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Coil A.L.,University of California at San Diego | Blanton M.R.,New York University | Burles S.M.,D. E. Shaw and Co. | Cool R.J.,Princeton University | And 8 more authors.
Astrophysical Journal | Year: 2011

We present the PRIsm MUlti-object Survey (PRIMUS), a spectroscopic faint galaxy redshift survey to z 1. PRIMUS uses a low-dispersion prism and slitmasks to observe 2500 objects at once in a 0.18deg2 field of view, using the Inamori Magellan Areal Camera and Spectrograph camera on the Magellan I Baade 6.5m telescope at Las Campanas Observatory. PRIMUS covers a total of 9.1deg2 of sky to a depth of i AB 23.5 in seven different deep, multi-wavelength fields that have coverage from the Galaxy Evolution Explorer, Spitzer, and either XMM or Chandra, as well as multiple-band optical and near-IR coverage. PRIMUS includes 130,000 robust redshifts of unique objects with a redshift precision of σz/(1 + z) 0.005. The redshift distribution peaks at z 0.6 and extends to z = 1.2 for galaxies and z = 5 for broad-line active galactic nuclei. The motivation, observational techniques, fields, target selection, slitmask design, and observations are presented here, with a brief summary of the redshift precision; a forthcoming paper presents the data reduction, redshift fitting, redshift confidence, and survey completeness. PRIMUS is the largest faint galaxy survey undertaken to date. The high targeting fraction (80%) and large survey size will allow for precise measures of galaxy properties and large-scale structure to z 1. © 2011 The American Astronomical Society. All rights reserved. Source

Chandar V.,D. E. Shaw and Co. | Tchamkerten A.,Telecom ParisTech
IEEE International Symposium on Information Theory - Proceedings | Year: 2015

In a recently proposed asynchronous communication setup, the receiver observes mostly pure background noise except for a brief and a priori unknown period of time when data is transmitted. Capacity per unit cost and minimum communication delay were characterized and shown to be unaffected by a sparse sampling at the receiver as long as the number of samples represents a constant fraction of the total channel outputs. This paper strengthens this result and shows that it continues to hold even if the sampling rate tends to zero. More specifically, if the sampling rate is ω(1/B), where B denotes the number of transmitted message bits, capacity per unit cost and minimum decoding delay are the same as under full output sampling. Conversely, if the sampling rate decreases as o(1/B), reliable communication is impossible. The main ingredient in the achievability argument is a time series sampling/detection procedure that detects transient changes in distribution. This procedure has the property of simultaneously minimizing detection delay and sampling rate, in the regime of vanishing false-alarm probability. © 2015 IEEE. Source

Aird J.,University of California at San Diego | Coil A.L.,University of California at San Diego | Moustakas J.,University of California at San Diego | Blanton M.R.,New York University | And 7 more authors.
Astrophysical Journal | Year: 2012

We present evidence that the incidence of active galactic nuclei (AGNs) and the distribution of their accretion rates do not depend on the stellar masses of their host galaxies, contrary to previous studies. We use hard (2-10keV) X-ray data from three extragalactic fields (XMM-LSS, COSMOS, and ELAIS-S1) with redshifts from the Prism Multi-object Survey to identify 242 AGNs with L 2-10 keV = 1042-44ergs-1 within a parent sample of ∼25,000 galaxies at 0.2 < z < 1.0 over ∼3.4 deg2 and to i ∼23. We find that although the fraction of galaxies hosting an AGN at fixed X-ray luminosity rises strongly with stellar mass, the distribution of X-ray luminosities is independent of mass. Furthermore, we show that the probability that a galaxy will host an AGN can be defined by a universal Eddington ratio distribution that is independent of the host galaxy stellar mass and has a power-law shape with slope -0.65. These results demonstrate that AGNs are prevalent at all stellar masses in the range 9.5 < M*/ M⊙ < 12 and that the same physical processes regulate AGN activity in all galaxies in this stellar mass range. While a higher AGN fraction may be observed in massive galaxies, this is a selection effect related to the underlying Eddington ratio distribution. We also find that the AGN fraction drops rapidly between z 1 and the present day and is moderately enhanced (factor ∼2) in galaxies with blue or green optical colors. Consequently, while AGN activity and star formation appear to be globally correlated, we do not find evidence that the presence of an AGN is related to the quenching of star formation or the color transformation of galaxies. © 2012. The American Astronomical Society. All rights reserved. Source

Borade S.,Massachusetts Institute of Technology | Borade S.,D. E. Shaw and Co. | Zheng L.,Massachusetts Institute of Technology
IEEE Transactions on Information Theory | Year: 2012

A wideband Rayleigh fading channel is considered with causal channel state information (CSI) at the transmitter and no receiver CSI. A simple orthogonal code with energy detection rule at the receiver (similar to pulse position modulation in IEEE Trans. Inf. Theory, vol. 46, no. 4, Apr. 2000 and IEEE Trans. Inf. Theory, vol. 52 no. 5, May 2006) is shown to achieve the capacity of this channel in the wideband limit. This strategy transmits energy only when the channel gain exceeds a threshold, hence only needs causal transmitter CSI. In the wideband limit, this capacity without any receiver CSI is the same as the capacity with full receiver CSI, which is proportional to the logarithm of the bandwidth. Similar threshold-based pulse position modulation is shown to achieve the capacity per unit cost of the dirty-tape channel (dirty paper channel with causal transmitter CSI and no receiver CSI), which equals its capacity per unit cost with full receiver CSI. Then, a general discrete channel with i.i.d. states is considered. Each input has an associated cost and a zero cost input 0 exists. The channel state is assumed to be known at the transmitter in a causal manner. Capacity per unit cost is found for this channel and a simple orthogonal code is shown to achieve this capacity. Later, a novel orthogonal coding scheme is proposed for the case of causal transmitter CSI and a condition for equivalence of capacity per unit cost for causal and noncausal transmitter CSI is derived. © 1963-2012 IEEE. Source

Tchamkerten A.,Telecom ParisTech | Chandar V.,Lincoln Laboratory | Chandar V.,D. E. Shaw and Co. | Caire G.,TU Berlin
IEEE Transactions on Information Theory | Year: 2014

The minimum energy, and, more generally, the minimum cost, to transmit 1 bit of information was recently derived for bursty communication when the information is available infrequently at random times at the transmitter. This result assumes that the receiver is always in the listening mode and samples all channel outputs until it makes a decision. Since sampling is in practice one of the receiver's most energy consuming functions, a natural question is to evaluate capacity per unit cost when the receiver is sampling constrained. This paper investigates such a setting where the receiver can sample only a given fraction ρ ε (0, 1] of the channel outputs. It is shown that regardless of ρ > 0 , the asynchronous capacity per unit cost is the same as under full sampling, i.e., when ρ = 1. Moreover, a sparse output sampling does not even impact decoding delay - the elapsed time between when information is available and when it is decoded. Hence, surprisingly, it suffices to sample an arbitrarily small fraction of the channel outputs and yet achieve the same (asymptotic) performance as under full output sampling. © 2014 IEEE. Source

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