Abstract
A key component of the Dark Energy Spectroscopic Instrument (DESI) survey validation (SV) is a detailed visual inspection (VI) of the optical spectroscopic data to quantify key survey ...metrics. In this paper we present results from VI of the quasar survey using deep coadded SV spectra. We show that the majority (≈70%) of the main-survey targets are spectroscopically confirmed as quasars, with ≈16% galaxies, ≈6% stars, and ≈8% low-quality spectra lacking reliable features. A nonnegligible fraction of the quasars are misidentified by the standard spectroscopic pipeline, but we show that the majority can be recovered using post-pipeline “afterburner” quasar-identification approaches. We combine these “afterburners” with our standard pipeline to create a modified pipeline to increase the overall quasar yield. At the depth of the main DESI survey, both pipelines achieve a good-redshift purity (reliable redshifts measured within 3000 km s
−1
) of ≈99%; however, the modified pipeline recovers ≈94% of the visually inspected quasars, as compared to ≈86% from the standard pipeline. We demonstrate that both pipelines achieve a median redshift precision and accuracy of ≈100 km s
−1
and ≈70 km s
−1
, respectively. We constructed composite spectra to investigate why some quasars are missed by the standard pipeline and find that they are more host-galaxy dominated (i.e., distant analogs of “Seyfert galaxies”) and/or more dust reddened than the standard-pipeline quasars. We also show example spectra to demonstrate the overall diversity of the DESI quasar sample and provide strong-lensing candidates where two targets contribute to a single spectrum.
Abstract
Broad-line regions (BLRs) in high-redshift quasars provide crucial information on chemical enrichment in the early universe. Here we present a study of BLR metallicities in 33 quasars at ...redshift 5.7 <
z
< 6.4. Using the near-IR spectra of the quasars obtained from the Gemini telescope, we measure their rest-frame UV emission-line flux and calculate flux ratios. We then estimate BLR metallicities with empirical calibrations based on photoionization models. The inferred median metallicity of our sample is a few times the solar value, indicating that the BLR gas had been highly metal enriched at
z
∼ 6. We compare our sample with a low-redshift quasar sample with similar luminosities and find no evidence of redshift evolution in quasar BLR metallicities. This is consistent with previous studies. The Fe
ii
/Mg
ii
flux ratio, a proxy for the Fe/
α
element abundance ratio, shows no redshift evolution as well, further supporting rapid nuclear star formation at
z
∼ 6. We also find that the black hole mass–BLR metallicity relation at
z
∼ 6 is consistent with the relation measured at 2 <
z
< 5, suggesting that our results are not biased by a selection effect due to this relation.
Abstract
We present a study of the mass–metallicity relation (MZR) of 51 dwarf galaxies (
M
⋆
≈ 10
6.5
–10
9.5
M
⊙
) at
z
= 2–3 from the A2744 and SMACS J0723-3732 galaxy cluster fields. These dwarf ...galaxies are identified and confirmed by deep JWST/NIRISS imaging and slitless grism spectroscopic observations. By taking advantage of the superior performance of JWST and the gravitational lensing effect, we extend the previous MZR relation at
z
= 2–3 to a much lower-mass regime down by ≈2.5 orders of magnitude as compared with previous studies. We find that the MZR has a shallower slope at the low-mass end (
M
⋆
< 10
9
M
⊙
), with a slope turnover point of ≈10
9
M
⊙
. This implies that the dominating feedback processes in dwarf galaxies may be different from that in massive galaxies. From
z
= 3, to
z
= 2, the metallicity of the dwarf galaxies is enhanced by ≈0.09 dex for a given stellar mass, consistent with the mild evolution found in galaxies with higher mass. Furthermore, we confirm the existence of a fundamental metallicity relation (FMR) between the gas-phase metallicity, stellar mass, and star formation rate in dwarf galaxies at
z
= 2–3. Our derived FMR, which has no significant redshift evolution, can be used as a benchmark to understand the origin of the anticorrelation between the star formation rate and metallicity of dwarf galaxies in the high-
z
Universe.
We present the study of a Lyman limit system (LLS) at zabs = 1.5441 toward quasar J134122.50+185213.9 observed with VLT X-shooter. This is a very peculiar system with strong C i absorption seen ...associated with a neutral hydrogen column density of log N(H i) (cm−2) = 18.10, too small to shield the gas from any external UV flux. The low-ionization absorption lines exhibit a simple kinematic structure consistent with a single component. Using CLOUDY models to correct for ionization, we find that the ionization parameter of the gas is in the range −4.5 < log U < -4.2 and the gas density -1.5 < log n(H) (cm−3) < -1.2. The models suggest that carbon is overabundant relative to iron, C/Fe > +2.2 at Fe/H ∼-1.6. Such a metal abundance pattern is reminiscent of carbon-enhanced metal-poor stars detected in the Galaxy halo. Metal enrichment by the first generation of supernovae provide a plausible explanation for the inferred abundance pattern in this system.
