173 research outputs found
An optimised energy saving model for pump scheduling in wastewater networks
The cost of electricity used for pumping in water and wastewater networks typically represents the largest part of the total operational costs. These days, South Australia has the highest electricity rate in Australia. Hence, energy management is becoming increasingly more critical in water and wastewater sectors in this state. Most sewer networks and pump stations operate based on the common high/low sewage levels and not taking into account energy costs associated with pumping. Scheduling the pumps in these systems is a smart choice for saving more electricity cost. The intelligent and smart control of the utility’s assets could present operational cost saving opportunities by considering the price of purchased electricity from the spot market; however, this must be balanced with the environmental constraints to manage system odours, spills and overflow. The purpose of this study is to improve and optimise the pump control switching with the aim of reducing electricity consumption costs. To this end, the hydraulic modelling approach using Infoworks ICM has been used to simulate the performance of the pump controller. This model considers both the electricity spot price and sump elevation as inputs into smart control logic programming to operate pumps more efficiently. Results show this smart controller improves conventional pump switching models in terms of energy optimising and cost savings.Neda Gorjian Jolfaei, Bo Jin, Christopher Chow, Flavio Bressan and Nima Gorjia
The Origin of the Silicate Emission Features in the Seyfert 2 Galaxy, NGC 2110
The unified model of active galactic nuclei (AGN) predicts silicate emission
features at 10 and 18 microns in type 1 AGN, and such features have now been
observed in objects ranging from distant QSOs to nearby LINERs. More
surprising, however, is the detection of silicate emission in a few type 2 AGN.
By combining Gemini and Spitzer mid-infrared imaging and spectroscopy of NGC
2110, the closest known Seyfert 2 galaxy with silicate emission features, we
can constrain the location of the silicate emitting region to within 32 pc of
the nucleus. This is the strongest constraint yet on the size of the silicate
emitting region in a Seyfert galaxy of any type. While this result is
consistent with a narrow line region origin for the emission, comparison with
clumpy torus models demonstrates that emission from an edge-on torus can also
explain the silicate emission features and 2-20 micron spectral energy
distribution of this object. In many of the best-fitting models the torus has
only a small number of clouds along the line of sight, and does not extend far
above the equatorial plane. Extended silicate-emitting regions may well be
present in AGN, but this work establishes that emission from the torus itself
is also a viable option for the origin of silicate emission features in active
galaxies of both type 1 and type 2.Comment: ApJL, accepte
The Infrared Array Camera Dark Field: Far-Infrared to X-ray Data
We present 20 band photometry from the far-IR to X-ray in the Spitzer Infrared Array Camera (IRAC) dark field. The bias for the near-IR camera on Spitzer is calibrated by observing a ~20' diameter "dark" field near the north ecliptic pole roughly every two-to-three weeks throughout the mission duration of Spitzer. The field is unique for its extreme depth, low background, high quality imaging, time-series information, and accompanying photometry including data taken with Akari, Palomar, MMT, KPNO, Hubble, and Chandra. This serendipitous survey contains the deepest mid-IR data taken to date. This data set is well suited for studies of intermediate-redshift galaxy clusters, high-redshift galaxies, the first generation of stars, and the lowest mass brown dwarfs, among others. This paper provides a summary of the data characteristics and catalog generation from all bands collected to date as well as a discussion of photometric redshifts and initial and expected science results and goals. To illustrate the scientific potential of this unique data set, we also present here IRAC color-color diagrams
Cosmic Optical Background: the View from Pioneer 10/11
We present the new constraints on the cosmic optical background (COB)
obtained from an analysis of the Pioneer 10/11 Imaging Photopolarimeter (IPP)
data. After careful examination of data quality, the usable measurements free
from the zodiacal light are integrated into sky maps at the blue (~0.44 um) and
red (~0.64 um) bands. Accurate starlight subtraction is achieved by referring
to all-sky star catalogs and a Galactic stellar population synthesis model down
to 32.0 mag. We find that the residual light is separated into two components:
one component shows a clear correlation with thermal 100 um brightness, while
another betrays a constant level in the lowest 100 um brightness region.
