1,691 research outputs found
The Colors Of Galaxies At 4 < Z < 8 And Their Contribution To Reionization
No full textWe present recent results on the rest-frame ultraviolet (UV) colors of galaxies at high-redshift, and the contribution of these galaxies to the reionization of the intergalactic medium (IGM). Using a combination of deep and wide data from the CANDELS, HUDF09 and ERS programs, we find that galaxies at z = 7 appear to be dust free, and they become substantially dustier by z = 4. Faint galaxies at z = 7 appear very blue, but they are consistent with the colors of very blue local galaxies, thus there is no evidence for the presence of exotic stellar populations. We find that the observable galaxy population can sustain a fully ionized IGM at z = 6 if the escape fraction of ionizing photons (f(esc)) is 30%. If the luminosity function extends much fainter, then the required f(esc) is lowered to similar to 10%. Examining the constraint on the emission rate of ionizing photons from Ly alpha forest measurements, we find that if the luminosity function extends to M-UV = -13, f(esc) must be less than 13% at z = 6. This escape fraction can still sustain a reionized IGM at z = 6, and even at z = 7, but unless it rises substantially at z > 6, the IGM may be similar to 20 - 50% neutral by z = 8.Astronom
The vanishing author in computer-generated works: a critical analysis of recent Australian case law
No full textAbstract
The use of software is ubiquitous in the creation of many copyright works, yet the requirement in copyright law that every work have a human author who engages in independent intellectual effort means that its use may prevent copyright subsistence. Several recent Australian cases have refocused attention on authorship as an essential criterion of copyright subsistence, and these cases suggest that much computer-produced output may be authorless and thus lack copyright protection. This article, the first in a two-part series, analyses how each case deals with the question of authorship of computer-produced works and why the use of software diminishes copyright protection for a significant number of computer-generated works. The article critiques the application of conventional notions of human authorship developed in the pre-computer age to modern productions and suggests alternative approaches to authorship that satisfy both the major objectives of copyright policy and the need to adapt to the computer age. The article argues that, without a broader judicial approach to authorship of computer-generated works, Parliament must remedy the lacuna in protection for these ‘authorless’ works. Possible solutions for reform are suggested. In a forthcoming article, the author comprehensively examines those reform proposals
Embedding Fundamental Aspects of the Relational Blockworld Interpretation in Geometric (or Clifford) Algebra
No full textI summarize Silberstein, et. al’s (2006) discussion of the derivation of the Heisenberg commutators, whose work is based on Kaiser (1981, 1990) and Bohr, et. al. (1995, 2004a,b). I argue that Bohr and Kaiser’s treatment is not geometric enough, as it still relies on some unexplained residual notions concerning the unitary representation of transformations in a Hilbert space. This calls for a more consistent characterization of the role of i than standard QM can offer. I summarize David Hestenes’ (1985,1986) major claims concerning the essential role Clifford algebras play in such a fundamental characterization of i, and I present a Clifford- algebraic derivation of the Heisenberg commutation relations (taken from Finkelstein, et. al. (2001)). I argue that their derivation exhibits a more fundamentally geometrical approach, which unifies geometric and ontological content. I also point out how some of Finkelstein’s ontological notions of “chronon dynamics” can give a plausible explanatory account of RBW’s “geometric relations.
