scholarly journals Ionizing radiation from AGNs at z > 3.3 with the Subaru Hyper Suprime-Cam Survey and the CFHT Large Area U-band Deep Survey (CLAUDS)

2021 ◽  
Author(s):  
Ikuru Iwata ◽  
Marcin Sawicki ◽  
Akio K Inoue ◽  
Masayuki Akiyama ◽  
Genoveva Micheva ◽  
...  
Keyword(s):  
Ionizing Radiation ◽  
Luminosity Function ◽  
Flux Ratio ◽  
Imaging Data ◽  
Large Area ◽  
Lyman Continuum ◽  
Deep Survey ◽  
Average Flux ◽  
Strategic Program ◽  
Uv Photons

Abstract We use deep and wide imaging data from the CFHT Large Area U-band Deep Survey (CLAUDS) and the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) to constrain the ionizing radiation (Lyman Continuum; LyC) escape fraction from AGNs at z ∼ 3–4. For 94 AGNs with spectroscopic redshifts at 3.3 < z < 4.0, we use their U-band / i-band flux ratios to estimate LyC transmission of individual AGNs. The distribution of their LyC transmission shows values lower than the range of LyC transmission values for IGM of the same redshift range, which suggests that LyC escape fraction of AGNs at z > 3.3 is considerably lower than unity in most cases. We do not find any trend in LyC transmission values depending on their UV luminosities. Based on the photometry of stacked images we find the average flux ratio of LyC and non-ionizing UV photons escaping from the objects (fLyC/fUV)out = 0.182 ± 0.043 for AGNs at 3.3 < z < 3.6, which corresponds to LyC escape fraction fesc = 0.303 ± 0.072 if we assume a fiducial intrinsic SED of AGN. Based on the estimated LyC escape fraction and the UV luminosity function of AGNs, we argue that UV-selected AGNs’ contribution to the LyC emissivity at the epoch is minor, although the size of their contribution largely depends on the shape of the UV luminosity function.

scholarly journals The CFHT Large Area U-band Deep Survey (CLAUDS)

2019 ◽  
Author(s):  
Marcin Sawicki ◽  
Stephane Arnouts ◽  
Jiasheng Huang ◽  
Jean Coupon ◽  
Anneya Golob ◽  
...  
Keyword(s):  
Data Reduction ◽  
Large Area ◽  
Photometric Redshifts ◽  
Data Merging ◽  
Deep Survey ◽  
Strategic Program ◽  
Number Counts

Abstract The Canada-France-Hawaii Telescope (CFHT) Large Area U-band Deep Survey (CLAUDS) uses data taken with the MegaCam mosaic imager on CFHT to produce images of 18.60 deg2 with median seeing of FWHM=0.92″ and to a median depth of U = 27.1 AB (5σ in 2″ apertures), with selected areas that total 1.36 deg2 reaching a median depth of U = 27.7 AB. These are the deepest U-band images assembled to date over this large an area. These data are located in four fields also imaged to comparably faint levels in grizy and several narrowband filters as part of the Hyper Suprime-Cam (HSC) Subaru Strategic Program (HSC-SSP). These CFHT and Subaru datasets will remain unmatched in their combination of area and depth until the advent of the Large Synoptic Survey Telescope (LSST). This paper provides an overview of the scientific motivation for CLAUDS and gives details of the observing strategy, observations, data reduction, and data merging with the HSC-SSP. Three early applications of these deep data are used to illustrate the potential of the dataset: deep U-band galaxy number counts, z∼3 Lyman break galaxy (LBG) selection, and photometric redshifts improved by adding CLAUDS U to the Subaru HSC grizy photometry.

scholarly journals Outside the Lyman-break box: detecting Lyman continuum emitters at 3.5 < z < 5.1 with CLAUDS

2020 ◽  
Vol 494 (4) ◽  
pp. 4986-5007 ◽  
Author(s):  
U Meštrić ◽  
E V Ryan-Weber ◽  
J Cooke ◽  
R Bassett ◽  
M Sawicki ◽  
...  
Keyword(s):  
Intergalactic Medium ◽  
Hubble Space Telescope ◽  
High Redshift ◽  
Large Area ◽  
Redshift Range ◽  
Space Telescope ◽  
High Redshift Galaxies ◽  
Lyman Continuum ◽  
Deep Survey ◽  
Individual Galaxies

