3 research outputs found
Global Mapping of Surface Composition on an Exo-Earth Using Sparse Modeling
The time series of light reflected from exoplanets by future direct imaging
can provide spatial information with respect to the planetary surface. We apply
sparse modeling to the retrieval method that disentangles the spatial and
spectral information from multi-band reflected light curves termed as
spin-orbit unmixing. We use the -norm and the Total Squared Variation
norm as regularization terms for the surface distribution. Applying our
technique to a toy model of cloudless Earth, we show that our method can infer
sparse and continuous surface distributions and also unmixed spectra without
prior knowledge of the planet surface. We also apply the technique to the real
Earth data as observed by DSCOVR/EPIC. We determined the representative
components that can be interpreted as cloud and ocean. Additionally, we found
two components that resembled the distribution of land. One of the components
captures the Sahara Desert, and the other roughly corresponds to vegetation
although their spectra are still contaminated by clouds. Sparse modeling
significantly improves the geographic retrieval, in particular, of cloud and
leads to higher resolutions for other components when compared with spin-orbit
unmixing using Tikhonov regularization.Comment: 26 pages, 10 figures, accepted for publication in Ap
GALAXY CRUISE: Deep Insights into Interacting Galaxies in the Local Universe
We present the first results from GALAXY CRUISE, a community (or citizen)
science project based on data from the Hyper Suprime-Cam Subaru Strategic
Program (HSC-SSP). The current paradigm of galaxy evolution suggests that
galaxies grow hierarchically via mergers, but our observational understanding
of the role of mergers is still limited. The data from HSC-SSP are ideally
suited to improve our understanding with improved identifications of
interacting galaxies thanks to the superb depth and image quality of HSC-SSP.
We have launched a community science project, GALAXY CRUISE, in 2019 and
collected over 2 million independent classifications of 20,686 galaxies at z <
0.2. We first characterize the accuracy of the participants' classifications
and demonstrate that it surpasses previous studies based on shallower imaging
data. We then investigate various aspects of interacting galaxies in detail. We
show that there is a clear sign of enhanced activities of super massive black
holes and star formation in interacting galaxies compared to those in isolated
galaxies. The enhancement seems particularly strong for galaxies undergoing
violent merger. We also show that the mass growth rate inferred from our
results is roughly consistent with the observed evolution of the stellar mass
function. The 2nd season of GALAXY CRUISE is currently under way and we
conclude with future prospects. We make the morphological classification
catalog used in this paper publicly available at the GALAXY CRUISE website,
which will be particularly useful for machine-learning applications.Comment: 23 pages, 22 figures, PASJ in press. Data available at
https://galaxycruise.mtk.nao.ac.jp/en/for_researchers.htm