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Register a new userMAGPHYS: a publicly available tool to interpret observed galaxy SEDs
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Elisabete da Cunha
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We present a simple, physically-motivated model to interpret consistently the emission from galaxies at ultraviolet, optical and infrared wavelengths. We combine this model with a Bayesian method to obtain robust statistical constraints on key parameters describing the stellar content, star formation activity and dust content of galaxies. Our model is now publicly available via a user-friendly code package, MAGPHYS at www.iap.fr/magphys. We present an application of this model to interpret a sample of ~1400 local (z<0.5) galaxies from the H-ATLAS survey. We find that, for these galaxies, the diffuse interstellar medium, powered mainly by stars older than 10 Myr, accounts for about half the total infrared luminosity. We discuss the implications of this result to the use of star formation rate indicators based on total infrared luminosity.
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Large-scale annotation of image segmentation datasets is often prohibitively expensive, as it usually requires a huge number of worker hours to obtain high-quality results. Abundant and reliable data has been, however, crucial for the advances on image understanding tasks achieved by deep learning models. In this paper, we introduce FreeLabel, an intuitive open-source web interface that allows users to obtain high-quality segmentation masks with just a few freehand scribbles, in a matter of seconds. The efficacy of FreeLabel is quantitatively demonstrated by experimental results on the PASCAL dataset as well as on a dataset from the agricultural domain. Designed to benefit the computer vision community, FreeLabel can be used for both crowdsourced or private annotation and has a modular structure that can be easily adapted for any image dataset.
We present a simple, largely empirical but physically motivated model, which is designed to interpret consistently multi-wavelength observations from large samples of galaxies in terms of physical parameters, such as star formation rate, stellar mass and dust content. Our model is both simple and versatile enough to allow the derivation of statistical constraints on the star formation histories and dust contents of large samples of galaxies using a wide range of ultraviolet, optical and infrared observations. We illustrate this by deriving median-likelihood estimates of a set of physical parameters describing the stellar and dust contents of local star-forming galaxies from the Spitzer Infrared Nearby Galaxy Sample (SINGS) and from a newly-matched sample of SDSS galaxies observed with GALEX, 2MASS, and IRAS. The model reproduces well the observed spectral energy distributions of these galaxies across the entire wavelength range from the far-ultraviolet to the far-infrared. We find important correlations between the physical parameters of galaxies which are useful to investigate the star formation activity and dust properties of galaxies. Our model can be straightforwardly applied to interpret observed ultraviolet-to-infrared spectral energy distributions (SEDs) from any galaxy sample.
I highlight several concerns regarding the consistency of Type Ia supernova data in the publicly available Pantheon and JLA compilations. The measured heliocentric redshifts (zhel) of $sim$150 SNe Ia as reported in the Pantheon catalogue are significantly discrepant from those in JLA - with 58 having differences amounting to between 5 and 137 times the quoted measurement uncertainty. The discrepancy seems to have been introduced in the process of rectifying a previously reported issue. The Pantheon catalogue until very recently had the redshifts of all SNe Ia up to z $sim$ 0.3 modified under the guise of peculiar velocity corrections - although there is no information on peculiar velocities at such high redshifts. While this has reportedly been rectified on Github by removing peculiar velocity corrections for z > 0.08, the impact of this on the published cosmological analysis of the Pantheon catalogue is not stated. In JLA, the effect of these corrections is to significantly bias the inferred value of $Omega_{Lambda}$ towards higher values, while the equivalent effect on Pantheon cannot be ascertained due to the unavailability of the individual components of the covariance matrix in the public domain. I provide Jupyter notebooks and URLs in order to allow the reader to ascertain the veracity of these assertions.
Utilizing the SDSS-DR13 spectroscopic dataset, we create a new publicly-available catalog of 1,800 galaxy clusters (GalWeight cluster catalog, $mathtt{GalWCat19}$) and a corresponding catalog of 34,471 identified member galaxies. The clusters are identified from overdensities in redshift-phase space. The GalWeight technique introduced in Abdullah, Wilson and Klypin (AWK18) is then applied to identify cluster members. The completeness of the cluster catalog ($mathtt{GalWCat19}$) and the procedure followed to determine cluster mass are tested on the Bolshoi N-body simulations. The 1,800 $mathtt{GalWCat19}$ clusters range in redshift between $0.01 - 0.2$ and in mass between $(0.4 - 14) times 10^{14}h^{-1}M_{odot}$. The cluster catalog provides a large number of cluster parameters including sky position, redshift, membership, velocity dispersion, and mass at overdensities $Delta = 500, 200, 100, 5.5$. The 34,471 member galaxies are identified within the radius at which the density is 200 times the critical density of the Universe. The galaxy catalog provides the coordinates of each galaxy and the ID of the cluster that the galaxy belongs to. The cluster velocity dispersion scales with mass as $log(sigma_{200})=log(946pm52~ mbox{km} ~ mbox{s}^{-1}) +(0.349pm0.142)logleft[h(z) ~ M_{200}/10^{15}M_odotright]$ with scatter of $delta_{logsigma} = 0.06$. The catalogs are publicly available at the following websitefootnote{url{https://mohamed-elhashash-94.webself.net/galwcat/}}.
Context. The solar chromosphere is the interface between the solar surface and the solar corona. Modelling of this region is difficult because it represents the transition from optically thick to thin radiation escape, from gas-pressure domination to magnetic-pressure domination, from a neutral to an ionised state, from MHD to plasma physics, and from near-equilibrium (LTE) to non-equilibrium conditions. Aims. Our aim is to provide the community with realistic simulations of the magnetic solar outer atmosphere. This will enable detailed comparison of existing and upcoming observations with synthetic observables from the simulations, thereby elucidating the complex interactions of magnetic fields and plasma that are crucial for our understanding of the dynamic outer atmosphere. Methods. We used the radiation magnetohydrodynamics code Bifrost to perform simulations of a computational volume with a magnetic field topology similar to an enhanced network area on the Sun. Results. The full simulation cubes are made available online. The general properties of the simulation are discussed, and limitations are discussed.
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