Radio continuum observations of local star-forming galaxies using the Caltech Continuum Backend on the Green Bank Telescope

We observed radio continuum emission in 27 local (D < 70 Mpc) star-forming galaxies with the Robert C. Byrd Green Bank Telescope between 26 GHz and 40 GHz using the Caltech Continuum Backend. We obtained detections for 22 of these galaxies at all four sub-bands and four more marginal detections by taking the average flux across the entire bandwidth. This is the first detection (full or marginal) at these frequencies for 22 of these galaxies. We fit spectral energy distributions (SEDs) for all of the four-sub-band detections. For 14 of the galaxies, SEDs were best fit by a combination of thermal free-free and nonthermal synchrotron components. Eight galaxies with four-sub-band detections had steep spectra that were only fit by a single nonthermal component. Using these fits, we calculated supernova rates, total number of equivalent O stars, and star formation rates within each ~23 arcsecond beam. For unresolved galaxies, these physical properties characterize the galaxies' recent star formation on a global scale. We confirm that the radio-far-infrared correlation holds for the unresolved galaxies' total 33 GHz flux regardless of their thermal fractions, though the scatter on this correlation is larger than that at 1.4 GHz. In addition, we found that for the unresolved galaxies, there is an inverse relationship between the ratio of 33 GHz flux to total far-infrared flux and the steepness of the galaxy's spectral index between 1.4 GHz and 33 GHz. This relationship could be an indicator of the timescale of the observed episode of star formation.Comment: 36 pages, 9 figures; accepted for publication in ApJ. First and second author affiliation updated to reflect departmental name chang

Structure and Star Formation in NGC 925

We present the results from an optical study of the stellar & star formation properties of NGC 925 using the WIYN 3.5m telescope. Images in B,V,R, & H-alpha reveal a galaxy that is fraught with asymmetries. From isophote fits we discover that the bar center is not coincident with the center of the outer isophotes nor with the dynamical center (from Pisano et al. 1998). Cuts across the spiral arms reveal that the northern arms are distinctly different from the southern arm. The southern arm not only appears more coherent, but the peaks in stellar and H-alpha emission are found to be coincident with those of the HI distribution, while no such consistency is present in the northern disk. We also examine the gas surface density criterion for massive star formation in NGC 925, and find that its behavior is more consistent with that for irregular galaxies, than with late-type spirals. In particular, star formation persists beyond the radius at which the gas surface density falls below the predicted critical value for star formation for late-type spirals. Such properties are characteristic of Magellanic spirals, but are present at a less dramatic level in NGC 925, a late-type spiral.Comment: accepted for publication in the August 2000 Astronomical Journal 12 pages, 3 tables, 14 figure

Control and ultrasonic actuation of a gas-liquid interface in a microfluidic chip

This article describes the design and manufacturing of a microfluidic chip, allowing for the actuation of a gas-liquid interface and of the neighboring fluid. A first way to control the interface motion is to apply a pressure difference across it. In this case, the efficiency of three different micro-geometries at anchoring the interface is compared. Also, the critical pressures needed to move the interface are measured and compared to theoretical result. A second way to control the interface motion is by ultrasonic excitation. When the excitation is weak, the interface exhibits traveling waves, which follow a dispersion equation. At stronger ultrasonic levels, standing waves appear on the interface, with frequencies that are half integer multiple of the excitation frequency. An associated microstreaming flow field observed in the vicinity of the interface is characterized. The meniscus and associated streaming flow have the potential to transport particles and mix reagents

Quantization of eletric charge, the neutrino and generation nonuniversality

text of abstract It is showed that the eletric charge quantization is unconnected to Majorana neutrino in the non-universal generations leptoquark-bilepton flavordynamics which includes the right-handed neutrino and an explicit U(1) factor in the gauge semisimple group.Comment: 4 pages, latex ps, no figure

New Probable Dwarf Galaxies in Northern Groups of the Local Supercluster

We have searched for nearby dwarf galaxies in 27 northern groups with characteristic distances 8-15 Mpc based on the Second Palomar Sky Survey prints. In a total area of about 2000 square degrees, we have found 90 low-surface-brightness objects, more than 60% of which are absent from known catalogs and lists. We have classified most of these objects (~80%) as irregular dwarf systems. The first 21-cm line observations of the new objects with the 100-m Effelsberg radio telescope showed that the typical linear diameters (1-2 kpc), internal motions (30 km/s), and hydrogen masses (~2*10^7M_sun) galaxies correspond to those expected for the dwarf population of nearby groups.Comment: 8 pages, 1 fugur

3-3-1 exotic quark search at CERN LEPII-LHC

The 3-3-1 electroweak model is the simplest chiral extension of the standard model which predicts single and double charged bileptons and exotic quarks carrying -4/3 and 5/3 units of the positron charge. In this paper we study the possibilities of the production and decay of one of these exotic quarks at CERN LEPII-LHC collider. For typical vector bilepton, exotic quark masses and mixing angles we obtained between 20 and 750 events per year. Angular distributions are also presented.Comment: 5 pages, RevTex 3.1, 9 eps figures, to appear in Phys. Rev.

