We present the results of a search for damped Lyman-α (DLA) systems in the Sloan Digital Sky Survey II (SDSS), Data Release 7. We use a fully automatic procedure to identify DLAs and derive their ...column densities. The procedure is checked against the results of previous searches for DLAs in SDSS. We discuss the agreements and differences and show the robustness of our procedure. For each system, we obtain an accurate measurement of the absorber's redshift, the H I column density and the equivalent width of associated metal absorption lines, without any human intervention. We find 1426 absorbers with $2.15 < z < 5.2$ with log N(H I) ≥ 20, out of which 937 systems have log N(H I) ≥ 20.3. This is the largest DLA sample ever built, made available to the scientific community through the electronic version of this paper. In the course of the survey, we discovered the intervening DLA with highest H I column density known to date with log N(H I) = 22.0±0.1. This single system provides a strong constraint on the high-end of the N(H I) frequency distribution now measured with high accuracy. We show that the presence of a DLA at the blue end of a QSO spectrum can lead to important systematic errors and propose a method to avoid them. This has important consequences for the measurement of the cosmological mass density of neutral gas at z ~ 2.2 and therefore on our understanding of galaxy evolution over the past 10 billion years. We find a significant decrease of the cosmological mass density of neutral gas in DLAs, $\Omega_{\rm g}^{\rm DLA}$, from $z = 4$ to $z = 2.2$, consistent with the result of previous SDSS studies. However, and contrary to other SDSS studies, we find that $\Omega_{\rm g}^{\rm DLA}$(z = 2.2) is about twice the value at $z = 0$. This implies that $\Omega_{\rm g}^{\rm DLA}$ keeps decreasing at $z < 2.2$.
We present the results of a search for cold gas at high redshift along quasar lines of sight carried out without any a priori assumption on the neutral atomic-hydrogen content of the absorption-line ...systems. To do this, we systematically looked for neutral- carbon (C I) AA1560, 1656 transition lines in 41696 low-resolution quasar spectra from the SDSS-II - Data Release 7 - database. C I absorption lines should indeed probe the shielded gas in the neutral interstellar medium of galaxies more efficiently than traditional tracers such as neutral atomic-hydrogen (H I) damped Lyman-a (DLA) and/or Mg II systems. We show that, at equal amount of reddening, the 2175 A feature is weak compared to Galactic lines of sight. This is probably the consequence of current or past star formation in the vicinity of the C I systems. The C I-absorber sample presented here hence provides ideal targets for detailed studies of the dust composition and molecular species at high redshift.
NF-κB and the cell cycle Ledoux, Adeline C; Perkins, Neil D
Biochemical Society transactions
42, Številka:
1
Journal Article
Recenzirano
The NF-κB (nuclear factor κB) transcription factor family is a pleiotropic regulator of many cellular pathways, providing a mechanism for the cell to respond to a wide variety of stimuli and ...environmental challenges. It is not surprising therefore that an important component of NF-κB's function includes regulation of the cell cycle. However, this aspect of its behaviour is often overlooked and receives less attention than its ability to induce inflammatory gene expression. In the present article, we provide an updated review of the current state of our knowledge about integration of NF-κB activity with cell cycle regulation, including newly characterized direct and indirect target genes in addition to the mechanisms through which NF-κB itself can be regulated by the cell cycle.
We analyse the redshift evolution of the mass-metallicity relation in a sample of 110 Damped Lyman α absorbers (DLAs) spanning the redshift range z = 0.11-5.06 and find that the zero-point of the ...correlation changes significantly with redshift. The evolution is such that the zero-point is constant at the early phases of galaxy growth (i.e. no evolution) but then features a sharp break at z = 2.6 ± 0.2 with a rapid incline towards lower redshifts such that damped absorbers of identical masses are more metal rich at later times than earlier. The slope of this mass-metallicity correlation evolution is 0.35 ± 0.07 dex per unit redshift.
We compare this result to similar studies of the redshift evolution of emission selected galaxy samples and find a remarkable agreement with the slope of the evolution of galaxies of stellar mass log(M
*/M) 8.5. This allows us to form an observational tie between damped absorbers and galaxies seen in emission.
We use results from simulations to infer the virial mass of the dark matter halo of a typical DLA galaxy and find a ratio (M
vir/M
*) 30.
We compare our results to those of several other studies that have reported strong transition-like events at redshifts around z = 2.5-2.6 and argue that all those observations can be understood as the consequence of a transition from a situation where galaxies were fed more unprocessed infalling gas than they could easily consume to one where they suddenly become infall starved and turn to mainly processing, or re-processing, of previously acquired gas.
