arXiv subjects

M. Haas

Publications and source records attributed to M. Haas.

69 records · Page 4Linked to original sources

arXiv2005

Discovery of 10 micron silicate emission in quasars. Evidence of the AGN unification scheme

According to the unified scheme, AGN are surrounded by a dust-torus, and the observed diversity of AGN properties results from the different orientations relative to our line of sight. The strong resonance of silicate dust at 10 micron is therefore, as expected, seen in absorption towards many type-2 AGN. In type-1 AGN, it should be seen in emission because the hot inner surface of the dust torus becomes visible. However, this has not been observed so far, thus challenging the unification scheme or leading to exotic modifications of the dust-torus model. Here we report the discovery of the 10 micron silicate feature in emission in two luminous quasars with the Infrared Spectrograph of the Spitzer Space Telescope.

astro-ph↗

arXiv2005

VPMS J1342+2840 - an unusual quasar from the variability and proper motion survey

We report the discovery of the highly peculiar, radio-loud quasar VPMS J1342+2840 (z ~ 1.3) from the variability and proper motion survey. We present spectroscopic, imaging and photometric observations. The unusual spectrum shows a strong depression of the continuum over a wide wavelength range in the blue part without the typical structures of broad absorption line (BAL) troughs. The image of the quasar is unresolved and there is no evidence for a foreground object on the line of sight. The broad-band spectral energy distribution is not consistent with obvious dust reddening with the standard SMC extinction curve. The downturn of the continuum flux of VPMS J1342+2840 at short wavelengths can be caused by dust reddening only if the reddening curve is steeper then the SMC curve in the ultraviolet and is very flat at longer wavelengths. Alternatively, the dominant spectral features can be explained by low-ionization BALs forming unusually wide, overlapping absorption troughs.

astro-ph↗

arXiv2004

The dust SED in the dwarf galaxy NGC 1569: Indications for an altered dust composition?

We discuss the interpretation of the dust SED from the mid-infrared to the millimeter range of NGC 1569. The model developed by Désert et al. (1990) including three dust components (Polyaromatic Hydrocarbons, Very Small Grains and big grains) can explain the data using a realistic interstellar radiation field and adopting an enhanced abundance of VSGs. A simple three-temperature model is also able to reproduce the data but requires a very low dust temperature which is considered to be unlikely in this low-metallicity starburst galaxy. The high abundance of Very Small Grains might be due to large grain destruction in supernova shocks. This possibility is supported by ISO data showing that the emission at 14.3 $μ$m, tracing VSGs, is enhanced with respect to the emission at 6.7 $μ$m and 850 $μ$m in regions of high star formation.

astro-ph↗

arXiv2004

Dust in 3CR radio galaxies: On the FR1-FR2 difference

We compare three 3CR samples of 11 FR1 galaxies, 17 FR2 galaxies and 18 lobe-dominated quasars contained in the ISO Data Archive. In contrast to the powerful FR2 galaxies with edge-brightened lobes, the low radio power FR1 galaxies in our sample do not exhibit any high MIR or FIR dust luminosity, which is typical for a buried, intrinsically more luminous AGN. This consolidates the fact already inferred from optical studies that their AGNs have only a relatively low luminosity. Also the FR1 galaxies show a high FIR/MIR luminosity ratio, compared to quasars, suggesting that their FIR luminosity is substantially powered by the interstellar radiation field (ISRF) of the giant elliptical hosts. Finally, we discuss the FR1-FR2 morphological dichotomy. FR1 galaxies do not have more interstellar matter (ISM) than FR2s as traced -- on the large scale -- by the cool FIR emitting dust and -- in the nuclear region -- by the warm MIR emitting dust. Due to the lack of central gas we suggest that the black holes of our FR1 galaxies are fed at a lower accretion rate than those of the FR2 galaxies.

astro-ph↗

arXiv2004

The ISOPHOT-MAMBO survey of 3CR radio sources: Further evidence for the unified schemes

