187 research outputs found
Exact Solution to Finite Temperature SFDM: Natural Cores without Feedback
Recent high-quality observations of low surface brightness (LSB) galaxies
have shown that their dark matter (DM) halos prefer flat central density
profiles. On the other hand, the standard cold dark matter model simulations
predict a more cuspy behavior. One mechanism to reconcile the simulations with
the observed data is the feedback from star formation, this might be successful
in isolated dwarf galaxies but its success in LSB galaxies remains unclear.
Additionally, including too much feedback in the simulations is a double-edged
sword, in order to obtain a cored DM distribution from an initially cuspy one,
the feedback recipes usually require to remove a large quantity of baryons from
the center of galaxies, however, some feedback recipes produce twice more
satellite galaxies of a given luminosity and with much smaller mass to light
ratios from those that are observed. Therefore, one DM profile that produces
cores naturally and that does not require large amounts of feedback would be
preferable. We find both requirements to be satisfied in the scalar field dark
matter model. Here, we consider that the dark matter is an auto-interacting
real scalar field in a thermal bath at temperature T with an initial
symmetric potential, as the universe expands, the temperature drops so that the
symmetry is spontaneously broken and the field rolls down to a new
minimum. We give an exact analytic solution to the Newtonian limit of this
system and show that it can satisfy the two desired requirements and that the
rotation curve profile is not longer universal.Comment: 11 pages, 3 figures, this version matches the one accepted for
publication in the Astrophysical Journa
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A Multi-Attribute Utility Decision Analysis for Treatment Alternatives for the DOE/SR Aluminum-Based Spent Nuclear Fuel
A multi-attribute utility analysis is applied to a decision process to select a treatment method for the management of aluminum-based spent nuclear fuel (Al-SNF) owned by the US Department of Energy (DOE). DOE will receive, treat, and temporarily store Al-SNF, most of which is composed of highly enriched uranium, at its Savannah River Site in South Carolina. DOE intends ultimately to send the treated Al-SNF to a geologic repository for permanent disposal. DOE initially considered ten treatment alternatives for the management of Al-SNF, and has narrowed the choice to two of these: the direct disposal and melt and dilute alternatives. The decision analysis presented in this document focuses on a formal decision process used to evaluate these two remaining alternatives
The star pile in Abell 545
Context:Struble (1988) found what appeared to be a cD halo without cD galaxy
in the center of the galaxy cluster Abell 545. This remarkable feature has been
passed almost unnoticed for nearly twenty years.
Aims:Our goal is to review Struble's claim by providing a first (preliminary)
photometric and spectroscopic analysis of this ''star pile''.
Methods:Based on archival VLT-images and long-slit spectra obtained with
Gemini-GMOS, we describe the photometric structure and measure the redshift of
the star pile and of the central galaxy.
Results:The star pile is indeed associated with Abell 545. Its velocity is
higher by about 1300 km/s than that of the central object. The spectra indicate
an old, presumably metal-rich population. Its brightness profile is much
shallower than that of typical cD-galaxies.
Conclusions:The formation history and the dynamical status of the star pile
remain elusive, until high S/N spectra and a dynamical analysis of the galaxy
cluster itself become available. We suggest that the star pile might provide an
interesting test of the Cold Dark Matter paradigm.Comment: 6 pages, 7 figures. Accepted for publication in A&
Flat Central Density Profile and Constant DM Surface Density in Galaxies from Scalar Field Dark Matter
The scalar field dark matter (SFDM) model proposes that galaxies form by
condensation of a scalar field (SF) very early in the universe forming
Bose-Einstein Condensates (BEC) drops, i.e., in this model haloes of galaxies
are gigantic drops of SF. Here big structures form like in the LCDM model, by
hierarchy, thus all the predictions of the LCDM model at big scales are
reproduced by SFDM. This model predicts that all galaxies must be very similar
and exist for bigger redshifts than in the LCDM model. In this work we show
that BEC dark matter haloes fit high-resolution rotation curves of a sample of
thirteen low surface brightness galaxies. We compare our fits to those obtained
using a Navarro-Frenk-White and Pseudo-Isothermal (PI) profiles and found a
better agreement with the SFDM and PI profiles. The mean value of the
logarithmic inner density slopes is -0.27 +/- 0.18. As a second result we find
a natural way to define the core radius with the advantage of being
model-independent. Using this new definition in the BEC density profile we find
that the recent observation of the constant dark matter central surface density
can be reproduced. We conclude that in light of the difficulties that the
standard model is currently facing the SFDM model can be a worthy alternative
to keep exploring further.Comment: Submitted to MNRAS, 9 pages, 32 Figures, 2 Tables.The paper with
better resolution figures can be downloaded at
"http://estudiantes.fis.cinvestav.mx/vrobles/SFDMfile.pd
The rotation curves shapes of late-type dwarf galaxies
We present rotation curves derived for a sample of 62 late-type dwarf
galaxies that have been observed as part of the Westerbork HI Survey of Spiral
and Irregular Galaxies (WHISP) project. The rotation curves were derived by
interactively fitting model data cubes to the observed cubes, taking rotation
curve shape, HI distribution, inclination, and the size of the beam into
account. This makes it possible to correct for the effects of beam smearing.
