REVIEW
Observational and Theoretical Constraints on Singular Dark Matter Halos
Astrophysics · Submitted 2 Feb 1994
Pith's verdict: A genuinely useful three-pronged attack on singular halos, but the word 'excluded' is doing more work than the eye-fits and the single cluster can support.
T0 · AI review
Why Pith says this
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Referee report
The paper
The paper claims
Singular dark matter halos are ruled out by dwarf-galaxy rotation curves, cluster lensing, and how spiral disks form, the authors argue.
The reading
What carries the argument
Three pieces of machinery carry the argument. First, the dark-matter-only rotation curve: the circular velocity of the fitted stellar exponential disk and the fitted HI disk is removed in quadrature from the observed curve, leaving the halo's contribution as a function of radius, which is then compared against the shapes predicted by a core, an $n=1.8$ cusp, and a Hernquist profile. Second, the lensing distortion $D(r)$ of Tyson, Valdes and Wenk, written in the Kaiser–Squires form as an integral over the Fourier transform of the normalized surface density with a kernel that cuts off at $r_{cut} = 300$ kpc; this converts a cluster mass profile into a directly measured shape-distortion curve. Third, the gas-infall model, in which a gas fraction $F$ cools and contracts inside a virialized halo with dimensionless angular momentum $n$, so that the post-infall rotation curve can be computed and its logarithmic slope compared with the observed slopes of large spirals.
Extended reading notes
Core claim
The central claim is that dark matter halos cannot have density profiles that rise monotonically as $n$ toward the center, and that the exclusion follows from ordinary observations rather than from new data. In the gas-rich dwarf DDO154, where gas dominates the luminous mass and the stellar mass-to-light ratio barely matters, subtracting the two luminous components in quadrature leaves a dark-matter rotation curve that rises linearly at small radii, as a constant-density core requires, while an $n=1.8$ cusp or a Hernquist profile fitted to the outer velocities overshoots the inner data badly; the same exercise on DDO168 with a deliberately minimal stellar mass-to-light ratio gives the same verdict, as does NGC3109. On cluster scales, the authors compute the Kaiser–Squires distortion integral for singular profiles and compare with the Tyson–Valdes–Wenk shape measurements of Abell 1689, finding that every singular profile except a very extended Hernquist case keeps the distortion rising well inside the cutoff radius, which the data do not show. Finally, they argue that if spiral galaxies form by gas infall inside such halos, the contraction of the baryons drags the dark matter inward and produces rotation curves that fall outside the optical radius for essentially all realistic protogalactic angular momenta and gas fractions, contrary to the flat or slightly rising curves actually measured.
Load-bearing premise
The exclusion rests on splitting each observed rotation curve into luminous and dark parts, using assumed stellar mass-to-light ratios and a two-piece fit to the HI surface density inside the HI scale length; if that split misjudges the inner baryonic contribution, the inferred dark matter velocity at small radii moves and the comparison that rules out the cusps changes with it.
Editorial extensions
If this is right
- Gamma-ray fluxes from WIMP annihilation in the galactic center should be far below the spike-enhanced estimates, so present radio and gamma-ray limits on neutralino mass are weakened rather than tightened.
- Any clustering theory that predicts a universal $n=1.8$ cusp down to sub-parsec scales, independent of the fluctuation power spectrum, is in conflict with the inner rotation curves of gas-rich dwarfs.
- Dark matter halo profiles inferred from CDM simulations that resolve only down to about a kiloparsec cannot be assumed to continue inward; the data demand a core at smaller radii.
- The shape of the inner dark matter profile becomes a diagnostic of the dark matter itself, since adding gas or a hot dark matter component to cold dark matter simulations could change it.
- Cluster lensing distortion curves provide a second, independent handle on the central mass profile, separate from rotation curves and from X-ray gas data.
Reading between the lines
- The argument is asymmetric in a useful way: a core is the harder prediction to fake, because any misestimate of the baryonic mass at small radii pushes the inferred dark matter curve in the same direction as a cusp, so the observation of a core is conservative evidence against cusps.
- If the exclusion holds, the natural next test is whether the core radius scales with the luminous extent, as the older isothermal picture assumed, which would turn a null result into a measurable relation.
- The lensing test could be sharpened without new telescopes by stacking distortion measurements from several clusters, since the paper's single-cluster comparison is limited by the precision of the Abell 1689 shape data.
- The gas-infall argument depends on the assumed initial angular momentum distribution, so a population of halos with unusually low angular momentum would evade it; measuring the spin distribution of dwarf halos would close that loophole.
