23 results on '"Dettmar, Ralf-Jürgen"'
Search Results
2. Wobbly discs – corrugations seen in the dust lanes of edge-on galaxies.
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Narayan, Chaitra A, Dettmar, Ralf-Jürgen, and Saha, Kanak
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DUST , *DISK galaxies , *GALAXIES , *FOURIER analysis , *LINEAR statistical models - Abstract
We report the detection of small-scale bending waves, also known as corrugations, in the dust lanes of five nearby edge-on disc galaxies. This phenomenon, where the disc mid-plane bends to become wavy, just as in warps but on a smaller scale, is seen here for the first time, in the dust lanes running across the discs. Because they are seen in absorption, this feature must be present in the dust disc in the outskirts of these galaxies. We enhance the visibility of these features using unsharp masking, trace the dust mid-plane across the disc, measure the corrugation amplitude by eye and the corrugation wavelength using Fourier analysis. The corrugation amplitude is found to be in the range of 70–300pc and the wavelengths lie between 1 and 5 kpc. In this limited sample, we find that the amplitude of the corrugations tends to be larger for lower mass galaxies, whereas the wavelength of corrugation does not seem to depend on the mass of host galaxies. Linear stability analysis is performed to find out the dynamical state of these dust discs. Based on WKB analysis, we find that the dust corrugations in about half of our sample are stable. Further analysis, on a larger sample would be useful to strengthen the above results. [ABSTRACT FROM AUTHOR]
- Published
- 2020
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3. Advective and diffusive cosmic ray transport in galactic haloes.
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Heesen, Volker, Dettmar, Ralf-Jürgen, Krause, Marita, Beck, Rainer, and Stein, Yelena
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SYNCHROTRON radiation , *COSMIC rays , *NUMERICAL solutions to equations , *EXPONENTIAL functions , *GALACTIC halos , *COSMIC magnetic fields - Abstract
We present 1D cosmic ray transport models, numerically solving equations of pure advection and diffusion for the electrons and calculating synchrotron emission spectra. We find that for exponential halo magnetic field distributions advection leads to approximately exponential radio continuum intensity profiles, whereas diffusion leads to profiles that can be better approximated by a Gaussian function. Accordingly, the vertical radio spectral profiles for advection are approximately linear, whereas for diffusion they are of 'parabolic' shape. We compare our models with deep Australia Telescope Compact Array observations of two edgeon galaxies, NGC 7090 and 7462, at λλ 22 and 6 cm. Our result is that the cosmic ray transport in NGC 7090 is advection dominated with V = 150+80-30 km s-1, and that the one in NGC 7462 is diffusion dominated with D = 3.0 ± 1.0 1028E0.5GeV cm² s-1. NGC 7090 has both a thin and thick radio disc with respective magnetic field scale heights of hB1 = 0.8 ± 0.1 kpc and hB2 = 4.7 ± 1.0 kpc. NGC 7462 has only a thick radio disc with hB2 = 3.8 ± 1.0 kpc. In both galaxies, the magnetic field scale heights are significantly smaller than what estimates from energy equipartition would suggest. A non-negligible fraction of cosmic ray electrons can escape from NGC 7090, so that this galaxy is not an electron calorimeter. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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4. Magnetic fields in halos of spiral galaxies and the interstellar disk-halo connection.
- Author
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Dettmar, Ralf-Jürgen
- Subjects
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COSMIC magnetic fields , *GALAXIES , *SPIRAL galaxies , *STAR formation , *ASTROPHYSICAL radiation , *SPACE environment - Abstract
Observations of magnetic fields in halos of edge-on disk galaxies are discussed in relation to the different gaseous phases of the interstellar medium. For this comparison the presence of diffuse ionized gas (DIG) is introduced as a valuable tracer for gaseous halos which are originating from the star-formation driven disk-halo connection of the interstellar medium. The distribution of extraplanar DIG correlates on local and global scales with cosmic rays and magnetic fields as inferred from observations of the non-thermal radio continuum radiation and its polarization. From the polarization a large scale and well ordered magnetic field in these gaseous halos can be deduced. These observations indicate the presence of physical processes which generate and maintain magnetic fields on galactic scales. The importance of differential rotation of the gaseous halos for such processes is briefly discussed and the possible influence of magnetic fields on the dynamics of dust particles is addressed. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2005
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5. The starformation driven interstellar disk-halo connection.
