arXiv subjects

C. Pearson

Publications and source records attributed to C. Pearson.

51 records · Page 3Linked to original sources

arXiv2010

Ultra deep AKARI observations of Abell 2218: resolving the 15 um extragalactic background light

We present extragalactic number counts and a lower limit estimate for the cosmic infrared background at 15 um from AKARI ultra deep mapping of the gravitational lensing cluster Abell 2218. This data is the deepest taken by any facility at this wavelength, and uniquely samples the normal galaxy population. We have de-blended our sources, to resolve photometric confusion, and de-lensed our photometry to probe beyond AKARI's blank-field sensitivity. We estimate a de-blended 5 sigma sensitivity of 28.7 uJy. The resulting 15 um galaxy number counts are a factor of three fainter than previous results, extending to a depth of ~ 0.01 mJy and providing a stronger lower limit constraint on the cosmic infrared background at 15 um of 1.9 +/- 0.5 nW m^-2 sr^-1.

astro-ph.CO↗

arXiv2010

In-flight calibration of the Herschel-SPIRE instrument

SPIRE, the Spectral and Photometric Imaging Receiver, is the Herschel Space Observatory's submillimetre camera and spectrometer. It contains a three-band imaging photometer operating at 250, 350 and 500 μm, and an imaging Fourier transform spectrometer (FTS) covering 194-671 μm (447-1550 GHz). In this paper we describe the initial approach taken to the absolute calibration of the SPIRE instrument using a combination of the emission from the Herschel telescope itself and the modelled continuum emission from solar system objects and other astronomical targets. We present the photometric, spectroscopic and spatial accuracy that is obtainable in data processed through the "standard" pipelines. The overall photometric accuracy at this stage of the mission is estimated as 15% for the photometer and between 15 and 50% for the spectrometer. However, there remain issues with the photometric accuracy of the spectra of low flux sources in the longest wavelength part of the SPIRE spectrometer band. The spectrometer wavelength accuracy is determined to be better than 1/10th of the line FWHM. The astrometric accuracy in SPIRE maps is found to be 2 arcsec when the latest calibration data are used. The photometric calibration of the SPIRE instrument is currently determined by a combination of uncertainties in the model spectra of the astronomical standards and the data processing methods employed for map and spectrum calibration. Improvements in processing techniques and a better understanding of the instrument performance will lead to the final calibration accuracy of SPIRE being determined only by uncertainties in the models of astronomical standards.

astro-ph.IM↗

arXiv2010

Herschel ATLAS: The cosmic star formation history of quasar host galaxies

We present a derivation of the star formation rate per comoving volume of quasar host galaxies, derived from stacking analyses of far-infrared to mm-wave photometry of quasars with redshifts 0 I_AB>-32. We use the science demonstration observations of the first ~16 deg^2 from the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) in which there are 240 quasars from the Sloan Digital Sky Survey (SDSS) and a further 171 from the 2dF-SDSS LRG and QSO (2SLAQ) survey. We supplement this data with a compilation of data from IRAS, ISO, Spitzer, SCUBA and MAMBO. H-ATLAS alone statistically detects the quasars in its survey area at >5sigma at 250, 350 and 500um. From the compilation as a whole we find striking evidence of downsizing in quasar host galaxy formation: low-luminosity quasars with absolute magnitudes in the range -22>I_AB>-24 have a comoving star formation rate (derived from 100um rest-frame luminosities) peaking between redshifts of 1 and 2, while high-luminosity quasars with I_AB<-26 have a maximum contribution to the star formation density at z~3. The volume-averaged star formation rate of -22>I_AB>-24 quasars evolves as (1+z)^{2.3 +/- 0.7} at z<2, but the evolution at higher luminosities is much faster reaching (1+z)^{10 +/- 1} at -26>I_AB>-28. We tentatively interpret this as a combination of a declining major merger rate with time and gas consumption reducing fuel for both black hole accretion and star formation.

