Ultraviolet Background Radiation Research Articles

A comprehensive model for the formation and evolution of the faintest Milky Way dwarf satellites

ABSTRACT In this study, we modify the semi-analytic model galacticus in order to accurately reproduce the observed properties of dwarf galaxies in the Milky Way. We find that reproducing observational determinations of the halo occupation fraction and mass–metallicity relation for dwarf galaxies requires us to include H2 cooling, an updated ultraviolet background radiation model, and to introduce a model for the metal content of the intergalactic medium. By fine-tuning various model parameters and incorporating empirical constraints, we have tailored the model to match the statistical properties of Milky Way dwarf galaxies, such as their luminosity function and size–mass relation. We have validated our modified semi-analytic framework by undertaking a comparative analysis of the resulting galaxy–halo connection. We predict a total of $300 ^{+75} _{-99}$ satellites with an absolute V-band magnitude (MV) less than 0 within 300 kpc from our Milky Way analogues. The fraction of subhaloes that host a galaxy at least this bright drops to 50 per cent by a halo peak mass of ∼8.9 × 107 M⊙, consistent with the occupation fraction inferred from the latest observations of Milky Way satellite population.

Decreased SIRT1 protein may promote HMGB1 translocation in the keratinocytes of patients with cutaneous lupus erythematosus.

Background Ultraviolet radiation causes DNA damage in keratinocytes, aggravating cutaneous lupus erythematosus (CLE). High mobility group box 1 (HMGB1) participates in nucleotide excision and may transfer from the nucleus to the cytoplasm in immune active cells and the translocation of HMGB1 may result in DNA repair defects. HMGB1 was observed to transfer from the nucleus to the cytoplasm in the keratinocytes of CLE patients. As a class III histone deacetylases (HDACs), sirtuin-1 (SIRT1) can induce HMGB1 deacetylation. Epigenetic modification of HMGB1 may lead to HMGB1 translocation. Aims We aimed to evaluate the expressions of SIRT1 and HMGB1 in the epidermis of CLE patients and whether decreased SIRT1 leads to HMGB1 translocation through HMGB1 acetylation in keratinocytes. Methods We measured the messenger RNA (mRNA) and protein expressions of SIRT1 and HMGB1 in CLE patients using real-time reverse transcription polymerase chain reaction (RT-qPCR) and western blotting. Keratinocytes were treated with SIRT1 activator resveratrol (Res) and irradiated with ultraviolet B (UVB). We detected the localization expression of HMGB1 by immunofluorescence. The apoptosis level and the cell cycle proportions were measured by flow cytometry. The acetyl-HMGB1 level was detected by immunoprecipitation. Results Compared to healthy controls, the mRNA and protein expressions of SIRT1 in the epidermis of CLE patients were significantly decreased and there was translocation of HMGB1 from the nucleus to the cytoplasm. In keratinocytes, UVB irradiation led to HMGB1 translocation from the nucleus to the cytoplasm. Res treatment inhibited HMGB1 translocation, attenuated the cell apoptosis induced by UVB and decreased the acetyl-HMGB1 level. Limitations We only treated keratinocytes with the SIRT1 activator but did not perform the relevant experiments in keratinocytes with SIRT1 knockdown or overexpression. In addition, the lysine residue site of action of SIRT1 deacetylation of HMGB1 is unclear. The specific mechanism of action of SIRT1 deacetylation of HMGB1 needs to be further investigated. Conclusion SIRT1 may inhibit HMGB1 translocation by HMGB1 deacetylation which inhibited the apoptosis of keratinocytes induced by UVB. Decreased SIRT1 may promote HMGB1 translocation in the keratinocytes of patients with CLE.