- Author
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Dettmar, Ralf-Jürgen
- Subjects
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SPIRAL galaxies , *IONIZED gases , *COSMIC magnetic fields , *SYNCHROTRONS , *HYDROGEN , *ASTROPHYSICS - Abstract
The evidence for starformation in the disks of spiral galaxies driving the disk-halo interaction is briefly reviewed. It is argued that diffuse ionized gas (DIG) in the halos of edge-on disk galaxies traces the presence of extraplanar gas well since it correlates with the star formation rate in the underlying disk as well as with other gaseous phases and components of the ISM such as X-ray hot gas, cosmic rays, and magnetic fields. The dependence on the starformation rate is demonstrated using a survey of H+ halos with more than 70 objects. This survey allows us to establish a minimum energy release per unit area that is required to start the disk-halo mass exchange. Observations of extraplanar HII regions let us conclude that also molecular hydrogen must be present. In addition, well ordered magnetic field in the gaseous halos can be deduced from the polarization of synchrotron radiocontinuum maps. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2005
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6. Diffuse ionized gas in halos of spiral galaxies.
- Author
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Dettmar, Ralf-Jürgen
- Subjects
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SPIRAL galaxies , *STARS , *GALACTIC halos , *IONIZED gases , *INTERSTELLAR medium , *ASTROPHYSICS , *SPACE sciences - Abstract
The presence of gaseous halos in star forming disk galaxies is reviewed in the context of a proposed disk-halo connection of the interstellar medium (ISM). Results from a new survey for H+ halos of edge-on galaxies are presented. The data confirm that the presence of diffuse ionized gas (DIG) in the disk-halo interface of spiral galaxies is related to star formation processes in the underlying disk. A discussion allows us to establish a minimum energy release per unit area that is required to start the disk-halo mass exchange. By comparing some recent observational results for diagnostic emission lines with model predictions from photoionization we demonstrate that the origin and excitation of the ionized halo gas is still not completely understood and that a discussion gives important constraints for models of the ISM. In comparison with similar findings for the Milky Way the need for an additional heating source is established. Special emphasis is given to some recent developments. In particular, new kinematical information for the DIG layer in NGC 5775 from ESO/VLT long-slit spectra is discussed in connection with the magnetic field structure in the halo of this object as deduced from VLA radio-continuum polarization data (Tüllmann et al., 2001). Finally, the role of dust for the physical processes in the disk-halo interface is briefly addressed. [ABSTRACT FROM AUTHOR]
- Published
- 2004
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7. MeerKAT discovery of a double radio relic and odd radio circle: connecting cluster and galaxy merger shocks.
- Author
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Koribalski, Bärbel S, Veronica, Angie, Dolag, Klaus, Reiprich, Thomas H, Brüggen, Marcus, Heywood, Ian, Andernach, Heinz, Dettmar, Ralf-Jürgen, Hoeft, Matthias, Zhang, Xiaoyuan, Bulbul, Esra, Garrel, Christian, Józsa, Gyula I G, and English, Jayanne
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GALAXY mergers , *GALAXY clusters , *MEERKAT , *RELICS , *RADIO galaxies , *ANGULAR distance - Abstract
We present the serendipitous discovery of (1) a large double radio relic associated with the galaxy cluster PSZ2 G277.93 + 12.34 and (2) a new odd radio circle, ORC J1027–4422, both found in the same deep MeerKAT 1.3 GHz wide-band radio continuum image. The angular separation of the two arc-shaped cluster relics is ∼16 arcmin or ∼2.6 Mpc for a cluster redshift of z ≈ 0.158. The thin southern relic, which shows several ridges/shocks including one possibly moving inwards, has a linear extent of ∼1.64 Mpc. In contrast, the northern relic is about twice as wide, twice as bright, but only has a largest linear size of ∼0.66 Mpc. Complementary SRG/eROSITA X-ray images reveal extended emission from hot intracluster gas between the two relics and around the narrow-angle tail (NAT) radio galaxy PMN J1033–4335 (z ≈ 0.153) located just east of the northern relic. The radio morphologies of the NAT galaxy and the northern relic, which are also detected with the Australian Square Kilometer Array Pathfinder (ASKAP) at 888 MHz, suggest both are moving in the same outward direction. The discovery of ORC J1027–4422 in a different part of the same MeerKAT image makes it the fourth known single ORC. It has a diameter of ∼90 arcsec corresponding to 400 kpc at a tentative redshift of z ≈ 0.3 and remains undetected in X-ray emission. Supported by simulations, we discuss similarities between outward moving galaxy and cluster merger shocks as the formation mechanisms for ORCs and radio relics, respectively. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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8. eDIG-CHANGES. II. Project Design and Initial Results on NGC 3556.
