2,908 research outputs found
Predicting spectral features in galaxy spectra from broad-band photometry
We explore the prospects of predicting emission line features present in
galaxy spectra given broad-band photometry alone. There is a general consent
that colours, and spectral features, most notably the 4000 A break, can predict
many properties of galaxies, including star formation rates and hence they
could infer some of the line properties. We argue that these techniques have
great prospects in helping us understand line emission in extragalactic objects
and might speed up future galaxy redshift surveys if they are to target
emission line objects only. We use two independent methods, Artifical Neural
Neworks (based on the ANNz code) and Locally Weighted Regression (LWR), to
retrieve correlations present in the colour N-dimensional space and to predict
the equivalent widths present in the corresponding spectra. We also investigate
how well it is possible to separate galaxies with and without lines from broad
band photometry only. We find, unsurprisingly, that recombination lines can be
well predicted by galaxy colours. However, among collisional lines some can and
some cannot be predicted well from galaxy colours alone, without any further
redshift information. We also use our techniques to estimate how much
information contained in spectral diagnostic diagrams can be recovered from
broad-band photometry alone. We find that it is possible to classify AGN and
star formation objects relatively well using colours only. We suggest that this
technique could be used to considerably improve redshift surveys such as the
upcoming FMOS survey and the planned WFMOS survey.Comment: 10 pages 7 figures summitted to MNRA
Estimating photometric redshifts with artificial neural networks
A new approach to estimating photometric redshifts - using Artificial Neural
Networks (ANNs) - is investigated. Unlike the standard template-fitting
photometric redshift technique, a large spectroscopically-identified training
set is required but, where one is available, ANNs produce photometric redshift
accuracies at least as good as and often better than the template-fitting
method. The Bayesian priors on the underlying redshift distribution are
automatically taken into account. Furthermore, inputs other than galaxy colours
- such as morphology, angular size and surface brightness - may be easily
incorporated, and their utility assessed.
Different ANN architectures are tested on a semi-analytic model galaxy
catalogue and the results are compared with the template-fitting method.
Finally the method is tested on a sample of ~ 20000 galaxies from the Sloan
Digital Sky Survey. The r.m.s. redshift error in the range z < 0.35 is ~ 0.021.Comment: Submitted to MNRAS, 9 pages, 9 figures, substantial improvements to
paper structur
Some Pattern Recognition Challenges in Data-Intensive Astronomy
We review some of the recent developments and challenges posed by the data
analysis in modern digital sky surveys, which are representative of the
information-rich astronomy in the context of Virtual Observatory. Illustrative
examples include the problems of an automated star-galaxy classification in
complex and heterogeneous panoramic imaging data sets, and an automated,
iterative, dynamical classification of transient events detected in synoptic
sky surveys. These problems offer good opportunities for productive
collaborations between astronomers and applied computer scientists and
statisticians, and are representative of the kind of challenges now present in
all data-intensive fields. We discuss briefly some emergent types of scalable
scientific data analysis systems with a broad applicability.Comment: 8 pages, compressed pdf file, figures downgraded in quality in order
to match the arXiv size limi
Data Driven Discovery in Astrophysics
We review some aspects of the current state of data-intensive astronomy, its
methods, and some outstanding data analysis challenges. Astronomy is at the
forefront of "big data" science, with exponentially growing data volumes and
data rates, and an ever-increasing complexity, now entering the Petascale
regime. Telescopes and observatories from both ground and space, covering a
full range of wavelengths, feed the data via processing pipelines into
dedicated archives, where they can be accessed for scientific analysis. Most of
the large archives are connected through the Virtual Observatory framework,
that provides interoperability standards and services, and effectively
constitutes a global data grid of astronomy. Making discoveries in this
overabundance of data requires applications of novel, machine learning tools.
We describe some of the recent examples of such applications.Comment: Keynote talk in the proceedings of ESA-ESRIN Conference: Big Data
from Space 2014, Frascati, Italy, November 12-14, 2014, 8 pages, 2 figure
Big Universe, Big Data: Machine Learning and Image Analysis for Astronomy
Astrophysics and cosmology are rich with data. The advent of wide-area
digital cameras on large aperture telescopes has led to ever more ambitious
surveys of the sky. Data volumes of entire surveys a decade ago can now be
acquired in a single night and real-time analysis is often desired. Thus,
modern astronomy requires big data know-how, in particular it demands highly
efficient machine learning and image analysis algorithms. But scalability is
not the only challenge: Astronomy applications touch several current machine
learning research questions, such as learning from biased data and dealing with
label and measurement noise. We argue that this makes astronomy a great domain
for computer science research, as it pushes the boundaries of data analysis. In
the following, we will present this exciting application area for data
scientists. We will focus on exemplary results, discuss main challenges, and
highlight some recent methodological advancements in machine learning and image
analysis triggered by astronomical applications
The buildup of stellar mass and the 3.6 micron luminosity function in clusters from z=1.25 to z=0.2
We have measured the 3.6 micron luminosity evolution of about 1000 galaxies
in 32 clusters at 0.2<z<1.25, without any a priori assumption about luminosity
evolution, i.e. in a logically rigorous way. We find that the luminosity of our
galaxies evolves as an old and passively evolving population formed at high
redshift without any need for additional redshift-dependent evolution. Models
with a prolonged stellar mass growth are rejected by the data with high
confidence. The data also reject models in which the age of the stars is the
same at all redshifts. Similarly, the characteristic stellar mass evolves, in
the last two thirds of the universe age, as expected for a stellar population
formed at high redshift. Together with the old age of stellar populations
derived from fundamental plane studies, our data seems to suggest that
early-type cluster galaxies have been completely assembled at high redshift,
and not only that their stars are old. The quality of the data allows us to
derive the LF and mass evolution homogeneously over the whole redshift range,
using a single estimator. The Schechter function describes the galaxy
luminosity function well. The characteristic luminosity at z=0.5 is is found to
be 16.30 mag, with an uncertainty of 10 per cent.Comment: appeared on A&A (A&A 448, 447
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