Dwarf Galaxies in Galaxy Clusters

Transcription

1 Dwarf Galaxies in Galaxy Clusters SS de Galaxies dominate in clusters Sandage et al. (1984) Binggeli et al. (1987) SS

2 The vol. density of dirrs fraction in clusters is the same as in the field. des dominate the morphology in clusters! What makes dirrs des? Which process drives gas loss? 1. Galactic winds, gas expulsion 2. Tidal stripping 3. Ram-pressure stripping SS How are dwarf elliptical galaxies formed? dirrs do not lose their gas completely by galactic winds! Are all des formed morphologically separately? How much environmental effects? How would dirrs without gas look like? 2

3 The vol. density of dirrs fraction in clusters is the same as in the field. des dominate the morphology in clusters! What makes dirrs des? Which process drives gas loss? 1. Galactic winds, gas expulsion 2. Tidal stripping 3. Ram-pressure stripping SS Dwarf Galaxies appear in CDM cosmological simulations The zoom-in Aquarius simulations: N-body DM-only make subhalos detectable; with mass resolution m SPH few x 10 4 few x 10 5 M (Springel et al. 2008, MNRAS, 391) SS

4 SS The complexity and variety of des in the Virgo Cluster (GH) SS

5 des in Virgo show a variety of shapes + properties that seem to correlate with the SS 2017 radial cluster distribution des distribution in the Virgo Cluster Janz et al. (GH), 2014, ApJ, 786, 105 SS

6 One-component des are rounder (b/a -> 1.), slower; The rounder the more centrally concentrated SS is the so-called Spin parameter; 2015, ApJ, 799, 172 the larger the faster the rotation; disky des rotate faster; the closer to the cluster center, the slower the rotation SS

7 5. How to distinguish between cluster-born des vs. fallen-in, ram-pressure stripped, and harassed former dirrs? Infalling field des not to be discussed! SS Distribution of Virgo de ages (all des; Hielscher, Janz et al.), with X-ray contours overplotted. red=older, blue=younger: des as products of infalling RPS dirrs are expected to be at higher ICM densities be at large clustercentric distances, to be flatter, to have smaller Z, move faster, eccentr. orbits SS Lisker, Janz, Hensler, et al. (2009) ApJ, 706 7

8 des originating from the cluster density fluctuations and evolving within the cluster are expected to show the morphol. concentration, be spherical, have larger Z, move slower on circular orbits des as products of RPS infalling dirrs are expected to show higher densities at large distances from the cluster center be flattened, have smallerer Z, move faster on eccentric orbits SS Lisker, Janz, G.H., et al. (2009) ApJ, Nov. 6. 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 SS et 2017 al., 2014, ApJ,

9 The KDCs of VCC1183 and VCC1453 are younger than the main body. Unsolved problem of the KDC formation: SS Star-formation history in Virgo des Koleva et al. 2009, MNRAS, 396 SS

10 Distribution of Virgo de ages (all des; Hielscher, Janz et al.), with X-ray contours overplotted. red=older, blue=younger: Problems: What about dirrs in Clusters? Where does gas in cluster des come from? Are des in the field transformed?.? SS SS

11 Gotthart et al. (GH) Structural signatures of Virgo des SS Conclusions on cluster des des in clusters are distinguishible between those born in the cluster and those fallen in (and passing through), respectively, within the last Gyrs, but not in all expected properties, multiple substructures anticorrelated with mass, kinematically decoupled cores; signature of group infall? bluish cores; more to be studied (e.g. spectra): SMAKCED collab. SS

12 8. Where do the transformed des come from? Search for candicates SS SS

13 9. The effect of Ram-pressure Stripping R strip Ram Pressure by the relative motion of the IGM : p v ram IGM 2 rel restoring energy density : d erest ( r ) ISM ( r ) dz v rel if p ram e rest RPS works until the stripping radius R SS strip Galaxies moving through intra-cluster medium are exposed to ram pressure! Ram Pressure by the relative motion of p IGM v 2 rel restoring energy density : e ram rest d ( r) dz ISM the IGM : ( r) R strip NGC 4569 if for R R 0 p e stripping radius R strip ram gas 1 2 r rest RPS until strip M gas 2 R 2 0 e r R0 G M * M gas ln 2 IGM vrel 2 R 4 0 v rel 13