- Author
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Li, Jiang-Tao, Lu, Li-Yuan, Qu, Zhijie, Benjamin, Robert A., Bregman, Joel N., Dettmar, Ralf-Jürgen, English, Jayanne, Fang, Taotao, Irwin, Judith A., Jiang, Yan, Li, Hui, Liu, Guilin, Martini, Paul, Rand, Richard J., Stein, Yelena, Strong, Andrew W., Vargas, Carlos J., Wang, Q. Daniel, Wang, Jing, and Wiegert, Theresa
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IONIZED gases , *DISK galaxies , *GAS dynamics , *ACTIVE galactic nuclei , *TRACE gases , *GALACTIC magnetic fields , *GALACTIC halos - Abstract
The extraplanar diffuse ionized gas (eDIG) represents ionized gases traced by optical/UV lines beyond the stellar extent of galaxies. We herein introduce a novel multislit narrow-band spectroscopy method to conduct spatially resolved spectroscopy of the eDIG around a sample of nearby edge-on disk galaxies (eDIG-CHANGES). In this paper, we introduce the project design and major scientific goals, as well as a pilot study of NGC 3556 (M108). The eDIG is detected to a vertical extent of a few kiloparsecs above the disk, comparable to the X-ray and radio images. We do not see significant vertical variation of the [N ii ]/H α line ratio. A rough examination of the pressure balance between different circumgalactic medium phases indicates the magnetic field is in a rough pressure balance with the X-ray emitting hot gas and may play an important role in the global motion of both the eDIG and the hot gas in the lower halo. At the location of an Hubble Space Telescope/Cosmic Origins Spectrograph observed UV bright background active galactic nucleus ∼29 kpc from the center of NGC 3556, the magnetic pressure is much lower than that of the hot gas and the ionized gas traced by UV absorption lines, although the extrapolation of the pressure profiles may cause some biases in this comparison. By comparing the position–velocity diagrams of the optical and CO lines, we also find the dynamics of the two gas phases are consistent with each other, with no evidence of a global inflow/outflow and a maximum rotation velocity of ∼150 km s−1. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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9. A Gaussian-processes approach to fitting for time-variable spherical solar wind in pulsar timing data.
- Author
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Niţu, Iuliana C, Keith, Michael J, Tiburzi, Caterina, Brüggen, Marcus, Champion, David J, Chen, Siyuan, Cognard, Ismaël, Desvignes, Gregory, Dettmar, Ralf-Jürgen, Grießmeier, Jean-Mathias, Guillemot, Lucas, Guo, Yanjun, Hoeft, Matthias, Hu, Huanchen, Jang, Jiwoong, Janssen, Gemma H, Jawor, Jedrzej, Karuppusamy, Ramesh, Keane, Evan F, and Kramer, Michael
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PULSARS , *SOLAR wind , *SOLAR oscillations , *INTERSTELLAR medium - Abstract
Propagation effects are one of the main sources of noise in high-precision pulsar timing. For pulsars below an ecliptic latitude of 5°, the ionized plasma in the solar wind can introduce dispersive delays of order |$100\, \mu \mathrm{s}$| around solar conjunction at an observing frequency of 300 MHz. A common approach to mitigate this assumes a spherical solar wind with a time-constant amplitude. However, this has been shown to be insufficient to describe the solar wind. We present a linear, Gaussian-process piecewise Bayesian approach to fit a spherical solar wind of time-variable amplitude, which has been implemented in the pulsar software run_enterprise. Through simulations, we find that the current EPTA+InPTA data combination is not sensitive to such variations; however, solar wind variations will become important in the near future with the addition of new InPTA data and data collected with the low-frequency LOFAR telescope. We also compare our results for different high-precision timing data sets (EPTA+InPTA, PPTA, and LOFAR) of 3 ms pulsars (J0030+0451, J1022+1001, J2145−0450), and find that the solar-wind amplitudes are generally consistent for any individual pulsar, but they can vary from pulsar to pulsar. Finally, we compare our results with those of an independent method on the same LOFAR data of the three millisecond pulsars. We find that differences between the results of the two methods can be mainly attributed to the modelling of dispersion variations in the interstellar medium, rather than the solar wind modelling. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
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10. Validation of global ionospheric models using long-term observations of pulsar Faraday rotation with the LOFAR radio telescope.
- Author
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Porayko, Nataliya K., Mevius, Maaijke, Hernández-Pajares, Manuel, Tiburzi, Caterina, Olivares Pulido, German, Liu, Qi, Verbiest, Joris P. W., Künsemöller, Jörn, Krishnakumar, Moochickal Ambalappat, Bak Nielsen, Ann-Sofie, Brüggen, Marcus, Graffigna, Victoria, Dettmar, Ralf-Jürgen, Kramer, Michael, Osłowski, Stefan, Schwarz, Dominik J., Shaifullah, Golam M., and Wucknitz, Olaf
- Abstract
Broad band pulsar radiation can be effectively used to monitor the properties of the magneto-ionic media through which it propagates. Faraday rotation calculated from polarised pulsar observations provides an integrated product of electron densities and the line-of-sight component of the magnetic field in the intervening plasma. In particular, a time-variable effect mainly associated with the rapidly changing column density of the Earth’s ionosphere and plasmasphere heavily dominates the observed Faraday rotation of pulsar radiation. In this work, we aim to carry out a performance test of three GNSS-based models of the ionosphere using observations of PSR J0332+5434 taken with the LOw Frequency ARray (LOFAR). As it was shown in Porayko et al. (Month Not Roy Astron Soc 483(3):4100–4113, 2019. . ), the conventional single layer model (SLM), which assumes that the ionosphere is a thin slab at a fixed effective height, is not capable of fully accounting for the ionospheric Faraday rotation in pulsar data. The simplified physics of the SLM is upgraded within IRI-Plas (International Reference Ionosphere and Plasmasphere) extended SLM and the dual-layer voxel TOmographic Model of the Ionosphere (TOMION), both of which partially account for the thickness and vertical dynamics of the terrestrial plasma. Although the last two improve the reconstruction of the ionospheric Faraday rotation, none of the considered models completely purge the observed residual variations. With this study, we show that the long term LOFAR observations of Faraday rotation of pulsars provide an excellent tool to test and improve models of the magneto-ionic content of the Earth’s atmosphere. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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11. In Memorium.
