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Articles 1 - 30 of 116
Full-Text Articles in Astrophysics and Astronomy
The Baryonic Tully-Fisher Relation. Ii. Stellar Mass Models, Francis Duey, Stacy Mcgaugh
The Baryonic Tully-Fisher Relation. Ii. Stellar Mass Models, Francis Duey, Stacy Mcgaugh
Faculty Scholarship
We present new color-ϒ* (mass-to-light ratio) models to convert Wide-field Infrared Survey Explorer W1 fluxes into stellar masses. We outline a range of possible star formation histories and chemical evolution scenarios to explore the confidence limits of stellar population models on the value of ϒ*. We conclude that the greatest uncertainties (around 0.1 dex in ϒ*) occur for the bluest galaxies with the strongest variation in recent star formation. For high-mass galaxies, the greatest uncertainty arises from the proper treatment of bulge-disk separation in which to apply different ϒ* relations appropriate for those differing underlying stellar populations. We compare our …
Accelerated Structure Formation: The Early Emergence Of Massive Galaxies And Clusters Of Galaxies, Stacy S. Mcgaugh
Accelerated Structure Formation: The Early Emergence Of Massive Galaxies And Clusters Of Galaxies, Stacy S. Mcgaugh
Faculty Scholarship
Galaxies in the early Universe appear to have grown too big too fast, assembling into massive, monolithic objects more rapidly than anticipated in the hierarchical Lambda cold dark matter (ΛCDM) structure formation paradigm. The available photometric data are consistent with there being a population of massive galaxies that form early (z ≳ 10) and quench rapidly over a short (≲1 Gyr) timescale, consistent with the traditional picture for the evolution of giant elliptical galaxies. Similarly, kinematic observations as a function of redshift show that massive spirals and their scaling relations were in place at early times. Explaining the early emergence …
Mhongoose Discovery Of A Gas-Rich Low Surface Brightness Galaxy In The Dorado Group, Stacy Mcgaugh
Mhongoose Discovery Of A Gas-Rich Low Surface Brightness Galaxy In The Dorado Group, Stacy Mcgaugh
Faculty Scholarship
We present the discovery of a low-mass, gas-rich low surface brightness galaxy in the Dorado group, at a distance of 17.7 Mpc. Combining deep MeerKAT 21-cm observations from the MeerKAT Hi Observations of Nearby Galactic Objects: Observing Southern Emitters (MHONGOOSE) survey with deep photometric images from the VST Early-type Galaxy Survey (VEGAS) we find a stellar and neutral atomic hydrogen (H i) gas mass of M∗ = 2:23 × 106M⊙ and MHI = 1:68 × 106 M⊙, respectively. This low surface brightness galaxy is the lowest-mass Hi detection found in a group beyond the local Universe (D ≳ 10 Mpc). …
Mhongoose: A Meerkat Nearby Galaxy H I Survey, Stacy S. Mcgaugh
Mhongoose: A Meerkat Nearby Galaxy H I Survey, Stacy S. Mcgaugh
Faculty Scholarship
The MHONGOOSE (MeerKAT H i Observations of Nearby Galactic Objects: Observing Southern Emitters) survey maps the distribution and kinematics of the neutral atomic hydrogen (H i) gas in and around 30 nearby star-forming spiral and dwarf galaxies to extremely low H i column densities. The H i column density sensitivity (3σ over 16 km s−1) ranges from ∼5 × 1017 cm−2 at 9000 resolution to ∼4 × 1019 cm−2 at the highest resolution of 700. The H i mass sensitivity (3σ over 50 km s−1) is ∼5.5×105 M at a distance of 10 Mpc (the median distance of the sample …
Satellite Group Infall Into The Milky Way: Exploring The Crater-Leo Case With New Hst Proper Motions, Stacy S. Mcgaugh
Satellite Group Infall Into The Milky Way: Exploring The Crater-Leo Case With New Hst Proper Motions, Stacy S. Mcgaugh
Faculty Scholarship
