Dust emission in star-forming dwarf galaxies: General properties and the nature of the sub-mm excess

We studied the global characteristics of dust emission in a large sample of emission-line star-forming galaxies. The sample consists of two subsamples. One subsample (SDSS sample) includes ~4000 compact star-forming galaxies from the SDSS, which were also detected in all four bands at 3.4, 4.6, 12, and 22 mum of the WISE all-sky survey. The second subsample (Herschel sample) is a sample of 28 compact star-forming galaxies observed with Herschel in the FIR range. Data of the Herschel sample were supplemented by the photometric data from the Spitzer observations, GALEX, SDSS, WISE, 2MASS, NVSS, and FIRST surveys, as well as optical and Spitzer spectra and data in sub-mm and radio ranges. It is found that warm dust luminosities of galaxies from the SDSS sample and cold and warm dust luminosities of galaxies from the Herschel sample are strongly correlated with Hbeta luminosities, which implies that one of the main sources of dust heating in star-forming galaxies is ionising UV radiation of young stars. Using the relation between warm and cold dust masses for estimating the total dust mass in star-forming galaxies with an accuracy better than ~0.5 dex is proposed. On the other hand, it is shown for both samples that dust temperatures do not depend on the metallicities. The dust-to-neutral gas mass ratio strongly declines with decreasing metallicity, similar to that found in other studies of local emission-line galaxies, high-redshift GRB hosts, and DLAs. On the other hand, the dust-to-ionised gas mass ratio is about one hundred times as high implying that most of dust is located in the neutral gas. It is found that thermal free-free emission of ionised gas in compact star-forming galaxies might be responsible for the sub-mm emission excess. This effect is stronger in galaxies with lower metallicities and is also positively affected by an increased star-formation rate.Comment: 22 pages, 15 figures, accepted for publication in Astronomy and Astrophysic

Ein neues Verfahren in der operativen Therapie der Rhizarthrose

Die Rhizarthrose ist eine der häufigsten Arthrosen der Hand. Eine durch konservative Behandlung nicht zu beherrschende Schmerzsymptomatik stellt eine Operationsindikation dar. Die einzelnen gebräuchlichen Operationsverfahren werden mit ihrer Indikation beschrieben. Zusammen mit der aufgezeigten Anatomie und Pathologie des Daumensattelgelenks werden die Überlegungen zu einem modifizierten Verfahren dargelegt und ein neues Operationsverfahren vorgestellt. Die Vorteile dieser Methode und ihre differenzierte Anzeigestellung werden erläutert. Die Ergebnisse der Nachuntersuchung lassen eine erste positive Bewertung der Methode zu

The Flux Ratio Method for Determining the Dust Attenuation of Starburst Galaxies

The presence of dust in starburst galaxies complicates the study of their stellar populations as the dust's effects are similar to those associated with changes in the galaxies' stellar age and metallicity. This degeneracy can be overcome for starburst galaxies if UV/optical/near-infrared observations are combined with far-infrared observations. We present the calibration of the flux ratio method for calculating the dust attenuation at a particular wavelength, Att(\lambda), based on the measurement of F(IR)/F(\lambda) flux ratio. Our calibration is based on spectral energy distributions (SEDs) from the PEGASE stellar evolutionary synthesis model and the effects of dust (absorption and scattering) as calculated from our Monte Carlo radiative transfer model. We tested the attenuations predicted from this method for the Balmer emission lines of a sample starburst galaxies against those calculated using radio observations and found good agreement. The UV attenuation curves for a handful of starburst galaxies were calculated using the flux ratio method, and they compare favorably with past work. The relationship between Att(\lambda) and F(IR)/F(\lambda) is almost completely independent of the assumed dust properties (grain type, distribution, and clumpiness). For the UV, the relationship is also independent of the assumed stellar properties (age, metallicity, etc) accept for the case of very old burst populations. However at longer wavelengths, the relationship is dependent on the assumed stellar properties.Comment: accepted by the ApJ, 18 pages, color figures, b/w version at http://mips.as.arizona.edu/~kgordon/papers/fr_method.htm

Differential Influence of Levodopa on Reward-Based Learning in Parkinson's Disease

