Gravitational waves are expected to be radiated by supermassive black hole binaries formed during galaxy mergers. A stochastic superposition of gravitational waves from all such binary systems would ...modulate the arrival times of pulses from radio pulsars. Using observations of millisecond pulsars obtained with the Parkes radio telescope, we constrained the characteristic amplitude of this background, Ac,yr, to be <1.0 × 10–15 with 95% confidence. This limit excludes predicted ranges for Ac,yr from current models with 91 to 99.7% probability. We conclude that binary evolution is either stalled or dramatically accelerated by galactic-center environments and that higher-cadence and shorter-wavelength observations would be more sensitive to gravitational waves.
Full text
Available for:
BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
Abstract
We compute the spherically averaged power spectrum from four seasons of data obtained for the Epoch of Reionization (EoR) project observed with the Murchison Widefield Array (MWA). We ...measure the EoR power spectrum over k = 0.07–3.0 h Mpc−1 at redshifts $z$ = 6.5–8.7. The largest aggregation of 110 h on EoR0 high band (3340 observations), yields a lowest measurement of (43 mK)2 = 1.8 × 103 mK2 at k = 0.14 h Mpc−1 and $z$ = 6.5 (2σ thermal noise plus sample variance). Using the Real-Time System to calibrate and the CHIPS pipeline to estimate power spectra, we select the best observations from the central five pointings within the 2013–2016 observing seasons, observing three independent fields and in two frequency bands. This yields 13 591 2-min snapshots (453 h), based on a quality assurance metric that measures ionospheric activity. We perform another cut to remove poorly calibrated data, based on power in the foreground-dominated and EoR-dominated regions of the two-dimensional power spectrum, reducing the set to 12 569 observations (419 h). These data are processed in groups of 20 observations, to retain the capacity to identify poor data, and used to analyse the evolution and structure of the data over field, frequency, and data quality. We subsequently choose the cleanest 8935 observations (298 h of data) to form integrated power spectra over the different fields, pointings, and redshift ranges.
We predict Lyman alpha (Ly alpha ) luminosity functions (LFs) of Ly alpha -selected galaxies (Ly alpha emitters, or LAEs) at z = 3-6 using the phenomenological model. This model combines observed ...UV-LFs of Lyman-break galaxies (LBGs, or drop-out galaxies), with constraints on their distribution of Ly alpha line strengths as a function of UV-luminosity and redshift. Our analysis shows that while Ly alpha LFs of LAEs are generally not Schechter functions, these provide a good description over the luminosity range of log sub(10)(L sub( alpha )/erg s super(-1)) = 41-44. Motivated by this result, we predict Schechter function parameters at z = 3-6. Our analysis further shows that (i) the faint-end slope of the Ly alpha LF is steeper than that of the UV-LF of LBGs, (with a median alpha sub(Ly alpha ) < -2.0 at z greater than or equal to 4), and (ii) a turnover in the Ly alpha LF of LAEs at Ly alpha luminosities 10 super(40) erg s super(-1) < L sub( alpha ) less than or equal to 10 super(41) erg s super(-1) may signal a flattening of UV-LF of LBGs at -12 > M sub(UV) > -14. We discuss the implications of these results -- which can be tested directly with upcoming surveys -- for the Epoch of Reionization.
We investigate the evolution of the star formation rate–stellar mass relation (SFR–M
⋆) and galaxy stellar mass function (GSMF) of z ∼ 4–7 galaxies, using cosmological simulations run with the ...smoothed particle hydrodynamics code P-GADGET3(XXL). We explore the effects of different feedback prescriptions (supernova-driven galactic winds and AGN feedback), initial stellar mass functions and metal cooling. We show that our fiducial model, with strong energy-driven winds and early active galactic nuclei (AGN) feedback, is able to reproduce the observed stellar mass function obtained from Lyman-break selected samples of star-forming galaxies at redshift 6 ≤ z ≤ 7. At z ∼ 4, observed estimates of the GSMF vary according to how the sample was selected. Our simulations are more consistent with recent results from K-selected samples, which provide a better proxy of stellar masses and are more complete at the high-mass end of the distribution. We find that in some cases simulated and observed SFR–M
⋆ relations are in tension, and this can lead to numerical predictions for the GSMF in excess of the GSMF observed. By combining the simulated SFR(M
⋆) relationship with the observed star formation rate function at a given redshift, we argue that this disagreement may be the result of the uncertainty in the SFR–M
⋆ (L
UV–M
⋆) conversion. Our simulations predict a population of faint galaxies not seen by current observations.
