Abstract Deep surveys with the James Webb Space Telescope (JWST) have revealed an emergent population of moderate-luminosity, broad-line active galactic nuclei (AGNs) at 4 ≲ z ≲ 13 powered by ...accretion onto early massive black holes. The high number densities reported, together with the large Lyman-continuum (LyC) production efficiency and leakiness into the intergalactic medium that are typical of UV-selected AGNs, lead us to reassess a scenario where AGNs are the sole drivers of the cosmic hydrogen/helium reionization process. Our approach is based on the assumptions, grounded in recent observations, that (a) the fraction of broad-line AGNs among galaxies is around 10%–15%; (b) the mean escape fraction of hydrogen LyC radiation is high, at ≳80%, in AGN hosts and is negligible otherwise; and (c) internal absorption at 4 ryd or a steep ionizing EUV spectrum delay full reionization of He ii until z ≃ 2.8–3.0, in agreement with observations of the He ii Ly α forest. In our fiducial models, (1) hydrogen reionization is 99% completed by redshift z ≃ 5.3–5.5 and reaches its midpoint at z ≃ 6.5–6.7; (2) the integrated Thomson scattering optical depth to reionization is ≃0.05, consistent with constraints from cosmic microwave background anisotropy data; and (3) the abundant AGN population detected by JWST does not violate constraints on the unresolved X-ray background.
ABSTRACT
A wealth of extragalactic populations completely missed at UV-optical wavelengths has been identified in the last decade, combining the deepest HST and Spitzer observations. These dark ...sources are thought to be dusty and star-forming systems at 3 < z < 5, and major contributors to the stellar mass build up. In this letter, we report an investigation of the deep JWST survey in the SMACS0723 cluster, analysing NIRCam and MIRI images. We search for sources in the F444W band that are undetected in the F200W catalogues. We characterize the properties of these sources via detailed Spectral Energy Distribution (SED) modelling, accounting for a wide set of parameters and star formation histories, after a careful determination of their photometry. Among a robust sample of 20 candidates, we identify a mixed population of very red sources. We highlight the identification of evolved systems, with stellar masses M* ∼ 109–11 M⊙ at 8 < z < 13 characterized by unexpectedly important dust content at those epochs (AV up to ∼5.8 mag), challenging current model predictions. We further identify an extremely red source (F200W-F440W ∼ 7 mag) that can be reproduced only by the spectrum of a passive, quenched galaxy of M* ∼ 1011.56 M⊙ at z ∼ 5, filled of dust (AV ∼ 5 mag).
Abstract
The origins of Lyman continuum (LyC) photons responsible for the reionization of the universe are as of yet unknown and highly contested. Detecting LyC photons from the Epoch of Reionization ...is not possible due to absorption by the intergalactic medium, which has prompted the development of several indirect diagnostics to infer the rate at which galaxies contribute LyC photons to reionize the universe by studying lower-redshift analogs. We present the Low-redshift Lyman Continuum Survey (LzLCS) comprising measurements made with the Hubble Space Telescope Cosmic Origins Spectrograph for a
z
= 0.2–0.4 sample of 66 galaxies. After careful processing of the far-UV spectra, we obtain a total of 35 Lyman continuum emitters (LCEs) detected with 97.725% confidence, nearly tripling the number of known local LCEs. We estimate escape fractions from the detected LyC flux and upper limits on the undetected LyC flux, finding a range of LyC escape fractions up to 50%. Of the 35 LzLCS LCEs, 12 have LyC escape fractions greater than 5%, more than doubling the number of known local LCEs with cosmologically relevant LyC escape.
We investigate the relation between star formation rate (SFR) and stellar mass (M), i.e., the main sequence (MS) relation of star-forming galaxies, at in the first four Hubble Space Telescope (HST) ...Frontier Fields, on the basis of rest-frame UV observations. Gravitational lensing combined with deep HST observations allows us to extend the analysis of the MS down to at and at higher redshifts, a factor of ∼10 below most previous results. We perform an accurate simulation to take into account the effect of observational uncertainties and correct for the Eddington bias. This step allows us to reliably measure the MS and in particular its slope. While the normalization increases with redshift, we fit an unevolving and approximately linear slope. We nicely extend to lower masses the results of brighter surveys. Thanks to the large dynamic range in mass and by making use of the simulation, we analyzed any possible mass dependence of the dispersion around the MS. We find tentative evidence that the scatter decreases with increasing mass, suggesting a larger variety of star formation histories in low-mass galaxies. This trend agrees with theoretical predictions and is explained as either a consequence of the smaller number of progenitors of low-mass galaxies in a hierarchical scenario and/or of the efficient but intermittent stellar feedback processes in low-mass halos. Finally, we observe an increase in the SFR per unit stellar mass with redshift milder than predicted by theoretical models, implying a still incomplete understanding of the processes responsible for galaxy growth.
