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IMPRS, April 81 “Definition” Importance Evolution and winds Gas mass and distribution Magnetic fields Kinematics and Dark Matter 3-D structure Winds: case.

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Presentation on theme: "IMPRS, April 81 “Definition” Importance Evolution and winds Gas mass and distribution Magnetic fields Kinematics and Dark Matter 3-D structure Winds: case."— Presentation transcript:

1 IMPRS, April 81 “Definition” Importance Evolution and winds Gas mass and distribution Magnetic fields Kinematics and Dark Matter 3-D structure Winds: case studies Future studies themes of an expiring graduate school... Dwarf Galaxies: Building Blocks of the Universe

2 2 but rather....The first stellar system deemed extragalactic wasn‘t.... L ~ 1  L * L ~  L * Hubble (1925): Cepheids  NGC6822 at D = 214 kpc (today: 670 kpc) assumed Gaussian LF.... Zwicky (1942): LF increases with decreasing luminosity  dwarf galaxies = most numerous stellar systems M31NGC6822 Kilborn et al. (1999)

3 3 Bingelli diagramme  linked to galaxy formation shape of potential total mass What is a dwarf galaxy? Tamman (1993): “... working definition all galaxies fainter than M B = (H 0 = 50 km s -1 Mpc -1 ) and more extended than globular clusters...” Gallagher (1998): “... there is consensus that this occurs somewhere around (0.03 ···· 0.1)  L B*,...” L B* = (1.2 ± 0.1) · h -2 · L   < M B < Binggeli (1994): location in the M -  plane  formation process! “Dwarf galaxies lack the E-component!” M B = M B = M B =

4 4 low mass: 10 6 ··· M  slow rotators: 10 ··· 100 km s -1 low luminosity: 10 6 ··· 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 (?) POSSHST GR 8 Im ESO 410- G005 dSph I Zw 18 BCDG Mkn 297 Cl. Irr. Irr’s (Im, IBm, Sm, SBm) dE’s, dSph’s LSBDGs BCDGs, HII galaxies clumpy irregulars tidal dwarfs Properties: The zoo: understanding distant galaxies galaxy evolution ICM evolution nature of Dark Matter structure formation Importance:

5 5 Moore et al. (1999) 2 Mpc 300 kpc Cluster halo 5·10 14 M  Galaxy halo 2·10 12 M  Dwarf galaxies are building blocks CDM: Bottom-up structure formation  CDM models predict scale-invariant structures (e.g. Moore et al. 1999, Klypin et al. 1999) galaxy merging important process power-law mass function  dwarf galaxies are most numerous (~10% of mass in substructures) e.g. HDF: large number of amorphous blue galaxies (B ~ 24) with  1/2 = 0.3”  significantly smaller than L * galaxy “missing satellite” problem mechanisms to hide low-mass systems: remove baryons by SN-driven winds (Dekel & Silk 1986; McLow & Ferrara 1999) photo-evaporation from, or prevention of gas collapse into, low-mass systems during reionization at high redshift (Efstathiou 1992; Navarro & Steinmetz 1997) Benson et al. (2001): ‘dark satellites’ with M HI ~ 10 5 M  should exist... soft merging (à la Sagittarius dwarf) Stoehr et al. (2002):  CDM simulations observed kinematics exactly those predcited for stellar populations with the observed spatial structure, orbiting within the most massive satellite substructures

6 6 small perturber... large effect! Mihos & Hernquist (1995)

7 7 Andersen & Burkert (2000): models including SF, heating, dissipation - model dwarf galaxies evolving towards equilibrium of ISM  balance between input and loss of energy - dynamical equilibrium: a suitable scenario to produce all types of dwarfs? - gas consumption time scales are long:  evolution of dE’s must have been different (winds, tidal/ram pressure stripping) - role of DM halos: self-regulated evolution; exponential profiles In bottom-up scenario: primordial DM halos filled with baryonic matter subsequent SF gas-rich dI’s evolution into gas-poor dSph’s first SF burst(s) decisive? Dwarf galaxy evolution Larson (1974): gas depletion through first starburst Vader (1986), Dekel & Silk (1986): application to dwarf galaxies many models meanwhile... Mayor et al. (2001): tidal stripping in DM galaxy halo (“harassment”) LSB dI’s dSph’s HSB dI’sdE’s

