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Articles 61 - 90 of 116
Full-Text Articles in Astrophysics and Astronomy
Andromeda Dwarfs In Light Of Mond. Ii. Testing Prior Predictions, Stacy S. Mcgaugh
Andromeda Dwarfs In Light Of Mond. Ii. Testing Prior Predictions, Stacy S. Mcgaugh
Faculty Scholarship
We employ recently published measurements of the velocity dispersions in the newly discovered dwarf satellite galaxies of Andromeda to test our previously published predictions of this quantity. The data are in good agreement with our specific predictions for each dwarf made a priori with modified Newtonian dynamics (MOND), with reasonable stellar mass-to-light ratios, and no dark matter, while Newtonian dynamics point to quite large mass discrepancies in these systems. MOND distinguishes between regimes where the internal field of the dwarf, or the external field of the host, dominates. The data appear to recognize this distinction, which is a unique feature …
Stellar Populations And The Star Formation Histories Of Low Surface Brightness Galaxies. Ii. H Ii Regions, Stacy S. Mcgaugh
Stellar Populations And The Star Formation Histories Of Low Surface Brightness Galaxies. Ii. H Ii Regions, Stacy S. Mcgaugh
Faculty Scholarship
The luminosities, colors, and Ha emission for 429 H II regions in 54 low surface brightness (LSB) galaxies are presented. While the number of H II regions per galaxy is lower in LSB galaxies compared to star-forming irregulars and spirals, there is no indication that the size or luminosity function of H II regions differs from other galaxy types. The lower number of Hii regions per galaxy is consistent with their lower total star formation rates. The fraction of the total LH α contributed by H II regions varies from 10% to 90% in LSB galaxies (the rest of the …
Galaxy Cluster Bulk Flows And Collision Velocities In Qumond, Stacy S. Mcgaugh
Galaxy Cluster Bulk Flows And Collision Velocities In Qumond, Stacy S. Mcgaugh
Faculty Scholarship
We examine the formation of clusters of galaxies in numerical simulations of a QUMOND cosmogony with massive sterile neutrinos. Clusters formed in these exploratory simulations develop higher velocities than those found in ΛCDM simulations. The bulk motions of clusters attain ∼1000 km s -1 by low redshift, comparable to observations whereas ΛCDM simulated clusters tend to fall short. Similarly, high pairwise velocities are common in cluster-cluster collisions like the Bullet Cluster. There is also a propensity for the most massive clusters to be larger in QUMOND and to appear earlier than in ΛCDM, potentially providing an explanation for "pink elephants" …
Andromeda Dwarfs In Light Of Modified Newtonian Dynamics, Stacy S. Mcgaugh
Andromeda Dwarfs In Light Of Modified Newtonian Dynamics, Stacy S. Mcgaugh
Faculty Scholarship
We compare the recently published velocity dispersions for 17 Andromeda dwarf spheroidals with estimates of the modified Newtonian dynamics predictions, based on the luminosities of these dwarfs, with reasonable stellar mass-to-light values and no dark matter. We find that the two are consistent within the uncertainties. We further predict the velocity dispersions of another 10 dwarfs for which only photometric data are currently available. © 2013. The American Astronomical Society. All rights reserved..
