Bolocam: a millimeter-wave bolometric camera

We describe the design of Bolocam, a bolometric camera for millimeter-wave observations at the Caltech Submillimeter Observatory. Bolocam will have 144 diffraction-limited detectors operating at 300 mK, an 8 arcminute field of view, and a sky noise limited NEFD of approximately 35 mJy Hz^(-1/2) per pixel at λ = 1.4 mm. Observations will be possible at one of (lambda) equals 1.1., 1.4, or 2.1 mm per observing run. The detector array consists of sensitive NTD Ge thermistors bonded to silicon nitride micromesh absorbers patterned on a single wafer of silicon. This is a new technology in millimeter-wave detector array construction. To increase detector packing density, the feed horns will be spaced by 1.26 fλ (at λ = 1.4 mm), rather than the conventional 2fλ . DC stable read out electronics will enable on-the-fly mapping and drift scanning. We will use Bolocam to map Galactic dust emission, to search for protogalaxies, and to observe the Sunyaev- Zel'dovich effect toward galaxy clusters

Young Stellar Objects and Triggered Star Formation in the Vulpecula OB Association

The Vulpecula OB association, VulOB1, is a region of active star formation located in the Galactic plane at 2.3 kpc from the Sun. Previous studies suggest that sequential star formation is propagating along this 100 pc long molecular complex. In this paper, we use Spitzer MIPSGAL and GLIMPSE data to reconstruct the star formation history of VulOB1, and search for signatures of past triggering events. We make a census of Young Stellar Objects (YSO) in VulOB1 based on IR color and magnitude criteria, and we rely on the properties and nature of these YSOs to trace recent episodes of massive star formation. We find 856 YSO candidates, and show that the evolutionary stage of the YSO population in VulOB1 is rather homogeneous - ruling out the scenario of propagating star formation. We estimate the current star formation efficiency to be ~8 %. We also report the discovery of a dozen pillar-like structures, which are confirmed to be sites of small scale triggered star formation.Comment: 30 pages, 11 figures, accepted for publication in Ap

Molecular gas in NGC6946

We present imaging of molecular gas emission in the star-forming spiral galaxy NGC6946. Our CO(1-0) and CO(3-2) images, made at 22" resolution with the IRAM 30-m and the Heinrich Hertz 10-m radio telescopes, are the most extensive CO observations of this galaxy and are among the most extensive observations of molecular gas in any spiral galaxy. The molecular component in NGC6946 is unusually massive, with a ratio of molecular to atomic Hydrogen of 0.57. A star formation efficiency image for NGC6946 ranges by over two orders of magnitude with highest values found in the northeastern spiral arm, and anticorrelates with the 6cm polarized emission image, which traces the regular part of the magnetic field. We analyse the ISM in NGC6946's disk by making 1-D and 2-D comparisons of images made in several wavebands. A point-by-point correlation technique finds that the molecular gas is closely associated with the 7micron-emitting dust. The high correlation found between the MIR emission and the radio continuum at 6cm cannot be due to dust heating and gas ionization in star-forming regions because the thermal radio emission is less correlated with the MIR than the nonthermal emission. A coupling of magnetic fields to gas clouds is proposed as a possible scenario.Comment: A&A accepted, 23 pages, 11 figures. Version with high resolution figures available at: http://cfa-www.harvard.edu/~wwalsh/sp.htm

Correlation of the radio continuum, infrared, and CO molecular emissions in NGC 3627

We present new radio continuum observations, taken at 1.4 GHz with the Very Large Array, and new observations in the CO line, taken with the Plateau de Bure interferometer, of two regions of the spiral galaxy NGC 3627. Comparing these observations with archival Spitzer and H_{alpha} data we study the correlation of the radio continuum (RC), infrared-8 um and CO emissions at a spatial resolution of 100 pc. We compare the point-by-point variations of the RC, CO, and 8um brightnesses in two distinct regions of 2 kpc \times 2 kpc in size of NGC 3627. We examined scale much lower than the electron diffusion scale, where a break down of the correlations would be expected. However no evidence for such correlation break down has been found. The RC emission follows well the distribution of CO and the widths of several structures, measured along slices across them, are comparable. Furthermore, we found that down to a spatial scale of 100 pc the radio continuum emission is correlated with dust emissions at 4.5, 5.8, and 8 um, that traces different dust temperatures. We present a new perspective with which visualizing and studying the RC-CO-24 um and RC-CO-8 um correlations, by using a three-dimensional representation. We fit the observed data with a three dimensional line, obtaining a rms of 0.25 dex. The observed correlation enhances the complexity of the electrons diffusion, losses and injection mechanisms, and of their connection to star formation processes, described by molecular and dust emissions. We plan to further investigate this connection using spatially resolved spectral index studies at low radio frequencies where the thermal emission component is seemingly negligible.Comment: 17 pages, 17 figures (low resolution). Accepted for publication in A&A. Some language and reference changes done. High resolution version of the paper is available at: http://erg.ca.astro.it/~rpaladin/PAPER/NGC3627/AA9135.p

