We present new measurements of the temperature of the intergalactic medium (IGM) derived from the Lyα forest over 2.0 ≤z≤ 4.8. The small-scale structure in the forest of 61 high-resolution ...quasi-stellar object spectra is quantified using a new statistic, the curvature, and the conversion to temperature calibrated using a suite of hydrodynamic simulations. At each redshift, we focus on obtaining the temperature at an optimal overdensity probed by the Lyα forest,
, where the temperature is nearly a one-to-one function of the curvature regardless of the slope of the temperature-density relation. The median 2σ statistical uncertainty in these measurements is 8 per cent, though there may be comparable systematic errors due to the unknown amount of Jeans smoothing in the IGM. We use our
results to infer the temperature at the mean density, T
0. Even for a maximally steep temperature-density relation, T
0 must increase from ∼8000 K at z≃ 4.4 to ≳12 000 K at z≃ 2.8. This increase is not consistent with the monotonic decline in T
0 expected in the absence of He ii reionization. We therefore interpret the observed rise in temperature as evidence of He ii reionization beginning at z≳ 4.4. The evolution of T
0 is consistent with an end to He ii reionization at z∼ 3, as suggested by opacity measurements of the He ii Lyα forest, although the redshift at which T
0 peaks will depend somewhat on the evolution of the temperature-density relation. These new temperature measurements suggest that the heat input due to the reionization of He ii dominates the thermal balance of the IGM over an extended period with Δz≳ 1.
The thermal state of the intergalactic medium (IGM) provides an indirect probe of both the H i and He ii reionization epochs. Current constraints on the IGM temperature from the Lyα forest are ...restricted to the redshift range 2 ≤z≤ 4.5, limiting the ability to probe the thermal memory of H i reionization towards higher redshift. In this work, we present the first direct measurement of the IGM temperature around a z= 6 quasar by analyzing the Doppler widths of Lyα absorption lines in the proximity zone of SDSS J0818+1722. We use a high-resolution (R= 40 000) Keck/HIRES spectrum in combination with detailed numerical modelling to obtain the temperature at mean density, T0= 23 600 ±50006900 K (±92009300 K) at 68 (95) per cent confidence assuming a prior probability following H i and He ii reionization. This enables us to place an upper limit on the redshift of H i reionization, zH, within 33 comoving Mpc of SDSS J0818+1722. If the quasar reionizes the He ii in its vicinity, then in the limit of instantaneous reionization we infer zH < 9.0(11.0) at 68 (95) per cent confidence assuming photoheating is the dominant heat source and that H i reionization is driven by ionizing sources with soft spectra, typical of Population II stars. If the H i and He ii in the IGM around SDSS J0818+1722 are instead reionized simultaneously by a population of massive metal-free stars, characterized by very hard ionizing spectra, we obtain a tighter upper limit of zH < 8.4(9.4). Initiating reionization at higher redshifts produces temperatures which are too low with respect to our constraint unless the H i ionizing sources or the quasar itself has spectra significantly harder than typically assumed.
Using Voigt-profile-fitting procedures on Keck High Resolution Spectrograph spectra of nine QSOs, we identify 1099 C IV absorber components clumped in 201 systems outside the Lyman forest over 1.6 <, ...~ z <, ~ 4.4. With associated Si IV, C II, Si II and N V where available, we investigate the bulk statistical and ionization properties of the components and systems and find no significant change in redshift for C IV and Si IV while C II, Si II and N V change substantially. The C IV components exhibit strong clustering, but no clustering is detected for systems on scales from 150 km s super(-1) out to 50,000 km s super(-1). We conclude that the clustering is due entirely to the peculiar velocities of gas present in the circumgalactic media of galaxies. Using specific combinations of ionic ratios, we compare our observations with model ionization predictions for absorbers exposed to the metagalactic ionizing radiation background augmented by proximity radiation from their associated galaxies and find that the generally accepted means of radiative escape by transparent channels from the internal star-forming sites is spectrally not viable for our stronger absorbers. We develop an active scenario based on runaway stars with resulting changes in the efflux of radiation that naturally enable the needed spectral convergence, and in turn provide empirical indicators of morphological evolution in the associated galaxies. Together with a coexisting population of relatively compact galaxies indicated by the weaker absorbers in our sample, the collective escape of radiation is sufficient to maintain the intergalactic medium ionized over the full range 1.9 < z <, ~ 4.4.