Challenges For Λcdm And Mond, Stacy S. Mcgaugh
Challenges For Λcdm And Mond, Stacy S. Mcgaugh
Faculty Scholarship
The Universe on large scales is well described by the ΛCDM cosmological model. There however remain some heavy clouds on our global understanding, especially on galaxy scales, which we review here. While some of these clouds might perhaps disappear through small compensatory adjustments of the model, such as changing the mass of the dark matter particles or accounting better for baryonic physics, others should rather be taken as strong indications that the physics of the dark sector is, at the very least, much richer and complex than currently assumed, and that our understanding of gravity and dynamics might also be …
Modified Newtonian Dynamics (Mond): Observational Phenomenology And Relativistic Extensions, Stacy S. Mcgaugh
Modified Newtonian Dynamics (Mond): Observational Phenomenology And Relativistic Extensions, Stacy S. Mcgaugh
Faculty Scholarship
A wealth of astronomical data indicate the presence of mass discrepancies in the Universe. The motions observed in a variety of classes of extragalactic systems exceed what can be explained by the mass visible in stars and gas. Either (i) there is a vast amount of unseen mass in some novel form - dark matter - or (ii) the data indicate a breakdown of our understanding of dynamics on the relevant scales, or (iii) both. Here, we first review a few outstanding challenges for the dark matter interpretation of mass discrepancies in galaxies, purely based on observations and independently of …
Stellar Populations And The Star Formation Histories Of Lsb Galaxies - Part I: Optical And Hα Imaging, Stacy S. Mcgaugh
Stellar Populations And The Star Formation Histories Of Lsb Galaxies - Part I: Optical And Hα Imaging, Stacy S. Mcgaugh
Faculty Scholarship
This paper presents optical and H imaging for a large sample of LSB galaxies selected from the PSS-II catalogs (Schombert et al., 1992). As noted in previous work, LSB galaxies span a range of luminosities (-10>MV>-20) and sizes (0.3kpc
The Baryonic Tully-Fisher Relation Of Gas-Rich Galaxies As A Test Of Λcdm And Mond, Stacy S. Mcgaugh
The Baryonic Tully-Fisher Relation Of Gas-Rich Galaxies As A Test Of Λcdm And Mond, Stacy S. Mcgaugh
Faculty Scholarship
The baryonic Tully-Fisher relation (BTFR) is an empirical relation between baryonic mass and rotation velocity in disk galaxies. It provides tests of galaxy formation models in ΛCDM and of alternative theories like modified Newtonian dynamics (MOND). Observations of gas-rich galaxies provide a measure of the slope and normalization of the BTFR that is more accurate (if less precise) than that provided by star-dominated spirals, as their masses are insensitive to the details of stellar population modeling. Recent independent data for such galaxies are consistent with M b = AV 4f with A = 47 6 M km -4 s 4. …
Novel Test Of Modified Newtonian Dynamics With Gas Rich Galaxies, Stacy S. Mcgaugh
Novel Test Of Modified Newtonian Dynamics With Gas Rich Galaxies, Stacy S. Mcgaugh
Faculty Scholarship
The current cosmological paradigm, the cold dark matter model with a cosmological constant, requires that the mass-energy of the Universe be dominated by invisible components: dark matter and dark energy. An alternative to these dark components is that the law of gravity be modified on the relevant scales. A test of these ideas is provided by the baryonic Tully-Fisher relation (BTFR), an empirical relation between the observed mass of a galaxy and its rotation velocity. Here, I report a test using gas rich galaxies for which both axes of the BTFR can be measured independently of the theories being tested …
Local Group Dwarf Spheroidals: Correlated Deviations From The Baryonic Tully-Fisher Relation, Stacy S. Mcgaugh
Local Group Dwarf Spheroidals: Correlated Deviations From The Baryonic Tully-Fisher Relation, Stacy S. Mcgaugh
Faculty Scholarship
Local Group dwarf spheroidal satellite galaxies are the faintest extragalactic stellar systems known. We examine recent data for these objects in the plane of the Baryonic Tully-Fisher Relation (BTFR). While some dwarf spheroidals adhere to the BTFR, others deviate substantially. We examine the residuals from the BTFR and find that they are not random. The residuals correlate with luminosity, size, metallicity, ellipticity, and susceptibility of the dwarfs to tidal disruption in the sense that fainter, more elliptical, and tidally more susceptible dwarfs deviate farther from the BTFR. These correlations disfavor stochastic processes and suggest a role for tidal effects. We …