Abstract
Spiral arms serve crucial purposes in star formation and galaxy evolution. In this paper, we report the identification of “A2744-DSG-
z
3,” a dusty, multiarm spiral galaxy at
z
= 3.059 using ...the James Webb Space Telescope (JWST) NIRISS imaging and grism spectroscopy. A2744-DSG-z3 was discovered as a gravitationally lensed submillimeter galaxy with the Atacama Large Millimeter/submillimeter Array (ALMA). This is the most distant stellar spiral structure seen thus far, consistent with cosmological simulations that suggest
z
≈ 3 as the epoch when spirals emerge. Thanks to the gravitational lensing and excellent spatial resolution of JWST, the spiral arms are resolved with a spatial resolution of ≈290 pc. Based on spectral energy distribution fitting, the spiral galaxy has a delensed star formation rate of 85 ± 30
M
⊙
yr
−1
, and a stellar mass of ≈10
10.6
M
⊙
, indicating that A2744-DSG-
z
3 is a main-sequence galaxy. After fitting the spiral arms, we find a stellar effective radius (
R
e,star
) of 5.0 ± 1.5 kpc. Combining with ALMA measurements, we find that the effective radii ratio between dust and stars is ≈0.4, similar to those of massive star‐forming galaxies (SFGs) at
z
∼ 2, indicating a compact dusty core in A2744-DSG-z3. Moreover, this galaxy appears to be living in a group environment: including A2744-DSG-z3, at least three galaxies at
z
= 3.05–3.06 are spectroscopically confirmed by JWST/NIRISS and ALMA, residing within a lensing-corrected projected scale of ≈70 kpc. This, along with the asymmetric brightness profile, further suggests that the spiral arms may be triggered by minor-merger events at
z
≳ 3.
Abstract
We present the first result in exploring the gaseous halo and galaxy correlation using the Dark Energy Spectroscopic Instrument survey validation data in the Cosmic Evolution Survey (COSMOS) ...and Hyper Suprime-Cam field. We obtain multiphase gaseous halo properties in the circumgalactic medium by using 115 quasar spectra (signal-to-noise ratio > 3). We detect Mg
ii
absorption at redshift 0.6 <
z
< 2.5, C
iv
absorption at 1.6 <
z
< 3.6, and H
i
absorption associated with the Mg
ii
and C
iv
. By crossmatching the COSMOS2020 catalog, we identify the Mg
ii
and C
iv
host galaxies in 10 quasar fields at 0.9<
z
< 3.1. We find that within the impact parameter of 250 kpc, a tight correlation is seen between the strong Mg
ii
equivalent width and the host galaxy star formation rate. The covering fraction
f
c
of the strong Mg
ii
selected galaxies, which is the ratio of the absorbing galaxy in a certain galaxy population, shows significant evolution in the main-sequence galaxies and marginal evolution in all the galaxy populations within 250 kpc at 0.9 <
z
< 2.2. The
f
c
increase in the main-sequence galaxies likely suggests the coevolution of strong Mg
ii
absorbing gas and the main-sequence galaxies at the cosmic noon. Furthermore, Mg
ii
and C
iv
absorbing gas is detected out of the galaxy virial radius, tentatively indicating the feedback produced by the star formation and/or the environmental effects.
To solve the problem of high temperature or long reaction time in hydrothermal synthesis of carbon dots （CDs）, a novel method based on the promoting carbonization by hydrochloric acid as catalysis ...was developed in present work. The acid catalyzed carbon dots （ACDs） were prepared facilely from tryptophan and phenylalanine at 200 ~C for 2 h. In our findings, the acids could promote significantly the formation of the ACDs＂ carbon core, as a result of the accelerating of the carbonization due to the easy deoxidation. The ACDs showed an average size of 4.8 nm, and consisted of high carbon crystalline core and various surface groups. The ACDs exhibited good optical properties and pH-dependent photoluminescence （PL） intensities. Furthermore, the ACDs were safe and biocompatible. The experimental results demonstrated that such new ACDs were connected with DNA-aptamer by EDC/NHS reaction maintaining both the bright fluorescence and recognizing ability on the cancer cells, which so could be served as an effective PL sensing platform. The resultant DNA-aptamer with ACDs （DNA-ACDs） could stick to human breast cancer cells （MCF-7） specifically, and exhibited high sensitivity and selectivity, indicating the potential applications in the cancer cells targeted imaging fields.
