Extended Cold Molecular Gas Reservoirs in z~3.4 Submillimeter Galaxies

We report the detection of spatially resolved CO(1-0) emission in the z~3.4 submillimeter galaxies (SMGs) SMM J09431+4700 and SMM J13120+4242, using the Expanded Very Large Array (EVLA). SMM J09431+4700 is resolved into the two previously reported millimeter sources H6 and H7, separated by ~30kpc in projection. We derive CO(1-0) line luminosities of L'(CO 1-0) = (2.49+/-0.86) and (5.82+/-1.22) x 10^10 K km/s pc^2 for H6 and H7, and L'(CO 1-0) = (23.4+/-4.1) x 10^10 K km/s pc^2 for SMM J13120+4242. These are ~1.5-4.5x higher than what is expected from simple excitation modeling of higher-J CO lines, suggesting the presence of copious amounts of low-excitation gas. This is supported by the finding that the CO(1-0) line in SMM J13120+4242, the system with lowest CO excitation, appears to have a broader profile and more extended spatial structure than seen in higher-J CO lines (which is less prominently seen in SMM J09431+4700). Based on L'(CO 1-0) and excitation modeling, we find M_gas = 2.0-4.3 and 4.7-12.7 x 10^10 Msun for H6 and H7, and M_gas = 18.7-69.4 x 10^10 Msun for SMM J13120+4242. The observed CO(1-0) properties are consistent with the picture that SMM J09431+4700 represents an early-stage, gas-rich major merger, and that SMM J13120+4242 represents such a system in an advanced stage. This study thus highlights the importance of spatially and dynamically resolved CO(1-0) observations of SMGs to further understand the gas physics that drive star formation in these distant galaxies, which becomes possible only now that the EVLA rises to its full capabilities.Comment: 6 pages, 4 figures, to appear in ApJL (EVLA Special Issue; accepted May 19, 2011

Aeroacoustic Measurements of the Bell 699 Rotor on the Tiltrotor Test Rig in the National Full-Scale Aerodynamics Complex 40- by 80-Foot Wind Tunnel

The Tiltrotor Test Rig (TTR) with the Bell 699 Rotor was tested in the National Full-Scale Aerodynamics Complex (NFAC) 40- by 80-Foot Wind Tunnel from 2017 to 2018. The primary goal of the test was to understand the operational capabilities of the TTR while also acquiring research data, including acoustic data. A data quality study revealed that the NFAC 40- by 80-Foot Wind Tunnel is an adequate acoustic environment to test the Bell 699 Rotor for helicopter, conversion, and airplane configurations. Representative acoustic data are presented, and selected acoustic data and corresponding test conditions are included

Solar irradiance at the earth's surface: long-term behavior observed at the South Pole

This research examines a 17-year database of UV-A (320–400 nm) and visible (400–600 nm) solar irradiance obtained by a scanning spectroradiometer located at the South Pole. The goal is to define the variability in solar irradiance reaching the polar surface, with emphasis on the influence of cloudiness and on identifying systematic trends and possible links to the solar cycle. To eliminate changes associated with the varying solar elevation, the analysis focuses on data averaged over 30–35 day periods centered on each year's austral summer solstice. The long-term average effect of South Polar clouds is a small attenuation, with the mean measured irradiances being about 5–6% less than the clear-sky values, although at any specific time clouds may reduce or enhance the signal that reaches the sensor. The instantaneous fractional attenuation or enhancement is wavelength dependent, where the percent deviation from the clear-sky irradiance at 400–600 nm is typically 2.5 times that at 320–340 nm. When averaged over the period near each year's summer solstice, significant correlations appear between irradiances at all wavelengths and the solar cycle as measured by the 10.7 cm solar radio flux. An approximate 1.8 ± 1.0% decrease in ground-level irradiance occurs from solar maximum to solar minimum for the wavelength band 320–400 nm. The corresponding decrease for 400–600 nm is 2.4 ± 1.9%. The best-estimate declines appear too large to originate in the sun. If the correlations have a geophysical origin, they suggest a small variation in atmospheric attenuation with the solar cycle over the period of observation, with the greatest attenuation occurring at solar minimum

Evidence for a clumpy, rotating gas disk in a submillimeter galaxy at z=4

We present Karl G. Jansky Very Large Array (VLA) observations of the CO(2-1) emission in the z=4.05 submillimeter galaxy (SMG) GN20. These high-resolution data allow us to image the molecular gas at 1.3 kpc resolution just 1.6 Gyr after the Big Bang. The data reveal a clumpy, extended gas reservoir, 14 +/- 4 kpc in diameter, in unprecedented detail. A dynamical analysis shows that the data are consistent with a rotating disk of total dynamical mass 5.4 +/- 2.4 X 10^11 M_sun. We use this dynamical mass estimate to constrain the CO-to-H_2 mass conversion factor (alpha_CO), finding alpha_CO=1.1 +/- 0.6 M_sun (K km s^-1 pc^2)^-1. We identify five distinct molecular gas clumps in the disk of GN20 with masses a few percent of the total gas mass, brightness temperatures of 16-31K, and surface densities of >3,200-4,500 X (alpha_CO/0.8) M_sun pc^-2. Virial mass estimates indicate they could be self-gravitating, and we constrain their CO-to-H_2 mass conversion factor to be <0.2-0.7 M_sun (K km s^-1 pc^2)^-1. A multiwavelength comparison demonstrates that the molecular gas is concentrated in a region of the galaxy that is heavily obscured in the rest-frame UV/optical. We investigate the spatially-resolved gas excitation and find that the CO(6-5)/CO(2-1) ratio is constant with radius, consistent with star formation occuring over a large portion of the disk. We discuss the implications of our results in the context of different fueling scenarios for SMGs.Comment: 15 pages, 9 figures, accepted for publication in Ap