The mesocorticolimbic dopamine (DA) system linking the dopaminergic midbrain to the prefrontal cortex and subcortical striatum has been shown to be sensitive to reinforcement in animals and humans. Within this system, coexistent segregated striato-frontal circuits have been linked to different functions. In the present study, we tested patients with Parkinson's disease (PD), a neurodegenerative disorder characterized by dopaminergic cell loss, on two reward-based learning tasks assumed to differentially involve dorsal and ventral striato-frontal circuits. 15 non-depressed and non-demented PD patients on levodopa monotherapy were tested both on and off medication. Levodopa had beneficial effects on the performance on an instrumental learning task with constant stimulus-reward associations, hypothesized to rely on dorsal striato-frontal circuits. In contrast, performance on a reversal learning task with changing reward contingencies, relying on ventral striato-frontal structures, was better in the unmedicated state. These results are in line with the “overdose hypothesis” which assumes detrimental effects of dopaminergic medication on functions relying upon less affected regions in PD. This study demonstrates, in a within-subject design, a double dissociation of dopaminergic medication and performance on two reward-based learning tasks differing in regard to whether reward contingencies are constant or dynamic. There was no evidence for a dose effect of levodopa on reward-based behavior with the patients’ actual levodopa dose being uncorrelated to their performance on the reward-based learning tasks

Modulation of Habit Formation by Levodopa in Parkinson's Disease

Dopamine promotes the execution of positively reinforced actions, but its role for the formation of behaviour when feedback is unavailable remains open. To study this issue, the performance of treated/untreated patients with Parkinson's disease and controls was analysed in an implicit learning task, hypothesising dopamine-dependent adherence to hidden task rules. Sixteen patients on/off levodopa and fourteen healthy subjects engaged in a Go/NoGo paradigm comprising four equiprobable stimuli. One of the stimuli was defined as target which was first consistently preceded by one of the three non-target stimuli (conditioning), whereas this coupling was dissolved thereafter (deconditioning). Two task versions were presented: in a ‘Go version’, only the target cue required the execution of a button press, whereas non-target stimuli were not instructive of a response; in a ‘NoGo version’, only the target cue demanded the inhibition of the button press which was demanded upon any non-target stimulus. Levodopa influenced in which task version errors grew from conditioning to deconditioning: in unmedicated patients just as controls errors only rose in the NoGo version with an increase of incorrect responses to target cues. Contrarily, in medicated patients errors went up only in the Go version with an increase of response omissions to target cues. The error increases during deconditioning can be understood as a perpetuation of reaction tendencies acquired during conditioning. The levodopa-mediated modulation of this carry-over effect suggests that dopamine supports habit conditioning under the task demand of response execution, but dampens it when inhibition is required. However, other than in reinforcement learning, supporting dopaminergic actions referred to the most frequent, i. e., non-target behaviour. Since this is passive whenever selective actions are executed against an inactive background, dopaminergic treatment could in according scenarios contribute to passive behaviour in patients with Parkinson's disease

NGC 2264 IRS1: The central engine and its cavity

We present a high-resolution study of NGC 2264 IRS1 in CS(2-1) and in the 3-mm continuum using the IRAM Plateau de Bure Interferometer. We complement these radio data with images taken at 2.2, 4.6, and 11.9 micron. The combined information allow a new interpretation of the closest environment of NGC 2264 IRS1. No disk around the B-type star IRS1 was found. IRS1 and its low-mass companions are located in a low-density cavity which is surrounded by the remaining dense cloud core which has a clumpy shell-like structure. Strong evidence for induced on-going star formation was found in the surroundings of IRS1. A deeply embedded very young stellar object 20 arcsec to the north of IRS1 is powering a highly collimated bipolar outflow. The object 8 in the closer environment of IRS1 is a binary surrounded by dusty circumbinary material and powering two bipolar outflows.Comment: 17 pages, 6 figures, The paper is accepted and will appear in the Astrophysical Journal, Vol 599, No 1 (issue December 10). A high-resolution postscript version of this paper is available here ( http://www.astro.uni-jena.de/Users/martin/publi.html). Furthermore, you can find a high resolution PDF file here ( http://www.tls-tautenburg.de/research/tls-research/pub2003.html