Context. Within Λ cold dark matter (ΛCDM) simulations, Milky Way-like galaxies accrete some of their satellite galaxies in groups of 3–5 members rather than individually, and this has been suggested as a possible mechanism driving the formation of satellite planes. Objects accreted in groups are expected to share similar specific total energy and angular momentum, and to also have identical orbital planes and directions. Aims. Looking at observatio ns of Milky Way satellites, the dwarf galaxies Leo II, IV, V, and Crater II, and the star cluster Crater 1 were proposed to be a vestige of group infall. The suggested …
Indefinitely Flat Circular Velocities And The Baryonic Tully-Fisher Relation From Weak Lensing, Tobias Mistele, Stacy Mcgaugh
Indefinitely Flat Circular Velocities And The Baryonic Tully-Fisher Relation From Weak Lensing, Tobias Mistele, Stacy Mcgaugh
Faculty Scholarship
We use a new deprojection formula to infer the gravitational potential around isolated galaxies from weak gravitational lensing. The results imply circular velocity curves that remain flat for hundreds of kiloparsecs, greatly extending the classic result from 21 cm observations. Indeed, there is no clear hint of a decline out to 1 Mpc, well beyond the expected virial radii of dark matter halos. Binning the data by mass reveals a correlation with the flat circular speed that closely agrees with the baryonic Tully-Fisher relation known from kinematic data. These results apply to both early- and late-type galaxies, indicating a common …
The Baryonic Tully-Fisher Relation. I. Wise/Spitzer Photometry, Francis Duey, Stacy Mcgaugh
The Baryonic Tully-Fisher Relation. I. Wise/Spitzer Photometry, Francis Duey, Stacy Mcgaugh
Faculty Scholarship
We present Wide-field Infrared Survey Explorer (WISE) W1 photometry of the Spitzer Photometry and Accurate Rotation Curves sample. The baseline of near-IR fluxes is established for use by stellar mass models, a key component to the baryonic Tully-Fisher relation and other kinematic galaxies scaling relations. We focus this paper on determination of the characteristics of the W1 fluxes compared to IRAC 3.6 μm fluxes, internal accuracy limitations from photometric techniques, external accuracy by comparison to other work in the literature and the range of W1 to IRAC 3.6 μm colors. We outline the behavior of SDSS g, W1 and IRAC …
A Distinct Radial Acceleration Relation Across The Brightest Cluster Galaxies And Galaxy Clusters, Pengfei Li, Stacy S. Mcgaugh
A Distinct Radial Acceleration Relation Across The Brightest Cluster Galaxies And Galaxy Clusters, Pengfei Li, Stacy S. Mcgaugh
Faculty Scholarship
Recent studies reveal a radial acceleration relation (RAR) in galaxies, which illustrates a tight empirical correlation connecting the observational acceleration and the baryonic acceleration with a characteristic acceleration scale. However, a distinct RAR has been revealed on brightest cluster galaxy (BCG) cluster scales with a seventeen-times-larger acceleration scale due to the gravitational lensing effect. In this work, we systematically explore the acceleration and mass correlations between dynamical and baryonic components in 50 BCGs. To investigate the dynamical RAR in BCGs, we derived their dynamical accelerations from the stellar kinematics using the Jeans equation through Abel inversion and adopted the baryonic …
Radial Acceleration Relation Of Galaxies With Joint Kinematic And Weak-Lensing Data, Tobias Mistele, Stacy S. Mcgaugh
Radial Acceleration Relation Of Galaxies With Joint Kinematic And Weak-Lensing Data, Tobias Mistele, Stacy S. Mcgaugh
Faculty Scholarship
We combine kinematic and gravitational lensing data to construct the Radial Acceleration Relation (RAR) of galaxies over a large dynamic range. We improve on previous weak-lensing studies in two ways. First, we compute stellar masses using the same stellar population model as for the kinematic data. Second, we introduce a new method for converting excess surface density profiles to radial accelerations. This method is based on a new deprojection formula which is exact, computationally efficient, and gives smaller systematic uncertainties than previous methods. We find that the RAR inferred from weak-lensing data smoothly continues that inferred from kinematic data by …
