33 research outputs found
Galactic cold dark matter as a Bose-Einstein condensate of WISPs
We propose here the dark matter content of galaxies as a cold bosonic fluid
composed of Weakly Interacting Slim Particles (WISPs), represented by spin-0
axion-like particles and spin-1 hidden bosons, thermalized in the Bose-Einstein
condensation state and bounded by their self-gravitational potential. We
analyze two zero-momentum configurations: the polar phases in which spin
alignment of two neighbouring particles is anti-parallel and the ferromagnetic
phases in which every particle spin is aligned in the same direction. Using the
mean field approximation we derive the Gross-Pitaevskii equations for both
cases, and, supposing the dark matter to be a polytropic fluid, we describe the
particles density profile as Thomas-Fermi distributions characterized by the
halo radii and in terms of the scattering lengths and mass of each particle. By
comparing this model with data obtained from 42 spiral galaxies and 19 Low
Surface Brightness (LSB) galaxies, we constrain the dark matter particle mass
to the range and we find the lower bound for the
scattering length to be of the order .Comment: 13 pages; 6 figures; references added; v.3: typo corrected in the
abstract, published in JCA
The baryonic Tully-Fisher relation and its implication for dark matter halos
The baryonic Tully-Fisher relation (BTF) is a fundamental relation between
baryonic mass and maximum rotation velocity. It can be used to estimate
distances, as well as to constrain the properties of dark matter and its
relation with the visible matter. In this paper, we explore if extremely
low-mass dwarf galaxies follow the same BTF relation as high-mass galaxies. We
quantify the scatter in the BTF relation and use this to constrain the allowed
elongations of dark matter halo potentials. We obtained HI synthesis data of 11
dwarf galaxies and derive several independent estimates for the maximum
rotation velocity. Constructing a BTF relation using data from the literature
for the high-mass end, and galaxies with detected rotation from our sample for
the low-mass end results in a BTF with a scatter of 0.33 mag. This scatter
constrains the ellipticities of the potentials in the plane of the disks of the
galaxies to an upper limit of 0-0.06 indicating that dwarf galaxies are at most
only mildly tri-axial. Our results indicate that the BTF relation is a
fundamental relation which all rotationally dominated galaxies seem to follow.Comment: Accepted for publication in A&
The dark matter content of the blue compact dwarf NGC 2915
NGC 2915 is a nearby blue compact dwarf with the HI properties of a late-type
spiral. Its large, rotating HI disk (extending out to R ~ 22 B-band scale
lengths) and apparent lack of stars in the outer HI disk make it a useful
candidate for dark matter studies. New HI synthesis observations of NGC 2915
have been obtained using the Australian Telescope Compact Array. These data are
combined with high-quality 3.6 m imaging from the Spitzer Infrared Nearby
Galaxies Survey. The central regions of the HI disk are shown to consist of two
distinct HI concentrations with significantly non-Gaussian line profiles. We
fit a tilted ring model to the HI velocity field to derive a rotation curve.
This is used as input for mass models that determine the contributions from the
stellar and gas disks as well as the dark matter halo. The galaxy is
dark-matter-dominated at nearly all radii. At the last measured point of the
rotation curve, the total mass to blue light ratio is ~ 140 times solar, making
NGC 2915 one of the darkest galaxies known. We show that the stellar disk
cannot account for the steeply-rising portion of the observed rotation curve.
The best-fitting dark matter halo is a pseudo-isothermal sphere with a core
density \msun pc and a core radius kpc.Comment: MNRAS in press. 17 pages, 15 figure
The star formation histories of red and blue low surface brightness disk galaxies
We study the star formation histories (SFH) and stellar populations of 213
red and 226 blue nearly face-on low surface brightness disk galaxies (LSBGs),
which are selected from the main galaxy sample of Sloan Digital Sky Survey
(SDSS) Data Release Seven (DR7). We also want to compare the stellar
populations and SFH between the two groups. The sample of both red and blue
LSBGs have sufficient signal-to-noise ratio in the spectral continua. We obtain
their absorption-line indices (e.g. Mg_2, H\delta_A), D_n(4000) and stellar
masses from the MPA/JHU catalogs to study their stellar populations and SFH.