ABSTRACT Identifying non-contaminated sample of high-redshift galaxies with escaping Lyman continuum (LyC) flux is important for understanding the sources and evolution of cosmic reionization. We present CLAUDS (CFHT Large Area u-band deep survey) u-band photometry of the COSMOS field to probe LyC radiation from spectroscopically confirmed galaxies at $z$ ≥ 3.5 and outside the standard Lyman-break galaxy colour-selection expectations. Complementary to the CLAUDS data, we use Subaru multifilter photometry, Hubble Space Telescope (HST) multifilter imaging, and the spectroscopic surveys D10K, VUDS, and 3D-HST. We present a sample of Lyman continuum galaxy (LCG) candidates in the redshift range 3.5 ≲ $z$ ≲ 5.1. Here, we introduce 5 LCG candidates, where two are flagged quality 1 and three quality 2. The estimated $f_{\rm esc}^{\rm abs}$ for quality 1 candidates are in the range $\sim 5 - 73{{\ \rm per\ cent}}$ and $\sim 30 - 93{{\ \rm per\ cent}}$. These estimates are based on our derived parameters from individual galaxies as inputs to a range of BPASS models as well as mean intergalactic medium (IGM) and maximal intergalactic and circumgalactic media (IGM+CGM) transmission. We conclude that our search for LCGs is most likely biased to lines of sight with low H i densities or free from Lyman limit systems. Our two best LCG candidates have EW (Lyα) ≤ 50 Å and we find no correlation or anticorrelation between EW (Lyα), $f_{\rm esc}^{\rm abs}$, and Robs, the ratio of ionizing to non-ionizing observed flux in the measured passbands. Stacking candidates without solid LyC detections (S/N &lt; 3) results in an estimated $f_{\rm esc}^{\rm abs}$ from galaxies not greater than $1{{\ \rm per\ cent}}$.

scholarly journals UV and U-band luminosity functions from CLAUDS and HSC-SSP – I. Using four million galaxies to simultaneously constrain the very faint and bright regimes to z ∼ 3

2020 ◽  
Vol 494 (2) ◽  
pp. 1894-1918
Author(s):  
Thibaud Moutard ◽  
Marcin Sawicki ◽  
Stéphane Arnouts ◽  
Anneya Golob ◽  
Jean Coupon ◽  
...  
Keyword(s):  
Galaxy Evolution ◽  
Rest Frame ◽  
Characteristic Number ◽  
Number Density ◽  
Large Area ◽  
Luminosity Functions ◽  
Deep Survey ◽  
Strategic Program

ABSTRACT We constrain the rest-frame FUV (1546 Å), NUV (2345 Å), and U-band (3690 Å) luminosity functions (LFs) and luminosity densities (LDs) with unprecedented precision from z ∼ 0.2 to z ∼ 3 (FUV, NUV) and z ∼ 2 (U band). Our sample of over 4.3 million galaxies, selected from the CFHT Large Area U-band Deep Survey (CLAUDS) and HyperSuprime-Cam Subaru Strategic Program (HSC-SSP) data lets us probe the very faint regime (down to MFUV, MNUV, MU ≃ −15 at low redshift), while simultaneously detecting very rare galaxies at the bright end down to comoving densities &lt;10−5 Mpc−3. Our FUV and NUV LFs are well fitted by single-Schechter functions, with faint-end slopes that are very stable up to z ∼ 2. We confirm, but self-consistently and with much better precision than previous studies, that the LDs at all three wavelengths increase rapidly with lookback time to z ∼ 1, and then much more slowly at 1 &lt; z &lt; 2–3. Evolution of the FUV and NUV LFs and LDs at z &lt; 1 is driven almost entirely by the fading of the characteristic magnitude, $M^\star _{\rm UV}$, while at z &gt; 1 it is due to the evolution of both $M^\star _{\rm UV}$ and the characteristic number density $\phi ^\star _{\rm UV}$. In contrast, the U-band LF has an excess of faint galaxies and is fitted with a double-Schechter form; $M^\star _{U}$, both $\phi ^\star _{U}$ components, and the bright-end slope evolve throughout 0.2 &lt; z &lt; 2, while the faint-end slope is constant over at least the measurable 0.05 &lt; z &lt; 0.6. We present tables of our Schechter parameters and LD measurements that can be used for testing theoretical galaxy evolution models and forecasting future observations.

scholarly journals Accurately predicting the escape fraction of ionizing photons using rest-frame ultraviolet absorption lines

