We present a new method to infer parameters of the temperature-density relation in the intergalactic medium in the post-reionization epoch at z ∼ 2-4. This method is based on the analysis of the ...distribution of Ly absorbers over column densities and Doppler parameters by the model joint probability density function. This approach allows us to measure the power-law index γ of the temperature-density relation and a certain combination of the temperature at the mean density T0 and hydrogen photoionization rate Γ. To estimate T0 and Γ separately, we employ measurements of the Ly forest effective opacity and the model gas probability density function. We show that γ tends to be lower than 1.6 and reaches 1.3 at redshift ∼3. The inferred temperatures at the mean density are ∼(2 0.5) × 104 K in the studied redshift range. Both these estimates favor He II reionization at z 3. We find that the hydrogen photoionization rate is ∼0.6 × 10−12 s−1, which is consistent with previous measurements.
ABSTRACT
We discuss observations of C ii*/C ii ratios and cooling rates due to C ii 158μm emission in high-redshift intervening damped Lyman-α (DLA) systems towards quasars. We show that the observed ...bimodality in the C ii cooling rates actually reflects a bimodality in the C ii*/C ii−metallicity plane that can be naturally explained by phase segregation of the neutral medium, without invoking differences in star-formation scenarios. Assuming realistic distributions of the physical parameters to calculate the phase diagrams, we also reproduce qualitatively the metallicity dependence of this bimodality. We emphasize that high-z DLAs mostly probe low-metallicity gas ($Z\lesssim 0.1 \, \mathrm{Z}_{\odot }$), where heating is dominated by cosmic rays (and/or turbulence), and not by photoelectric heating. Therefore, even if the gas of DLA is predominantly cold (where the cooling is dominated by C ii), the excitation of C ii can be used to derive the cosmic ray ionization rate (and/or turbulent heating), but not the UV field, as was previously considered. Alternatively, if the gas in DLA is predominantly warm, C ii*/C ii can be used to constrain its number density. Finally, we also discuss the importance of the ionized medium, which, if also present along the line of sight, can significantly increase the average C ii*/C ii ratio.
We calculate the mean density profiles for luminous and dark matter on distance scales D ∼ 1–100 Mpc around us using recent all‐sky catalogs of galaxy groups. Within the Local Volume (D < 11 Mpc), we ...derived the mean stellar density Ω* = 0.44% in the critical density units and the mean total matter density Ωm = 0.17. Within a sphere of radius 40 Mpc, these quantities drop to Ω* = 0.24–0.32% and Ωm = 0.09–0.14. In a larger volume within D ∼ 135 Mpc, the discussed densities become more uncertain: Ω* = 0.20–0.24% and Ωm = 0.05–0.16. We summarize that the major part of the cosmic dark matter is located outside the virial and collapsing zones of groups and clusters.
ABSTRACT
We present a spectroscopic investigation with the Very Large Telescope/X-shooter of seven candidate extremely strong damped Lyman-α absorption systems ESDLAs, N(H i) ≥ 5 × 1021 cm−2 observed ...along quasar sightlines. We confirm the extremely high column densities, albeit slightly (0.1 dex) lower than the original ESDLA definition for four systems. We measured low-ionization metal abundances and dust extinction for all systems. For two systems, we also found strong associated H$\rm _2$ absorption $\log N(\rm{H\rm _2})\,\text{(cm$^{-2}$)}=18.16\pm 0.03$ and 19.28 ± 0.06 at z = 3.26 and 2.25 towards J2205+1021 and J2359+1354, respectively, while for the remaining five we measured conservative upper limits on the H$\rm _2$ column densities of typically $\log N(\rm{H\rm _2})\,\text{(cm$^{-2}$)}\,\lt\, 17.3$. The increased H2 detection rate (10–55 per cent at 68 per cent confidence level) at high H i column density compared with the overall damped Lyman-α population (∼5–10 per cent) confirms previous works. We find that these seven ESDLAs have similar observed properties as those previously studied towards quasars and γ-ray burst afterglows, suggesting they probe inner regions of galaxies. We use the abundance of ionized carbon at the excited fine-structure level to calculate the cooling rates through the C ii λ158 μm emission, and compare them with the cooling rates from damped Lyman-α systems in the literature. We find that the cooling rate distribution of ESDLAs also presents the same bimodality as previously observed for the general (mostly lower H i column density) damped Lyman-α population.