Moreover we fit their optical spectra (stellar absorption lines and continua)
by using the spectral synthesis code STARLIGHT on the basis of the templates of
Simple Stellar Populations (SSPs). We find that red LSBGs tend to be relatively
older, higher metallicity, more massive and have higher surface mass density
than blue LSBGs. The D_n(4000)-H\delta_A plane shows that perhaps red and blue
LSBGs have different SFH: blue LSBGs are more likely to be experiencing a
sporadic star formation events at the present day, whereas red LSBGs are more
likely to form stars continuously over the past 1-2 Gyr. Moreover, the fraction
of galaxies that experienced recent sporadic formation events decreases with
increasing stellar mass. Furthermore, two sub-samples are defined for both red
and blue LSBGs: the sub-sample within the same stellar mass range of 9.5 <=
log(M_\star/M_\odot) <= 10.3, and the surface brightness limiting sub-sample
with \mu_0(R) <= 20.7 mag arcsec^{-2}. They show consistent results with the
total sample in the corresponding relationships, which confirm that our results
to compare the blue and red LSBGs are robust.Comment: 9 pages, 7 figures, 2 tables, Accepted for publication in A&
Quantified HI Morphology I: Multi-Wavelengths Analysis of the THINGS Galaxies
Galaxy evolution is driven to a large extent by interactions and mergers with
other galaxies and the gas in galaxies is extremely sensitive to the
interactions. One method to measure such interactions uses the quantified
morphology of galaxy images. Well-established parameters are Concentration,
Asymmetry, Smoothness, Gini, and M20 of a galaxy image. Thus far, the
application of this technique has mostly been restricted to restframe
ultra-violet and optical images. However, with the new radio observatories
being commissioned (MeerKAT, ASKAP, EVLA, WSRT/APERTIF, and ultimately SKA), a
new window on the neutral atomic hydrogen gas (HI) morphology of a large
numbers of galaxies will open up. The quantified morphology of gas disks of
spirals can be an alternative indicator of the level and frequency of
interaction. The HI in galaxies is typically spatially more extended and more
sensitive to low-mass or weak interactions. In this paper, we explore six
morphological parameters calculated over the extent of the stellar (optical)
disk and the extent of the gas disk for a range of wavelengths spanning UV,
Optical, Near- and Far-Infrared and 21 cm (HI) of 28 galaxies from The HI
Nearby Galaxy Survey (THINGS). Though the THINGS sample is small and contains
only a single ongoing interaction, it spans both non-interacting and
post-interacting galaxies with a wealth of multi-wavelength data. We find that
the choice of area for the computation of the morphological parameters is less
of an issue than the wavelength at which they are measured. The signal of
interaction is as good in the HI as in any of the other wavelengths in which
morphology has been used to trace the interaction rate to date, mostly
star-formation dominated ones (near- and far-ultraviolet). The Asymmetry and
M20 parameters are the ones which show the most promise as tracers of
interaction in 21 cm line observations.Comment: 16 pages, 11 figure, table 1, accepted by MNRAS, appendix not
include
Very High Gas Fractions and Extended Gas Reservoirs in z=1.5 Disk Galaxies
We present evidence for very high gas fractions and extended molecular gas
reservoirs in normal, near-infrared selected (BzK) galaxies at z~1.5, based on
multi-configuration CO[2-1] observations obtained at the IRAM PdBI. Six of the
six galaxies observed were securely detected. High resolution observations
resolve the CO emission in four of them, implying sizes of order of 6-11 kpc
and suggesting the presence of rotation. The UV morphologies are consistent
with clumpy, unstable disks, and the UV sizes are consistent with the CO sizes.
