Some implications of nonluminous matter in dwarf spheroidal galaxies

Lin, Da-Bin; Faber, S. M.

doi:10.1086/183971

Cited by 237 publications

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“…Finally, Fig. 3 compares our PM measurement to previous estimates 1 . More details and a thorough description of the extensive tests we have performed are reported in the Methods section.…”

Section: +004mentioning

confidence: 77%

“…The 3D motions of stars in small galaxies beyond our own are minute and yet they are crucial for our understanding of the nature of gravity and dark matter 1,2 . Even for the dwarf galaxy Sculptor which is one of the best studied systems and inferred to be strongly dark matter dominated 3,4 , there are conflicting reports 5,6,7 on its mean motion around the Milky Way and the 3D internal motions of its stars have never been measured.…”

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confidence: 99%

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Three-dimensional motions in the Sculptor dwarf galaxy as a glimpse of a new era

et al. 2017

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The 3D motions of stars in small galaxies beyond our own are minute and yet they are crucial for our understanding of the nature of gravity and dark matter 1,2 . Even for the dwarf galaxy Sculptor which is one of the best studied systems and inferred to be strongly dark matter dominated 3,4 , there are conflicting reports 5,6,7 on its mean motion around the Milky Way and the 3D internal motions of its stars have never been measured. Here we report, based on data from the Gaia space mission 8 and the Hubble Space Telescope, a new precise measurement of Sculptor's mean proper motion. From this we deduce that Sculptor is currently at its closest approach to the Milky Way and moving on an elongated highinclination orbit that takes it much farther away than previously thought. For the first time we are also able to measure the internal motions of stars in Sculptor. We find σ R = 11.5 ± 4.3 km s −1 and σ T = 8.5 ± 3.2 km s −1 along the projected radial and tangential directions, implying that the stars in our sample move preferentially on radial orbits as quantified by the anisotropy parameter, which we find to be β ∼ 0.86 +0.12 −0.83 at a location beyond the core radius. Taken at face value such a high radial anisotropy requires abandoning conventional models 9 for the mass distribution in Sculptor. Our sample is dominated by metal-rich stars and for these we find β M R ∼ 0.95−0.27 , a value consistent with multi-component models where Sculptor is embedded in a cuspy dark halo 10 as expected for cold dark matter.To measure the proper motions (PMs) of individual stars in Sculptor we used data taken 12.27 years apart. The first epoch was acquired with the Advanced Camera for Surveys on board HST. The data set consists of two overlapping pointings separated by about 2 ′ (∼ 50 pc, see Fig. 1), each split in several 400 sec exposures in the F775W filter. The overlapping field-of-view has been observed 11 times. We obtained a catalog of positions, instrumental magnitudes and Point Spread Function (PSF) fitting-quality parameters by treating each chip of each exposure independently. Stellar positions were corrected for filter-dependent geometric distortions 11 . We then cross-matched the single catalogs to compute 3σ-clipped * Corresponding author: massariATastro.rug.nl -2 -average positions, magnitudes and corresponding uncertainties. We built the complete HST catalog after excluding all the saturated sources and those that were measured less than 4 times. The second epoch is provided by the Gaia first data release 12 . We extracted from the Gaia archive all sources in the direction of Sculptor.We transformed the HST positions to the equatorial reference frame defined by the Gaia data (right ascension, RA, and declination, DEC), using a six-parameter linear transformation 14 . We found 126 stars in common and their PMs were computed as the difference between the Gaia and HST positions, divided by the temporal baseline. The uncertainties on the PMs were computed as the sum in quadrature between the Gaia and HST positional e...

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“…Finally, Fig. 3 compares our PM measurement to previous estimates 1 . More details and a thorough description of the extensive tests we have performed are reported in the Methods section.…”

Section: +004mentioning

confidence: 77%

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confidence: 99%

Three-dimensional motions in the Sculptor dwarf galaxy as a glimpse of a new era

et al. 2017

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“…found evidence for outer disks in three out of a sample of 18 Coma early-type dwarfs, modeling the surface brightness profiles using a Sérsic function in combination with either a central point source or a resolved central Gaussian component using high-resolution HST images. While it is still unclear whether all early-type dwarfs with disk structure represent a distinct class of galaxies that are the product of a single formation mechanism, one plausible scenario is that they are formed through processing of faint, late-type spirals and irregulars in cluster environments (e.g., Kormendy 1985;Lin & Faber 1983;Lisker et al 2006). This processing includes the loss of their gas through ram-pressure stripping (e.g., Gunn & Gott 1972) as well as the cumulative effects of harassment in a cluster environment (e.g., Moore et al 1996).…”