ABSTRACT
We present high-resolution VLT/UVES spectroscopy and a detailed analysis of the unique broad absorption-line system towards the quasar SDSS J 165252.67+265001.96. This system exhibits ...low-ionization metal absorption lines from the ground states and excited energy levels of Fe ii and Mn ii, and the meta-stable $2\, ^3S$ excited state of He i. The extended kinematics of the absorber encompasses three main clumps with velocity offsets of −5680, −4550, and −1770 km s−1 from the quasar emission redshift, z = 0.3509 ± 0.0003, derived from O ii emission. Each clump shows moderate partial covering of the background continuum source, Cf ≈ 0.53; 0.24; 0.81. We discuss the excitation mechanisms at play in the gas, which we use to constrain the distance of the clouds from the active galactic nucleus (AGN) as well as the density, temperature, and typical sizes of the clouds. The number density is found to be nH ∼ 104 cm−3 and the temperature Te ∼ 104 K, with longitudinal cloudlet sizes of ≳0.01 pc. cloudy photoionization modelling of He i⋆, which is also produced at the interface between the neutral and ionized phases, assuming the number densities derived from Fe ii, constrains the ionization parameter to be log U ∼ −3. This corresponds to distances of a few 100 pc from the AGN. We discuss these results in the more general context of associated absorption-line systems and propose a connection between FeLoBALs and the recently identified molecular-rich intrinsic absorbers. Studies of significant samples of FeLoBALs, even though rare per se, will soon be possible due to large dedicated surveys paired with high-resolution spectroscopic follow-ups.
Abstract
We investigate evolution of physical parameters of the intergalactic medium using an analysis of Lya forest lines detected towards distant quasars. We used the enlarged sample of 98 quasars ...obtained with Keck/HIRES and VLT/UVES. We show that taking into account a finite spatial size of absorbers, regulated by pressure smoothing, significantly affects the inferred thermal parameters of the intergalactic gas, such as the hydrogen photoionization rate and parameters of the temperature-density relation. Using Bayesian framework we constrained for the first time the scale parameter between the Jeans length and characteristic size of the absorbers. We also discuss limitations of the method based on the analysis of the minimal broadending of Lya lines, which stem from the patchy nature of He II reionization.
We investigate a contribution of the Jeans smoothing to the minimal width of Ly forest lines and discuss how the accounting for this additional broadening affects the inferred parameters of the ...intergalactic matter equation of state. We estimate a power-law index γ of the equation of state, a temperature at the mean density T0 and a hydrogen photoionization rate Γ within 4 redshift bins. Furthermore, in each bin we obtain an upper limit on the scale-parameter fJ, which sets the relation between the Jeans length and the characteristic physical size of the absorber clouds.
Quasar spectra provide a unique opportunity to investigate the intergalactic medium at high redshifts. The spectral analysis of the Lya forest allows us to constrain the effective equation of state ...of the intergalactic medium and its changes during the evolution of the Universe. Based on the Voigt profile fitting of Lya forest lines in 50 high-resolution QSO spectra obtained at Keck telescope we present new measurements of the power-law index γ of temperature-density relation in IGM for six redshift bins in the range z = 1.6 - 3.7. We find that the IGM state is close to isothermal (γ ≈ 1) at z ∼ 3 which may indicate that HeII reionization occurred at this redshift.
We present a spectroscopic analysis of seven Extremely Strong Damped Lyα systems at redshifts z = 2-3, obtained with the intermediate-resolution spectrograph X-shooter on the Very Large Telescope. ...For all systems we estimated column densities of the neutral atomic hydrogen HI, metal abundances and dust depletion. We firmly detected molecular hydrogen H2 in two systems in our sample; for the remaining systems we set a conservative upper limits on the H2 column densities. The properties of the obtained systems are in consistency with the sample of the Extremely Strong Damped Lyα systems available in the literature.
Spectroscopy of the Lya forest in quasar spectra proved to be a useful tool for probing the intergalactic gas. We developed the automatic program for Voigt profile fitting of Lya forest lines. We run ...this code on 9 high resolution (∼ 50000) quasars spectra with a high signal-to-noise ratio (∼ 50 - 100) from the Keck telescope archive and obtained the sample of single well-fitted Lya lines. Fitting the joint 2d distribution of column density and Doppler parameter from this sample by physically reasonable model we estimate a power law index, γ, of the equation of state of the intergalactic medium in the redshift range z ∼ 2 - 3. We found that our measurement is in an agreement with measurements by other groups obtained with Voigt profile fitting technique.
PDF