Bst1047+1156: A (Failing) Ultradiffuse Tidal Dwarf In The Leo I Group, J. Christopher Mihos, Stacy S. Mcgaugh
Bst1047+1156: A (Failing) Ultradiffuse Tidal Dwarf In The Leo I Group, J. Christopher Mihos, Stacy S. Mcgaugh
Faculty Scholarship
We use deep Hubble Space Telescope imaging to study the resolved stellar populations in BST1047+1156, a gas-rich, ultradiffuse dwarf galaxy found in the intragroup environment of the Leo I galaxy group. While our imaging reaches approximately two magnitudes below the tip of the red giant branch at the Leo I distance of 11 Mpc, we find no evidence for an old red giant sequence that would signal an extended star formation history for the object. Instead, we clearly detect the red and blue helium-burning sequences of its stellar populations, as well as the fainter blue main sequence, all indicative of …
Discord In Concordance Cosmology And Anomalously Massive Early Galaxies, Stacy S. Mcgaugh
Discord In Concordance Cosmology And Anomalously Massive Early Galaxies, Stacy S. Mcgaugh
Faculty Scholarship
Cosmological parameters are constrained by a wide variety of observations. We examine the concordance diagram for modern measurements of the Hubble constant, the shape parameter from the large-scale structure, the cluster baryon fraction, and the age of the universe, all from non-CMB data. There is good agreement for (Formula presented.) and (Formula presented.). This concordance value is indistinguishable from the WMAP3 cosmology but is not consistent with that of Planck: there is a tension in (Formula presented.) as well as (Formula presented.). These tensions have emerged as progressively higher multipoles have been incorporated into CMB fits. This temporal evolution is …
Superfluid Dark Matter In Tension With Weak Gravitational Lensing Data, Tobias Mistele, Stacy S. Mcgaugh
Superfluid Dark Matter In Tension With Weak Gravitational Lensing Data, Tobias Mistele, Stacy S. Mcgaugh
Faculty Scholarship
Superfluid dark matter (SFDM) is a model that promises to reproduce the successes of both particle dark matter on cosmological scales and those of Modified Newtonian Dynamics (MOND) on galactic scales. SFDM reproduces MOND only up to a certain distance from the galactic center, and only for kinematic observables: it does not affect trajectories of light. We test whether this is consistent with a recent analysis of weak gravitational lensing that has probed accelerations around galaxies to unprecedentedly large radii. This analysis found the data to be close to the prediction of MOND, suggesting they might be difficult to fit …
Measuring Galaxy Cluster Mass Profiles Into The Low-Acceleration Regime With Galaxy Kinematics, Pengfei Li, Stacy S. Mcgaugh
Measuring Galaxy Cluster Mass Profiles Into The Low-Acceleration Regime With Galaxy Kinematics, Pengfei Li, Stacy S. Mcgaugh
Faculty Scholarship
We probed the dynamical mass profiles of ten galaxy clusters from the HIghest X-ray FLUx Galaxy Cluster Sample (HIFLUGCS) using galaxy kinematics. We numerically solved the spherical Jeans equation and parameterize the dynamical mass profile and the galaxy velocity anisotropy profile using two general functions to ensure that our results are not biased toward any specific model. The mass-velocity anisotropy degeneracy is ameliorated by using two virial shape parameters that depend on the fourth moment of velocity distribution. The resulting velocity anisotropy estimates consistently show a nearly isotropic distribution in the inner regions, with an increasing radial anisotropy toward large …