Validation of Foreground Emission Model using GALEX Medium Observations

The study of diffuse ultraviolet (UV) background radiation is vital in the investigation of stellar and galactic evolution. Space-based UV observations are comprised of both foreground and background radiations. The foreground emission in an observation is a result of solar contamination in the direction of observation. In our previous work, we modeled airglow (one of the major constituents of the foreground emission) as a function of 10.7 cm Solar Flux and Sun Angle with great accuracy using GALEX deep observations. We adopt a similar methodology to validate the obtained model and run equivalent experiments here using far-UV (FUV) and near-UV (NUV) GALEX medium imaging surveys (MIS) with a total exposure time greater than 3300 s. We obtained a predictive model having excellent compatibility with the earlier model. Our analysis shows that the total foreground emission varies between 59 and 295 photon units in FUV whereas in NUV, it varies between 671 and 1195 photon units depending upon the date and time of observation. We also noticed a strong correlation between the background emission and optical depth both in FUV and NUV, especially in the low density regions. This clearly indicates that the major contributor in diffuse background radiation is the starlight scattered by interstellar dust grains.

Skin cancer mortality in Spain: adjusted mortality rates by province and related risk factors.

Ultraviolet radiation is the main environmental risk factor responsible for the development of skin cancer. Other occupational, socioeconomic, and environmental factors appear to be related to the risk of skin cancer. Furthermore, the factors appear to differ for melanoma and non-melanoma skin cancer (NMSC). The purpose of this study is to analyze mortality rates of skin cancer in the different provinces of Spain and to determine the influence of socioeconomic conditions and other environmental and demographic factors in rates. Deaths from melanoma and NMSC in the period 2000-2019 were obtained as well as socioeconomic and environmental variables. Annual standardized mortality rates (SMR) were calculated for all Spanish provinces. The Pearson correlation coefficient was calculated. The SMR of melanoma was 2.10/100,000 inhabitants, while that of NMSC was 1.28/100,000. At the provincial level, a great variability is confirmed. Gross domestic product showed a positive correlation with melanoma mortality but a negative correlation with NMSC. Other environmental and socioeconomic variables also showed correlation, as a positive correlation between tobacco sales and melanoma and between agricultural development and the NMSC. There are still important differences between each province that must be taken into account when planning health care and resource distribution. This ecological and province-wise study helps to elucidate the relationship between social and ambient exposure determinants and skin cancer mortality in Spain.

A new in vitro method to predict in vivo photoprotection of skin hyperpigmentation induced by visible light.

BackgroundUltraviolet radiation is the main cause of skin pigmentation, but more recently visible light has been shown to be an important contributor especially in melano‐competent subjects. Photoprotection from visible light can improve several hyperpigmentation disorders. Recently, a visible light photoprotection assessment method has been proposed based on in vivo pigmentation; the visible light photoprotection factor (VL‐PF) is determined by assessment of the change in colorimetry parameter ITA over several days measured using a chromameter. Although in vivo methods remain the most representative of real life, in vitro methods are more suited to screening sunscreen formulations.ObjectiveThe aim of this study was to evaluate the correlation between in vivo and in vitro methods in assessing protection against visible light induced pigmentation.MethodsWe first analysed the in vitro protective properties of the 10 commercially available sunscreens using transmission measurements in the visible spectrum. Then, we performed a monocentric, double‐blind, randomized controlled study with intra‐individual comparisons in 20 healthy subjects and measure the VL‐PF in vivo of those sunscreens. The correlation between the VL‐PF and the percentage of blocked light was evaluated using the coefficient of determination R 2.ResultsA strong significant correlation was demonstrated between in vivo visible light protection factor and in vitro transmittance measurements, with the highest correlation factor at 420 nm and in the spectrum covering from 400 to 469 nm.ConclusionTransmittance measurements were found to be a good predictive tool to evaluate sunscreen visible light photoprotection efficacy and could be used to select formulations for final in vivo testing.