14 Motion in Clusters Motion of a galaxy through a cluster with r 0 1 r c where ρ 0,tot = M /pc 3, r c =0.32 Mpc and for the IGM n 0 = cm -3, r c =13.4 Mpc, β=0.5 Hensler, Roediger & Köppen (2009) SS RPS in NGC 4522 vs. Models Kenney & Koopman (1999), AJ, 117 Toennesen & Bryant (2012) ApJ, 422 NGC 4522 moves with ~1300 km/s relat.ly to the Virgo IGM. Gas is stripped off in one direction and shines in H, but w/o SF. Models produce a lot of star-f. clumps. Numerical artefact! 14

15 Gas Loss of DGs by strong RPS Mori & Burkert (2000) SS see also: Roediger & Hensler (2005) Applicability of ram-pressure stripping Ram pressure : p Binding energy density : e kick off timescale : ram grav τesc v Gyrs v IGM ISM esc IGM How to treat RPS dynamically? v v 2 ICM 2 rot 1 cm n IGM -3 v km/s v IGM esc mean free path of electrons : mean free path within HI gas : λ λ e HI 6 2 (T/10 K) pc 3 3 ( nigm /10 cm ) pc 3 ( n /1 cm ) IGM Hydrodynamical treatment requires multi-scale description! 15

16 Expectations from theory/model/simulations and demands from observations questions on galaxy evolution Modelling RPS DGs M gas,i = 1.4 x10 8 M ; M s,i = 0 M DM = 8.4 x10 8 M v rot = 30 km/s v rel = 290 km/s, n ICM = 10-4 cm -3 No enhanced SF No total gas evacuation SS

17 original properties cluster forms, condenses, virial T = hot gas environment field negligible high galaxy density low frequent gal. interact.s seldom heated, gas loss by continuous RPS, tidal eff.s, evaporation ISM gas rich, accr./ infall round, press.-supp. shape flat, rot.-supported delayed init.: downsiz., strong initial burst? SF continuous, low-level or bursting des morphology dirrs solar metallicity sub-solar SS evolution in the cluster v 2 orb M ~ r cluster cl orb vorb vvir circular, r orb diminishs with cluster mass velocity orbit (former) field infall to cluster with virial vel. v vir eccentric, reaching the outskirts of cl.s centrally concentr. R-distrib. flat? no! gas loss by RPS f(r)? total? add.: tidal eff.s, evap. Gas accretion poss.? ISM stripped by ram P; totally: core gas survive? Gas re-acc./self-replen. in the cl. outskirts round, press.-supp. shape flat, rot.-supported old; but nucleated? const. stellar pop. intermed. age possibly enhanced with age of Gyrs SS

18 The Origin of des in Galaxy Clusters SS SS

19 The case of VCC1217 Transformation by RPS RGB UV,U,B,V Hα-off Hα-on not nec. SF! SS Questions: When is the gas stripped? Does RPS lead to gas compression and enhance SF? How to keep gas despite Gunn/Gott conditions? Which fraction of des can escape from the cluster? SS

20 SS SS

21 Dwarf Galaxies are expected to lose gas at cluster infall already by the low-density ICM ram pressure How much gas loss? Ram-pressure effects on star formation: In the DG body? In the RPS gas tail? SS The detection of ESO Star formation in the RPS blobs SS

22 4.5kpc Noeske et al. (2000) A&A, 361, 33 Transformation of dirrs by RPS should be visible already in a dilute environment, if v rel is sufficiently large. SS Consequences for their abundances? Star formation? Thuan et al. (1999) Cometary BCDs SS