Testing Modified Newtonian Dynamics With Rotation Curves Of Dwarf And Low Surface Brightness Galaxies, Stacy S. Mcgaugh
Testing Modified Newtonian Dynamics With Rotation Curves Of Dwarf And Low Surface Brightness Galaxies, Stacy S. Mcgaugh
Faculty Scholarship
Dwarf and low surface brightness (LSB) galaxies are ideal objects to test modified Newtonian dynamics (MOND), because in most of these galaxies the accelerations fall below the threshold where MOND supposedly applies. We have selected from the literature a sample of 27 dwarf and LSB galaxies. MOND is successful in explaining the general shape of the observed rotation curves for roughly three quarters of the galaxies in the sample presented here. However, for the remaining quarter, MOND does not adequately explain the observed rotation curves. Considering the uncertainties in distances and inclinations for the galaxies in our sample, a small …
Comparing The Dark Matter Halos Of Spiral, Low Surface Brightness, And Dwarf Spheroidal Galaxies, Stacy S. Mcgaugh
Comparing The Dark Matter Halos Of Spiral, Low Surface Brightness, And Dwarf Spheroidal Galaxies, Stacy S. Mcgaugh
Faculty Scholarship
We consider dark masses measured from kinematic tracers at discrete radii in galaxies for which baryonic contributions to overall potentials are either subtracted or negligible. Recent work indicates that rotation curves due to dark matter (DM) halos at intermediate radii in spiral galaxies are remarkably similar, with a mean rotation curve given by log10(V c,DM/(km s-1)) = 1.47+0.15-0.19 + 0.5log10(r/kpc). Independent studies show that while estimates of the dark mass of a given dwarf spheroidal (dSph) galaxy are robust only near the half-light radius, data from the Milky Way's (MW's) dSph satellites are consistent with a narrow range of mass …
The Baryon Content Of Cosmic Structures, Stacy S. Mcgaugh
The Baryon Content Of Cosmic Structures, Stacy S. Mcgaugh
Faculty Scholarship
We make an inventory of the baryonic and gravitating mass in structures ranging from the smallest galaxies to rich clusters of galaxies. We find that the fraction of baryons converted to stars reaches a maximum between M 500 = 1012 and 1013 M ·, suggesting that star formation is most efficient in bright galaxies in groups. The fraction of baryons detected in all forms deviates monotonically from the cosmic baryon fraction as a function of mass. On the largest scales of clusters, most of the expected baryons are detected, while in the smallest dwarf galaxies, fewer than 1% are detected. …
Kinematic And Photometric Evidence For A Bar In Ngc 2683, Stacy S. Mcgaugh
Kinematic And Photometric Evidence For A Bar In Ngc 2683, Stacy S. Mcgaugh
Faculty Scholarship
We present optical long-slit and SparsePak Integral Field Unit emission line spectroscopy along with optical broadband and near-IR images of the edge-on spiral galaxy NGC 2683. We find a multi-valued, figure-of-eight velocity structure in the inner 45″ of the long-slit spectrum and twisted isovelocity contours in the velocity field. We also find, regardless of wavelength, that the galaxy isophotes are boxy. We argue that taken together, these kinematic and photometric features are evidence for the presence of a bar in NGC 2683. We use our data to constrain the orientation and strength of the bar.
The Baryonic Tully-Fisher Relation And Its Implication For Dark Matter Halos, Stacy S. Mcgaugh
The Baryonic Tully-Fisher Relation And Its Implication For Dark Matter Halos, Stacy S. Mcgaugh
Faculty Scholarship
Context. 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.Aims. 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.Methods. We obtained H I synthesis data of 11 dwarf galaxies and derive several independent estimates for the maximum rotation velocity.Results. …
A First Attempt To Calibrate The Baryonic Tully-Fisher Relation With Gas-Dominated Galaxies, Stacy S. Mcgaugh
A First Attempt To Calibrate The Baryonic Tully-Fisher Relation With Gas-Dominated Galaxies, Stacy S. Mcgaugh
Faculty Scholarship
We calibrate the baryonic Tully-Fisher (BTF) relation using a sample of gas-dominated galaxies. These determine the absolute scale of the baryonic mass-rotation speed relation independent of the choice of stellar mass estimator. We find a BTF slope of 3.94±0.07 (random) 0.08 (systematic) and a zero point of 1.79±0.26 (random) ±0.25 (systematic). We apply this relation to estimate the stellar masses of star-dominated galaxies. This procedure reproduces the trend of mass-to-light ratio with color predicted by population synthesis models. The normalization is also correct, consistent with empirical estimates of the initial mass function used in such models.