Aims. We present the current status of ongoing searches for molecular hydrogen in high-redshift (1.8 < z_{\rm abs} \le 4.2) Damped Lyman- \alpha systems (DLAs) capitalising on observations performed ...with the ESO Very Large Telescope (VLT) Ultraviolet and Visual Echelle Spectrograph (UVES). Methods. We identify 77 DLAs/strong sub-DLAs, with log N (H I) \ge 20 and z_{\rm abs} >1.8, which have data that include redshifted H sub(2) Lyman and/or Werner-band absorption lines. This sample of H I, H sub(2) and metal line measurements, performed in an homogeneous manner, is more than twice as large as our previous sample (Ledoux et al. 2003) considering every system in which searches for H sub(2) could be completed so far, including all non-detections. Results. H sub(2) is detected in thirteen of the systems, which have molecular fractions of values between f \simeq 5\times10 super(- 7) and f \simeq 0.1, where f = 2 N (H sub(2)) /(2 N (H sub(2)) +N(H I)). Upper limits are measured for the remaining 64 systems with detection limits of typically log N (H sub(2)) similar to 14.3, corresponding to log f <-5. We find that about 35% of the DLAs with metallicities relative to solar X/H \ge-1.3 (i.e., 1/20th solar), with X = Zn, S or Si, have molecular fractions log f >-4.5, while H sub(2) is detected-regardless of the molecular fraction-in \sim 50% of them. In contrast, only about 4% of the X/H <-1.3 DLAs have log f >-4.5. We show that the presence of H sub(2) does not strongly depend on the total neutral hydrogen column density, although the probability of finding log f >-4.5 is higher for log N (H I) \ge 20.8 than below this limit (19% and 7% respectively). The overall H sub(2) detection rate in log N (H I) \ge 20 DLAs is found to be about 16% (10% considering only log f >-4.5 detections) after correction for a slight bias towards large N (H I). There is a strong preference for H sub(2)-bearing DLAs to have significant depletion factors, X/Fe > 0.4. In addition, all H sub(2)-bearing DLAs have column densities of iron into dust grains larger than log N({\rm Fe}) _{\rm dust} similar to 14.7, and about 40% of the DLAs above this limit have detected H sub(2) lines with log f >-4.5. This demonstrates the importance of dust in governing the detectability of H sub(2) in DLAs. Our extended sample supports neither the redshift evolution of the detection fraction of H sub(2)-bearing DLAs nor that of the molecular fraction in systems with H sub(2) detections over the redshift range 1.8 < z_{\rm abs} \le 3.
ABSTRACT
We present the detection of excited fine-structure energy levels of singly ionized silicon and neutral carbon associated with the proximate damped Lyman-α system at zabs = 2.811 towards Q ...0528−250. This absorber has an apparent relative velocity that is inconsistent with the Hubble flow indicating motion along the line-of-sight towards the quasar, i.e. zabs > zem. We measure the metallicity of the system to be Zn/H = −0.68 ± 0.02. Using the relative populations of the fine-structure levels of Si ii and C i, as well as the populations of H2 rotational levels, we constrain the physical conditions of the gas. We derive hydrogen number densities of $n_{\rm H}=190^{+70}_{-50}$ cm−3 and $260^{+30}_{-20}$ cm−3 in two velocity components where both C i and H2 are detected. Taking into account the kinetic temperature in each component, ∼150 K, we infer high values of thermal pressure in the cold neutral medium probed by the observations. The strengths of the UV field in Draine’s unit are $I_{\rm UV} = 10^{+5}_{-3}$ and $14^{+3}_{-3}$ in each of these two components, respectively. Such enhanced UV fluxes and thermal pressure compared to intervening DLAs are likely due to the proximity of the quasar. The typical size of the absorber is ∼104 au. Assuming the UV flux is dominated by the quasar, we constrain the distance between the quasar and the absorber to be ∼150−200 kpc. This favours a scenario where the absorption occurs in a companion galaxy located in the group where the quasar-host galaxy resides. This is in line with studies in emission that revealed the presence of several galaxies around the quasar.
A milestone of modern cosmology was the prediction and serendipitous discovery of the cosmic microwave background (CMB), the radiation leftover after decoupling from matter in the early evolutionary ...stages of the Universe. A prediction of the standard hot Big-Bang model is the linear increase with redshift of the black-body temperature of the CMB (TCMB). This radiation excites the rotational levels of some interstellar molecules, including carbon monoxide (CO), which can serve as cosmic thermometers. Using three new and two previously reported CO absorption-line systems detected in quasar spectra during a systematic survey carried out using VLT/UVES, we constrain the evolution of TCMB to z ~ 3. Combining our precise measurements with previous constraints, we obtain TCMB(z) = (2.725 ± 0.002) × (1 + z)1-β K with β = -0.007 ± 0.027, a more than two-fold improvement in precision. The measurements are consistent with the standard (i.e. adiabatic, β = 0) Big-Bang model and provide a strong constraint on the effective equation of state of decaying dark energy (i.e. weff = -0.996 ± 0.025). Based on observations carried out at the European Southern Observatory (ESO) using the Ultraviolet and Visual Echelle Spectrograph (UVES) at the Very Large Telescope (VLT, UT2-Kueyen) under Prgm. IDs 278.A-5062(A), 081.A-0334(B), 082.A-0544(A), and 083.A-0454(A).