We present the complete set of ISOPHOT observations of 3CR radio galaxies and quasars, which are contained in the ISO Data Archive, providing 75 mid- and far-infrared spectral energy distributions (SEDs) between 5 and 200 micron. For 28 sources they are supplemented with MAMBO 1.2 mm observations and for 15 sources with new submillimetre data from the SCUBA archive. We check the orientation-dependent unified scheme, in which the powerful FR2 narrow line galaxies are quasars viewed at high inclination, so that their nuclei are hidden behind a dust torus intercepting the optical-ultraviolet AGN radiation and reemitting it in the infrared. We find that (1) both the quasars and the galaxies show a high mid- to far-infrared luminosity ratio typical for powerful AGNs and (2) -- when matched in 178 MHz luminosity -- both show the same ratio of isotropic far-infrared to isotropic 178 MHz lobe power. Therefore, from our large sample investigated here we find strong evidence for the orientation-dependent unification of the powerful FR2 galaxies with the quasars.

astro-ph↗

arXiv2004

New Limits to the Drift of Fundamental Constants from Laboratory Measurements

We have remeasured the absolute $1S$-$2S$ transition frequency $ν_{\rm {H}}$ in atomic hydrogen. A comparison with the result of the previous measurement performed in 1999 sets a limit of $(-29\pm 57)$ Hz for the drift of $ν_{\rm {H}}$ with respect to the ground state hyperfine splitting $ν_{\rm {Cs}}$ in $^{133}$Cs. Combining this result with the recently published optical transition frequency in $^{199}$Hg$^+$ against $ν_{\rm {Cs}}$ and a microwave $^{87}$Rb and $^{133}$Cs clock comparison, we deduce separate limits on $\dotα/α= (-0.9\pm 2.9)\times 10^{-15}$ yr$^{-1}$ and the fractional time variation of the ratio of Rb and Cs nuclear magnetic moments $μ_{\rm {Rb}}/μ_{\rm {Cs}}$ equal to $(-0.5 \pm 1.7)\times 10^{-15}$ yr$^{-1}$. The latter provides information on the temporal behavior of the constant of strong interaction.

physics.optics↗

arXiv2004

ISOCAM survey and dust models of 3CR radio galaxies and quasars

We present a survey of all 3CR sources imaged with ISOCAM onboard the Infrared Space Observatory (ISO). For the source, we present spatially integrated mid--infrared (MIR, 5 - 18mic.) fluxes measured from newly calibrated ISOCAM images. In total, we detected 68 AGN of the 3CR catalogue, at redshifts z < 2.5. The one with the highest redshift is 4C+72.26 at z = 3.53. ISOCAM data are combined with other photometric measurements to construct the spectral energy distribution (SED) from optical to radio wavelengths. In order to describe dust emission we apply new radiative transfer models. By varying three parameters, luminosity, effective size and extinction, we obtain a fit to the SED for our objects. In the MIR the hot dust component is mainly due to small grains and PAHs. In the models, a type 1 AGN is represented by a compact dust distribution, the dust is therefore very warm and emission of PAHs is weak because of photo--destruction. In AGNs of type 2, the dust is relatively colder but PAH bands are strong.

astro-ph↗

arXiv2003

MgB2 Energy Gap Determination by Scanning Tunneling Spectroscopy

We report scanning tunneling spectroscopy (STS) measurements of the gap properties of both ceramic MgB2 and c-axis oriented epitaxial MgB2 thin films. Both show a temperature dependent zero bias conductance peak and evidence for two superconducting gaps. We report tunneling spectroscopy of superconductor-insulator-superconductor (S-I-S) junctions formed in two ways in addition to normal metal-insulator-superconductor (N-I-S) junctions. We find a gap delta=2.3-2.8 meV, with spectral features and temperature dependence that are consistent between S-I-S junction types. In addition, we observe evidence of a second, larger gap, delta=7.2 meV, consistent with a proposed two-band model.

cond-mat.supr-con↗

arXiv2003

Lamb Shift of Laser-Dressed Atomic States

We discuss radiative corrections to an atomic two-level system subject to an intense driving laser field. It is shown that the Lamb shift of the laser-dressed states, which are the natural state basis of the combined atom-laser system, cannot be explained in terms of the Lamb shift received by the atomic bare states which is usually observed in spectroscopic experiments. In the final part, we propose an experimental scheme to measure these corrections based on the incoherent resonance fluorescence spectrum of the driven atom.

