A Kinematic Measurement of Ram Pressure in the Outer Disk of Regular Galaxies

While most ram pressure studies have focused on ram pressure stripping in galaxy clusters, we devise a novel approach based on a kinematic measurement of ram pressure perturbations in HI velocity fields for intergalactic material (IGM) densities and relative velocities that are one to two orders of magnitude lower than in galaxies showing ram pressure stripping. Our model evaluates ram pressure induced kinematic terms in gas disks with constant inclination as well as those with a warped geometry. Ram pressure perturbations are characterized by kinematic modes of even order, m=0 and m=2, corresponding to a ram wind perpendicular and parallel to the gas disk, respectively. Long-term consequences of ram pressure, such as warped disks as well as uncertainties in the disk geometry typically generate uneven modes (m=1 and m=3), that are clearly distinguishable from the kinematic ram pressure terms. We have applied our models to three nearby isolated galaxies, utilizing Markov Chain Monte Carlo fitting routines to determine ram pressure perturbations in the velocity fields of NGC 6946 and NGC 3621 of ~30km s$^{-1}$ (effective line-of-sight velocity change) at HI column densities below (4-10)$\times$10$^{20}$cm$^{-2}$ (at radial scales greater than ~15kpc). In contrast, NGC 628 is dominated by a strongly warped disk. Our model fits reveal the three-dimensional vector of the galaxies' movement with respect to the IGM rest-frame and provide constraints on the product of speed with IGM density, opening a new window for extragalactic velocity measurements and studies of the intergalactic medium.Comment: 34 pages, 28 figures, accepted for publication in MNRA

On the Formation of Warped Gas Disks in Galaxies

We consider the most commonly occurring circumstances which apply to galaxies, namely membership in galaxy groups of about $10^{13}h^{-1} M_\odot$ total mass, and estimate the accompanying physical conditions of intergalactic medium (IGM) density and the relative galaxy-IGM space velocity. We then investigate the dynamical consequences of such a typical galaxy-IGM interaction on a rotating gaseous disk within the galaxy potential. We find that the rotating outer disk is systematically distorted into a characteristic "warp" morphology, of the type that has been well-documented in the majority of well-studied nearby systems. The distortion is established rapidly, within two rotation periods, and is long-lived, surviving for at least ten. A second consequence of the interaction is the formation of a one arm retrograde spiral wave pattern that propagates in the disk. We suggest that the ubiquity of the warp phenomenon might be used to reconstruct both the IGM density profile and individual member orbits within galaxy groups.Comment: 7 pages, 7 figures, accepted for publication in MNRAS Letters. For supplementary material, see http://www.atnf.csiro.au/people/Sebastian.Haan/publications.htm

Feeding Black Holes : Gas Dynamics from the Outer Disk to the Very Nucleus in AGN Galaxies

Wesentlich für das Verständnis der Galaxienentwicklung und der Aktivität von galaktischen Kernen ist ein genaues Bild der zugrunde liegenden Prozesse, die für die Umverteilung von interstellarem Material verantwortlich sind. Um den Gastransport aus den äußeren Bereichen (mehrere kpc Abstand) bis in das Zentrum (einige 10 pc) von Galaxien zu untersuchen, sind Beobachtungen des molekularen Gases (CO, mit dem IRAM PdBI) aus dem NUGA Projekt mit Beobachtungen des atomaren Gases (HI, mit dem VLA) für 16 aktive Galaxien kombiniert worden. Ein Ergebnis ist, dass die Gasverteilung sowie die Häufigkeit von dynamisch gestörten äußeren Galaxienscheiben davon abzuhängen scheint, welche Art von nuklearer Aktivität vorliegt (Seyfert oder LINER). Dies wiederum weist auf eine gemeinsame Entwicklung von nuklearer Aktivität und der Umverteilung des neutralen Gases hin. Eine genaue Untersuchung zweidimensionaler Abbildungen der Gasbewegung, basierend auf gravitativen Drehmomenten in den Galaxienscheiben, hat ergeben, dass Spiralgalaxien in der Tat sehr dynamische Systeme sind und ständigen Gasumverteilungen mit Zeitskalen von wenigen Rotationsperioden unterliegen. Aufgrund dieser gravitativen Drehmomente ist es Galaxien möglich, Gas aus der äußeren Scheibe bis zu ~100 pc an das Zentrum zu transportieren. Interessanterweise können somit sogar Korotationsresonanzen von Galaxienbalken überwunden werden, von denen urspünglicherweise angenommen wurde, dass sie eine definitive Barriere für den Gastransport darstellen

