10 research outputs found
Predicting dust extinction properties of star-forming galaxies from H-alpha/UV ratio
Using star-forming galaxies sample in the nearby Universe (0.02<z<0.10)
selected from the SDSS (DR7) and GALEX all-sky survey (GR5), we present a new
empirical calibration for predicting dust extinction of galaxies from
H-alpha-to-FUV flux ratio. We find that the H-alpha dust extinction (A(Ha))
derived with H-alpha/H-beta ratio (Balmer decrement) increases with increasing
H-alpha/UV ratio as expected, but there remains a considerable scatter around
the relation, which is largely dependent on stellar mass and/or H-alpha
equivalent width (EW(Ha)). At fixed H-alpha/UV ratio, galaxies with higher
stellar mass (or galaxies with lower EW(Ha)) tend to be more highly obscured by
dust. We quantify this trend and establish an empirical calibration for
predicting A(Ha) with a combination of H-alpha/UV ratio, stellar mass and
EW(Ha), with which we can successfully reduce the systematic uncertainties
accompanying the simple H-alpha/UV approach by ~15-30%. The new recipes
proposed in this study will provide a convenient tool for predicting dust
extinction level of galaxies particularly when Balmer decrement is not
available. By comparing A(Ha) (derived with Balmer decrement) and A(UV)
(derived with IR/UV luminosity ratio) for a subsample of galaxies for which
AKARI FIR photometry is available, we demonstrate that more massive galaxies
tend to have higher extra extinction towards the nebular regions compared to
the stellar continuum light. Considering recent studies reporting smaller extra
extinction towards nebular regions for high-redshift galaxies, we argue that
the dust geometry within high-redshift galaxies resemble more like low-mass
galaxies in the nearby Universe.Comment: 14 pages, 14 figures, Accepted for publication in MNRA
Calibration and Performance of the AKARI Far-Infrared Surveyor (FIS) -- Slow-Scan Observation Mode for Point Sources
We present the characterization and calibration of the Slow-Scan observation
mode of the Far-Infrared Surveyor (FIS) onboard the AKARI satellite. The FIS,
one of the two focal-plane instruments on AKARI, has four photometric bands
between 50--180 um with two types of Ge:Ga array detectors. In addition to the
All-Sky Survey, FIS has also taken detailed far-infrared images of selected
targets by using the Slow-Scan mode. The sensitivity of the Slow-Scan mode is
one to two orders of magnitude better than that of the All-Sky Survey, because
the exposure time on a targeted source is much longer. The point spread
functions (PSFs) were obtained by observing several bright point-like objects
such as asteroids, stars, and galaxies. The derived full widths at the half
maximum (FWHMs) are ~30'' for the two shorter wavelength bands and ~40'' for
the two longer wavelength bands, being consistent with those expected by the
optical simulation, although a certain amount of excess is seen in the tails of
the PSFs. The flux calibration has been performed by the observations of
well-established photometric calibration standards (asteroids and stars) in a
wide range of fluxes. After establishing the method of aperture photometry, the
photometric accuracy for point-sources is better than +-15% in all of the bands
expect for the longest wavelength.Comment: 25 pages, 7 figures, accepted publication in PAS
AKARI infrared imaging of reflection nebulae IC4954 and IC4955
We present the observations of the reflection nebulae IC4954 and IC4955
region with the Infrared Camera (IRC) and the Far-Infrared Surveyor (FIS) on
board the infrared astronomical satellite AKARI during its performance
verification phase. We obtained 7 band images from 7 to 160um with higher
spatial resolution and higher sensitivities than previous observations. The
mid-infrared color of the S9W (9um) and L18W (18um) bands shows a systematic
variation around the exciting sources. The spatial variation in the
mid-infrared color suggests that the star-formation in IC4954/4955 is
progressing from south-west to north-east. The FIS data also clearly resolve
two nebulae for the first time in the far-infrared. The FIS 4-band data from
65um to 160um allow us to correctly estimate the total infrared luminosity from
the region, which is about one sixth of the energy emitted from the existing
stellar sources. Five candidates for young stellar objects have been detected
as point sources for the first time in the 11um image. They are located in the
red S9W to L18W color regions, suggesting that current star-formation has been
triggered by previous star-formation activities. A wide area map of the size of
about 1 x 1 (deg^2) around the IC4954/4955 region was created from the AKARI
mid-infrared all-sky survey data. Together with the HI 21cm data, it suggests a
large hollow structure of a degree scale, on whose edge the IC4954/4955 region
has been created, indicating star formation over three generations in largely
different spatial scales.Comment: 23 pages, 7 figures, accepted for publication in PASJ AKARI special
issu
A deep ATCA 20cm radio survey of the AKARI Deep Field South near the South Ecliptic Pole
The results of a deep 20 cm radio survey at 20 cm are reported of the AKARI
Deep Field South (ADF-S) near the South Ecliptic Pole (SEP), using the
Australia Telescope Compact Array telescope, ATCA. The survey has 1 sigma
detection limits ranging from 18.7--50 microJy per beam over an area of ~1.1 sq
degrees, and ~2.5 sq degrees to lower sensitivity. The observations, data
reduction and source count analysis are presented, along with a description of