astro-ph.CO↗

arXiv2010

The Herschel-ATLAS: Extragalactic Number Counts from 250 to 500 Microns

Aims. The Herschel-ATLAS survey (H-ATLAS) will be the largest area survey to be undertaken by the Herschel Space Observatory. It will cover 550 sq. deg. of extragalactic sky at wavelengths of 100, 160, 250, 350 and 500 microns when completed, reaching flux limits (5 sigma) from 32 to 145mJy. We here present galaxy number counts obtained for SPIRE observations of the first ~14 sq. deg. observed at 250, 350 and 500 microns. Methods. Number counts are a fundamental tool in constraining models of galaxy evolution. We use source catalogs extracted from the H-ATLAS maps as the basis for such an analysis. Correction factors for completeness and flux boosting are derived by applying our extraction method to model catalogs and then applied to the raw observational counts. Results. We find a steep rise in the number counts at flux levels of 100-200mJy in all three SPIRE bands, consistent with results from BLAST. The counts are compared to a range of galaxy evolution models. None of the current models is an ideal fit to the data but all ascribe the steep rise to a population of luminous, rapidly evolving dusty galaxies at moderate to high redshift.

astro-ph.CO↗

arXiv2010

Herschel-ATLAS: Dust temperature and redshift distribution of SPIRE and PACS detected sources using submillimetre colours

We present colour-colour diagrams of detected sources in the Herschel-ATLAS Science Demonstration Field from 100 to 500 microns using both PACS and SPIRE. We fit isothermal modified black bodies to the spectral energy distribution (SED) to extract the dust temperature of sources with counterparts in Galaxy And Mass Assembly (GAMA) or SDSS surveys with either a spectroscopic or a photometric redshift. For a subsample of 330 sources detected in at least three FIR bands with a significance greater than 3 $σ$, we find an average dust temperature of $(28 \pm 8)$K. For sources with no known redshift, we populate the colour-colour diagram with a large number of SEDs generated with a broad range of dust temperatures and emissivity parameters, and compare to colours of observed sources to establish the redshift distribution of this sample. For another subsample of 1686 sources with fluxes above 35 mJy at 350 microns and detected at 250 and 500 microns with a significance greater than 3$σ$, we find an average redshift of $2.2 \pm 0.6$.

astro-ph.CO↗

arXiv2010

The AGN fraction of submm-selected galaxies and contributions to the submm/mm-wave extragalactic background light

We present a comparison of the SCUBA Half Degree Extragalactic Survey (SHADES) at 450, 850 and 1100 microns with deep guaranteed time 15 microns AKARI FU-HYU survey data and Spitzer guaranteed time data at 3.6-24 microns in the Lockman Hole East. The AKARI data was analysed using bespoke software based in part on the drizzling and minimum-variance matched filtering developed for SHADES, and was cross calibrated against Infrared Space Observatory (ISO) fluxes. Our stacking analyses find AKARI 15um galaxies with >~200 microJy contribute >10% of the 450 micron background, but only <4% of the 1100 micron background, suggesting that different populations contribute at mm-wavelengths. We confirm our earlier result that the ultra-deep 450 micron SCUBA-2 Cosmology Survey will be dominated by populations already detected by AKARI and Spitzer mid-infrared surveys. The superb mid-infrared wavelength coverage afforded by combining Spitzer and AKARI photometry is an excellent diagnostic of AGN contributions, and we find that (23-52)% of submm-selected galaxies have AGN bolometric fractions f_AGN>0.3.

astro-ph.CO↗

arXiv2010

Evolution of Infrared Luminosity functions of Galaxies in the AKARI NEP-Deep field: Revealing the cosmic star formation history hidden by dust

Dust-obscured star-formation becomes much more important with increasing intensity, and increasing redshift. We aim to reveal cosmic star-formation history obscured by dust using deep infrared observation with the AKARI. We construct restframe 8um, 12um, and total infrared (TIR) luminosity functions (LFs) at 0.15<z<2.2 using 4128 infrared sources in the AKARI NEP-Deep field. A continuous filter coverage in the mid-IR wavelength (2.4, 3.2, 4.1, 7, 9, 11, 15, 18, and 24um) by the AKARI satellite allows us to estimate restframe 8um and 12um luminosities without using a large extrapolation based on a SED fit, which was the largest uncertainty in previous work. We have found that all 8um (0.38<z<2.2), 12um (0.15<z<1.16), and TIR LFs (0.2<z<1.6), show a continuous and strong evolution toward higher redshift. In terms of cosmic infrared luminosity density (Omega_IR), which was obtained by integrating analytic fits to the LFs, we found a good agreement with previous work at z<1.2, and that the Omega_IR evolves as propto (1+z)^4.4+-1.0. When we separate contributions to Omega_IR by LIRGs and ULIRGs, we found more IR luminous sources are increasingly more important at higher redshift. We found that the ULIRG (LIRG) contribution increases by a factor of 10 (1.8) from z=0.35 to z=1.4.