- Author
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Dettmar, Ralf-Jürgen
- Subjects
- ROSSA, Jorn
- Abstract
The article presents an obituary for astronomer Jörn Rossa is presented.
- Published
- 2012
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12. Pulsar scintillation studies with LOFAR: II. Dual-frequency scattering study of PSR J0826+2637 with LOFAR and NenuFAR.
- Author
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Wu, Ziwei, Coles, William A, Verbiest, Joris P W, Ambalappat, Krishnakumar Moochickal, Tiburzi, Caterina, Grießmeier, Jean-Mathias, Main, Robert A, Liu, Yulan, Kramer, Michael, Wucknitz, Olaf, Porayko, Nataliya, Osłowski, Stefan, Nielsen, Ann-Sofie Bak, Donner, Julian Y, Hoeft, Matthias, Brüggen, Marcus, Vocks, Christian, Dettmar, Ralf-Jürgen, Theureau, Gilles, and Serylak, Maciej
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POWER spectra , *PULSARS , *INTERSTELLAR medium , *TEST validity - Abstract
Interstellar scattering (ISS) of radio pulsar emission can be used as a probe of the ionized interstellar medium (IISM) and causes corruptions in pulsar timing experiments. Two types of ISS phenomena (intensity scintillation and pulse broadening) are caused by electron density fluctuations on small scales (< 0.01 au). Theory predicts that these are related, and both have been widely employed to study the properties of the IISM. Larger scales (∼1 – 100 au) cause measurable changes in dispersion and these can be correlated with ISS observations to estimate the fluctuation spectrum over a very wide scale range. IISM measurements can often be modelled by a homogeneous power-law spatial spectrum of electron density with the Kolmogorov (−11/3) spectral exponent. Here, we aim to test the validity of using the Kolmogorov exponent with PSR J0826+2637. We do so using observations of intensity scintillation, pulse broadening and dispersion variations across a wide fractional bandwidth (20–180 MHz). We present that the frequency dependence of the intensity scintillation in the high-frequency band matches the expectations of a Kolmogorov spectral exponent, but the pulse broadening in the low-frequency band does not change as rapidly as predicted with this assumption. We show that this behaviour is due to an inhomogeneity in the scattering region, specifically that the scattering is dominated by a region of transverse size ∼40 au. The power spectrum of the electron density, however, maintains the Kolmogorov spectral exponent from spatial scales of 5 × 10−6 au to ∼100 au. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
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13. Disc-halo gas outflows driven by stellar clusters as seen in multiwavelength tracers.
- Author
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Vasiliev, Evgenii O, Drozdov, Sergey A, Nath, Biman B, Dettmar, Ralf-Jürgen, and Shchekinov, Yuri A
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STELLAR mass , *DUST , *STELLAR activity , *MILKY Way , *STAR formation , *GALACTIC halos , *GALAXY clusters , *STELLAR radiation - Abstract
We consider the dynamics of and emission from growing superbubbles in a stratified interstellar gaseous disc driven by energy release from supernovae explosions in stellar clusters with masses Mcl = 105 − 1.6 × 106 M⊙. Supernovae are spread randomly within a sphere of rc = 60 pc, and inject energy episodically with a specific rate |$1/130~\mathrm{M}_\odot ^{-1}$| proportional to the star formation rate (SFR) in the cluster. Models are run for several values of SFR in the range 0.01 to 0.1 M⊙ yr−1, with the corresponding average surface energy input rate ∼0.04–0.4 erg cm−2 s−1. We find that the discrete energy injection by isolated SNe are more efficient in blowing superbubbles: Asymptotically they reach heights of up to 3 to 16 kpc for Mcl = 105 − 1.6 × 105 M⊙, correspondingly, and stay filled with a hot and dilute plasma for at least 30 Myr. During this time, they emit X-ray, Hα and dust infrared emission. X-ray luminosities LX ∝SFR3/5 that we derive here are consistent with observations in star-forming galaxies. Even though dust particles of small sizes a ≤ 0.03 μm are sputtered in the interior of bubbles, larger grains still contribute considerably ensuring the bubble luminosity |$L_{\rm IR}/{\rm SFR}\sim 5\times 10^7 \, \mathrm{L}_\odot \, \mathrm{M}_\odot ^{-1} ~{\rm yr}$|. It is shown that the origin of the North Polar Spur in the Milky Way can be connected with activity of a cluster with the stellar mass of ∼105 M⊙ and the SFR ∼ 0.1 M⊙ yr−1 some 25–30 Myr ago. Extended luminous haloes observed in edge-on galaxies (NGC 891 as an example) can be maintained by disc spread stellar clusters of smaller masses M * ≲ 105 M⊙. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
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14. eDIG-CHANGES I: extended Hα emission from the extraplanar diffuse ionized gas (eDIG) around CHANG-ES galaxies.
