Galaxies surface brightness

Figure 13. O/H at fixed value of galaxy surface brightness vs. Mb- Top abundances at 22 mags arcsec-2. Bottom abundances at 24 mag arcsec 2. More luminous spirals have higher abundances at a fixed surface brightness. Open symbols are from Garnett et al. (1997a) filled symbols represent additional data obtained from the literature.

The predictions of chemical evolution models can be tested in a cosmological context to study the galaxy surface brightness and size evolution as a function of redshift. Roche et al. (1998) have already done that and suggested that a size and luminosity evolution, as suggested by the inside-out scenario fits better the observations. 

Scl is a close companion of the Milky Way, at a distance of 72 5 kpc [7], with a low total (dynamical) mass, (1.4 0.6) x 107Mq [8], and modest luminosity, My = —10.7 0.5, and central surface brightness, Soy = 23.5 0.5 mag/arcsec2 [9] with no HI gas [10]. CMD analysis, including the oldest Main Sequence turnoffs, has determined that this galaxy is predominantly old and that the entire star formation history can have lasted only a few Gyr [11]. 

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.

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... 

We begin with an introduction to a simple model first proposed by Cavaliere and Fusco-Femiano (1976). This model assumes that the gas and galaxies are in equilibrium within the same gravitational potential. Through a measure of the X-ray surface brightness, the model relates the gas temperature to the cluster velocity dispersion, measured from the galaxies. 

Figure 2.7. The X-ray observables surface brightness profile and projected gas temperature and their simple derivatives, deprojected temperature, gas density, and gas pressure for the regular galaxy A478 (Sun et al. 2003). (top left) Surface brightness (0.5 - 5 keV) distribution, (upper right) electron density, (lower left) gas temperature, (lower right) gas pressure. Only statistical uncertainties are shown (1 a random errors). In the temperature profile, the data points with small circles are projected temperatures, while the data points with large filled circles are deprojected (three dimensional) values.

Unfortunately, observations seem to be in mild disagreement with this predicted profile merr. A low CDM concentration is observed in low surface brightness dwarf galaxies where the rotation curve is well measured. The predicted dark matter cusp is not usually seen the typical profile has a soft core, although the interpretation is compounded by issues of disk inclination, of the HI distribution which is usually used to measure the rotation curve, and of the possible mismatch between baryon and CDM potential well depths. 

Figure 8. Predicted and observed color gradients for some field elliptical galaxies. From Menan-teau et al. (2001).Figure shows from left to right /si4-band surface brightness map, V606- 8i4 color pixel map and V606--l8i4(r) color gradient. Open circles represent observed gradients while solid lines are the model predictions obtained by means of the Martinelli et al. (1998) model.

For a subsample of 16 galaxies for which the surface brightness profiles cotdd be fitted well by an exponential, we have determined the B-E color in the center, at te,Ki and at 3 as, and looked at the inclination dq>endence of these colors. The data seem to indicate that the central area, including the region around re, is optically thick in B. At 3 as (arotmd D2s,b) the obscuration apparently is much less. 

Fig. 2. Apparent size V8. average surface-brightness for I and K band for different galaxy spectral types (labeled) as a function of redshift. Heavy solid lines are loci of constant red-shift (labeled) light lines are redshifts tracks for eadi galaxy type (soHd qo=0.1 dashed qo==0.5). Arrows indicate decoupling of the effects of evolution, A -conections, and cosmology.

Spinrad 1981). Here we illustrate that very basic measures of galaxy size and surface-brightness C2in be combined with colors to derive redsbifts, or with known redsbifts to make measurements of certain types of evolution that are unaffected by cosmological curvature. Such measurements are feasible and can be made optimally at high redshift in the near-lR. 

---