Aether Scalar Tensor Theory Confronted With Weak Lensing Data At Small Accelerations, Tobias Mistele, Stacy S. Mcgaugh
Aether Scalar Tensor Theory Confronted With Weak Lensing Data At Small Accelerations, Tobias Mistele, Stacy S. Mcgaugh
Faculty Scholarship
Context. The recently proposed aether scalar tensor (AeST) model reproduces both the successes of particle dark matter on cosmological scales and those of modified Newtonian dynamics (MOND) on galactic scales. But the AeST model reproduces MOND only up to a certain maximum galactocentric radius. Since MOND is known to fit very well to observations at these scales, this raises the question of whether the AeST model comes into tension with data. Aims. We tested whether or not the AeST model is in conflict with observations using a recent analysis of data for weak gravitational lensing. Methods. We solved the equations …
Cold Gas Disks In Main-Sequence Galaxies At Cosmic Noon: Low Turbulence, Flat Rotation Curves, And Disk-Halo Degeneracy, Stacy S. Mcgaugh
Cold Gas Disks In Main-Sequence Galaxies At Cosmic Noon: Low Turbulence, Flat Rotation Curves, And Disk-Halo Degeneracy, Stacy S. Mcgaugh
Faculty Scholarship
We study the dynamics of cold molecular gas in two main-sequence galaxies at cosmic noon (zC-488879 at z ≃ 1.47 and zC-400569 at z ≃ 2.24) using new high-resolution ALMA observations of multiple 12CO transitions. For zC-400569 we also reanalyze high-quality Hα data from the SINS/zC-SINF survey. We find that (1) both galaxies have regularly rotating CO disks and their rotation curves are flat out to ∼8 kpc contrary to previous results pointing to outer declines in the rotation speed Vrot; (2) the intrinsic velocity dispersions are low (σCO ≲ 15 km s-1 for CO and σHα ≲ 37 km …
Estimating The Oblateness Of Dark Matter Halos Using Neutral Hydrogen Velocity Dispersion, Stacy S. Mcgaugh
Estimating The Oblateness Of Dark Matter Halos Using Neutral Hydrogen Velocity Dispersion, Stacy S. Mcgaugh
Faculty Scholarship
We derive the oblateness parameter q of the dark matter halo of a sample of gas-rich, face-on disk galaxies. We have assumed that the halos are triaxial in shape but their axes in the disk plane (a and b) are equal, so that q = c/a measures the halo flattening. We have used the H i velocity dispersion, derived from the stacked H i emission lines and the disk surface density, determined from the H i flux distribution, to determine the disk potential and the halo shape at the R 25 and 1.5R 25 radii. We have applied our model …
Deep Narrowband Photometry Of The M101 Group: Strong-Line Abundances Of 720 H Ii Regions, Ray Garner Iii, J. Christopher Mihos, Paul Harding, Stacy S. Mcgaugh
Deep Narrowband Photometry Of The M101 Group: Strong-Line Abundances Of 720 H Ii Regions, Ray Garner Iii, J. Christopher Mihos, Paul Harding, Stacy S. Mcgaugh
Faculty Scholarship
We present deep, narrowband imaging of the nearby spiral galaxy M101 and its satellites to analyze the oxygen abundances of their H ii regions. Using Case Western Reserve University’s Burrell Schmidt telescope, we add to the narrowband data set of the M101 Group, consisting of Hα, Hβ, and [O iii] emission lines and the blue [O ii] λ3727 emission line for the first time. This allows for complete spatial coverage of the oxygen abundance of the entire M101 Group. We used the strong-line ratio R 23 to estimate oxygen abundances for the H ii regions in our sample, utilizing three …
Testing Modified Gravity Theories With Numerical Solutions Of The External Field Effect In Rotationally Supported Galaxies, Stacy S. Mcgaugh
Testing Modified Gravity Theories With Numerical Solutions Of The External Field Effect In Rotationally Supported Galaxies, Stacy S. Mcgaugh
Faculty Scholarship