- Author
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(芦李源), Li-Yuan Lu, (李江涛), Jiang-Tao Li, Vargas, Carlos J, Beck, Rainer, Bregman, Joel N, Dettmar, Ralf-Jürgen, English, Jayanne, (方陶陶), Taotao Fang, Heald, George H, Li, Hui, Qu, Zhijie, Rand, Richard J, Stein, Michael, Wang, Q Daniel, (王菁), Jing Wang, Wiegert, Theresa, and Zheng, Yun
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IONIZED gases , *COSMIC rays , *GALAXIES , *THERMAL electrons , *GAS reservoirs , *SPIRAL galaxies - Abstract
The extraplanar diffuse ionized gas (eDIG) represents the cool/warm ionized gas reservoir around galaxies. We present spatial analysis of the Hα images of 22 nearby edge-on spiral galaxies taken with the Apache Point Observatory 3.5-m telescope (eDIG-CHANGES). We conduct an exponential fit to the vertical Hα intensity profiles of the galaxies, of which 16 can be decomposed into thin + thick disk components. The median value of the Hα scale height of the thick disk is |$\langle h_{\rm H\alpha }\rangle =1.13\pm 0.14\rm ~kpc$|. We further examine the dependence of h Hα on the stellar mass, SFR, and SFR surface density (SFRSD) of the galaxies. We find a tight sublinear correlation between h Hα and SFR, expressed in h Hα ∝ SFRα, where α ≈ 0.29. Moreover, the offset of individual galaxies from the best-fit SFR- h Hα relation, expressed in h Hα/SFRα, shows significant anti-correlation with SFRSD. We further compare the vertical extension of the eDIG to multi-wavelength measurements of other CGM phases. We find the eDIG slightly more extended than the neutral gas. This indicates the existence of some extended ionizing sources, in addition to the leaking photons from the disk star formation regions. Most galaxies have an X-ray scale height smaller than Hα, suggesting the majority of the X-ray photons are actually from the thick disk instead of the extended CGM. h Hα is comparable to the L-band radio continuum scale height. This indicates that the thermal and non-thermal electrons have similar spatial distributions, a natural result if both are transported outwards by a galactic wind. This further indicates the thermal gas, cosmic rays, and magnetic field may be close to energy equipartition. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
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15. CHANG-ES - VI. Probing Supernova energy deposition in spiral galaxies through multiwavelength relationships.
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Jiang-Tao Li, Beck, Rainer, Dettmar, Ralf-Jürgen, Heald, George, Irwin, Judith, Johnson, Megan, Kepley, Amanda A., Krause, Marita, Murphy, E. J., Orlando, Elena, Rand, Richard J., Strong, A. W., Vargas, Carlos J., Walterbos, Rene, Daniel Wang, Q., and Wiegert, Theresa
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SUPERNOVAE , *FORCE & energy , *SPIRAL galaxies , *WAVELENGTHS , *INTERSTELLAR medium , *GALACTIC evolution - Abstract
How a galaxy regulates its supernovae (SNe) energy into different interstellar/circumgalactic medium components strongly affects galaxy evolution. Based on the JVLA D-configuration C- (6 GHz) and L-band (1.6 GHz) continuum observations, we perform statistical analysis comparing multiwavelength properties of the Continuum Haloes in Nearby Galaxies - an EVLA Survey galaxies. The high-quality JVLA data and edge-on orientation enable us for the first time to include the halo into the energy budget for a complete radio-flux-limited sample. We find tight correlations of Lradio with the mid-IR-based star formation rate (SFR). The normalization of our I1.6 GHz/WHz-1-SFR relation is ~2-3times of those obtained for face-on galaxies, probably a result of enhanced IR extinction at high inclination. We also find tight correlations between Lradio and the SNe energy injection rate ĖSN(Ia+CC), indicating the energy loss via synchrotron radio continuum accounts for ~1 of ĖSN, comparable to the energy contained in cosmic ray electrons. The integrated C-to-L-band spectral index is α ~ 0.5-1.1 for non-active galactic nucleus galaxies, indicating a dominance by the diffuse synchrotron component. The low-scatter Lradio-SFR/Lradio-ĖSN(Ia+CC) relationships have superlinear logarithmic slopes at ~2σ in L band (1.132 ± 0.067/1.175 ± 0.102) while consistent with linear in C band (1.057 ± 0.075/1.100 ± 0.123). The superlinearity could be naturally reproduced with non-calorimeter models for galaxy discs. Using Chandra halo X-ray measurements, we find sublinear LX-Lradio relations. These results indicate that the observed radio halo of a starburst galaxy is close to electron calorimeter, and a galaxy with higher SFR tends to distribute an increased fraction of SNe energy into radio emission (than X-ray). [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