Chandra Observations Of Nuclear X-Ray Emission From Low Surface Brightness Galaxies, Stacy S. Mcgaugh
Chandra Observations Of Nuclear X-Ray Emission From Low Surface Brightness Galaxies, Stacy S. Mcgaugh
Faculty Scholarship
We present Chandra detections of X-ray emission from the active galactic nuclei (AGN) in two giant low surface brightness (LSB) galaxies, UGC 2936 and UGC 1455. Their X-ray luminosities are 1.8 × 1042 ergs s -1 and 1.1 × 1040 ergs s-1 respectively. Of the two galaxies, UGC 2936 is radio loud. Together with another LSB galaxy UGC 6614 (XMM-Newton archival data) both appear to lie above the X-ray-radio fundamental plane, and their AGN have black hole masses that are low compared to similar galaxies lying on the correlation. However, the bulges in these galaxies are well developed, and we …
Constraining The Nfw Potential With Observations And Modeling Of Low Surface Brightness Galaxy Velocity Fields, Stacy S. Mcgaugh, J. Christopher Mihos
Constraining The Nfw Potential With Observations And Modeling Of Low Surface Brightness Galaxy Velocity Fields, Stacy S. Mcgaugh, J. Christopher Mihos
Faculty Scholarship
We model the Navarro-Frenk-White (NFW) potential to determine if, and under what conditions, the NFW halo appears consistent with the observed velocity fields of low surface brightness (LSB) galaxies. We present mock DensePak Integral Field Unit (IFU) velocity fields and rotation curves of axisymmetric and nonaxisymmetric potentials that are well matched to the spatial resolution and velocity range of our sample galaxies. We find that the DensePak IFU can accurately reconstruct the velocity field produced by an axisymmetric NFW potential and that a tilted-ring fitting program can successfully recover the corresponding NFW rotation curve. We also find that nonaxisymmetric potentials …
Vimos-Vlt Integral Field Kinematics Of The Giant Low Surface Brightness Galaxy Eso 323-G064, Stacy S. Mcgaugh
Vimos-Vlt Integral Field Kinematics Of The Giant Low Surface Brightness Galaxy Eso 323-G064, Stacy S. Mcgaugh
Faculty Scholarship
Aims. We have studied the bulge and the disk kinematics of the giant low surface brightness galaxy ESO 323-G064 in order to investigate its dynamical properties and the radial mass profile of the dark matter (DM) halo. Methods. We observed the galaxy with integral field spectroscopy (VLT/VIMOS, in IFU configuration), measured the positions of the ionized gas by fitting Gaussian functions to the [O III] λλ4959,5007 and Hβ emission lines, and fit stellar templates to the galaxy spectra to determine velocity and velocity dispersions. We modeled the stellar kinematics in the bulge with spherical Isotropie Jeans models and explored the …
Milky Way Mass Models And Mond, Stacy S. Mcgaugh
Milky Way Mass Models And Mond, Stacy S. Mcgaugh
Faculty Scholarship
Using the Tuorla-Heidelberg model for the mass distribution of the Milky Way, I determine the rotation curve predicted by MOND (modified Newtonian dynamics). The result is in good agreement with the observed terminal velocities interior to the solar radius and with estimates of the Galaxy's rotation curve exterior thereto. There are no fit parameters: given the mass distribution, MOND provides a good match to the rotation curve. The Tuorla-Heidelberg model does allow for a variety of exponential scale lengths; MOND prefers short scale lengths in the range 2.0 kpc ≲ Rd ≲ 2.5 kpc. The favored value of Rd depends …
Mass Models For Low Surface Brightness Galaxies With High-Resolution Optical Velocity Fields, Stacy S. Mcgaugh
Mass Models For Low Surface Brightness Galaxies With High-Resolution Optical Velocity Fields, Stacy S. Mcgaugh
Faculty Scholarship
We present high-resolution optical velocity fields from DensePak integral field spectroscopy, along with derived rotation curves, for a sample of low surface brightness galaxies. In the limit of no baryons, we fit the NFW and pseudoisothermal halo models to the data and find the rotation curve shapes and halo central densities to be better described by the isothermal halo. For those galaxies with photometry, we present halo fits for three assumptions of the stellar mass-to-light ratio, Υ*. We find that the velocity contribution from the baryons is significant enough in the maximum disk case that maximum disk and the NFW …
The Rotation Velocity Attributable To Dark Matter At Intermediate Radii In Disk Galaxies, Stacy S. Mcgaugh
The Rotation Velocity Attributable To Dark Matter At Intermediate Radii In Disk Galaxies, Stacy S. Mcgaugh
Faculty Scholarship
