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Spiral structure of the giant galaxy UGC 2885: Hα kinematics
Abstract
The TAURUS I imaging Fabry-Perot spectrometer is used to map the
velocity field of the giant spiral galaxy UGC 2885 in H-alpha emission
at 5-arcsec resolution. Ripples in the velocity field around the minor
axis indicate radial flows across the spiral arms. The radial flow
speeds in the plane of the disk show 50-70 km/s peak-to-peak variation,
suggesting that a strong density wave is present in the underlying
stellar disk. Such high speeds may alternatively be a natural
consequence of the open arm spiral patterns. Strong density waves may
naturally occur in large spiral galaxies or in spiral galaxies as
massive as UGC 2885.
... Hence this study allows for a heuristic parameterization of Dark Matter within the context of General Relativity maintaining as the asymptotic limit the cosmological standard model which is useful to investigate the local properties of Dark Matter. Assuming a thin exponential disk approximation we apply such parameterization to a simplified lattice model matching the characteristics of the galaxy UGC2885 [7][8][9][10] and numerically estimate the mass-energy density required to match the observed galaxy rotation curve. ...
... For exemplification purposes we are modeling the galaxy UGC2885. Experimental photometric data and red-shift measurements for this galaxy are available in the works [4,[7][8][9][10]. We note that within the analysis carried in these references there are discrepancies in the derived physical parameters of the galaxy. ...
... These discrepancies are mainly due to the distinct estimates for the Heliocentric distance D, which is derived from the systemic velocity V sys which, in turn, is computed from the average of the measured red-shift. While in [4,7] it is considered the uncorrected systemic velocity V sys = 5794 km s −1 corresponding to a Heliocentric distance of D = 118 M pc, in [8,9] the systemic velocity is converted to the motion relative to the local group and the cosmic microwave background ¯ V sys = 5683 km s −1 corresponding to the Heliocentric distance of D = 76 M pc. In addition, given a estimate for ¯ V sys , the estimate for D also depends on the today's Hubble rate value H 0 and deceleration parameter q 0 which has been updated [16] with respect to the values considered in these references. ...
In this paper are discussed possible many body generalizations of the expanding locally anisotropic metric ansatz with respect to approximately Newtonian gravitational systems. This ansatz consistently describes local point-like matter distributions on the expanding Universe also allowing for a covariant parameterization of gravitational interactions at intermediate length scales.
As an example of applicability it is modeled a disk galaxy model matching the physical parameters of the galaxy UGC2885 and it is shown that, by fine-tuning the metric functional parameter, the flattening of the galaxy rotation curve is fully parameterized by this metric. In addition it is numerically computed the mass-energy density corrections due to the expanding anisotropic background and explicitly shown that although there are negative contributions within the galaxy plane the total mass-energy density is strictly positive both at the galaxy plane and outside the galaxy plane. As the functional parameter for this metric is an exponential factor is required a floating point precision of 250 significant digits for root finding routines and 200 significant digits to evaluate the effective mass-energy density rendering a final precision of the results presented above double precision (16 significant digits).
It is further shown that these results are consistent with the interpretation of the gravitational corrections as due to Dark Matter, in particular constituting a novel heuristic local parameterization for the Dark Matter distribution within the galaxy plane consistent with both local scale and cosmological scale physical laws which is useful to further investigate the local properties of Dark Matter.
... Galaxies that are dominated by spiral density waves (Lin & Shu, 1964) are most compatible with measurements of distance. Density waves are thought to be present in UGC2885 (Canzian et al., 1993), meaning distance measures are expected to be useful for classification of galaxy components. Young stars typically form in the dense spiral arms and disperse as they age ...
