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Register a new userGemini Near-infrared Spectroscopy of Luminous z~6 Quasars: Chemical Abundances, Black Hole Masses, and MgII Absorption
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We present Gemini near-infrared spectroscopic observations of six luminous quasars at z=5.8$sim$6.3. Five of them were observed using Gemini-South/GNIRS, which provides a simultaneous wavelength coverage of 0.9--2.5 $mu$m in cross dispersion mode. The other source was observed in K band with Gemini-North/NIRI. We calculate line strengths for all detected emission lines and use their ratios to estimate gas metallicity in the broad-line regions of the quasars. The metallicity is found to be supersolar with a typical value of $sim$4 Z_{sun}, and a comparison with low-redshift observations shows no strong evolution in metallicity up to z$sim$6. The FeII/MgII ratio of the quasars is 4.9+/-1.4, consistent with low-redshift measurements. We estimate central BH masses of 10^9 to 10^{10} M_{sun} and Eddington luminosity ratios of order unity. We identify two MgII $lambdalambda$2796,2803 absorbers with rest equivalent width W_0^{lambda2796}>1 AA at 2.2<z<3 and three MgII absorbers with W_0^{lambda2796}>1.5 AA at z>3 in the spectra, with the two most distant absorbers at z=4.8668 and 4.8823, respectively. The redshift number densities (dN/dz) of MgII absorbers with W_0^{lambda2796}>1.5 AA are consistent with no cosmic evolution up to z>4.
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We present the results of new infrared spectroscopic observations of 37 quasars at z~3, selected based on the optical r-band magnitude and the availability of nearby bright stars for future imaging follow-up with Adaptive Optics system. The supermassive black hole (SMBH) masses (M_BH) were successfully estimated in 28 out of 37 observed objects from the combination of the H_beta emission linewidth and continuum luminosity at rest-frame 5100A. Comparing these results with those from previous studies of quasars with similar redshift, our sample exhibited slightly lower (~ -0.11 dex in median) Eddington ratios; and, the SMBH masses are slightly (~ 0.38 dex in median) higher. The SMBH growth time, t_grow, was calculated by dividing the estimated SMBH mass by the mass accretion rate measured using optical luminosity. We found, given reasonable assumptions, that t_grow was smaller than the age of the universe at the redshift of individual quasars for a large fraction of observed sources, suggesting that the SMBHs in many of our observed quasars are in growing phase with high accretion rates. A comparison of the SMBH masses derived from our H_beta data and archived CIV data indicated considerable scattering, as indicated in previous studies. All quasars with measured SMBH masses have at least one nearby bright star, such that they are suitable targets for adaptive optics observations to study the mass relationship between SMBHs and host galaxies stellar component at high redshift.
We present the rest-frame optical spectral properties of 155 luminous quasars at 3.3<z<6.4 taken with the AKARI space telescope, including the first detection of H$alpha$ emission line as far out as z~6. We extend the scaling relation between the rest-frame optical continuum and line luminosity of active galactic nuclei (AGNs) to the high luminosity, high redshift regime that has rarely been probed before. Remarkably, we find that a single log-linear relation can be applied to the 5100${rm AA}$ and H$alpha$ AGN luminosities over a wide range of luminosity (10$^{42}$<$L_{5100}$<10$^{47}$ergs/s) or redshift (0<z<6), suggesting that the physical mechanism governing this relation is unchanged from z=0 to 6, over five decades in luminosity. Similar scaling relations are found between the optical and the UV continuum luminosities or line widths. Applying the scaling relations to the H$beta$ black hole mass ($M_{rm BH}$) estimator of local AGNs, we derive the $M_{rm BH}$ estimators based on H$alpha$, MgII, and CIV lines, finding that the UV-line based masses are overall consistent with the Balmer-line based, but with a large intrinsic scatter of 0.40dex for the CIV estimates. Our 43 $M_{rm BH}$ estimates from H$alpha$ confirm the existence of BHs as massive as ~10$^{10}M_{odot}$ out to z~5, and provide a secure footing for previous MgII-line based studies that a rapid $M_{rm BH}$ growth has occurred in the early universe.
Here we explore the infrared (IR) properties of the progenitors of high-z quasar host galaxies. Adopting the cosmological, data constrained semi-analytic model GAMETE/QSOdust, we simulate several independent merger histories of a luminous quasar at z ~ 6, following black hole growth and baryonic evolution in all its progenitor galaxies. We find that a fraction of progenitor galaxies (about 0.4 objects per single luminous quasar) at 6.5 < z < 8 has an IR luminosity of L_IR > 10^13 Lsun (hyper-luminous IR galaxies; HyLIRGs). HyLIRGs progenitors reside in the most massive halos, with dark matter (DM) masses of M_DM ~ 10^12.5 - 10^13 Msun. These systems can be easily observed in their ~ 1 mm-continuum emission in a few seconds of integration time with the Atacama Large Millimeter/submillimeter Array (ALMA), and at least 40% of them host nuclear BH activity that is potentially observable in the soft and hard X-ray band. Our findings are in line with recent observations of exceptional massive DM halos hosting HyLIRGs at z ~ 7, suggesting that z ~ 6 luminous quasars are indeed the signposts of these observed rare peaks in the high-z cosmic density field, and that massive IR-luminous galaxies at higher z are their natural ancestors.
We present chemical abundances in a sample of luminous cool stars located within 30 pc of the Galactic Center. Abundances of carbon, nitrogen, oxygen, calcium, and iron were derived from high-resolution infrared spectra in the H- and K-bands. The abundance results indicate that both [O/Fe] and [Ca/Fe] are enhanced respectively by averages of +0.2 and +0.3 dex, relative to either the Sun or the Milky Way disk at near solar Fe abundances. The Galactic Center stars show a nearly uniform and nearly solar iron abundance. The mean value of A(Fe) = 7.59 +- 0.06 agrees well with previous work. The total range in Fe abundance among Galactic Center stars, 0.16 dex, is significantly narrower than the iron abundance distributions found in the literature for the older bulge population. Our snapshot of the current-day Fe abundance within 30 pc of the Galactic Center samples stars with an age less than 1 Gyr; a larger sample in time (or space) may find a wider spread in abundances.
Using new J-band VLT-ISAAC and Keck-NIRSPEC spectroscopy, we have measured Halpha and [NII] line fluxes for 0.47<z<0.92 CFRS galaxies which have [OII], Hbeta and [OIII]a line fluxes available from optical spectroscopy, to investigate how the properties of the star forming gas in galaxies evolve with redshift. We derive the extinction and oxygen abundances for the sample using a method based on a set of ionisation parameter and oxygen abundance diagnostics, simultaneously fitting the [OII], Hbeta,[OIII], Halpha, and [NII] line fluxes. The individual reddening measurements allow us to accurately correct the Halpha-based star formation rate (SFR) estimates for extinction. Our most salient conclusions are: a) in all 30 CFRS galaxies the source of gas ionisation is not due to AGN activity; b) we find a range of 0<AV<3, suggesting that it is important to determine the extinction for every single galaxy in order to reliably measure SFRs and oxygen abundances in high redshift galaxies; c) high values of [NII]/Halpha >0.1 for most (but not all) of the CFRS galaxies indicate that they lie on the high-metallicity branch of the R23 calibration; d) about one third of the 0.47<z<0.92 CFRS galaxies in our sample have lower metallicities than local galaxies with similar luminosities and star formation rates; e) comparison with a chemical evolution model indicates that these low metallicity galaxies are unlikely to be the progenitors of metal-poor dwarf galaxies at z~0.
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