A GBT Survey of the HALOGAS Galaxies and Their Environments I: Revealing the full extent of HI around NGC891, NGC925, NGC4414 & NGC4565

We present initial results from a deep neutral hydrogen (HI) survey of the HALOGAS galaxy sample, which includes the spiral galaxies NGC891, NGC925, NGC4414, and NGC4565, performed with the Robert C. Byrd Green Bank Telescope (GBT). The resulting observations cover at least four deg$^2$ around these galaxies with an average 5$\sigma$ detection limit of 1.2$\times$10$^{18}$ cm$^{-2}$ over a velocity range of 20 km s$^{-1}$ and angular scale of 9.1$'$. In addition to detecting the same total flux as the GBT data, the spatial distribution of the GBT and original Westerbork Synthesis Radio Telescope (WSRT) data match well at equal spatial resolutions. The HI mass fraction below HI column densities of 10$^{19}$ cm$^{-2}$ is, on average, 2\%. We discuss the possible origins of low column density HI of nearby spiral galaxies. The absence of a considerable amount of newly detected HI by the GBT indicates these galaxies do not have significant extended diffuse HI structures, and suggests future surveys planned with the SKA and its precursors must go \textit{at least} as deep as 10$^{17}$ cm$^{-2}$ in column density to significantly increase the probability of detecting HI associated with the cosmic web and/or cold mode accretion.Comment: Accepted for publication in The Astrophysical Journal; 28 pages, 15 figure

Very Large Array And Atca Search For Natal Star Clusters In Nearby Star-Forming Galaxies

In order to investigate the relationship between the local environment and the properties of natal star clusters, we obtained radio observations of 25 star-forming galaxies within 20 Mpc using the Very Large Array and the Australia Telescope Compact Array. Natal star-forming regions can be identified by their characteristic thermal radio emission, which is manifest in their spectral index at centimeter wavelengths. The host galaxies in our sample were selected based upon their likelihood of harboring young star formation. In star-forming regions, the ionizing flux of massive embedded stars powers the dominant thermal free-free emission of those sources, resulting in a spectral index of {alpha} {approx}\u3e -0.2 (where S{sub {nu}} {proportional_to} {nu}{sup {alpha}}), which we compute. With the current sensitivity, we find that of the 25 galaxies in this sample only 5 have radio sources with spectral indices that are only consistent with a thermal origin, 4 have radio sources that are only consistent with a non-thermal origin, 6 have radio sources whose nature is ambiguous due to uncertainties in the spectral index, and 16 have no detected radio sources. For those sources that appear to be dominated by thermal emission, we infer the ionizing flux of the star clusters andmore » the number of equivalent O7.5 V stars that are required to produce the observed radio flux densities. The most radio-luminous clusters that we detect have an equivalent of {approx}7 x 10{sup 3} O7.5 V stars, and the smallest only have an equivalent of {approx}10{sup 2} O7.5 V stars; thus these star-forming regions span the range of large OB associations to moderate \u27super star clusters\u27. With the current detection limits, we also place upper limits on the masses of clusters that could have recently formed; for a number of galaxies we can conclusively rule out the presence of natal clusters significantly more massive than the Galactic star-forming region W49A ({approx}5 x 10{sup 4} M{sub sun}). The dearth of current massive cluster formation in these galaxies suggests that either their current star formation intensities have fallen to near or below that of the Milky Way and/or the evolutionary state that gives rise to thermal radio emission is short-lived.« les

The H I Environment Of The M101 Group

We present a wide (8. Degree-Sign 5 Multiplication-Sign 6. Degree-Sign 7, 1050 Multiplication-Sign 825 kpc), deep ({sigma}{sub N{sub H{sub {sub {sub i}}}}}10{sup 16.8}-10{sup 17.5} cm{sup -2}) neutral hydrogen (H I) map of the M101 galaxy group. We identify two new H I sources in the group environment, one an extremely low surface brightness (and hitherto unknown) dwarf galaxy, and the other a starless H I cloud, possibly primordial in origin. Our data show that M101\u27s extended H I envelope takes the form of a {approx}100 kpc long tidal loop or plume of H I extending to the southwest of the galaxy. The plume has an H I mass of {approx}10{sup 8} M{sub Sun} and a peak column density of N{sub H{sub i}}= 5 Multiplication-Sign 10{sup 17} cm{sup -2}, and while it rotates with the main body of M101, it shows kinematic peculiarities suggestive of a warp or flaring out of the rotation plane of the galaxy. We also find two new H I clouds near the plume with masses {approx}10{sup 7} M{sub Sun }, similar to H I clouds seen in the M81/M82 group, and likely also tidal in nature. Comparing to deep optical imaging of the M101 group, neithermore » the plume nor the clouds have any extended optical counterparts down to a limiting surface brightness of {mu}{sub B} = 29.5. We also trace H I at intermediate velocities between M101 and NGC 5474, strengthening the case for a recent interaction between the two galaxies. The kinematically complex H I structure in the M101 group, coupled with the optical morphology of M101 and its companions, suggests that the group is in a dynamically active state that is likely common for galaxies in group environments.« les