Section: Discussion: Barred Dwarf Galaxies In the Coma Corementioning

confidence: 99%

“…Are bar/spiral arm instabilities commonplace for dwarf galaxies? Some early-type dwarfs in clusters are believed to have originated from late-type spirals or dwarf irregulars (e.g., Lin & Faber 1983;Kormendy 1985) that have been stripped of their gas by external processes. This is especially true in a cluster setting where environmental processes like ram-pressure stripping and harassment are commonplace.…”

Section: Introductionmentioning

confidence: 99%

THEHST/ACS COMA CLUSTER SURVEY. VIII. BARRED DISK GALAXIES IN THE CORE OF THE COMA CLUSTER

Marinova

Jogee

Weinzirl

et al. 2012

ApJ

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We use high-resolution (∼0. 1) F814W Advanced Camera for Surveys (ACS) images from the Hubble Space Telescope ACS Treasury survey of the Coma cluster at z ∼ 0.02 to study bars in massive disk galaxies (S0s), as well as low-mass dwarf galaxies in the core of the Coma cluster, the densest environment in the nearby universe. Our study helps to constrain the evolution of bars and disks in dense environments and provides a comparison point for studies in lower density environments and at higher redshifts. Our results are: (1) we characterize the fraction and properties of bars in a sample of 32 bright (M V −18, M * > 10 9.5 M ) S0 galaxies, which dominate the population of massive disk galaxies in the Coma core. We find that the measurement of a bar fraction among S0 galaxies must be handled with special care due to the difficulty in separating unbarred S0s from ellipticals, and the potential dilution of the bar signature by light from a relatively large, bright bulge. The results depend sensitively on the method used: the bar fraction for bright S0s in the Coma core is 50% ± 11%, 65% ± 11%, and 60% ± 11% based on three methods of bar detection, namely, strict ellipse fit criteria, relaxed ellipse fit criteria, and visual classification. (2) We compare the S0 bar fraction across different environments (the Coma core, A901/902, and Virgo) adopting the critical step of using matched samples and matched methods in order to ensure robust comparisons. We find that the bar fraction among bright S0 galaxies does not show a statistically significant variation (within the error bars of ±11%) across environments which span two orders of magnitude in galaxy number density (n ∼ 300-10,000 galaxies Mpc −3 ) and include rich and poor clusters, such as the core of Coma, the A901/902 cluster, and Virgo. We speculate that the bar fraction among S0s is not significantly enhanced in rich clusters compared to low-density environments for two reasons. First, S0s in rich clusters are less prone to bar instabilities as they are dynamically heated by harassment and are gas poor as a result of ram pressure stripping and accelerated star formation. Second, high-speed encounters in rich clusters may be less effective than slow, strong encounters in inducing bars. (3) We also take advantage of the high resolution of the ACS (∼50 pc) to analyze a sample of 333 faint (M V > −18) dwarf galaxies in the Coma core. Using visual inspection of unsharp-masked images, we find only 13 galaxies with bar and/or spiral structure. An additional eight galaxies show evidence for an inclined disk. The paucity of disk structures in Coma dwarfs suggests that either disks are not common in these galaxies or that any disks present are too hot to develop instabilities.

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“…If fermionic dark matter was too light, the Pauli exclusion principle would not allow for the densities that have been observed in dwarf galaxies. Thus fermionic dark matter must have a mass larger than ≈ 0.5 keV [41,42]. The bound can vary by factors of a few depending on the assumptions on the dark matter phase space distribution [43,44] and can be affected by dark matter selfinteractions.…”

Section: The Dark Matter Massmentioning

confidence: 99%

Spontaneous baryogenesis from extremely light asymmetric dark matter

D’Agnolo

Hook

2015

Phys. Rev. D

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We present a mechanism where a particle asymmetry in one sector is used to generate an asymmetry in another sector. The two sectors are not coupled through particle number violating interactions and are not required to be in thermal contact with each other. When this mechanism is applied to baryogenesis in asymmetric dark matter models, we find that the dark matter particles can be extremely light, e.g. much lighter than an eV, and that in some cases there is no need to annihilate away the symmetric component of dark matter. We discuss a concrete realization of the mechanism with signals in direct detection, at the LHC, at B-factories or future beam dump experiments.

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Some implications of nonluminous matter in dwarf spheroidal galaxies

Cited by 237 publications

References 0 publications

Three-dimensional motions in the Sculptor dwarf galaxy as a glimpse of a new era

Three-dimensional motions in the Sculptor dwarf galaxy as a glimpse of a new era

THEHST/ACS COMA CLUSTER SURVEY. VIII. BARRED DISK GALAXIES IN THE CORE OF THE COMA CLUSTER

Spontaneous baryogenesis from extremely light asymmetric dark matter

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