Max Planck Insitut fur Extraterrestrische Physik

Garching bei München, Germany

Max Planck Insitut fur Extraterrestrische Physik

Garching bei München, Germany
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Gonzalez O.A.,Astronomy Technology Center | Debattista V.P.,University of Central Lancashire | Ness M.,Max Planck Institute for Astronomy | Erwin P.,Max Planck Insitut fur extraterrestrische Physik | Gadotti D.A.,European Southern Observatory
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2017

Bulges of edge-on galaxies are often boxy/peanut-shaped (B/PS), and unsharp masks reveal the presence of an X shape. Simulations show that these shapes can be produced by dynamical processes driven by a bar which vertically thickens the centre. In the Milky Way, which contains such a B/PS bulge, the X-shaped structure is traced by the metal-rich stars but not by the metal-poor ones. Recently, Debattista et al. interpreted this property as a result of the varying effect of the bar on stellar populations with different starting kinematics. This kinematic fractionation model predicts that cooler populations at the time of bar formation go on to trace the X shape, whereas hotter populations are more uniformly distributed. As this prediction is not specific to the Milky Way, we test it with Multi Unit Spectroscopic Explorer (MUSE) observations of the B/PS bulge in the nearby galaxy NGC 4710. We show that the metallicity map is more peanut-shaped than the density distribution itself, in good agreement with the prediction. This result indicates that the X-shaped structure in B/PS bulges is formed of relatively metal-rich stars that have been vertically redistributed by the bar, whereas the metal-poor stars have a more uniform, box-shaped distribution. © 2016 The Authors.

Bosman A.D.,Leiden University | Bruderer S.,Max Planck Insitut fur Extraterrestrische Physik | Van Dishoeck E.F.,Leiden University
Astronomy and Astrophysics | Year: 2017

Context. The infrared ro-vibrational emission lines from organic molecules in the inner regions of protoplanetary disks are unique probes of the physical and chemical structure of planet-forming regions and the processes that shape them. These observed lines are mostly interpreted with local thermal equilibrium (LTE) slab models at a single temperature. Aims. We aim to study the non-LTE excitation effects of carbon dioxide (CO2) in a full disk model to evaluate: (i) what the emitting regions of the different CO2 ro-vibrational bands are; (ii) how the CO2 abundance can be best traced using CO2 ro-vibrational lines using future JWST data and; (iii) what the excitation and abundances tell us about the inner disk physics and chemistry. CO2 is a major ice component and its abundance can potentially test models with migrating icy pebbles across the iceline. Methods. A full non-LTE CO2 excitation model has been built starting from experimental and theoretical molecular data. The characteristics of the model are tested using non-LTE slab models. Subsequently the CO2 line formation was modelled using a two-dimensional disk model representative of T Tauri disks where CO2 is detected in the mid-infrared by the Spitzer Space Telescope. Results. The CO2 gas that emits in the 15 μm and 4.5 μm regions of the spectrum is not in LTE and arises in the upper layers of disks, pumped by infrared radiation. The v2 15 μm feature is dominated by optically thick emission for most of the models that fit the observations and increases linearly with source luminosity. Its narrowness compared with that of other molecules stems from a combination of the low rotational excitation temperature (~ 250 K) and the inherently narrower feature for CO2. The inferred CO2 abundances derived for observed disks range from 3 × 10-9 to 1 × 10-7 with respect to total gas density for typical gas/dust ratios of 1000, similar to earlier LTE disk estimates. Line-to-continuum ratios are low, in the order of a few percent, stressing the need for high signal-to-noise (S/N > 300) observations for individual line detections. Conclusions. The inferred CO2 abundances are much lower than those found in interstellar ices (~ 10-5), indicating a reset of the chemistry by high temperature reactions in the inner disk. JWST-MIRI with its higher spectral resolving power will allow a much more accurate retrieval of abundances from individual P- and R-branch lines, together with the 13CO2Q-branch at 15 μm. The 13CO2Q-branch is particularly sensitive to possible enhancements of CO2 due to sublimation of migrating icy pebbles at the iceline(s). Prospects for JWST-NIRSpec are discussed as well. © ESO, 2017.