Presence of the second component is significant after all the uncertainties and
possible residual light in the Galaxy are taken into account, thus it most
likely has the extragalactic origin (i.e., the COB). The derived COB brightness
is (1.8 +/- 0.9) x 10^(-9) and (1.2 +/- 0.9) x 10^(-9) erg/s/cm2/sr/A at the
blue and red band, respectively, or 7.9 +/- 4.0 and 7.7 +/- 5.8 nW/m2/sr. Based
on a comparison with the integrated brightness of galaxies, we conclude that
the bulk of the COB is comprised of normal galaxies which have already been
resolved by the current deepest observations. There seems to be little room for
contributions of other populations including "first stars" at these
wavelengths. On the other hand, the first component of the IPP residual light
represents the diffuse Galactic light (DGL) - scattered starlight by the
interstellar dust. We derive the mean DGL-to-100 um brightness ratios of 2.1 x
10^(-3) and 4.6 x 10^(-3) at the two bands, which are roughly consistent with
the previous observations toward denser dust regions. Extended red emission in
the diffuse interstellar medium is also confirmed.Comment: Accepted for publication in the Astrophysical Journal; Typos
correcte
An extragalactic supernebula confined by gravity
Little is known about the origins of the giant star clusters known as
globular clusters. How can hundreds of thousands of stars form simultaneously
in a volume only a few light years across the distance of the sun to its
nearest neighbor? Radiation pressure and winds from luminous young stars should
disperse the star-forming gas and disrupt the formation of the cluster.
Globular clusters in our Galaxy cannot provide answers; they are billions of
years old. Here we report the measurement of infrared hydrogen recombination
lines from a young, forming super star cluster in the dwarf galaxy, NGC 5253.
The lines arise in gas heated by a cluster of an estimated million stars, so
young that it is still enshrouded in gas and dust, hidden from optical view. We
verify that the cluster contains 4000-6000 massive, hot "O" stars. Our
discovery that the gases within the cluster are bound by gravity may explain
why these windy and luminous O stars have not yet blown away the gases to allow
the cluster to emerge from its birth cocoon. Young clusters in "starbursting"
galaxies in the local and distant universe may be similarly gravitationally
confined and cloaked from view.Comment: Letter to Natur
The Mid-Infrared Properties of X-ray Sources
We combine the results of the Spitzer IRAC Shallow Survey and the Chandra
XBootes Survey of the 8.5 square degrees Bootes field of the NOAO Deep Wide-
Field Survey to produce the largest comparison of mid-IR and X-ray sources to
date. The comparison is limited to sources with X-ray fluxes >8x10-15 erg
cm-2s-1 in the 0.5-7.0 keV range and mid-IR sources with 3.6 um fluxes brighter
than 18.4 mag (12.3 uJy). In this most sensitive IRAC band, 85% of the 3086
X-ray sources have mid-IR counterparts at an 80% confidence level based on a
Bayesian matching technique. Only 2.5% of the sample have no IRAC counterpart
at all based on visual inspection. Even for a smaller but a significantly
deeper Chandra survey in the same field, the IRAC Shallow Survey recovers most
of the X-ray sources. A majority (65%) of the Chandra sources detected in all
four IRAC bands occupy a well-defined region of IRAC [3.6] - [4.5] vs [5.8] -
[8.0] color-color space. These X-ray sources are likely infrared luminous,
unobscured type I AGN with little mid-infrared flux contributed by the AGN host
galaxy. Of the remaining Chandra sources, most are lower luminosity type I and
type II AGN whose mid-IR emission is dominated by the host galaxy, while
approximately 5% are either Galactic stars or very local galaxies.Comment: Accepted for publication in Ap
A large population of mid-infrared selected, obscured active galaxies in the Bootes field
We identify a population of 640 obscured and 839 unobscured AGNs at redshifts
0.7<z<~3 using multiwavelength observations of the 9 deg^2 NOAO Deep Wide-Field
Survey (NDWFS) region in Bootes. We select AGNs on the basis of Spitzer IRAC
colors obtained by the IRAC Shallow Survey. Redshifts are obtained from optical
spectroscopy or photometric redshift estimators. We classify the IR-selected
AGNs as IRAGN 1 (unobscured) and IRAGN 2 (obscured) using a simple criterion
based on the observed optical to mid-IR color, with a selection boundary of
R-[4.5]=6.1, where R and [4.5] are the Vega magnitudes in the R and IRAC 4.5
micron bands, respectively. We verify this selection using X-ray stacking
analyses with data from the Chandra XBootes survey, as well as optical
photometry from NDWFS and spectroscopy from MMT/AGES. We show that (1) these
sources are indeed AGNs, and (2) the optical/IR color selection separates
obscured sources (with average N_H~3x10^22 cm^-2 obtained from X-ray hardness
ratios, and optical colors and morphologies typical of galaxies) and unobscured
sources (with no X-ray absorption, and quasar colors and morphologies), with a
reliability of >~80%. The observed numbers of IRAGNs are comparable to
predictions from previous X-ray, optical, and IR luminosity functions, for the
given redshifts and IRAC flux limits. We observe a bimodal distribution in
R-[4.5] color, suggesting that luminous IR-selected AGNs have either low or
significant dust extinction, which may have implications for models of AGN
obscuration.Comment: 23 emulateapj pages, 24 figures, 4 tables, v2: minor changes match
version to appear in Ap
Dust-Bounded ULIRGs? Model Predictions for Infrared Spectroscopic Surveys
The observed faintness of infrared fine-structure line emission along with
the warm far-infrared (FIR) colors of ultraluminous infrared galaxies (ULIRGs)
is a long-standing problem. In this work, we calculate the line and continuum
properties of a cloud exposed to an Active Galactic Nucleus (AGN) and starburst
spectral energy distribution (SED). We use an integrated modeling approach,
predicting the spectrum of ionized, atomic, and molecular environments in
pressure equilibrium. We find that the effects of high ratios of impinging
ionizing radiation density to particle density (i.e. high ionization
parameters, or U) can reproduce many ULIRG observational characteristics.
