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Register a new userThe Role of Galaxies and AGN in Reionising the IGM - I: Keck Spectroscopy of 5 < z < 7 Galaxies in the QSO Field J1148+5251
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We introduce a new method for determining the influence of galaxies and active galactic nuclei (AGN) on the physical state of the intergalactic medium (IGM) at high redshift and illustrate its potential via a first application to the field of the $z=6.42$ QSO J1148+5251. By correlating the spatial positions of spectroscopically-confirmed Lyman break galaxies (LBGs) with fluctuations in the Lyman alpha forest seen in the high signal-to-noise spectrum of a background QSO, we provide a statistical measure of the typical escape fraction of Lyman continuum photons close to the end of cosmic reionisation. Here we use Keck DEIMOS spectroscopy to locate 7 colour-selected LBGs in the redshift range $5.3lesssim zlesssim 6.4$ and confirm a faint $z=5.701$ AGN. We then examine the spatial correlation between this sample and Ly$alpha$/Ly$beta$ transmission fluctuations in a Keck ESI spectrum of the QSO. Interpreting the statistical HI proximity effect as arising from faint galaxies clustered around the detected LBGs, we translate the observed mean Ly$alpha$ transmitted flux around an average detected LBG into a constraint on the mean escape fraction $langle f_{rm esc}ranglegeq0.08$ at $zsimeq6$. We also report evidence of the individual transverse HI proximity effect of a $z=6.177$ luminous LBG via a Ly$beta$ transmission spike and two broad Ly$alpha$ transmission spikes around the $z=5.701$ AGN. We discuss the possible origin of such associations which suggest that while faint galaxies are primarily driving reionisation, luminous galaxies and AGN may provide important contributions to the UV background or thermal fluctuations of the IGM at $zsimeq6$. Although a limited sample, our results demonstrate the potential of making progress using this method in resolving one of the most challenging aspects of the contribution of galaxies and AGN to cosmic reionisation.
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We present improved results of the measurement of the correlation between galaxies and the intergalactic medium (IGM) transmission at the end of reionisation. We have gathered a sample of $13$ spectroscopically confirmed Lyman-break galaxies (LBGs) and $21$ Lyman-$alpha$ emitters (LAEs) at angular separations $20 lesssim theta lesssim 10$ ($sim 0.1-4$ pMpc at $zsim 6$) from the sightlines to $8$ background $zgtrsim 6$ quasars. We report for the first time the detection of an excess of Lyman-$alpha$ transmission spikes at $sim 10-60$ cMpc from LAEs ($3.2sigma$) and LBGs ($1.9sigma$). We interpret the data with an improved model of the galaxy-Lyman-$alpha$ transmission and two-point cross-correlations which includes the enhanced photoionisation due to clustered faint sources, enhanced gas densities around the central bright objects and spatial variations of the mean free path. The observed LAE(LBG)-Lyman-$alpha$ transmission spike two-point cross-correlation function (2PCCF) constrains the luminosity-averaged escape fraction of all galaxies contributing to reionisation to $langle f_{rm esc} rangle_{M_{rm UV}<-12} = 0.14_{-0.05}^{+0.28},(0.23_{-0.12}^{+0.46})$. We investigate if the 2PCCF measurement can determine whether bright or faint galaxies are the dominant contributors to reionisation. Our results show that a contribution from faint galaxies ($M_{rm UV} > -20 , (2sigma)$) is necessary to reproduce the observed 2PCCF and that reionisation might be driven by different sub-populations around LBGs and LAEs at $zsim 6$.
We present Karl G. Jansky Very Large Array (VLA) observations of the CO ($J = 2 rightarrow 1$) line emission towards the $z = 6.419$ quasar SDSS J$114816.64+525150.3$ (J$1148+5251$). The molecular gas is found to be marginally resolved with a major axis of $0.9$ (consistent with previous size measurements of the CO ($J = 7 rightarrow 6$) emission). We observe tentative evidence for extended line emission towards the south west on a scale of ~$1.4$, but this is only detected at $3.3sigma$ significance and should be confirmed. The position of the molecular emission region is in excellent agreement with previous detections of low frequency radio continuum emission as well as [C ii] line and thermal dust continuum emission. These CO ($J = 2 rightarrow 1$) observations provide an anchor for the low excitation part of the molecular line SED. We find no evidence for extended low excitation component, neither in the spectral line energy distribution nor the image. We fit a single kinetic gas temperature model of 50 K. We revisit the gas and dynamical masses in light of this new detection of a low order transition of CO, and confirm previous findings that there is no extended reservoir of cold molecular gas in J$1148+5251$, and that the source departs substantially from the low $z$ relationship between black hole mass and bulge mass. Hence, the characteristics of J$1148+5251$ at $z = 6.419$ are very similar to $z$~$2$ quasars, in the lack of a diffuse cold gas reservoir and kpc-size compactness of the star forming region.