astro-ph.CO↗

arXiv2009

Environmental dependence of 8um luminosity functions of galaxies at z~0.8: Comparison between RXJ1716.4+6708 and the AKARI NEP deep field

We aim to reveal environmental dependence of infrared luminosity functions (IR LFs) of galaxies at z~0.8 using the AKARI satellite. We construct restframe 8um IR LFs in the cluster region RXJ1716.4+6708 at z=0.81, and compare them with a blank field using the AKARI North Ecliptic Pole deep field data at the same redshift. AKARI's wide field of view (10'x10') is suitable to investigate wide range of galaxy environments. AKARI's 15um filter is advantageous here since it directly probes restframe 8um at z~0.8, without relying on a large extrapolation based on a SED fit, which was the largest uncertainty in previous work. We have found that cluster IR LFs at restframe 8um have a factor of 2.4 smaller L^* and a steeper faint-end slope than that of the field. Confirming this trend, we also found that faint-end slopes of the cluster LFs becomes flatter and flatter with decreasing local galaxy density. These changes in LFs cannot be explained by a simple infall of field galaxy population into a cluster. Physics that can preferentially suppress IR luminous galaxies in high density regions is required to explain the observed results.

astro-ph.CO↗

arXiv2009

The Herschel ATLAS

The Herschel ATLAS is the largest open-time key project that will be carried out on the Herschel Space Observatory. It will survey 510 square degrees of the extragalactic sky, four times larger than all the other Herschel surveys combined, in five far-infrared and submillimetre bands. We describe the survey, the complementary multi-wavelength datasets that will be combined with the Herschel data, and the six major science programmes we are undertaking. Using new models based on a previous submillimetre survey of galaxies, we present predictions of the properties of the ATLAS sources in other wavebands.

astro-ph.CO↗

arXiv2008

Photometric redshift accuracy in AKARI Deep Surveys

We investigate the photometric redshift accuracy achievable with the AKARI infrared data in deep multi-band surveys, such as in the North Ecliptic Pole field. We demonstrate that the passage of redshifted policyclic aromatic hydrocarbons and silicate features into the mid-infrared wavelength window covered by AKARI is a valuable means to recover the redshifts of starburst galaxies. To this end we have collected a sample of ~60 galaxies drawn from the GOODS-North Field with spectroscopic redshift 0.5<~z_spec<~1.5 and photometry from 3.6 to 24 micron, provided by the Spitzer, ISO and AKARI satellites. The infrared spectra are fitted using synthetic galaxy Spectral Energy Distributions which account for starburst and active nuclei emission. For ~90% of the sources in our sample the redshift is recovered with an accuracy |z_phot-z_spec|/(1+z_spec)<~10%. A similar analysis performed on different sets of simulated spectra shows that the AKARI infrared data alone can provide photometric redshifts accurate to |z_phot-z_spec|/(1+z_spec)<~10% (1-sigma) at z<~2. At higher redshifts the PAH features are shifted outside the wavelength range covered by AKARI and the photo-z estimates rely on the less prominent 1.6 micron stellar bump; the accuracy achievable in this case on (1+z) is ~10-15%, provided that the AGN contribution to the infrared emission is subdominant. Our technique is no more prone to redshift aliasing than optical-uv photo-z, and it may be possible to reduce this aliasing further with the addition of submillimetre and/or radio data.

astro-ph↗

arXiv2007

Double Spin Asymmetries A_NN and A_SS at sqrt{s}=200 GeV in Polarized Proton-Proton Elastic Scattering at RHIC

We present the first measurements of the double spin asymmetries A_NN and A_SS at sqrt{s}=200 GeV, obtained by the pp2pp experiment using polarized proton beams at the Relativistic Heavy Ion Collider (RHIC). The data were collected in the four momentum transfer t range 0.01<|t|<0.03 (GeV/c)^2. The measured asymmetries, which are consistent with zero, allow us to estimate upper limits on the double helicity-flip amplitudes phi_2 and phi_4 at small t as well as on the difference Delta(sigma_T) between the total cross sections for transversely polarized protons with antiparallel or parallel spin orientations.