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16. Galactic winds in dwarf galaxies
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Bomans, Dominik J., van Eymeren, Janine, Dettmar, Ralf-Jürgen, Weis, Kerstin, and Hopp, Ulrich
- Subjects
- *
GALAXY formation , *GALACTIC evolution , *GALAXY spectra , *GALAXY clusters , *ASTROPHYSICS - Abstract
Abstract: Galactic winds are mayor ingredients of our current paradigms of galaxy formation and evolution. They are needed to explain the chemical evolution of galaxies and the intergalactic medium, the luminosity function of galaxies, the formation of galaxies, and the reionization of the universe, just to name a few topics. While the observational support for the presence of galactic winds in massive galaxies and gas-rich mergers is quite strong, the case for galactic winds in dwarf galaxies is much weaker. This is rather surprising, given their shallow potential well and the many examples of star bursts in local dwarf galaxies. Apparently, the physics is complicated in the low-mass case. In this paper we first comment on the theoretical framework for galactic winds in dwarf galaxies and the problems of the observational verification in massive, intermediate mass, and true dwarf galaxies. We then present new observations underlining the complexity of the gas structure of gas halos of dwarf galaxies and the resulting effects on the formation of galactic winds. [Copyright &y& Elsevier]
- Published
- 2007
- Full Text
- View/download PDF
17. CHANG-ES -- XI. Circular polarization in the cores of nearby galaxies.
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Irwin, Judith A., Henriksen, Richard N., Weżgowiec, Marek, Damas-Segovia, Ancor, Wang, Q. Daniel, Krause, Marita, Heald, George, Dettmar, Ralf-Jürgen, Jiang-Tao Li, Wiegert, Theresa, Stein, Yelena, Braun, Timothy T., Jisung Im, Schmidt, Philip, Macdonald, Scott, Miskolczi, Arpad, Merritt, Alison, Mora-Partiarroyo, S. C., Saikia, D. J., and Sotomayor, Carlos
- Subjects
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GALAXIES , *COSMIC rays , *MAGNETIC fields , *ELECTRONS , *ACTIVE galactic nuclei - Abstract
We detect five galaxies in the Continuum Halos in Nearby Galaxies -- an EVLA Survey (CHANG-ES) sample that show circular polarization (CP) at L band in our high-resolution data sets. Two of the galaxies (NGC 4388 and NGC4845) show strong Stokes V/I ≡ mC *** 2 per cent, two (NGC 660 and NGC3628) have values of mC *** 0.3 per cent, and NGC3079 is a marginal detection at mC *** 0.2 per cent. The two strongest mC galaxies also have the most luminous X-ray cores and the strongest internal absorption in X-rays. We have expanded on our previous Faraday conversion interpretation and analysis and provide analytical expressions for the expected V signal for a general case in which the cosmic ray (CR) electron energy spectral index can take on any value. We provide examples as to how such expressions could be used to estimate magnetic field strengths and the lower energy cut-off for CR electrons. Four of our detections are resolved, showing unique structures, including a jet in NGC4388 and a CP 'conversion disc' in NGC4845. The conversion disc is inclined to the galactic disc but is perpendicular to a possible outflow direction. Such CP structures have never before been seen in any galaxy to our knowledge. None of the galaxy cores show linear polarization at L band. Thus radio CP may provide a unique probe of the physical conditions in the cores of active galactic nuclei. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
18. CHANG-ES IX. Radio scale heights and scale lengths of a consistent sample of 13 spiral galaxies seen edge-on and their correlations.
- Author
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Krause, Marita, Irwin, Judith, Wiegert, Theresa, Miskolczi, Arpad, Damas-Segovia, Ancor, Beck, Rainer, Li, Jiang-Tao, Heald, George, Müller, Peter, Stein, Yelena, Rand, Richard J., Heesen, Volker, Walterbos, Rene A. M., Dettmar, Ralf-Jürgen, Vargas, Carlos J., English, Jayanne, and Murphy, Eric J.