Motivated by the anomalous dust-to-metal ratios derived in the literature for gamma -ray burst (GRB) damped Lyman- alpha absorbers (DLAs), we measure these ratios using the dust-depletion pattern ...observed in UV/optical afterglow spectra associated with the interstellar medium (ISM) at the GRB host-galaxy redshifts. Our sample consists of 20 GRB absorbers and a comparison sample of 72 DLAs toward quasars (QSOs) with redshift 1.2 < z < 4.0 and down to Z = 0.002 Z# metallicities. The dust-to-metal ratio in QSO- and GRB-DLAs increases both with metallicity and metal column density, spanning ~10-110% of the Galactic value and pointing to a nonuniversal dust-to-metal ratio. The dust extinction AV increases steeply with the column density of iron in dust, N(Fe)dust, calculated from relative metal abundances, confirming that dust extinction is mostly occurring in the host galaxy ISM. Most GRB-DLAs display log N(Fe)dust > 14.7, above which several QSO-DLAs reveal molecular hydrogen, making GRB-DLAs promising candidates for molecular detection and study.
Context. Dust is known to be produced in the envelopes of asymptotic giant branch (AGB) stars, the expanded shells of supernova (SN) remnants, and in situ grain growth within the interstellar medium ...(ISM), although the corresponding efficiency of each of these dust formation mechanisms at different redshifts remains a topic of debate. During the first Gyr after the Big Bang, it is widely believed that there was not enough time to form AGB stars in high numbers, hence the dust at this epoch is expected to be purely from SNe or subsequent grain growth in the ISM. The time period corresponding to z ~ 5−6 is thus expected to display the transition from SN-only dust to a mixture of both formation channels as is generally recognized at present. Aims. Here we aim to use afterglow observations of gamma-ray bursts (GRBs) at redshifts larger than z > 4 to derive host galaxy dust column densities along their line of sight and to test if a SN-type dust extinction curve is required for some of the bursts. Methods. We performed GRB afterglow observations with the seven-channel Gamma-Ray Optical and Near-infrared Detector (GROND) at the 2.2 m MPI telescope in La Silla, Chile (ESO), and we combined these observations with quasi-simultaneous data gathered with the XRT telescope on board the Swift satellite. Results. We increase the number of measured AV values for GRBs at z > 4 by a factor of ~2–3 and find that, in contrast to samples at mostly lower redshift, all of the GRB afterglows have a visual extinction of AV < 0.5 mag. Analysis of the GROND detection thresholds and results from a Monte Carlo simulation show that although we partly suffer from an observational bias against highly extinguished sight-lines, GRB host galaxies at 4 < z < 6 seem to contain on average less dust than at z ~ 2. Additionally, we find that all of the GRBs can be modeled with locally measured extinction curves and that the SN-like dust extinction curve, as previously found toward GRB 071025, provides a better fit for only two of the afterglow SEDs. However, because of the lack of highly extinguished sight lines and the limited wavelength coverage we cannot distinguish between the different scenarios. For the first time we also report a photometric redshift of zphot = 7.88-0.94+0.75 for GRB 100905A, making it one of the most distant GRBs known to date.
We present the results from VLT/X-shooter spectroscopic observations of 11 extremely strong intervening damped Lyman-α absorbers (ESDLAs) that were initially selected as high N(H I) (i.e. ≥5 × 1021 ...cm−2) candidates from the Sloan Digital Sky Survey (SDSS). We confirm the high H I column densities, which we measure to be in the range log N(H I) = 21.6 − 22.4. Molecular hydrogen is detected with high column densities (N(H2)≥1018 cm−2) in 5 out of 11 systems, 3 of which are reported here for the first time, and we obtain conservative upper limits on N(H2) for the remaining 6 systems. We also measure the column density of various metal species (Zn II, Fe II, Si II, Cr II, and C I), quantify the absorption-line kinematics (Δv90), and estimate the extinction of the background quasar light (AV) by dust in the absorbing gas. We compare the chemical properties of this sample of ESDLAs, supplemented with literature measurements, to that of DLAs located at the redshift of long-duration γ-ray bursts (GRB-DLAs). We confirm that the two populations are almost indistinguishable in terms of chemical enrichment and gas kinematics. In addition, we find no marked differences in the incidence of H2. All this suggests that ESDLAs and GRB-DLAs probe similar galactic environments. We search for the galaxy counterparts of ESDLAs and find associated emission lines in 3 out of 11 systems, 2 of which are reported here for the first time (at zabs = 2.304 and 2.323 towards the quasars SDSS J002503.03+114547.80 and SDSS J114347.21+142021.60, respectively). The measured separations between the quasar sightlines and the emission associated with the ESDLA galaxy (for a total of five sightlines) are all very small (ρ < 3 kpc). Because our observations are complete up to ρ ∼ 7 kpc, we argue that the emission counterparts of the remaining systems are more likely below the detection limit than outside the search area. While the small impact parameters are similar to what is observed for GRB-DLAs, the associated star formation rates are on average lower than for GRB host galaxies. This is explained by long-duration GRBs being associated with the death of massive stars and therefore pinpointing regions of active star formation in the GRB host galaxies. Our observations support the suggestion from the literature that ESDLAs could act as blind analogues of GRB-DLAs, probing neutral gas with high column density in the heart of high-redshift galaxies, without any prior on the instantaneous star formation rate.
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