8 8 Wind models (a selection....) Mc Low & Ferrara (1999): - dwarfs with masses 10 6 M   M  10 6 M , - mechanical luminosities L ~ ··· erg s -1 (over 50 Myr) - significant ejection of ISM only for galaxies with M  10 6 M  - efficient metal depletion for galaxies with M  10 9 M  Mac Low & Ferrara (1999) D’Ercole & Brighenti (1999): - starburst in typical gas-rich dwarfs  NGC mechanical luminosities L = 3.8 ·10 39 ··· 3.8 ·10 40 erg s -1 - efficient metal ejection into IGM - ‘recovery’ for next starburst after 0.5 ··· 1 Gyr t = 100 Myr D’Ercole & Brighenti (1999) Recchi et al. (2001): - SNe Ia included - SN Ia ejecta lost more efficiently (explosions occur in hot and rarefied medium)  I Zw 18 seems to fit well - important for late evolution of starburst (  500 Myr) - metal-enriched winds produced more efficiently models require:- distribution of mass - distribution and state of ISM - properties of magnetic field (?)

9 9 How much mass, how much gas? neutral atomic hydrogen easy to recover (21 cm line): dwarfs easily tidally disturbed e.g. NGC M tot ~ 2 ·10 10 M  (?) - M HI ~ 2 ·10 9 M  - heavily disturbed by 10 9 M  companion (DDO 125) - irregular velocity field in centre total (dynamical) mass: dwarfs gas-rich (except dE’s, dSph’s) van Zee et al. (1998) IZw 18 HI Hunter et al. (1998) Bomans et al. (1997) Hunter (priv. comm.) Gentile (in prep.) yet M tot difficult to assess at low-mass end: - ill-defined inclinations (3-D structure?) - disturbed velocity fields  v ~ v rot at low-mass end N6822M31cubes

10 10 Molecular (“hidden”?) gas H 2 most abundant molecule, but lacks dipole moment  CO is the tracer [CO/H 2 ] ~ (excitation by collisions with H 2 ) rotational transitions at 115, 230,.... GHz (mm waves) HI :pervasive T s ~ 100 K n H ~ 1 ···100 cm -3 H 2 :pervasive T k ~ 10 ··· 30 K n H2  1000 cm -3 GMCs T k ~ 20 K n H2 ~ 10 2 cm -3 dark cloudsT k ~ 10 K n H2 ~ 10 3 ···10 4 cm -3 cores T k  40 K n H2  10 4 cm -3 H 2 formed on dust grains (catalysts) at n H2  50 cm -3 requires column densities N H2  cm -2 to shield against dissociation by  11 eV photons mostly optically thick 12 C 16 O measured 13 CO, C 18 O optically thin, but much weaker methods to derive molecular masses: extinction (Dickman 1978): A V ~ N HI + 2·N H2 FIR & submm emission (Thronson 1986) S ~ N HI + 2·N H2  -rays (Bloemen et al. 1986) I  ~ N HI + 2·N H2 virialized clouds (Solomon et al. 1987) most widely resorted to.... Kohle (1999) Böttner et al. (2001) NGC 4449 (center): M HI ~ 1.5 ·10 8 M  M H2 ~ 4.4 ·10 8 M 

11 11 virialized clouds: measure - radius R - line width  v - CO intensity I CO Milky Way: X CO = 2.3 ·10 20 mol. cm -2 (K km s -1 ) -1 implications: I CO measures (‘counts’) the number of individual clouds within the telescope beam, weighted by their temperatures M vir (the total cloud mass) equals the sum of the atomic and molecular gas mass  I CO is a good measure for the H 2 column density (or L CO is a good measure for the H 2 mass) Caveat: depends on metallicity (C & O abundance) radiation fields (dissociation) excitation conditions (line intensity) density (shielding)