Automating classification of galaxy components is important for understanding the formation and evolution of galaxies. Traditionally, only the larger galaxy structures such as the spiral arms, bulge, and disc are classified. Here we use machine learning (ML) pixel-by-pixel classification to automatically classify all galaxy components within digital imagery of massive spiral galaxy UGC 2885. Galaxy components include young stellar population, old stellar population, dust lanes, galaxy center, outer disc, and celestial background. We test three ML models: maximum likelihood classifier (MLC), random forest (RF), and support vector machine (SVM). We use high-resolution Hubble Space Telescope (HST) digital imagery along with textural features derived from HST imagery, band ratios derived from HST imagery, and distance layers. Textural features are typically used in remote sensing studies and are useful for identifying patterns within digital imagery. We run ML classification models with different combinations of HST digital imagery, textural features, band ratios, and distance layers to determine the most useful information for galaxy component classification. Textural features and distance layers are most useful for galaxy component identification, with the SVM and RF models performing the best. The MLC model performs worse overall but has comparable performance to SVM and RF in some circumstances. Overall, the models are best at classifying the most spectrally unique galaxy components including the galaxy center, outer disc, and celestial background. The most confusion occurs between the young stellar population, old stellar population, and dust lanes. We suggest further experimentation with textural features for astronomical research on small-scale galactic structures.
... But such a duration explains the formation of galaxies. For example, now a galaxy such as UGC 2885 [10] will have more than The important result of this chapter is that the issue of critical Universe density [13], [14], is solved directly and in a simple manner by SMT. No more cosmological constant is needed. ...
S.M.T. (Surrounding Matter Theory), an alternative theory to dark matter, is presented. It is based on a modification of Newton's law. This modification is done by multiplying a Newtonian potential by a given factor, which is varying with local distribution of matter, at the location where the gravitational force is exerted. With this new equation the model emphasizes that a gravitational force is roughly inversely proportional to mass density at the location where this force is applied. After presentation of the model, its dynamic is quickly applied to cosmology and galaxy structure. Some possible caveats of the model are identified. But the simple mechanism described above suggests the idea of a straightforward solution to the following issues: virial theorem mystery, the bullet cluster (“1E 0657-56” galaxy clusters) issue, the strong relative velocity of its subclusters, the value of cosmological critical density, the fine tuning issue, and expansion acceleration. Nucleosynthesis is not explained and would require a different model for radiation era. But a de Sitter Universe is predicted, this means that the spatial curvature, K, is 0, and today's deceleration parameter, q, is -1. The predicted time since last scattering is 68 h ⁻¹ Gyr. With this value SMT explains heterogeneities of large scale structure and galaxy formation. Each kind of experimental speed profiles are retrieved by a simulation of a virtual galaxy. In the simulations, ring galaxies are generated by SMT dynamic itself, without the help of any particular external event. Those studies give motivation for scientific comparisons with experimental data.
Automating classification of galaxy components is important for understanding the formation and evolution of galaxies. Traditionally, only the larger galaxy structures such as the spiral arms, bulge, and disc are classified. Here we use machine learning (ML) pixel-by-pixel classification to automatically classify all galaxy components within digital imagery of massive spiral galaxy UGC 2885. Galaxy components include young stellar population, old stellar population, dust lanes, galaxy center, outer disc, and celestial background. We test three ML models: maximum likelihood classifier (MLC), random forest (RF), and support vector machine (SVM). We use high-resolution Hubble Space Telescope (HST) digital imagery along with textural features derived from HST imagery, band ratios derived from HST imagery, and distance layers. Textural features are typically used in remote sensing studies and are useful for identifying patterns within digital imagery. We run ML classification models with different combinations of HST digital imagery, textural features, band ratios, and distance layers to determine the most useful information for galaxy component classification. Textural features and distance layers are most useful for galaxy component identification, with the SVM and RF models performing the best. The MLC model performs worse overall but has comparable performance to SVM and RF in some circumstances. Overall, the models are best at classifying the most spectrally unique galaxy components including the galaxy center, outer disc, and celestial background. The most confusion occurs between the young stellar population, old stellar population, and dust lanes. We suggest further experimentation with textural features for astronomical research on small-scale galactic structures.
