Tunneling magnetic force microscopy

We have developed a powerful new tool for studying the magnetic patterns on magnetic recording media. This was accomplished by modifying a conventional scanning tunneling microscope. The fine-wire probe that is used to image surface topography was replaced with a flexible magnetic probe. Images obtained with these probes reveal both the surface topography and the magnetic structure. We have made a thorough theoretical analysis of the interaction between the probe and the magnetic fields emanating from a typical recorded surface. Quantitative data about the constituent magnetic fields can then be obtained. We have employed these techniques in studies of two of the most important issues of magnetic record: data overwrite and maximizing data-density. These studies have shown: (1) overwritten data can be retrieved under certain conditions; and (2) improvements in data-density will require new magnetic materials. In the course of these studies we have developed new techniques to analyze magnetic fields of recorded media. These studies are both theoretical and experimental and combined with the use of our magnetic force scanning tunneling microscope should lead to further breakthroughs in the field of magnetic recording

The SCUBA Bright Quasar Survey II: unveiling the quasar epoch at submillimetre wavelengths

We present results of the first systematic search for submillimetre continuum emission from z=2, radio-quiet, optically-luminous quasars, using the SCUBA/JCMT. We have observed a homogeneous sample of 57 quasars in the redshift range 1.54) redshift. The target sensitivity of the survey (3sigma=10mJy at 850um) was chosen to enable efficient identification of bright submm sources, suitable for detailed follow-up. 9 targets are detected, with fluxes in the range 7-17mJy. Although there is a suggestion of variation of submm detectability between z=2 and z=4, this is consistent with the K-correction of a characteristic far-infrared spectrum. Additionally, the weighted mean fluxes of non-detections at z=2 and z>4 are comparable

Radio Observations of Infrared Luminous High Redshift QSOs

We present Very Large Array (VLA) observations at 1.4 GHz and 5 GHz of a sample of 12 Quasi-stellar Objects (QSOs) at z = 3.99 to 4.46. The sources were selected as the brightest sources at 250 GHz from the recent survey of Omont et al. (2001). We detect seven sources at 1.4 GHz with flux densities, S_{1.4} > 50 microJy. These centimeter (cm) wavelength observations imply that the millimeter (mm) emission is most likely thermal dust emission. The radio-through-optical spectral energy distributions for these sources are within the broad range defined by lower redshift, lower optical luminosity QSOs. For two sources the radio continuum luminosities and morphologies indicate steep spectrum, radio loud emission from a jet-driven radio source. For the remaining 10 sources the 1.4 GHz flux densities, or limits, are consistent with those expected for active star forming galaxies. If the radio emission is powered by star formation in these systems, then the implied star formation rates are of order 1e3 M_solar/year. We discuss the angular sizes and spatial distributions of the radio emitting regions, and we consider briefly these results in the context of co-eval black hole and stellar bulge formation in galaxies.Comment: to appear in the A

Mid-J CO Emission in Nearby Seyfert Galaxies

We study for the first time the complete sub-millimeter spectra (450 GHz to 1550 GHz) of a sample of nearby active galaxies observed with the SPIRE Fourier Transform Spectrometer (SPIRE/FTS) onboard Herschel. The CO ladder (from Jup = 4 to 12) is the most prominent spectral feature in this range. These CO lines probe warm molecular gas that can be heated by ultraviolet photons, shocks, or X-rays originated in the active galactic nucleus or in young star-forming regions. In these proceedings we investigate the physical origin of the CO emission using the averaged CO spectral line energy distribution (SLED) of six Seyfert galaxies. We use a radiative transfer model assuming an isothermal homogeneous medium to estimate the molecular gas conditions. We also compare this CO SLED with the predictions of photon and X-ray dominated region (PDR and XDR) models.Comment: Proceedings of the Torus Workshop 2012 held at the University of Texas at San Antonio, 5-7 December 2012. C. Packham, R. Mason, and A. Alonso-Herrero (eds.); 6 pages, 3 figure