The dwarf galaxies in our sample have rotation-curve shapes that are similar to
those of late-type spiral galaxies, in the sense that their rotation curves,
when expressed in units of disk scale lengths, rise as steeply in the inner
parts and start to flatten at two disk scale lengths. None of the galaxies in
our sample have solid-body rotation curves that extend beyond three scale
lengths. The logarithmic outer rotation curve slopes are similar between
late-type dwarf and spiral galaxies. Thus, whether the flat part of the
rotation curve is reached seems to depend more on the extent of the rotation
curve than on its amplitude. We also find that the outer rotation curve shape
does not strongly depend on luminosity, at least for galaxies fainter than
M_R~-19. We find that in spiral galaxies and in the central regions of
late-type dwarf galaxies, the shape of the central distribution of light and
the inner rise of the rotation curve are related. This implies that galaxies
with stronger central concentrations of light also have higher central mass
densities, and it suggests that the luminous mass dominates the gravitational
potential in the central regions, even in low surface brightness dwarf
galaxies.Comment: 22 pages, 2009 A&A 493, 87
Stellar mass map and dark matter distribution in M31
Stellar mass distribution in M31 is estimated using optical and infrared
imaging data. Combining the derived stellar mass model with various kinematical
data, properties of the DM halo of the galaxy are constrained.
SDSS observations through the ugriz filters and the Spitzer imaging at 3.6
microns are used to sample the SED of the galaxy at each imaging pixel.
Intrinsic dust extinction effects are taken into account by using far-infrared
observations. Synthetic SEDs created with different stellar population
synthesis models are fitted to the observed SEDs, providing estimates for the
stellar mass surface density. The stellar mass distribution of the galaxy is
described with a 3D model consisting of a nucleus, a bulge, a disc, a young
disc and a halo component, each following the Einasto density distribution
(relations between different functional forms of the Einasto density
distribution are given in App. B). By comparing the stellar mass distribution
to the observed rotation curve and kinematics of outer globular clusters and
satellite galaxies, the DM halo parameters are estimated.
Stellar population synthesis models suggest that M31 is dominated by old
stars throughout the galaxy. The total stellar mass is (10-15)10^10Msun, 30% of
which is in the bulge and 56% in the disc. None of the tested DM distribution
models can be falsified on the basis of the stellar matter distribution and the
rotation curve of the galaxy. The virial mass of the DM halo is
(0.8-1.1)10^12Msun and the virial radius is 189-213kpc, depending on the DM
distribution. The central density of the DM halo is comparable to that of
nearby dwarf galaxies, low-surface-brightness galaxies and distant massive disc
galaxies, thus the evolution of central DM halo properties seems to be
regulated by similar processes for a broad range of halo masses, environments,
and cosmological epochs.Comment: 11 pages, 13 figures, 6 tables, accepted for publication in Astronomy
and Astrophysic
High-resolution mass models of dwarf galaxies from LITTLE THINGS
We present high-resolution rotation curves and mass models of 26 dwarf galaxies from LITTLE THINGS. LITTLE THINGS is a high-resolution Very Large Array HI survey for nearby dwarf galaxies in the local volume within 11 Mpc. The rotation curves of the sample galaxies derived in a homogeneous and consistent manner are combined with Spitzer archival 3.6 micron and ancillary optical U, B, and V images to construct mass models of the galaxies. We decompose the rotation curves in terms of the dynamical contributions by baryons and dark matter halos, and compare the latter with those of dwarf galaxies from THINGS as well as Lambda CDM SPH simulations in which the effect of baryonic feedback processes is included. Being generally consistent with THINGS and simulated dwarf galaxies, most of the LITTLE THINGS sample galaxies show a linear increase of the rotation curve in their inner regions, which gives shallower logarithmic inner slopes alpha of their dark matter density profiles. The mean value of the slopes of the 26 LITTLE THINGS dwarf galaxies is alpha =-0.32 +/- 0.24 which is in accordance with the previous results found for low surface brightness galaxies (alpha = -0.2 +/- 0.2) as well as the seven THINGS dwarf galaxies (alpha =-0.29 +/- 0.07). However, this significantly deviates from the cusp-like dark matter distribution predicted by dark-matter-only Lambda CDM simulations. Instead our results are more in line with the shallower slopes found in the Lambda CDM SPH simulations of dwarf galaxies in which the effect of baryonic feedback processes is included. In addition, we discuss the central dark matter distribution of DDO 210 whose stellar mass is relatively low in our sample to examine the scenario of inefficient supernova feedback in low mass dwarf galaxies predicted from recent Lambda SPH simulations of dwarf galaxies where central cusps still remain.Peer reviewe
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