Morphological Composition of z~0.4 Groups: The site of S0 Formation?

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1 Morphological Composition of z~0.4 Groups: The site of S0 Formation? Dave Wilman Wilman, Oemler, Mulchaey, McGee, Balogh & Bower 2009, ApJ, 692, 298 * *Also described as a Research Highlight in Nature, March , Vol 458, Issue 7234

2 Decline of Star Formation at low z e.g. Madau et al, 98 COMBINED: Declining SFR in individual galaxies AND Lower fraction of star forming galaxies

3 Decline of Star Formation at low z e.g. Madau et al, 98 COMBINED: Declining SFR in individual galaxies AND Lower fraction of star forming galaxies

4 Evolution in Clusters - Blue Galaxies Butcher & Oemler, 1984 Strongly evolving fraction of blue (star forming) galaxies

5 Ellipticals and S0s Both typically passive - but morphologies relate to dynamical state of galaxy - information about formation

6 Morphologies of cluster early-types Fasano et al, 00 following Dressler et al, 97 Strongly increasing fraction of S0s

7 Morphology traces local density Dressler, 1980 Morphology imprinted inside groups prior to infall? or by cluster-centric processes?

8 The group regime Postman & Geller, 1984 Morphology-Density relation exists in low-z groups

9 Visual Morphological Classification ACS F775W coverage of <z<0.55 CNOC2 F-O-F groups (see Balogh talk, Carlberg et al, 01; Wilman et al, 05). Groups velocity dispersions km/s (& a couple of ~700km/s systems) Serendipitous Field sample (galaxies not in groups). Classifications by Gus Oemler and John Mulchaey: 2 stretch levels displayed to identify high and low SB features Randomly ordered galaxies -> no bias with group/field environment Classification using the MORPHS scheme: Group into categories of classification: E (E, E/S0), S0 (S0/E, S0, S0/a, SB0/a), esp (Sa-Sbc includes bars), lsp (Sc-Sm includes bars), Irr.

10 Visual Morphological Classifications The most difficult classification decisions are: E vs S0, non edge-on: Look for a break in SB profile = hard outer edge to the bulge S0 vs Sa: Look for surface brightness irregularities in the disk (spiral arms) Classifications highly consistent: 222/310 identical 69 T=0.5, 17 T=1, 2 T=1.5

11 GIM2D Decompositions of S0s, esps Decompositions: McGee et al, 08

12 GIM2D Decompositions of S0s, esps S0s have MUCH higher B/T than spirals Decompositions: McGee et al, 08

13 Composition of Groups/Field as f(luminosity) Luminosity limits at: z=0.55 z=0.3 Jackknife errors S0s: 40/178 group 10/109 field All Spirals (esp+lsp) Early-Type Spirals (esp) r-band luminosity

14 Significance of Difference between Group and Field With Field Sample Luminosity-Matched to Groups: Resampled field: >=f(s0) grp 0 times (>99.999%) >=f(e) grp (85%) <=f(sp) grp (99.95%) of which most difference for late-type spirals No difference to f(s0) grp, and still very significant excess, if: Most massive groups ignored S0/a ignored

15 Radial Trends Compare inner (<300kpc) and outer group populations at fixed luminosity. Interesting Trends: More Bright Ellipticals in inner group: >99.999% confidence More S0s in OUTER group: 97% confidence

16 Composition vs environment and z to M V =-20.53, for comparison with Fasano et al, 00 cluster sample Ellipticals: No clear dependence on environment OR z! S0s: Clear dependence on z At least as populous in Groups as Clusters Spirals:Clear dependence on z. As populous in Clusters as Groups

17 Similar early-type fraction in the supergroup SG1120 to clusters Kautsch et al, 2008 see also poster by Dennis Just

18 S0s have MUCH higher B/T than spirals Bulge growth

19 Late-Type Spiral -> S0? Poggianti et al, 2008 will need: significant bulge growth (will be esp for a stage) and eventually: a truncated gas supply (stop SF)

20 Late-Type Spiral -> S0? Poggianti et al, 2008 will need: significant bulge growth (will be esp for a stage) and eventually: a truncated gas supply (stop SF)

