Christof Iserlohe

A Black Hole in the Galactic Center Complex IRS 13E

The IRS 13E complex is an unusual concentration of massive, early-type stars at a projected distance of ~0.13 pc from the Milky Ways central supermassive black hole Sagittarius A* (Sgr A*). Because of their similar proper motion and their common nature as massive, young stars, it has recently been suggested that IRS 13E may be the remnant of a massive stellar cluster containing an intermediate-mass black hole (IMBH) that binds its members gravitationally in the tidal field of Sgr A*. Here, we present an analysis of the proper motions in the IRS 13E environment that combines the currently best available data with a time line of 10 years. We find that an IMBH in IRS 13E must have a minimum mass of ~104 M☉ in order to bind the source complex gravitationally. This high-mass limit in combination with the absence so far of compelling evidence for a nonthermal radio and X-ray source in IRS 13E make it appear unlikely that an IMBH exists in IRS 13E that is sufficiently massive to bind the system gravitationally.

SINFONI: integral field spectroscopy at 50-milli-arcsecond resolution with the ESO VLT

SINFONI is an adaptive optics assisted near-infrared integral field spectrometer for the ESO VLT. The Adaptive OPtics Module (built by the ESO Adaptive Optics Group) is a 60-elements curvature-sensor based system, designed for operations with natural or sodium laser guide stars. The near-infrared integral field spectrometer SPIFFI (built by the Infrared Group of MPE) provides simultaneous spectroscopy of 32 x 32 spatial pixels, and a spectral resolving power of up to 3300. The adaptive optics module is in the phase of integration; the spectrometer is presented tested in the laboratory. We provide an overview of the project, with particular emphasis on the problems encountered in designing and building an adaptive optics assisted spectrometer.

Ultraluminous Infrared Galaxies: QSOs in Formation?

We present new near-infrared (NIR) Keck and Very Large Telescope (VLT) spectroscopic data on the stellar dynamics in late-stage, ultraluminous infrared galaxy (ULIRG) mergers. We now have information on the structural and kinematic properties of 18 ULIRGs, eight of which contain QSO-like active galactic nuclei (AGNs). The host properties (σ, reff, μeff, MK) of AGN-dominated and star formation dominated ULIRGs are similar. ULIRGs fall remarkably close to the fundamental plane of early-type galaxies. They populate a wide range of the plane, are on average similar to L* rotating ellipticals, but are well offset from giant ellipticals and optically/UV-bright, low-z QSOs/radio galaxies. ULIRGs and local QSOs/radio galaxies are very similar in their distributions of bolometric and extinction-corrected NIR luminosities, but ULIRGs have smaller effective radii and velocity dispersions than the local QSO/radio galaxy population. Hence, their host masses and inferred black hole masses are correspondingly smaller. The latter are more akin to those of local Seyfert galaxies. ULIRGs thus resemble local QSOs in their NIR and bolometric luminosities because they are (much more) efficiently forming stars and/or feeding their black holes, and not because they have QSO-like, very massive black holes. We conclude that ULIRGs as a class cannot evolve into optically bright QSOs. They will more likely become quiescent, moderate mass field ellipticals or, when active, might resemble the X-ray-bright, early-type galaxies that have recently been found by the Chandra observatory.

First High-Contrast Science with an Integral Field Spectrograph: The Substellar Companion to GQ Lupi

We present commissioning data from the OSIRIS integral field spectrograph (IFS) on the Keck II 10 m telescope that demonstrate the utility of adaptive optics IFS spectroscopy in studying faint close-in substellar companions in the halos of bright stars. Our R ≈ 2000 J- and H-band spectra of the substellar companion to the 1-10 Myr old GQ Lup complement existing K-band spectra and photometry and improve on the original estimate of its spectral type. We find that GQ Lup B is somewhat hotter (M6-L0) than reported in the discovery paper by Neuhauser and collaborators (M9-L4), mainly due to the surface gravity sensitivity of the K-band spectral classification indices used by the discoverers. Spectroscopic features characteristic of low surface gravity objects, such as lack of alkali absorption and a triangular H-band continuum, are indeed prominent in our spectrum of GQ Lup B. The peculiar shape of the H-band continuum and the difference between the two spectral type estimates is well explained in the context of the diminishing strength of H2 collision-induced absorption with decreasing surface gravity, as recently proposed for young ultracool dwarfs by Kirkpatrick and collaborators. Using our updated spectroscopic classification of GQ Lup B and a reevaluation of the age and heliocentric distance of the primary, we perform a comparative analysis of the available substellar evolutionary models to estimate the mass of the companion. We find that the mass of GQ Lup B is 0.010-0.040 M☉. Hence, it is unlikely to be a wide-orbit counterpart to the known radial velocity extrasolar planets, whose masses are 0.015 M☉. Instead, GQ Lup A/B is probably a member of a growing family of very low mass ratio widely separated binaries discovered through high-contrast imaging.