- Subjects
- *
SPIRAL galaxies , *GALACTIC halos , *GALACTIC magnetic fields , *INTERSTELLAR medium , *COSMIC rays - Abstract
Aims. The vertical halo scale height is a crucial parameter to understand the transport of cosmic-ray electrons (CRE) and their energy loss mechanisms in spiral galaxies. Until now, the radio scale height could only be determined for a few edge-on galaxies because of missing sensitivity at high resolution. Methods. We developed a sophisticated method for the scale height determination of edge-on galaxies. With this we determined the scale heights and radial scale lengths for a sample of 13 galaxies from the CHANG-ES radio continuum survey in two frequency bands. Results. The sample average values for the radio scale heights of the halo are 1:1 ± 0:3 kpc in C-band and 1:4 ± 0:7 kpc in L-band. From the frequency dependence analysis of the halo scale heights we found that the wind velocities (estimated using the adiabatic loss time) are above the escape velocity. We found that the halo scale heights increase linearly with the radio diameters. In order to exclude the diameter dependence, we defined a normalized scale height h which is quite similar for all sample galaxies at both frequency bands and does not depend on the star formation rate or the magnetic field strength. However, h shows a tight anticorrelation with the mass surface density. Conclusions. The sample galaxies with smaller scale lengths are more spherical in the radio emission, while those with larger scale lengths are flatter. The radio scale height depends mainly on the radio diameter of the galaxy. The sample galaxies are consistent with an escape-dominated radio halo with convective cosmic ray propagation, indicating that galactic winds are a widespread phenomenon in spiral galaxies. While a higher star formation rate or star formation surface density does not lead to a higher wind velocity, we found for the first time observational evidence of a gravitational deceleration of CRE outflow, e.g. a lowering of the wind velocity from the galactic disk. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
19. On the non-thermal electron-to-proton ratio at cosmic ray acceleration sites.
- Author
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Merten, Lukas, Becker Tjus, Julia, Eichmann, Björn, and Dettmar, Ralf-Jürgen
- Subjects
- *
LUMINOSITY , *COSMIC rays , *ELECTRONS , *PROTONS , *RADIANT intensity , *ASTROPHYSICS - Abstract
The luminosity ratio of electrons to protons as it is produced in stochastic acceleration processes in cosmic ray sources is an important quantity relevant for several aspects of the modeling of the sources themselves. It is usually assumed to be around 1: 100 in the case of Galactic sources, while a value of 1: 10 is typically assumed when describing extragalactic sources. It is supported by observations that the average ratios should be close to these values. At this point, however, there is no possibility to investigate how each individual source behaves. When looking at the physics aspects, a 1: 100 ratio is well supported in theory when making the following assumptions: (1) the total number of electrons and protons that is accelerated are the same; (2) the spectral index of both populations after acceleration is α e = α p ≈ 2.2 . In this paper, we reinvestigate these assumptions. In particular, assumption (2) is not supported by observational data of the sources and PIC simulation yield different spectral indices as well. We present the detailed calculation of the electron-to-proton ratio, dropping the assumption of equal spectral indices. We distinguish between the ratio of luminosities and the ratio of the differential spectral behavior, which becomes necessary for cases where the spectral indices of the two particle populations are not the same. We discuss the possible range of values when allowing for different spectral indices concerning the spectral behavior of electrons and protons. Additionally, it is shown that the minimum energy of the accelerated population can have a large influence on the results. We find, in the case of the classical minimum energy of T 0 , e = T 0 , p = 10 keV, that when allowing for a difference in the spectral indices of up to 0.1 with absolute spectral indices varying between 2.0 < α < 2.3, the luminosity ratio varies between 0.008 < K ep < 0.12. The differential particle number ratio is in the range 0.008 < K ˜ ep < 0.25 and depends on the energy. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
20. The Radio Halo of the Starburst Galaxy NGC 253.
- Author
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Heesen, Volker, Krause, Marita, Beck, Rainer, and Dettmar, Ralf-Jürgen
- Subjects
- *
GALAXIES , *MAGNETIC fields , *MATHEMATICAL continuum , *RADIO (Medium) , *TELESCOPES , *STARBURSTS - Abstract
We have conducted 3.6 cm radio continuum observations of the nearby starburst galaxy NGC 253 with the Effelsberg 100-m telescope. The polarized emission reveals a prominent radio halo with the magnetic field mainly aligned parallel to the galactic disk. In the south-east of NGC 253 a huge spur dominates, where the magnetic field lines are along the spur. As this spur can be interpreted as a starburst-driven outflow, magnetic fields trace (or even control) the occurrence of collimated galactic outflows (chimneys). Thus NGC 253 serves as an ideal case to study the connection between galactic winds and the large-scale magnetic field structure. With recently obtained VLA-D observations at 6 cm, to be combined with the Effelsberg data, we will be able to examine this connection in more detail. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2005
