S. Levin

ARCADE 2 Measurement of the Absolute Sky Brightness at 3-90 GHz

The ARCADE 2 instrument has measured the absolute temperature of the sky at frequencies 3, 8, 10, 30, and 90 GHz, using an open-aperture cryogenic instrument observing at balloon altitudes with no emissive windows between the beam-forming optics and the sky. An external blackbody calibrator provides an in situ reference. Systematic errors were greatly reduced by using differential radiometers and cooling all critical components to physical temperatures approximating the cosmic microwave background (CMB) temperature. A linear model is used to compare the output of each radiometer to a set of thermometers on the instrument. Small corrections are made for the residual emission from the flight train, balloon, atmosphere, and foreground Galactic emission. The ARCADE 2 data alone show an excess radio rise of 54 ± 6 mK at 3.3 GHz in addition to a CMB temperature of 2.731 ± 0.004 K. Combining the ARCADE 2 data with data from the literature shows an excess power-law spectrum of T = 24.1 ± 2. 1( K) (ν/ν0) −2.599±0.036 from 22 MHz to 10 GHz (ν0 = 310 MHz) in addition to a CMB temperature of 2.725 ± 0.001 K.The ARCADE 2 instrument has measured the absolute temperature of the sky at frequencies 3, 8, 10, 30, and 90 GHz, using an open-aperture cryogenic instrument observing at balloon altitudes with no emissive windows between the beam-forming optics and the sky. An external blackbody calibrator provides an in situ reference. Systematic errors were greatly reduced by using differential radiometers and cooling all critical components to physical temperatures approximating the CMB temperature. A linear model is used to compare the output of each radiometer to a set of thermometers on the instrument. Small corrections are made for the residual emission from the flight train, balloon, atmosphere, and foreground Galactic emission. The ARCADE 2 data alone show an extragalactic rise of 50 ± 7 mK at 3.3 GHz in addition to a CMB temperature of 2.730 ± .004 K. Combining the ARCADE 2 data with data from the literature shows a background power law spectrum of T = 1.26 ± 0.09 [K] (�/�0) −2.60±0.04 from 22 MHz to 10 GHz (�0 = 1 GHz) in addition to a CMB temperature of 2.725 ± .001 K. Subject headings: cosmology: Cosmic Microwave Background — cosmology: Observations

Study of Structure and Small-Scale Fragmentation in TMC-1

Large-scale C(sup 18)O maps show that the Taurus molecular cloud 1 (TMC-1) has numerous cores located along a ridge which extends about 12 minutes by at least 35 minutes. The cores traced by C(sup 18)O are about a few arcminutes (0.1-0.2 pc) in extent, typically contain about 0.5-3 solar mass, and are probably gravitationally bound. We present a detailed study of the small-scale fragmentary structure of one of these cores, called core D, within TMC-1 using very high spectral and spatial resolution maps of CCS and CS. The CCS lines are excellent tracers for investigating the density, temperature, and velocity structure in dense cores. The high spectral resolution, 0.008 km /s, data consist mainly of single-dish, Nyquist-sampled maps of CCS at 22 GHz with 45 sec spatial resolution taken with NASAs 70 m DSN antenna at Goldstone. The high spatial resolution spectral line maps were made with the Very Large Array (9 sec resolution) at 22 GHz and with the OVRO millimeter array in CCS and CS at 93 GHz and 98 GHz, respectively, with 6 sec resolution. These maps are supplemented with single-dish observations of CCS and CC(sup 34)S spectra at 33 GHz using a NASA 34 m DSN antenna, CCS 93 GHz, C(sup 34)S (2-1), and C(sup 18)O (1-0) single-dish observations made with the AT&T Bell Laboratories 7 m antenna. Our high spectral and spatial CCS and CS maps show that core D is highly fragmented. The single-dish CCS observations map out several clumps which range in size from approx. 45 sec to 90 sec (0.03-0.06 pc). These clumps have very narrow intrinsic line widths, 0.11-0.25 km/s, slightly larger than the thermal line width for CCS at 10 K, and masses about 0.03-0.2 solar mass. Interferometer observations of some of these clumps show that they have considerable additional internal structure, consisting of several condensations ranging in size from approx. 10 sec- 30 sec (0.007-0.021 pc), also with narrow line widths. The mass of these smallest fragments is of order 0.01 solar mass. These small-scale structures traced by CCS appear to be gravitationally unbound by a large factor. Most of these objects have masses that fall below those of the putative proto-brown dwarfs (approx. less than 0.1 solar mass). The presence of many small gravitationally unbound clumps suggests that fragmentation mechanisms other than a purely Jeans gravitational instability may be important for the dynamics of these cold dense cores.

ARCADE 2 OBSERVATIONS OF GALACTIC RADIO EMISSION

We use absolutely calibrated data from the ARCADE 2 flight in 2006 July to model Galactic emission at frequencies 3, 8, and 10 GHz. The spatial structure in the data is consistent with a superposition of free–free and synchrotron emission. Emission with spatial morphology traced by the Haslam 408 MHz survey has spectral index βsynch =− 2.5 ± 0.1, with free–free emission contributing 0.10 ± 0.01 of the total Galactic plane emission in the lowest ARCADE 2 band at 3.15 GHz. We estimate the total Galactic emission toward the polar caps using either a simple plane-parallel model with csc |b| dependence or a model of high-latitude radio emission traced by the COBE/FIRAS map of Cii emission. Both methods are consistent with a single power law over the frequency range 22 MHz to 10 GHz, with total Galactic emission toward the north polar cap TGal = 10.12 ± 0.90 K and spectral index β =− 2.55 ± 0.03 at reference frequency 0.31 GHz. Emission associated with the plane-parallel structure accounts for only 30% of the observed high-latitude sky temperature, with the residual in either a Galactic halo or an isotropic extragalactic background. The well-calibrated ARCADE 2 maps provide a new test for spinning dust emission, based on the integrated intensity of emission from the Galactic plane instead of cross-correlations with the thermal dust spatial morphology. The Galactic plane intensity measured by ARCADE 2 is fainter than predicted by models without spinning dust and is consistent with spinning dust contributing 0.4 ± 0.1 of the Galactic plane emission at 23 GHz.

Measuring the Magnetic Field Strength in L1498 with Zeeman-splitting Observations of CCS

We have measured the Zeeman splitting of the CCS JN = 32-21 line at 33 GHz toward L1498, a dense preprotostellar core, in an effort to measure the line-of-sight component of its magnetic field. With approximately 35 hr of data on source (70 hr total) in good weather, the data suggest a line-of-sight component of the magnetic field in L1498 of 48 ± 31 μG, yielding an upper limit of Blos < 100 μG at the 95% confidence level. This upper limit provides some constraints on models. Our results show that the technique we have adopted to measure CCS Zeeman splitting holds great promise for determining magnetic field strengths in cloud cores using lower-frequency transitions, in particular the CCS JN = 10-00 line at 11 GHz. At this transition, the frequency splitting per gauss is 3 times that at 33 GHz, the brightness temperature is comparable to the 32-21 line, and receiver systems can be made more sensitive.