Abstract
Motivated by evidences favoring a rapid and late hydrogen reionization process completing at
z
∼ 5.2–5.5 and mainly driven by rare and luminous sources, we have reassessed the estimate of ...the space density of ultra-luminous QSOs at
z
∼ 5 in the framework of the QUBRICS survey. A ∼ 90% complete sample of 14 spectroscopically confirmed QSOs at
M
1450
≤ −28.3 and 4.5 ≤
z
≤ 5.0 has been derived in an area of 12,400 deg
2
, thanks to multiwavelength selection and Gaia astrometry. The space density of
z
∼ 5 QSOs within −29.3 ≤
M
1450
≤ −28.3 is three times higher than previous determinations. Our results suggest a steep bright-end slope for the QSO luminosity function at
z
∼ 5 and a mild redshift evolution of the space density of ultrabright QSOs (
M
1450
∼ −28.5) at 3 <
z
< 5.5, in agreement with the redshift evolution of the much fainter active galactic nucleus (AGN) population at
M
1450
∼ −23. These findings are consistent with a pure density evolution for the AGN population at
z
> 3. Adopting our
z
∼ 4 QSO luminosity function and applying a mild density evolution in redshift, a photoionization rate of
Γ
HI
=
0.46
−
0.09
+
0.17
×
10
−
12
s
−
1
has been obtained at
z
= 4.75, assuming an escape fraction of ∼70% and a steep faint-end slope of the AGN luminosity function. The derived photoionization rate is ∼50–100% of the ionizing background measured at the end of the reionization epoch, suggesting that AGNs could play an important role in the cosmological reionization process.
Abstract
Based on results by recent surveys, the number of bright quasars at redshifts
z
> 3 is being constantly revised upward. The current consensus is that at bright magnitudes (
M
1450
≤ −27) the ...number densities of such sources could have been underestimated by a factor of 30%–40%. In the framework of the QUBRICS survey, we identified 58 bright QSOs at 3.6 ≤
z
≤ 4.2, with magnitudes
i
psf
≤ 18, in an area of 12400 deg
2
. The uniqueness of our survey is underlined by the fact that it allows us, for the first time, to extend the sampled absolute magnitude range up to
M
1450
= −29.5. We derived a bright-end slope of
β
= −4.025 and a space density at 〈
M
1450
〉 = −28.75 of 2.61 × 10
−10
Mpc
−3
comoving, after taking into account the estimated incompleteness of our observations. Taking into account the results of fainter surveys, active galactic nuclei (AGNs) brighter than
M
1450
= −23 could produce at least half of the ionizing emissivity at
z
∼ 4. Considering a mean escape fraction of 0.7 for the QSO and AGN population, combined with a mean free path of 41.3 proper Mpc at
z
= 3.9, we derive a photoionization rate of
, produced by AGNs at
M
1450
< −18, that is, ∼100% of the measured ionizing background at
z
∼ 4.
Abstract
The relationship between galaxy characteristics and the reionization of the universe remains elusive, mainly due to the observational difficulty in accessing the Lyman continuum (LyC) at ...these redshifts. It is thus important to identify low-redshift LyC-leaking galaxies that can be used as laboratories to investigate the physical processes that allow LyC photons to escape. The weakness of the S
ii
nebular emission lines relative to typical star-forming galaxies has been proposed as a LyC predictor. In this paper, we show that the S
ii
deficiency is an effective method to select LyC-leaking candidates using data from the Low-redshift LyC Survey, which has detected flux below the Lyman edge in 35 out of 66 star-forming galaxies with the Cosmic Origins Spectrograph on board the Hubble Space Telescope. We show that LyC leakers tend to be more S
ii
deficient and that the fraction of their detections increases as S
ii
deficiency becomes more prominent. Correlational studies suggest that S
ii
deficiency complements other LyC diagnostics (such as strong Ly
α
emission and high O
iii
/O
ii
). Our results verify an additional technique by which reionization-era galaxies could be studied.
Crossing the Rubicon of Reionization with z ∼ 5 QSOs Grazian, Andrea; Boutsia, Konstantina; Giallongo, Emanuele ...