23 Metal-Poor cometary BCDs HST V image of SBS Guseva et al. (2003, A&A 407, 105) SS Metal-Poor cometary BCDs ( 169 Fricke et al. (2001, AJ 121, ( L57 Papaderos et al. (1999, A&A 352, SS

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25 RPS for very low-mass DGs M gas,i = 6.3 x10 6 M ; M s,i = 0 M DM = 1.2 x10 8 M v rot = 2 km/s moderate infall: v rel = 290 km/s, n ICM = 10-4 cm -3 SF enhanced when v rel reaches max. No SF in RPS gas tails Gas almost totally lost, but condensed clouds survive with varying SFRs Steyrleithner et al. in prep. SS fast RPS DGs M gas,i = 6.3 x10 6 M ; M s,i = 0 M DM = 1.2 x10 8 M v rot = 2 km/s fast infall: v rel = 1000 km/s, n ICM = 10-4 cm -3 Steyrleithner et al. in prep. Critical velocity for enhanced SF is reached earlier not when v rel max. Gas almost totally lost, but condensed clouds survive When these condensed clumps get RP stipped at later stages, they bear SF SS

26 10. Star Formation-Density Relation Suppression of star formation at high densities Galaxies in dense environments form fewer stars Evolution of the star formation-density relation Does environment drive the decline in the star formation rate? Or are the galaxies simply running out of gas? Observed HI deficiency in cluster galaxies SS Harassment Galaxies in Clusters suffer multiple highspeed passages with other cluster members, called harassment. Distortion by Impuls Approximation heats up the stellar velocity dispersion G M2 M1 2 ΔE r 4 2 h 3b v In contrast, angular momentum is reduced. SS

27 SS Galaxy Cluster DGs: DGs are RP stripped in low-density inter-galactic medium! Star formation enhanced due to ram pressure! SF in stripped clumps: Under which conditions? Where observable? Steyrleithner et al. (GH) 2017, MN, to be submitted Gas loss + harassment! Smith et al. (GH) 2015, MNRAS, 454 How do transformed des look like? See SMAKCED publ.s SS

28 Stellar content, MAss and Kinematics of Cluster Early-type Dwarfs (SMAKCED): project of des in Virgo Cl. Urich, L., Lisker, T., Janz, J., et al. (HENSLER, G.): Young, metal-enriched cores in early-type dwarf galaxies in the Virgo cluster based on colour gradients, 2017, Astron. Astrophys., submitted Sen, S., Peletier, R.F., Boselli, A., et al. (HENSLER, G.): Na and Ca abundances in dwarf elliptical galaxies, 2017, MNRAS, submitted Toloba, E., Guhathakurta, P., Boselli, A., et al. (HENSLER, G.): Stellar Kinematics and structural Properties of Virgo Cluster Dwarf early-type Galaxies from the SMAKCED Project. III. Trends as a Function of projected Distance from the Cluster Center. 2015, ApJ., 799, 172 Toloba, E., Guhathakurta, P., Peletier, R.F., et al. (HENSLER, G.): Stellar Kinematics and structural Properties of Virgo Cluster Dwarf early-type Galaxies from the SMAKCED Project. II. The Survey and a systematic Analysis of kinematic Anomalies and Asymmetries , ApJ. Suppl., 215, 17 Janz, J., Laurikainen,, E.,Lisker, T., et al. (HENSLER, G.): A Near-Infrared Census of the Multi-Component Stellar Structure of Early-Type Dwarf Galaxies in the Virgo Cluster. 2014, ApJ, 786, 105 Toloba, E., Guhathakurta, P., van de Ven, G., et al. (HENSLER, G.): Stellar Kinematics and Structural Properties of Virgo Cluster Dwarf Early-Type Galaxies from the SMAKCED Project. I. Kinematically Decoupled Cores and Implications for Infallen Groups in Clusters. 2014, ApJ, 783, 120 Janz, J. Laurikainen, SS 2017 E. Lisker, T., et al. (HENSLER, G.): Dissecting early-type dwarf galaxies into their multiple components. 2012, ApJL, 745, L