Warm-Dense Molecular Gas in the ISM of Starbursts, LIRGs and ULIRGs

The role of star formation in luminous and ultraluminous infrared galaxies is a hotly debated issue: while it is clear that starbursts play a large role in powering the IR luminosity in these galaxies, the relative importance of possible enshrouded AGNs is unknown. It is therefore important to better understand the role of star forming gas in contributing to the infrared luminosity in IR-bright galaxies. The J=3 level of 12CO lies 33K above ground and has a critical density of ~1.5 X 10^4 cm^-3. The 12CO(J=3-2) line serves as an effective tracer for warm-dense molecular gas heated by active star formation. Here we report on 12CO (J=3-2) observations of 17 starburst spirals, LIRGs and ULIRGs which we obtained with the Heinrich Hertz Submillimeter Telescope on Mt. Graham, Arizona. Our main results are the following: 1. We find a nearly linear relation between the infrared luminosity and warm-dense molecular gas such that the infrared luminosity increases as the warm-dense molecular gas to the power 0.92; We interpret this to be roughly consistent with the recent results of Gao & Solomon (2004a,b). 2. We find L_IR/M_H2 ratios ranging from ~10 to ~128 L_sun/M_sun using a standard CO-H2 conversion factor of 3 X 10^20 cm^-2 (K km s^-1)^-1. If this conversion factor is ~an order of magnitude less, as suggested in a recent statistical survey (Yao et al. 2003), then 2-3 of our objects may have significant contributions to the L_IR by dust-enshrouded AGNs.Comment: 15 Pages, 2 figures, Accepted for Publication in Ap

Dark cloud cores and gravitational decoupling from turbulent flows

We test the hypothesis that the starless cores may be gravitationally bound clouds supported largely by thermal pressure by comparing observed molecular line spectra to theoretical spectra produced by a simulation that includes hydrodynamics, radiative cooling, variable molecular abundance, and radiative transfer in a simple one-dimensional model. The results suggest that the starless cores can be divided into two categories: stable starless cores that are in approximate equilibrium and will not evolve to form protostars, and unstable pre-stellar cores that are proceeding toward gravitational collapse and the formation of protostars. The starless cores might be formed from the interstellar medium as objects at the lower end of the inertial cascade of interstellar turbulence. Additionally, we identify a thermal instability in the starless cores. Under par ticular conditions of density and mass, a core may be unstable to expansion if the density is just above the critical density for the collisional coupling of the gas and dust so that as the core expands the gas-dust coupling that cools the gas is reduced and the gas warms, further driving the expansion.Comment: Submitted to Ap

Dust and gas in luminous infrared galaxies - results from SCUBA observations

We present new data taken at 850 $\mu$m with SCUBA at the JCMT for a sample of 19 luminous infrared galaxies. Fourteen galaxies were detected. We have used these data, together with fluxes at 25, 60 and 100 $\mu$m from IRAS, to model the dust emission. We find that the emission from most galaxies can be described by an optically thin, single temperature dust model with an exponent of the dust extinction coefficient ($k_\lambda \propto \lambda^{-\beta}$) of $\beta \simeq 1.5 - 2$. A lower $\beta\simeq 1$ is required to model the dust emission from two of the galaxies, Arp 220 and NGC 4418. We discuss various possibilities for this difference and conclude that the most likely is a high dust opacity. In addition, we compare the molecular gas mass derived from the dust emission, $M_{dust}$, with the molecular gas mass derived from the CO emission, $M_{CO}$, and find that $M_{CO}$ is on average a factor 3 higher than $M_{dust}$.Comment: 10 pages, 6 figures, latex, with MN-macros, accepted by MNRAS - revised version (changed flux values for some galaxies

VLA H53alpha and H92alpha line observations of the central region of NGC 253

We present new Very Large Array (VLA) observations toward NGC 253 of the recombination line H53alpha (43 GHz) at an angular resolution of 1.''5 X 1.''0. The free-free emission at 43 GHz is estimated to be ~100 mJy, implying a star formation rate of ~1.3 Msun/yr in the nuclear region of this starburst galaxy. A reanalysis is made for previously reported H92alpha observations carried out with angular resolution of 1.''5 X 1.''0 and 0.''36 X 0.''21. Based on the line and continuum emission models used for the 1.''5 X 1.''0 angular resolution observations, the RRLs H53alpha and H92alpha are tracers of the high-density (~10^5 cm-3) and low-density (~10^3 cm^-3) thermally ionized gas components in NGC 253, respectively. The velocity fields observed in the H53alpha and H92alpha lines 1.''5 X 1.''0) are consistent. The velocity gradient in the central ~18 pc of the NE component, as observed in both the H53alpha and H92alpha lines, is in the opposite direction to the velocity gradient determined from the CO observations. The enclosed virial mass, as deduced from the H53alpha velocity gradient over the NE component, is ~5 X 10^6 Msun in the central ~18 pc region. The H92alpha line observations at high angular resolution (0.''36 X 0.''21) reveal a larger velocity gradient, along a P.A. ~ -45 deg on the NE component, of ~110 km/s/arcsec. The dynamical mass estimated using the high angular resolution H92alpha data (~7 X 10^6 Msun) supports the existence of an accreted massive object in the nuclear region of NGC 253.Comment: Accepted for publication in Ap