 10 yr. We
compare the position of our BCDs with the Mass-metallicity (M-Z) and
Luminosity-metallicity (L-Z) relation derived from the Local Volume Legacy
sample. We find the scatter around the M-Z relation is smaller than the scatter
around the L-Z relation. We identify a correlation between the offsets from the
M-Z and L-Z relation that we suggest is due to the contribution of metal-poor
inflows. Finally, we explore the validity of the mass-metallicity-SFR
fundamental plane in the mass range probed by our galaxies. We find that BCDs
with stellar masses smaller than M do not follow the
extrapolation of the fundamental plane. This result suggests that mechanisms
other than the balance between inflows and outflows may be at play in
regulating the position of low mass galaxies in the M-Z-SFR space.Comment: 16 pages, 10 figures, submitted to ApJ, We invite comments from the
communit
First Light And Reionisation Epoch Simulations (FLARES) XIV: The Balmer/4000~\AA\ Breaks of Distant Galaxies
With the successful launch and commissioning of JWST we are now able to
routinely spectroscopically probe the rest-frame optical emission of galaxies
at for the first time. Amongst the most useful spectral diagnostics used
in the optical is the Balmer/4000~\AA\ break; this is, in principle, a
diagnostic of the mean ages of composite stellar populations. However, the
Balmer break is also sensitive to the shape of the star formation history, the
stellar (and gas) metallicity, the presence of nebular continuum emission, and
dust attenuation. In this work we explore the origin of the Balmer/4000~\AA\
break using the SYNTHESIZER synthetic observations package. We then make
predictions of the Balmer/4000~\AA\ break using the First Light and
Reionisation Epoch Simulations (FLARES) at . We find that the average
break strength weakly correlates with stellar mass and rest-frame far-UV
luminosity, but that this is predominantly driven by dust attenuation. We also
find that break strength provides a weak diagnostic of the age but performs
better as a means to constrain star formation and stellar mass, alongside the
UV and optical luminosity, respectively.Comment: 9 pages, 9 figures, submitted to MNRA
Efficient NIRCam Selection of Quiescent Galaxies at 3 < z < 6 in CEERS
© 2024 The Author(s). Published by the American Astronomical Society. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/Substantial populations of massive quiescent galaxies at z ≥ 3 challenge our understanding of rapid galaxy growth and quenching over short timescales. In order to piece together this evolutionary puzzle, more statistical samples of these objects are required. Established techniques for identifying massive quiescent galaxies are increasingly inefficient and unconstrained at z > 3. As a result, studies report that as much as 70% of quiescent galaxies at z > 3 may be missed from existing surveys. In this work, we propose a new empirical color selection technique designed to select massive quiescent galaxies at 3 ≲ z ≲ 6 using JWST NIRCam imaging data. We use empirically constrained galaxy spectral energy distribution (SED) templates to define a region in the F277W − F444W versus F150W − F277W color plane that captures quiescent galaxies at z > 3. We apply these color selection criteria to the Cosmic Evolution Early Release Science (CEERS) Survey and use SED fitting on sources in the region to identify 44 candidate z ≳ 3 quiescent galaxies. Over half of these sources are newly discovered and, on average, exhibit specific star formation rates of poststarburst galaxies. Most of these sources would not be discovered using canonical UVJ diagrams. We derive volume density estimates of n ∼ 1–4 × 10−5 Mpc−3 at 3 < z < 5, finding excellent agreement with existing reports on similar populations in the CEERS field. Thanks to NIRCam’s wavelength coverage and sensitivity, this technique provides an efficient tool to search for large samples of these rare galaxies.Peer reviewe
Spectroscopic verification of very luminous galaxy candidates in the early universe
During the first 500 million years of cosmic history, the first stars and
galaxies formed and seeded the cosmos with heavy elements. These early galaxies
illuminated the transition from the cosmic "dark ages" to the reionization of
the intergalactic medium. This transitional period has been largely
