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Register a new userImaging of SDSS z>6 quasar fields: gravitational lensing, companion galaxies and the host dark matter halos
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We have undertaken deep optical imaging observations of three 6.2<z<6.5 quasar fields in the i and z filters. These data are used to search for foreground galaxies which are gravitationally lensing the quasars and distant galaxies physically associated with the quasars. Foreground galaxies are found closer than 5 arcsec from the lines-of-sight of two of the three quasars. However, the faintness of these galaxies suggests they have fairly low masses and provide only weak magnifications (mu<1.1). No convincing galaxies physically associated with the quasars are found and the number of i-band dropouts is consistent with that found in random fields. We consider the expected dark matter halo masses which host these quasars under the assumption that a correlation between black hole mass and dark matter halo mass exists. We show that the steepness of the high-mass tail of the halo mass function at this redshift, combined with realistic amounts of scatter in this correlation, lead to expected halo masses substantially lower than previously believed. This analysis can explain the lack of companion galaxies found here and the low dynamical mass recently published for one of the quasars.
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We explore the kinematics of 27 z~6 quasar host galaxies observed in [CII]-158 micron ([CII]) emission with the Atacama Large Millimeter/sub-millimeter Array at a resolution of ~0.25. We find that nine of the galaxies show disturbed [CII] emission, either due to a close companion galaxy or recent merger. Ten galaxies have smooth velocity gradients consistent with the emission arising from a gaseous disk. The remaining eight quasar host galaxies show no velocity gradient, suggesting that the gas in these systems is dispersion-dominated. All galaxies show high velocity dispersions with a mean of 129+-10 km/s. To provide an estimate of the dynamical mass within twice the half-light radius of the quasar host galaxy, we model the kinematics of the [CII] emission line using our publicly available kinematic fitting code, qubefit. This results in a mean dynamical mass of 5.0+-0.8(+-3.5) x 10^10 Msun. Comparison between the dynamical mass and the mass of the supermassive black hole reveals that the sample falls above the locally derived bulge mass--black hole mass relation at 2.4sigma significance. This result is robust even if we account for the large systematic uncertainties. Using several different estimators for the molecular mass, we estimate a gas mass fraction of >10%, indicating gas makes up a large fraction of the baryonic mass of z~6 quasar host galaxies. Finally, we speculate that the large variety in [CII] kinematics is an indication that gas accretion onto z~6 super massive black holes is not caused by a single precipitating factor.
Wave Dark Matter (WaveDM) has recently gained attention as a viable candidate to account for the dark matter content of the Universe. In this paper we explore the extent to which dark matter halos in this model, and under what conditions, are able to reproduce strong lensing systems. First, we analytically explore the lensing properties of the model -- finding that a pure WaveDM density profile, a soliton profile, produces a weaker lensing effect than other similar cored profiles. Then we analyze models with a soliton embedded in an NFW profile, as has been found in numerical simulations of structure formation. We use a benchmark model with a boson mass of $m_a=10^{-22}{rm eV}$, for which we see that there is a bi-modality in the contribution of the external NFW part of the profile, and actually some of the free parameters associated with it are not well constrained. We find that for configurations with boson masses $10^{-23}$ -- $10^{-22}{rm eV}$, a range of masses preferred by dwarf galaxy kinematics, the soliton profile alone can fit the data but its size is incompatible with the luminous extent of the lens galaxies. Likewise, boson masses of the order of $10^{-21}{rm eV}$, which would be consistent with Lyman-$alpha$ constraints and consist of more compact soliton configurations, necessarily require the NFW part in order to reproduce the observed Einstein radii. We then conclude that lens systems impose a conservative lower bound $m_a > 10^{-24}$ and that the NFW envelope around the soliton must be present to satisfy the observational requirements.
We report on ~0.35(~2 kpc) resolution observations of the [CII] and dust continuum emission from five z>6 quasar host-companion galaxy pairs obtained with the Atacama Large Millimeter/submillimeter Array. The [CII] emission is resolved in all galaxies, with physical extents of 3.2-5.4 kpc. The dust continuum is on-average 40% more compact, which results in larger [CII] deficits in the center of the galaxies. However, the measured [CII] deficits are fully consistent with those found at lower redshifts. Four of the galaxies show [CII] velocity fields that are consistent with ordered rotation, while the remaining six galaxies show no clear velocity gradient. All galaxies have high (~80-200 km/s) velocity dispersions, consistent with the interpretation that the interstellar medium (ISM) of these high redshift galaxies is turbulent. By fitting the galaxies with kinematic models, we estimate the dynamical mass of these systems, which range between (0.3 -> 5.4) x 1E10 Msun. For the three closest separation galaxy pairs, we observe dust and [CII] emission from gas in between and surrounding the galaxies, which is an indication that tidal interactions are disturbing the gas in these systems. Although gas exchange in these tidal interactions could power luminous quasars, the existence of quasars in host galaxies without nearby companions suggests that tidal interactions are not the only viable method for fueling their active centers. These observations corroborate the assertion that accreting supermassive black holes do not substantially contribute to the [CII] and dust continuum emission of the quasar host galaxies, and showcase the diverse ISM properties of galaxies when the universe was less than one billion years old.
We study the interstellar medium in a sample of 27 high-redshift quasar host galaxies at z>6, using the [CII] 158um emission line and the underlying dust continuum observed at ~1kpc resolution with ALMA. By performing uv-plane spectral stacking of both the high and low spatial resolution data, we investigate the spatial and velocity extent of gas, and the size of the dust-emitting regions. We find that the average surface brightness profile of both the [CII] and the dust continuum emission can be described by a steep component within a radius of 2kpc, and a shallower component with a scale length of 2kpc, detected up to ~10kpc. The surface brightness of the extended emission drops below ~1% of the peak at radius of ~5kpc, beyond which it constitutes 10-20% of the total measured flux density. Although the central component of the dust continuum emission is more compact than that of the [CII] emission, the extended components have equivalent profiles. The observed extended components are consistent with those predicted by hydrodynamical simulations of galaxies with similar infrared luminosities, where the dust emission is powered by star formation. The [CII] spectrum measured in the mean uv-plane stacked data can be described by a single Gaussian, with no observable [CII] broad-line emission (velocities in excess of >500km/s), that would be indicative of outflows. Our findings suggest that we are probing the interstellar medium and associated star formation in the quasar host galaxies up to radii of 10kpc, whereas we find no evidence for halos or outflows.
We use the statistics of strong gravitational lenses to investigate whether mass profiles with a flat density core are supported. The probability for lensing by halos modeled by a nonsingular truncated isothermal sphere (NTIS) with image separations greater than a certain value (ranging from zero to ten arcseconds) is calculated. NTIS is an analytical model for the postcollapse equilibrium structure of virialized objects derived by Shapiro, Iliev & Raga. This profile has a soft core and matches quite well with the mass profiles of dark matter-dominated dwarf galaxies deduced from their observed rotation curves. It also agrees well with the NFW (Navarro-Frenk-White) profile at all radii outside of a few NTIS core radii. Unfortunately, comparing the results with those for singular lensing halos (NFW and SIS+NFW) and strong lensing observations, the probabilities for lensing by NTIS halos are far too low. As this result is valid for any other nonsingular density profiles (with a large core radius), we conclude that nonsingular density profiles (with a large core radius) for CDM halos are ruled out by statistics of strong gravitational lenses.
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