The Effect of Pension Wealth on Employment

This study provides novel evidence about the pension wealth elasticity of employment. For the identification we exploit reform-induced variation of pension wealth that is related to the number of children but which does not affect the implicit tax rate of employment. We use a difference-in-differences estimator based on administrative data from the German pension insurance and find that, on average, the negative employment effect of pension wealth is significant and economically important. Heterogeneity analyses document a strong age pattern showing that the employment effects are driven by behavioral responses of women close to retirement. The age pattern is partly explained by the positive effect of pension wealth on disability pensions after the age of 60

The Spatial Extent of (U)LIRGs in the Mid-Infrared. II. Feature Emission

We present results from the second part of our analysis of the extended mid-infrared (MIR) emission of the Great Observatories All-Sky LIRG Survey (GOALS) sample based on 5-14 micron low-resolution spectra obtained with the IRS on Spitzer. We calculate the fraction of extended emission as a function of wavelength for all galaxies in the sample, FEE_lambda, and spatially separate the MIR spectrum of galaxies into their nuclear and extended components. We find that the [NeII] emission line is as compact as the hot dust MIR continuum, while the polycyclic aromatic hydrocarbon (PAH) emission is more extended. The 6.2 and 7.7 micron PAH emission is more compact than that of the 11.3 micron PAH, which is consistent with the formers being enhanced in a more ionized medium. The presence of an AGN or a powerful nuclear starburst increases the compactness of the hot dust MIR continuum, but has a negligible effect on the spatial extent of the PAH emission on kpc-scales. Globally, the spectra of the extended emission component are homogeneous for all galaxies in GOALS. This suggests that the physical properties of star formation taking place at distances farther than 1.5 kpc from the nuclei of (U)LIRGs are very similar, resembling local star-forming galaxies with L_IR < 10^11 Lsun, as well as star formation-dominated ULIRGs at z~2. In contrast, the MIR spectra of the nuclear component of local (U)LIRGs are very diverse. This implies that the observed variety of their integrated MIR properties arise, on average, only from the processes that are taking place in their cores.Comment: 16 pages, 7 figures, accepted for publication in Ap

Complex Radio Spectral Energy Distributions in Luminous and Ultraluminous Infrared Galaxies

We use the Expanded Very Large Array to image radio continuum emission from local luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs) in 1 GHz windows centered at 4.7, 7.2, 29, and 36 GHz. This allows us to probe the integrated radio spectral energy distribution (SED) of the most energetic galaxies in the local universe. The 4-8 GHz flux densities agree well with previous measurements. They yield spectral indices \alpha \approx -0.67 (where F_\nu \propto \nu^\alpha) with \pm 0.15 (1\sigma) scatter, typical of nonthermal (synchrotron) emission from star-forming galaxies. The contrast of our 4-8 GHz data with literature 1.5 and 8.4 GHz flux densities gives further evidence for curvature of the radio SED of U/LIRGs. The SED appears flatter near \sim 1 GHz than near \sim 6 GHz, suggesting significant optical depth effects at the lower frequencies. The high frequency (28-37 GHz) flux densities are low compared to extrapolations from the 4-8 GHz data. We confirm and extend to higher frequency a previously observed deficit of high frequency radio emission for luminous starburst galaxies.Comment: 7 pages, 3 figures, 1 table, accepted for publication in the EVLA Special Issue of ApJ Letter

Dynamical evolution of AGN host galaxies -— gas in/out-flow rates in seven NUGA galaxies