Atomic and molecular gas from the epoch of reionisation down to redshift 2

Context. Cosmic gas makes up about 90% of the baryonic matter in the Universe and H2 molecule is the most tightly linked to star formation. Aims. In this work we study cold neutral gas, its H2 component at different epochs, and corresponding depletion times. Methods. We perform state-of-the-art hydrodynamic simulations that include time-dependent atomic and molecular non-equilibrium chemistry coupled to star formation, feedback effects, different UV backgrounds presented in the recent literature and a number of additional processes occurring during structure formation (COLDSIM). We predict gas evolution and contrast the mass density parameters and gas depletion timescales. We also investigate their relation to cosmic expansion in light of the latest infrared and (sub)millimetre observations in the redshift range 2 ≲ z ≲ 7. Results. By performing updated non-equilibrium chemistry calculations we are able to broadly reproduce the latest HI and H2 observations. We find neutral-gas mass density parameters Ωneutral ≃ 10−3 and increasing from lower to higher redshift, in agreement with available HI data. Because of the typically low metallicities during the epoch of reionisation, time-dependent H2 formation is mainly led by the H− channel in self-shielded gas, while H2 grain catalysis becomes important in locally enriched sites at any redshift. Ultraviolet (UV) radiation provides free electrons and facilitates H2 build-up while heating cold metal-poor environments. Resulting H2 fractions can be as high as ∼50% of the cold gas mass at z ∼ 4–8, in line with the latest measurements from high-redshift galaxies. The H2 mass density parameter increases with time until a plateau of ΩH2 ≃ 10−4 is reached. Quantitatively, we find agreement between the derived ΩH2 values and the observations up to z ∼ 7 and both HI and H2 trends are better reproduced by our non-equilibrium H2-based star formation modelling. The predicted gas depletion timescales decrease at lower z in the whole time interval considered, with H2 depletion times remaining below the Hubble time and comparable to the dynamical time at all z. This implies that non-equilibrium molecular cooling is efficient at driving cold-gas collapse in a broad variety of environments and has done so since very early cosmic epochs. While the evolution of chemical species is clearly affected by the details of the UV background and gas self shielding, the assumptions on the adopted initial mass function, different parameterizations of H2 dust grain catalysis, photoelectric heating, and cosmic-ray heating can affect the results in a non-trivial way. In the Appendix, we show detailed analyses of individual processes, as well as simple numerical parameterizations and fits to account for them. Conclusions. Our findings suggest that, in addition to HI, non-equilibrium H2 observations are pivotal probes for assessing cold-gas cosmic abundances and the role of UV background radiation at different epochs.

A panoramic view of the circumgalactic medium in the photoionized precipitation model

ABSTRACT We consider a model of the circumgalactic medium (CGM) in which feedback maintains a constant ratio of cooling time to free-fall time throughout the halo, so that the entire CGM is marginally unstable to multiphase condensation. This ‘precipitation model’ is motivated by observations of multiphase gas in the cores of galaxy clusters and the haloes of massive ellipticals. From the model, we derive the density and temperature profiles for the CGM around galaxies with masses similar to the Milky Way. After taking into consideration the geometrical position of our Solar system in the Milky Way, we show that the CGM model is consistent with observed O vi, O vii, O viii column densities and the ratio of O vii and O viii column densities only if temperature fluctuations with a lognormal dispersion σln T ∼ 0.6–1.0 are included. We show that O vi column densities observed around star-forming galaxies require systematically greater values of σln T than around passive galaxies, implying a connection between star formation in the disc and the state of the CGM. Photoionization by an extragalactic ultraviolet background radiation does not significantly change these CGM features for galaxies like the Milky Way but has much greater and significant effects on the CGM of lower mass galaxies.

The AGORA High-resolution Galaxy Simulations Comparison Project. III. Cosmological Zoom-in Simulation of a Milky Way–mass Halo