We analyse radial stellar metallicity and kinematic profiles out to 1Re in 244 CALIFA galaxies ranging from morphological type E to Sd, to study the evolutionary mechanisms of stellar population gradients. We find that linear metallicity gradients exhibit a clear correlation with galaxy morphological type – with early-type galaxies showing the steepest gradients. We show that the metallicity gradients simply reflect the local mass–metallicity relation within a galaxy. This suggests that the radial stellar population distribution within a galaxy’s effective radius is primarily a result of the in situ local star formation history. In this simple picture, the dynamically derived stellar surface mass density gradient directly predicts the metallicity gradient of a galaxy. We show that this correlation and its scatter can be reproduced entirely by using independent empirical galaxy structural and chemical scaling relations. Using Schwarzschild dynamical models, we also explore the link between a galaxy’s local stellar populations and their orbital structures. We find that galaxies’ angular momentum and metallicity gradients show no obvious causal link. This suggests that metallicity gradients in the inner disc are not strongly shaped by radial migration, which is confirmed by the lack of correlation between the metallicity gradients and observable probes of radial migration in the galaxies, such as bars and spiral arms. Finally, we find that galaxies with positive metallicity gradients become increasingly common towards low mass and late morphological types – consistent with stellar feedback more efficiently modifying the baryon cycle in the central regions of these galaxies.
Summary This document is part of Subvolume C ‘Interstellar Matter, Galaxy, Universe’ of Volume 3 ‘Astronomy and Astrophysics’ of Landolt-Börnstein - Group VI Astronomy and Astrophysics.
Summary This document is part of Subvolume C ‘Interstellar Matter, Galaxy, Universe’ of Volume 3 ‘Astronomy and Astrophysics’ of Landolt-Börnstein - Group VI Astronomy and Astrophysics.
Using Australia Telescope Compact Array neutral hydrogen and
Anglo-Australian Telescope optical observations, we investigate the
distribution of luminous and dark matter in the giant, gas-rich,
low-surface-brightness galaxy NGC 289. The observations show NGC 289 to
have a high H 1-to-stellar mass ratio (M_HI/M_* ~ 0.4), and an extremely
large H 1 radius (70 kpc, or ~ 13 disk scale-lengths), making the H 1
velocity field an excellent probe of a galaxy dark halo to an unusually
large radius. Between ~ 10 kpc and 30 kpc the rotation curve dips by 14%
of the maximum velocity. Warped disk and spiral density wave models are
investigated to explain this dip and to determine the cause of
significant velocity deviations in the vicinity of the H 1 spiral arms.
The best-fit kinematic model has M / L_I = 2.1
Msun/Lsun for the stellar disk, only slightly
lower than the maximum disk value of 2.3. A dark matter halo of 3.5x
10(11) Msun is present, which is ~ 3.5 times as massive as
the combined stellar and gaseous components at the last measured point
on the rotation curve.
Kinematic data on the minor axis of the giant spiral galaxy UGC 2885
show a change in the sign of the radial velocity across spiral arms.
Such a sign change indicates that corotation has been crossed. In fact,
two sign changes are seen, implying that there are two spiral patterns.
The morphology of the galaxy supports this interpretation. A general
method is also presented that can be used to locate the corotation
resonance in a grand design spiral galaxy. The method relies on the
effects of geometric phase, and assumes only that the spiral flow is
wave based and periodic in azimuth.
Preliminary but precise micowave maps are presented of the sky, and thus
of the early universe, derived as the first results from the
Differential Microwave Radiometers experiment aboard COBE. The dipole
anisotropy attributed to the motion of the solar system with respect to
the CMB reference frame shows strongly in all six sky maps and is
consistent with a Doppler-shifted thermal spectrum. The best-fitted
dipole has amplitude 3.3 + or - 0.2 mK in the direction (alpha, delta) =
11.2 h + or - 0.2 h, -7 deg + or - 2 deg (J2000) or (l,b) = 265 deg + or
- 2 deg, 48 deg + or - 2 deg. There is no clear evidence in the maps for
any other large angular-scale feature. Limits on Delta T/T0 of 3 x 10 to
the -5th (T0 = 2.735 K), 4 x 10 to the -5th, and 4 x 10 to the -5th are
found for the rms quadrupole amplitude, monochromatic fluctuations, and
Gaussian fluctuations, respectively. These measurements place the most
severe constraints to date on many potential physical processes in the
early universe.