We present a theoretical model for the evolution of mass, angular momentum and size of galaxy discs and bulges, and we implement it into the semi-analytic galaxy formation code, Semi-Analytic Galaxy ...Evolution. The model follows both secular and violent evolutionary channels, including smooth accretion, disc instabilities, minor and major mergers. We find that the combination of our recipe with hierarchical clustering produces two distinct populations of bulges: merger-driven bulges, akin to classical bulges and ellipticals, and instability-driven bulges, akin to secular (or pseudo-)bulges. The model mostly reproduces the mass–size relation of gaseous and stellar discs, the evolution of the mass–size relation of ellipticals, the Faber–Jackson relation, and the magnitude–colour diagram of classical and secular bulges. The model predicts only a small overlap of merger-driven and instability-driven components in the same galaxy, and predicts different bulge types as a function of galaxy mass and disc fraction. Bulge type also affects the star formation rate and colour at a given luminosity. The model predicts a population of merger-driven red ellipticals that dominate both the low-mass and high-mass ends of the galaxy population, and span all dynamical ages; merger-driven bulges in disc galaxies are dynamically old and do not interfere with subsequent evolution of the star-forming component. Instability-driven bulges dominate the population at intermediate galaxy masses, especially thriving in massive discs. The model green valley is exclusively populated by instability-driven bulge hosts. Through the present implementation, the mass accretion history is perceivable in the galaxy structure, morphology and colours.
Intensity mapping of the neutral hydrogen (H i) is a new observational tool to efficiently map the large-scale structure over wide redshift ranges. The cross-correlation of intensity maps with galaxy ...surveys is a robust measure of the cosmological power spectrum and the H i content of galaxies which diminishes systematics caused by instrumental effects and foreground removal. We examine the cross-correlation signature at redshift 0.9 using a semi-analytical galaxy formation model in order to model the H i gas of galaxies as well as their optical magnitudes. We determine the scale-dependent clustering of the cross-correlation power for different types of galaxies determined by their colours, which act as a proxy for their star formation activity. We find that the cross-correlation coefficient with H i density for red quiescent galaxies falls off more quickly on smaller scales k > 0.2 h Mpc−1 than for blue star-forming galaxies. Additionally, we create a mock catalogue of highly star-forming galaxies to mimic the WiggleZ Dark Energy Survey, and use this to predict existing and future measurements using data from the Green Bank telescope and Parkes telescope. We find that the cross-power of highly star-forming galaxies shows a higher clustering on small scales than any other galaxy type and that this significantly alters the power spectrum shape on scales k > 0.2 h Mpc−1. We show that the cross-correlation coefficient is not negligible when interpreting the cosmological cross-power spectrum and additionally contains information about the H i content of the optically selected galaxies.
The formation and growth processes of supermassive black holes (SMBHs) are not well constrained. SMBH population models, however, provide specific predictions for the properties of the ...gravitational-wave background (GWB) from binary SMBHs in merging galaxies throughout the universe. Using observations from the Parkes Pulsar Timing Array, we constrain the fractional GWB energy density (Ω GW ) with 95% confidence to be Ω GW (H₀/73 kilometers per second per megaparsec)² < 1.3 × 10⁻⁹ (where H₀ is the Hubble constant) at a frequency of 2.8 nanohertz, which is approximately a factor of 6 more stringent than previous limits. We compare our limit to models of the SMBH population and find inconsistencies at confidence levels between 46 and 91%. For example, the standard galaxy formation model implemented in the Millennium Simulation Project is inconsistent with our limit with 50% probability.
