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Register a new userA Simple Technique for Predicting High-Redshift Galaxy Evolution
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We show that the ratio of galaxies specific star formation rates (SSFRs) to their host halos specific mass accretion rates (SMARs) strongly constrains how the galaxies stellar masses, specific star formation rates, and host halo masses evolve over cosmic time. This evolutionary constraint provides a simple way to probe z>8 galaxy populations without direct observations. Tests of the method with galaxy properties at z=4 successfully reproduce the known evolution of the stellar mass--halo mass (SMHM) relation, galaxy SSFRs, and the cosmic star formation rate (CSFR) for 5<z<8. We then predict the continued evolution of these properties for 8<z<15. In contrast to the non-evolution in the SMHM relation at z<4, the median galaxy mass at fixed halo mass increases strongly at z>4. We show that this result is closely linked to the flattening in galaxy SSFRs at z>2 compared to halo specific mass accretion rates; we expect that average galaxy SSFRs at fixed stellar mass will continue their mild evolution to z~15. The expected CSFR shows no breaks or features at z>8.5; this constrains both reionization and the possibility of a steep falloff in the CSFR at z=9-10. Finally, we make predictions for stellar mass and luminosity functions for the James Webb Space Telescope (JWST), which should be able to observe one galaxy with M* > ~10^8 Msun per 10^3 Mpc^3 at z=9.6 and one such galaxy per 10^4 Mpc^3 at z=15.
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Knowledge of the number density of H$alpha$ emitting galaxies is vital for assessing the scientific impact of the Euclid and WFIRST missions. In this work we present predictions from a galaxy formation model, Galacticus, for the cumulative number counts of H$alpha$-emitting galaxies. We couple Galacticus to three different dust attenuation methods and examine the counts using each method. A $chi^2$ minimisation approach is used to compare the model predictions to observed galaxy counts and calibrate the dust parameters. We find that weak dust attenuation is required for the Galacticus counts to be broadly consistent with the observations, though the optimum dust parameters return large values for $chi^2$, suggesting that further calibration of Galacticus is necessary. The model predictions are also consistent with observed estimates for the optical depth and the H$alpha$ luminosity function. Finally we present forecasts for the redshift distributions and number counts for two Euclid-like and one WFIRST-like survey. For a Euclid-like survey with redshift range $0.9leqslant zleqslant 1.8$ and H$alpha+{rm [NII]}$ blended flux limit of $2times 10^{-16}{rm erg},{rm s}^{-1},{rm cm}^{-2}$ we predict a number density between 3900--4800 galaxies per square degree. For a WFIRST-like survey with redshift range $1leqslant zleqslant 2$ and blended flux limit of $1times 10^{-16}{rm erg},{rm s}^{-1},{rm cm}^{-2}$ we predict a number density between 10400--15200 galaxies per square degree.
Massive black holes (MBHs) are nowadays recognized as integral parts of galaxy evolution. Both the approximate proportionality between MBH and galaxy mass, and the expected importance of feedback from active MBHs in regulating star formation in their host galaxies point to a strong interplay between MBHs and galaxies. MBHs must form in the first galaxies and be fed by gas in these galaxies, with continuous or intermittent inflows that, at times, can be larger than the Eddington rate. Feedback from supernovae and from the MBHs themselves modulates the growth of the first MBHs. While current observational data only probe the most massive and luminous MBHs, the tip of the iceberg, we will soon be able to test theoretical models of MBH evolution on more normal MBHs: the MBHs that are indeed relevant in building the population that we observe in local galaxies, including our own Milky Way.