Abstract We present a suite of high-resolution cosmological zoom-in simulations to z = 4 of a 1012 M ⊙ halo at z = 0, obtained using seven contemporary astrophysical simulation codes (Art-I, Enzo, Ramses, Changa, Gadget-3, Gear, and Gizmo) widely used in the numerical galaxy formation community. The physics prescriptions for gas cooling and heating and star formation are the same as the ones used in our previous Assembling Galaxies of Resolved Anatomy (AGORA) disk comparison but now account for the effects of cosmological processes such as the expansion of the universe, intergalactic gas inflow, and the cosmic ultraviolet background radiation emitted by massive stars and quasars. In this work, we introduce the most careful comparison yet of galaxy formation simulations run by different code groups, together with a series of four calibration steps each of which is designed to reduce the number of tunable simulation parameters adopted in the final run. In the first two steps, we methodically calibrate the gas physics, such as cooling and heating, in simulations without star formation. In the third step, we seek agreement on the total stellar mass produced with the common star formation prescription used in the AGORA disk comparison, in stellar-feedback-free simulations. In the last calibration step, we activate stellar feedback, where each code group is asked to set the feedback prescription to as close to the most widely used one in its code community as possible, while aiming for convergence in the stellar mass at z = 4 to the values predicted by semiempirical models. After all the participating code groups successfully complete the calibration steps, we achieve a suite of cosmological simulations with similar mass assembly histories down to z = 4. With numerical accuracy that resolves the internal structure of a target halo (≲100 physical pc at z = 4), we find that the codes overall agree well with one another, e.g., in gas and stellar properties, but also show differences, e.g., in circumgalactic medium (CGM) properties. We argue that, if adequately tested in accordance with our proposed calibration steps and common parameters, high-resolution cosmological zoom-in simulations can have robust and reproducible results. New code groups are invited to join and enrich this comparison by generating equivalent models or to test the code’s compatibility on their own, by adopting the common initial conditions, the common easy-to-implement physics package, and the proposed calibration steps. Further analyses of the zoom-in simulations presented here will be presented in forthcoming reports from the AGORA Collaboration, including studies of the CGM, simulations by additional codes, and results at lower redshift.

The physical origins and dominant emission mechanisms of Lyman alpha haloes: results from the TNG50 simulation in comparison to MUSE observations

ABSTRACT Extended Lyman alpha emission is now commonly detected around high-redshift galaxies through stacking and even on individual basis. Despite recent observational advances, the physical origin of these Lyman alpha haloes (LAHs), as well as their relationships to galaxies, quasars, circumgalactic gas, and other environmental factors remains unclear. We present results from our new Lyman alpha full radiative transfer code voroiltis which runs directly on the unstructured Voronoi tessellation of cosmological hydrodynamical simulations. We make use of the TNG50 simulation and simulate LAHs from redshift z = 2 to z = 5, focusing on star-forming galaxies with $8.0 \lt \log _{10}{(M_\star /\rm {M}_\odot)} \lt 10.5$. While TNG50 does not directly follow ionizing radiation, it includes an on-the-fly treatment for active galactic nuclei (AGNs) and ultraviolet background radiation with self-shielding, which are important processes impacting the cooling and ionization of the gas. Based on this model, we present the predictions for the stacked radial surface brightness profiles of Ly α as a function of galaxy mass and redshift. Comparison with data from the MUSE UDF at z > 3 reveals a promising level of agreement. We measure the correlations of LAH size and central brightness with galaxy properties, finding that at the masses of $8.5 \le \log _{10} \left(M_\star /\rm {M}_\odot \right) \le 9.5$, physical LAH sizes roughly double from z = 2 to z = 5. Finally, we decompose the profiles into contributions from diffuse emission and scattered photons from star-forming regions. In our simulations, we find rescattered photons from star-forming regions to be the major source in observed LAHs. Unexpectedly, we find that the flattening of LAH profiles at large radii becomes dominated by photons originating from other nearby haloes rather than diffuse emission itself.

Protection of the Eye from Ultraviolet Radiation Damage Among Adults in Addis Zemen Town, Northwest Ethiopia.

