1,720,992 research outputs found
The detectability of Lyα emission from galaxies during the epoch of reionization
No full textWe study the visibility of the Lyα emission line during the epoch of reionization. Combining galactic outflow models with large-scale seminumeric simulations of reionization, we quantify the probability distribution function of the fraction of Lyα photons transmitted through the intergalactic medium (IGM). Our study focuses on galaxies populating dark matter haloes with masses of Mhalo= 1010M⊙ at z= 8.6, which is inspired by the recent reported discovery of a galaxy at z= 8.6 with strong Lyα line emission. For reasonable assumptions, we find that the combination of winds and reionization morphology results in per cent (50 per cent), for the majority of galaxies, even when the Universe is ~80 per cent (60 per cent) neutral by volume. Thus, the observed strong Lyα emission from the reported z= 8.6 galaxy is consistent with a highly neutral IGM, and cannot be used to place statistically significant constraints on the volume-averaged neutral fraction of hydrogen in the IGM. We also investigate the implications of the recent tentative evidence for an observed decrease in the 'Lyman alpha emitter fraction' among drop-out galaxies between z= 6 and 7. If confirmed, we show that a rapid evolution in will be required to explain this observation via the effects of reionization. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS
Fluctuations in the high-redshift Lyman-Werner background: close halo pairs as the origin of supermassive black holes
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Gravitational lensing modification of the high-redshift galaxy luminosity function
No full textABSTRACT
The bright end of the rest-frame ultraviolet luminosity function (UVLF) of high-redshift galaxies is modified by gravitational lensing magnification bias. Motivated by recent discoveries of very high-z galaxies with JWST, we study the dependence of magnification bias on the finite size of sources at 6 < z < 14. We calculate the magnification probability distributions and use these to calculate the magnification bias assuming a rest-frame Schechter UVLF for galaxies at redshift 6 < z < 14. We find that the finite size of bright high-redshift galaxies together with lens ellipticity significantly suppresses magnification bias, producing an observed bright end which declines more sharply than the power law resulting from assumption of point sources. By assuming a luminosity–size relation for the source population and comparing with the observed z = 6 galaxy luminosity function from Harikane et al. (2022), we show that the UVLF can be used to set mild constraints on the galaxies intrinsic size, favouring smaller galaxies compared to the fiducial luminosity–size relation. In the future, wide surveys using Euclid and Roman Space Telescope will place stronger constraints. We also tabulate the maximum magnification possible as a function of source size and lens ellipticity
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The relation between star-formation rate and stellar mass of galaxies at Z - 1-4
No full textAbstract
The relation between the star-formation Rate and stellar mass (M⋆) of galaxies represents a fundamental constraint on galaxy formation, and has been studied extensively both in observations and cosmological hydrodynamic simulations. However, the observed amplitude of the star-formation rate—stellar mass relation has not been successfully reproduced in simulations, indicating either that the halo accretion history and baryonic physics are poorly understood/modelled or that observations contain biases. In this paper, we examine the evolution of the SFR −M⋆relation ofz~ 1–4 galaxies and display the inconsistency between observed relations that are obtained using different techniques. We employ cosmological hydrodynamic simulations from various groups which are tuned to reproduce a range of observables and compare these with a range of observed SFR −M⋆relations. We find that numerical results are consistent with observations that use Spectral Energy Distribution techniques to estimate star-formation rates, dust corrections, and stellar masses. On the contrary, simulations are not able to reproduce results that were obtained by combining only UV and IR luminosities (UV+IR). These imply star-formation rates at a fixed stellar mass that are larger almost by a factor of 5 than those of Spectral Energy Distribution measurements forz~ 1.5–4. Forz< 1.5, the results from simulations, Spectral Energy Distribution fitting techniques and IR+UV conversion agree well. We find that surveys that preferably select star-forming galaxies (e.g. by adopting Lyman-break or blue selection) typically predict a larger median/average star-formation rate at a fixed stellar mass especially for high mass objects, with respect to mass selected samples and hydrodynamic simulations. Furthermore, we find remarkable agreement between the numerical results from various authors who have employed different cosmological codes and run simulations with different resolutions. This is interesting for two reasons. (A) simulations can produce realistic populations of galaxies within representative cosmological volumes even at relatively modest resolutions. (B) It is likely that current numerical codes that rely on similar subgrid multiphase interstellar medium models and are tuned to reproduce statistical properties of galaxies, produce similar results for the SFR −M⋆relation by construction, regardless of resolution, box size and, to some extent, the adopted feedback prescriptions
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Fisher matrix forecasts on the astrophysics of galaxies during the epoch of reionization from the 21-cm power spectra
No full textABSTRACT
The hyperfine 21-cm transition of neutral hydrogen from the early Universe (z &gt; 5) is a sensitive probe of the formation and evolution of the first luminous sources. Using the Fisher matrix formalism we explore the complex and degenerate high-dimensional parameter space associated with the high-z sources of this era and forecast quantitative constraints from a future 21-cm power spectrum (21-cm PS) detection. This is achieved using , a coupled semi-analytic galaxy formation model and reionization simulation, applied to an N-body halo merger tree with a statistically complete population of all atomically cooled galaxies out to z ∼ 20. Our mock observation assumes a 21-cm detection spanning z ∈ [5, 24] from a 1000 h mock observation with the forthcoming Square Kilometre Array, and is calibrated with respect to ultraviolet luminosity functions (UV LFs) at z ∈ [5, 10], the optical depth of CMB photons to Thompson scattering from Planck, and various constraints on the IGM neutral fraction at z &gt; 5. In this work, we focus on the X-ray luminosity, ionizing UV photon escape fraction, star formation, and supernova feedback of the first galaxies. We demonstrate that it is possible to recover five of the eight parameters describing these properties with better than 50 per cent precision using just the 21-cm PS. By combining with UV LFs, we are able to improve our forecast, with five of the eight parameters constrained to better than 10 per cent (and all below 50 per cent)
The stellar mass function and star formation rate-stellar mass relation of galaxies at z ~ 4-7
No full textWe 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⋆ (LUV–M⋆) conversion. Our simulations predict a population of faint galaxies not seen by current observations
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