2018 ◽  
Vol 616 ◽  
pp. A30 ◽  
Author(s):  
J. Chisholm ◽  
S. Gazagnes ◽  
D. Schaerer ◽  
A. Verhamme ◽  
J. R. Rigby ◽  
...  
Keyword(s):  
Early Universe ◽  
Rest Frame ◽  
High Redshift ◽  
Flux Ratio ◽  
Companion Paper ◽  
Absorption Lines ◽  
Indirect Methods ◽  
High Redshift Galaxies ◽  
Lyman Continuum ◽  
Redshift Galaxies

The fraction of ionizing photons that escape high-redshift galaxies sensitively determines whether galaxies reionized the early Universe. However, this escape fraction cannot be measured from high-redshift galaxies because the opacity of the intergalactic medium is large at high redshifts. Without methods to measure the escape fraction of high-redshift galaxies indirectly, it is unlikely that we will know what reionized the Universe. Here, we analyze the far-ultraviolet (UV) H I (Lyman series) and low-ionization metal absorption lines of nine low-redshift, confirmed Lyman continuum emitting galaxies. We use the H I covering fractions, column densities, and dust attenuations measured in a companion paper to predict the escape fraction of ionizing photons. We find good agreement between the predicted and observed Lyman continuum escape fractions (within 1.4σ) using both the H I and ISM absorption lines. The ionizing photons escape through holes in the H I, but we show that dust attenuation reduces the fraction of photons that escape galaxies. This means that the average high-redshift galaxy likely emits more ionizing photons than low-redshift galaxies. Two other indirect methods accurately predict the escape fractions: the Lyα escape fraction and the optical [O III]/[O II] flux ratio. We use these indirect methods to predict the escape fraction of a sample of 21 galaxies with rest-frame UV spectra but without Lyman continuum observations. Many of these galaxies have low escape fractions (fesc ≤ 1%), but 11 have escape fractions >1%. Future studies will use these methods to measure the escape fractions of high-redshift galaxies, enabling upcoming telescopes to determine whether star-forming galaxies reionized the early Universe.

How much is the effective dose from medical imaging in pediatric patients in the neurosurgery department?

2021 ◽  
Author(s):  
B. Zeinali-Rafsanjani ◽  
S. Haseli ◽  
R. Jalli ◽  
M. Saeedi-Moghadam
Keyword(s):  
Medical Imaging ◽  
Ionizing Radiation ◽  
Ct Scan ◽  
Effective Dose ◽  
Pediatric Patients ◽  
Ct Scans ◽  
Imaging Data ◽  
Plain Radiographs ◽  
Brain Ct ◽  
Abdomen Ct

Medical imaging with ionizing radiation in pediatric patients is rising, and their radiation sensitivity is 2–3 times more than adults. The objective of this study was to estimate the total effective dose (ED) of all medical imaging by CT scan and plain radiography in patients in pediatric neurosurgery department. Patients with at least one brain CT scan and recorded dose length product (DLP) were included. Patients’ imaging data were collected from the picture-archiving-and-communicating system (PACS) using their national code to find all their medical imaging. Total ED (mSv) from CT scans and plain radiographs were calculated. A total of 300 patients were included, of which 129 were females and 171 males with a mean age of 5.45 ± 4.34 years. Mean DLPs of brain, abdomen, and chest CT were 329.16, 393.06, 284.46 mGy.cm. The most frequent CT scans in these children were brain CT scans with ED range of 0.09 to 47.09 mSv. Total ED due to all CT scans and plain radiographs were in the range of 0.38 to 63.41 mSv. Although the mean DLP of each brain, chest, and abdomen CT of patients was in the range of DRLs reported by previous studies, the patients with numerous CT scans received more radiation doses than mean ED (6.21 mSv between all age groups). The most frequent CT scan was the brain, and the most frequent plain radiographs were chest and lower extremities. It can be concluded that reducing the number of CT scans or plain radiographs by appropriate physical exams or replacing them with modalities that do not use ionizing radiation can reduce ED.

scholarly journals The Ionization of Planetary Nebulae

1968 ◽  
Vol 34 ◽  
pp. 190-204 ◽  
Author(s):  
Robert E. Williams
Keyword(s):  
Ionizing Radiation ◽  
Emission Line ◽  
Radiation Field ◽  
Planetary Nebulae ◽  
Model Atmosphere ◽  
Evolutionary Sequence ◽  
Lyman Continuum ◽  
The Mean ◽  
Central Stars

