Article

Two-Dimensional Line Strength Maps in Three Well-studied Early-Type Galaxies

Department of Physics, Durham University, Durham, England, United Kingdom
Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.11). 07/1999; 310(3). DOI: 10.1046/j.1365-8711.1999.02998.x
Source: arXiv

ABSTRACT

Integral field spectroscopy has been obtained for the nuclear regions of three large, well-studied, early-type galaxies. From these spectra we have obtained line-strength maps for about 20 absorption lines, mostly belonging to the Lick system. An extensive comparison with multilenslet spectroscopy shows that accurate kinematic maps can be obtained, and also reproducible line-strength maps. Comparison with long-slit spectroscopy also produces good agreement.
We show that Mg is enhanced with respect to Fe in the inner disc of one of the three galaxies studied, the Sombrero. [Mg/Fe] there is larger than in the rest of the bulge. The large values of Mg/Fe in the central disc are consistent with the centres of other early-type galaxies, and not with large discs, like the disc of our Galaxy, where [Mg/Fe] ∼0. We confirm with this observation a recent result of Worthey: that Mg/Fe is determined only by the central kinetic energy, or escape velocity, of the stars, and not by the formation time-scale of the stars.
A stellar population analysis using the models of Vazdekis et al. shows that our observed Hγ agrees well with what is predicted based on the other lines. Given the fact that Hβ is often contaminated by emission lines, we confirm the statement of Worthey & Ottaviani, Kuntschner & Davies and others that if one tries to measure ages of galaxies, Hγ is a much better index to use than Hβ. Using the line strength of the Ca ii IR triplet as an indicator of the abundance of Ca, we find that Ca follows Fe, and not Mg, in these galaxies. This is peculiar, given the fact that Ca is an α element. Finally, by combining the results of this paper with those of Vazdekis et al., we find that the line-strength gradients in the three galaxies are primarily caused by variations in metallicity.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The relationship of an AGN to its host galaxy is one crucial question in the study of galaxy evolution. We present a method to estimate the stellar contribution in active galactic nuclei. We perform stellar population synthesis in the central regions of a sample of 12 galaxies of different levels of activity: normal galaxies, starburst galaxies, LINERs, Seyfert 2 and Seyfert 1 galaxies. Quantification of the stellar contribution is carried out in the visible range (5000 to 8800 Ä) using the equivalent widths of the absorption features throughout the spectrum. The synthesis is done by a variant of the new GPG method (Pelat, 1997). This method, contrary to previous ones, gives a unique solution. We find quite different stellar populations for the different types of activity, which seems to be indicative of an age sequence. The starburst galaxies present the youngest populations of the sample. The Seyfert 2 nuclei and NGC 1275, a Seyfert 1 with signs of interaction and where young stellar clusters have been found, also show the contribution of a young population, less intense than in the starburst galaxies but metal rich. NGC 3516, a typical Seyfert 1, has a normal population characteristic of galaxies of the same Hubble type and finally the LINERs show the oldest populations in the sample, metal rich, with little star formation still going on. It is found that a strong CaII triplet, even though these lines are sensitive to gravity, does not imply necessarily a stellar population dominated by supergiant stars. Based on observations collected at the Canadian-French-Hawaiian Telescope, Hawaii, and Observatoire de Haute Provence, France.
    Preview · Article · Apr 2000 · Astronomy and Astrophysics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present integral field spectroscopy of the circumnuclear region of M32 obtained with the 2D_FIS fibre optics spectrographs installed at the 4.2-m William Herschel Telescope. From these spectra line-strength maps have been made for about 20 absorption lines, mostly belonging to the Lick system. We find good agreement with long-slit line-strength profiles in the literature, and no radial gradients in the azimuthally averaged absorption line indices. We fit the mean values of each spectral index and colours from the literature for the inner regions of M32 to the models of Vazdekis et al. and Worthey, finding that the present data can be well interpreted for a single stellar population of an intermediate age (∼4 Gyr) and a metallicity similar to solar
    Preview · Article · Sep 2000 · Monthly Notices of the Royal Astronomical Society
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A new photometric system suitable for deep, precise and quick metallicity mapping in galaxies is proposed. We find a linear correlation between our metallicity index and the Mg2 index for stellar, globular-cluster, and early-type galaxy spectra, and model spectral energy distributions of the simple stellar populations.
    Full-text · Article · Jan 2001 · Astrophysics and Space Science
Show more