the overall scientific objectives, and a catalogue containing 530 radio sources
detected with a resolution of 6.2" x 4.9". The derived differential source
counts show a pronounced excess of sources fainter than ~1 mJy, consistent with
an emerging population of star forming galaxies. Cross-correlating the radio
with AKARI sources and archival data we find 95 cross matches, with most
galaxies having optical R-magnitudes in the range 18-24 mag, and 52 components
lying within 1" of a radio position in at least one further catalogue (either
IR or optical). We have reported redshifts for a sub-sample of our catalogue
finding that they vary between galaxies in the local universe to those having
redshifts of up to 0.825. Associating the radio sources with the Spitzer
catalogue at 24 microns, we find 173 matches within one Spitzer pixel, of which
a small sample of the identifications are clearly radio loud compared to the
bulk of the galaxies. The radio luminosity plot and a colour-colour analysis
suggest that the majority of the radio sources are in fact luminous star
forming galaxies, rather than radio-loud AGN. There are additionally five cross
matches between ASTE or BLAST submillimetre galaxies and radio sources from
this survey, two of which are also detected at 90 microns, and 41 cross-matches
with submillimetre sources detected in the Herschel HerMES survey Public Data
release.Comment: MNRAS accepted and in press 9 July 2012: 28 pages, 15 Figures, 17
Table
The Far-Infrared Surveyor (FIS) for AKARI
The Far-Infrared Surveyor (FIS) is one of two focal plane instruments on the
AKARI satellite. FIS has four photometric bands at 65, 90, 140, and 160 um, and
uses two kinds of array detectors. The FIS arrays and optics are designed to
sweep the sky with high spatial resolution and redundancy. The actual scan
width is more than eight arcmin, and the pixel pitch is matches the diffraction
limit of the telescope. Derived point spread functions (PSFs) from observations
of asteroids are similar to the optical model. Significant excesses, however,
are clearly seen around tails of the PSFs, whose contributions are about 30% of
the total power. All FIS functions are operating well in orbit, and its
performance meets the laboratory characterizations, except for the two longer
wavelength bands, which are not performing as well as characterized.
Furthermore, the FIS has a spectroscopic capability using a Fourier transform
spectrometer (FTS). Because the FTS takes advantage of the optics and detectors
of the photometer, it can simultaneously make a spectral map. This paper
summarizes the in-flight technical and operational performance of the FIS.Comment: 23 pages, 10 figures, and 2 tables. Accepted for publication in the
AKARI special issue of the Publications of the Astronomical Society of Japa
Embodied energy assessment of building materials in India using process and input-output analysis
Growing demand for urban built spaces has resulted in unprecedented exponential rise in production and consumption of building materials in construction. Production of materials requires significant energy and contributes to pollution and green house gas (GHG) emissions. Efforts aimed at reducing energy consumption and pollution involved with the production of materials fundamentally requires their quantification. Embodied energy (EE) of building materials comprises the total energy expenditure involved in the material production including all upstream processes such as raw material extraction and transportation. The current paper deals with EE of a few common building materials consumed in bulk in Indian construction industry. These values have been assessed based on actual industrial survey data. Current studies on EE of building materials lack agreement primarily with regard to method of assessment and energy supply assumptions (whether expressed in terms of end use energy or primary energy). The current paper examines the suitability of two basic methods; process analysis and input-output method and identifies process analysis as appropriate for EE assessment in the Indian context. A comparison of EE values of building materials in terms of the two energy supply assumptions has also been carried out to investigate the associated discrepancy. The results revealed significant difference in EE of materials whose production involves significant electrical energy expenditure relative to thermal energy use. (C) 2014 Elsevier B.V. All rights reserved
The infrared astronomical mission AKARI
AKARI, the first Japanese satellite dedicated to infrared astronomy, was launched on 2006 February 21, and started observations in May of the same year. AKARI has a 68.5 cm cooled telescope, together with two focal-plane instruments, which survey the sky in six wavelength bands from mid- to far-infrared. The instruments also have a capability for imaging and spectroscopy in the wavelength range 2-180 mu m in the pointed observation mode, occasionally inserted into a continuous survey operation. The in-orbit cryogen lifetime is expected to be one and a half years. The All-Sky Survey will cover more than 90% of the whole sky with a higher spatial resolution and a wider wavelength coverage than that of the previous IRAS all-sky survey. Point-source catalogues of the All-Sky Survey will be released to the astronomical community. Pointed observations will be used for deep surveys of selected sky areas and systematic observations of important astronomical targets. These will become an additional future heritage of this mission