ABSTRACT
Scaling laws of dust, H i gas, and metal mass with stellar mass, specific star formation rate, and metallicity are crucial to our understanding of the build-up of galaxies through their ...enrichment with metals and dust. In this work, we analyse how the dust and metal content varies with specific gas mass (MH i/M⋆) across a diverse sample of 423 nearby galaxies. The observed trends are interpreted with a set of Dust and Element evolUtion modelS (DEUS) – including stellar dust production, grain growth, and dust destruction – within a Bayesian framework to enable a rigorous search of the multidimensional parameter space. We find that these scaling laws for galaxies with −1.0 ≲ log MH i/M⋆ ≲ 0 can be reproduced using closed-box models with high fractions (37–89 ${{\ \rm per\ cent}}$) of supernova dust surviving a reverse shock, relatively low grain growth efficiencies (ϵ = 30–40), and long dust lifetimes (1–2 Gyr). The models have present-day dust masses with similar contributions from stellar sources (50–80 ${{\ \rm per\ cent}}$) and grain growth (20–50 ${{\ \rm per\ cent}}$). Over the entire lifetime of these galaxies, the contribution from stardust (>90 ${{\ \rm per\ cent}}$) outweighs the fraction of dust grown in the interstellar medium (<10 ${{\ \rm per\ cent}}$). Our results provide an alternative for the chemical evolution models that require extremely low supernova dust production efficiencies and short grain growth time-scales to reproduce local scaling laws, and could help solving the conundrum on whether or not grains can grow efficiently in the interstellar medium.
We present the results from our search for C IV absorption systems at redshifts z = 5.3-6.0. We have observed four z ~ 6 QSOs with Keck/NIRSPEC in echelle mode. The data are the most sensitive yet ...taken to search for C IV at these redshifts, being 50% complete at column densities log N C IV 13.4(cm-2). We find no clear C IV systems in any of the four sight lines. Taking into account our completeness, this translates into a decline in the number density of C IV absorbers in the range 13.2 < log N C IV < 15.0 of at least a factor ~4.1 (95% confidence) from z ~ 2-4.5, over which the number density is relatively constant. We use our lack of detections, along with results from previous studies, to set limits on the slope and normalization of the column density distribution at z = 5.3-6.0. The rapid evolution of C IV at these redshifts suggests that the decrease in the number density may largely be due to ionization effects, in which case many of the metals in the z ~ 4.5 intergalactic medium (IGM) could already be in place at z ~ 5.3, but in lower ionization states. The lack of weak systems in our data, combined with the presence of strong C IV absorbers along at least one other sight line, further suggests that there may be large-scale variations in the enrichment and/or ionization state of the z ~ 6 IGM. Alternatively, the known C IV absorbers at these redshifts may not reside in the general IGM, but may be associated with rare, UV-bright star-forming galaxies.
We present observations of a peculiar Lyα-emitting galaxy at redshift z = 3.344, discovered in a deep, blind spectroscopic survey for faint Lyα emitters with the Magellan II telescope in the Hubble ...Ultra Deep Field. The galaxy exhibits complex Lyα emission, including an extended, asymmetric component that is partially suppressed by damped Lyα absorption, and two spatially elongated, narrow emission features. Archival Hubble Space Telescope Advanced Camera for Surveys imaging shows evidence for tidal disruption of the stellar component. This V = 27 galaxy appears to give us unprecedented insight into two fundamental stages in the formation of structure at high redshift: the inflow of gas into ordinary galaxies, and the escape of ionizing radiation into the intergalactic medium. Neutral hydrogen, falling in partly in the form of a narrow filament, appears to emit fluorescent Lyα photons induced by the stellar ionizing flux escaping from the disturbed galaxy. The in-falling material may represent primary cold accretion or an interaction-triggered inflow. The rate of ionizing photons required by the observed Lyα emission is consistent with the rate of photons produced by the observed stellar population, with roughly 50 per cent of ionizing photons escaping from the immediate galaxy and encountering the in-falling gas. We briefly discuss cooling radiation and large-scale shocks as additional sources for Lyα and ionizing radiation in high-redshift galaxies, but find that stellar radiation is likely to be the dominant source of ionizing photons for most faint galaxies. The observational properties of the galaxy lend support to a picture where galaxy interactions facilitate the escape of both Lyα and ionizing radiation. We argue that galaxies like the present object may be common at high redshift. This galaxy may therefore be a late example of an interacting population of dwarf galaxies that contribute significantly to the reionization of the universe.
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