755 research outputs found
The Spitzer discovery of a galaxy with infrared emission solely due to AGN activity
We present a galaxy (SAGE1CJ053634.78-722658.5) at a redshift of 0.14 of
which the IR is entirely dominated by emission associated with the AGN. We
present the 5-37 um Spitzer/IRS spectrum and broad wavelength SED of
SAGE1CJ053634, an IR point-source detected by Spitzer/SAGE (Meixner et al
2006). The source was observed in the SAGE-Spec program (Kemper et al., 2010)
and was included to determine the nature of sources with deviant IR colours.
The spectrum shows a redshifted (z=0.14+-0.005) silicate emission feature with
an exceptionally high feature-to-continuum ratio and weak polycyclic aromatic
hydrocarbon (PAH) bands. We compare the source with models of emission from
dusty tori around AGNs from Nenkova et al. (2008). We present a diagnostic
diagram that will help to identify similar sources based on Spitzer/MIPS and
Herschel/PACS photometry. The SED of SAGE1CJ053634 is peculiar because it lacks
far-IR emission and a clear stellar counterpart. We find that the SED and the
IR spectrum can be understood as emission originating from the inner ~10 pc
around an accreting black hole. There is no need to invoke emission from the
host galaxy, either from the stars or from the interstellar medium, although a
possible early-type host galaxy cannot be excluded based on the SED analysis.
The hot dust around the accretion disk gives rise to a continuum, which peaks
at 4 um, whereas the strong silicate features may arise from optically thin
emission of dusty clouds within ~10 pc around the black hole. The weak PAH
emission does not appear to be linked to star formation, as star formation
templates strongly over-predict the measured far-IR flux levels. The SED of
SAGE1CJ053634 is rare in the local universe but may be more common in the more
distant universe. The conspicuous absence of host-galaxy IR emission places
limits on the far-IR emission arising from the dusty torus alone.Comment: Accepted for publication in A&A, 7 pages, 6 figure
The Dust-to-Gas Ratio in the Small Magellanic Cloud Tail
The Tail region of the Small Magellanic Cloud (SMC) was imaged using the MIPS
instrument on the Spitzer Space Telescope as part of the SAGE-SMC Spitzer
Legacy. Diffuse infrared emission from dust was detected in all the MIPS bands.
The Tail gas-to-dust ratio was measured to be 1200 +/- 350 using the MIPS
observations combined with existing IRAS and HI observations. This gas-to-dust
ratio is higher than the expected 500-800 from the known Tail metallicity
indicating possible destruction of dust grains. Two cluster regions in the Tail
were resolved into multiple sources in the MIPS observations and local
gas-to-dust ratios were measured to be ~440 and ~250 suggests dust formation
and/or significant amounts of ionized gas in these regions. These results
support the interpretation that the SMC Tail is a tidal tail recently stripped
from the SMC that includes gas, dust, and young stars.Comment: 6 pages, 3 figures, ApJ Letters, in press, (version with full
resolution figures at
http://www.stsci.edu/~kgordon/papers/PS_files/sage-smc_taildust_v1.62.pdf
Modification of human placental alkaline phosphatase by periodate-oxidized 1,N6-ethenoadenosine monophosphate
Performance of two Askaryan Radio Array stations and first results in the search for ultra-high energy neutrinos
Ultra-high energy neutrinos are interesting messenger particles since, if
detected, they can transmit exclusive information about ultra-high energy
processes in the Universe. These particles, with energies above
, interact very rarely. Therefore, detectors that
instrument several gigatons of matter are needed to discover them. The ARA
detector is currently being constructed at South Pole. It is designed to use
the Askaryan effect, the emission of radio waves from neutrino-induced cascades
in the South Pole ice, to detect neutrino interactions at very high energies.
With antennas distributed among 37 widely-separated stations in the ice, such
interactions can be observed in a volume of several hundred cubic kilometers.
Currently 3 deep ARA stations are deployed in the ice of which two have been
taking data since the beginning of the year 2013. In this publication, the ARA
detector "as-built" and calibrations are described. Furthermore, the data
reduction methods used to distinguish the rare radio signals from overwhelming
backgrounds of thermal and anthropogenic origin are presented. Using data from
only two stations over a short exposure time of 10 months, a neutrino flux
limit of is
calculated for a particle energy of 10^{18}eV, which offers promise for the
full ARA detector.Comment: 21 pages, 34 figures, 1 table, includes supplementary materia
Fundamental parameters, integrated RGB mass loss and dust production in the Galactic globular cluster 47 Tucanae
Fundamental parameters and time-evolution of mass loss are investigated for
post-main-sequence stars in the Galactic globular cluster 47 Tucanae (NGC 104).
This is accomplished by fitting spectral energy distributions (SEDs) to
existing optical and infrared photometry and spectroscopy, to produce a true
Hertzsprung--Russell diagram. We confirm the cluster's distance as 4611 (+213,
-200) pc and age as 12 +/- 1 Gyr. Horizontal branch models appear to confirm
that no more RGB mass loss occurs in 47 Tuc than in the more-metal-poor omega
Centauri, though difficulties arise due to inconsistencies between the models.
Using our SEDs, we identify those stars which exhibit infrared excess, finding
excess only among the brightest giants: dusty mass loss begins at a luminosity
of ~ 1000 Lsun, becoming ubiquitous above 2000 Lsun. Recent claims of dust
production around lower-luminosity giants cannot be reproduced, despite using
the same archival Spitzer imagery.Comment: 22 pages, 17 figures, accepted ApJ
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