Integral field spectroscopy of a sample of nearby galaxies

Abstract

We analyse the spectroscopic properties of thousands of H ii regions identified in 38 face-on spiral galaxies. All galaxies were observed out to 2.4 effective radii using integral field spectroscopy (IFS) over the wavelength range ∼3700 to ∼6900 Å. The near uniform sample has been assembled from the PPAK IFS Nearby Galaxy (PINGS) survey and a sample described in Paper I. We develop a new automatic procedure to detect H ii regions, based on the contrast of the Hα intensity maps extracted from the datacubes. Once detected, the algorithm provides us with the integrated spectra of each individual segmented region. In total, we derive good quality spectroscopic information for ∼2600 independent H ii regions/complexes. This is by far the largest H ii region survey of its kind. Our selection criteria and the use of 3D spectroscopy guarantee that we cover the regions in an unbiased way. A welltested automatic decoupling procedure has been applied to remove the underlying stellar population, deriving the main properties (intensity, dispersion and velocity) of the strongest emission lines in the considered wavelength range (covering from [O ii] λ3727 to [S ii] λ6731). A final catalogue of the spectroscopic properties of H ii regions has been created for each galaxy, which includes information on morphology, spiral structure, gas kinematics, and surface brightness of the underlying stellar population. In the current study, we focus on the understanding of the average properties of the H ii regions and their radial distributions. We find a significant change in the ionisation characteristics of H ii regions within r < 0.25 r e due to contamination from sources with different ionising characteristics, as we discuss. We find that the gas-phase oxygen abundance and the Hα equivalent width present a negative and positive gradient, respectively. The distribution of slopes is statistically compatible with a random Gaussian distribution around the mean value, if the radial distances are measured in units of the respective effective radius. No difference in the slope is found for galaxies of different morphologies, e.g. barred/non-barred, grand-design/flocculent. Therefore, the effective radius is a universal scale length for gradients in the evolution of galaxies. Some properties have a large variance across each object and between galaxies (e.g. electron density) without a clear characteristic value. But other properties are well described by an average value either galaxy by galaxy or among the different galaxies (e.g. dust attenuation).

The CALIFA Survey: Exploring the Oxygen Abundance in the Local Universe

“…These results agree with the main conclusion of our previous study [41], where a limited sample of 38 face-on spiral galaxies was analyzed, using similar methods. In a companion article [20], we analyze the radial gradient of stellar metallicity, where we have found consistent results.…”

“…The existence of a universal radial decrease in the oxygen abundance has been already reported in many previous studies e.g., [8,41,43,55,[62][63][64]. This observational property is compatible with our current understanding of the formation and evolution of spiral galaxies, e.g., [65] and the references therein.…”

“…In [41], we presented a new method to detect, segregate and extract the main spectroscopic properties of H II regions from IFS data (HIIEXPLORER). Figure 1, left-panel, illustrates how this method works, showing the Hα intensity map of NGC 6155 as observed by CALIFA, together with the segmentation map of the ionized regions detected.…”

“…The same catalog allows us to explore the galactocentric radial gradient of the oxygen abundance [41]. Figure 1, right-panel, shows a typical radial abundance gradient for the galaxies within the CALIFA sample, derived using the O3N2 calibrator by 12 + log(O/H) = 8.73 − 0.32 log(O3N2) [42].…”

The Black Hole in the Compact, High-Dispersion Galaxy NGC 1271

“…We note that the line-spread function is measured as a function of wavelength and fiber position from arc lamps during the wavelength calibration stepand then homogenized to a common value prior to the extraction of the PPAK kinematics. The details of these steps are discussed at length by Sánchez et al (2012) and Husemann et al (2013), and we refer the reader to those publications for additional information.…”