The strong equivalence principle is violated by gravity theories of Milgromian dynamics [modified Newtonian dynamics (MOND)] through the action of the external field effect. We test two different Lagrangian theories Aquadratic-Lagrangian (AQUAL) and quasilinear MOND (QUMOND) based on their numerical solutions of the external field effect, by comparing two independent estimates of the mean external field strength of the nearby universe: a theory-deduced value from fitting the outer rotation curves of 114 galaxies and an empirical value from the large-scale distribution of cosmic baryons. The AQUAL-deduced external field strength from rotation curves agrees with that from the large-scale cosmic environment, …
Incorporating Baryon-Driven Contraction Of Dark Matter Halos In Rotation Curve Fits, Pengfei Li, Stacy S. Mcgaugh
Incorporating Baryon-Driven Contraction Of Dark Matter Halos In Rotation Curve Fits, Pengfei Li, Stacy S. Mcgaugh
Faculty Scholarship
The condensation of baryons within a dark matter (DM) halo during galaxy formation should result in some contraction of the halo as the combined system settles into equilibrium. We quantify this effect on the cuspy primordial halos predicted by DM-only simulations for the baryon distributions observed in the galaxies of the SPARC database. We find that the DM halos of high surface brightness galaxies (with Σeff 3; 100L pc-2 at 3.6 μm) experience strong contraction. Halos become more cuspy as a result of compression: the inner DM density slope increases with the baryonic surface mass density. We iteratively fit rotation …
Galactic Mass-To-Light Ratios With Superfluid Dark Matter, Tobias Mistele, Stacy S. Mcgaugh
Galactic Mass-To-Light Ratios With Superfluid Dark Matter, Tobias Mistele, Stacy S. Mcgaugh
Faculty Scholarship
Context. We make rotation curve fits to test the superfluid dark matter model. Aims. In addition to verifying that the resulting fits match the rotation curve data reasonably well, we aim to evaluate how satisfactory they are with respect to two criteria, namely, how reasonable the resulting stellar mass-to-light ratios are and whether the fits end up in the regime of superfluid dark matter where the model resembles modified Newtonian dynamics (MOND). Methods. We fitted the superfluid dark matter model to the rotation curves of 169 galaxies in the SPARC sample. Results. We found that the mass-to-light ratios obtained with …
The Effect Of Adiabatic Compression On Dark Matter Halos And The Radial Acceleration Relation, Pengfei Li, Stacy S. Mcgaugh
The Effect Of Adiabatic Compression On Dark Matter Halos And The Radial Acceleration Relation, Pengfei Li, Stacy S. Mcgaugh
Faculty Scholarship
We use a semiempirical model to investigate the radial acceleration relation (RAR) in a cold dark matter (CDM) framework. Specifically, we build 80 model galaxies covering the same parameter space as the observed galaxies in the SPARC database, assigning them to dark matter (DM) halos using abundance-matching and halo mass-concentration relations. We consider several abundance-matching relations, finding some to be a better match to the kinematic data than others. We compute the unavoidable gravitational interactions between baryons and their DM halos, leading to an overall compression of the original Navarro-Frenk-White (NFW) halos. Before halo compression, high-mass galaxies lie approximately on …
Stellar Mass-To-Light Ratios: Composite Bulge+Disk Models And The Baryonic Tully-Fisher Relation, Stacy S. Mcgaugh
Stellar Mass-To-Light Ratios: Composite Bulge+Disk Models And The Baryonic Tully-Fisher Relation, Stacy S. Mcgaugh
Faculty Scholarship