inaccessible to direct observation until the recent commissioning of JWST,
which has extended our observational reach into that epoch. Excitingly, the
first JWST science observations uncovered a surprisingly high abundance of
early star-forming galaxies. However, the distances (redshifts) of these
galaxies were, by necessity, estimated from multi-band photometry. Photometric
redshifts, while generally robust, can suffer from uncertainties and/or
degeneracies. Spectroscopic measurements of the precise redshifts are required
to validate these sources and to reliably quantify their space densities,
stellar masses, and star formation rates, which provide powerful constraints on
galaxy formation models and cosmology. Here we present the results of JWST
follow-up spectroscopy of a small sample of galaxies suspected to be amongst
the most distant yet observed. We confirm redshifts z > 10 for two galaxies,
including one of the first bright JWST-discovered candidates with z = 11.4, and
show that another galaxy with suggested z ~ 16 instead has z = 4.9, with strong
emission lines that mimic the expected colors of more distant objects. These
results reinforce the evidence for the rapid production of luminous galaxies in
the very young Universe, while also highlighting the necessity of spectroscopic
verification for remarkable candidates.Comment: Submitted to Natur
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
Uncovering a Massive z~7.65 Galaxy Hosting a Heavily Obscured Radio-Loud QSO Candidate in COSMOS-Web
In this letter, we report the discovery of the highest redshift, heavily
obscured, radio-loud QSO candidate selected using JWST NIRCam/MIRI, mid-IR,
sub-mm, and radio imaging in the COSMOS-Web field. Using multi-frequency radio
observations and mid-IR photometry, we identify a powerful, radio-loud (RL),
growing supermassive black hole (SMBH) with significant spectral steepening of
the radio SED ( mJy, ,
, ). In conjunction
with ALMA, deep ground-based observations, ancillary space-based data, and the
unprecedented resolution and sensitivity of JWST, we find no evidence of QSO
contribution to the UV/optical/NIR data and thus infer heavy amounts of
obscuration (N cm). Using the wealth of deep UV
to sub-mm photometric data, we report a singular solution photo-z of
= 7.65 and estimate an extremely massive
host-galaxy (). This
source represents the furthest known obscured RL QSO candidate, and its level
of obscuration aligns with the most representative but observationally scarce
population of QSOs at these epochs.Comment: Submitted to ApJL, Comments welcom
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
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
CEERS Key Paper. V. Galaxies at 4 < z < 9 Are Bluer than They Appear-Characterizing Galaxy Stellar Populations from Rest-frame ∼1 μm Imaging
We present results from the Cosmic Evolution Early Release Survey on the stellar population parameters for 28 galaxies with redshifts 4 < z < 9 using imaging data from the James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI) combined with data from the Hubble Space Telescope and the Spitzer Space Telescope. The JWST/MIRI 5.6 and 7.7 μm data extend the coverage of the rest-frame spectral energy distribution to nearly 1 μm for galaxies in this redshift range. By modeling the galaxies’ SEDs the MIRI data show that the galaxies have, on average, rest-frame UV (1600 Å)—I-band colors 0.4 mag bluer than derived when using photometry that lacks MIRI. Therefore, the galaxies have lower ratios of stellar mass to light. The MIRI data reduce the stellar masses by 〈 Δ log M * 〉 = 0.25 dex at 4 < z < 6 and 0.37 dex at 6 < z < 9. This also reduces the star formation rates (SFRs) by 〈ΔlogSFR〉 = 0.14 dex at 4 < z < 6 and 0.27 dex at 6 < z < 9. The MIRI data also improve constraints on the allowable stellar mass formed in early star formation. We model this using a star formation history that includes both a “burst” at z f = 100 and a slowly varying (“delayed-τ”) model. The MIRI data reduce the allowable stellar mass by 0.6 dex at 4 < z < 6 and by ≈1 dex at 6 < z < 9. Applying these results globally, this reduces the cosmic stellar-mass density by an order of magnitude in the early Universe (z ≈ 9). Therefore, observations of rest-frame ≳1 μm are paramount for constraining the stellar-mass buildup in galaxies at very high redshifts.</p