nucl-ex↗

arXiv2006

Dissecting the Cosmic Infrared Background with 3D Instruments

The cosmic infrared background (CIB) consists of emission from distant, dusty, star-forming galaxies. Energetically, the CIB is very important as it contains as much energy as the extragalactic optical background. The nature and evolutionary status of the objects making up the background are, however, unclear. The CIB peaks at ~150 microns, and as such is most effectively studied from space. The limited apertures of space-borne telescopes set the angular resolution that can be attained, and so even Herschel, with its 3.5m diameter, will be confusion-limited at this wavelengths at ~5mJy. The bulk of the galaxies contributing to the CIB are fainter than this, so it is difficult to study them without interferometry. Here we present the results of a preliminary study of an alternative way of probing fainter than the continuum confusion limit using far-IR imaging spectroscopy. An instrument capable of such observations is being planned for SPICA - a proposed Japanese mission with an aperture equivalent to that of Herschel and more than 2 orders of magnitude more sensitive. We investigate the potential of imaging spectrometers to break the continuum confusion limit. We have simulated the capabilities of a spectrometer with modest field of view (2'x2'), moderate spectral resolution (R~1-2000) and high sensitivity. We find that such an instrument is capable of not only detecting line emission from sources with continuum fluxes substantially below the confusion limit, but also of determining their redshifts and, where multiple lines are detected, some emission line diagnostics. We conclude that 3-D imaging spectrometers on cooled far-IR space telescopes will be powerful new tools for extragalactic far-IR astronomy.

astro-ph↗

arXiv2001

Room temperature accelerator structures for linear colliders

Early tests of short low group velocity and standing wave structures indicated the viability of operating X-band linacs with accelerating gradients in excess of 100 MeV/m. Conventional scaling of traveling wave traveling wave linacs with frequency scales the cell dimensions with l. Because Q scales as l1/2, the length of the structures scale not linearly but as l3/2 in order to preserve the attenuation through each structure. For NLC we chose not to follow this scaling from the SLAC S-band linac to its fourth harmonic at X-band. We wanted to increase the length of the structures to reduce the number of couplers and waveguide drives which can be a significant part of the cost of a microwave linac. Furthermore, scaling the iris size of the disk-loaded structures gave unacceptably high short range dipole wakefields. Consequently, we chose to go up a factor of about 5 in average group velocity and length of the structures, which increases the power fed to each structure by the same factor and decreases the short range dipole wakes by a similar factor. Unfortunately, these longer (1.8 m) structures have not performed nearly as well in high gradient tests as the short structures. We believe we have at least a partial understanding of the reason and will discuss it below. We are now studying two types of short structures with large apertures with moderately good efficiency including: 1) traveling wave structures with the group velocity lowered by going to large phase advance per period with bulges on the iris, 2) pi mode standing wave structures

physics.acc-ph↗

arXiv2000

Design, fabrication and measurement of the first rounded damped detuned accelerator structure (RDDS1)

As a joint effort in the JLC/NLC research program, we have developed a new type of damped detuned accelerator structure with optimized round-shaped cavities (RDDS). This paper discusses some important R&D aspects of the first structure in this series (RDDS1). The design aspects covered are the cell design with sub-MHz precision, HOM detuning, coupling and damping technique and wakefield simulation. The fabrication issues covered are ultra-precision cell machining with micron accuracy, assembly and diffusion bonding technologies to satisfactorily meet bookshelf, straightness and cell rotational alignment requirements. The measurements described are the RF properties of single cavities and complete accelerator section, as well as wakefields from the ASSET tests at SLAC. Finally, future improvements are also discussed.

physics.acc-ph↗

arXiv2000

The Next Linear Collider Klystron Development Program*

Klystrons capable of 75 MW output power at 11.4 GHz have been under development at SLAC for the last decade. The work has been part of the program to realize all the components necessary for the construction of the Next Linear Collider (NLC). The effort has produced a family of solenoid-focused 50 MW klystrons, which are currently powering a 0.5 GeV test accelerator at SLAC and several test stands, where high power components are evaluated and fundamental research is performed studying rf breakdown and dark current production. Continuing development has resulted in a Periodic Permanent Magnet (PPM) focused 50 MW klystron, tested at SLAC and subsequently contracted for manufacture by industry in England and Japan. A 75 MW version of that PPM klystron was built at SLAC and reached 75 MW, with 2.8 microsecond pulses. Based on this design, a prototype 75 MW klystron, designed for low-cost manufacture, is currently under development at SLAC, and will eventually be procured from industry in modest quantities for advanced NLC tests. Beyond these developments, the design of Multiple Beam Klystrons (MBKs) is under study at SLAC. MBKs offer the possibility of considerably lower modulator costs by producing comparable power to the klystrons now available, at much lower voltages. * This work supported by the Department of Energy under contract DE-AC03-76SF00515

hep-ex↗