Erwin P.,Max Planck Insitut fur Extraterrestrische Physik | Erwin P.,Universitats Sternwarte Munich
Astrophysical Journal | Year: 2015

I describe a new, open-source astronomical image-fitting program called imfit, specialized for galaxies but potentially useful for other sources, which is fast, flexible, and highly extensible. A key characteristic of the program is an object-oriented design that allows new types of image components (two-dimensional surfacebrightness functions) to be easily written and added to the program. Image functions provided with imfit include the usual suspects for galaxy decompositions (Sérsic, exponential, Gaussian), along with Core-Sérsic and brokenexponential profiles, elliptical rings, and three components that perform line-of-sight integration through threedimensional luminosity-density models of disks and rings seen at arbitrary inclinations. Available minimization algorithms include Levenberg-Marquardt, Nelder-Mead simplex, and Differential Evolution, allowing trade-offs between speed and decreased sensitivity to local minima in the fit landscape. Minimization can be done using the standard χ2 statistic (using either data or model values to estimate per-pixel Gaussian errors, or else user-supplied error images) or Poisson-based maximum-likelihood statistics; the latter approach is particularly appropriate for cases of Poisson data in the low-count regime. I show that fitting low-signal-to-noise ratio galaxy images using χ2 minimization and individual-pixel Gaussian uncertainties can lead to significant biases in fitted parameter values, which are avoided if a Poisson-based statistic is used; this is true even when Gaussian read noise is present. © 2015. The American Astronomical Society. All rights reserved.

Cole D.R.,University of Central Lancashire | Debattista V.P.,University of Central Lancashire | Erwin P.,Max Planck Insitut fur extraterrestrische Physik | Erwin P.,Universitats Sternwarte Munich | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

The role of gas in themass assembly at the nuclei of galaxies is still subject to some uncertainty. Stellar nuclear discs bridge the gap between the large-scale galaxy and the central massive objects that reside there. Using a high-resolution simulation of a galaxy forming out of gas cooling and settling into a disc, we study the formation and properties of nuclear discs. Gas, driven to the centre by a bar, settles into a rotating star-forming nuclear disc (ND). This ND is thinner, younger, kinematically cooler and more metal rich than the surrounding bar. The ND is elliptical and orthogonal to the bar. The complex kinematics in the region of the ND are a result of the superposition of older stars streaming along the bar and younger stars circulating within the ND. The signature of the ND is therefore subtle in the kinematics. Instead the ND stands out clearly in metallicity and age maps. We compare the model to the density and kinematics of real galaxies with NDs finding qualitative similarities. Our results suggest that gas dissipation is very important for forming nuclear structures.

Wilman D.J.,Max Planck Insitut fur Extraterrestrische Physik | Erwin P.,Max Planck Insitut fur Extraterrestrische Physik | Erwin P.,Universitats Sternwarte Munich
Astrophysical Journal | Year: 2012

We present results of an analysis of the local (z ∼ 0) morphology-environment relation for 911 bright (MB < -19) galaxies, based on matching classical RC3 morphologies with the Sloan Digital Sky Survey based group catalog of Yang et al., which includes halo mass estimates. This allows us to study how the relative fractions of spirals, lenticulars, and ellipticals depend on halo mass over a range of 10 11.7-1014.8 h -1 M·, from isolated single-galaxy halos to massive groups and low-mass clusters. We pay particular attention to how morphology relates to central versus satellite status (where "central" galaxies are the most massive within their halo). The fraction of galaxies which are elliptical is a strong function of stellar mass; it is also a strong function of halo mass, but only for central galaxies. We interpret this as evidence for a scenario where elliptical galaxies are always formed, probably via mergers, as central galaxies within their halos, with satellite ellipticals being previously central galaxies accreted onto a larger halo. The overall fraction of galaxies which are S0 increases strongly with halo mass, from ∼10% to ∼70%. Here, too, we find striking differences between the central and satellite populations. 20% 2% of central galaxies with stellar masses M* > 1010.5 M · are S0 regardless of halo mass, but satellite S0 galaxies are only found in massive (>1013 h -1 M ·) halos, where they are 69% ± 4% of the M * > 1010.5 M· satellite population. This suggests two channels for forming S0 galaxies: one which operates for central galaxies and another which transforms lower-mass (M * ≲ 1011 M·) accreted spirals into satellite S0 galaxies in massive halos. Analysis of finer morphological structure (bars and rings in disk galaxies) shows some trends with stellar mass, but none with halo mass; this is consistent with other recent studies which indicate that bars are not strongly influenced by galaxy environment. Radio sources in high-mass central galaxies are common, similarly so for elliptical and S0 galaxies, with a frequency that increases with the halo mass. Emission-line active galactic nuclei (mostly LINERs) are more common in S0s, but show no strong trends with environment. © 2012 The American Astronomical Society. All rights reserved.