For a sample of 21 Sc galaxies ranging from very low to very high
luminosity, we have previously presented rotational velocities across
∼83% of the galaxy isophotal radius, R25. We now
analyze the mass distributions for this same sample, and show that for
all galaxies, the mass distribution has a single unique form, when the
masses are each scaled by a mass scale length, Rm. Unlike
luminosity scale lengths which are larger for more luminous (larger)
galaxies, mass scale lengths are smaller for galaxies of high
luminosity. As normalized here (the radius encompassing a mass of
1010 Msun), Rm is near 4 kpc for a
low luminosity Sc and is near 1.5 kpc for a high luminosity Sc. A low
luminosity Sc contains a single mass scale length, a high luminosity
Sc contains many tens of scale lengths within its isophotal radius. At
similar multiples of their scale lengths, all Sc's have equal interior
masses.
The form of the characteristic mass curve implies that rotation curves
are still rising slightly at radii of many scale lengths, V ∝
r0.1 or r0.2, and local density falls off slower
than 1/r2 (ρ ∝ r-1.7). We conclude that
the rotational velocities remain high at large nuclear distances due
to the presence of significant nonluminous mass at large radii.
Correlations between integral mass, luminosity, mass scale length,
isophotal radius, and velocity at the isophotal radius are determined
and discussed. The correlation of luminosity with V(R25)) is
as steep as that found in the infrared. The ratio of mass to
luminosity interior to the isophotal radius is independent of
luminosity and equals 3.0 ± 0.3 for Sc galaxies.
Observations of CO emission from the prototypical spiral galaxy M51 reveal density wave streaming motions in molecular gas coincident with the dust lanes. This is strong evidence that spiral density waves assemble pre-existing molecular clouds into giant associations and trigger the collapse of suitably primed clouds, leading to the formation of stars.
The H I and H-alpha emission lines in the grand-design spiral galaxy M51 were observed with the Westerbork Synthesis Radio Telescope and the Taurus Fabry-Perot imaging spectrometer, respectively. Strong tangential and radial streaming motions across the inner spiral arms in the ionized gas were detected. The deviations from circular rotations are found to have rotations that agree qualitatively with predictions of the gas flow in galactic disks under the effect of a density wave. It is shown that a simple qualitative model of the dissociation-recombination process is capable of yielding the observed H I column densities in the arms.
A comprehensive review of the theory of galactic dynamics is presented. Key empirical facts about stellar systems are briefly reviewed, and the ingredients needed to construct galaxy models are assembled, including potential theory, stellar orbits, and the theory of the equilibrium configurations of stellar systems. The stability of these configurations and the theory of spiral structures are discussed. Collisions and encounters between stellar systems are considered, and two-body realization and the approach to statistical equilibrium in star clusters are addressed. It is shown how the observable properties of galaxies such as their luminosities and colors are changed by the aging of their constituent stellar populations. Finally, it is shown that most of the mass in the universe is locked up in some still invisible form.
The interpretation of the spectra of H II regions in the disks of spiral
galaxies is reconsidered along with the systematic variation of these
spectra with distance from the center of a galaxy. Data of improved
accuracy are presented for three previously studied H II regions in M101
and analyzed on the basis of models that take into account the effect of
metal absorption edges in the ionizing stellar radiation. It is shown
that an excellent fit to the observed spectra can be obtained if the
three H II regions differ in the temperature of the ionizing stars and
if the models employed are self-consistent in the sense that the
ionizing stars have the same metal abundance as the gas. Reliable
abundance estimates of the inner H II regions are obtained and used to
investigate the form of the abundance-radius relation. The results
indicate that the observed form is in conflict with the predictions of
simple models of galactic evolution.