12 12 a normal galaxy... a dwarf galaxy... LMC! M51

13 13 NGC 4214 D = 4.1 Mpc Walter et al. (2001): 3 molecular complexes in distinct evolutionary stages NW: no massive SF yet excitation process? centre: evolved starburstISM affected SE: SF commenced recentlyI CO as in NW canonical threshold column density for SF: N HI ~ cm -2 comparison with HI  above cm -2 primarily molecular Haro 2 D = 20 Mpc Fritz (2000): complex velocity field and distribution of (visible!) molecular gas  advanced merger? CO and HI concentrated strong starburst, SFR ~1.5 M  yr -1 de Vaucouleurs stellar profile (r 1/4 ) CO emission from regions with rather different properties Fritz (2000)... puzzling cases:

14 14 certainly depends on spatial scale.... Milky Way, Local Group, Virgo Cluster, ULIRGs, high-z galaxies metallicity (Wilson 1995) CR heating (Glasgold & Langer 1973) heating by - energetic particles (1 ··· 100 MeV CRs) - hard X-rays(  0.25 keV) process: H 2 + CR  H e - (~35 eV) + CR primary e - heats gas by (ionizing or non-ionizing) energy transfer X CO dependence Klein (1999) bottom line: detailed case studies indispensable! circumstantial evidence for this process on large (~ 200 ··· 400 pc) scales but: CR flux at E  100 MeV not known in galaxies.... heating rate (Cravens & Dalgarno 1978; van Dishoek & Black 1986):

15 15 WLM D = 0.9 Mpc: - little SF, weak radiation field & CR flux - X CO ~ 30  X Gal (Taylor & Klein 2001) - below 12 + log(O/H) = 7.9 no CO detections of galaxies (Taylor et al. 1998) M 82 D = 3.6 Mpc: - intense SF, strong radiation field and CR flux high gas density, large amount of dust - X CO ~ 0.3  X Gal in central region (Weiß 2000) from radiative transfer models; requires many transitions, including isotopomers  true gas distribution - strong spatial variation of X CO - blind use of X CO leads to false results.... Two contrasting examples:

16 16 Star formation history in dwarf galaxies GR 8Sextans A

17 17 B-fields play an important role in SF process B-fields provide a large-scale storage for relativistic particles low-mass galaxies may have strong winds  less containment for CRs (Klein et al. 1991) NGC4565 NGC4631 B-fields in dwarf galaxies exhibit less coherent structure Dumke et al. (1995) Klein et al. (1991) Klein et al. (1996) Chy  y et al. (2000) Magnetic fields magnetization of IGM by primeval galaxies? (Kronberg et al. 1999)

18 18 Ott et al. (2001) Ho I Kinematics and Dark Matter early recognition that dwarfs have high M/L Sargent (1986): “The estimated M/L are high ··· 3. This is not simply a consequence of the objects being rich in HI gas”. at low-mass end: - mostly rigid rotation -  v   v - annular distribution of HI - dSph’s show high M/L (stellar  v in Local Group galaxies, e.g. Mateo 1998) large number of HI rotation curves: WHISP (de Block 1997; Stil 1999; Swaters 1999) - systematic production of rotation curves of LSBGs and dwarfs - probably DM dominated, but:  maximum disk solution fits rotation curves well  scaling the HI “ “ “ “ “ - problem of beam smearing and velocity resolution (van den Bosch et al. 2000) Mateo (1998)

19 19 CDM models: e.g. ‘NFW’ (Navarro et al. 1996): problems: -reconcile with TF relation (Navarro & Steinmetz 2000) -number of satellites around MW (Moore et al. 1999)  effects of reionization (Benson et al. 2001) - no spirals (Steinmetz et al. 2000) - rotation curves seem to be at odds with NFW.  beam smearing? (van den Bosch et al. 2000)  stellar feedback? (Gnedin & Zhao 2001) Swaters (1999) need high-quality rotation curves (H  + HI) in particular: undisturbed dwarf galaxies better fit to inner RCs: ‘Burkert’ profile (Burkert 1995)  no cusps? Blais-Ouellette et al. (2001)

