The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Scott Schnee - One of the best experts on this subject based on the ideXlab platform.
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the dust emissivity Spectral Index in the starless core tmc 1c
The Astrophysical Journal, 2010Co-Authors: Scott Schnee, A Noriegacrespo, Melissa L Enoch, Jack Sayers, Susan Terebey, P Caselli, Jonathan B Foster, Alyssa A Goodman, Jens Kauffmann, Deborah L PadgettAbstract:In this paper, we present a dust emission map of the starless core TMC-1C taken at 2100 μm. Along with maps at 160, 450, 850, and 1200 μm, we study the dust emissivity Spectral Index from the (sub)millimeter Spectral energy distribution, and find that it is close to the typically assumed value of β = 2. We also map the dust temperature and column density in TMC-1C, and find that at the position of the dust peak (A_V ~ 50) the line-of-sight-averaged temperature is ~7 K. Employing simple Monte Carlo modeling, we show that the data are consistent with a constant value for the emissivity Spectral Index over the whole map of TMC-1C.
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the dust emissivity Spectral Index in the starless core tmc 1c
arXiv: Astrophysics of Galaxies, 2009Co-Authors: Scott Schnee, A Noriegacrespo, Melissa L Enoch, Jack Sayers, Susan Terebey, P Caselli, Jonathan B Foster, Alyssa A Goodman, Jens Kauffmann, Deborah L PadgettAbstract:In this paper we present a dust emission map of the starless core TMC-1C taken at 2100 microns. Along with maps at 160, 450, 850 and 1200 microns, we study the dust emissivity Spectral Index from the (sub)millimeter Spectral energy distribution, and find that it is close to the typically assumed value of beta = 2. We also map the dust temperature and column density in TMC-1C, and find that at the position of the dust peak (A_V ~ 50), the line-of-sight-averaged temperature is ~7 K. Employing simple Monte Carlo modeling, we show that the data are consistent with a constant value for the emissivity Spectral Index over the whole map of TMC-1C.
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the effect of line of sight temperature variation and noise on dust continuum observations
The Astrophysical Journal, 2009Co-Authors: Rahul Shetty, Scott Schnee, Alyssa A Goodman, Jens Kauffmann, Barbara ErcolanoAbstract:We investigate the effect of line-of-sight temperature variations and noise on two commonly used methods to determine dust properties from dust-continuum observations of dense cores. One method employs a direct fit to a modified blackbody Spectral energy distribution (SED); the other involves a comparison of flux ratios to an analytical prediction. Fitting fluxes near the SED peak produces inaccurate temperature and dust Spectral Index estimates due to the line-of-sight temperature (and density) variations. Longer wavelength fluxes in the Rayleigh-Jeans part of the spectrum (≳ 600 μm for typical cores) may more accurately recover the Spectral Index, but both methods are very sensitive to noise. The temperature estimate approaches the density-weighted temperature, or "column temperature," of the source as short wavelength fluxes are excluded. An inverse temperature-Spectral Index correlation naturally results from SED fitting, due to the inaccurate isothermal assumption, as well as noise uncertainties. We show that above some "threshold" temperature, the temperatures estimated through the flux ratio method can be highly inaccurate. In general, observations with widely separated wavelengths, and including shorter wavelengths, result in higher threshold temperatures; such observations thus allow for more accurate temperature estimates of sources with temperatures less than the threshold temperature. When only three fluxes are available, a constrained fit, where the Spectral Index is fixed, produces less scatter in the temperature estimate when compared to the estimate from the flux ratio method.
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the effect of noise on the dust temperature Spectral Index correlation
The Astrophysical Journal, 2009Co-Authors: Rahul Shetty, Scott Schnee, Jens Kauffmann, Alyssa A GoodmanAbstract:We investigate how uncertainties in flux measurements affect the results from modified blackbody Spectral energy distribution (SED) fits. We show that an inverse correlation between the dust temperature T and Spectral Index β naturally arises from least-squares fits due to the uncertainties, even for sources with a single T and β. Fitting SEDs to noisy fluxes solely in the Rayleigh-Jeans regime produces unreliable T and β estimates. Thus, for long wavelength observations (λ 200 μm), or for warm sources (T 60 K), it becomes difficult to distinguish sources with different temperatures. We assess the role of noise in recent observational results that indicate an inverse and continuously varying T-β relation. Though an inverse and continuous T-β correlation may be a physical property of dust in the interstellar medium, we find that the observed inverse correlation may be primarily due to noise.
