The SAURON sample consists of 18 Sb–Sd nearby late-type spiral galaxies with Hubble types ranging from Sb to Sd. The sample selection, observations, and data reduction are presented in detail inGanda et al. (2006, 2009). The galaxies were chosen from imaging projects with the Hubble Space Telescope, thus WFPC2 and/or NICMOS data were available (Carollo et al. 1997,
1998,2002;Laine et al. 2002;B¨oker et al. 2002). All targets had to be brighter than BT = 12.5
according to the values listed in the de Vaucouleurs (1991) catalogue, where interacting and Seyfert galaxies were discarded. Additionally, visibility constraints have been applied.
Figure 2.1: The main techniques for achieving integral field spectroscopy (credit:
http://ifs.wikidot.com/what-is-ifs).
To complete the SAURON sample across Hubble sequence, we choose 8 E–Sb galaxies from the observed CALIFA targets (S´anchez 2006;Husemann et al. 2013) based on the following criterias: different morphological types (from elliptical to Sb spirals), inclination that allows us to avoid dust obscuration at maximum (25◦ < i < 80◦), and available kinematic data with sufficient signal-to-noise ratio (20< S/N < 60).
2.2.1
SAURON and CALIFA integral-field spectroscopy
The dynamical modeling could be simple if the galaxy components had spherical shapes. How- ever, many of them are axisymmetric or even triaxial (Binney 1976, Binney 1978, Davies & Illingworth 1983b,Bender & Nieto 1990, de Zeeuw & Franx 1991). It is difficult to map them with the traditional long-slit spectroscopy (e.g., STIS on the Hubble Space Telescope,Woodgate et al. 1998; Davies & Birkinshaw 1988;Statler & Smecker-Hane 1999). The two-dimensional integral-field spectroscopy of stars and gas is essential for deriving the dynamical structure of these systems and understanding their formation and evolution. Integral-field unit (IFU) indi- cates an instrument, providing spectra at each position on the sky and maintaining the informa- tion on the spatial location from which each light beam originated (Bacon et al. 2001b;S´anchez et al. 2012b). The output is a three-dimensional datacube with spatial and spectral information, giving information about the stellar kinematics and populations of the galaxies.
Data and Sample selection 27
SAURONcharacteristic HR mode spatial sampling 0′′.94
field of view 33′′× 41′′ spectral resolution (FWHM) 4.2 Å
instrumental dispersion 108 km s−1 spectral sampling 1.1 Å pixel−1
spectral range 4800-5400 Å emission features Hβ, [OIII],[NI]
absorption features Hβ, Fe5015, Mgb
Table 2.1: Specifications of SAURON spectrograph in its low-resolution mode.
CALIFAcharacteristic
sample SDSS DR7,δ >7◦ redshift 0.005 < z < 0.03 diameter 45′′ < D25 < 80′′
field of view 74′′× 64′′hexagon spatial resolution ∼ 2′′(FWHM) Grating V500 V1200
3σ depth ∼ 23.0 mag/arcsec2 ∼ 22.8 mag/arcsec2 wavelength 3745-7300 Å 3400-4750 Å spectral resolution ∼ 6.5Å (FWHM) ∼ 2.7Å (FWHM)
Table 2.2: Specifications of CALIFA spectrograph in V500 and V1200 mode.
The 18 spiral galaxies were observed with the integral-field unit spectrograph SAURON at the 4.2- m William Herschel Telescope of the Observatorio del Roque de los Muchachos on La Palma, Spain. It presents a larger field of view with respect to its predecessors: integral-field spectro- graph TIGER and OASIS at the Canada-France-Hawaii telescope to study galactic nuclei (Bacon et al. 1995b,2000). It consists of a filter, which selects a fixed wavelength range and an enlarger that images the sky on a lenslet array (Bacon et al. 2001b). Each lenslet produces a micropupil. Its light, first passes through a collimator and then dispersed by a grism. Finally, the resulting spectra are imaged on a CCD camera. The instrument measures the mean streaming velocity V, the velocity dispersionσ and the velocity profile (or line-of-sight velocity distribution, LOSVD) of the stellar absorption lines and the emission lines of the ionized gas, the two-dimensional dis- tribution of line-strengths and line-ratios. In this thesis, we focuse on the measured V andσ of the stellar absorption lines for dynamical modeling.
The SAURON IFU (Bacon et al. 2001b) has a 33′′× 41′′field-of-view (FoV), sampled by an array of 0.94′′×0.94′′square lenses. It corresponds to a radial extend of 1/5 to 1/3 of the galaxy’s half- light radius (Re). The spectral resolution is 4.2 Å (FWHM), corresponding to an instrumental
dispersion of 105 km s−1in the selected spectral range 4800-5380 Å (1.1 Å per pixel). This range includes a number of absorption features at the redshift of the selected galaxies – Fe, Mgb and Hβ, which we use to measure the stellar kinematics. Emission lines like [OIII], [NI] and Hβ can be used to probe the ionised gas properties (see Table2.1).
The observations were reduced by Ganda et al. (2006) using the dedicated software XSAURON (Bacon et al. 2001b). To obtain a sufficient signal-to-noise ratio (S/N), we spatially binned the data cubes using the Voronoi 2D binning algorithm ofCappellari & Copin(2003). The Voronoi Binning method optimally solves the problem of preserving the maximum spatial resolution of general two-dimensional data, given a constraint on the minimum signal-to-noise ratio. We created compact bins with a minimum S/N ∼ 60 per spectral resolution element. In the central regions many individual spectra have S/N > 60 and thus remained un-binned.
Together with the SAURON data, we use the most recent integral-field spectroscopic survey CALIFA (S´anchez 2006;Husemann et al. 2013) with the 3.5-m telescope at Calar Alto Observatory to ex- tend our study on the mass distribution of galaxies from the stellar kinematics. The final sample of the survey includes around 600 nearby galaxies. CALIFA is the largest and the most compre- hensive wide integral-field unit (IFU) survey of galaxies carried out to date. CALIFA will increase our knowledge of the baryonic physics of galaxy evolution: star formation, AGN, shocks; mea- surement of ionized oxygen and nitrogen abundences in the galaxies; measurement of stellar population properties; measurement of galaxy kinematics in gas and stars.
The observations of the 8 (E–Sb) galaxies have been made by using the integral-field spectro- scopic instrument PMAS/PPAK on the Calar Alto 3.5-m telescope. Each galaxy has been targeted with a mid-resolution (V1200) prism covering the nominal wavelength range 3850–4600 Å at a Full Width at Half Maximum (FWHM) spectral resolution of ∼2.3 Å, i.e., σ ∼ 85 km s−1 and a 74′′ × 64′′ hexagonal field-of-view (FoV). The exposure time per pointing has been fixed to 1800 s, split into 2 or 3 individual exposures (S´anchez 2006;Husemann et al. 2013; see Table
2.2) .
The PMAS/PPAK integral-field unit provides a three-dimensional datacube with spatially resolved spectra for a grid of points across the FoV (Husemann et al. 2013). Here, we spatially binned our datacube using the Voronoi 2D binning algorithm of Cappellari & Copin (2003) to obtain signal-to-noise ratio of∼20 and, hence, better stellar kinematics.
Stellar kinematics extraction 29
Figure 2.2:pPXF fit (magenta) to SAURON spectra (black) of NGC 488 galaxy in the wavelength region 480-538nm. The fit residuals are plotted in green and the non-fitted gas emission lines in red.