We examine the amplitude of the rotation velocity that can be attributed to the dark matter halos of disk galaxies, focusing on well-measured intermediate radii. The data for 60 galaxies spanning a large range of mass and Hubble types, taken together, are consistent with a dark halo velocity log Vh = C + B log R with C = 1.47-0.19+0.15 and B ≈1/2 over the range of 1 < R < 74 kpc. The range in C stems from different choices of the stellar mass estimator, from minimum to maximum disk. For all plausible choices of stellar mass, the implied densities of the dark halos are lower than expected from structure formation simulations in ACDM, which anticipate C > 1.6. This problem is not specific to a particular type of galaxy or to the innermost region of the halo (cusp or core); the velocity attributable to dark matter is too low …
Co Detection And Millimeter Continuum Emission From Low Surface Brightness Galaxies, Stacy S. Mcgaugh
Co Detection And Millimeter Continuum Emission From Low Surface Brightness Galaxies, Stacy S. Mcgaugh
Faculty Scholarship
We present BIMA and IRAM CO (1-0) observations of seven low surface brightness (LSB) galaxies, including three large spiral galaxies with faint disks but prominent bulges and four relatively small LSB galaxies with irregular disks. The giant LSB galaxies are UGC 5709, UGC 6614, and F568-6 (Malin 2). The smaller LSB galaxies are NGC 5585, UGC 4115, UGC 5209, and F583-1. The galaxies were selected based on their relatively high metallicity and apparent signs of star formation in their disks. The BIMA maps suggested the presence of molecular gas in two of the giant LSB galaxies: F568-6 and UGC 6614. …
High-Resolution Optical Velocity Fields Of 11 Low Surface Brightness Galaxies, Stacy S. Mcgaugh
High-Resolution Optical Velocity Fields Of 11 Low Surface Brightness Galaxies, Stacy S. Mcgaugh
Faculty Scholarship
We present high-resolution two-dimensional velocity fields from integral field spectroscopy, along with derived rotation curves for 11 low surface brightness galaxies. We fit NFW and pseudoisothermal halo models to the new data combined with previous long-slit and H I data. In most cases, we find the pseudoisothermal halo to better represent the data than the NFW halo, as the NFW concentrations are often lower than expected for a ACDM cosmology. We also compare our results to previous studies and find that including the new two-dimensional optical data does not significantly alter the halo parameters but does decrease the uncertainties by …
The Compression Of Dark Matter Halos By Baryonic Infall, Stacy S. Mcgaugh
The Compression Of Dark Matter Halos By Baryonic Infall, Stacy S. Mcgaugh
Faculty Scholarship
The initial radial density profiles of dark matter halos are laid down by gravitational collapse in hierarchical structure formation scenarios and are subject to further compression as baryons cool and settle to the halo centers. Here we describe an explicit implementation of the algorithm, originally developed by Young, to calculate changes to the density profile as the result of adiabatic infall in a spherical halo model. Halos with random motion are more resistant to compression than are those in which random motions are neglected, which is a key weakness of the simple method widely employed. Young's algorithm results in density …
The Baryonic Tully-Fisher Relation Of Galaxies With Extended Rotation Curves And The Stellar Mass Of Rotating Galaxies, Stacy S. Mcgaugh
The Baryonic Tully-Fisher Relation Of Galaxies With Extended Rotation Curves And The Stellar Mass Of Rotating Galaxies, Stacy S. Mcgaugh
Faculty Scholarship
I investigate the baryonic Tully-Fisher relation for a sample of galaxies with extended 21 cm rotation curves spanning the range 20 km s-1 ≲ Vf ≤ 300 km s-1. A variety of scalings of the stellar mass-to-light ratio Υ* are considered. For each prescription for Υ*, I give fits of the form Md = AVfx. Presumably, the prescription that comes closest to the correct value will minimize the scatter in the relation. The fit with minimum scatter has A = 50 M⊙ km-4 s4 and x = 4. This relation holds over five decades in mass. Galaxy color, stellar fraction, …
Balance Of Dark And Luminous Mass In Rotating Galaxies, Stacy S. Mcgaugh
Balance Of Dark And Luminous Mass In Rotating Galaxies, Stacy S. Mcgaugh
Faculty Scholarship
A fine balance between dark and baryonic mass is observed in spiral galaxies. As the contribution of the baryons to the total rotation velocity increases, the contribution of the dark matter decreases by a compensating amount. This poses a fine-tuning problem for ÎCDM galaxy formation models, and may point to new physics for dark matter particles or even a modification of gravity.