BackgroundUltraviolet radiation is electromagnetic radiation or light having a wavelength of less than 400 nm but greater than 100 nm. Ultraviolet radiation, majorly from sunlight, can potentially damage any organ that is exposed to any part of its spectrum. Aside from the skin, the organ most susceptible to sunlight-induced damage is the eye. Ultraviolet radiation is reported to be the cause of multiple ocular problems ranging from benign conditions like pterygium and pinguecula to ocular malignancies such as basal cell carcinoma which finally leads to visual impairment and blindness. Protection practice is mandatory to avoid the burden of diseases caused by ultraviolet exposure and maximizing the protection measures implementation is important. To maximize this, it is essential to know the current practice and the associated factors affecting the usage of protective devices in the study area.MethodsCommunity-based cross-sectional study was conducted from April to May 2019 on 453 study participants. The study participants were selected through a systematic random sampling method. Data were collected using a pretested structured questionnaire. The analyzed result was summarized and presented using texts, tables and charts. A Chi-square test was applied to assess the significant association.ResultsA total of 430 study subjects were participated and completed the questionnaire with a response rate of 94.92%. The mean age of the study participants was 35.3 (SD±6.68). Two hundred forty-three (56.5%) study participants were males. About 228 (53%) of participants were married, and 356 (82.8%) were Christian in religion. From the total study participants, 173 (40.23%) had good practice in protecting the eye from ultraviolet radiation damages while the remaining 59.77% had poor practice. A significant association was found between sex and protection practice of the eye from ultraviolet radiation damages.ConclusionThe majority of the study participants had poor protection practice of the eye from ultraviolet radiation damages. Improving awareness and protection practice are vital to reduce the burden of ocular abnormalities due to excessive exposure to ultraviolet radiation.

Photoevaporation of Minihalos During Cosmic Reionization: Primordial and Metal-enriched Halos

Abstract The density distribution of the intergalactic medium is an uncertain but highly important issue in the study of cosmic reionization. It is expected that there are abundant gas clouds hosted by low-mass “minihalos” in the early universe, which act as photon sinks until being photoevaporated by the emerging ultraviolet background (UVB) radiation. We perform a suite of radiation-hydrodynamic simulations to study the photoevaporation of minihalos. Our simulations follow hydrodynamics, nonequilibrium chemistry, and the associated cooling processes in a self-consistent manner. We conduct a parametric study by considering a wide range of gas metallicities (0 Z ⊙ ≤ Z ≤ 10−3 Z ⊙), halo mass (103 M ⊙ ≤ M ≤ 108 M ⊙), UVB intensity (0.01 ≤ J 21 ≤ 1), and turn-on redshift of ionizing sources (10 ≤ z IN ≤ 20). We show that small halos are evaporated in a few tens of millions of years, whereas larger mass halos survive 10 times longer. The gas mass evolution of a minihalo can be characterized by a scaling parameter that is given by a combination of the halo mass, background radiation intensity, and redshift. Efficient radiative cooling in metal-enriched halos induces fast condensation of the gas to form a dense, self-shielded core. The cold, dense core can become gravitationally unstable in halos with high metallicities. Early metal enrichment may allow star formation in minihalos during cosmic reionization.

The detailed structure and the onset of galaxy formation in low-mass gaseous dark matter haloes

ABSTRACT We present a model for the formation of the first galaxies before and after the reionization of hydrogen in the early universe. In this model, galaxy formation can only take place in dark matter haloes whose mass exceeds a redshift-dependent critical value, which, before reionization, is equal (in the simplest case) to the mass at which atomic hydrogen cooling becomes effective and, after reionization, is equal to the mass above which gas cannot remain in hydrostatic equilibrium. We define the Halo Occupation Fraction (HOF) as the fraction of haloes that host a luminous galaxy as a function of halo mass. The HOF is established by the interplay between the evolution of the critical mass and the assembly history of haloes and depends on three factors: the minimum halo mass for galaxy formation before reionization, the redshift of reionization, and the intensity of the (evolving) external photoheating rate. Our fiducial model predicts a cutoff in the galaxy mass function at a present-day halo mass, $M_{200} \sim 3\times 10^{8} \, \mathrm{M}_{\odot }$; 100 per cent occupation at $M_{200} \gt 5\times 10^9 \, \mathrm{M}_{\odot }$; and a population of starless gaseous haloes of present-day mass in the range 106 ≲ M200/M⊙ ≲ 5 × 109, in which the gas is in thermal equilibrium with the ultraviolet background radiation and in hydrostatic equilibrium in the gravitational potential of the halo. The transition between HOF = 0 and HOF = 1 reflects the stochastic nature of halo mass growth. We explore how these characteristic masses vary with model assumptions and parameter values. The results of our model are in excellent agreement with cosmological hydrodynamic simulations of galaxy formation.