Original abstract
The distribution of dark matter around galactic or cluster halos has usually been assumed to be approximately isothermal with a non-zero core radius, which is expected to be of the order of the size of the visible matter distribution. Recently, the possibility has been raised that dark matter halos might be singular in the sense that the dark matter density $\rho$ could increase monotonically with radius $r$ down to a very small distance from the center of galaxies or clusters. Such central cusps in the dark matter density could lead to a high flux of gamma rays from WIMP dark matter annihilation. Here we analyze two possibilities that have been discussed in the literature, $\rho \propto r^{-n}$ with $n \approx 1\ {\rm or}\ 2$, and point out that such density profiles are excluded by gravitional lensing analyses on cluster scales and by the rotation curves of gas-rich, halo-dominated dwarf spirals on small scales. We also point out that if spiral galaxies form by gas infall inside dark matter halos, as they are expected to do in any hierarchical clustering model, such profiles almost always lead to falling rotation curves after infall, contrary to observations.
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
The distribution of dark matter around galactic or cluster halos has usually been assumed to be approximately isothermal with a non-zero core radius, which is expected to be of the order of the size of the visible matter distribution. Recently, the possibility has been raised that dark matter halos might be singular in the sense that the dark matter density $\rho$ could increase monotonically with radius $r$ down to a very small distance from the center of galaxies or clusters. Such central cusps in the dark matter density could lead to a high flux of gamma rays from WIMP dark matter annihilation. Here we analyze two possibilities that have been discussed in the literature, $\rho \propto r^{-n}$ with $n \approx 1\ {\rm or}\ 2$, and point out that such density profiles are excluded by gravitional lensing analyses on cluster scales and by the rotation curves of gas-rich, halo-dominated dwarf spirals on small scales. We also point out that if spiral galaxies form by gas infall inside dark matter halos, as they are expected to do in any hierarchical clustering model, such profiles almost always lead to falling rotation curves after infall, contrary to observations.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | The distribution of dark matter around galactic or cluster halos has usually been assumed to be approximately isothermal with a non-zero core radius, which is expected to be of the order of the size of the visible matter distribution. | background 1.00 | 0.03 | 0.02 | asserted 0.79 |
| s1 | Recently, the possibility has been raised that dark matter halos might be singular in the sense that the dark matter density $\rho$ could increase monotonically with radius $r$ down to a very small distance from the center of galaxies or clusters. | background 0.87 | 0.04 | 0.04 | hedged possibility 0.65 |
| s2 | Such central cusps in the dark matter density could lead to a high flux of gamma rays from WIMP dark matter annihilation. | background 0.81 | 0.05 | 0.03 | hedged possibility 1.00 |
| s3 | Here we analyze two possibilities that have been discussed in the literature, $\rho \propto r^{-n}$ with $n \approx 1\ {\rm or}\ 2$, and point out that such density profiles are excluded by gravitional lensing analyses on cluster scales and by the rotation curves of gas-rich, halo-dominated dwarf spirals on small scales. | result 0.81 | 0.59 | 0.81 | asserted 1.00 |
| s4 | We also point out that if spiral galaxies form by gas infall inside dark matter halos, as they are expected to do in any hierarchical clustering model, such profiles almost always lead to falling rotation curves after infall, contrary to observations. | result 0.90 | 0.55 | 0.16 | asserted 0.65 |
What was examined, and what was not
- arXiv listing abstract v1
- full text
- figures and tables
- references and citing sentences
- relations to other papers
- P abstract
- S sections
- T body sentences
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- R cross-paper relations
Figures
Figures reproduced from arXiv:astro-ph/9402004 by the authors.
References
How the literature uses it
143 arXiv papers cite this in 152 sentences
Papers citing it · 131 sentences without a confident label
Cites it as support 1 paper
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Indeed, experiments show a core profile in the inner region of halos [ref] .
Producing and constraining self-interacting hidden sector dark matter · Core-vs-cusp · 0.96
Cites it as background 20 papers
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The former refers to the tendency of CDM simulations to produce `cuspy' halos whose densities diverge at small radii [ref] , in contrast to observations of dwarf and low surface brightness galaxies that indicate a flattening density profile at small radii (cored) [ref] .
Early formation of supermassive black holes via dark matter self-interactions · Self-interacting dark matter · 0.82
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Over two decades ago, it was proposed that dark matter (DM) with strong self-interactions [ref] could address a discrepancy between gravitational $N$-body simulations of galaxy formation, which predict cuspy central density profiles [ref] , versus observations that indicate otherwise [ref] .
Self-interacting dark baryons · Introduction · 0.92
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The Milky Way dwarf spheroidal (dSph) satellite galaxies are broadly believed to be dominated by dark matter (DM) [ref] [See, however, a contrary claim in [ref] .], and this fact combined with their small sizes and nearby locations makes them interesting test beds of the small-scale behavior of DM [ref] .
Assessing the Fornax globular cluster timing problem in different models of dark matter · Introduction · 0.88
Discussion
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