128 research outputs found
Background Subtraction Uncertainty from Submillimetre to Millimetre Wavelengths
Photometric observations of galaxies at submillimetre to millimetre
wavelengths (50 - 1000 GHz) are susceptible to spatial variations in both the
background CMB temperature and CIB emission that can be comparable to the flux
from the target galaxy. We quantify the residual uncertainty when background
emission inside a circular aperture is estimated by the mean flux in a
surrounding annular region, assumed to have no contribution from the source of
interest. We present simple formulae to calculate this uncertainty as a
function of wavelength and aperture size. Drawing on examples from the
literature, we illustrate the use of our formalism in practice and highlight
cases in which uncertainty in the background subtraction needs to be considered
in the error analysis. We make the code used to calculate the uncertainties
publicly available on the web.Comment: 7 pages, 5 figures, comments welcom
Characterizing Extragalactic Anomalous Microwave Emission in NGC 6946 with CARMA
Using 1 cm and 3 mm CARMA and 2 mm GISMO observations, we follow up the first
extragalactic detection of anomalous microwave emission (AME) reported by
Murphy et al. 2010 in an extranuclear region (Enuc. 4) of the nearby face-on
spiral galaxy NGC 6946. We find the spectral shape and peak frequency of AME in
this region to be consistent with models of spinning dust emission. However,
the strength of the emission far exceeds the Galactic AME emissivity given the
abundance of polycyclic aromatic hydrocarbons (PAHs) in that region. Using our
galaxy-wide 1 cm map (21" resolution), we identify a total of eight 21"x21"
regions in NGC 6946 that harbour AME at >95% significance at levels comparable
to that observed in Enuc. 4. The remainder of the galaxy has 1 cm emission
consistent with or below the observed Galactic AME emissivity per PAH surface
density. We probe relationships between the detected AME and dust surface
density, PAH emission, and radiation field, though no environmental property
emerges to delineate regions with strong versus weak or non-existent AME. On
the basis of these data and other AME observations in the literature, we
determine that the AME emissivity per unit dust mass is highly variable. We
argue that the spinning dust hypothesis, which predicts the AME power to be
approximately proportional to the PAH mass, is therefore incomplete.Comment: 12 pages, submitted to MNRAS, comments welcom
New Age, Old Discourse: National Geographic, Orientialism, and Coverage of Afghanistan in the 21st Century
This paper explores National Geographic magazine\u27s coverage of Afghanistan in 2002. In total, 7 of the 12 issues from 2002 have articles about Afghanistan regarding the war, continuous hardship and unrest, and an Afghan woman refugee with green eyes who was on the cover in 1985 and disappeared until 2002. Through a critical examination of these articles as textual representations of the Orient, I intend to draw upon Said\u27s framework of Orientalism to explore how the discourse in National Geographic coverage of Afghanistan is embedded in a hegemonic reproduction of the indigenous other and the West\u27s benevolent role in stabilizing and assisting those in the region
A new, large-scale map of interstellar reddening derived from HI emission
We present a new map of interstellar reddening, covering the 39\% of the sky
with low {\rm HI} column densities (
or ) at resolution, based on
all-sky observations of Galactic HI emission by the HI4PI Survey. In this low
column density regime, we derive a characteristic value of for gas with and find no significant reddening associated with gas at
higher velocities. We compare our HI-based reddening map with the Schlegel,
Finkbeiner, and Davis (1998, SFD) reddening map and find them consistent to
within a scatter of . Further, the differences between our
map and the SFD map are in excellent agreement with the low resolution
() corrections to the SFD map derived by Peek and Graves
(2010) based on observed reddening toward passive galaxies. We therefore argue
that our HI-based map provides the most accurate interstellar reddening
estimates in the low column density regime to date. Our reddening map is made
publicly available (http://dx.doi.org/10.7910/DVN/AFJNWJ).Comment: Re-submitted to ApJ. The reddening map is available at
http://dx.doi.org/10.7910/DVN/AFJNW
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