Confrontation Of Modified Newtonian Dynamics Predictions With Wilkinson Microwave Anisotropy Probe First Year Data, Stacy S. Mcgaugh
Confrontation Of Modified Newtonian Dynamics Predictions With Wilkinson Microwave Anisotropy Probe First Year Data, Stacy S. Mcgaugh
Faculty Scholarship
I present a model devoid of nonbaryonic cold dark matter (CDM) that provides an acceptable fit to the Wilkinson Microwave Anisotropy Probe (WMAP) data for the power spectrum of temperature fluctuations in the cosmic background radiation. An a priori prediction of such no-CDM models was a first-to-second peak amplitude ratio A1:2 ≈ 2.4. WMAP measures A1:2 = 2.34 ± 0.09. The baryon content is the dominant factor in fixing this ratio; no-CDM models that are consistent with the WMAP data are also consistent with constraints on the baryon density from the primordial abundances of 2H, 4He, and 7Li. However, in …
The Mass Discrepancy-Acceleration Relation: Disk Mass And The Dark Matter Distribution, Stacy S. Mcgaugh
The Mass Discrepancy-Acceleration Relation: Disk Mass And The Dark Matter Distribution, Stacy S. Mcgaugh
Faculty Scholarship
The mass discrepancy in disk galaxies is shown to be well correlated with acceleration, increasing systematically with decreasing acceleration below a critical scale a0 ≈ 3700 km2 s-2 kpc -1 = 1.2 × 10-10 m s-2. For each galaxy, there is an optimal choice of stellar mass-to-light ratio that minimizes the scatter in this mass discrepancy-acceleration relation. The same mass-to-light ratios also minimize the scatter in the baryonic Tully-Fisher relation and are in excellent agreement with the expectations of stellar population synthesis. Once the disk mass is determined in this fashion, the dark matter distribution is specified. The circular velocity …
A Limit On The Cosmological Mass Density And Power Spectrum From The Rotation Curves Of Low Surface Brightness Galaxies, Stacy S. Mcgaugh
A Limit On The Cosmological Mass Density And Power Spectrum From The Rotation Curves Of Low Surface Brightness Galaxies, Stacy S. Mcgaugh
Faculty Scholarship
The concentrations of the cuspy dark matter halos predicted by simulations of cold dark matter are related to the cosmology in which the halos form. Observational constraints on halo concentration therefore map into constraints on cosmological parameters. In order to explain the observed concentrations of dark matter-dominated low surface brightness galaxies, we require a cosmology with rather little power on galaxy scales. Formally, we require σ 8Γ0.6 < 0.23, where Γ0.6 is a modified shape parameter appropriate to this problem. Practically, this means that either Ωm < 0.2 or σ8 < 0.8. These limits apply as long as we insist that the cuspy halos found in simulations must describe the halos of low surface brightness galaxies. A low-density cosmology helps with the low observed concentrations, but it offers no explanation of the many cases where the shape of the density profile deviates from the predicted cuspy form. These cases must have suffered very extensive mass redistribution if the current halo formation picture is not to fail outright. It is far from clear whether any of the mass redistribution mechanisms that have been suggested (e.g., feedback) are viable.