Planck early results XVIII : The power spectrum of cosmic infrared background anisotropies

Peer reviewe

Planck Early Results XVIII: The power spectrum of cosmic infrared background anisotropies

Using Planck maps of six regions of low Galactic dust emission with a total area of about 140 deg2, we determine the angular power spectra of cosmic infrared background (CIB) anisotropies from multipole ℓ = 200 to ℓ = 2000 at 217, 353, 545 and 857 GHz. We use 21-cm observations of Hi as a tracer of thermal dust emission to reduce the already low level of Galactic dust emission and use the 143 GHz Planck maps in these fields to clean out cosmic microwave background anisotropies. Both of these cleaning processes are necessary to avoid significant contamination of the CIB signal. We measure correlated CIB structure across frequencies. As expected, the correlation decreases with increasing frequency separation, because the contribution of high-redshift galaxies to CIB anisotropies increases with wavelengths. We find no significant difference between the frequency spectrum of the CIB anisotropies and the CIB mean, with ∆I/I=15% from 217 to 857 GHz. In terms of clustering properties, the Planck data alone rule out the linear scale- and redshift-independent bias model. Non-linear corrections are significant. Consequently, we develop an alternative model that couples a dusty galaxy, parametric evolution model with a simple halo-model approach. It provides an excellent fit to the measured anisotropy angular power spectra and suggests that a different halo occupation distribution is required at each frequency, which is consistent with our expectation that each frequency is dominated by contributions from different redshifts. In our best-fit model, half of the anisotropy power at ℓ=2000 comes from redshifts z 2 at 353 and 217 GHz, respectively

Planck Early Results: The Planck View of Nearby Galaxies

The all-sky coverage of the Planck Early Release Compact Source Catalogue (ERCSC) provides an unsurpassed survey of galaxies at submillimetre (submm) wavelengths, representing a major improvement in the numbers of galaxies detected, as well as the range of far-IR/submm wavelengths over which they have been observed. We here present the first results on the properties of nearby galaxies using these data. We match the ERCSC catalogue to IRAS-detected galaxies in the Imperial IRAS Faint Source Redshift Catalogue (IIFSCz), so that we can measure the spectral energy distributions (SEDs) of these objects from 60 to 850 microns. This produces a list of 1717 galaxies with reliable associations between Planck and IRAS, from which we select a subset of 468 for SED studies, namely those with strong detections in the three highest frequency Planck bands and no evidence of cirrus contamination. The SEDs are fitted using parametric dust models to determine the range of dust temperatures and emissivities. We find evidence for colder dust than has previously been found in external galaxies, with T<20K. Such cold temperatures are found using both the standard single temperature dust model with variable emissivity beta, or a two dust temperature model with beta fixed at 2. We also compare our results to studies of distant submm galaxies (SMGs) which have been claimed to contain cooler dust than their local counterparts. We find that including our sample of 468 galaxies significantly reduces the distinction between the two populations. Fits to SEDs of selected objects using more sophisticated templates derived from radiative transfer models confirm the presence of the colder dust found through parameteric fitting. We thus conclude that cold (T<20K) dust is a significant and largely unexplored component of many nearby galaxies.Comment: 16 pages, 14 figure

Potential of Small-Scale Turbomachinery for Waste Heat Recovery on Automotive Internal Combustion Engines

This paper investigates the waste heat recovery potential of internal combustion engines, using organic Rankine cycles running on small-scale radial turbomachinery. ORC are promising candidates for low-grade thermal sources and the use of dynamic expanders yields very compact systems, which is advantageous for automotive applications. As engine coolant and exhaust gases are the major available heat sources, different cycle configurations and working fluids have been investigated to capture them, in both urban and highway car operation. Pareto fronts showing the compromise between net power output and total heat exchange area have been identified for a set of cycle’s variables including turbine inlet conditions and heat exchanger pinches. A preliminary optimization, including only R-1234yf working fluid, shows that a single-source regenerative cycle harvesting the high temperature exhaust gas stream performs averagely better than coolant-driven and dual-source cycles. A more in-depth optimization including eight working fluids as well as aerodynamic and conceptual limitations related to radial turbomachinery and automotive design constraints, finally shows that an ICE exhaust heat recovery ORC could improve the first law efficiency of the driving system by up to 10% when implemented with fluid R-1233zd