HST Imaging of the Brightest z similar to 8-9 Galaxies from UltraVISTA: The Extreme Bright End of the UV Luminosity Function

We report on the discovery of three especially bright candidate ${z}_{\mathrm{phot}}\gtrsim 8$ galaxies. Five sources were targeted for follow-up with the Hubble Space Telescope (HST)/Wide Field Camera 3 (WFC3), selected from a larger sample of 16 bright ($24.8\lesssim H\lesssim 25.5$ mag) candidate $z\gtrsim 8$ Lyman break galaxies (LBGs) identified over 1.6 degrees2 of the COSMOS/UltraVISTA field. These were selected as Y and J dropouts by leveraging the deep (Y-to-{K}_{{\rm{S}}}\sim 25.3\mbox{--}24.8 mag, $5\sigma$) NIR data from the UltraVISTA DR3 release, deep ground-based optical imaging from the CFHTLS and Suprime-Cam programs, and Spitzer/IRAC mosaics combining observations from the SMUVS and SPLASH programs. Through the refined spectral energy distributions, which now also include new HyperSuprimeCam g-, r-, i-, z-, and Y-band data, we confirm that 3/5 galaxies have robust {z}_{\mathrm{phot}}\sim 8.0\mbox{--}8.7, consistent with the initial selection. The remaining 2/5 galaxies have a nominal ${z}_{\mathrm{phot}}\sim 2$. However, with HST data alone, these objects have increased probability of being at $z\sim 9$. We measure mean UV continuum slopes $\beta =-1.74\pm 0.35$ for the three z\sim 8\mbox{--}9 galaxies, marginally bluer than similarly luminous z\sim 4\mbox{--}6 in CANDELS but consistent with previous measurements of similarly luminous galaxies at $z\sim 7$. The circularized effective radius for our brightest source is 0.9 ± 0.3 kpc, similar to previous measurements for a bright $z\sim 11$ galaxy and bright $z\sim 7$ galaxies. Finally, enlarging our sample to include the six brightest $z\sim 8$ LBGs identified over UltraVISTA (i.e., including three other sources from Labbé et al.) we estimate for the first time the volume density of galaxies at the extreme bright end (${M}_{\mathrm{UV}}\sim -22$ mag) of the $z\sim 8$ UV luminosity function. Despite this exceptional result, the still large statistical uncertainties do not allow us to discriminate between a Schechter and a double-power-law form

UNCOVER: A NIRSpec Identification of a Broad-line AGN at z = 8.50

Deep observations with the James Webb Space Telescope (JWST) have revealed an emerging population of red pointlike sources that could provide a link between the postulated supermassive black hole seeds and observed quasars. In this work, we present a JWST/NIRSpec spectrum from the JWST Cycle 1 UNCOVER Treasury survey of a massive accreting black hole at z = 8.50 displaying a clear broad-line component as inferred from the Hβ line with FWHM = 3439 ± 413 km s−1, typical of the broad-line region of an active galactic nucleus (AGN). The AGN nature of this object is further supported by high ionization, as inferred from emission lines, and a point-source morphology. We compute a black hole mass of log 10 ( M BH / M ⊙ ) = 8.17 ± 0.42 and a bolometric luminosity of L bol ∼ 6.6 × 1045 erg s−1. These values imply that our object is accreting at ∼40% of the Eddington limit. Detailed modeling of the spectral energy distribution in the optical and near-infrared, together with constraints from ALMA, indicate an upper limit on the stellar mass of log 10 ( M * / M ⊙ ) < 8.7 , which would lead to an unprecedented ratio of black hole to host mass of at least ∼30%. This is orders of magnitude higher compared to the local QSOs but consistent with recent AGN studies at high redshift with JWST. This finding suggests that a nonnegligible fraction of supermassive black holes either started out from massive seeds and/or grew at a super-Eddington rate at high redshift. Given the predicted number densities of high-z faint AGN, future NIRSpec observations of larger samples will allow us to further investigate galaxy-black hole coevolution in the early Universe

Shedding Light on the Galaxy Luminosity Function

From as early as the 1930s, astronomers have tried to quantify the statistical nature of the evolution and large-scale structure of galaxies by studying their luminosity distribution as a function of redshift - known as the galaxy luminosity function (LF). Accurately constructing the LF remains a popular and yet tricky pursuit in modern observational cosmology where the presence of observational selection effects due to e.g. detection thresholds in apparent magnitude, colour, surface brightness or some combination thereof can render any given galaxy survey incomplete and thus introduce bias into the LF. Over the last seventy years there have been numerous sophisticated statistical approaches devised to tackle these issues; all have advantages -- but not one is perfect. This review takes a broad historical look at the key statistical tools that have been developed over this period, discussing their relative merits and highlighting any significant extensions and modifications. In addition, the more generalised methods that have emerged within the last few years are examined. These methods propose a more rigorous statistical framework within which to determine the LF compared to some of the more traditional methods. I also look at how photometric redshift estimations are being incorporated into the LF methodology as well as considering the construction of bivariate LFs. Finally, I review the ongoing development of completeness estimators which test some of the fundamental assumptions going into LF estimators and can be powerful probes of any residual systematic effects inherent magnitude-redshift data.Comment: 95 pages, 23 figures, 3 tables. Now published in The Astronomy & Astrophysics Review. This version: bring in line with A&AR format requirements, also minor typo corrections made, additional citations and higher rez images adde

Anisotropic resistivity effects on the minimum dissipation states of tokamak plasmas sustained by coaxial helicity injection

The minimum dissipation states of a tokamak-like plasma sustained by helicity injection are determined. The Ohmic energy dissipation rate is minimized using the helicity balance as a constraint and considering different resistivity values in the directions parallel and perpendicular to the magnetic field inside the plasma. The resulting Euler-Lagrange equations are solved, assuming axial symmetry, for different values of the ratio between the parallel and perpendicular resistivities (eta (parallel to)/eta (perpendicular to)) It is shown that previously published results are not completely correct and that the radial profile of mu (0)j(phi)/B-phi, (the ratio between the toroidal current density and the toroidal magnetic field) changes significantly when eta (parallel to)/eta (perpendicular to) decreases

Anisotropic resistivity effects on the minimum dissipation states of tokamak plasmas sustained by coaxial helicity injection

The minimum dissipation states of a tokamak-like plasma sustained by helicity injection are determined. The Ohmic energy dissipation rate is minimized using the helicity balance as a constraint and considering different resistivity values in the directions parallel and perpendicular to the magnetic field inside the plasma. The resulting Euler-Lagrange equations are solved, assuming axial symmetry, for different values of the ratio between the parallel and perpendicular resistivities (eta (parallel to)/eta (perpendicular to)) It is shown that previously published results are not completely correct and that the radial profile of mu (0)j(phi)/B-phi, (the ratio between the toroidal current density and the toroidal magnetic field) changes significantly when eta (parallel to)/eta (perpendicular to) decreases