Erwin P.,Max Planck Insitut fur extraterrestrische Physik | Erwin P.,Universitats Sternwarte Munich | Debattista V.P.,University of Central Lancashire
Monthly Notices of the Royal Astronomical Society | Year: 2013

We show that direct detection and measurement of the vertically thickened parts of bars (so-called 'boxy' or 'peanut-shaped' bulges) are possible not only for edge-on galaxies but also for galaxies with moderate inclinations (i< 70°), and that examples are relatively common in the nearby Universe. The analysis of a sample of 78 nearby, moderately inclined (i ≲ 65°) early-type (S0-Sb) barred galaxies shows that the isophotal signature of the box/peanut can usually be detected for inclinations as low as i ∼ 40° - and in exceptional cases down to i ∼ 30°. In agreement with the predictions from N-body simulations, the signature is most easily detectable when the bar's position angle is within ∼50° of the galaxy major axis; in particular, galaxies where the bar lies very close to the minor axis do not show the signature clearly or at all. For galaxies with i= 40°-65° and relative angles <45°, we find evidence for the signature ≈2/3 of the time; the true frequency of box/peanut structures in bars may be higher. Comparison with N-body models also allows us to link observed photometric morphology with 3D physical structures, and thus estimate the relative sizes of box/peanut structures and bars. For our local sample, we find that box/peanut structures range in radial size (measured along the bar major axis) from 0.4 to 3.8 kpc (mean 1.5 ± 0.9 kpc) and span 0.26-0.58 of the bar length (mean of 0.38 ± 0.08). This is a clear observational confirmation that when bars thicken, it is not the entire bar which does so, but only the inner part. This technique can also be used to identify galaxies with bars which have not vertically thickened. We suggest that NGC 3049 and IC 676 may be particularly good examples, and that the fraction of S0-Sb bars which lack box/peanut structures is at least ∼13 per cent. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Bailey J.D.,Max Planck Insitut fur Extraterrestrische Physik | Landstreet J.D.,Armagh Observatory | Landstreet J.D.,University of Western Ontario
Astronomy and Astrophysics | Year: 2015

Context. In recent years, significant effort has been made to understand how the magnetic field strengths and atmospheric chemical abundances of Ap/Bp stars evolve during their main sequence lifetime by identifying a large number of Ap/Bp stars with accurately known ages. As a next step, these stars should be studied individually and in detail to offer further insight into the physics of how such main sequence stars evolve. Aims. We have obtained high resolution spectra using the ESPaDOnS spectropolarimeter and FEROS spectrograph of the chemically peculiar, magnetic Bp star HD 133652. Using these data, we present a simple magnetic field model and abundance determinations of He, O, Mg, Si, Ti, Cr, Fe, Pr, and Nd. Methods. Abundance analysis was performed using zeeman.f, a spectral synthesis program that includes the effects of magnetic fields on line formation. The magnetic field structure is approximated as a simple, co-linear multipole expansion that reproduces the observed variations of the line-of-sight magnetic field with phase. The abundance distribution of each element was modelled using a uniform abundance in each of the two magnetic hemispheres. Results. Using the new magnetic field measurements, we were able to refine the rotation period of HD 133652 to P = 2.30405 ± 0.00002 d. The abundance analysis reveals that the elements modelled (except He, O and Mg) are overabundant compared to the Sun; however most elements studied do not show substantial differences in the large-scale mean abundances between the two magnetic hemispheres. The individual line profiles are very complex and clearly indicate the presence of significant small-scale abundance variations on the stellar surface. Conclusions. These data are adequate to perform a useful investigation of the magnetic field structure and abundance distribution over the stellar surface. HD 133652 is now one of a growing list of hotter Bp stars of known age for which this type of analysis has been performed. © ESO 2015.

Bailey J.D.,Max Planck Insitut fur Extraterrestrische Physik | Grunhut J.,ESO | Landstreet J.D.,Armagh Observatory | Landstreet J.D.,University of Western Ontario
Astronomy and Astrophysics | Year: 2015