The ionization of the most abundant elements in planetary nebulae has been determined for a number of models of nebulae at different epochs in their expansion. The values used for the temperatures and radii of the central stars and the sizes and densities of the shells have come from Seaton's evolutionary sequence. The ionizing radiation field has been taken from model atmosphere calculations of the central stars by Gebbie and Seaton, and Böhm and Deinzer. Emission-line fluxes have been calculated for the models and compared with observations of planetary nebulae by O'Dell, Osterbrock's group, and Aller and his collaborators. Results indicate that the central stars have strong He+ Lyman continuum excesses, similar to those predicted by Gebbie and Seaton. The mean abundance determinations for the nebulae made by Aller are confirmed, with the exception of nitrogen, which appears to be 3 or 4 times more abundant than his value. It is also seen that the electron temperatures of the nebulae are higher than previous theoretical determinations, providing better agreement with empirically derived values.

scholarly journals Prediction of H α and [O iii] emission line galaxy number counts for future galaxy redshift surveys

2019 ◽  
Vol 490 (3) ◽  
pp. 3667-3678 ◽  
Author(s):  
Zhongxu Zhai ◽  
Andrew Benson ◽  
Yun Wang ◽  
Gustavo Yepes ◽  
Chia-Hsun Chuang
Keyword(s):  
Emission Line ◽  
Galaxy Formation ◽  
Luminosity Function ◽  
Large Scale ◽  
High Redshift ◽  
Flux Ratio ◽  
Formation Model ◽  
Line Flux ◽  
Emission Line Galaxies ◽  
Number Counts

ABSTRACT We perform a simulation with Galacticus, a semi-analytical galaxy formation model, to predict the number counts of H α and [O iii] emitting galaxies. With a state-of-the-art N-body simulation, UNIT, we first calibrate Galacticus with the current observation of H α luminosity function. The resulting model coupled with a dust attenuation model, can reproduce the current observations, including the H α luminosity function from HiZELS and number density from WISP. We extrapolate the model prediction to higher redshift and the result is found to be consistent with previous investigations. We then use the same galaxy formation model to predict the number counts for [O iii] emitting galaxies. The result provides further validation of our galaxy formation model and dust model. We present number counts of H α and [O iii] emission line galaxies for three different line flux limits: 5 × 10−17erg s−1 cm−2, 1 × 10−16 erg s−1 cm−2 (6.5σ nominal depth for WFIRST GRS), and 2 × 10−16 erg s−1 cm−2 (3.5σ depth of Euclid GRS). At redshift 2 &lt; z &lt; 3, our model predicts that WFIRST can observe hundreds of [O iii] emission line galaxies per square degree with a line flux limit of 1 × 10−16 erg s−1 cm−2. This will provide accurate measurement of large-scale structure to probe dark energy over a huge cosmic volume to an unprecedented high redshift. Finally, we compare the flux ratio of H α/[O iii] within the redshift range of 0 &lt; z &lt; 3. Our results show the known trend of increasing H α/[O iii] flux ratio with H α flux at low redshift, which becomes a weaker trend at higher redshifts.

scholarly journals The WIRCam Ultra Deep Survey (WUDS)

2018 ◽  
Vol 620 ◽  
pp. A51 ◽  
Author(s):  
R. Pelló ◽  
P. Hudelot ◽  
N. Laporte ◽  
Y. Mellier ◽  
H. J. McCracken ◽  
...  
Keyword(s):  
Luminosity Function ◽  
Formation Rate ◽  
Forthcoming Paper ◽  
Spectroscopic Studies ◽  
Photometric Redshifts ◽  
Near Ir ◽  
Luminosity Functions ◽  
The Galaxy ◽  
Deep Survey ◽  
Galaxy Population