Sensitive Radio Observations of High Redshift Dusty QSOs

We present sensitive radio continuum imaging at 1.4 GHz and 4.9 GHz of seven high redshift QSOs selected for having a 240 GHz continuum detection, which is thought to be thermal dust emission. We detect radio continuum emission from four of the sources: BRI 0952-0115, BR 1202-0725, LBQS 1230+1627B, and BRI 1335-0417. The radio source in BR 1202-0725 is resolved into two components, coincident with the double mm and CO sources. We compare the results at 1.4 GHz and 240 GHz to empirical and semi-analytic spectral models based on star forming galaxies at low redshift. The radio-to-submm spectral energy distribution for BR 1202-0725, LBQS 1230+1627B, and BRI 1335-0417 are consistent with that expected for a massive starburst galaxy, with implied massive star formation rates of order 1000 solar masses per year (without correcting for possible amplification by gravitational lensing). The radio-to-submm spectral energy distribution for BRI 0952-0115 suggests a low-luminosity radio jet source driven by the AGN.Comment: 12 pages, Latex emulateapj format, including 1 table and 3 figures. The Astrophysical Journal, to appear in the January 2000 issu

350 Micron Dust Emission from High Redshift Objects

We report observations of a sample of high redshift sources (1.8<z<4.7), mainly radio-quiet quasars, at 350 microns using the SHARC bolometer camera at the Caltech Submillimeter Observatory. Nine sources were detected (>4-sigma) and upper limits were obtained for 11 with 350 micron flux density limits (3-sigma) in the range 30-125mJy. Combining published results at other far-infrared and millimeter wavelengths with the present data, we are able to estimate the temperature of the dust, finding relatively low values, averaging 50K. From the spectral energy distribution, we derive dust masses of a few 10^8 M_sun and luminosities of 4-33x10^{12} L_sun (uncorrected for any magnification) implying substantial star formation activity. Thus both the temperature and dust masses are not very different from those of local ultraluminous infrared galaxies. For this redshift range, the 350 micron observations trace the 60-100 micron rest frame emission and are thus directly comparable with IRAS studies of low redshift galaxies.Comment: 5 pages, 2 PS figures. Accepted for publication in Astrophysical Journal Letter

Star-formation at z=4.7 in the environment of the QSO BR1202-07

We present here the spectrum of the galaxy companion to the z=4.7 quasar BR1202-0725, in the optical range 6000-9000 A, corresponding to 1050-1580 A rest-frame. We detect a strong Lya emission line at z=4.702, with an integrated flux of 2x10^{-16} ergs/cm^2/s, and a UV continuum longward of the Lya emission at a flux level of 3x10^{-19}ergs/cm^2/s/A. We fail to detect any CIV[1550] emission with a 3 sigma upper limit of 3x10^{-17} ergs/cm^2/s $. We show that the ratio between Lya and continuum intensity and the absence of a strong CIV emission imply that the UV continuum radiation is the result of an intense star-formation activity rather than of a reprocessing of the QSO flux. The total estimated SFR of this z=4.7 star-forming region is about 15-54 Msun/yr, depending on the IMF and the metallicity. The present data suggest that the Lya emission has a velocity and spatial structure, with possible velocity differences of about 500 km/s on scales of few kpc. These velocity patterns may be a signature of collapsing or merging phenomena in the QSO and its environment, as expected from current models of galaxy formation at high z.Comment: 14 pages + 2 figures. To appear on AJ, April 199

The solar core: new low-l p-mode fine-spacing results from BiSON

The fine-structure spacing $d_{\ell}(n) = \nu_{\ell,n} - \nu_{\ell+2,n-1}$ for low-degree solar p modes of angular degree $\ell$ and radial order n, is sensitive to conditions in the deep radiative interior of the Sun. Here, we present fine-structure spacings derived from the analysis of nearly five years of helioseismological data collected between 1991 July and 1996 February by the Birmingham Solar-Oscillations Network (BiSON). These data cover $9 \le n \le 28$ for $d_{0}(n)$, and $11 \le n \le 27$ for $d_{1}(n)$. The measured spacings are much more precise, and cover a greater range, than earlier measurements from BiSON data (Elsworth et al. 1990a). The predicted fine-structure spacings for a ``standard'' solar model are clearly excluded by the BiSON data (at $\approx 10\sigma$); models that include helium and heavy element settling provide a much better match to the observed spacings (see also Elsworth et al. 1995). Since the inclusion of core settling in solar models will tend to slightly increase the predicted neutrino flux, the BiSON fine-structure data appear to reinforce previous conclusions, i.e., an astrophysical solution to the solar neutrino problem seems unlikely.Comment: 14 pages, LaTex 2e, 1 figure (2 encapsulated .PS files); ApJ Letters, in pres