Halo Geometry and Dark Matter Annihilation Signal

We study the impact of the halo shape and geometry on the expected weakly interacting massive particle (WIMP) dark matter annihilation signal from the galactic center. As the halo profile in the innermost region is still poorly constrained, we consider different density behaviors like flat cores, cusps and spikes, as well as geometrical distortions. We show that asphericity has a strong impact on the annihilation signal when the halo profile near the galactic center is flat, but becomes gradually less significant for cuspy profiles, and negligible in the presence of a central spike. However, the astrophysical factor is strongly dependent on the WIMP mass and annihilation cross-section in the latter case.Comment: 5 pages, 4 figures, PR

Radial Dependence of the Pattern Speed of M51

The grand-design spiral galaxy M51 has long been a crucial target for theories of spiral structure. Studies of this iconic spiral can address the question of whether strong spiral structure is transient (e.g. interaction-driven) or long-lasting. As a clue to the origin of the structure in M51, we investigate evidence for radial variation in the spiral pattern speed using the radial Tremaine-Weinberg (TWR) method. We implement the method on CO observations tracing the ISM-dominant molecular component. Results from the method's numerical implementation--combined with regularization, which smooths intrinsically noisy solutions--indicate two distinct patterns speeds inside 4 kpc at our derived major axis PA=170 deg., both ending at corotation and both significantly higher than the conventionally adopted global value. Inspection of the rotation curve suggests that the pattern speed interior to 2 kpc lacks an ILR, consistent with the leading structure seen in HST near-IR observations. We also find tentative evidence for a lower pattern speed between 4 and 5.3 kpc measured by extending the regularized zone. As with the original TW method, uncertainty in major axis position angle (PA) is the largest source of error in the calculation; in this study, where \delta PA=+/-5 deg. a ~20% error is introduced to the parameters of the speeds at PA=170 deg. Accessory to this standard uncertainty, solutions with PA=175 deg. (also admitted by the data) exhibit only one pattern speed inside 4 kpc, and we consider this circumstance under the semblance of a radially varying PA.Comment: 14 pages in emulateapj format, 12 figures, accepted for publication in Ap

Characterizing Bars at z~0 in the optical and NIR: Implications for the Evolution of Barred Disks with Redshift

Critical insights on galaxy evolution stem from the study of bars. With the advent of HST surveys that trace bars in the rest-frame optical out to z~1, it is critical to provide a reference baseline for bars at z~0 in the optical band. We present results on bars at z~0 in the optical and NIR bands based on 180 spirals from OSUBSGS. (1) The deprojected bar fraction at z~0 is ~60% +/-6% in the NIR H-band and ~44% +/-6% in the optical B-band. (2) The results before and after deprojection are similar, which is encouraging for high-redshift studies that forego deprojection. (3) Studies of bars at z~0.2-1.0 (lookback time of 3-8 Gyr) have reported an optical bar fraction of ~30% +/-6%, after applying cutoffs in absolute magnitude (M_V = 1.5 kpc), and bar ellipticity (e_bar >= 0.4). Applying these exact cutoffs to the OSUBSGS data yields a comparable optical B-band bar fraction at z~0 of ~ 34%+/-6%. This rules out scenarios where the optical bar fraction in bright disks declines strongly with redshift. (4) Most (~70%) bars have moderate to high strentgh or ellipticity (0.50 <= e_bar <= 0.75). There is no bimodality in the distribution of e_bar. The H-band bar fraction and e_bar show no substantial variation across RC3 Hubble types Sa to Scd. (5) RC3 bar types should be used with caution. Many galaxies with RC3 types "AB" turn out to be unbarred and RC3 bar classes "B" and "AB" have a significant overlap in e_bar. (6) Most bars have sizes below 5 kpc. Bar and disk sizes correlate, and most bars have a_bar/R_25~0.1-0.5. This suggests that the growths of bars and disks are intimately tied.Comment: 11 pages, 17 figures, 3 tables, ApJ accepted, abridged abstract below. Minor changes and shortened paper for ApJ limits. For high resolution figures see http://www.as.utexas.edu/~marinova/paper1-highres.pd

The Lifetime of Grand Design

The lifetime of the structure in grand design spiral galaxies is observationally ill-determined, but is essentially set by how accurately the pattern's rotation can be characterized by a single angular pattern speed. This paper derives a generalized version of the Tremaine-Weinberg method for observationally determining pattern speeds, in which the pattern speed is allowed to vary arbitrarily with radius. The departures of the derived pattern speed from a constant then provides a simple metric of the lifetime of the spiral structure. Application of this method to CO observations of NGC 1068 reveal that the pattern speed of the spiral structure in this galaxy varies rapidly with radius, and that the lifetime of the spiral structure is correspondingly very short. If this result turns out to be common in grand-design spiral galaxies, then these features will have to be viewed as highly transient phenomena.Comment: 6 pages, 3 figures, accepted for publication in MNRA

