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Register a new userA galaxy as the source of a Civ absorption system close to the epoch of reionization
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Carlos Gonzalo Diaz
Publication date
2011
fields
Physics
and research's language is
English
Authors
C. Gonzalo Diaz
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We find a bright (L_{UV}=2.5 L*_{z=6}) Lyman alpha emitter at redshift z=5.719 at a projected distance of 79 physical kpc from a strong triply ionized carbon (Civ) absorption system at redshift z=5.7238 previously reported in the spectrum of the z_{em} = 6.309 QSO SDSS J1030+0524. This is the highest redshift galaxy-absorber pair detected to-date, supporting the idea that galaxy-wide outflows were already in place at the end of the epoch of reionization. The proximity of this object makes it the most likely source of metals, consistent with models of outflows at lower redshift where significant observational evidence relates metal absorption systems with galaxies hosting outflows. In a typical outflow scenario, a wind of 200 km/s, active since the universe was only 0.6 Gyr old (z ~8.4), could eject metals out to 79 kpc at z=5.719. Although the origin of metals in the intergalactic medium (IGM) is still under debate, our results are consistent with predictions from cosmological simulations which reproduce the evolution of the cosmic density of Civ, from z ~ 6 to the present day based on outflow-driven enrichment of the IGM. We also report two more Lyman alpha emitters in this field, at z=5.973pm 0.002 and z=5.676pm 0.002 respectively, the former confirming the original identification by Stiavelli et al. Our results suggest that the colour cut typically used to identify i-dropouts (i_{775}-z_{850}>1.3) misses a non-negligible fraction of blue galaxies with faint UV continuum at z geq 5.7.
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Absorption signatures in the spectra of QSOs are one of our most powerful tools for studying galactic and intergalactic environments at high redshifts. With the discovery of QSOs out to z > 7, QSO absorption lines are now tracing the end stages of reionization on multiple fronts using the hydrogen Lyman-$alpha$ forest and heavy element absorbers. Next-generation QSO absorption line studies with large optical/IR telescopes will reveal in detail how the first galaxies emerged form the cosmic web, transformed their circum- and inter-galactic environments, and completed the last major phase transition of the Universe. These efforts will complement other upcoming studies of reionization, such as those with JWST, ALMA, and redshifted 21cm experiments.
This white paper highlights the crucial and urgent synergies required between WFIRST, Subaru Hyper Suprime-Cam or other >25m-class telescopes galaxy observations and SKA 21cm measurements to constrain the nature of reionization (ionization history and topology) and its sources.
The reionization of the Universe ends the dark ages that started after the recombination era. In the case of H, reionization finishes around $zsim 6$. Faint star-forming galaxies are the best candidate sources of the H-ionizing radiation, although active galactic nuclei may have also contributed. We have explored whether the termination regions of the jets from active galactic nuclei may have contributed significantly to the ionization of H in the late reionization epoch, around $zsim 6-7$. We assumed that, as it has been proposed, active galactic nuclei at $zsim 6$ may have presented a high jet fraction, accretion rate, and duty cycle, and that non-thermal electrons contribute significantly to the pressure of jet termination regions. Empirical black-hole mass functions were adopted to characterize the population of active galactic nuclei. From all this, estimates were derived for the isotropic H-ionizing radiation produced in the jet termination regions, at $zsim 6$, through inverse Compton scattering off CMB photons. We find that the termination regions of the jets of active galactic nuclei may have radiated most of their energy in the form of H-ionizing radiation at $zsim 6$. For typical black-hole mass functions at that redshift, under the considered conditions (long-lasting, common, and very active galactic nuclei with jets), the contribution of these jets to maintain (and possibly enhance) the ionization of H may have been non-negligible. We conclude that the termination regions of jets from active galactic nuclei could have had a significant role in the reionization of the Universe at $zgtrsim 6$.
Far infrared fine-structure transitions of CI and CII and rotational transitions of CO are used to probe hypothetical variations of the electron-to-proton mass ratio mu = m_e/m_p at the epoch of reionization (z > 6). A constraint on Delta mu/mu = (mu_obs - mu_lab)/mu_lab = (0.7 +/- 1.2)x10^-5 (1sigma) obtained at <z> = 6.31 is the most stringent up-to-date limit on the variation of mu at such high redshift. For all available estimates of Delta mu/mu ranging between z = 0 and z = 1100, - the epoch of recombination, - a regression curve Delta mu/mu = k_mu (1+z)^p, with k_mu = (1.6 +/- 0.3) x10^-8 and p = 2.00 +/- 0.03, is deduced. If confirmed, this would imply a dynamical nature of dark matter/dark energy.
Candidates for the modest galaxies that formed most of the stars in the early universe, at redshifts $z > 7$, have been found in large numbers with extremely deep restframe-UV imaging. But it has proved difficult for existing spectrographs to characterise them in the UV. The detailed properties of these galaxies could be measured from dust and cool gas emission at far-infrared wavelengths if the galaxies have become sufficiently enriched in dust and metals. So far, however, the most distant UV-selected galaxy detected in dust emission is only at $z = 3.25$, and recent results have cast doubt on whether dust and molecules can be found in typical galaxies at this early epoch. Here we report thermal dust emission from an archetypal early universe star-forming galaxy, A1689-zD1. We detect its stellar continuum in spectroscopy and determine its redshift to be $z = 7.5pm0.2$ from a spectroscopic detection of the Ly{alpha} break. A1689-zD1 is representative of the star-forming population during reionisation, with a total star-formation rate of about 12M$_odot$ yr$^{-1}$. The galaxy is highly evolved: it has a large stellar mass, and is heavily enriched in dust, with a dust-to-gas ratio close to that of the Milky Way. Dusty, evolved galaxies are thus present among the fainter star-forming population at $z > 7$, in spite of the very short time since they first appeared.
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