We present stellar population models to calculate the mass-to-light ratio (Γ∗) based on galaxies' colors ranging from GALEX far-UV to Spitzer IRAC1 at 3.6 μm. We present a new composite bulge+disk Γ∗ model that considers the varying contribution from bulges and disks based on their optical and near-IR colors. Using these colors, we build plausible star formation histories and chemical enrichment scenarios based on the star formation rate-stellar mass and mass-metallicity correlations for star-forming galaxies. The most accurate prescription is to use the actual colors for the bulge and disk components to constrain Γ∗; however, a reasonable bulge+disk model plus …
Testing The Strong Equivalence Principle. Ii. Relating The External Field Effect In Galaxy Rotation Curves To The Large-Scale Structure Of The Universe, Stacy S. Mcgaugh
Testing The Strong Equivalence Principle. Ii. Relating The External Field Effect In Galaxy Rotation Curves To The Large-Scale Structure Of The Universe, Stacy S. Mcgaugh
Faculty Scholarship
Theories of modified gravity generically violate the strong equivalence principle, so that the internal dynamics of a self-gravitating system in freefall depends on the strength of the external gravitational field (the external field effect). We fit rotation curves (RCs) from the SPARC database with a model inspired by Milgromian dynamics (MOND), which relates the outer shape of an RC to the external Newtonian field from the large-scale baryonic matter distribution through a dimensionless parameter e N. We obtain a > 4σ statistical detection of the external field effect (i.e. e N > 0 on average), confirming previous results. We then locate the …
The Baryonic Tully-Fisher Relation In The Local Group And The Equivalent Circular Velocity Of Pressure-Supported Dwarfs, Stacy S. Mcgaugh, Pengfei Li, Tiffany Visgaitis
The Baryonic Tully-Fisher Relation In The Local Group And The Equivalent Circular Velocity Of Pressure-Supported Dwarfs, Stacy S. Mcgaugh, Pengfei Li, Tiffany Visgaitis
Faculty Scholarship
We explore the baryonic Tully-Fisher relation in the Local Group. Rotationally-supported Local Group galaxies adhere precisely to the relation defined by more distant galaxies. For pressure-supported dwarf galaxies, we determine the scaling factor β c that relates their observed velocity dispersion to the equivalent circular velocity of rotationally-supported galaxies of the same mass such that V o = β c σ ∗. For a typical mass-to-light ratio ϒ∗ = 2 M /L in the V band, we find that β c = 2. More generally, β {c}=0.25∗ +0.226. This provides a common kinematic scale relating pressure and rotationally-supported dwarf galaxies.
Mass-Velocity Dispersion Relation In Manga Brightest Cluster Galaxies, Stacy S. Mcgaugh
Mass-Velocity Dispersion Relation In Manga Brightest Cluster Galaxies, Stacy S. Mcgaugh
Faculty Scholarship
We investigate a kinematic scaling relation between the baryonic mass and the flat velocity dispersion, i.e., mass- velocity dispersion relation (MVDR), from the brightest cluster galaxies (BCGs) to the galaxy clusters. In our studies, the baryonic mass of BCGs is mainly estimated by photometry. The velocity dispersion profiles are explored with the integrated field unit by Mapping Nearby Galaxies at Apache Point Observatory (MaNGA). For the first time, we reveal two significant results with 54 MaNGA BCGs: (1) the flat velocity dispersion profiles; (2) a tight empirical relation on the BCG-cluster scale together with cluster samples, i.e., MVDR, = - …
Testing Galaxy Formation And Dark Matter With Low Surface Brightness Galaxies, Stacy S. Mcgaugh
Testing Galaxy Formation And Dark Matter With Low Surface Brightness Galaxies, Stacy S. Mcgaugh
Faculty Scholarship
Galaxies are the basic structural element of the universe; galaxy formation theory seeks to explain how these structures came to be. I trace some of the foundational ideas in galaxy formation, with emphasis on the need for non-baryonic cold dark matter. Many elements of early theory did not survive contact with observations of low surface brightness galaxies, leading to the need for auxiliary hypotheses like feedback. The failure points often trace to the surprising predictive successes of an alternative to dark matter, the Modified Newtonian Dynamics (MOND). While dark matter models are flexible in accommodating observations, they do not provide …