Monitoring the Low-Energy Gamma-Ray Sky Using Earth Occultation with GLAST GBM

Long term all-sky monitoring of the 20 keV – 2 MeV gamma-ray sky using the Earth occultation technique was demonstrated by the BATSE instrument on the Compton Gamma Ray Observatory. The principles and techniques used for the development of an end-to-end earth occultation data analysis system for BATSE can be extended to the GLAST Burst Monitor (GBM), resulting in multiband light curves and time-resolved spectra in the energy range 8 keV to above 1 MeV for known gamma-ray sources and transient outbursts, as well as the discovery of new sources of gamma-ray emission. In this paper we describe the application of the technique to the GBM. We also present the expected sensitivity for the GBM

Earth Occultation Imaging of the Low Energy Gamma-Ray Sky with GBM

The Earth Occultation Technique (EOT) has been applied to Fermi's Gamma-ray Burst Monitor (GBM) to perform all-sky monitoring for a predetermined catalog of hard X-ray/soft gamma-ray sources. In order to search for sources not in the catalog, thus completing the catalog and reducing a source of systematic error in EOT, an imaging method has been developed -- Imaging with a Differential filter using the Earth Occultation Method (IDEOM). IDEOM is a tomographic imaging method that takes advantage of the orbital precession of the Fermi satellite. Using IDEOM, all-sky reconstructions have been generated for ~sim 4 years of GBM data in the 12-50 keV, 50-100 keV and 100-300 keV energy bands in search of sources otherwise unmodeled by the GBM occultation analysis. IDEOM analysis resulted in the detection of 57 sources in the 12-50 keV energy band, 23 sources in the 50-100 keV energy band, and 7 sources in the 100-300 keV energy band. Seventeen sources were not present in the original GBM-EOT catalog and have now been added. We also present the first joined averaged spectra for four persistent sources detected by GBM using EOT and by the Large Area Telescope (LAT) on Fermi: NGC 1275, 3C 273, Cen A, and the Crab

Star-Formation in Low Radio Luminosity AGN from the Sloan Digital Sky Survey

We investigate faint radio emission from low- to high-luminosity Active Galactic Nuclei (AGN) selected from the Sloan Digital Sky Survey (SDSS). Their radio properties are inferred by co-adding large ensembles of radio image cut-outs from the FIRST survey, as almost all of the sources are individually undetected. We correlate the median radio flux densities against a range of other sample properties, including median values for redshift, [OIII] luminosity, emission line ratios, and the strength of the 4000A break. We detect a strong trend for sources that are actively undergoing star-formation to have excess radio emission beyond the ~10^28 ergs/s/Hz level found for sources without any discernible star-formation. Furthermore, this additional radio emission correlates well with the strength of the 4000A break in the optical spectrum, and may be used to assess the age of the star-forming component. We examine two subsamples, one containing the systems with emission line ratios most like star-forming systems, and one with the sources that have characteristic AGN ratios. This division also separates the mechanism responsible for the radio emission (star-formation vs. AGN). For both cases we find a strong, almost identical, correlation between [OIII] and radio luminosity, with the AGN sample extending toward lower, and the star-formation sample toward higher luminosities. A clearer separation between the two subsamples is seen as function of the central velocity dispersion of the host galaxy. For systems with similar redshifts and velocity dispersions, the star-formation subsample is brighter than the AGN in the radio by an order of magnitude. This underlines the notion that the radio emission in star-forming systems can dominate the emission associated with the AGN.Comment: Accepted for publication in Astronomical Journal; 15 pages, 8 color figure

CO(1-0) line imaging of massive star-forming disc galaxies at z=1.5-2.2

We present detections of the CO(J= 1-0) emission line in a sample of four massive star-forming galaxies at z~1.5-2.2 obtained with the Karl G. Jansky Very Large Array (VLA). Combining these observations with previous CO(2-1) and CO(3-2) detections of these galaxies, we study the excitation properties of the molecular gas in our sample sources. We find an average line brightness temperature ratios of R_{21}=0.70+\-0.16 and R_{31}=0.50+\-0.29, based on measurements for three and two galaxies, respectively. These results provide additional support to previous indications of sub-thermal gas excitation for the CO(3-2) line with a typically assumed line ratio R_{31}~0.5. For one of our targets, BzK-21000, we present spatially resolved CO line maps. At the resolution of 0.18'' (1.5 kpc), most of the emission is resolved out except for some clumpy structure. From this, we attempt to identify molecular gas clumps in the data cube, finding 4 possible candidates. We estimate that <40 % of the molecular gas is confined to giant clumps (~1.5 kpc in size), and thus most of the gas could be distributed in small fainter clouds or in fairly diffuse extended regions of lower brightness temperatures than our sensitivity limit