- Full Text
- View/download PDF
21. Lyman break galaxies at z∼3 and z∼4 in the Chandra Deep Field South.
- Author
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Bomans, Dominik J., Hildebrandt, Hendrik, Erben, Thomas, Haberzettl, Lutz, Schneider, Peter, and Dettmar, Ralf-Jürgen
- Subjects
- *
GALAXIES , *SURVEYS , *ASTRONOMY , *PHYSICAL sciences , *ASTROPHYSICS - Abstract
We present first results of a Lyman break galaxy survey in the complete 30′ by 30′ Chandra Deep Field South (CDFS) based on deep, multi-color CCD mosaic images. We find more than 1100 U-band and 600 B-band drop-outs, consistent with the expectations from earlier searches in smaller fields. The results of the 2-point correlation functions agree well with earlier results on smaller fields, too. Due to the full coverage of the survey field with HST-ACS images, we can study the structure of the Lyman break galaxies, which turn out to span a large range in morphologies. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2005
- Full Text
- View/download PDF
22. A kinematic study of the neutral and ionized gas in the irregular dwarf galaxies IC 4662 and NGC 5408.
- Author
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van Eymeren, Janine, Koribalski, Bärbel S., López-Sánchez, Ángel R., Dettmar, Ralf-Jürgen, and Bomans, Dominik J.
- Subjects
- *
KINEMATICS , *IONIZED gases , *DWARF galaxies , *ASTRONOMY , *INTERSTELLAR medium - Abstract
The feedback between massive stars and the interstellar medium is one of the most important processes in the evolution of dwarf galaxies. This interaction results in numerous neutral and ionized gas structures that have been found both in the disc and in the halo of these galaxies. However, their origin and fate are still poorly understood. We here present new H i and optical data of two Magellanic irregular dwarf galaxies in the Local Volume: IC 4662 and NGC 5408. The H i line data were obtained with the Australia Telescope Compact Array and are part of the ‘Local Volume H i Survey’. They are complemented by optical images and spectroscopic data obtained with the European Southern Observatory (ESO) New Technology Telescope and the ESO 3.6-m telescope. Our main aim is to study the kinematics of the neutral and ionized gas components in order to search for outflowing gas structures and to make predictions about their fate. Therefore, we perform a Gaussian decomposition of the H i and Hα line profiles. We find the H i gas envelopes of IC 4662 and NGC 5408 to extend well beyond the optical discs, with H i to optical diameter ratios of above 4. The optical disc is embedded into the central H i maximum in both galaxies. However, higher resolution H i maps show that the H i intensity peaks are typically offset from the prominent H ii regions. While NGC 5408 shows a fairly regular H i velocity field, which allows us to derive a rotation curve, IC 4662 reveals a rather twisted H i velocity field, possibly caused by a recent merger event. We detect outflows with velocities between 20 and 60 km s−1 in our Hα spectra of both galaxies, sometimes with H i counterparts of similar velocity. We suggest the existence of expanding superbubbles, especially in NGC 5408. This is also supported by the detection of full width at half-maxima as high as 70 km s−1 in Hα, which cannot be explained by thermal broadening alone. In the case of NGC 5408, we compare our results with the escape velocity of the galaxy, which shows that the measured expansion velocities are in all cases too low to allow the gas to escape from the gravitational potential of NGC 5408. This result is consistent with studies of other dwarf galaxies. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
23. On the three-dimensional structure of edge-on disc galaxies.
- Author
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Pohlen, Michael, Zaroubi, Saleem, Peletier, Reynier F., and Dettmar, Ralf-Jürgen
- Subjects
- *
GALAXIES , *DISKS (Astrophysics) , *ALGORITHMS , *DISTRIBUTION of stars , *ASTRONOMICAL photometry - Abstract
A simple algorithm is employed to deproject the two-dimensional images of a pilot sample of 12 high-quality images of edge-on disc galaxies and to study their intrinsic three-dimensional (3D) stellar distribution. We examine the radial profiles of the stars as a function of height above the plane and report a general trend within our sample of an increasing radial scalelength with height outside of the dust lane. This could be explained by the widespread presence of a thick disc component in these galaxies. In addition, the 3D view allows the study of the vertical distribution of the outer disc, beyond the break region, where we detect a significant increase in scalelength with vertical distance from the major axis for the truncated discs. This could be regarded as a weakening of the ‘truncation’ with increasing distance from the plane. Furthermore, we conclude that the recently revised classification of the radial surface brightness profiles found for face-on galaxies is indeed independent of geometry. In particular, we find at least one example of each of the three main profile classes as defined in complete samples of intermediate to face-on galaxies: not-truncated, truncated and antitruncated. The position and surface brightness that mark the break location in the radial light distribution are found to be consistent with those of face-on galaxies. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
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