Astrophysical journal/The Astrophysical journal,
09/2023, Volume:
955, Issue:
1
Journal Article
Peer reviewed
Open access
Abstract
One of the key open questions in cosmology is the nature of sources that completed cosmological hydrogen reionization at
z
∼ 5.2. High-
z
primeval galaxies have been long considered the main ...drivers of reionization, with a minor role played by high-
z
active galactic nuclei (AGN). However, in order to confirm this scenario, it is fundamental to measure the photoionization rate produced by active SMBHs close to the Epoch of Reionization. Given the pivotal role played by spectroscopically complete observations of high-
z
QSOs, in this paper we present the first results of the RUBICON (Reionizing the Universe with Bright Cosmological Nuclei) survey. It consists of a color-selected sample of bona fide
z
∼ 5 QSO candidates from the Hyper Suprime-Cam Subaru Strategic Survey. Our QSO candidates have been validated both by photometric redshifts based on spectral energy distribution fitting and by spectroscopic redshifts, confirming that they lie at 4.5 <
z
spec
< 5.2. A relatively high space density of QSOs (Φ ∼ 1.4 × 10
−8
c Mpc
−3
) is thus confirmed at
z
∼ 5 and
M
1450
∼ −27, consistent with a pure density evolution of the AGN luminosity function from
z
= 4 to
z
= 5, with a mild density evolution rate of 0.25 dex. This indicates that AGN could play a nonnegligible role in cosmic reionization. The Rubicon of reionization has been crossed.
Abstract
We present a large-scale galaxy structure Cl J021734−0513 at z ∼ 0.65 discovered in the UKIDSS UDS field, made of ∼20 galaxy groups and clusters, spreading over 10 Mpc. We report on a ...VLT/VIMOS spectroscopic follow-up program that, combined with past spectroscopy, allowed us to confirm four galaxy clusters (M200 ∼ 1014 M⊙) and a dozen associated groups and star-forming galaxy overdensities. Two additional filamentary structures at z ∼ 0.62 and 0.69 and foreground and background clusters at 0.6 < z < 0.7 were also confirmed along the line of sight. The structure subcomponents are at different formation stages. The clusters have a core dominated by passive galaxies and an established red sequence. The remaining structures are a mix of star-forming galaxy overdensities and forming groups. The presence of quiescent galaxies in the core of the latter shows that ‘pre-processing’ has already happened before the groups fall into their more massive neighbours. Our spectroscopy allows us to derive spectral index measurements e.g. emission/absorption line equivalent widths, strength of the 4000 Å break, valuable to investigate the star formation history of structure members. Based on these line measurements, we select a population of ‘post-starburst’ galaxies. These galaxies are preferentially found within the virial radius of clusters, supporting a scenario in which their recent quenching could be prompted by gas stripping by the dense intracluster medium. We derive stellar age estimates using Markov Chain Monte Carlo-based spectral fitting for quiescent galaxies and find a correlation between ages and colours/stellar masses which favours a top–down formation scenario of the red sequence. A catalogue of ∼650 redshifts in UDS is released alongside the paper (via MNRAS online data).
A new set of color selection criteria (VJL) analogous with the BzK method is designed to select both star-forming galaxies (SFGs) and passively evolving galaxies (PEGs) at 2.3 <, ~ z <, ~ 3.5 by ...using rest-frame UV-optical (V - J versus J - L) colors. The criteria are thoroughly tested with theoretical stellar population synthesis models and real galaxies with spectroscopic redshifts to evaluate their efficiency and contamination. We apply the well-tested VJL criteria to the HST/WFC3 Early Release Science field and study the physical properties of selected galaxies. The redshift distribution of selected SFGs peaks at z ~ 2.7, slightly lower than that of Lyman break galaxies at z ~ 3. Comparing the observed mid-infrared fluxes of selected galaxies with the prediction of pure stellar emission, we find that our VJL method is effective at selecting massive dusty SFGs that are missed by the Lyman break technique. About half of the star formation in massive (M sub(star) > 10 super(10) M sub(middot in circle)) galaxies at 2.3 <, ~ z <, ~ 3.5 is contributed by dusty (extinction E(B - V) > 0.4) SFGs, which, however, only account for ~20% of the number density of massive SFGs. We also use the mid-infrared fluxes to clean our PEG sample and find that galaxy size can be used as a secondary criterion to effectively eliminate the contamination of dusty SFGs. The redshift distribution of the cleaned PEG sample peaks at z ~ 2.5. We find six PEG candidates at z > 3 and discuss possible methods to distinguish them from dusty contamination. We conclude that at least part of our candidates are real PEGs at z ~ 3, implying that these types of galaxies began to form their stars at z > ~ 5. We measure the integrated stellar mass density (ISMD) of PEGs at z ~ 2.5 and set constraints on it at z > 3. We find that the ISMD grows by at least about a factor of 10 in 1 Gyr at 3 < z <5 and by another factor of 10 in the next 3.5 Gyr (1 < z < 3).
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