17,673 research outputs found
Dust and Molecules in Early Galaxies: Prediction and Strategy for Observations
The interplay between dust and molecules is of fundamental importance in
early galaxy evolution. First we present the prediction for the dust emission
from forming galaxies. Then we discuss the observational strategy for molecules
in early galaxies by infrared absorption lines of a bright continuum source
behind the clouds. By combining these two approaches, we will be able to have a
coherent picture of the very early stage of galaxy evolution.Comment: 10 pages, 4 figures, to appear in the proceedings of `Hunt for
Molecules', IA
Star-galaxy separation by far-infrared color-color diagrams for the AKARI FIS All-Sky Survey (Bright Source Catalogue Version beta-1)
To separate stars and galaxies in the far infrared AKARI All-Sky Survey data,
we have selected a sample with the complete color information available in the
low extinction regions of the sky and constructed color-color plots for these
data. We looked for the method to separate stars and galaxies using the color
information. We performed an extensive search for the counterparts of these
selected All-Sky Survey sources in the NED and SIMBAD databases. Among 5176
objects, we found 4272 galaxies, 382 other extragalactic objects, 349 Milky Way
stars, 50 other Galactic objects, and 101 sources detected before in various
wavelengths but of an unknown origin. 22 sources were left unidentified. Then,
we checked colors of stars and galaxies in the far-infrared flux-color and
color-color plots. In the resulting diagrams, stars form two clearly separated
clouds. One of them is easy to be distinguished from galaxies and allows for a
simple method of excluding a large part of stars using the far-infrared data.
The other smaller branch, overplotting galaxies, consists of stars known to
have an infrared excess, like Vega and some fainter stars discovered by IRAS or
2MASS. The color properties of these objects in any case make them very
difficult to distinguish from galaxies. We conclude that the FIR color-color
diagrams allow for a high-quality star-galaxy separation. With the proposed
simple method we can select more that 95 % of galaxies rejecting at least 80 %
of stars.Comment: 20 pages, 41 figures, "Astronomy & Astrophysics", accepted, to appear
in the AKARI special issu
Mid-infrared luminosity as an indicator of the total infrared luminosity of galaxies
The infrared (IR) emission plays a crucial role for understanding the star
formation in galaxies hidden by dust. We first examined four estimators of the
IR luminosity of galaxies, L_fir (Helou et al. 1988), L_tir (Dale et al. 2001),
revised version of L_tir (Dale & Helou 2002) (we denote L_tir2), and L_ir
(Sanders & Mirabel 1996) by using the observed SEDs of well-known galaxies. We
found that L_ir provides excellent estimates of the total IR luminosity for a
variety of galaxy SEDs. The performance of L_tir2 was also found to be very
good. Using L_ir, we then statistically analyzed the IRAS PSCz galaxy sample
(Saunders et al. 2000) and found useful formulae relating the MIR monochromatic
luminosities [L(12um) and L(25um)], and L_ir. For this purpose we constructed a
subsample of 1420 galaxies with all IRAS four band (12, 25, 60, and 100um) flux
densities. We found linear relations between L_ir and MIR luminosities, L(12um)
and L(25um). The prediction error with 95-% confidence level is a factor of
4-5. Hence, these formulae are useful for the estimation of the total IR
luminosity only from 12um or 25um observations. We further tried to make an
`interpolation' formula for galaxies at 0<z<1. For this purpose we construct
the formula of the relation between 15-um luminosity and the total IR
luminosity. We conclude that the 15-um formula can be used as an estimator of
the total IR luminosity from 24um observation of galaxies at z \simeq 0.6.Comment: A&A in press, 8 pages, 9 figures, numerical errors correcte
Clustering of Far-Infrared Galaxies in the AKARI All-Sky Survey
We present the first measurement of the angular two-point correlation
function for AKARI 90-m point sources, detected outside of the Milky Way
plane and other regions characterized by high Galactic extinction, and
categorized as extragalactic sources according to our far-infrared-color based
criterion (Pollo et al. 2010). This is the first measurement of the large-scale
angular clustering of galaxies selected in the far-infrared after IRAS
measurements. Although a full description of clustering properties of these
galaxies will be obtained by more detailed studies, using either spatial
correlation function, or better information about properties and at least
photometric redshifts of these galaxies, the angular correlation function
remains the first diagnostics to establish the clustering properties of the
catalog and observed galaxy population. We find a non-zero clustering signal in
both hemispheres extending up to degrees, without any significant
fluctuations at larger scales. The observed correlation function is well fitted
by a power law function. The notable differences between a northern and
southern hemisphere are found, which can be probably attributed to the
photometry problems and point out to a necessity of performing a better
calibration in the data from southern hemisphere.Comment: 6 pages, 6 figures, accepted for publication in Earth, Planets, and
Spac
The Evolution of the Visible and Hidden Star Formation in the Universe: Implication from the Luminosity Functions at FUV and FIR
Based on GALEX and IRAS/Spitzer datasets, we have found that both FUV and FIR
luminosity functions (LFs) show a strong evolution from z=0 to z=1, but the FIR
LF evolves much stronger than the FUV one. Consequently, the FIR/FUV luminosity
density ratio increases from 4 (z=0) to 15 (z=1). It means that more than 80%
of the star-forming activity in the Universe is hidden by dust at z=1. To
explore this issue further, we have performed a combined analysis of the galaxy
sample in FUV and FIR. For the Local Universe we used GALEX-IRAS sample,
whereas at z=1 we used the Lyman-break galaxy sample selected by GALEX bands
constructed by Burgarella et al. (2005), which is known to be representative of
visible (i.e., non-obscured) star-forming galaxies at z=1. From these datasets,
we constructed the LFs of the FUV-selected galaxies by the survival analysis
to, take into account the upper-limit data properly. We discovered that the FIR
LF of the Lyman-break galaxies show a significant evolution comparing with the
local FIR LF, but it is a factor of 2-3 lower than the global FIR LF (Le Floc'h
et al. 2005). This indicates that the evolution of visible galaxies is not
strong enough to explain the drastic evolution of the FIR LF. Namely, a
FIR-luminous, rapidly diminishing population of galaxies is required.Comment: 4 pages, 4 figures, conference proceedings of "At the Edge of the
Universe", Sintra 9-13 October 200
Social and Cultural Contexts of Alcohol Use: Influences in a Social-Ecological Framework.
Alcohol use and misuse account for 3.3 million deaths every year, or 6 percent of all deaths worldwide. The harmful effects of alcohol misuse are far reaching and range from individual health risks, morbidity, and mortality to consequences for family, friends, and the larger society. This article reviews a few of the cultural and social influences on alcohol use and places individual alcohol use within the contexts and environments where people live and interact. It includes a discussion of macrolevel factors, such as advertising and marketing, immigration and discrimination factors, and how neighborhoods, families, and peers influence alcohol use. Specifically, the article describes how social and cultural contexts influence alcohol use/misuse and then explores future directions for alcohol research
Virtual audio reproduced in a headrest
When virtual audio reproduction is simultaneously required in many seats, such as in aircraft or
cinemas, it may be convenient to use loudspeakers mounted inside each seat's headrest. In
this preliminary study, the feasibility of virtual audio reproduction in the headrest of a single seat
is explored using an inversion technique to compensate for crosstalk and the synthesis of head
related transfer functions. Although large changes in the magnitude of the signals reproduced
at the listener's ears are observed as the listener moves their head within the headrest, informal
listening tests indicate that the reproduced acoustic images are surprisingly stable in about an
eighth of an arc either side of the loudspeaker positions. Not surprisingly, frontal images are
more difficult to reproduce with headrest loudspeakers
- …