Elinor Leven, Janice Finkelstein, Ron Tikofsky, Thomas Bodenheimer, Jeffrey Gillman, David S. Dolowitz, Steven Rosen, Frances Shlafer, Sydney Carson, Marcia Alder, Laura Lovinger, Rabbi Mordecai Podet, Judy Lovinger, Joan Schwartz
No full textBlack and white photograph of Elinor Leven, Janice Finkelstein, Ron Tikofsky, Thomas Bodenheimer, Jeffrey Gillman, David S. Dolowitz, Steven Rosen, Frances Shlafer, Sydney Carson, Marcia Alder, Laura Lovinger, Rabbi Mordecai Podet, Judy Lovinger, and Joan Schwartz
Probing The Star Formation History And Initial Mass Function Of The Z Similar To 2.5 Lensed Galaxy Smm J163554.2+661225 With Herschel
No full textWe present the analysis of Herschel Spectral and Photometric Imaging Receiver far-infrared (FIR) observations of the z = 2.515 lensed galaxy SMM J163554.2+661225. Combining new 250, 350, and 500 mu m observations with existing data, we make an improved fit to the FIR spectral energy distribution of this galaxy. We find a total infrared (IR) luminosity of L(8-1000 mu m) = 6.9 +/- 0.6 x 10(11) L-circle dot, a factor of three more precise over previous L-IR estimates for this galaxy, and one of the most accurate measurements for any galaxy at these redshifts. This FIR luminosity implies an unlensed star formation rate (SFR) for this galaxy of 119 +/- 10 M-circle dot yr(-1), which is a factor of 1.9 +/- 0.35 lower than the SFR derived from the nebular Pa alpha emission line (a 2.5 sigma discrepancy). Both SFR indicators assume an identical Salpeter initial mass function (IMF) with slope Gamma = 2.35 over a mass range of 0.1-100 M-circle dot; thus this discrepancy suggests that more ionizing photons may be necessary to account for the higher Pa alpha-derived SFR. We examine a number of scenarios and find that the observations can be explained with a varying star formation history (SFH) due to an increasing SFR, paired with a slight flattening of the IMF. If the SFR is constant in time, then larger changes need to be made to the IMF by either increasing the upper mass cutoff to similar to 200 M-circle dot, or a flattening of the IMF slope to 1.9 +/- 0.15, or a combination of the two. These scenarios result in up to double the number of stars with masses above 20 M-circle dot, which produce the requisite increase in ionizing photons over a Salpeter IMF with a constant SFH.NASA HST-HF-51288.01, NAS 5-26555Texas AM UniversitySpace Telescope Science InstituteAstronom
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Sizing Up Ly Alpha and Lyman Break Galaxies
No full textWe measure the sizes for a sample of 174 Ly alpha-selected galaxies with broadband imaging with the Hubble Space Telescope. Over the redshift range 2.25 < z < 6, Ly alpha-selected galaxies have a characteristic, constant, small size in rest-frame ultraviolet (UV) light. Coupled with a characteristic star Formation intensity (i.e., UV luminosity per unit area), this can explain their non-evolving ultraviolet continuum luminosity function. This is in contrast to Lyman break galaxies (LBGs) over the same redshift range, which have been previously shown to increase in linear size as H(z) (1). The compact physical size seems to be a critical determining factor in whether a galaxy will show Ly alpha emission or not. The L-* of LBGs and its evolution with redshift can be derived from a simple model where the star Formation intensity has an upper limit set by feedback processes, independent of redshift. The increase in L-* of LBGs is mainly driven by the increase in linear size over redshifts for z = 2-7. Since Ly alpha galaxies do not grow in linear size, they do not show an increase in L-*.US National Science Foundation AST-0808165Astronom
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The Role Of Bulge Formation In The Homogenization Of Stellar Populations At Z Similar To 2 As Revealed By Internal Color Dispersion In CANDELS
No full textWe use data from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey to study how the spatial variation in the stellar populations of galaxies relates to the formation of galaxies at 1.5 < z < 3.5. We use the internal color dispersion (ICD), measured between the rest-frame UV and optical bands, which is sensitive to age (and dust attenuation) variations in stellar populations. The ICD shows a relation with the stellar masses and morphologies of the galaxies. Galaxies with the largest variation in their stellar populations as evidenced by high ICD have disk-dominated morphologies (with Sersic indexes < 2) and stellar masses between 10 < log (M/M-circle dot) < 11. There is a marked decrease in the ICD as the stellar mass and/or the Sersic index increases. By studying the relations between the ICD and other galaxy properties including size, total color, star formation rate, and dust attenuation, we conclude that the largest variations in stellar populations occur in galaxies where the light from newly, high star-forming clumps contrasts older stellar disk populations. This phase reaches a peak for galaxies only with a specific stellar mass range, 10 < log (M/M-circle dot) < 11, and prior to the formation of a substantial bulge/spheroid. In contrast, galaxies at higher or lower stellar masses and/or higher Sersic index (n > 2) show reduced ICD values, implying a greater homogeneity of their stellar populations. This indicates that if a galaxy is to have a quiescent bulge along with a star-forming disk, typical of Hubble sequence galaxies, this is most common for stellar masses 10 < log (M/M-circle dot) < 11 and when the bulge component remains relatively small (n < 2).NASA NAS5-26555NSF AST-0808133Astronom