Aims. Detailed information about the magnetic geometry, atmospheric abundances and radial velocity variations has been obtained for the magnetic standard star HD 94660 based on high-dispersion spectroscopic and spectropolarimetric observations from the UVES, HARPSpol and ESPaDOnS instruments. Methods. We perform a detailed chemical abundance analysis using the spectrum synthesis code ZEEMAN for a total of 17 elements. Using both line-of-sight and surface magnetic field measurements, we derive a simple magnetic field model that consists of dipole, quadrupole and octupole components. Results. The observed magnetic field variations of HD 94660 are complex and suggest an inhomogeneous distribution of chemical elements over the stellar surface. This inhomogeneity is not reflected in the abundance analysis, from which all available spectra are modelled, but only a mean abundance is reported for each element. The derived abundances are mostly non-solar, with striking overabundances of Fe-peak and rare-earth elements. Of note are the clear signatures of vertical chemical stratification throughout the stellar atmosphere, most notably for the Fe-peak elements. We also report on the detection of radial velocity variations with a total range of 35 kms-1 in the spectra of HD 94660. A preliminary analysis shows the most likely period of these variations to be of order 840 d and, based on the derived orbital parameters of this star, suggests the first detection of a massive compact companion for a main sequence magnetic star. Conclusions. HD 94660 exhibits interestingly complex magnetic field variations and remarkable radial velocity variations. Long term monitoring is necessary to provide further constraints on the nature of these radial velocity variations. Detection of a companion will help establish the role of binarity in the origin of magnetism in stars with radiative envelopes. © ESO, 2015.

Vollmer B.,11 Rue Of Luniversite | Davies R.I.,Max Planck Insitut fur extraterrestrische Physik
Astronomy and Astrophysics | Year: 2013

Galactic gas-gas collisions involving a turbulent multiphase interstellar medium (ISM) share common ISM properties: dense extraplanar gas visible in CO, large linewidths (≳3;50 km s-1), strong mid-infrared H 2 line emission, low star formation activity, and strong radio continuum emission. Gas-gas collisions can occur in the form of ram pressure stripping caused by the rapid motion of a spiral galaxy within the intracluster medium, galaxy head-on collisions, compression of the intragroup gas and/or galaxy ISM by an intruder galaxy which flies through the galaxy group at a high velocity, or external gas accretion on an existing gas torus in a galactic center. We suggest that the common theme of all these gas-gas interactions is adiabatic compression of the ISM leading to an increase of the turbulent velocity dispersion of the gas. The turbulent gas clouds are then overpressured and star formation is quenched. Within this scenario we developed a model for turbulent clumpy gas disks where the energy to drive turbulence is supplied by external infall or the gain of potential energy by radial gas accretion within the disk. The cloud size is determined by the size of a continuous (C-type) shock propagating in dense molecular clouds with a low ionization fraction at a given velocity dispersion. We give expressions for the expected volume and area filling factors, mass, density, column density, and velocity dispersion of the clouds. The latter is based on scaling relations of intermittent turbulence whose open parameters are estimated for the circumnuclear disk in the Galactic center. The properties of the model gas clouds (~0.1 pc, ~100 M ⊙, Δv ≳ 6 km s-1) and the external mass accretion rate necessary for the quenching of the star formation rate due to adiabatic compression (Ṁ ~ 1-10 M⊙ yr-1) are consistent with those derived from high-resolution H2 2.12 μm line observations. Based on these findings, a scenario for the evolution of gas tori in galactic centers is proposed and the implications for star formation in the Galactic center are discussed. © ESO, 2013.

Rusli S.P.,Max Planck Insitut fur extraterrestrische Physik | Rusli S.P.,Universitatssternwarte | Thomas J.,Max Planck Insitut fur extraterrestrische Physik | Thomas J.,Universitatssternwarte | And 8 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

The masses of the most massive supermassive black holes (SMBHs) predicted by the MBH-σ and MBH-L relations appear to be in conflict. Which of the two relations is the more fundamental one remains an open question. NGC 1332 is an excellent example that represents the regime of conflict. It is a massive lenticular galaxy which has a bulge with a high velocity dispersion σ of 320 km s-1; bulge-disc decomposition suggests that only 44 per cent of the total light comes from the bulge. The MBH-σ and the MBH-L predictions for the central black hole mass of NGC 1332 differ by almost an order of magnitude. We present a stellar dynamical measurement of the SMBH mass using an axisymmetric orbit superposition method. Our SINFONI integral-field unit (IFU) observations of NGC 1332 resolve the SMBH's sphere of influence which has a diameter of 0.76 arcsec. The σ inside 0.2 arcsec reaches 400 km s-1. The IFU data allow us to increase the statistical significance of our results by modelling each of the four quadrants separately. We measure an SMBH mass of (1.45 ± 0.20) × 109-M- with a bulge mass-to-light ratio of 7.08 ± 0.39 in the R band. With this mass, the SMBH of NGC 1332 is offset from the MBH-L relation by a full order of magnitude but is consistent with the MBH-σ relation. © 2010 The Authors. Journal compilation © 2010 RAS.

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