TGF-β3 suppresses melanogenesis in human melanocytes cocultured with UV-irradiated neighboring cells and human skin

BackgroundUltraviolet radiation (UVR) is the most well-known cause of skin pigmentation accompanied with photoaging. Transforming growth factor (TGF)-β1 was previously shown to have anti-melanogenic property; however, it can induce scarring in skin. ObjectiveWe investigated the effect of TGF-β3 on melanogenesis in human melanocytes cocultured with UV-irradiated skin constituent cells, and UV-irradiated human skin. MethodsUVB irradiation or treatment with stem cell factor (SCF) and endothelin-1 (ET-1) was applied to human melanocytes cocultured with keratinocytes and/or fibroblasts and ex vivo human skin. Mechanistic pathways were further explored after treatment with TGF-β3. ResultsWhile UVB irradiation or SCF/ET-1 enhanced melanogenesis, TGF-β3 effectively inhibited melanin accumulation and tyrosinase activity via downregulation of the extracellular signal-regulated kinase (ERK)/microphthalmia-associated transcription factor (MITF) pathway. TGF-β3 increased the expression of differentiation markers of keratinocytes. ConclusionTGF-β3 effectively suppressed UVR-stimulated melanogenesis indicating that topical TGF-β3 may be a suitable candidate for the treatment of UV-associated hyperpigmentation disorders.

The use of tissue-engineered skin to demonstrate the negative effect of CXCL5 on epidermal ultraviolet radiation-induced cyclobutane pyrimidine dimer repair efficiency.

Ultraviolet radiation (UVR) is responsible for keratinocyte cancers through the induction of mutagenic cyclobutane pyrimidine dimers (CPDs). Many factors influence CPD repair in epidermal keratinocytes, and a better understanding of those factors might lead to prevention strategies against skin cancer. To evaluate the impact of dermal components on epidermal CPD repair efficiency and to investigate potential factors responsible for the dermal-epidermal crosstalk modulating UVR-induced DNA damage repair in keratinocytes. A model of self-assembled tissue-engineered skin containing human primary keratinocytes and fibroblasts was used in this study. We showed that CPD repair in keratinocytes is positively influenced by the presence of a dermis. We investigated the secretome and found that the cytokine CXCL5 is virtually absent from the culture medium of reconstructed skin, compared with media from fibroblasts and keratinocytes alone. By modulating CXCL5 levels in culture media of keratinocytes, we have shown that CXCL5 is an inhibitor of CPD repair. This work outlines the impact of the secreted dermal components on epidermal UVR-induced DNA damage repair and sheds light on a novel role of CXCL5 in CPD repair.

Galaxy Cluster Contribution to the Diffuse Extragalactic Ultraviolet Background

Abstract The diffuse ultraviolet background radiation has been mapped over most of the sky with 2′ resolution using data from the Galaxy Evolution Explorer survey. We utilize this map to study the correlation between the UV background and clusters of galaxies discovered via the Sunyaev–Zeldovich effect in the Planck survey. We use only high Galactic latitude ( ) galaxy clusters to avoid contamination by Galactic foregrounds, and we only analyze clusters with a measured redshift. This leaves us with a sample of 142 clusters over the redshift range of 0.02 ≤ z ≤ 0.72, which we further subdivide into four redshift bins. In analyzing our stacked samples binned by redshift, we find evidence for a central excess of UV background light compared to local backgrounds for clusters with z < 0.3. We then stacked these z < 0.3 clusters to find a statistically significant excess of 12 ± 2.3 photon cm−2 s−1 sr−1 Å−1 over the median of ∼380 photon cm−2 s−1 sr−1 Å−1 measured around random blank fields. We measure the stacked radial profile of these clusters, and find that the excess UV radiation decays to the level of the background at a radius of ∼1 Mpc, roughly consistent with the maximum radial extent of the clusters. Analysis of possible physical processes contributing to the excess UV brightness indicates that non-thermal emission from relativistic electrons in the intracluster medium and faint, unresolved UV emission from cluster member galaxies and intracluster light are likely the dominant contributors.