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Probing reionization with the Hubble Space Telescope (HST)
No full textWe present the results of an unbiased search for Lyα emission from continuum-selected 5.6 < z < 8.7 galaxies. Our dataset consists of 160 orbits of G102 slitless grism spectroscopy obtained with HST/WFC3 as part of the Faint Infrared Grism Survey (FIGS; PI: Malhotra), which obtains deep slitless spectra of all sources in four fields, and was designed to minimize contamination in observations of previously-identified high-redshift galaxy candidates. The FIGS data can potentially spectroscopically confirm the redshifts of galaxies, and as Lyα emission is resonantly scattered by neutral gas, FIGS can also constrain the ionization state of the intergalactic medium (IGM) during the epoch of reionization. These data have sufficient depth to detect Lyα emission in this epoch, as Tilvi et al. (2016) have published the FIGS detection of previously known (Finkelstein et al., 2013) Lyα emission at z =7.51. The FIGS data use five separate roll-angles of HST to mitigate the contamination by nearby galaxies. We created a method that accounts for and removes the contamination from surrounding galaxies and also removes any dispersed continuum light from each individual spectrum (Pirzkal et al., 2017). We searched for significant (> 4σ) emission lines using two different automated detection methods, free of any visual inspection biases. Applying these methods on photometrically-selected high-redshift candidates between 5.6 < z < 8.7 we find two emission lines, one previously published by Tilvi et al. (2016), and a new line at 1.028 μm, which we identify as Lyα at z = 7.452 ± 0.003. This newly spectroscopically confirmed galaxy has the highest Lyα rest-frame equivalent width (EW [subscript Lyα]) yet published at z > 7 (140.3 ± 19.0Å).Astronom
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Rapid Decline Of Ly Alpha Emission Toward The Reionization Era
No full textThe observed deficit of strongly Ly alpha emitting galaxies at z > 6.5 is attributed to increasing neutral hydrogen in the intergalactic medium (IGM) and/or to the evolving galaxy properties. To investigate this we have performed very deep near-IR spectroscopy of z greater than or similar to 7 galaxies using MOSFIRE on the Keck-I Telescope. We measure the Lya fraction at z similar to 8 using two methods. First, we derived N-Ly alpha/N-tot directly, using extensive simulations to correct for incompleteness. Second, we used a Bayesian formalism (introduced by Treu et al.) that compares the z > 7 galaxy spectra to models of the Ly alpha equivalent width (WLy alpha) distribution at z similar to 6. We explored two simple evolutionary scenarios: pure number evolution where Lya is blocked in some fraction of galaxies (perhaps due to the IGM being opaque along only some fraction of sightlines) and uniform dimming evolution where Ly alpha is attenuated in all galaxies by a constant factor (perhaps owing to processes from galaxy evolution or a slowly increasing IGM opacity). The Bayesian formalism places stronger constraints compared with the direct method. Combining our data with that in the literature, we find that at z similar to 8 the Lya fraction has dropped by a factor of > 3 (84% confidence interval) using both the dimming and number evolution scenarios, compared to the z similar to 6 values. Furthermore, we find a tentative positive Bayesian evidence favoring the number evolution scenario over dimming evolution, extending trends observed at z less than or similar to 7 to higher redshift. A comparison of our results with theoretical models implies the IGM volume averaged neutral hydrogen fraction greater than or similar to 0.3, suggesting that we are likely witnessing reionization in progress at z similar to 8.HST program by NASA through STScI GO-12060Astronom
An enzymatic Finkelstein reaction : fluorinase catalyses direct halogen exchange
No full textWe thank the Engineering and Physical Sciences Research Council, UK, for a research grant.The fluorinase enzyme from Streptomyces cattleya is shown to catalyse a direct displacement of bromide and iodide by fluoride ion from 5′-bromodeoxyadenosine (5′-BrDA) and 5′-iododeoxyadenosine (5′-IDA) respectively to form 5′-fluorodeoxyadenosine (5′-FDA) in the absence of L-methionine (L-Met) or S-adenosyl-L-methionine (SAM). 5′-BrDA is the most efficient substrate for this enzyme catalysed Finkelstein reaction.Peer reviewe
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