Elliptical galaxies

The mass fluctuation spectrum gives rise to collapsed objects from galaxies to groups to rich clusters. The systems dominated by old stars - early type galaxies, elliptical-dominated groups, and rich clusters - all have gaseous halos... 

The question now is whether it is observable or not. This signal has to be above the systematics (that depends on what you use to do the measurements) and above the (white) noise due to the intrinsic shape fluctuations of the source galaxies. In practice the measurement is made in the following way. Galaxy ellipticity,25000 e, are measured and a "super" pixel (say of the order of a few arcmin size) and averaged out. In the weak lensing regime we have,... 

The three broad classifications (elliptical, spiral and irregular) of star clusters that also cluster together to form the Local Group that contains the Milky Way and the Andromeda Galaxy, along with the Small and Large Magellanic Clouds... 

A type II Cepheid variable is observed in the elliptical galaxy M49 in the Virgo cluster of galaxies with a period of 30 days. Calculate the absolute magnitude of this star. If the total flux on the Earth from the star is 4.2 x 10 22 W m-2, estimate the distance to the Virgo cluster. 

LINERs are weaker emission-line regions in certain elliptical and early-type spiral galaxies (e.g. M51 and M81) showing relatively strong lines of [O I], [N ii] and [S n], similar to SNR. It is not clear whether they are excited by shocks like SNR or by a very dilute (i.e. low u) non-thermal spectrum. 

Fig. 3.46. Radial trend of Mg2 index in the elliptical galaxy NGC 4881, after Thomsen and Baum (1987). 1 arcsec = 500 pc, the surface brightness in the adjoining continuum decreases from 17th to 26th magnitude per square arcsec over the range of the diagram in accordance with de Vaucouleurs law I a e r/a)V4 and a and b refer to observations taken on separate dates. Courtesy Bjarne Thomsen.

R. B. C. Henry and Guy Worthey, The Distribution of Heavy Elements in Spiral and Elliptical Galaxies , Publ. Astr Soc. Pacific, 111, 919, 1999. 

A relationship also exists between abundances and luminosity of the host galaxy, whether gas-rich or otherwise (Fig. 3.44), and especially with the rotational velocity in disk galaxies (Fig. 8.13). Similarly, studies of elliptical galaxies in general suggest that the primary factor fixing the mean metallicity of their stellar... 

Fig. 11.2. Mean stellar iron abundances as a function of luminosity in dwarf spheroidals (filled circles), dwarf ellipticals (open circles), dSph/dlrr transition galaxies (filled diamonds) and dwarf irregulars (open diamonds). Baryonic luminosity in the right panel includes the additional luminosity that irregulars would have if their gas were converted into stars. After Grebel, Gallagher and Harbeck (2003).

Chemical evolution of elliptical galaxies 11.3.1 Data sources... 

Parameters of dynamically hot galaxies , i.e. various classes of ellipticals and the bulges of spirals, generally lie close to a Fundamental Plane in the 3-dimensional space of central velocity dispersion, effective surface brightness and effective radius or equivalent parameter combinations (Fig. 11.10). This is explained by a combination of three factors the Virial Theorem, some approximation to... 

Colour and line-strength gradients are also observed across elliptical galaxies, as is to be expected from dissipative effects (see Appendix 5). However, the detailed... 

Two reservations need to be expressed about models for elliptical galaxies compared to colours or spectra in integrated light. 

Detailed numerical models for the photometric and chemical evolution of elliptical galaxies have been computed by Yoshii and Arimoto (1987), Matteucci and Tomambe (1987), Brocato et al. (1990) and Matteucci (1992,1994). These are terminal wind models similar in their basic assumptions to that of Larson (1974b), but with differing assumptions as to IMFs and scaling laws that specify how the... 

Some of these problems are addressed in the inverse wind scenario of Pipino and Matteucci (2004), in which they allow for inflow and assume ad hoc that, the higher the mass of the galaxy, the shorter the infall and especially the star formation timescales. This makes the more massive objects older, in the sense that star formation is stopped by a terminal wind at earlier times, permitting enhanced metallicities and a/Fe ratios in the framework of the classical Salpeter(O.l) IMF. Abundance gradients within elliptical galaxies are reproduced within their very considerable uncertainties by an outside-in scenario in which star formation... 

Fig. 11.16. Median metal abundance per unit true yield as a function of final mass with observations of dwarf spheroidal and elliptical galaxies superposed.

Fig. 11.17. Metallicities of stars and gas as a function of the total mass of stars in an elliptical galaxy growing by mergers, assuming a true yield of 0.02. The trend is for stellar Z to increase approximately as A/1/2 for small masses, flattening to Af1/4 for larger ones. Filled circles show the point beyond which there will be little star formation in mergers because the gas cannot cool sufficiently between collisions arrows indicate possible outcomes of further mergers without star formation. After Tinsley and Larson (1979).

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