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the effect of noise on the dust temperature Spectral Index correlation
arXiv: Astrophysics of Galaxies, 2009Co-Authors: Rahul Shetty, Scott Schnee, Jens Kauffmann, Alyssa A GoodmanAbstract:We investigate how uncertainties in flux measurements affect the results from modified blackbody SED fits. We show that an inverse correlation between the dust temperature T and Spectral Index (beta) naturally arises from least squares fits due to the uncertainties, even for sources with a single T and beta. Fitting SEDs to noisy fluxes solely in the Rayleigh-Jeans regime produces unreliable T and beta estimates. Thus, for long wavelength observations (lambda >~ 200 micron), or for warm sources (T >~ 60 K), it becomes difficult to distinguish sources with different temperatures. We assess the role of noise in recent observational results that indicate an inverse and continuously varying T - beta relation. Though an inverse and continuous T - beta correlation may be a physical property of dust in the ISM, we find that the observed inverse correlation may be primarily due to noise.
Jens Kauffmann - One of the best experts on this subject based on the ideXlab platform.
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the dust emissivity Spectral Index in the starless core tmc 1c
The Astrophysical Journal, 2010Co-Authors: Scott Schnee, A Noriegacrespo, Melissa L Enoch, Jack Sayers, Susan Terebey, P Caselli, Jonathan B Foster, Alyssa A Goodman, Jens Kauffmann, Deborah L PadgettAbstract:In this paper, we present a dust emission map of the starless core TMC-1C taken at 2100 μm. Along with maps at 160, 450, 850, and 1200 μm, we study the dust emissivity Spectral Index from the (sub)millimeter Spectral energy distribution, and find that it is close to the typically assumed value of β = 2. We also map the dust temperature and column density in TMC-1C, and find that at the position of the dust peak (A_V ~ 50) the line-of-sight-averaged temperature is ~7 K. Employing simple Monte Carlo modeling, we show that the data are consistent with a constant value for the emissivity Spectral Index over the whole map of TMC-1C.
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the dust emissivity Spectral Index in the starless core tmc 1c
arXiv: Astrophysics of Galaxies, 2009Co-Authors: Scott Schnee, A Noriegacrespo, Melissa L Enoch, Jack Sayers, Susan Terebey, P Caselli, Jonathan B Foster, Alyssa A Goodman, Jens Kauffmann, Deborah L PadgettAbstract:In this paper we present a dust emission map of the starless core TMC-1C taken at 2100 microns. Along with maps at 160, 450, 850 and 1200 microns, we study the dust emissivity Spectral Index from the (sub)millimeter Spectral energy distribution, and find that it is close to the typically assumed value of beta = 2. We also map the dust temperature and column density in TMC-1C, and find that at the position of the dust peak (A_V ~ 50), the line-of-sight-averaged temperature is ~7 K. Employing simple Monte Carlo modeling, we show that the data are consistent with a constant value for the emissivity Spectral Index over the whole map of TMC-1C.
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the effect of line of sight temperature variation and noise on dust continuum observations
The Astrophysical Journal, 2009Co-Authors: Rahul Shetty, Scott Schnee, Alyssa A Goodman, Jens Kauffmann, Barbara ErcolanoAbstract:We investigate the effect of line-of-sight temperature variations and noise on two commonly used methods to determine dust properties from dust-continuum observations of dense cores. One method employs a direct fit to a modified blackbody Spectral energy distribution (SED); the other involves a comparison of flux ratios to an analytical prediction. Fitting fluxes near the SED peak produces inaccurate temperature and dust Spectral Index estimates due to the line-of-sight temperature (and density) variations. Longer wavelength fluxes in the Rayleigh-Jeans part of the spectrum (≳ 600 μm for typical cores) may more accurately recover the Spectral Index, but both methods are very sensitive to noise. The temperature estimate approaches the density-weighted temperature, or "column temperature," of the source as short wavelength fluxes are excluded. An inverse temperature-Spectral Index correlation naturally results from SED fitting, due to the inaccurate isothermal assumption, as well as noise uncertainties. We show that above some "threshold" temperature, the temperatures estimated through the flux ratio method can be highly inaccurate. In general, observations with widely separated wavelengths, and including shorter wavelengths, result in higher threshold temperatures; such observations thus allow for more accurate temperature estimates of sources with temperatures less than the threshold temperature. When only three fluxes are available, a constrained fit, where the Spectral Index is fixed, produces less scatter in the temperature estimate when compared to the estimate from the flux ratio method.
