211 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
A Dust Emission Model for Very Young Galaxies: Expected Properties and Far Infrared Diagnostics
Dust plays crucial roles in galaxy formation and evolution. In the early
epoch of galaxy evolution dust is only supplied by supernovae (SNe). With the
aid of a new physical model of dust production by SNe, we constructed a model
of dust emission from forming galaxies. We show the evolution of the spectral
energy distribution (SED). Then we adopt this model to a local starbursting
dwarf galaxy SBS 0335052. Further we discuss the SEDs of high redshift
galaxies, and consider their observational feasibility.Comment: 8 pages, 4 figures, to appear in the proceedings of "Infrared
Diagnostics of Galaxy Evolution
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
Deblurring galaxy images with Tikhonov regularization on magnitude domain
We propose a regularization-based deblurring method that works efficiently
for galaxy images. The spatial resolution of a ground-based telescope is
generally limited by seeing conditions and much worse than space-based
telescopes. This circumstance has generated considerable research interest in
restoration of spatial resolution. Since image deblurring is a typical inverse
problem and often ill-posed, solutions tend to be unstable. To obtain a stable
solution, much research has adopted regularization-based methods for image
deblurring, but the regularization term is not necessarily appropriate for
galaxy images. Although galaxies have an exponential or Sersic profile, the
conventional regularization assumes the image profiles to behave linear in
space. The significant deviation between the assumption and real situation
leads to blurring the images and smoothing out the detailed structures.
Clearly, regularization on logarithmic, i.e. magnitude domain, should provide a
more appropriate assumption, which we explore in this study. We formulate a
problem of deblurring galaxy images by an objective function with a Tikhonov
regularization term on magnitude domain. We introduce an iterative algorithm
minimizing the objective function with a primal-dual splitting method. We
investigate the feasibility of the proposed method using simulation and
observation images. In the simulation, we blur galaxy images with a realistic
point spread function and add both Gaussian and Poisson noises. For the
evaluation with the observed images, we use galaxy images taken by the Subaru
HSC-SSP. Both of these evaluations show that our method successfully recovers
the spatial resolution of the images and significantly outperforms the
conventional methods. The code is publicly available from the Github (
https://github.com/kzmurata-astro/PSFdeconv_amag ).Comment: 14 pages, 9 figures, accepted for publication in PASJ. The code is
available at https://github.com/kzmurata-astro/PSFdeconv_ama
A model for the infrared dust emission from forming galaxies
In the early epoch of galaxy evolution, dust is only supplied by supernovae
(SNe). With the aid of a new physical model of dust production by SNe developed
by Nozawa et al. (2003) (N03), we constructed a model of dust emission from
forming galaxies on the basis of the theoretical framework of Takeuchi et al.
(2003) (T03). N03 showed that the produced dust species depends strongly on the
mixing within SNe. We treated both unmixed and mixed cases and calculated the
infrared (IR) spectral energy distribution (SED) of forming galaxies for both
cases. Our model SED is less luminous than the SED of T03 model by a factor of
2-3. The difference is due to our improved treatment of UV photon absorption
cross section, as well as different grain size and species newly adopted in
this work. The SED for the unmixed case is found to have an enhanced near to
mid-IR (N-MIR) continuum radiation in its early phase of the evolution (age <
10^{7.25} yr) compared with that for the mixed case. The strong N--MIR
continuum is due to the emission from Si grains, which only exist in the
species of the unmixed dust production. We also calculated the IR extinction
curves for forming galaxies. Then we calculated the SED of a local starbursting
dwarf galaxy SBS 0335-052. Our present model SED naturally reproduced the
strong N--MIR continuum and the lack of cold FIR emission of SBS 0335-052. We
found that only the SED of unmixed case can reproduce the NIR continuum of this
galaxy. We then made a prediction for the SED of another typical star-forming
dwarf, I Zw 18. We also presented the evolution of the SED of LBGs. Finally, we
discussed the possibility of observing forming galaxies at z > 5.Comment: MNRAS, in press. 18 pages, 15 figures. Abstract abridge
Deep 15um AKARI observations in the CDFS: estimating dust luminosities for a MIR-selected sample and for Lyman Break Galaxies and the evolution of L(dust)/L(UV) with the redshift
Deep observations of the CDFS have been secured at 15um with AKARI/IRC
infrared space telescope (ESA open time). From these observations, we define a
sample of MIR-selected galaxies at 15um and we also obtain 15um flux densities
for a sample of LBGs at z=1 already observed at 24um with Spitzer/MIPS. Number
counts for the MIR-selected sample show a bump around a 15um flux density of
0.2mJy that can be attributed to galaxies at z>0.4 and at z>0.8 for the fainter
part of the bump. This bump seems to be shifted as compared to other works and
a possible origin can be the Cosmic variance. Thanks to this dataset, we have
tested, on the two above samples at z=1, the validity of the conversions from
monochromatic luminosities nu.f(nu) at a rest-frame wavelength of 8um by a
comparison with total dust luminosities estimated from Spitzer rest-frame 12um
data that we use as a reference. We find that the 8um dust luminosities are not
all consistent and that some of them are better when compared to L(dust)
evaluated from longer wavelength luminosities. We also find that the rest-frame
8um luminosities provide globally good estimates of L(dust). By comparing our
data for the two samples to several libraries of SEDs, we find that models can
explain the diversity of the observed f(24)/f(15) ratio quite reasonably for
the MIR-selected sample and better for the LBG sample which are less dispersed
than the MIR selection. However, when we analyse the luminosity dependence of
this ratio, we find important discrepancies. Finally, we revisit the evolution
of L(dust)/L(UV) ratio with the redshift z by re-calibrating previous L(dust)
at z=2 based on our results and added new data points at higher redshifts. The
decreasing trend is amplified as compared to the previous estimate.Comment: Paper accepted for publication in PAS
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