Log Phi Research Articles

The Bright-end Galaxy Candidates at z ∼ 9 from 79 Independent HST Fields

Abstract We present a full data analysis of the pure-parallel Hubble Space Telescope (HST) imaging observations in the Brightest of Reionizing Galaxies Survey (BoRG[z9]) in Cycle 22. The medium-deep exposures with five HST/WFC3IR+UVIS filter bands from 79 independent sightlines (∼370 arcmin2) provide the least biased determination of number density for z ≳ 9 bright galaxies against cosmic variance. After a strict two-step selection for candidate galaxies, including dropout color and photometric redshift analyses, and revision of previous BoRG candidates, we identify one source at z ∼ 10 and two sources at z ∼ 9. The z ∼ 10 candidate shows evidence of line-of-sight lens magnification (μ ∼ 1.5), yet it appears surprisingly luminous ( mag), making it one of the brightest candidates at known (∼0.3 mag brighter than the z = 8.68 galaxy EGSY8p7, spectroscopically confirmed by Zitrin and collaborators). For z ∼ 9 candidates, we include previous data points at fainter magnitudes and find that the data are well fitted by a Schechter luminosity function with , mag, and Mpc−3 mag−1, for the first time without fixing any parameters. The inferred cosmic star formation rate density is consistent with unaccelerated evolution from lower redshift.

A new multifield determination of the galaxy luminosity function at z = 7–9 incorporating the 2012 Hubble Ultra-Deep Field imaging

We present a new determination of the UV galaxy luminosity function (LF) at redshift z ~ 7 and z ~ 8, and a first estimate at z ~ 9. An accurate determination of the form and evolution of the LF at high z is crucial for improving our knowledge of early galaxy evolution and cosmic reionization. Our analysis exploits fully the new, deepest WFC3/IR imaging from our HST UDF12 campaign, and includes a new, consistent analysis of all appropriate, shallower/wider-area HST data. Our new measurement of the evolving LF at z ~ 7-8 is based on a final catalogue of ~600 galaxies, and involves a step-wise maximum likelihood determination based on the redshift probability distribution for each object; this makes full use of the 11-band imaging now available in the HUDF, including the new UDF12 F140W data, and the deep Spitzer IRAC imaging. The final result is a determination of the z ~ 7 LF extending down to M_UV = -16.75, and the z ~ 8 LF down to M_UV = -17.00. Fitting a Schechter function, we find M* = -19.90 (+0.23/-0.28), log phi* = -2.96 (+0.18/-0.23), and a faint-end slope alpha=-1.90 (+0.14/-0.15) at z~7, and M* = -20.12 (+0.37/-0.48), log phi* = -3.35 (+0.28/-0.47), alpha=-2.02 (+0.22/-0.23) at z~8. These results strengthen suggestions that the evolution at z > 7 is more akin to `density evolution' than the apparent `luminosity evolution' seen at z ~ 5-7. We also provide the first meaningful information on the LF at z ~ 9, explore alternative extrapolations to higher z, and consider the implications for the evolution of UV luminosity density. Finally, we provide catalogues (including z_phot, M_UV and all photometry) for the 100 most robust z~6.5-11.9 galaxies in the HUDF used in this analysis. We discuss our results in the context of earlier work and the results of an independent analysis of the UDF12 data based on colour-colour selection (Schenker et al. 2013).

The H-alpha luminosity function at redshift 2.2

We aim to place new, strengthened constraints on the luminosity function (LF) of H-alpha emitting galaxies at redshift z=2.2, and to further constrain the instantaneous star-formation rate density of the universe (rho*). We have used the new HAWK-I instrument at ESO-VLT to obtain extremely deep narrow-band (line; NB2090) and broad-band (continuum; Ks) imaging observations. The target field is in the GOODS-South, providing us with a rich multi-wavelength auxiliary data set, which we utilise for redshift confirmation and to estimate dust content. We use this new data to measure the faint-end slope (alpha) of LF(H-alpha) with unprecedented precision. The data are well fit by a Schechter function and also a single power-law, yielding alpha=(-1.72 +/- 0.20) and (-1.77 +/- 0.21), respectively. Thus we are able to confirm the steepening of alpha from low- to high-z predicted by a number of authors and observed at other wavelengths. We combine our LF data-points with those from a much shallower but wider survey at z=2.2 (Geach et al. 2008), constructing a LF spanning a factor of 50 in luminosity. Re-fitting the Schechter parameters, we obtain log L*=(43.07+/-0.22)erg s^-1 ; log phi*=(-3.45+/-0.52)Mpc^-3 ; alpha=(-1.60+/-0.15). We integrate over LF(Halpha) and apply a correction for dust attenuation to determine the instantaneous cosmic star-formation rate density at z=2 without assuming alpha or extrapolating it from lower-z. Our measurement of rho* is (0.215+/-0.090) Msun yr^-1 Mpc^-3, integrated over a range of 37 <log(LHhalpha / erg s^-1) < 47.

Fault-Tolerant Real-Time Scheduling

We use competitive analysis to study how best to use redundancy to achieve fault-tolerance in online real-time scheduling. We show that the optimal way to use spatial redundancy depends on a complex interaction of the benefits, execution times, release times, and latest start times of the jobs. We give a randomized online algorithm whose competitive ratio is O( logΦ log Delta ( log 2 n log m/ log log m)) for transient faults. Here n is the number of jobs, m is the number of processors, Φ is the ratio of the maximum value density of a job to the minimum value density of a job, and Δ is the ratio of the longest possible execution time to the shortest possible execution time. We show that this bound is close to optimal by giving an Ω(( log ΔΦ/ log log m) ( log m log log m) 2 ) lower bound on the competitive ratio of any randomized algorithm. In the case of permanent faults, there is a randomized online algorithm that has a competitive ratio of O( log Phi log Δ (log m/log log m)). We also show a lower bound of Ω((log ΔΦ/ log log m) ( log m/log log m)) on the competitive ratio for interval scheduling with permanent faults.

Plasticity of the mechanism subserving inspiratory load perception

The objective of this study was to determine the stability of the function describing subjects' magnitude estimates of added inspiratory resistive loads following short-term exposure (STE) to a high but nonfatiguing, inspiratory load. Four inspiratory resistive loads (8.9-35.7 cmH2O X l-1 X s) were presented twice each in random order. Subjects were asked to estimate load magnitude by force of handgrip. Perceptual performance was quantified using Stevens power law, psi = k phi n, where psi is the subject's estimate, k is a constant, and phi is the peak mouth pressure developed against the load. The exponent n represents the slope of the line in the plot of log psi vs. log phi. After a 2-min period in which subjects were required to generate 80% of their maximum inspiratory pressure against a high resistance, the load estimation protocol was repeated. Estimates were significantly reduced compared to control; however, there was no significant difference in the exponent for magnitude functions between conditions. Similar results were obtained in a second parallel experiment involving magnitude estimation of weights lifted by the elbow flexors. The results suggest plasticity in the mechanism(s) subserving sensation of added loads to breathing and that such plasticity is a general feature of sensation arising from nonrespiratory muscles as well.