New synthesis models of consistent extragalactic background light over cosmic time

We present new synthesis models of the extragalactic background light (EBL) from far infra-red (FIR) to TeV gamma-rays, with an emphasis on the extreme ultraviolet (UV) background which is responsible for the observed ionization and thermal state of the intergalactic medium across the cosmic time. Our models use updated values of the star formation rate density and dust attenuation in galaxies, QSO emissivity, and the distribution of H I gas in the IGM. Two of the most uncertain parameters in these models, the escape fraction of H I ionizing photons from galaxies and the spectral energy distribution (SED) of QSOs, are determined to be consistent with the latest measurements of H I and He II photoionization rates, the He II Lyman-alpha effective optical depths, various constraints on H I and He II reionization history and many measurements of the local EBL from soft X-rays till gamma-rays. We calculate the EBL from FIR to TeV gamma-rays by using FIR emissivities from our previous work and constructing an average SED of high-energy emitting QSOs, i.e, type-2 QSOs and blazars. For public use, we also provide the EBL models obtained using different QSO SEDs at extreme-UV energies over a wide range of redshifts. These can be used to quantify uncertainties in the parameters derived from photoionization models and numerical simulations originating from the allowed variations in the UV background radiation.

Redshift space distortion of 21 cm line at 1 < $z$ < 5 with cosmological hydrodynamic simulations

We measure the scale dependence and redshift dependence of 21 cm line emitted from the neutral hydrogen gas at redshift 1<z<5 using full cosmological hydrodynamic simulations by taking the ratios between the power spectra of HI-dark matter cross correlation and dark matter auto-correlation. The neutral hydrogen distribution is computed in full cosmological hydrodynamic simulations including star formation and supernova feedback under a uniform ultra-violet background radiation. We find a significant scale dependence of HI bias at z>3 on scales of k>1h/Mpc, but it is roughly constant at lower redshift z<3. The redshift evolution of HI bias is relatively slow compared to that of QSOs at similar redshift range. We also measure a redshift space distortion (RSD) of HI gas to explore the properties of HI clustering. Fitting to a widely applied theoretical prediction, we find that the constant bias is consistent with that measured directly from the real-space power spectra, and the velocity dispersion is marginally consistent with the linear perturbation prediction. Finally we compare the results obtained from our simulation and the Illustris simulation, and conclude that the detailed astrophysical effects do not affect the scale dependence of HI bias very much, which implies that the cosmological analysis using 21 cm line of HI will be robust against the uncertainties arising from small-scale astrophysical processes such as star formation and supernova feedback.

Physical conditions in high-z optically thin C iii absorbers: origin of cloud sizes and associated correlations

We present detailed photoionization models of well aligned optically thin C III absorption components at $2.1 < z < 3.4$. Using our models we estimate density ($n_{\rm \tiny H}$), metallicity ($[C/H]$), total hydrogen column density and line-of-sight thickness ($L$) in each C III components. We estimate the systematic errors in these quantities contributed by the allowed range of the quasar spectral index used in the ultraviolet background radiation calculations. Our inferred $n_{\rm \tiny H}$ and overdensity ($\Delta$) are much higher than the measurements available in the literature and favor the absorption originating from gas associated with circumgalactic medium and probably not in hydrostatic equilibrium. We also notice $n_{\rm \tiny H}$, $L$ and $[C/H]$ associated with C III components show statistically significant redshift evolution. To some extent, these redshift evolutions are driven by the appearance of compact, high $n_{\rm \tiny H}$ and high $[C/H]$ components only in the low$-z$ end. We find more than 5$\sigma$ level correlation between $[C/H]$ and $L$, $L$ and neutral hydrogen column density (N (HI)), N (HI) and $[C/H]$. We show $L$ versus $[C/H]$ correlation can be well reproduced if $L$ is governed by the product of gas cooling time and sound speed as expected in the case of cloud fragmentation under thermal instabilities. This allows us to explain other observed correlations by simple photoionization considerations. Studying the optically thin C III absorbers over a large $z$ range and probably correlating their $z$ evolution with global star formation rate density evolution can shed light into the physics of cold clump formation and their evolution in the circumgalactic medium.

