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The Various Origins of Early-Type Dwarf Galaxies An Observer´s Perspective

The Various Origins of Early-Type Dwarf Galaxies An Observer´s Perspective. Thorsten Lisker Zentrum für Astronomie der Uni Heidelberg (ZAH) Heidelberg Graduate School of Fundamental Physics.

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The Various Origins of Early-Type Dwarf Galaxies An Observer´s Perspective

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  1. The Various Origins of Early-Type Dwarf GalaxiesAn Observer´s Perspective Thorsten Lisker Zentrum für Astronomie der Uni Heidelberg (ZAH)Heidelberg Graduate School of Fundamental Physics Eva K. Grebel (ZAH), Bruno Binggeli (U Basel), Joachim Janz (ZAH),Burkhard Fuchs (ZAH), Katharina Glatt (U Basel / ZAH), Pieter Westera (U Rio de Janeiro) http://x-astro.net

  2. Introduction

  3. 3x MB=-18 Early-type dwarfs Sandage & Binggeli 1984 dSph MB=-13 Classification „ dE ”

  4. Binggeli et al. 1987 log(projected density) Most numerous type of galaxy in clusters!~950/1300 in the Virgo cluster >3 times more dEs in Virgo than the sumof groups could provide (Conselice et al. 2001)  Probing environmental processes with dEs Why dEs?

  5. Characterizationof Virgo dEs Mainly relying on SDSS data

  6. The classical picture: ”dEs have no star formation and almost no gas”

  7. Lisker et al. (2006), AJ 132, 2432 dEs with blue centers - „dE(bc)“

  8. Lisker et al. (2006),AJ 132, 2432 The classical picture: ”dEs have no star formation and almost no gas” ”dEs are spheroidal”

  9. Lisker et al. (2006), AJ 132, 497 dEs with disks - dE(di) We identified 37 dE(di)s (42 incl. possible members)13 with unambiguous disks, 8 with ‚probable‘ disks, and 16 with ‚possible‘ disks. ~ one third of brighter dEs!

  10. Lisker et al. (2006),AJ 132, 497 The classical picture: Lisker et al. (2006),AJ 132, 2432 ”dEs have no star formation and almost no gas” ”dEs are spheroidal” ”dEs are found preferentially in high-density regions”

  11. Lisker et al. (2007), ApJ 660, 1186 Distribution within the cluster

  12. Dark = mostly non-nucleated, bright = mostly nucleated

  13. Lisker et al. (2007),ApJ 660, 1186 The classical picture: Lisker et al. (2006),AJ 132, 2432 ”dEs have no star formation and almost no gas” Lisker et al. (2006),AJ 132, 497 ”dEs are spheroidal” ”dEs are found preferentially in high-density regions” ”dEs have exponential profiles”

  14. Light profiles „dEs are exponential“ Sérsic-n varies with luminosity!

  15. Lisker et al. (2007),ApJ 660, 1186 The classical picture: A more complete picture: Lisker et al. (2006),AJ 132, 2432 ”dEs have no star formation and almost no gas” ”dEs are spheroidal” Lisker et al. (2006),AJ 132, 497 ”dEs are found preferentially in high-density regions” ”dEs have exponential profiles”

  16. The classical picture: A more complete picture: ”dEs have no star formation and almost no gas”  ~15% of the brightest dEs do have star formation and some gas ”dEs are spheroidal”  dEs with disks reach 50% at the bright end of dEs, dEs with blue center & bright non-nucleated dEs are thick-disk-like ”dEs are found preferentially in high-density regions”  Only nucleated dEs are centrally concentrated within the cluster ”dEs have exponential profiles”  Continuum in Sérsic-n with luminosity Only nucleated dEs without disks are ’classical’ dEs

  17. Lisker et al. (2007), ApJ 660, 1186 (age/metallicity between dENs and dEnNs) youngest older/more metals younger/fewer metals

  18. age metallicity  Colours

  19. Discussionand also somequestions...for you!

  20. More than one formation mechanism neededto explain the heterogeneity of the early-type dwarfs Dynamical state & evolution? Relaxation timescales? Two-body relaxation >> Hubble timeViolent relaxation: few crossing times??1 crossing time  1.7 Gyr Too long in both cases (?) Conselice et al.: Es are the only Virgo population that is relaxed - based on width of velocity distribution But should velocity distribution for dwarfs be similar to giants at all, even if they were relaxed? (We‘re also neglecting here that the whole cluster is dynamically young...) Small but significant color dependence on density! They‘ve known about their present density regime for quite some time

  21. dE(nN) dE(nN) dE(pec) Irr dIrr dIrr dIrr dE(nN)>16 Mastropietro et al. (2005) Origin(s)? Boselli et al. (2008):Ram-pressure stripping of infalling galaxiescould have produced the majority of dEswithin the last few Gyr!  but these shouldn‘t be centrally concentrated (?)  Infall & subsequent processes responsible for the „outer“ subclasses (disks, blue cores, non-nucleated) e.g. dIrr  dE via stripping... ...but: surface brightness offset! metallicity offset! e.g. Spiral  dE(di) via harassment...

  22. Origin(s)? Boselli et al. (2008):Ram-pressure stripping of infalling galaxiescould have produced the majority of dEswithin the last few Gyr!  but these shouldn‘t be centrally concentrated (?)  Infall & subsequent processes responsible for the „outer“ subclasses (disks, blue cores, non-nucleated) e.g. dIrr  dE via stripping... ...but: surface brightness offset! metallicity offset! e.g. Spiral  dE(di) via harassment... ...but: dE(di)s appear regular, undistorted...no tidal debris seen so far around them...and some of them actually look like real disk galaxies! By the way:What surface brightness profiles should harassed disk galaxies have in the end?Remember dEs are not just exponential...!

  23. Moore et al. Origin(s)? And the dE(N)s...have always been ‚there‘? If most dEs were produced by infall & transformation, their positions in the diagram would not represent their DM halos - right? Therefore, only those that were born as dEs (in a morphological sense) should enter the diagram - right??  The dE(N)s might be the predicted DM subhalos, which were born in the high-density environment -all other dE subtypes might have been born in the field

  24. Lisker & Han (2008),ApJ in press,arXiv:0803.2512 Boselli et al. (2005) Dwarfs vs. Giants Joachim Janz & TL, in prep.

  25. Relation of dEs and Es? • Ages and metallicities of dEs and their nuclei? • Which late-type galaxies would qualify as dE progenitors? • Age/metallicity distribution across the cluster? • Dwarf populations of different clusters? • Ultraviolet properties of dE subclasses? First results at the JENAM 2008 in Vienna! Hagen Meyer Sanjaya Paudel Joachim Janz & Oliver Hielscher, Alexander Hansson http://x-astro.net Summary • The early-type dwarf zoo:dEs with disks, central star formation, (no) nucleushave differentshapes, distributions, colors, dynamical states • More than one formation process needede.g.dE(N)s born in their own DM (sub)halos in the (proto)cluster,all others formed out of other galaxy types through infall & transformation Outlook

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