The star formation efficiencies are homogeneously low and similar to local
spirals - the resulting gas depletion times are ~0.5 Gyr, much higher than what
is seen in high-z submm galaxies and quasars. The CO luminosities can be
predicted to within 0.15 dex from the star formation rates and stellar masses,
implying a tight correlation of the gas mass with these quantities. We use
dynamical models of clumpy disk galaxies to derive dynamical masses. These
models are able to reproduce the peculiar spectral line shapes of the CO
emission. After accounting for the stellar and dark matter masses we derive gas
masses of 0.4-1.2x10^11 Msun. The conversion factor is very high:
alpha_CO=3.6+-0.8, consistent with the Galaxy but four times higher than that
of local ultra-luminous IR galaxies. The gas accounts for an impressive 50-65%
of the baryons within the galaxies' half light radii. We are witnessing truly
gas-dominated galaxies at z~1.5, a finding that explains the high specific SFRs
observed for z>1 galaxies. The BzK galaxies can be viewed as scaled-up versions
of local disk galaxies, with low efficiency star formation taking place inside
extended, low excitation gas disks. They are markedly different than local
ULIRGs and high-z submm galaxies, which have more excited and compact gas.Comment: Accepted for publication in Astrophysical Journal, 22 pages, 18
figures, minor revision
High-Resolution Rotation Curves and Galaxy Mass Models from THINGS
We present rotation curves of 19 galaxies from THINGS, The HI Nearby Galaxy
Survey. The high spatial and velocity resolution of THINGS make these the
highest quality HI rotation curves available to date for a large sample of
nearby galaxies, spanning a wide range of HI masses and luminosities. The high
quality of the data allows us to derive the geometrical and dynamical
parameters using HI data alone. We do not find any declining rotation curves
unambiguously associated with a cut-off in the mass distribution out to the
last measured point. The rotation curves are combined with 3.6 um data from
SINGS (Spitzer Infrared Nearby Galaxies Survey) to construct mass models. Our
best-fit, dynamical disk masses, derived from the rotation curves, are in good
agreement with photometric disk masses derived from the 3.6 um images in
combination with stellar population synthesis arguments and two different
assumptions for the stellar Initial Mass Function (IMF). We test the Cold Dark
Matter-motivated cusp model, and the observationally motivated central density
core model and find that (independent of IMF) for massive, disk-dominated
galaxies, all halo models fit apparently equally well; for low-mass galaxies,
however, a core-dominated halo is clearly preferred over a cuspy halo. The
empirically derived densities of the dark matter halos of the late-type
galaxies in our sample are half of what is predicted by CDM simulations, again
independent of the assumed IMF.Comment: Accepted for publication in the AJ special THINGS issue. For a
high-resolution version visit: http://www.mpia.de/THINGS/Publications.html
[v2 typo fixed
Understanding Dwarf Galaxies in order to Understand Dark Matter
Much progress has been made in recent years by the galaxy simulation
community in making realistic galaxies, mostly by more accurately capturing the
effects of baryons on the structural evolution of dark matter halos at high
resolutions. This progress has altered theoretical expectations for galaxy
evolution within a Cold Dark Matter (CDM) model, reconciling many earlier
discrepancies between theory and observations. Despite this reconciliation, CDM
may not be an accurate model for our Universe. Much more work must be done to
understand the predictions for galaxy formation within alternative dark matter
models.Comment: Refereed contribution to the Proceedings of the Simons Symposium on
Illuminating Dark Matter, to be published by Springe
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
Dark Matter Universal Properties in Galaxies
In the past years a wealth of observations has unraveled the structural
properties of dark and luminous mass distribution in galaxies, a benchmark for
understanding dark matter and the process of galaxy formation. The study of the
kinematics of over thousand spirals has evidenced a dark-luminous matter
coupling and the presence of a series of scaling laws, pictured by the
Universal Rotation Curve paradigm, an intriguing observational scenario not
easily explained by present theories of galaxy formation.Comment: Proceedings of the VI International Workshop on the Dark side of the
Universe. June 01-06, 2010. Le\'on, M\'exic