II. Morphology and Structure of Dwarf Galaxies Ferguson & Binggeli 1994, A&ARev 6, 67 1 1. Properties low mass : 10 6 10 10 M slow rotators : 10 100 km s -1 low luminosity : 10 6 10 10 L low surface brightness (faint end) high surface brightness (BCDGs) low metallicity : 1/3 1/50 Z gas-poor (de s, dsph s) gas-rich (all others) numerous DM dominated (?) 2 1
2. Dwarf Galaxies Morphology Elliptical Irregular Blue Compact surface brightness increases...... brightness distribut./colour exponential red patchy blue/ expon. red blue nucleus/ expon. red morphology Ε like ges disk structure bright core gas -- HI (~0.3 M tot ) circumgalactic Z/Z 1/3... 1 1/40... 1/3 des Star formation past continuous starburst fraction 4 :1 5 :1 3 Kormendy (1985) 4 2
3. Dwarf Irregular galaxies The Large Magellanic Clouds a dirr on its passage of the Milky Way: 6 Type Examples: BCD & dirrs 7 3
optical : stars 3.1. The many + lumin. gas faces of the LMC Star-forming Regions: H HI withl21cm 8 LMC Star-forming Regions: H Stars + lumin. Gas: optical FIR HI: l21cm 9 4
The LMC, a gas-rich dirr 10 X-ray At the front edge of its CO motion through the Milky Way halo gas compression leads to the formation of molecular gas. Stars form delayed by the disk rotation. 11 5
(J. van Loon) 12 3.2. More distant dirrs 13 6
Carina II dirr 14 15 7
Leo A in the solar vicinity 16 IC 10, dirr, D 1.4 Mpc, M V =1.3 m, Local Group Galaxy 17 8
Dwarf Irregular Galaxies are characterized by large gas content and active present star formation. 18 Dwarf irregular galaxies are charaterized by a significant gas content, irregular structure, active star formation, patchy SF regions, blue colours. 19 9
3.3. Phenomenology of dirr Galaxies Brightness distribution in V is dominated by star-frorming regions (HII) irregular structure Brightness distribution in the IR is dominated by old stellar populations (smooth radial exponential decrease) Ellipticity similar to des dirrs are not (really) flat and disky (b/a>1:10) HI gas dominates baryonic mass (M stars < M HI ) because it exceeds radially the stellar extent 3.4. Star-formation signatures Integrated spectra of dirrs resemble mostly those of HII regions. Def.: If the whole optical body represents HII region characteristics: HII Galaxies Also strong in UV and B! When SF region concentrated to the center: Blue Compact DGs 22 10
3.5. Star-formation histories 23 SF timescale from element abundances Assumptions: closed box, constant Yields y i O+Fe from SNeII of massive stars, Fe by SN Ia from WD-WD or WD-RG slow evolution fast gas consumption Effects: The ratio of element abundances from particular precursor stars allow the age dating of their lifetimes and the derivation of the gas consumption. 25 11
SNeII of massive stars produce a constant ratio [O/Fe] 0.5, while Fe increases continuously. After the typical formation timescale of SN Ia Fe is further enhanced independently of the O enrichment. Thus, O/Fe decreases. From the age of the disk, the SN Ia timescale must be of the same order. Tolstoy & Venn, 2003 26 3.7. Metallicity of Dwarf Galaxies 28 12
29 [O/H] -0.4 L B 30 Skillman 1989 13
For galaxies a wide but significant correlation exists between M B and O abundance Kunth & Östlin 2000 31 Skillman 1989 Mass-Z relation 32 14
33 Outliers in the M B -Z relation There are isolated dirr outliers from the mass- Z relation observed. Yet interpreted as transition galaxies because of their low gas content. Stellar pop. synthesis necessary! ( 2008 ) al. Peeples et 35 15
et al. 2009, ApJ, 695 36 3.8. Blue Compact Dwarf galaxy NGC 2915, AAT (optisch) und ATCA (21cm) 37 16
BCDs 38 Koleva et al. 2014, MNRAS, 441 39 17
Disturbed brightness profiles Disturbed rotation Kinemat. decoupled cores (partly counterrotating) Largely varying vel. dispersion Younger central parts Metal-enhanced centers 40 41 18