Physically, as U increases, the fraction of UV photons absorbed by dust
increases, corresponding to fewer photons available to photoionize and heat the
gas, producing what is known as a "dust-bounded" nebula. We show that high U
effects can explain the "[C II] deficit", the ~1 dex drop in the [C II] 158
micron /FIR ratio seen in ULIRGs when compared to starburst or normal galaxies.
Additionally, by increasing U through increasing the ionizing photon flux,
warmer dust and thus higher IRAS F(60)/F(100) ratios result. High U effects
also predict an increase in [O I]63 micron /[C II] 158 micron and a gradual
decline in [O III] 88 micron /FIR, similar to the magnitude of the trends
observed, and yield a reasonable fit to [Ne V]14 micron /FIR ratio AGN
observations.Comment: 34 pages, 13 figures, accepted for publication in the Astrophysical
Journa
Galaxy Clusters in the IRAC Dark Field I: Growth of the red sequence
Using three newly identified galaxy clusters at z~1 (photometric redshift) we
measure the evolution of the galaxies within clusters from high redshift to the
present day by studying the growth of the red cluster sequence. The clusters
are located in the Spitzer Infrared Array Camera (IRAC) Dark Field, an
extremely deep mid-infrared survey near the north ecliptic pole with photometry
in 18 total bands from X-ray through far-IR. Two of the candidate clusters are
additionally detected as extended emission in matching Chandra data in the
survey area allowing us to measure their masses to be M_{500}= 6.2 \pm 1.0
\times 10^{13} and 3.6 \pm 1.1 \times 10^{13} solar masses. For all three
clusters we create a composite color magnitude diagram in rest-frame B-K using
our deep HST and Spitzer imaging. By comparing the fraction of low luminosity
member galaxies on the composite red sequence with the corresponding population
in local clusters at z=0.1 taken from the COSMOS survey, we examine the effect
of a galaxy's mass on its evolution. We find a deficit of faint galaxies on the
red sequence in our z~1 clusters which implies that more massive galaxies have
evolved in clusters faster than less massive galaxies, and that the less
massive galaxies are still forming stars in clusters such that they have not
yet settled onto the red sequence.Comment: 10 pages including 6 figures and 1 table, ApJ accepte
The IRAC Dark Field; Far- Infrared to X-ray Data
We present 20 band photometry from the far-IR to X-ray in the Spitzer IRAC
dark field. The bias for the near-IR camera on Spitzer is calibrated by
observing a ~20 arcminute diameter "dark" field near the north ecliptic pole
roughly every two-to-three weeks throughout the mission duration of Spitzer.
The field is unique for its extreme depth, low background, high quality
imaging, time-series information, and accompanying photometry including data
taken with Akari, Palomar, MMT, KPNO, Hubble, and Chandra. This serendipitous
survey contains the deepest mid-IR data taken to date. This dataset is well
suited for studies of intermediate redshift galaxy clusters, high redshift
galaxies, the first generation of stars, and the lowest mass brown dwarfs,
among others. This paper provides a summary of the data characteristics and
catalog generation from all bands collected to date as well as a discussion of
photometric redshifts and initial and expected science results and goals. To
illustrate the scientific potential of this unique dataset, we also present
here IRAC color color diagrams.Comment: 12 pages, ApJS accepte
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