3,132 research outputs found
Comparing PyMorph and SDSS photometry. II. The differences are more than semantics and are not dominated by intracluster light
The Sloan Digital Sky Survey pipeline photometry underestimates the
brightnesses of the most luminous galaxies. This is mainly because (i) the SDSS
overestimates the sky background and (ii) single or two-component Sersic-based
models better fit the surface brightness profile of galaxies, especially at
high luminosities, than does the de Vaucouleurs model used by the SDSS
pipeline. We use the PyMorph photometric reductions to isolate effect (ii) and
show that it is the same in the full sample as in small group environments, and
for satellites in the most massive clusters as well. None of these are expected
to be significantly affected by intracluster light (ICL). We only see an
additional effect for centrals in the most massive halos, but we argue that
even this is not dominated by ICL. Hence, for the vast majority of galaxies,
the differences between PyMorph and SDSS pipeline photometry cannot be ascribed
to the semantics of whether or not one includes the ICL when describing the
stellar mass of massive galaxies. Rather, they likely reflect differences in
star formation or assembly histories. Failure to account for the SDSS
underestimate has significantly biased most previous estimates of the SDSS
luminosity and stellar mass functions, and therefore Halo Model estimates of
the z ~ 0.1 relation between the mass of a halo and that of the galaxy at its
center. We also show that when one studies correlations, at fixed group mass,
with a quantity which was not used to define the groups, then selection effects
appear. We show why such effects arise, and should not be mistaken for physical
effects.Comment: 15 pages, 17 figures, accepted for publication in MNRAS. The PyMorph
luminosities and stellar masses are available at
https://www.physics.upenn.edu/~ameert/SDSS_PhotDec
Tunneling Potentials to Nothing
The catastrophic decay of a spacetime with compact dimensions, via bubbles of
nothing (BoNs), is probably a generic phenomenon. BoNs admit a 4-dimensional
description as singular Coleman-de Luccia bounces of the size modulus field,
stabilized by some potential . We apply the tunneling potential
approach to this 4d description to provide a very simple picture of BoNs. Using
it we identify four different types of BoN, corresponding to different classes
of higher dimensional theories. We study the quenching of BoN decays and their
interplay with standard vacuum decays.Comment: 7 page
The high mass end of the stellar mass function: Dependence on stellar population models and agreement between fits to the light profile
We quantify the systematic effects on the stellar mass function which arise
from assumptions about the stellar population, as well as how one fits the
light profiles of the most luminous galaxies at z ~ 0.1. When comparing results
from the literature, we are careful to separate out these effects. Our analysis
shows that while systematics in the estimated comoving number density which
arise from different treatments of the stellar population remain of order < 0.5
dex, systematics in photometry are now about 0.1 dex, despite recent claims in
the literature. Compared to these more recent analyses, previous work based on
Sloan Digital Sky Survey (SDSS) pipeline photometry leads to underestimates of
rho_*(> M_*) by factors of 3-10 in the mass range 10^11 - 10^11.6 M_Sun, but up
to a factor of 100 at higher stellar masses. This impacts studies which match
massive galaxies to dark matter halos. Although systematics which arise from
different treatments of the stellar population remain of order < 0.5 dex, our
finding that systematics in photometry now amount to only about 0.1 dex in the
stellar mass density is a significant improvement with respect to a decade ago.
Our results highlight the importance of using the same stellar population and
photometric models whenever low and high redshift samples are compared.Comment: 18 pages, 17 figures, accepted for publication in MNRAS. The PyMorph
luminosities and stellar masses are available at
https://www.physics.upenn.edu/~ameert/SDSS_PhotDec
Improving the accuracy of RF alternate test using multi-VDD conditions: application to envelope-based test of LNAs
Trabajo presentado al "20 Asina Test Symposium" celebrado en Nueva Delhi (India) del 20 al 23 de Noviembre del 2011.-- Reprinted from (relevant publication info). This material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of the products or services of CSIC Spanish National Research Council, Digital.CSIC. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to [email protected]. By choosing to view this document, you agree to all provisions of the copyright laws protecting it.This work demonstrates that multi-VDD conditions may be used to improve the accuracy of machine learning mod- els, significantly decreasing the prediction error. The proposed technique has been successfully applied to a previous alternate test strategy for LNAs based on response envelope detection. A prototype has been developed to show its feasibility. The prototype consists of a low-power 2.4GHz LNA and a simple envelope detector, integrated in a 90nm CMOS technology. Post- layout simulation results are provided to verify the functionality of the approach. Copyright © 2011 IEEE.This work has been partially funded by a CSIC JAE-Doc contract (cofinanced by FSE), a Spanish MAE-AECID grant and projects: SR2 - Short Range Radio (Catrene European project 2A105SR2 and Avanza I+D Spanish project TSI-020400-2010-55, cofinanced with FEDER program), Auto-calibración y auto-test en circuitos analógicos, mixtos y de
radio frecuencia (Andalusian Government project P09-TIC-5386, cofinanced with FEDER program), and Catrene project TOETS (CT 302).Peer reviewe
AVOCADO: A Virtual Observatory Census to Address Dwarfs Origins
Dwarf galaxies are by far the most abundant of all galaxy types, yet their
properties are still poorly understood -especially due to the observational
challenge that their intrinsic faintness represents. AVOCADO aims at
establishing firm conclusions on their formation and evolution by constructing
a homogeneous, multiwavelength dataset for a statistically significant sample
of several thousand nearby dwarfs (-18 < Mi < -14). Using public data and
Virtual Observatory tools, we have built GALEX+SDSS+2MASS spectral energy
distributions that are fitted by a library of single stellar population models.
Star formation rates, stellar masses, ages and metallicities are further
complemented with structural parameters that can be used to classify them
morphologically. This unique dataset, coupled with a detailed characterization
of each dwar's environment, allows for a fully comprehensive investigation of
their origins and to track the (potential) evolutionary paths between the
different dwarf types.Comment: 4 pages, 1 figure. To appear in the proceedings of IAU Symposium 277,
"Tracing the Ancestry of Galaxies on the Land of our Ancestors", Carignan,
Freeman, and Combes, ed
Dynamic exchange coupling and Gilbert damping in magnetic multilayers
We theoretically study dynamic properties of thin ferromagnetic films in
contact with normal metals. Moving magnetizations cause a flow of spins into
adjacent conductors, which relax by spin flip, scatter back into the
ferromagnet, or are absorbed by another ferromagnet. Relaxation of spins
outside the moving magnetization enhances the overall damping of the
magnetization dynamics in accordance with the Gilbert phenomenology. Transfer
of spins between different ferromagnets by these nonequilibrium spin currents
leads to a long-ranged dynamic exchange interaction and novel collective
excitation modes. Our predictions agree well with recent
ferromagnetic-resonance experiments on ultrathin magnetic films.Comment: 15 pages, 3 figures, for MMM'02 proceeding
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