21 Late-Type Spiral -> S0? Poggianti et al, 2008 will need: significant bulge growth (will be esp for a stage) and eventually: a truncated gas supply (stop SF)

22 IR-bright progenitors? Geach et al, m bright galaxies mainly in infall regime

23 Bulge Growth by Star Formation Maximal Case: For a B/T=0 galaxy to evolve into a B/T=0.7 galaxy with total final M * =2x10 11 M sol : Require ~1.4x10 11 M sol bulge growth in ~4 Gyr. -> SFR ~ 35 M sol /yr Quite reasonable for a dusty star former i.e. 24 m strong galaxies typically forming stars at these rates at intermediate-high z (Bell et al, 05; Bai et al, 07; Marcillac et al, 07; Saintonge et al, 08; Geach et al, 08)

24 field group IR-bright progenitors? MIPS 24 m data: No particularly bright Starbursts in groups All log(l TIR /L sun ) Tyler et al, in prep

25 Stripping? McGee et al, 08 No difference in Group/Field Disk scaling relations Disk scaling relation: black (red) solid line best fit to field (group) galaxies. Dotted (dashed) line: effect of truncating SF in field galaxies 1 (3) Gyr earlier.

26 Possible lack of truly passive spirals? IR colour reveals low level SF 0.4 [f(8)/f(3.6)] 0.5 SSP Wilman et al, 08 Wilman et al., 08 M * (x10 10 M )

27 Possible lack of truly passive spirals? IR colour reveals low level SF 0.4 [f(8)/f(3.6)] 0.5 SSP Wilman et al, 08 InfraRed Passive Sequence (IPS) Wilman et al., 08 M * (x10 10 M )

28 Possible lack of truly passive spirals? IR colour reveals low level SF Weak / no [OII] 0.4 [f(8)/f(3.6)] 0.5 SSP Wilman et al, 08 InfraRed Passive Sequence (IPS) Wilman et al., 08 M * (x10 10 M )

29 Mechanisms in and around Clusters Moran et al, 07 Spirals with no UV emission tend to live in cluster regions where ram-pressure should be important. Young S0s and UV-bright low- [OII] spirals only exist at lower density.

30 Mechanisms in and around Clusters Moran et al, 07 Spirals with no UV emission tend to live in cluster regions where ram-pressure should be important. Young S0s and UV-bright low- [OII] spirals only exist at lower density. Stripping

31 Other Mechanisms Minor Mergers: A few of intermediate mass ratio minor mergers should produce galaxies with structural parameters typical of S0 (Bournard et al, 05) Should be common: with halo central galaxies (but many merger events should often lead to formation of Elliptical) in filamentary structure surrounding group / cluster Shapiro/Bureau et al see such events with SF / CO rich cores in SAURON S0 galaxies - often counter-rotating in stars/gas/both Tidal Interactions / Group-scale Harassment: Low velocity encounters should be common in groups (but lack of IR-bright SBs) Bournard et al., 07 Neither method directly explains lack of star formation in S0s BUT Bulge growth accompanied by SMBH growth: Most low accretion (optical) AGN live in intermediate density environments

32 What we know: Conclusions & Status S0s common in group environment (and not limited to cores): Stripping processes unlikely to be important in majority of cases Late type spiral fraction a strong function of environment: lsps as progenitor requires significant bulge growth Bright Ellipticals prefer cores of groups but otherwise exist in similar fraction for groups/field/clusters Mergers most common at halo centre - consistent with many/ major merger hypothesis for E formation Consistent with hypothesis that most new early types are S0s Likely Mechanisms for S0 formation: Minor Mergers, Tidal Interactions / Group Harassment Fingerprinting the IGM with X-ray and Optically selected groups - see poster by J. Connelly

Morphological Composition of z~0.4 Groups: The site of S0 Formation?

Morphological Composition of z~0.4 Groups: The site of S0 Formation? Dave Wilman Max Planck Institute for Extraterrestrial Physics, Munich Wilman, Oemler, Mulchaey, McGee, Balogh & Bower 2009, ApJ, 692,