Abstract
We present findings of the detection of Magnesium II (Mg
ii
,
λ
= 2796, 2803 Å) absorbers from the early data release of the Dark Energy Spectroscopic Instrument (DESI). DESI is projected to ...obtain spectroscopy of approximately 3 million quasars (QSOs), of which over 99% are anticipated to be at redshifts greater than
z
> 0.3, such that DESI would be able to observe an associated or intervening Mg
ii
absorber illuminated by the background QSO. We have developed an autonomous supplementary spectral pipeline that detects these systems through an initial line-fitting process and then confirms the line properties using a Markov Chain Monte Carlo sampler. Based upon a visual inspection of the resulting systems, we estimate that this sample has a purity greater than 99%. We have also investigated the completeness of our sample in regard to both the signal-to-noise properties of the input spectra and the rest-frame equivalent width (
W
0
) of the absorber systems. From a parent catalog containing 83,207 quasars, we detect a total of 23,921 Mg
ii
absorption systems following a series of quality cuts. Extrapolating from this occurrence rate of 28.8% implies a catalog at the completion of the five-year DESI survey that will contain over eight hundred thousand Mg
ii
absorbers. The cataloging of these systems will enable significant further research because they carry information regarding circumgalactic medium environments, the distribution of intervening galaxies, and the growth of metallicity across the redshift range 0.3 ≤
z
< 2.5.
Abstract
Extremely metal-poor galaxies (XMPGs) at relatively low redshift are excellent laboratories for studying galaxy formation and evolution in the early universe. Much effort has been spent on ...identifying them from large-scale spectroscopic surveys or spectroscopic follow-up observations. Previous work has identified a few hundred XMPGs. In this work, we obtain a large sample of 223 XMPGs at
z
< 1 from the early data of the Dark Energy Spectroscopic Instrument (DESI). The oxygen abundance is determined using the direct
T
e
method based on the detection of the O
iii
λ
4363 line. The sample includes 95 confirmed XMPGs based on the oxygen abundance uncertainty; the remaining 128 galaxies are regarded as XMPG candidates. These XMPGs are only 0.01% of the total DESI observed galaxies. Their coordinates and other properties are provided in the paper. The most XMPGs have an oxygen abundance of ∼1/34
Z
⊙
, a stellar mass of about 1.5 × 10
7
M
⊙,
and a star formation rate of 0.22
M
⊙
yr
−1
. The two most XMPGs present distinct morphologies suggesting different formation mechanisms. The local environmental investigation shows that XMPGs preferentially reside in relatively low-density regions. Many of them fall below the stellar mass–metallicity relations (MZRs) of normal star-forming galaxies. From a comparison of the MZR with theoretical simulations, it appears that XMPGs are good analogs to high-redshift star-forming galaxies. The nature of these XMPG populations will be further investigated in detail with larger and more complete samples from the ongoing DESI survey.
Abstract
Direct observations of low-mass, low-metallicity galaxies at
z
≳ 4 provide an indispensable opportunity for detailed inspection of the ionization radiation, gas flow, and metal enrichment in ...sources similar to those that reionized the universe. Combining the James Webb Space Telescope (JWST), Very Large Telescope/MUSE, and Atacama Large Millimeter/submillimeter Array, we present detailed observations of a strongly lensed, low-mass (≈10
7.6
M
⊙
) galaxy at
z
= 3.98 (also see Vanzella et al.). We identify strong narrow nebular emission, including C
iv
λ
λ
1548, 1550, He
ii
λ
1640, O
iii
λ
λ
1661, 1666, Ne
iii
λ
3868, O
ii
λ
3727, and the Balmer series of hydrogen from this galaxy, indicating a metal-poor H
ii
region (≲0.12
Z
⊙
) powered by massive stars. Further, we detect a metal-enriched damped Ly
α
system (DLA) associated with the galaxy with the H
i
column density of
N
H I
≈ 10
21.8
cm
−2
. The metallicity of the associated DLA may reach the supersolar metallicity (≳
Z
⊙
). Moreover, thanks to JWST and gravitational lensing, we present the resolved UV slope (
β
) map at the spatial resolution of ≈100 pc at
z
= 4, with steep UV slopes reaching
β
≈ −2.5 around three star-forming clumps. Combining with low-redshift analogs, our observations suggest that low-mass, low-metallicity galaxies, which dominate reionization, could be surrounded by a high covering fraction of the metal-enriched, neutral-gaseous clouds. This implies that the metal enrichment of low-mass galaxies is highly efficient, and further supports that in low-mass galaxies, only a small fraction of ionizing radiation can escape through the interstellar or circumgalactic channels with low-column-density neutral gas.
PDF