3.9. HI Holes and Supershells in HoII 42 HI holes are not as expected always driven by star-forming regions! 43 19
HI Holes in NGC 2574 44 DDO 88: galaxy-sized Hole in the ISM 45 20
4. Dwarf Elliptical Galaxies 47 Dwarf elliptical (de de,n ds0) Galaxies FCC266 (de0,n) FCC136 (de2,n) FCC150 (de4,n) FCC288 (ds0) 21
Type Examples: ds0 & de 49 Type Examples: de bc, dsph, de blue 50 22
4.1. King profile King (1966) introduced two dynamical models of self-gravitating stellar systems. These were successfully applied to globular clusters and later extended to elliptical galaxies ( King, 1982). A King profile can be described in terms of the following parameters: Σ, brightnesscentral. 1 0. 2. Core radius, r c Σbrightnessthewhichat, 0 /2. 3. Tidal radius, r t. The brightness vanishes at this point. Generally the curves are labeled in terms of a quantity c = log(r t /r c ). For sufficiently small r, all King curves have a zero gradient. The model with c=infinity has a slope of -1 at large r and corresponds to the isothermal sphere. King's profiles are based on specific dynamical models, and provide good fits to globular cluster surface brightness. However, studies by Lauer et al. (1995) have shown that these are not really suitable for elliptical galaxies. 51 4.2. Sérsic Profile 1 n r I( r ) I e exp bn 1 re r I r ) I exp 0 r0 I ( r) 1 ( n n 4 I e n 1 1 n 15 bn 2n 0.324 n b 2 3.676 3 5.676 4 7.676 5 9.676 r r e n Sérsic Exponent n = 1: Exponential Law n = 4: de Vaucouleurs Law Trujillo et al. 2001, MNRAS 326, 869 23
4.3. The complexity and variety of des in the Virgo Cluster (GH) 55 56 24
Boxy and disky shapes possible in des as in Es! (GH), 2014, ApJ, 786 57 de with spiral patterns IC SS 3328 2017 58 25
4.4. Virgo des with kinematically decoupled cores VCC 1183 So far only known in Es and caused by gas/galaxy accretion! Yet no plausible explanation for des! Toloba et al. (GH), 2014, ApJ, 783 59 The KDCs of VCC1183 and VCC1453 are younger than the main body. Unsolved problem of the KDC formation: 60 26
4.5. Very faint gas-free DGs: dsphs Fornax dsph D= 138 kpc M v = -13.5 62 Faint dsphs pure stellar systems, no gas, metal-poor: Z< Z, faint end of dwarf Es, extremely faint: M v >-8 m, very small: ~ few kpc, close to the MWG Leo I with Regulus = Leo 63 27
Ursa Minor dsph 65 Leo I: D = 250 kpc 67 28
4.6. The massmetallicity relation at the faint end of des: dsphs Kirby et al. 2008, ApJ,685 68 4.7. Radial gradients in [Fe/H] EK et al., ApJ, submitted 69/42 29
Walker et al. 70, 2004 71 30
5. Stellar populations 72 74 31
76 5.1. CMD 82 32
The SF history deconvolution 83 84 33
85 The chart above demonstrates the previous conclusions by showing the abundances of alpha elements in dsphs versus solar metallicity. The symbols are as follows: blue triangles, Carina blue triangles plus circles, Leo I red triangles, Sculptor red triangles plus circles, Fornax green triangles, Draco, Ursa Minor, and Sextans from SCS01 black crosses, Glactic disk stars open squares, halo data from McWilliam et al. 1995 light blue stars, UVES data from a study of LMC star clusters of different ages light blue crosses, Galactic globular cluster measurements 87 34
Koleva et al. 2009, MNRAS, 396 88 Koleva et al. 2009, MNRAS, 396 89 35
5.2. The Population Box 90 with courtesy by Eva Grebel 91 SF continues also through the re-ion.epoch 36
dirrs of the MW show stronger and more continuous star formation with an increase of Z. Phoenix is in a stage of morphological transition. 92 93 37
6. Correlations of different galaxy types Tolstoy et al. (2010) ARAA, 47 94 Correlations of different galaxy types Tolstoy et al. (2010) ARAA, 47 95 38
96 97 39
98 99 40