Data reduction pipeline for OSIRIS, the new NIR diffraction-limited imaging field spectrograph for the Keck adaptive optics system

OSIRIS is a near infrared diffraction limited imaging field spectrograph under development for the Keck observatory adaptive optics system and scheduled for commissioning in fall 2004. Based upon lenslet pupil imaging, diffraction grating, and a 2Kx2K Hawaii2 HgCdTe array, OSIRIS is a highly efficient instrument at the forefront of todays technology. OSIRIS will deliver per readout up to 4096 diffraction limited spectra in a complex interleaved format, requiring new challenges to be met regarding user interaction and data reduction. A data reduction software package is under development, aiming to provide the observer with a facility instrument allowing him to concentrate on science rather than dealing with instrumental as well as telescope and atmosphere related effects. Together with OSIRIS, a pipeline for basic data reduction will be provided for a new Keck instrument for the first time. A status report is presented here together with some aspects of the data reduction pipeline.

Mrk 609 : resolving the circumnuclear structure with near-infrared integral field spectroscopy

Aims. We present first results of near-infrared (NIR) J and H + K ESO-SINFONI integral field spectroscopy of the composite starburst/Seyfert 1.8 galaxy Mrk 609. The data were taken during the science verification period of SINFONI. We aim to investigate the morphology and excitation conditions within the central 2 kpc. Additional Nobeyama 45 m CO(1-0) data are presented, which we used to estimate the molecular gas mass. The source was selected from a sample of SDSS/ROSAT-based, X-ray bright AGN with red-shifts of 0.03 < z < 1 that are suitable for adaptive optics observations. This sample allows for a detailed study of the NIR properties of the nuclear and host environments with high spectral and spatial resolution. Methods. Integral field spectroscopy with SINFONI delivers simultaneous spatial and spectral coverage of the circumnuclear environment. The NIR light is influenced less by dust extinction than by optical light and is sensitive to mass- dominating stellar populations. Furthermore, several NIR emission lines allow us to distinguish between Seyfert and starburst activities. Results. Our NIR data reveal a complex emission-line morphology that is possibly associated with a nuclear bar seen in the reconstructed continuum images. The detections of [Si VI] and a broad Paa component are clear indicators of the presence of an accreting super-massive black hole at the center of Mrk 609. In agreement with previous observations, we find that the circumnuclear emission is not significantly extincted. Analysis of the high angular-resolution, molecular hydrogen emission and [Fell] emission reveals the LINER character of the nucleus. The large H 2 gas mass deduced from the CO(1-0) observation provides the fuel needed to feed the starburst and Seyfert activity in Mrk 609. Conclusions. High angular resolution imaging spectroscopy provides an ideal tool for resolving the nuclear and starburst contributions in active galaxies. We show that Mrk 609 exhibits LINER features that appear to be hidden in visible/NIR spectra with larger apertures.

Nearby AGN and their hosts in the near infrared

We present near infrared ISAAC VLT observations of nine nearby (0.01 ≤ z ≤ 0.06) Active Galactic Nuclei selected from the Hamburg/ESO Survey and the Veron-Cetty & Veron catalog. Hydrogen recombination lines Paα and Brγ are observed in seven of the nine sources of which five show a broad component. In three sources, extended 1-0S(1) rotational-vibrational molecular hydrogen emission is detected. Stellar CO absorption is seen in four sources. In one of these objects, an upper limit of the central mass can be determined from the stellar velocity field. H -a ndKs-band imaging allow us to determine the morphology class of the host galaxies. Colors (with supplementary J-band 2MASS images) show that the four galaxies with detected CO absorption are characterized by an overall strong stellar contribution. One galaxy shows an increased extinction towards the nucleus. After removal of the nuclear point source, the host galaxies show colors typical for non-active spiral galaxies.

Diffraction-limited Imaging Spectroscopy of the Sagittarius A* Region Using OSIRIS, a New Keck Instrument

We present diffraction-limited spectroscopic observations of an infrared flare associated with the radio source Sgr A*. These are the first results obtained with OSIRIS, the new facility infrared imaging spectrograph for the Keck Observatory operated with the laser guide star (LGS) adaptive optics (AO) system. After subtracting the spectrum of precursor emission at the location of Sgr A*, we find that the flare has a spectral index [F(ν) ∝ να] of α = -2.6 ± 0.9. If we do not subtract the precursor light, then our spectral index is consistent with earlier observations by Ghez et al. All observations published so far suggest that the spectral index is a function of the flares K-band flux.

Is IRAS 01072+4954 a True-Seyfert 2? - Hints from near-infrared integral field spectroscopy

In contrast to the predictions of the unified model, some X-ray unobscured Seyfert 2 galaxies have been discovered in the last decade. One of them, the starburst/Seyfert composite galaxy IRAS 01072+4954 (z = 0.0236), has a typical Type-1 X-ray emission, while its optical spectrum resembles an Hii galaxy and lacks the expected broad lines. We performed near-infrared integral-field observations of this object with the aim to determine the nature of its nuclear emission and to find indications for the existence or absence of a broad-line region. Several reasons have been proposed to explain this peculiar emission. We studied the validity of these hypotheses, including the possibility for this galaxy to be a True-Seyfert 2. We found little obscuration toward the nucleus AV = 2. 5m ag, and �

Observing Exoplanets with SOFIA

In this article we present an analysis of possible science cases for NASAs Stratospheric Obser- vatory for Infrared Astronomy (SOFIA) in the field of extrasolar planet detection and characterization. Advantages of SOFIA and its instruments for exoplanet observations are illustrated and possible targets are introduced. Possible future instrumentation is discussed. Online material: color figure