quant-ph↗

arXiv2003

The spiral galaxy M33 mapped in the FIR by ISOPHOT: A spatially resolved study of the warm and cold dust

The Sc galaxy M33 has been mapped with ISOPHOT in the far-infrared, at 60, 100, and 170mue. The spatial resolution of these FIR maps allows the separation of spiral arms and interarm regions and the isolation of a large number of star-forming regions. The spectral energy distribution in the FIR indicates a superposition of two components, a warm one originating from dust at ~45K, and a cold one, at ~16K. The warm component is concentrated towards the spiral arms and the star-forming regions, and is likely heated by the UV radiation from OB stars. The cold component is more smoothly distributed over the disk, and heated by the diffuse interstellar radiation. For the about 60 star-forming regions detected the H-alpha/FIR flux ratio increases significantly with the distance from the galaxy center, probably due to decreasing extinction. An anti-correlation of F_Ha/F_60 with F_170 suggests the intrinsic extinction to be related to the cold dust surface brightness according to A_V/S_170~0.03mag/MJy*sr. For the total galaxy the star formation rate (SFR) derived from the FIR is in agreement with that derived from the de-extincted H-alpha emission. For individual star-forming regions, a consistency between SFRs derived from the optical and from the FIR requires only a fraction of the UV radiation to be absorbed locally. The individual star-forming regions also show a local radio-FIR correlation. This local correlation is, however, due to quite different components than to those that lead to the well-known global radio-FIR correlation for entire galaxies.

astro-ph↗

arXiv2002

A very young star forming region detected by the ISOPHOT Serendipity Survey

We present a multi-wavelength study of the star forming region ISOSS J 20298+3559, which was identified by a cross-correlation of cold compact sources from the 170 micron ISOPHOT Serendipity Survey (ISOSS) database coinciding with objects detected by the MSX, 2MASS and IRAS infrared surveys. ISOSS J 20298+3559 is associated with a massive dark cloud complex (M ~ 760 M$_{\odot}$) and located in the Cygnus X giant molecular cloud. We derive a distance of 1800 pc on the basis of optical extinction data. The low average dust temperature (T ~ 16 K) and large mass (M ~ 120 M$_{\odot}$) of the dense inner part of the cloud, which has not been dispersed, indicates a recent begin of star formation. The youth of the region is supported by the early evolutionary stage of several pre- and protostellar objects discovered across the regio n: I) Two candidate Class 0 objects with masses of 8 and 3.5 M$_{\odot}$, II) a gravitationally bound, cold (T ~ 12 K) and dense (n(H$_{2}$) \~ 2 x 10$^{5}$ cm$^{-3}$) cloud core with a mass of 50 M$_{\odot}$ and III) a Herbig B2 star with a mass of 6.5 M$_{\odot}$ and a bolometric luminosity of 2200 L$_{\odot}$, showing evidence for ongoing accretion and a stellar age of less than 40000 years. The dereddened SED of the Herbig star is well reproduced by an accretion disc + star model. The externally heated cold cloud core is a good candidate for a massive pre-protostellar object. The star formation efficiency in the central cloud region is about 14 %.

astro-ph↗

arXiv2001

Infrared to millimetre photometry of ultra-luminous IR galaxies: new evidence favouring a 3-stage dust model

Infrared to millimetre spectral energy distributions have been obtained for 41 bright ultra-luminous infrared galaxies. The observations were carried out with ISOPHOT between 10 and 200 micron and supplemented for 16 sources with SCUBA at 450 and 850 micron and with SEST at 1.3 mm. In addition, seven sources were observed at 1.2 and 2.2 $μ$m with the 2.2 m telescope on Calar Alto. These new SEDs represent the most complete set of infrared photometric templates obtained so far on ULIRGs in the local universe.

astro-ph↗

arXiv2001

Dust emission from 3C radio galaxies and quasars: New ISO observations favour the unified scheme