To examine the role of the host galaxy structure in fueling nuclear activity, we estimated gas flow rates from several kpc down to the inner few 10 pc for seven nearby spiral galaxies, selected from the NUclei of GAlaxies sample. We calculated gravitational torques from near-infrared images and determined gas in/out-flow rates as a function of radius and location within the galactic disks, based on high angular resolution interferometric observations of molecular (CO using Plateau de Bure interferometer) and atomic (H I using the Very Large Array) gas. The results are compared with kinematic evidence for radial gas flows and the dynamical state of the galaxies (via resonances) derived from several different methods. We show that gravitational torques are very efficient at transporting gas from the outer disk all the way into the galaxies centers at ~100 pc; previously assumed dynamical barriers to gas transport, such as the corotation resonance of stellar bars, seem to be overcome by gravitational torque induced gas flows from other nonaxisymmetric structures. The resulting rates of gas mass inflow range from 0.01 to 50 M⊙ yr^(–1) and are larger for the galaxy center than for the outer disk. Our gas flow maps show the action of nested bars within larger bars for three galaxies. Noncircular streaming motions found in the kinematic maps are larger in the center than in the outer disk and appear to correlate only loosely with the in/out-flow rates as a function of radius. We demonstrate that spiral gas disks are very dynamic systems that undergo strong radial evolution on timescales of a few rotation periods (e.g., 5 × 10^8 yrs at a radius of 5 kpc), due to the effectiveness of gravitational torques in redistributing the cold galactic gas

Mid-Infrared Properties of Luminous Infrared Galaxies II: Probing the Dust and Gas Physics of the GOALS Sample

The Great Observatories All-Sky LIRG Survey (GOALS) is a comprehensive, multiwavelength study of luminous infrared galaxies (LIRGs) in the local universe. Here we present the results of a multi-component, spectral decomposition analysis of the low resolution mid-IR Spitzer IRS spectra from 5-38um of 244 LIRG nuclei. The detailed fits and high quality spectra allow for characterization of the individual PAH features, warm molecular hydrogen emission, and optical depths for silicate dust grains and water ices. We find that starbursting LIRGs, which make up the majority of GOALS, are very consistent in their MIR properties (i.e. tau_9.7um, tau_ice, neon line and PAH feature ratios). However, as their PAH EQW decreases, usually an indicator of an increasingly dominant AGN, LIRGs cover a larger spread in these MIR parameters. The contribution from PAHs to the total L(IR) in LIRGs varies from 2-29% and LIRGs prior to their first encounter show higher L(PAH)/L(IR) ratios on average. We observe a correlation between the strength of the starburst (IR8) and the PAH fraction at 8um but not with the 7.7 to 11.3 PAH ratio, suggesting the fractional PDR emission, and not the overall grain properties, is associated with the rise in IR8 for galaxies off the starburst main sequence. We detect crystalline silicate features in 6% of the sample but only in the most obscured sources (s_9.7um < -1.24). Ice absorption features are observed in 11% (56%) of GOALS LIRGs (ULIRGs). Most GOALS LIRGs have L(H2)/L(PAH) ratios elevated above those observed for normal star-forming galaxies and exhibit a trend for increasing L(H2)/L(PAH) ratio with increasing L(H2). While star formation appears to be the dominant process responsible for exciting the H2 in most of the GOALS galaxies, a subset of LIRGs (10%) show excess H2 emission that is inconsistent with PDR models and may be excited by shocks or AGN-induced outflows.Comment: 21 pages with 20 figures plus 2 table

Convergence to stable laws for multidimensional stochastic recursions: the case of regular matrices

Given a sequence $(M_{n},Q_{n})_{n\ge 1}$ of i.i.d.\ random variables with generic copy $(M,Q) \in GL(d, \R) \times \R^d$, we consider the random difference equation (RDE) $$R_{n}=M_{n}R_{n-1}+Q_{n},$$ $n\ge 1$, and assume the existence of $\kappa >0$ such that \lim_{n \to \infty}(\E{\norm{M_1 ... M_n}^\kappa})^{\frac{1}{n}} = 1 . We prove, under suitable assumptions, that the sequence $S_n = R_1 + ... + R_n$, appropriately normalized, converges in law to a multidimensional stable distribution with index $\kappa$. As a by-product, we show that the unique stationary solution $R$ of the RDE is regularly varying with index $\kappa$, and give a precise description of its tail measure. This extends the prior work http://arxiv.org/abs/1009.1728v3 .Comment: 15 page