The Pattern Speed of the Galactic Bar

Most late-type stars in the solar neighborhood have velocities similar to the local standard of rest (LSR), but there is a clearly separated secondary component corresponding to a slower rotation and a mean outward motion. Detailed simulations of the response of a stellar disk to a central bar show that such a bi-modality is expected from outer-Lindblad resonant scattering. When constraining the run of the rotation curve by the proper motion of Sgr A* and the terminal gas velocities, the value observed for the rotation velocity separating the two components results in a value of (53+/-3)km/s/kpc for the pattern speed of the bar, only weakly dependent on the precise values for Ro and bar angle phi.Comment: 5 pages LaTeX, 2 Figs, accepted for publication in ApJ Letter

Exploring Disk Galaxy Dynamics Using IFU Data

In order to test the basic equations believed to dictate the dynamics of disk galaxies, we present and analyze deep two-dimensional spectral data obtained using the PPAK integral field unit for the early-type spiral systems NGC 2273, NGC 2985, NGC 3898 and NGC 5533. We describe the care needed to obtain and process such data to a point where reliable kinematic measurements can be obtained from these observations, and a new more optimal method for deriving the rotational motion and velocity dispersions in such disk systems. The data from NGC 2273 and NGC 2985 show systematic variations in velocity dispersion with azimuth, as one would expect if the shapes of their velocity ellipsoids are significantly anisotropic, while the hotter disks in NGC 3898 and NGC 5533 appear to have fairly isotropic velocity dispersions. Correcting the rotational motion for asymmetric drift using the derived velocity dispersions reproduces the rotation curves inferred from emission lines reasonably well, implying that this correction is quite robust, and that the use of the asymmetric drift equation is valid. NGC 2985 is sufficiently close to face on for the data, combined with the asymmetric drift equation, to determine all three components of the velocity ellipsoid. The principal axes of this velocity ellipsoid are found to be in the ratio sigma_z:sigma_phi:sigma_R ~ 0.7:0.7:1, which shows unequivocally that this disk distribution function respects a third integral of motion. The ratio is also consistent with the predictions of epicyclic theory, giving some confidence in the application of this approximation to even fairly early-type disk galaxies.Comment: 15 pages, 7 figures, accepted for publication in MNRA

Bar Diagnostics in Edge-On Spiral Galaxies. III. N-Body Simulations of Disks

Present in over 45% of local spirals, boxy and peanut-shaped bulges are generally interpreted as edge-on bars and may represent a key phase in the evolution of bulges. Aiming to test such claims, the kinematic properties of self-consistent 3D N-body simulations of bar-unstable disks are studied. Using Gauss-Hermite polynomials to describe the stellar kinematics, a number of characteristic bar signatures are identified in edge-on disks: 1) a major-axis light profile with a quasi-exponential central peak and a plateau at moderate radii (Freeman Type II profile); 2) a ``double-hump'' rotation curve; 3) a sometime flat central velocity dispersion peak with a plateau at moderate radii and occasional local central minimum and secondary peak; 4) an h3-V correlation over the projected bar length. All those kinematic features are spatially correlated and can easily be understood from the orbital structure of barred disks. They thus provide a reliable and easy-to-use tool to identify edge-on bars. Interestingly, they are all produced without dissipation and are increasingly realized to be common in spirals, lending support to bar-driven evolution scenarios for bulge formation. So called ``figure-of-eight'' position-velocity diagrams are never observed, as expected for realistic orbital configurations. Although not uniquely related to triaxiality, line-of-sight velocity distributions with a high velocity tail (i.e. an h3-V correlation) appear as particularly promising tracers of bars. The stellar kinematic features identified grow in strength as the bar evolves and vary little for small inclination variations. Many can be used to trace the bar length. Comparisons with observations are encouraging and support the view that boxy and peanut-shaped bulges are simply thick bars viewed edge-on.Comment: 32 pages, 4 figures, AASTeX preprint. Revised following referees' comments. Now accepted for publication in The Astrophysical Journal. We strongly suggest you download the version with full resolution figures at http://www.astro.columbia.edu/~bureau/Publications/Nbody_ApJ04.ps.g

Study of arc-jet propulsion devices Final report, 20 Nov. 1964 - 19 Dec. 1965

Energy transfer mechanisms in radiation, water, and regeneratively cooled, and MPD arc jet propulsion device

Quantifying Resonant Structure in NGC 6946 from Two-dimensional Kinematics

We study the two-dimensional kinematics of the H-alpha-emitting gas in the nearby barred Scd galaxy, NGC 6946, in order to determine the pattern speed of the primary m=2 perturbation mode. The pattern speed is a crucial parameter for constraining the internal dynamics, estimating the impact velocities of the gravitational perturbation at the resonance radii, and to set up an evolutionary scenario for NGC 6946. Our data allows us to derive the best fitting kinematic position angle and the geometry of the underlying gaseous disk, which we use to derive the pattern speed using the Tremaine-Weinberg method. We find a main pattern speed Omega_p=22 km/s/kpc, but our data clearly reveal the presence of an additional pattern speed Omega_p=47 km/s/kpc in a zone within 1.25 kpc of the nucleus. Using the epicyclic approximation, we deduce the location of the resonance radii and confirm that inside the outer Inner Lindblad Resonance radius of the main oval, a primary bar has formed rotating at more than twice the outer pattern speed. We further confirm that a nuclear bar has formed inside the Inner Lindblad Resonance radius of the primary bar, coinciding with the inner Inner Lindblad Resonance radius of the large-scale m=2 mode oval.Comment: Accepted for publication in ApJ Letter