Bulges and Disks: How galaxy structure and star formation changes with environment. Claire Lackner Kavli IPMU, University of Tokyo February 21, 2014

Transcription

1 Bulges and Disks: How galaxy structure and star formation changes with environment Claire Lackner Kavli IPMU, University of Tokyo February 21, 2014

2 Galaxy Environment Low Density High Density Low Mass Star-forming Disk-dominated High Mass Passive Bulge-dominated SDSS SDSS 2

3 Density-Morphology Relation Rise in lenticular galaxies (S0s) suggest they are transition population 3

4 Known Environmental Effects NGC 4402 (HST-NASA/ESA) To Center of Virgo Ram pressure stripping Strangulation: removal of halo gas supply Galaxy harassment: high-speed, close encounters Mergers 4

5 Known Environmental Effects NGC 4402 (HST-NASA/ESA) To Center of Virgo Ram pressure stripping Strangulation: removal of halo gas supply Galaxy harassment: high-speed, close encounters Mergers 5

6 Environmental effects on disks Low Density High Density Disk destruction: Harassment OR Star formation truncation: strangulation, ram pressure stripping 6

7 Questions At fixed stellar mass, is the color-density relation due to changes in color (SF) or morphology (B/T)? Does present day environment determine if an elliptical-like bulge acquires and retains a disk? Where does environment matter? What does environment do? 8

8 Two-Component Galaxies Galaxies with an elliptical-like classical bulge and a disk (including S0s) How does environment affect the disk formation and evolution around these bulges? 9

9 Sample 29,728 SDSS galaxies with bulge+disk fits (Lackner & Gunn, 2012) Volume-limited: Mr and 0.02 < z < 0.05 Galaxies statistically divided into: Ellipticals (13%) S0s (classical bulge and disk) (13%) Classical bulge and disk (28%) Pseudo-bulge and disk (8%) Bulge-less disk galaxies (29%) Unclassifiable (10%) 10

10 Sample 29,728 SDSS galaxies with bulge+disk fits (Lackner & Gunn, 2012) Volume-limited: Mr and 0.02 < z < 0.05 Galaxies statistically divided into: Ellipticals (13%) S0s (classical bulge and disk) (13%) Classical bulge and disk (28%) Pseudo-bulge and disk (8%) Bulge-less disk galaxies (29%) Unclassifiable (10%) galaxies 11

11 Two Kinds of bulges: Classical bulges and Pseudo-bulges Classical bulges are ellipticals that happen to have a prominent disk around them (Renzini, 1999). Elliptical-like bulges Pseudo-bulges form by secular processes in a disk and retain a memory of their disky- origin (Kormendy & Kennicutt, 2004). Disk-like bulges 12

12 Classical and Pseudo-bulges 13

13 Classical and Pseudo-bulges NGC 2775 Sa(r) NGC 4030 Sbc 14

14 Classical Bulges and Pseudo-bulges Galaxies with recent star formation in the center are considered pseudobulges Classical bulges have 4000 Å break strength similar to ellipticals (S0s) Division by Dn(4000) gives ~ flat distributions in disk axis ratios Lackner,

15 Classical Bulge Galaxies S0 Galaxies 17

16 Environment Measures B+D sample matched to FoF group catalog (Berlind+, 2006) Group size varies from galaxies Environment measures: Σ5 = 5/(distance to 5th nearest projected neighbor)2 z-slice set by group velocity dispersion (σ) Ngal = number of bright (Mr -19) galaxies in group tcross = time galaxy takes to cross host group = (distance from group center)/(group σ) 18

17 Environment and Stellar Mass Density-morphology/color relations exist at fixed galaxy stellar mass. Morphologies from Galaxy Zoo project. 19

18 Color-Density for B+D galaxies 21

19 Color-Density for B+D galaxies Lackner, 2013 Trends at fixed bulge mass (large range in disk mass) Total and disk color changes are statistically significant Δ(g-r)disk ~ 0.05 from the lowest to the highest Σ5 22

20 No Morphological Changes Disk-to-total mass ratio and disk scale length are independent of Σ5 At fixed bulge mass the color-density relation is due to change in disk color only Star formation quenching is not associated with morphological changes in disks Lackner,

21 Bulges Changes in bulge color are modeling effects Suppressing central disk flux eliminates Δ(g-r) bulge Functional form of central disk is uncertain 24

22 Bulges Changes in bulge color are modeling effects Suppressing central disk flux eliminates Δ(g-r) bulge Functional form of central disk is uncertain 25

23 HI Gas Content Total HI masses from GASS survey (Catinella+, 2013) 760 galaxies (473 with HI detections) 10 < log M* < < z < ellipticals 195 S0s 170 classical bulge 30 pseudo-bulge 90 bulge-less 45 unclassified 26

24 HI Gas Detected Fraction At fixed total stellar mass, fraction of galaxies with HI detection is lower in more massive halos Sign of HI gas stripping Lackner, in prep 29

25 HI Gas Detected Fraction log Mhalo > 13 log Mhalo < 13 D/T the same for all halo masses. Disk color is redder in high mass halos (at low galaxy mass) 31

26 HI and disk color At fixed disk color, fraction of galaxies with HI detection is lower in more massive halos Suggests rampressure stripping (gas removed first) Molecular gas?? 32

27 Rich and Poor Groups Relation between disk color and Σ5 breaks down in rich(er) groups Star formation quenching occurs in low density environments 33

28 Rich and Poor Groups Gomez+, 2003 Relation between disk color and Σ5 breaks down in rich(er) groups Star formation quenching occurs in low density environments Star formation drops at ~4 virial radii 34

29 Disks in Rich Groups Total color tcross relation is significant; disk color relation is weaker 35

30 Disks in Rich Groups Total color tcross relation is significant; disk color relation is weaker ~2 3σ statistical significance in D/T ratio increase Morphological changes occur in large groups 36

31 Color & Morphology vs. Density Star formation quenching (color change) and morphology changes are distinct quenched disk galaxies Environmental processes which quench SF do not destroy stellar disks strangulation or ram pressure stripping Quenched disk galaxies from SDSS 37

32 Questions (and answers) At fixed stellar mass, is the color-density relation due to changes in color (SF) or morphology (B/T)? Color-density relation driven by changes in disk color, not morphology Does present day environment determine if an elliptical-like bulge acquires and retains a disk? Stellar disks unaffected except in densest regions Where does environment matter? SF quenching happens at group scales What does environment do? Removes neutral gas: ram pressure stripping 38

33 Outlook Increasingly detailed observational data and higher resolution simulations will require multi-component models for galaxies Comparing to high redshift studies of bulges and disks will show how bulges and disks grow with time (and density) Bruce+, 2012; based on WFC3-HST 39