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the effect of noise on the dust temperature Spectral Index correlation
The Astrophysical Journal, 2009Co-Authors: Rahul Shetty, Scott Schnee, Jens Kauffmann, Alyssa A GoodmanAbstract:We investigate how uncertainties in flux measurements affect the results from modified blackbody Spectral energy distribution (SED) fits. We show that an inverse correlation between the dust temperature T and Spectral Index β naturally arises from least-squares fits due to the uncertainties, even for sources with a single T and β. Fitting SEDs to noisy fluxes solely in the Rayleigh-Jeans regime produces unreliable T and β estimates. Thus, for long wavelength observations (λ 200 μm), or for warm sources (T 60 K), it becomes difficult to distinguish sources with different temperatures. We assess the role of noise in recent observational results that indicate an inverse and continuously varying T-β relation. Though an inverse and continuous T-β correlation may be a physical property of dust in the interstellar medium, we find that the observed inverse correlation may be primarily due to noise.
-
the effect of noise on the dust temperature Spectral Index correlation
arXiv: Astrophysics of Galaxies, 2009Co-Authors: Rahul Shetty, Scott Schnee, Jens Kauffmann, Alyssa A GoodmanAbstract:We investigate how uncertainties in flux measurements affect the results from modified blackbody SED fits. We show that an inverse correlation between the dust temperature T and Spectral Index (beta) naturally arises from least squares fits due to the uncertainties, even for sources with a single T and beta. Fitting SEDs to noisy fluxes solely in the Rayleigh-Jeans regime produces unreliable T and beta estimates. Thus, for long wavelength observations (lambda >~ 200 micron), or for warm sources (T >~ 60 K), it becomes difficult to distinguish sources with different temperatures. We assess the role of noise in recent observational results that indicate an inverse and continuously varying T - beta relation. Though an inverse and continuous T - beta correlation may be a physical property of dust in the ISM, we find that the observed inverse correlation may be primarily due to noise.
Alyssa A Goodman - One of the best experts on this subject based on the ideXlab platform.
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the dust emissivity Spectral Index in the starless core tmc 1c
The Astrophysical Journal, 2010Co-Authors: Scott Schnee, A Noriegacrespo, Melissa L Enoch, Jack Sayers, Susan Terebey, P Caselli, Jonathan B Foster, Alyssa A Goodman, Jens Kauffmann, Deborah L PadgettAbstract:In this paper, we present a dust emission map of the starless core TMC-1C taken at 2100 μm. Along with maps at 160, 450, 850, and 1200 μm, we study the dust emissivity Spectral Index from the (sub)millimeter Spectral energy distribution, and find that it is close to the typically assumed value of β = 2. We also map the dust temperature and column density in TMC-1C, and find that at the position of the dust peak (A_V ~ 50) the line-of-sight-averaged temperature is ~7 K. Employing simple Monte Carlo modeling, we show that the data are consistent with a constant value for the emissivity Spectral Index over the whole map of TMC-1C.
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the dust emissivity Spectral Index in the starless core tmc 1c
arXiv: Astrophysics of Galaxies, 2009Co-Authors: Scott Schnee, A Noriegacrespo, Melissa L Enoch, Jack Sayers, Susan Terebey, P Caselli, Jonathan B Foster, Alyssa A Goodman, Jens Kauffmann, Deborah L PadgettAbstract:In this paper we present a dust emission map of the starless core TMC-1C taken at 2100 microns. Along with maps at 160, 450, 850 and 1200 microns, we study the dust emissivity Spectral Index from the (sub)millimeter Spectral energy distribution, and find that it is close to the typically assumed value of beta = 2. We also map the dust temperature and column density in TMC-1C, and find that at the position of the dust peak (A_V ~ 50), the line-of-sight-averaged temperature is ~7 K. Employing simple Monte Carlo modeling, we show that the data are consistent with a constant value for the emissivity Spectral Index over the whole map of TMC-1C.