In order to test the unified scheme for luminous radio galaxies and quasars we observed 10 galaxy/quasar pairs from the 3CR catalogue with ISOPHOT at infrared wavelengths between 5 and 180 micron. Each pair was selected such that both the 178 MHz luminosity and the redshift match as close as possible between the radio galaxy and the quasar in order to minimize effects of cosmic evolution. 13 of the 20 sources were detected in at least one waveband. 12 sources show clear evidence of a thermal bump at FIR wavelength, while in the remaining 7 sources the upper limits are still compatible with the presence of luminous dust emission. In agreement with the predictions of the unified scheme, the quasars and galaxies in our sample cannot be distinguished by their observed mid- and far-infrared properties. This is in contrast to the IRAS results which indicated that radio galaxies radiate significantly less mid- to far-infrared emission than quasars. However, the IRAS samples are dominated by low-redshift sources (z < 0.5), while our sample contains several of the most luminous radio galaxies at redshift z ~ 1. The latter have already been suspected to contain a hidden quasar for other reasons, e.g. an extended emission line region aligned with the radio axis. From the ratio between FIR luminosity emitted by dust and the radio power at 178 MHz, we conclude that the radio galaxy/quasar unification might be perfectly valid for the most luminous 3C sources at high redshift (z > 0.8). At lower redshifts (z < 0.5), however, some of the FRII radio galaxies contain active nuclei which emit less UV-optical continuum than the quasars of similar radio power. (abrigded)

astro-ph↗

arXiv2001

Strongly linked current flow in polycrystalline forms of the new superconductor MgB2

The discovery of superconductivity at 39 K in MgB2[1] raises many issues. One of the central questions is whether this new superconductor resembles a high-temperature-cuprate superconductor or a low-temperature metallic superconductor in terms of its current carrying characteristics in applied magnetic fields. In spite of the very high transition temperatures of the cuprate superconductors, their performance in magnetic fields has several drawbacks[2]. Their large anisotropy restricts high bulk current densities to much less than the full magnetic field-temperature (H-T) space over which superconductivity is found. Further, weak coupling across grain boundaries makes transport current densities in untextured polycrystalline forms low and strongly magnetic field sensitive[3,4]. These studies of MgB2 address both issues. In spite of the multi-phase, untextured, nano-scale sub-divided nature of our samples, supercurrents flow throughout without the strong sensitivity to weak magnetic fields characteristic of Josephson-coupled grains[3]. Magnetization measurements over nearly all of the superconducting H-T plane show good temperature scaling of the flux pinning force, suggestive of a current density determined by flux pinning. At least two length scales are suggested by the magnetization and magneto optical (MO) analysis but the cause of this seems to be phase inhomogeneity, porosity, and minority insulating phase such as MgO rather than by weakly coupled grain boundaries. Our results suggest that polycrystalline ceramics of this new class of superconductor will not be compromised by the weak link problems of the high temperature superconductors, a conclusion with enormous significance for applications if higher temperature analogs of this compound can be discovered.

cond-mat.supr-con↗

arXiv2000

The bright 175um knots of the Andromeda Galaxy

Discrete far-infrared (FIR) sources of M31 are identified in the ISO 175um map and characterized via their FIR colours, luminosities and masses. With a mean size of 800pc, they probably represent several clouds in chance projection or giant cloud complexes. The 175um data point provides crucial information in addition to the IRAS 60 and 100um data: At least two modified Planck curves with temperatures of about 40K and 15-21K are necessary to fit the SEDs of the knots. We distinguish between three types of knots - cold, medium, warm - in order to recognize trends. Comparisons with radio and optical tracers show that - statistically - the cold knots can be identified well with CO and HI radio sources and thus might represent mainly molecular cloud complexes. The warm knots coincide with known HII regions and supernova remnants. The medium knots might contain a balanced mixture of molecular clouds and HII regions. The cold knots have a considerable luminosity and their discovery raises the question of hidden star formation. Though the optically dark dust lanes in M31 generally match the FIR ring, surprisingly we do not find a convincing coincidence of our knots with individual dark clouds which might therefore show mainly foreground dust features. The ratio of FIR luminosity to dust mass, L/M, is used to measure the energy content of the dust. The knots have a clear L/M excess over the rest of M31, providing evidence that they are powered by star formation in addition to the interstellar radiation field. The L/M ratio of the warm knots is comparable to that of Galactic HII regions like M42 or NGC2024, while that of the cold knots still reaches values like in the average Orion complex. Thus both the warm and the cold knots are interpreted as containing large cloud complexes with considerable ongoing star formation.

astro-ph↗