8,914 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
Steven Johnson Author Talk Poster
No full textK-State Book NetworkA poster advertising an author talk by Steven Johnson at Kansas State University on September 3, 2014. Steven Johnson's book "The Ghost Map" was the 2014-2015 common book
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
Steven Bialer and Patti Smith, July 1978
No full textMusician, poet, and author Patti Smith sits on a bed in a hotel room in July 1978. The photograph was taken by Don Hamerman as part of a session for "Unicorn Times," an alternative performing arts periodical in Washington, D.C. Steven Bialer, the Design Director for "Unicorn Times," is seated on the bed next to Smith
Steven Garber
No full textSteven Garber speaks on the importance and value of truth.
Steven Garber is the principal of The Washington Institute for Faith, Vocation & Culture, which is focused on reframing the way people understand life, especially the meaning of vocation and the common good. A consultant to foundations, corporations and educational institutions, he is a teacher of many people in many places. The author of The Fabric of Faithfulness: Weaving Together Belief and Behavior, and Visions of Vocation: Common Grace for the Common Good, he is also a contributor to the books, Faith Goes to Work: Reflections from the Marketplace, and Get Up Off Your Knees: Preaching the U2 Catalogue. He lives with his wife Meg in Virginia
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
Steven Yedinak Interview
No full textLTC (RET) Steven M. Yedinak commissioned in the U. S. Army Infantry in 1963 and subsequently spent 26 years in Special Forces and Airborne Infantry. He served two combat tours in Vietnam (1966-67 & 1971-1972), and started the Mobile Guerrilla Force. He is the author of Hard to Forget: An American with the Mobile Guerrilla Force in Vietnam (Random House, 1998). He retired from the Army in 1989
Gamification is broken. An interview with Steven Poole
No full textSteven Poole is the author of Trigger Happy (2000. New York, NY: Arcade Publish), Unspeak (2006. New York, NY: Grove Press), and You Aren’t What You Eat (2012. In press). He has written extensively on books, culture, and videogames for The Guardian and other publications
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