-
the effect of line of sight temperature variation and noise on dust continuum observations
The Astrophysical Journal, 2009Co-Authors: Rahul Shetty, Scott Schnee, Alyssa A Goodman, Jens Kauffmann, Barbara ErcolanoAbstract:We investigate the effect of line-of-sight temperature variations and noise on two commonly used methods to determine dust properties from dust-continuum observations of dense cores. One method employs a direct fit to a modified blackbody Spectral energy distribution (SED); the other involves a comparison of flux ratios to an analytical prediction. Fitting fluxes near the SED peak produces inaccurate temperature and dust Spectral Index estimates due to the line-of-sight temperature (and density) variations. Longer wavelength fluxes in the Rayleigh-Jeans part of the spectrum (≳ 600 μm for typical cores) may more accurately recover the Spectral Index, but both methods are very sensitive to noise. The temperature estimate approaches the density-weighted temperature, or "column temperature," of the source as short wavelength fluxes are excluded. An inverse temperature-Spectral Index correlation naturally results from SED fitting, due to the inaccurate isothermal assumption, as well as noise uncertainties. We show that above some "threshold" temperature, the temperatures estimated through the flux ratio method can be highly inaccurate. In general, observations with widely separated wavelengths, and including shorter wavelengths, result in higher threshold temperatures; such observations thus allow for more accurate temperature estimates of sources with temperatures less than the threshold temperature. When only three fluxes are available, a constrained fit, where the Spectral Index is fixed, produces less scatter in the temperature estimate when compared to the estimate from the flux ratio method.
-
the effect of noise on the dust temperature Spectral Index correlation
The Astrophysical Journal, 2009Co-Authors: Rahul Shetty, Scott Schnee, Jens Kauffmann, Alyssa A GoodmanAbstract:We investigate how uncertainties in flux measurements affect the results from modified blackbody Spectral energy distribution (SED) fits. We show that an inverse correlation between the dust temperature T and Spectral Index β naturally arises from least-squares fits due to the uncertainties, even for sources with a single T and β. Fitting SEDs to noisy fluxes solely in the Rayleigh-Jeans regime produces unreliable T and β estimates. Thus, for long wavelength observations (λ 200 μm), or for warm sources (T 60 K), it becomes difficult to distinguish sources with different temperatures. We assess the role of noise in recent observational results that indicate an inverse and continuously varying T-β relation. Though an inverse and continuous T-β correlation may be a physical property of dust in the interstellar medium, we find that the observed inverse correlation may be primarily due to noise.
-
the effect of noise on the dust temperature Spectral Index correlation
arXiv: Astrophysics of Galaxies, 2009Co-Authors: Rahul Shetty, Scott Schnee, Jens Kauffmann, Alyssa A GoodmanAbstract:We investigate how uncertainties in flux measurements affect the results from modified blackbody SED fits. We show that an inverse correlation between the dust temperature T and Spectral Index (beta) naturally arises from least squares fits due to the uncertainties, even for sources with a single T and beta. Fitting SEDs to noisy fluxes solely in the Rayleigh-Jeans regime produces unreliable T and beta estimates. Thus, for long wavelength observations (lambda >~ 200 micron), or for warm sources (T >~ 60 K), it becomes difficult to distinguish sources with different temperatures. We assess the role of noise in recent observational results that indicate an inverse and continuously varying T - beta relation. Though an inverse and continuous T - beta correlation may be a physical property of dust in the ISM, we find that the observed inverse correlation may be primarily due to noise.
Deborah L Padgett - One of the best experts on this subject based on the ideXlab platform.
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the dust emissivity Spectral Index in the starless core tmc 1c
The Astrophysical Journal, 2010Co-Authors: Scott Schnee, A Noriegacrespo, Melissa L Enoch, Jack Sayers, Susan Terebey, P Caselli, Jonathan B Foster, Alyssa A Goodman, Jens Kauffmann, Deborah L PadgettAbstract:In this paper, we present a dust emission map of the starless core TMC-1C taken at 2100 μm. Along with maps at 160, 450, 850, and 1200 μm, we study the dust emissivity Spectral Index from the (sub)millimeter Spectral energy distribution, and find that it is close to the typically assumed value of β = 2. We also map the dust temperature and column density in TMC-1C, and find that at the position of the dust peak (A_V ~ 50) the line-of-sight-averaged temperature is ~7 K. Employing simple Monte Carlo modeling, we show that the data are consistent with a constant value for the emissivity Spectral Index over the whole map of TMC-1C.