Thermal and non-thermal components of the interstellar medium at sub-kiloparsec scales in galaxies

Aims: We present new radio continuum observations of ten BIMA SONG galaxies, taken at 1.4 GHz with the Very Large Array. These observations allow us to extend the study of the relationships between the radio continuum (RC) and CO emission to 22 CO luminous galaxies for which single dish CO images have been added to interferometric data. New Spitzer infrared (IR) images of six of these galaxies have been released. The analysis of these high resolution images allowed us to probe the RC-IR-CO correlations down to linear scales of a few hundred pc. Results: for the 22 galaxies analysed, the RC-CO correlation on scales from $\sim10$ kpc down to $\sim100$ pc is nearly linear and has a scatter of a factor of two, i.e. comparable to that of the global correlations. There is no evidence for any severe degradation of the scatter below the kpc scale. This also applies to the six galaxies for which high-resolution mid-IR data are available. In the case of NGC 5194, we find that the non-thermal radio spectral index is correlated with the RC/FIR ratio. Conclusions: The scatter of the point-by-point correlations does not increase significantly with spatial resolution. We thus conclude that we have not yet probed the physical scales at which the correlations break down. However, we observe local deviations from the correlations in regions with a high star formation rate, such as the spiral arms, where we observe a flat radio spectrum and a low RC/FIR ratio. In the intra-arm regions and in the peripheral regions of the disk, the RC/FIR is generally higher and it is characterized by a steepening of the radio spectrum.Comment: 27 pages, 9 figures (low resolution), accepted for publication in A&A. High resolution version of the paper is available at: http://lucipher.ca.astro.it/~rpaladin/PAPER/RC-C

The Balloon-borne Large Aperture Submillimeter Telescope: BLAST

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) is a sub-orbital surveying experiment designed to study the evolutionary history and processes of star formation in local galaxies (including the Milky Way) and galaxies at cosmological distances. The BLAST continuum camera, which consists of 270 detectors distributed between 3 arrays, observes simultaneously in broad-band (30%) spectral-windows at 250, 350, and 500 microns. The optical design is based on a 2m diameter telescope, providing a diffraction-limited resolution of 30" at 250 microns. The gondola pointing system enables raster mapping of arbitrary geometry, with a repeatable positional accuracy of ~30"; post-flight pointing reconstruction to ~5" rms is achieved. The on-board telescope control software permits autonomous execution of a pre-selected set of maps, with the option of manual override. In this paper we describe the primary characteristics and measured in-flight performance of BLAST. BLAST performed a test-flight in 2003 and has since made two scientifically productive long-duration balloon flights: a 100-hour flight from ESRANGE (Kiruna), Sweden to Victoria Island, northern Canada in June 2005; and a 250-hour, circumpolar-flight from McMurdo Station, Antarctica, in December 2006.Comment: 38 Pages, 11 figures; Replaced with version accepted for publication in the Astrophysical Journal; related results available at http://blastexperiment.info

Movable genetic elements and antibiotic resistance in enterococci

The enterococci possess genetic elements able to move from one strain to another via conjugation. Certain enterococcal plasmids exhibit a broad host range among gram-positive bacteria, but only when matings are performed on solid surfaces. Other plasmids are more specific to enterococci, transfer efficiently in broth, and encode a response to recipient-produced sex phermones. Transmissible non-plasmid elements, the conjugative transposons, are widespread among the enterococci and determine their own fertility properties. Drug resistance, hemolysin, and bacteriocin determinants are commonly found on the various transmissible enterococcal elements. Examples of the different systems are discussed in this review.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47900/1/10096_2005_Article_BF01963632.pd