Comparing The Inner And Outer Star-Forming Complexes In The Nearby Spiral Galaxies Ngc 628, Ngc 5457, And Ngc 6946 Using Uvit Observations, Stacy S. Mcgaugh
Comparing The Inner And Outer Star-Forming Complexes In The Nearby Spiral Galaxies Ngc 628, Ngc 5457, And Ngc 6946 Using Uvit Observations, Stacy S. Mcgaugh
Faculty Scholarship
We present a far-UV (FUV) study of the star-forming complexes (SFCs) in three nearby galaxies using the Ultraviolet Imaging Telescope. The galaxies are close to face-on and show significant outer disk star formation. Two of them are isolated (NGC 628 and NGC 6946), and one is interacting with distant companions (NGC 5457). We compared the properties of the SFCs inside and outside the optical radius (R 25). We estimated the sizes, star formation rates (SFRs), metallicities, and Toomre Q parameter of the SFCs. We find that the outer disk SFCs are at least 10 times smaller in area than those …
Mass-Velocity Dispersion Relation In Hiflugcs Galaxy Clusters, Pengfei Li, Stacy S. Mcgaugh
Mass-Velocity Dispersion Relation In Hiflugcs Galaxy Clusters, Pengfei Li, Stacy S. Mcgaugh
Faculty Scholarship
We investigate the mass-velocity dispersion relation (MVDR) in 29 galaxy clusters in the HIghest X-ray FLUx Galaxy Cluster Sample (HIFLUGCS). We measure the spatially resolved, line-of-sight velocity dispersion profiles of these clusters, which we find to be mostly flat at large radii, reminiscent of the rotation curves of galaxies. We discover a tight empirical relation between the baryonic mass M bar and the flat velocity dispersion σ of the member galaxies, i.e., MVDR,, with the lognormal intrinsic scatter of 12 -3 +3. The residuals of the MVDR are uncorrelated with other cluster properties like temperature, cluster radius, baryonic mass surface …
A Cautionary Tale In Fitting Galaxy Rotation Curves With Bayesian Techniques: Does Newton's Constant Vary From Galaxy To Galaxy?, Pengfei Li, Stacy Mcgaugh
A Cautionary Tale In Fitting Galaxy Rotation Curves With Bayesian Techniques: Does Newton's Constant Vary From Galaxy To Galaxy?, Pengfei Li, Stacy Mcgaugh
Faculty Scholarship
The application of Bayesian techniques to astronomical data is generally non-trivial because the fitting parameters can be strongly degenerated and the formal uncertainties are themselves uncertain. An example is provided by the contradictory claims over the presence or absence of a universal acceleration scale (g†) in galaxies based on Bayesian fits to rotation curves. To illustrate this we present an analysis in which the Newtonian gravitational constant GN is allowed to vary from galaxy to galaxy when fitting rotation curves from the SPARC database, in analogy to g† in the recently debated Bayesian analyses. When imposing flat priors on GN, …
Anomalous Stellar Populations In Low-Surface-Brightness Galaxies, Stacy S. Mcgaugh
Anomalous Stellar Populations In Low-Surface-Brightness Galaxies, Stacy S. Mcgaugh
Faculty Scholarship
We present new Hubble Space Telescope WFC3 near-IR observations of the color-magnitude diagrams (CMDs) in two low-surface-brightness galaxies, F575-3 and F615-1, notable for having no current star formation based on a lack of Ha emission. Key features of the near-IR CMDs are resolved, such as the red giant branch (RGB), the asymptotic giant branch (AGB) region, and the top of the blue main sequence. F575-3 has the bluest RGB of any CMD in the literature, indicating an extremely low mean metallicity. F615-1 has unusually wide RGB and AGB sequences, suggesting multiple episodes of star formation from metal-poor gas, and possibly …