Full text
Available for:
BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
ABSTRACT
Current attempts to measure the 21 cm power spectrum of neutral hydrogen during the epoch of reionization (EoR) are limited by systematics that produce measured upper limits above both the ...thermal noise and the expected cosmological signal. These systematics arise from a combination of observational, instrumental, and analysis effects. In order to further understand and mitigate these effects, it is instructive to explore different aspects of existing data sets. One such aspect is the choice of observing field. To date, MWA EoR observations have largely focused on the EoR0 field. In this work, we present a new detailed analysis of the EoR1 field. The EoR1 field is one of the coldest regions of the southern radio sky, but contains the very bright radio galaxy Fornax-A. The presence of this bright extended source in the primary beam of the interferometer makes the calibration and analysis of EoR1 particularly challenging. We demonstrate the effectiveness of a recently developed shapelet model of Fornax-A in improving the results from this field. We also describe and apply a series of data quality metrics that identify and remove systematically contaminated data. With substantially improved source models, upgraded analysis algorithms and enhanced data quality metrics, we determine EoR power spectrum upper limits based on analysis of the best ∼14-h data observed during 2015 and 2014 at redshifts 6.5, 6.8, and 7.1, with the lowest 2σ upper limit at z = 6.5 of Δ2 ≤ (73.78 mK)2 at k = 0.13 h Mpc−1, improving on previous EoR1 measurement results.
We predict Lyman α (Lyα) luminosity functions (LFs) of Lyα-selected galaxies (Lyα emitters, or LAEs) at z = 3–6 using the phenomenological model. This model combines observed UV-LFs of Lyman-break ...galaxies (LBGs, or drop-out galaxies), with constraints on their distribution of Lyα line strengths as a function of UV-luminosity and redshift. Our analysis shows that while Lyα LFs of LAEs are generally not Schechter functions, these provide a good description over the luminosity range of log10(L
α/erg s−1) = 41–44. Motivated by this result, we predict Schechter function parameters at z = 3–6. Our analysis further shows that (i) the faint-end slope of the Lyα LF is steeper than that of the UV-LF of LBGs, (with a median αLyα < −2.0 at z ≳ 4), and (ii) a turnover in the Lyα LF of LAEs at Lyα luminosities 1040 ≲ L
α ≲ 1041 erg s−1 may signal a flattening of UV-LF of LBGs at −12 > M
UV > −14. We discuss the implications of these results – which can be tested directly with upcoming surveys – for the Epoch of Reionization.
We study the role of feedback from supernovae (SN) and black holes in the evolution of the star formation rate function (SFRF) of z ∼ 4-7 galaxies. We use a new set of cosmological hydrodynamic ...simulations, Angus (AustraliaN
GADGET-3
early Universe Simulations), run with a modified and improved version of the parallel TreePM-smoothed particle hydrodynamics code GADGET-3 called P-GADGET3(XXL), that includes a self-consistent implementation of stellar evolution and metal enrichment. In our simulations both SN-driven galactic winds and active galactic nuclei (AGN) act simultaneously in a complex interplay. The SFRF is insensitive to feedback prescription at z > 5, meaning that it cannot be used to discriminate between feedback models during reionization. However, the SFRF is sensitive to the details of feedback prescription at lower redshift. By exploring different SN-driven wind velocities and regimes for the AGN feedback, we find that the key factor for reproducing the observed SFRFs is a combination of 'strong' SN winds and early AGN feedback in low-mass galaxies. Conversely, we show that the choice of initial mass function and inclusion of metal cooling have less impact on the evolution of the SFRF. When variable winds are considered, we find that a non-aggressive wind scaling is needed to reproduce the SFRFs at z 4. Otherwise, the amount of objects with low SFRs is greatly suppressed and at the same time winds are not effective enough in the most massive systems.
PDF