Gravitational stability and fragmentation condition for discs around accreting supermassive stars

Supermassive stars (SMSs) with mass $\sim10^{5}~\rm{M}_{\odot}$ are promising candidates for the origin of supermassive black holes observed at redshift $\gtrsim6$. They are supposed to form as a result of rapid accretion of primordial gas, although it can be obstructed by the time variation caused by circum-stellar disc fragmentation due to gravitational instability. To assess the occurrence of fragmentation, we study the structure of marginally gravitationally unstable accretion discs, by using a steady one-dimensional thin disc model with detailed treatment of chemical and thermal processes. Motivated by two SMS formation scenarios, i.e., those with strong ultraviolet radiation background or with large velocity difference between the baryon and the dark matter, we consider two types of flows, i.e., atomic and molecular flows, respectively, for a wide range of the central stellar mass $10-10^5~\rm{M}_{\odot}$ and the accretion rate $10^{-3}-1~\rm{M}_{\odot}~\rm{yr}^{-1}$. In the case of a mostly atomic gas flowing to the disc outer boundary, the fragmentation condition is expressed as the accretion rate being higher than the critical value of $10^{-1}~\rm{M}_{\odot}~\rm{yr}^{-1}$ regardless of the central stellar mass. On the other hand, in the case of molecular flows, there is a critical disc radius outside of which the disc becomes unstable. Those conditions appears to be marginally satisfied according to numerical simulations, suggesting that disc fragmentation can be common during SMS formation.

Brahma deficiency in keratinocytes promotes UV carcinogenesis by accelerating the escape from cell cycle arrest and the formation of DNA photolesions

BackgroundUltraviolet radiation (UVR) is the principal cause of keratinocyte skin cancers. Previous work found that levels of the chromatin remodelling protein, Brahma (Brm), are diminished during the progression from actinic keratoses to cutaneous squamous cell carcinomas in humans, and its loss in UV-irradiated mouse skin causes epidermal hyperplasia and increased tumour incidence. MethodsThe skins of mice and mouse and human keratinocytes deficient in Brm were exposed to UVR and evaluated for cell cycle progression and DNA damage response. ObjectiveTo identify the mechanisms by which loss of Brm contributes to UVR-induced skin carcinogenesis. ResultsIn both mouse keratinocytes and HaCaT cells, Brm deficiency led to an increased cell population growth following UVR exposure compared to cells with normal levels of Brm. Cell cycle analysis using a novel assay showed that Brm-deficient keratinocytes entered cell cycle arrest normally, but escaped from cell cycle arrest faster, enabling them to begin proliferating earlier. In mouse keratinocytes, Brm primarily affected accumulation in G0/G1-phase, whereas in HaCaT cells, which lack normal p53, accumulation in G2/M-phase was affected. Brm-deficient keratinocytes in mouse skin and human cell cultures also had higher levels of UVR-induced cyclobutane pyrimidine dimer photolesions. These effects occurred without any compensatory increase in DNA repair or cell death to remove photolesions or the cells that harbor them from the keratinocyte population. ConclusionThe loss of Brm in keratinocytes exposed to UVR enables them to resume proliferation while harboring DNA photolesions, leading to an increased fixation of mutations and, consequently, increased carcinogenesis.