-
the dust emissivity Spectral Index in the starless core tmc 1c
arXiv: Astrophysics of Galaxies, 2009Co-Authors: Scott Schnee, A Noriegacrespo, Melissa L Enoch, Jack Sayers, Susan Terebey, P Caselli, Jonathan B Foster, Alyssa A Goodman, Jens Kauffmann, Deborah L PadgettAbstract:In this paper we present a dust emission map of the starless core TMC-1C taken at 2100 microns. Along with maps at 160, 450, 850 and 1200 microns, we study the dust emissivity Spectral Index from the (sub)millimeter Spectral energy distribution, and find that it is close to the typically assumed value of beta = 2. We also map the dust temperature and column density in TMC-1C, and find that at the position of the dust peak (A_V ~ 50), the line-of-sight-averaged temperature is ~7 K. Employing simple Monte Carlo modeling, we show that the data are consistent with a constant value for the emissivity Spectral Index over the whole map of TMC-1C.
Sigurd Naess - One of the best experts on this subject based on the ideXlab platform.
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spatial variations in the Spectral Index of polarized synchrotron emission in the 9 yr wmap sky maps
The Astrophysical Journal, 2014Co-Authors: U Fuskeland, I K Wehus, H K Eriksen, Sigurd NaessAbstract:We estimate the Spectral Index, β, of polarized synchrotron emission as observed in the 9 yr Wilkinson Microwave Anisotropy Probe sky maps using two methods, linear regression ("T-T plot") and maximum likelihood. We partition the sky into 24 disjoint sky regions and evaluate the Spectral Index for all polarization angles between 0° and 85° in steps of 5°. Averaging over polarization angles, we derive a mean Spectral Index of βall-sky = –2.99 ± 0.01 in the frequency range of 23-33 GHz. We find that the synchrotron Spectral Index steepens by 0.14 from low to high Galactic latitudes, in agreement with previous studies, with mean Spectral indices of βplane = –2.98 ± 0.01 and βhigh-lat = –3.12 ± 0.04. In addition, we find a significant longitudinal variation along the Galactic plane with a steeper Spectral Index toward the Galactic center and anticenter than toward the Galactic spiral arms. This can be well modeled by an offset sinusoidal, β(l) = –2.85 + 0.17sin (2l – 90°). Finally, we study synchrotron emission in the BICEP2 field, in an attempt to understand whether the claimed detection of large-scale B-mode polarization could be explained in terms of synchrotron contamination. Adopting a Spectral Index of β = –3.12, typical for high Galactic latitudes, we find that the most likely bias corresponds to about 2% of the reported signal (r = 0.003). The flattest Index allowed by the data in this region is β = –2.5, and under the assumption of a straight power-law frequency spectrum, we find that synchrotron emission can account for at most 20% of the reported BICEP2 signal.
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spatial variations in the Spectral Index of polarized synchrotron emission in the 9 yr wmap sky maps
arXiv: Cosmology and Nongalactic Astrophysics, 2014Co-Authors: U Fuskeland, I K Wehus, H K Eriksen, Sigurd NaessAbstract:We estimate the Spectral Index, beta, of polarized synchrotron emission as observed in the 9 yr WMAP sky maps using two methods, linear regression ("T-T plot") and maximum likelihood. We partition the sky into 24 disjoint sky regions, and evaluate the Spectral Index for all polarization angles between 0 deg and 85 deg in steps of 5. Averaging over polarization angles, we derive a mean Spectral Index of beta_all-sky=-2.99+-0.01 in the frequency range of 23-33 GHz. We find that the synchrotron Spectral Index steepens by 0.14 from low to high Galactic latitudes, in agreement with previous studies, with mean Spectral indices of beta_plane=-2.98+-0.01 and beta_high-lat=-3.12+-0.04. In addition, we find a significant longitudinal variation along the Galactic plane with a steeper Spectral Index toward the Galactic center and anticenter than toward the Galactic spiral arms. This can be well modeled by an offset sinusoidal, beta(l)=-2.85+0.17sin(2l-90). Finally, we study synchrotron emission in the BICEP2 field, in an attempt to understand whether the claimed detection of large-scale B-mode polarization could be explained in terms of synchrotron contamination. Adopting a Spectral Index of beta=-3.12, typical for high Galactic latitudes, we find that the most likely bias corresponds to about 2% of the reported signal (r=0.003). The flattest Index allowed by the data in this region is beta=-2.5, and under the assumption of a straight power-law frequency spectrum, we find that synchrotron emission can account for at most 20% of the reported BICEP2 signal.
