important to find out whether the scaling relations used for “normal” galaxies are also valid for merger remnants. In Chapter5,M•of the merger remnant and FR I radio galaxy Fornax A is measured and conclusions regarding the validity of the M•-σ andM•-Lbulgeare drawn.
1.5 Outline of the thesis
There are still many open questions regarding theM•-bulge relations, in particular at the low and at the high-mass end, for pseudobulges, barred galaxies and merger remnants. The behaviour of the M•-bulge relations and possible differences be-tween galaxy types can tell us about the relative importance of different growing mechanisms. Stellar dynamics can be generally used for all galaxies to reliably determine M• regardless of the galaxy type, as long as the sphere of influence is resolved. In the past, however, it was impossible to obtain adequate data for the derivation of stellar dynamical SMBH masses in many galaxies except for the most nearby brightest ellipticals or early-type spirals. Low-mass black holes have a very small sphere of influence well below 1′′. In almost all low-σ, late-type and pseu-dobulge galaxies and AGN dust obscuration is a serious problem. To measure the stellar kinematics a S/N of at least 30 per pixel is needed, which for most instru-ments means unrealistically high exposure times if the galaxy is faint (i.e. almost all low-mass galaxies and core galaxies). In AGN the non-stellar emission of the active nucleus often dilutes the stellar absorption features. A large fraction of the black hole mass measurements performed so far are based onHST STIS spectra.
They have a very high spatial resolution, but as STIS is an optical instrument and the light collecting power ofHST is quite low, it could only be used for massive, bright galaxies without a significant amount of dust. Only since the advent of adaptive-optics assisted near-infrared instruments at large ground-based telescopes (e.g. SINFONI at the Very Large Telescope or NIFS at Gemini North) a few years ago it is now possible to overcome most of the difficulties for a reasonable num-ber of interesting objects. It is now possible to reach a diffraction-limited spatial resolution comparable to HST from the ground, the large light collecting power of 8m-class telescopes reduces the needed integration time for faint objects to a fair amount, and dust obscuration plays only a minor role in the near-infrared.
The instrument SINFONI (see Chapter 2) was built by the Max-Planck-Institut für extraterrestrische Physik (MPE), the European Southern Observatory (ESO) and the Netherlands Research School for Astronomy (NOVA). As our group (the
1.5. OUTLINE OF THE THESIS
Opinas group at MPE, led by Prof. Dr. Ralf Bender), was involved in the devel-opment of SINFONI, seven nights of guaranteed time observations (GTO) were awarded to us by ESO. Thanks to Ralf Bender all seven nights were assigned to the black hole project, which made this thesis possible. I got the opportunity to observe low-σ and pseudobulge galaxies and a merger remnant with SINFONI and to measure the mass of the central black holes. More recently also data for high-σ and core galaxies were taken with SINFONI by our group, but they will not be discussed in this thesis.
In Chapter 2the instrument SINFONI is introduced and the selection of the galaxies and the observations are described. The derivation of the stellar kine-matics from SINFONI spectra is explained in detail in Chapter3. The SINFONI data, the derived kinematics, the photometry of the galaxies and the stellar dynam-ical modelling of the black hole masses are presented in Chapter 4for the low-σ galaxy NGC 4486a, in Chapter 5 for the merger remnant and radio galaxy For-nax A (NGC 1316) and in Chapter 6for the composite pseudobulges NGC 3368 and NGC 3489. Chapter7summarises the results, shows the implications on the M•-σ andM•-Lbulge relations of these four galaxies and outlines the present status of the SINFONI observations, the data analysis and the next steps.
Observations and data reduction 2
Traditionally spectroscopy is done by dispersing the light of an object that falls through a narrow slit. While this is very useful in general, it becomes rather un-satisfactory e.g. when studying the dynamical structure and stellar populations of galaxies. To obtain a full set of information about a galaxy (i.e. photometry and kinematics) is impossible with pure longslit spectroscopy. Based on longslit kinematics only, multiple kinematic components, central bars, discs or counter-rotating cores are very difficult to detect. Placing the slit on many positions of the galaxy (e.g. along the major and the minor axis and some angles in between) would be a possible solution, but this is extremely expensive in terms of exposure time and does not allow to obtain spatially contiguous spectra. The positioning of a slit is always connected with a small error, which can result in differences be-tween the kinematics or black hole mass measurements that are based on different longslit data. It therefore can be dangerous to determine black hole masses based on only one longslit position. Also the orbital distribution of a galaxy can only be unambiguously determined if the velocity distributions at all spatial positions are known.
During the last decade, the development of a novel type of spectrographs, the so-called integral-field spectrographs (IFS), progressed a lot and nowadays almost all large telescopes are equipped with such instruments. IFSs overcome all major disadvantages of longslit spectroscopy. They are able to obtain spectra at all
spa-2.1. SINFONI
tial resolution elements (“spaxels”) in a 2-dimensional field in a single shot and the result is a 3-dimensional datacube (the spatial coordinates x and y and the wave-lengthλ). Compared to other 3D techniques like Fabry-Perot interferometry IFSs have the advantages that the spectral range is much larger and that all data are obtained simultaneously.
2.1 SINFONI
The instrument used for all observations in this thesis is SINFONI (Spectrograph for INtegral Field Observations in the Near Infrared, Bonnet et al. 2004; Eisen-hauer et al. 2003a), which consists of the integral-field unit SPIFFI (SPectrometer for Infrared Faint Field Imaging,Eisenhauer et al. 2003b) and the adaptive optics module MACAO (Multi-Application Curvature Adaptive Optics, Bonnet et al.
2003) and is mounted at the fourth unit telescope (UT4) of the Very Large Tele-scope (VLT) in Chile. SPIFFI (see Fig. 2.1) belongs to the class of image slicers.
Fig.2.2shows the basic working principle of the SPIFFI image slicer. The field of view, which can be chosen between 0.8′′×0.8′′, 3′′×3′′and 8′′×8′′, is slit into 32 slitlets of 64 resolution elements each by a set of 32 mirrors. These slitlets are then combined by a second set of 32 mirrors to a pseudolongslit with a width of 25 mas, 100 mas or 250 mas (1 mas≡10−3arcseconds), depending on the field of view cho-sen, and then dispersed by a grating. There are four gratings available, a J-band (1.1−1.4µm), anH-band (1.45−1.85µm), aK-band (1.95−2.45µm) and a com-binedH+K-band (1.45−2.45µm) grating. The dispersed light is then directed to a Rockwell 2k×2k pixel Hawaii 2RG detector. The spectral resolutionR=λ/∆λis around 2000, 3000, 4000 and 1500 inJ,H,K andH+Krespectively. With the data reduction software (Abuter et al.,2006;Modigliani, 2009; Schreiber et al.,2004) a three-dimensional datacube is reconstructed from the two-dimensional spatial information and the spectral information (32 slitlets of 64 spaxels length ×2048 pixels in wavelength direction). This datacube can be used to analyse the spectra at each position in the field of view, and to analyse the photometry by collapsing the cube along the wavelength direction. SINFONI has been commissioned in 2004 and is officially operational since April 1st, 2005. In the following the smallest selectable field of view (0.8′′×0.8′′ with spaxels of the size 0.0125′′×0.025′′) will be referred to as the “25mas scale”, the intermediate field of view (3′′×3′′ with spaxels of the size 0.05′′×0.1′′) as the “100mas scale” and the largest field of view (8′′×8′′with spaxels of the size 0.125′′×0.25′′) as the “250mas scale”.