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Thorsten LiskerEarly-Type Dwarf Galaxies The Various Origins of Early-Type Dwarf Galaxies An Observer´s Perspective Thorsten Lisker Zentrum für Astronomie.

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Presentation on theme: "Thorsten LiskerEarly-Type Dwarf Galaxies The Various Origins of Early-Type Dwarf Galaxies An Observer´s Perspective Thorsten Lisker Zentrum für Astronomie."— Presentation transcript:

1 Thorsten LiskerEarly-Type Dwarf Galaxies 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 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)

2 Thorsten LiskerEarly-Type Dwarf Galaxies Introduction

3 Thorsten LiskerEarly-Type Dwarf Galaxies Classification Sandage & Binggeli 1984 Early-type dwarfs „ dE ” dSph M B =-18 M B =-13 3x

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

5 Thorsten LiskerEarly-Type Dwarf Galaxies Characterization of Virgo dEs Mainly relying on SDSS data

6 Thorsten LiskerEarly-Type Dwarf Galaxies The classical picture: ”dEs have no star formation and almost no gas”

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

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

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

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

11 Thorsten LiskerEarly-Type Dwarf Galaxies Distribution within the cluster Lisker et al. (2007), ApJ 660, 1186

12 Thorsten LiskerEarly-Type Dwarf Galaxies Dark = mostly non-nucleated, bright = mostly nucleated

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

14 Thorsten LiskerEarly-Type Dwarf Galaxies Light profiles „dEs are exponential“ Sérsic-n varies with luminosity!

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

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

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

18 Thorsten LiskerEarly-Type Dwarf Galaxies Colours metallicity  age 

19 Thorsten LiskerEarly-Type Dwarf Galaxies Discussion and also some questions...for you!

20 Thorsten LiskerEarly-Type Dwarf Galaxies Dynamical state & evolution? Relaxation timescales? Two-body relaxation >> Hubble time Violent 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 More than one formation mechanism needed to explain the heterogeneity of the early-type dwarfs

21 Thorsten LiskerEarly-Type Dwarf Galaxies...but: surface brightness offset! metallicity offset! e.g. Spiral  dE(di) via harassment... Irr dE(nN)>16 Boselli et al. (2008): Ram-pressure stripping of infalling galaxies could have produced the majority of dEs within 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... Origin(s)? dE(nN) dE(pec) dIrr Mastropietro et al. (2005)

22 Thorsten LiskerEarly-Type Dwarf Galaxies Boselli et al. (2008): Ram-pressure stripping of infalling galaxies could have produced the majority of dEs within 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... Origin(s)?...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 Thorsten LiskerEarly-Type Dwarf Galaxies Origin(s)? And the dE(N)s...have always been ‚there‘? Moore et al. 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 Thorsten LiskerEarly-Type Dwarf Galaxies Dwarfs vs. Giants Lisker & Han (2008), ApJ in press, arXiv: Boselli et al. (2005) Joachim Janz & TL, in prep.

25 Thorsten LiskerEarly-Type Dwarf Galaxies Summary  The early-type dwarf zoo: dEs with disks, central star formation, (no) nucleus have different shapes, distributions, colors, dynamical states  More than one formation process needed e.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 Hagen MeyerSanjaya PaudelJoachim Janz & Oliver Hielscher, Alexander Hansson  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!

26 Thorsten LiskerEarly-Type Dwarf Galaxies

27 Thorsten LiskerEarly-Type Dwarf Galaxies


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