20 20 irregular morphologies  inclination often unknown HI holes in low-mass galaxies grow larger  thicker disks (e.g. Brinks & Walter 1998) Compare z 0 with sizes of largest holes less gravity  larger z 0  larger holes Brinks & Walter (1998) Galaxyscale height [pc] M M IC Ho I400 Ho II625 IC D structure of dwarf galaxies

21 21 Galactic winds: winds play an important role in the evolution of (small) galaxies (Matteucci & Chiosi 1983); may explain - metal deficiency of dwarf galaxies - enrichment of IGM Different masses, different winds.... modern numerical simulations (e.g. Mac Low & Ferrara 1999; Ferrara & Tolstoy 2000): for mechanical luminosity L = erg s -1 blow-out occurs in 10 9 M  galaxy  only ~30% metals retained Galaxy DM tot starburst [Mpc][10 9 M  ] M ongoing NGC post Ho I † past † visible (stellar) mass Devine & Bally (1999)

22 22 Kronberg et al. (1981): L FIR = 1.6 · erg s -1 L X = 2.0 · erg s -1 SN ~ 0.1 yr -1 M 82 Weiß et al. (1999): discovery of expanding molecular superbubble, broken out of the disk  result of high ambient pressure and dense ISM centred on (most powerful SNR) main contributor to high-brightness X-ray outflow! v exp  45 km s -1 Ø  130 pc M  8 ·10 6 M  E inp  erg  kin  10 6 yr SN ~ yr -1 10% of E inp  hot X-ray gas 10% of E inp  expansion of molecular shell Wills et al. (1999) M MHzWills et al. (1997)

23 23 Weiß et al. (2001) Weiß et al. (1999)

24 24 - prominent HI hole around star clusters (Israël & van Driel (1990) - inner gaseous disk completely disrupted (Stil 1999) - partly v w  v esc (H  velocities: Martin 1998; X-ray temperature: Della Ceca et al. 1996; Martin 1999) Heckman et al. (1995), Della Ceca et al. (1996): L FIR = 8 · erg s -1 L X = 3 · erg s -1 SN ~ 0.01 ··· yr -1 Israël & de Bruyn (1988), Greggio et al. (1998): starburst ceased ~5 ··· 10 Myr ago SFR  0.5 M  yr -1 NGC 1569 Martin (1999) - giant molecular clouds near central HI hole formed by shocks from central burst? - strong CO(3  2) line I CO(3-2) /I CO(21-1) ~ 2 (!)  copious warm gas - evidence for blown-out/piled-up gas - radial magnetic fields! Ott (2002)

25 25 Hunter et al. (1993) Taylor et al. ( 1999) Mühle (in prep.) CO(3  2) Mühle (in prep.) Disrupted gas in a dwarf galaxy: kinematics of HI (Stil 1999): inner part (r  0.6 kpc) completely disrupted by starburst just two regions of dense gas left (Taylor et al. 1999) warm, diffuse gas out to ~400 pc (Mühle in prep.) radial configuration of magnetic field (Mühle in prep.)

26 26 Ho I LSB dwarf galaxy M tot ~ 2.4 · 10 9 M  (stars + gas) Ott et al. (2001): HI arranged in huge shell Ø  1.7 kpc M HI  10 8 M  E inp  erg  kin  80  60 Myr (kin. + CMD) - BCDG phase in the past? - recollapse? Major axis Minor axis

27 27 Outlook study of low-mass galaxies important for our understanding of galaxies in the early universe detailed case studies indispensable (dwarf galaxies are individuals!) - different environments (field, group, cluster) - different masses and SFR’s - recover full gas content - derive gravitational potentials (DM) - study interplay between SF and ISM (disk - halo) numerical simulations must incorporate realistic conditions - gas distribution - mass distribution - attempt to ‘reproduce’ observed galaxies interpreting distant galaxies requires scrutiny of nearby ones, in particular at low-mass end relevant observations of (more) distant galaxies - SKA - ALMA - NGST - X-ray satellites

28 28

29 29

30 30 L B ~ 0.5  L MW L B ~ 0.06  L MW L B ~  L MW

31 31 Ott et al. (in prep.)

32 32


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