2,572 research outputs found
Sensitivity below the standard quantum limit in gravitational wave detectors with Michelson-Fabry-Perot readout
We calculate the quantum noise limited displacement sensitivity of a
Michelson-Fabry-Perot (MFP) with detuned cavities, followed by phase-sensitive
homodyne detection. We show that the standard quantum limit can be surpassed
even with resonant cavities and without any signal-recycling mirror nor
additional cavities. Indeed, thanks to the homodyne detection, the output field
quadrature can be chosen in such a way to cancel the effect of input amplitude
fluctuations, i.e., eliminating the force noise. With detuned cavities, the
modified opto-mechanical susceptivity allows to reach unlimited sensitivity for
large enough (yet finite) optical power. Our expressions include mirror losses
and cavity delay effect, for a realistic comparison with experiments. Our study
is particularly devoted to gravitational wave detectors and we consider both an
interferometer with free-falling mirrors, and a MFP as readout for a massive
detector. In the latter case, the sensitivity curve of the recently conceived
'DUAL' detector, based on two acoustic modes, is obtained
Radial distribution of gas and dust in spiral galaxies: The case of Mâ99 (NGCâ4254) and Mâ100 (NGCâ4321)
By combining Herschel-SPIRE data with archival Spitzer, Hâiâ, and CO maps, we investigate the spatial distribution of gas and dust in the two famous grand-design spirals Mâ99 and Mâ100 in the Virgo cluster. Thanks to the unique resolution and sensitivity of the Herschel-SPIRE photometer, we are for the first time able to measure the distribution and extent of cool, submillimetre (submm)-emitting dust inside and beyond the optical radius. We compare this with the radial variation in both the gas mass and the metallicity. Although we adopt a model-independent, phenomenological approach, our analysis provides important insights. We find the dust extending to at least the optical radius of the galaxy and showing breaks in its radial profiles at similar positions as the stellar distribution. The colour indices f350/f500 and f250/f350 decrease radially consistent with the temperature decreasing with radius. We also find evidence of an increasing gas to dust ratio with radius in the outer regions of both galaxies
Mapping the interstellar medium in galaxies with Herschel/SPIRE
The standard method of mapping the interstellar medium in a galaxy, by observing the molecular gas in the CO 1-0 line and the atomic gas in the 21-cm line, is largely limited with current telescopes to galaxies in the nearby universe. In this letter, we use SPIRE observations of the galaxies
M99 and M100 to explore the alternative approach of mapping the interstellar medium using the continuum emission from the dust. We have compared the methods by measuring the relationship between the star-formation rate and the surface density of gas in the galaxies using both
methods. We find the two methods give relationships with a similar dispersion, confirming that observing the continuum emission from the dust is a promising method of mapping the interstellar medium in galaxies
SPIRE imaging of Mâ82: Cool dust in the wind and tidal streams
Mâ82 is a unique representative of a whole class of galaxies, starbursts with superwinds, in the Very Nearby Galaxy Survey with Herschel. In addition, its interaction with the Mâ81 group has stripped a significant portion of its interstellar medium from its disk. SPIRE maps now afford better characterization of the far-infrared emission from cool dust outside the disk, and sketch a far more complete picture of its mass distribution and energetics than previously possible. They show emission coincident in projection with the starburst wind and in a large halo, much more extended than the PAH band emission seen with Spitzer. Some complex substructures coincide with the brightest PAH filaments, and others with tidal streams seen in atomic hydrogen. We subtract the far-infrared emission of the starburst and underlying disk from the maps, and derive spatially-resolved far-infrared colors for the wind and halo. We interpret the results in terms of dust mass, dust temperature, and global physical conditions. In particular, we examine variations in the dust physical properties as a function of distance from the center and the wind polar axis, and conclude that more than two thirds of the extraplanar dust has been removed by tidal interaction, and not entrained by the starburst wind
The Herschel Space Observatory view of dust in M81
We use Herschel Space Observatory data to place observational constraints on the peak and Rayleigh-Jeans slope of dust emission observed at 70â500 ÎŒm in the nearby spiral galaxy M81. We find that the ratios of wave bands between 160 and 500 ÎŒm are primarily dependent on radius but that the ratio of 70 to 160 ÎŒm emission shows no clear dependence on surface brightness or radius. These
results along with analyses of the spectral energy distributions imply that the 160â500 ÎŒm emission traces 15â30 K dust heated by evolved stars in the bulge and disc whereas the 70 ÎŒm emission includes dust heated by the active galactic nucleus and young stars in star forming regions
The dust morphology of the elliptical Galaxy M86 with SPIRE
We present Herschel-SPIRE observations at 250â500âÎŒm of the giant elliptical galaxy Mâ86 and examine the distribution of the resolved cold dust emission and its relation with other galactic tracers. The SPIRE images reveal three dust components: emission from the central region; a dust lane extending north-south; and a bright emission feature 10âkpc to the south-east. We estimate that ~10^6âM_â of dust is spatially coincident with atomic and ionized hydrogen, originating from stripped material from the nearby spiral NGC 4438 due to recent tidal interactions with Mâ86. The gas-to-dust ratio of the cold gas component ranges from ~20â80. We discuss the different heating mechanisms for the dust features
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