The aim of this paper is to introduce the WIRCam Ultra Deep Survey (WUDS), a near-IR photometric survey carried out at the CFH Telescope in the field of the CFHTLS-D3 field (Groth Strip). WUDS includes four near-IR bands (Y, J, H and Ks) over a field of view of ∼400 arcmin2. The typical depth of WUDS data reaches between ∼26.8 in Y and J, and ∼26 in H and Ks (AB, 3σ in 1.3″ aperture), whereas the corresponding depth of the CFHTLS-D3 images in this region ranges between 28.6 and 29 in ugr, 28.2 in i and 27.1 in z (same S/N and aperture). The area and depth of this survey were specifically tailored to set strong constraints on the cosmic star formation rate and the luminosity function brighter or around L⋆ in the z ∼ 6 − 10 redshift domain, although these data are also useful for a variety of extragalactic projects. This first paper is intended to present the properties of the public WUDS survey in details: catalog building, completeness and depth, number counts, photometric redshifts, and global properties of the galaxy population. We have also concentrated on the selection and characterization of galaxy samples at z ∼ [4.5 − 7] in this field. For these purposes, we include an adjacent shallower area of ∼1260 arcmin2 in this region, extracted from the WIRCam Deep Survey (WIRDS), and observed in J, H and Ks bands. UV luminosity functions were derived at z ∼ 5 and z ∼ 6 taking advantage from the fact that WUDS covers a particularly interesting regime at intermediate luminosities, which allows a combined determination of M⋆ and Φ⋆ with increased accuracy. Our results on the luminosity function are consistent with a small evolution of both M⋆ and Φ⋆ between z = 5 and z = 6, irrespective of the method used to derive them, either photometric redshifts applied to blindly-selected dropout samples or the classical Lyman Break Galaxy color-preselected samples. Our results lend support to higher Φ⋆ determinations at z = 6 than usually reported. The selection and combined analysis of different galaxy samples at z ≥ 7 will be presented in a forthcoming paper, as well as the evolution of the UV luminosity function between z ∼ 4.5 and 9. WUDS is intended to provide a robust database in the near-IR for the selection of targets for detailed spectroscopic studies, in particular for the EMIR/GTC GOYA Survey.

scholarly journals Lyman continuum escape fraction and mean free path of hydrogen ionizing photons for bright z ∼ 4 QSOs from SDSS DR14

2019 ◽  
Vol 632 ◽  
pp. A45 ◽  
Author(s):  
M. Romano ◽  
A. Grazian ◽  
E. Giallongo ◽  
S. Cristiani ◽  
F. Fontanot ◽  
...  
Keyword(s):  
Distribution Function ◽  
Free Path ◽  
Rest Frame ◽  
Rapid Evolution ◽  
Cosmic Time ◽  
Flux Ratio ◽  
Mean Free Path ◽  
Skewed Distribution ◽  
Observational Cosmology ◽  
Lyman Continuum

Context. One of the main challenges in observational cosmology is related to the redshift evolution of the average hydrogen (HI) ionization in the Universe, as evidenced by the changing in ionization level of the intergalactic medium (IGM) through cosmic time. Starting from the first cosmic reionization, the rapid evolution of the IGM physical properties in particular poses severe constraints for the identification of the sources responsible for maintaining its high level of ionization up to lower redshifts. Aims. In order to probe the ionization level of the IGM and the ionization capabilities of bright quasi-stellar objects (QSOs) at z = 4, we selected a sample of 2508 QSOs drawn from the Sloan Digital Sky Survey (SDSS, DR14) in the redshift interval 3.6 ≤ z ≤ 4.6 and absolute magnitude range −29.0 ≲ M1450 ≲ −26.0. Particularly, we focus on the estimate of the escape fraction of HI-ionizing photons and their mean free path (MFP), which are fundamental for characterizing the surrounding IGM. Methods. Starting from UV/optical rest-frame spectra of the whole QSO sample from the SDSS survey, we estimated the escape fraction and free path individually for each of the QSOs. We calculated the Lyman continuum (LyC) escape fraction as the flux ratio blueward (∼900 Å rest frame) and redward (∼930 Å rest frame) of the Lyman limit. We then obtained the probability distribution function (PDF) of the individual free paths of the QSOs in the sample and studied its evolution in luminosity and redshift, comparing our results with those in literature. Results. We find a lower limit to the mean LyC escape fraction of 0.49, in agreement with the values obtained for both brighter and fainter sources at the same redshift. We show that the free paths of ionizing photons are characterized by a skewed distribution function that peaks at low values, with an average of ∼49 − 59 proper Mpc at z ∼ 4, after possible associated absorbers (AAs) were excluded. This value is higher than the one obtained at the same redshift by many authors in the literature using different techniques. Moreover, the PDF of free path gives information that is complementary to the MFP derived through the stacking technique. Finally, we also find that the redshift evolution of this parameter might be milder than previously thought. Conclusions. Our new determination of the MFP at z ∼ 4 implies that previous estimates of the HI photoionization rate ΓHI available in the literature should be corrected by a factor of 1.2−1.7. These results have important implications when they are extrapolated at the epoch of reionization.

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