The brightness profiles of the spiral galaxies

Tsvetan B. Georgiev,

Institute of Astronomy and Rozhen NAO

3.9.2008, Sozopol

(In collaboration with O.Stanchev, Yu.Goranova, P.Nedialkov, I.Georgiev,

N.Koleva, I.Yankulov, B.Deshev, T.Velchev, N.Draganova,

R.-J. Dettmar, D.Bomans, P.Grosbol)

These investigations aim:

1) Quantitative describing of the Hubble sequence; 2) Tools for studying the galaxy structures and evolutions;

3) Calibrating the distance indicators (luminosity, size)

Morphological types and codes of the galaxies

Type codes: -1 1 3 5 7 9

The fundamental structures of the spiral galaxies

Dependence of Simien & de Vaucouleurs (1986)

• Fig.1. Changes of the bulge to disk ratio along the Hubble sequence (Simien & de Vaucouleurs 1986). The ordinate values 0.6, 0.4, 0.2 and 0.01 correspond to differences between the magnitudes of the bulge and disk 0.55, 1.0, 1.75 and 5.0 magnitudes, respectively.

Profiles of ellipticals (Binggeli & Cameron 1993)

• Fig.2. Profile shapes of Virgo cluster ellipticals (Binggeli & Cameron 1993). The giant galaxues have concave profiles with strong central peak and large periphery. The normal galaxies have approximatelly flat (exponential in I) profiles. The profiles of the dwarfs are compact, tending to be partabola-like (Gaussians in I).

Correlations of Andredakis et al. (1995)

• Fig.3. Correlations between the bulge exponential power number n=1/N and the morphological type (a) or bulge to disk luminosity ratio (b) by Andredakis et al (1995). The profile shapes of the bulges in early type galaxies are concave, close to the de Vaucouleurs “n=1/4” law, but toward the late type galaxies the bulge profile shapes become flats, close to the Freeman exponetials (n=1)

Convex shapes of the disk profiles

•

• Fig.4. a) Deep major axes profile of the edge-on galaxy ESO 189-G12 (solid line), the edge-on view of the respective exponential model of the bright part of the disk (dotted line) (Barteldress & Dettmar 1994) and the general shape of the profile, modeled by parabola (dashed line) b) - deep major-axis profiles of the galaxies M 31 and M 33 (de Vaucouleurs 1958; 1959b) (solid lines), modeled by parabolas (dashed lines).

Sersic’s (1968) exponential - power formula: IR= I0 exp(-(R/H)N); μR= μ0 + C RN

• Fig.5. Shapes of 5 radial Sersic profiles with I0 = H = 1 for N=0.25, 0.5, 1, 2, 4 (solid lines) and 3 radial profiles, modeled by the second order Sersic formula for disk with central depressions (dashed lines).

The Whirlpool Galaxy (M 51)

M 51

Examples and problems: central peak blurring, faint periphery revealing, profile details removal, profile reproducibility

Fig.6. Profile decomposition for the galaxies M 74, M 83,NGC 6946 and IC 342 in J-band from 2MASS (dots) andB-band from different works (circles). Short vertical linesshow the positions of the optimal dividing points.

Iterative procedure and problems:reverse problem; sampling, noise, dividing point

Fig.7 Iterative decompositions of the profiles of the galaxies M 33 and UGC 1400 (edge-on). The solid curves represent the results.

Typical profiles of the galatic disks:the massive disks tend to be ring-like

– Fig.8. Comparison of Sersic’s models of disks profiles.

– a): equivalent profiles of de Vaucouleurs for SMC, LMC, M 33, M 31 (from left to the right, solid curves) and MW (dashed curve with arbitrary vertical shift, representing the MW model discussed in Freeman (1970)) (Georgiev 2002).

– b): major axis disk shapes of edge-ons UGCA 193, NGC 3109, UGCA 61, NGC 5907 and NGC 7814 (from left to the right) (Georgiev & Stanchev 2004).

Early types: concave bulges and convex disks Late types: tendency to flat bulges and disks

• Fig.9. Correlation between the morphological type code and optimal bulge (a) and disk (b) exponential numbers Nb and Nd, respectively, for 20 elite galaxies in B-band. The solid lines represent the linear regressions and the dashed lines represent the respective reverse regressions (Georgiev et al. 2004).

31 elite galaxies in J-band from 2MASS:the bulge shapes follow expected correlation, but the disk shapes don’t;

the disk shapes seem to be convex, but not deep enough

• Fig.10. Correlation between the morphological type code and optimal bulge (a) and disk (b) exponential numbers Nb and Nd, respectively, for 31 galaxies. The solid lines represent the linear regressions and the dashed lines represent the respective reverse regressions (Yankulov 2005).

119 elite edge-ons in R-band: the disk shapes of the early types are more convex

• Fig.11. Correlations between the central disk brightness 0 or disk exponential number Nd and the difference between the integral magnitudes of the bulge and disk Mb-Md for 119 edge-on galaxies in R-band The disks of the early type galaxies tend to have convex shapes and central depressions (Georgiev et al. 2004).

26 LSB galaxies from the SDSS: toward the late types the disk profile becomes flat

• Fig.12. Left - the scale lengths ratio Hd/Hb against the total magnitude Mgor Mr (left) and. the exponential power number of the disk Nd (right) for 26 galaxies from LSB SDSS. The g-band data is shown with dots and the r-band one with circles. The best-fit lines are solid and dashed respectively (Dehsev, 2006).

Conclusions:• 1. The EPM of Sersic is able to describe wide range of

shapes of convex disk profiles.

• 2. The shapes of the bulge and disk profiles correlate with the Hubble type, but the correlations are not enough close to be called dependances.

• 3. New attempts on better galaxy samples need for better correlations.

• 4. New simulate investigations of the decomposition method must be carried out for elucidation of its limitations.