We explore the connections between the evolving galaxy and AGN populations. We present a simple phenomenological model that links the evolving galaxy mass function and the evolving quasar luminosity function, which makes specific and testable predictions for the distribution of host galaxy masses for AGN of different luminosities. We show that the $phi^{*}$ normalisations of the galaxy mass function and of the AGN luminosity function closely track each other over a wide range of redshifts, implying a constant duty cycle of AGN activity. The strong redshift evolution in the AGN $L^*$ can be produced by either an evolution in the distribution of Eddington ratios, or in the $m_{bh}/m_{*}$ mass ratio, or both. To try to break this degeneracy we look at the distribution of AGN in the SDSS ($m_{bh},L$) plane, showing that an evolving ratio $m_{bh}/m_{*} propto (1+z)^2$ reproduces the observed data and also reproduces the local relations which connect the black hole population with the host galaxies for both quenched and star-forming populations. We stress that observational studies that compare the masses of black holes in active galaxies at high redshift with those in quiescent galaxies locally will always see much weaker evolution. Evolution of this form would produce, or could be produced by, a redshift-independent $m_{bh} - sigma$ relation and could explain why the local $m_{bh} - sigma$ relation is tighter than $m_{bh} - m_{*}$ even if $sigma$ is not directly linked to black hole growth. Irrespective of the evolution of $m_{bh}/m_{*}$, the model reproduces both the appearance of downsizing and the so-called sub-Eddington boundary without any mass-dependence in the evolution of black hole growth rates.
We report on the diversity in quasar spectra from the Baryon Oscillation Spectroscopic Survey. After filtering the spectra to mitigate selection effects and Malmquist bias associated with a nearly flux-limited sample, we create high signal-to-noise ratio composite spectra from 58,656 quasars (2.1 le z le 3.5), binned by luminosity, spectral index, and redshift. With these composite spectra, we confirm the traditional Baldwin effect (BE, i.e., the anticorrelation of C IV equivalent width (EW) and luminosity) that follows the relation W_lambda propto L^{beta_w} with slope beta_w = -0.35 pm 0.004, -0.35 pm 0.005, and -0.41 pm 0.005 for z = 2.25, 2.46, and 2.84, respectively. In addition to the redshift evolution in the slope of the BE, we find redshift evolution in average quasar spectral features at fixed luminosity. The spectroscopic signature of the redshift evolution is correlated at 98% with the signature of varying luminosity, indicating that they arise from the same physical mechanism. At a fixed luminosity, the average C IV FWHM decreases with increasing redshift and is anti-correlated with C IV EW. The spectroscopic signature associated with C IV FWHM suggests that the trends in luminosity and redshift are likely caused by a superposition of effects that are related to black hole mass and Eddington ratio. The redshift evolution is the consequence of a changing balance between these two quantities as quasars evolve toward a population with lower typical accretion rates at a given black hole mass.
Damped Lyman-alpha (DLA) and sub-DLA absorbers in quasar spectra provide the most sensitive tools for measuring element abundances of distant galaxies. Estimation of abundances from absorption lines depends sensitively on the accuracy of the atomic data used. We have started a project to produce new atomic spectroscopic parameters for optical/UV spectral lines using state-of-the-art computer codes employing very broad configuration interaction basis. Here we report our results for Zn II, an ion used widely in studies of the interstellar medium (ISM) as well as DLA/sub-DLAs. We report new calculations of many energy levels of Zn II, and the line strengths of the resulting radiative transitions. Our calculations use the configuration interaction approach within a numerical Hartree-Fock framework. We use both non-relativistic and quasi-relativistic one-electron radial orbitals. We have incorporated the results of these atomic calculations into the plasma simulation code Cloudy, and applied them to a lab plasma and examples of a DLA and a sub-DLA. Our values of the Zn II {lambda}{lambda} 2026, 2062 oscillator strengths are higher than previous values by 0.10 dex. Cloudy calculations for representative absorbers with the revised Zn atomic data imply ionization corrections lower than calculated before by 0.05 dex. The new results imply Zn metallicities should be lower by 0.1 dex for DLAs and by 0.13-0.15 dex for sub-DLAs than in past studies. Our results can be applied to other studies of Zn II in the Galactic and extragalactic ISM.
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