On the controllability of bimodal piecewise linear systems

This paper studies controllability of bimodal systems that consist of two linear dynamics on each side of a given hyperplane. We show that the controllability properties of these systems can be inferred from those of linear systems for which the inputs are constrained in a certain way. Inspired by the earlier work on constrained controllability of linear systems, we derive necessary and sufficient conditions for a bimodal piecewise linear system to be controllable.Natl Sci Fdn; Univ Penn, Sch Engn & Appl Sci

A Spectroscopic Follow-up Program of Very Massive Galaxies at 3 < z < 4: Confirmation of Spectroscopic Redshifts, and a High Fraction of Powerful AGNs

Large scale structure and cosmolog

‘Good Farmers’ in Sub-Saharan Africa: Evolving Narratives

In this paper the example of cocoa production in Ghana is used to explore how the narratives portraying African farmers have changed over the last 70 years. These evolving narratives are explored through the notion of a ‘good farmer’. The argument is that over this period the image of African farmers has been progressively rehabilitated, from ignorant and tradition-bound to skilled and research-minded. Over the same time period the image of formal research and extension was undermined. With the recent renewed interest in agriculture, narratives around African farmers are again evolving: ‘good farmers’ are now increasingly being defined as those who approach their farming as a proper business.DfI

3D-HST+CANDELS : the evolution of the galaxy size-mass distribution since z=3

Spectroscopic+photometric redshifts, stellar mass estimates, and rest-frame colors from the 3D-HST survey are combined with structural parameter measurements from CANDELS imaging to determine the galaxy size-mass distribution over the redshift range 0 < z < 3. Separating early- and late-type galaxies on the basis of star-formation activity, we confirm that early-type galaxies are on average smaller than late-type galaxies at all redshifts, and we find a significantly different rate of average size evolution at fixed galaxy mass, with fast evolution for the early-type population, R eff∝(1 + z)–1.48, and moderate evolution for the late-type population, R eff∝(1 + z)-0.75Peer reviewedFinal Accepted Versio

Spatially Resolved Dust Maps from Balmer Decrements in Galaxies at z 1.4

Galaxie

ZFOURGE catalogue of AGN candidates: an enhancement of 160-μm-derived star formation rates in active galaxies to z = 3.2

We investigate active galactic nuclei (AGN) candidates within the FourStar Galaxy Evolution Survey (ZFOURGE) to determine the impact they have on star formation in their host galaxies. We first identify a population of radio, X-ray, and infrared-selected AGN by cross-matching the deep Ks-band imaging of ZFOURGE with overlapping multiwavelength data. From this, we construct a mass-complete (log(M∗/M⊙M∗/M⊙) ≥9.75), AGN luminosity limited sample of 235 AGN hosts over z = 0.2–3.2. We compare the rest-frame U − V versus V − J (UVJ) colours and specific star formation rates (sSFRs) of the AGN hosts to a mass-matched control sample of inactive (non-AGN) galaxies. UVJ diagnostics reveal AGN tend to be hosted in a lower fraction of quiescent galaxies and a higher fraction of dusty galaxies than the control sample. Using 160 μm Herschel PACS data, we find the mean specific star formation rate of AGN hosts to be elevated by 0.34 ± 0.07 dex with respect to the control sample across all redshifts. This offset is primarily driven by infrared-selected AGN, where the mean sSFR is found to be elevated by as much as a factor of ∼5. The remaining population, comprised predominantly of X-ray AGN hosts, is found mostly consistent with inactive galaxies, exhibiting only a marginal elevation. We discuss scenarios that may explain these findings and postulate that AGN are less likely to be a dominant mechanism for moderating galaxy growth via quenching than has previously been suggested

Mergers and Star Formation: The Environment and Stellar Mass Growth of the Progenitors of Ultra-massive Galaxies since z = 2

Stars and planetary systemsGalaxie

The near-infrared imager and slitless spectrograph for the James Webb Space Telescope. II. Wide field slitless spectroscopy

We acknowledge support from the Natural Sciences and Engineering Research Council of Canada (NSERC) through a variety of its funding programs. This work is in part supported by Canadian Space Agency grant 18JWSTGTO1. C.P., S.R. and K.V. are supported by the Canadian Space Agency under a contract with NRC Herzberg Astronomy and Astrophysics. K.M. acknowledges funding by the Science and Technology Foundation of Portugal (FCT), grants No. IF/00194/2015, PTDC/FIS-AST/28731/2017, UIDB/00099/2020.We present the wide field slitless spectroscopy mode of the NIRISS instrument on the James Webb Space Telescope. This mode employs two orthogonal low-resolution (resolving power ≈150) grisms in combination with a set of six blocking filters in the wavelength range 0.8–2.3 μm to provide a spectrum of almost every source across the field-of-view. When combined with the low background, high sensitivity and high spatial resolution afforded by the telescope, this mode will enable unprecedented studies of the structure and evolution of distant galaxies. We describe the performance of the as-built hardware relevant to this mode and expected imaging and spectroscopic sensitivity. We discuss operational and calibration procedures to obtain the highest quality data. As examples of the observing mode usage, we present details of two planned Guaranteed Time Observations programs: The Canadian NIRISS Unbiased Cluster Survey and The NIRISS Survey for Young Brown Dwarfs and Rogue Planets.Publisher PDFPeer reviewe

Improved constraints on the expansion rate of the Universe up to z~1.1 from the spectroscopic evolution of cosmic chronometers

We present new improved constraints on the Hubble parameter H(z) in the redshift range 0.15 < z < 1.1, obtained from the differential spectroscopic evolution of early-type galaxies as a function of redshift. We extract a large sample of early-type galaxies (\sim11000) from several spectroscopic surveys, spanning almost 8 billion years of cosmic lookback time (0.15 < z < 1.42). We select the most massive, red elliptical galaxies, passively evolving and without signature of ongoing star formation. Those galaxies can be used as standard cosmic chronometers, as firstly proposed by Jimenez & Loeb (2002), whose differential age evolution as a function of cosmic time directly probes H(z). We analyze the 4000 {\AA} break (D4000) as a function of redshift, use stellar population synthesis models to theoretically calibrate the dependence of the differential age evolution on the differential D4000, and estimate the Hubble parameter taking into account both statistical and systematical errors. We provide 8 new measurements of H(z) (see Tab. 4), and determine its change in H(z) to a precision of 5-12% mapping homogeneously the redshift range up to z \sim 1.1; for the first time, we place a constraint on H(z) at z \neq 0 with a precision comparable with the one achieved for the Hubble constant (about 5-6% at z \sim 0.2), and covered a redshift range (0.5 < z < 0.8) which is crucial to distinguish many different quintessence cosmologies. These measurements have been tested to best match a \Lambda CDM model, clearly providing a statistically robust indication that the Universe is undergoing an accelerated expansion. This method shows the potentiality to open a new avenue in constrain a variety of alternative cosmologies, especially when future surveys (e.g. Euclid) will open the possibility to extend it up to z \sim 2.Comment: 34 pages, 15 figures, 6 tables, published in JCAP. It is a companion to Moresco et al. (2012b, http://arxiv.org/abs/1201.6658) and Jimenez et al. (2012, http://arxiv.org/abs/1201.3608). The H(z) data can be downloaded at http://www.physics-astronomy.unibo.it/en/research/areas/astrophysics/cosmology-with-cosmic-chronometer

The LEGA-C survey completed: stellar populations and stellar kinematics of galaxies 7 Gyr ago

Galaxie