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Register a new userStar formation rate and dynamical mass of 10^8 solar mass black hole host galaxies at redshift 6
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We present ALMA observations of two moderate luminosity quasars at redshift 6. These quasars from the Canada-France High-z Quasar Survey (CFHQS) have black hole masses of ~10^8 M_solar. Both quasars are detected in the [CII] line and dust continuum. Combining these data with our previous study of two similar CFHQS quasars we investigate the population properties. We show that z>6 quasars have a significantly lower far-infrared luminosity than bolometric-luminosity-matched samples at lower redshift, inferring a lower star formation rate, possibly correlated with the lower black hole masses at z=6. The ratios of [CII] to far-infrared luminosities in the CFHQS quasars are comparable with those of starbursts of similar star formation rate in the local universe. We determine values of velocity dispersion and dynamical mass for the quasar host galaxies based on the [CII] data. We find that there is no significant offset from the relations defined by nearby galaxies with similar black hole masses. There is however a marked increase in the scatter at z=6, beyond the large observational uncertainties.
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ALMA [CII] line and continuum observations of five redshift z>6 quasars are presented. This sample was selected to probe lower black hole mass quasars than most previous studies. We find a wide dispersion in properties with CFHQS J0216-0455, a low-luminosity quasar with absolute magnitude M_1450=-22.2, remaining undetected implying a limit on the star formation rate in the host galaxy of <10 solar masses per year, whereas other host galaxies have star formation rates up to hundreds of solar masses per year. Two other quasars have particularly interesting properties. VIMOS2911 is one of the least luminous z>6 quasars known with M_1450=-23.1, yet its host galaxy is experiencing a very powerful starburst. PSO J167-13 has a broad and luminous [CII] line and a neighbouring galaxy a projected distance of 5kpc away that is also detected in the [CII] line and continuum. Combining with similar observations from the literature, we study the ratio of [CII] line to far-infrared luminosity finding this ratio increases at high-redshift at a fixed far-infrared luminosity, likely due to lower dust content, lower metallicity and/or higher gas masses. We compile a sample of 21 high-redshift quasars with dynamical masses and investigate the relationship between black hole mass and dynamical mass. The new observations presented here reveal dynamical masses consistent with the relationship defined by local galaxies. However, the full sample shows a very wide scatter across the black hole mass - dynamical mass plane, whereas both the local relationship and simulations of high-redshift quasars show a much lower dispersion in dynamical mass.
We present a new suite of hydrodynamical simulations and use it to study, in detail, black hole and galaxy properties. The high time, spatial and mass resolution, and realistic orbits and mass ratios, down to 1:6 and 1:10, enable us to meaningfully compare star formation rate (SFR) and BH accretion rate (BHAR) timescales, temporal behaviour and relative magnitude. We find that (i) BHAR and galaxy-wide SFR are typically temporally uncorrelated, and have different variability timescales, except during the merger proper, lasting ~0.2-0.3 Gyr. BHAR and nuclear (<100 pc) SFR are better correlated, and their variability are similar. Averaging over time, the merger phase leads typically to an increase by a factor of a few in the BHAR/SFR ratio. (ii) BHAR and nuclear SFR are intrinsically proportional, but the correlation lessens if the long-term SFR is measured. (iii) Galaxies in the remnant phase are the ones most likely to be selected as systems dominated by an active galactic nucleus (AGN), because of the long time spent in this phase. (iv) The timescale over which a given diagnostic probes the SFR has a profound impact on the recovered correlations with BHAR, and on the interpretation of observational data.
Recent analysis of strongly-lensed sources in the Hubble Frontier Fields indicates that the rest-frame UV luminosity function of galaxies at $z=$6--8 rises as a power law down to $M_mathrm{UV}=-15$, and possibly as faint as -12.5. We use predictions from a cosmological radiation hydrodynamic simulation to map these luminosities onto physical space, constraining the minimum dark matter halo mass and stellar mass that the Frontier Fields probe. While previously-published theoretical studies have suggested or assumed that early star formation was suppressed in halos less massive than $10^9$--$10^{11} M_odot$, we find that recent observations demand vigorous star formation in halos at least as massive as (3.1, 5.6, 10.5)$times10^9 M_odot$ at $z=(6,7,8)$. Likewise, we find that Frontier Fields observations probe down to stellar masses of (8.1, 18, 32)$times10^6 M_odot$; that is, they are observing the likely progenitors of analogues to Local Group dwarfs such as Pegasus and M32. Our simulations yield somewhat different constraints than two complementary models that have been invoked in similar analyses, emphasizing the need for further observational constraints on the galaxy-halo connection.
The local black hole mass function (BHMF) is of great interest to a variety of astrophysical problems, ranging from black hole binary merger rates to an indirect census of the dominant seeding mechanism of supermassive black holes. In this Letter, we combine the latest galaxy stellar mass function from the Galaxy And Mass Assembly survey with X-ray-based constraints to the local black hole occupation fraction to probe the BHMF below $10^6$ $M_{odot}$. Notwithstanding the large uncertainties inherent to the choice of a reliable observational proxy for black hole mass, the resulting range of BHMFs yields a combined normalization uncertainty of $lesssim$1 dex over the $[10^5-10^6]$ $M_{odot}$ range, where upcoming, space-based gravitational wave detectors are designed to be most sensitive.
Quasars are the most luminous non-transient objects known and as a result they enable studies of the Universe at the earliest cosmic epochs. Despite extensive efforts, however, the quasar ULAS J1120+0641 at z=7.09 has remained the only one known at z>7 for more than half a decade. Here we report observations of the quasar ULAS J134208.10+092838.61 (hereafter J1342+0928) at redshift z=7.54. This quasar has a bolometric luminosity of 4e13 times the luminosity of the Sun and a black hole mass of 8e8 solar masses. The existence of this supermassive black hole when the Universe was only 690 million years old---just five percent of its current age---reinforces models of early black-hole growth that allow black holes with initial masses of more than about 1e4 solar masses or episodic hyper-Eddington accretion. We see strong evidence of absorption of the spectrum of the quasar redwards of the Lyman alpha emission line (the Gunn-Peterson damping wing), as would be expected if a significant amount (more than 10 per cent) of the hydrogen in the intergalactic medium surrounding J1342+0928 is neutral. We derive a significant fraction of neutral hydrogen, although the exact fraction depends on the modelling. However, even in our most conservative analysis we find a fraction of more than 0.33 (0.11) at 68 per cent (95 per cent) probability, indicating that we are probing well within the reionization epoch of the Universe.
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