We investigate the origin of the FIR continuum of SDSS J1148+5251, using it as a prototype for the more general class of high-luminosity high-redshift QSOs. We run the radiative transfer code TRADING to follow the transfer of radiation from the central source and from stellar sources through the dusty environment of the host galaxy. The model is based on the output of the semi-analytical merger tree code, GAMETE/QSOdust, which enables to predict the evolution of the host galaxy and of its nuclear black hole, following the star formation history and chemical evolution -- including dust -- in all the progenitor galaxies of SDSS J1148+5251. We find that the radiation emitted by the central source can also provide an important source of heating for the dust distributed in the host galaxy, powering at least 30% and up to 70% of the observed far infrared emission at rest-frame wavelengths [20 - 1000]micron. The remaining fraction is contributed by stellar sources and can only be achieved if the host galaxy is able to sustain a star formation rate of ~ 900 Msun/yr at z=6.4. This points to a co-evolution scenario where, during their hierarchical assembly, the first SMBHs and their host galaxies first grow at the same pace until the black hole reaches a mass of ~ 2 10^8 Msun and starts growing faster than its host, reaching the bright quasar phase when the black hole and stellar mass fall within the scatter of the scaling relation observed in local galaxies. This same evolutionary scenario has been recently shown to explain the properties of a larger sample of 5 < z <6.4 QSOs, and imply that current dynamical mass measurements may have missed an important fraction of the host galaxy stellar mass. We conclude that the FIR luminosity of high-z quasars is a sensitive tracer of the rapidly changing physical conditions in the host galaxy.
We use sensitive observations of three high redshift sources; [CII] fine structure and CO(2-1) rotational transitions for the z=6.4 Quasar host galaxy (QSO) J1148+5251, and [CII] and CO(5-4) transitions from the QSO BR1202-0725 and its sub-millimeter companion (SMG) galaxy at z=4.7. We use these observations to place constraints on the quantity Dz = z(CO) - z(CII) for each source where z(CO) and z(CII) are the observed redshifts of the CO rotational transition and [CII] fine structure transition respectively, using a combination of approaches; 1) By modelling the emission line profiles using `shapelets to compare both the emission redshifts and the line profiles themselves, in order to make inferences about the intrinsic velocity differences between the molecular and atomic gas, and 2) By performing a marginalisation over all model parameters in order to calculate a non-parametric estimate of Dz. We derive 99% confidence intervals for the marginalised posterior of Dz of (-1.9 pm 1.3) x10^-3, (-3 pm 8) x10^-4 and (-2 pm 4) x10^-3 for J1148+5251, and the BR1202-0725 QSO and SMG respectively. We show the [CII] and CO(2-1) line profiles for J1148+5251 are consistent with each other within the limits of the data, whilst the [CII] and CO(5-4) line profiles from the BR1202-0725 QSO and SMG respectively have 65 and >99.9% probabilities of being inconsistent, with the CO(5-4) lines ~ 30% wider than the [CII] lines. Therefore whilst the observed values of Dz can correspond to variations in the quantity Delta F/F with cosmic time, where F=alpha^2/mu, with alpha the fine structure constant, and mu the proton-to-electron mass ratio, of both (-3.3 pm 2.3) x10^-4 for a look back time of 12.9 Gyr and of (-5 pm 15) x10^-5 for a look back time of 12.4 Gyr we propose that they are the result of the two species of gas being spatially separated as indicated by the inconsistencies in their line profiles.
Feedback likely plays a vital role in the formation of dwarf galaxies. While stellar processes have long been considered the main source of feedback, recent studies have revealed tantalizing signs of AGN feedback in dwarf galaxies. In this paper, we report the results from an integral-field spectroscopic study of a sample of eight dwarf galaxies with known AGN and suspected outflows. Outflows are detected in seven of them. The outflows are fast, with 50-percentile (median) velocity of up to $sim$240 km s$^{-1}$ and 80-percentile line width reaching $sim$1200 km s$^{-1}$, in clear contrast with the more quiescent kinematics of the host gas and stellar components. The outflows are generally spatially extended on a scale of several hundred pc to a few kpc, although our data do not clearly resolve the outflows in three targets. The outflows appear to be primarily photoionized by the AGN rather than shocks or young, massive stars. The kinematics and energetics of these outflows suggest that they are primarily driven by the AGN, although the star formation activity in these objects may also contribute to the energy input. A small but non-negligible portion of the outflowing material likely escapes the main body of the host galaxy and contributes to the enrichment of the circumgalactic medium. Overall, the impact of these outflows on their host galaxies is similar to those taking place in the more luminous AGN in the low-redshift universe.
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