3,225 research outputs found
Revisiting the Hubble sequence in the SDSS DR7 spectroscopic sample: a publicly available bayesian automated classification
We present an automated morphological classification in 4 types
(E,S0,Sab,Scd) of ~700.000 galaxies from the SDSS DR7 spectroscopic sample
based on support vector machines. The main new property of the classification
is that we associate to each galaxy a probability of being in the four
morphological classes instead of assigning a single class. The classification
is therefore better adapted to nature where we expect a continuos transition
between different morphological types. The algorithm is trained with a visual
classification and then compared to several independent visual classifications
including the Galaxy Zoo first release catalog. We find a very good correlation
between the automated classification and classical visual ones. The compiled
catalog is intended for use in different applications and can be downloaded at
http://gepicom04.obspm.fr/sdss_morphology/Morphology_2010.html and soon from
the CasJobs database.Comment: A&A in press, english corrections from language editor adde
Galaxy size trends as a consequence of cosmology
We show that recently documented trends in galaxy sizes with mass and
redshift can be understood in terms of the influence of underlying cosmic
evolution; a holistic view which is complimentary to interpretations involving
the accumulation of discreet evolutionary processes acting on individual
objects. Using standard cosmology theory, supported with results from the
Millennium simulations, we derive expected size trends for collapsed cosmic
structures, emphasising the important distinction between these trends and the
assembly paths of individual regions. We then argue that the observed variation
in the stellar mass content of these structures can be understood to first
order in terms of natural limitations of cooling and feedback. But whilst these
relative masses vary by orders of magnitude, galaxy and host radii have been
found to correlate linearly. We explain how these two aspects will lead to
galaxy sizes that closely follow observed trends and their evolution, comparing
directly with the COSMOS and SDSS surveys. Thus we conclude that the observed
minimum radius for galaxies, the evolving trend in size as a function of mass
for intermediate systems, and the observed increase in the sizes of massive
galaxies, may all be considered an emergent consequence of the cosmic
expansion.Comment: 14 pages, 13 figures. Accepted by MNRA
Volatile organic compounds in the atmosphere of Mexico City
The Mexico City Metropolitan Area (MCMA) is one of the most polluted megacities in North America. Therefore, it is an excellent benchmark city to understand atmospheric chemistry and to implement pilot countermeasures. Air quality in the MCMA is not within acceptable levels, mainly due to high ground levels of ozone (O3). Tropospheric O3 is a secondary pollutant formed from the oxidation of volatile organic compounds (VOCs) in the presence of nitrogen oxides and sunlight. To gain a better understanding of O3 formation in megacities, evaluate the effectiveness of already-implemented countermeasures, and identify new cost-effective alternatives to reduce tropospheric O3 concentrations, researchers and environmental authorities require updated concentrations for a broader range of VOCs. Moreover, in an effort to protect human health and the environment, it is important to understand which VOCs exceed reference safe values or most contribute to O3 formation, as well as to identify the most probable emission sources of those VOCs. In this work, 64 VOCs, including 36 toxic VOCs, were measured at four sites in the MCMA during 2011-2012. VOCs related to liquefied petroleum gas leakages exhibited the highest concentrations. Toxic VOCs with the highest average concentrations were acetone and ethanol. The toxic VOC benzene represented the highest risk to Mexican citizens, and toluene contributed the most to O3 formation. Correlation analysis indicated that the measured VOCs come from vehicular emissions and solvent-related industrial sources. VOC measurements revealed that compounds related to liquefied petroleum gas leakages are the most abundant, the toxic VOC benzene represents the highest risk to citizens, and toluene is the greatest VOC contributor to O3 formation in Mexico City. © 2015 Elsevier Ltd.Japan Science and Technology Agency, Science and Technology Research Partnership for Sustainable Development, Japan International Cooperation Agency1,3 butadiene, 106-99-0, 25339-57-5; 1,4 dichlorobenzene, 106-46-7; acetone, 67-64-1; alcohol, 64-17-5; benzene, 71-43-2; ethylbenzene, 100-41-4; gasoline, 86290-81-5; methyl chloride, 74-87-3; ozone, 10028-15-6; propane, 74-98-6; styrene, 100-42-5; toluene, 108-88-3; xylene, 1330-20-
Automatic Rock Detection and Mapping from HiRISE Imagery
This system includes a C-code software program and a set of MATLAB software tools for statistical analysis and rock distribution mapping. The major functions include rock detection and rock detection validation. The rock detection code has been evolved into a production tool that can be used by engineers and geologists with minor training
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