Análisis de la información

The selection of galaxies to be observed depends on several aspects: - object category,

- availability of high-resolution imaging (e.g. HST) and kinematic informa- tion,

- distance and estimated sphere of influence, - inclination,

- K-band surface brightness, - observability,

- availability of an NGS or TTS, - availability of the LGS.

All selected galaxies that have been observed so far are listed in Table2.1together with some of their properties. Most of them belong to one of the categories dis- cussed in the last chapter. Pseudobulges or composite bulges and low-σ galaxies with only a small classical bulge are of main interest in this thesis. Thus it is im- portant that high-resolution imaging of the pseudobulge region (e.g. fromHST, preferrably in several bands) and some kinematic information (v andσ along the major axis) are available which can verify the presence of a pseudobulge or com- posite bulge in a certain galaxy. Samples of pseudobulges or disc galaxies with candidate pseudobulges used for the selection of galaxies were taken e.g. from

Carollo et al.(1998),Kormendy & Kennicutt, Jr. (2004),Erwin(2004),Drory & Fisher(2007),Fisher & Drory(2008) andFisher et al.(2009). For all other galaxies (in particular low-σ and late-types) it is also important to have some photometric

and kinematic information in order to (1) have an idea of the velocity dispersion and thus the angular size of the sphere of influence, and (2) distinguish them from pseudobulges. Low-σ galaxies can be found in collections of catalogues of galax-

ies provided by VizieR,1 _{a list of bulgeless galaxies is given e.g. by Böker et al.}

(2002). Accurate photometry is also required to determine the stellar mass density for the dynamical modelling, and kinematics outside the SINFONI field of view may help to constrain the SMBH mass.

2.2. SELECTION OF GALAXIES (km/s) σ 50 100 150 200 250 300 350 400 (a rcse c) So I d −3 10 −2 10 −1 10 1 5Mpc 10Mpc 20Mpc 50Mpc 100Mpc 200Mpc

Figure 2.3: Diameter of the sphere of influence in arcseconds as a function of veloc- ity dispersionσ for different distances, assuming thatM_• follows the M_•-σ relation of

Tremaine et al.(2002). The red shaded region marks the spatial resolution range achieved with SINFONI in_∼75% of the observing time, when the weather conditions were good

or excellent.

Each selected galaxy has a well-known distance (e.g. from Tonry et al. 2001), such that together with the velocity dispersion of the galaxy the mass of the central black hole (via the M_•-σ relation of Tremaine et al. 2002) and thus the diameter

of the sphere of influence can be estimated. Dynamical modelling also requires to know the distance and thus the angular scale of the object as accurate as possible, in order to determine a precise stellar mass density. If the distance is overestimated, the mass of the SMBH would also be overestimated. The diameter of the SoI has to be resolvable with SINFONI under good to average seeing conditions, i.e. it has to be at least in the range ∼ 0.08′′_−0.2′′ _{(see Fig. 2.3). This limits the}

list of pseudobulge and low-σ objects to galaxies at distances D ®20 Mpc. The

smaller the velocity dispersion of the galaxy the smaller the limiting distance out to which the SoI can be resolved. The SoI of high-σ galaxies (σ >300 km s−1_{) can}

be resolved out to at least 100−200 Mpc, but unfortunately the spectral features

used to determine the kinematics are redshifted out of theK-band with increasing distance. Already at 60 Mpc the first two CO bandheads are shifted to a region with enhanced sky absorption, such that this distance is imposed as an upper limit. The number density of these objects is very small, therefore also in this object category only very few objects are left. As many nearby late-type galaxies do not have a velocity dispersion measurement, we took major and minor axis longslit

CHAPTER 2. OBSERVATIONS AND DATA REDUCTION

spectra of a number of those galaxies using the low-resolution spectrograph (LRS) at the Hobby-Eberly Telescope (HET) in Texas.

The inclination is also an important factor. The inclinations of galaxies close to face-on (i ®40◦) usually cannot be determined very accurately, which inhibits

the determination of the deprojected rotation velocity v_circ = v_rot/sin(i). For

truly face-on galaxies, the measured rotation velocity is close to zero, thus no circular velocity can be derived. In truly edge-on galaxies the circular velocity can be directly measured and also the deprojection of the photometry has a unique solution, which makes dynamical modelling easier. It is not possible, however, to assess the presence or absence of a pseudobulge or classical bulge in the centre. Thus the selected pseudobulge objects have an inclination between 40◦_{and 80}◦_.

The remaining selection criteria are of more technical nature. The AO correc- tion depends on the airmass, as the seeing increases with increasing airmass. The shorter the way of the galaxy light through the Earth’s atmosphere, the better the AO correction, which is best when the object is in the zenith. The elevation limit of the VLT is 20◦_{, but for a reasonable AO correction the object should be above} ∼45◦ _{(corresponding to an airmass of ∼1.4) for a few hours per night. This is}

particularly important for galaxies that are observed with the LGS, as the LGS AO correction depends stronger on the seeing than NGS AO correction. Therefore only objects within a declination range−70◦_®δ®13◦_{have been considered. In}

addition, due to the Earth’s rotation around the Sun, each galaxy is visible at night only for some months per year, thus the observation time and the objects have been chosen carefully in order to be able to observe the selected galaxy sample during the few nights which were assigned to us by ESO per semester.

Most late-type galaxies, pseudobulges and core galaxies have a very low central surface brightness. It is not reasonable to spend an excessive amount of time on one galaxy, therefore the sample was restricted to objects that do not need more than 0.5−1 night of exposure time (including overhead) to obtain a minimum

S/N per pixel of around 40. This means effectively that the centralK-band surface brightness should not be fainter than∼15 mag/arcsec2. 2MASS (Skrutskie et al.,

2006) provides near-IR surface brightness profiles for many nearby galaxies. The last criteria (which turned out to be the most stringent ones) are the avail- ability of the LGS and a TTS or the availability of an NGS. Whether the criteria for a TTS or NGS are fulfilled can be checked by measuring the R-band magni- tude of the nucleus or a nearby star using availableR-band imaging (e.g. fromHST