The interplay between star formation and galaxy structure. Sara Ellison University of Victoria

Transcription

1 The interplay between star formation and galaxy structure. Sara Ellison University of Victoria

2 The interplay between star formation and galaxy structure. Sara Ellison University of Victoria

3 The structural main sequence Wuyts et al. (2011) A reflection of the Hubble sequence: star forming galaxies are disk dominated, quiescent galaxies are (n=4) bulge dominated.

4 Galaxies with the highest local SFRs: ULIRGs Merger driven star formation

5 Mergers also implicated at low masses: See also the Tiny Titans survey (Stierwalt et al 2014) Lelli, Verheijen & Fraternali (2014)

6 Merger driven star formation: Theoretical prediction: Torrey et al. (2012) See also Mihos & Hernquist (1994); Barnes & Hernquist (1996); Perez et al. (2006); Robertson et al. (2006); Di Matteo et al. (2008); Cox et al. (2008); Lotz et al. (2010); Renaud et al. (2014); Bournaud et al. (2011) and many others.

7 Observational confirmation: Scudder et al. (2012) Δ SFR = log (SFR pair /<SFR> control ) Elevated SFRs in mergers seen in many studies, e.g. Barton et al. (2000); Woods & Geller (2007); Nikolic et al. (2004); Lambas et al. (2003); Knapen & James (2009); Scott & Kaviraj (2014); Ellison et al. (2008) and many others.

8 Extending observational pairs samples to wide separations. Enhanced SFRs out to 150 kpc: Patton et al. (2013) 2/3 of merger-induced star formation occurs at r p > 30 kpc

9 Where does the triggered star formation happen? Detailed CALIFA IFU study of The Mice Wild et al. (2014)

10 Where does the triggered star formation happen? Δ SFR = log (SFR pair /<SFR> control ) Coarse resolution, but good statistics with SDSS inside/ outside fibre. Ellison et al. (2013)

11 75 binary major merger simulations with varying orbits. Δ SFR = log (SFR pair /<SFR> control ) Moreno et al. (in prep) On average: 1) Both galaxies, in any orbit, show SFR enhancement in central regions, with a declining enhancement at larger radii. 2) less massive galaxy shows lower SFR in outer disk than isolated galaxy in all orbits. 3) Trends are most exagerated for aligned orbits.

12 Shorter depletion times in mergers (but beware X CO ). However, elevated starburst lifetimes are short, so gas consumption may be modest. Renaud et al. (2014) Saintonge et al. (2012) See also Daddi et al. (2010), Genzel et al. (2010).

13 Is gas consumed during merger leading to quenching? No gas consumption in pre-merger phase, and high HI gas fractions in (early) post-merger phase. See also Braine & Combes (1993); Bettoni et al. (2001); Casasola et al. (2004); Huchtmeier et al. (2008); Stark et al. (2013); Fertig et al. (submitted) Ellison et al. (submitted)

14 The merger-bar connection: bars created by interactions (e.g. Elmegreen et al. 1990; Lang et al. 2014; Athanassoula 2002) Large scale bars may be destroyed in mergers (funneling mechanism on a smaller scale?), see also Mendez-Hernandez et al (2011), Lee et al. (2012); Skibba et al. (2012). Casteels et al. (2013)

15 Bar triggered star formation: theoretical predictions Star formation happens all along bar, but becomes increasingly centralized with time Martel et al. (2013) See also Schlosman et al. 1989; Combes & Gerin 1985; Friedli et al. 1993, 1994, 1995; Combes & Elmegreen 1993; Athanasoula et al. 1992; Regan & Teuben 2004 and many others.

16 Bar triggered star formation: observational confirmation 60% enhancement Ellison et al. (2011) See also Hummel et al. (1990); Martin (1995); Huang et al. (1996), Jogee et al. (2005), Menendez-Delmestre (2007), Martinet & Friedli (2007), James et al. (2009), Wang et al. (2012) and many others.

17 Wang et al. (2012) When bar ellipticity is higher, SF is more centrally concentrated (relative to unbarred control). Bulge fraction may also play a role (e.g. Athanassoula et al 1992; Gadotti 2011)? Low central SF in galaxies with smaller bulge fractions.

18 Evidence about mode of star formation from studies of the gas. Fisher et al. (2013) Bars fuel centralized gas build-up, which feeds star formation and can increase SFE. See also Sandstrom et al. (in prep), Saintonge et al. (2012) and NUGA results, e.g. Garcia-Burillo et al. (2009)

19 Evidence about mode of star formation from studies of the gas. Sandstrom et al. (in prep) Saintonge et al. (2012) Also implicated by gas deficiency in some barred galaxies (Sheth et al. 2005; Walter et al. 2008). Bars are long-lived, so higher depletion times might actually indicate a quenching pathway.

20 Bars may also quench? At fixed stellar mass, there are elevated bar fractions for the most concentrated and least concentrated SFRs. Wang et al. (2012) See also Hoyle et al. (2011), Masters et al. (2012), Cheung et al. (2013)

21 Bar (pseudo) bulge connection: Pseudo-bulges more common in barred galaxies: bars build (or rejuvenate) bulges? See also Coelho & Gadotti (2011); Fisher et al. (2013)

22 Although most star-forming galaxies are disk-dominated, starbursts have dominant bulge component. Wuyts et al. (2011)

23 Also evidence that the bulge is ultimately linked to cessation of star formation. ssfr log M* (Pure) disk star formation efficiency is invariant? Main sequence slope is due to increasing bulge fraction with M*? Abramson et al. (2014)

24 Quenching associated with bulges? E.g. Fisher (2006); Lackner & Gunn (2012); Cheung et al. (2012); Barro et al. (2013); Bluck et al. (2014), Lang et al. (2014); Woo et al. (2014), Lagos et al. (2014). Mendel et al. (2013) Fang et al. (2013) Other works suggest that quenching is more sensitive to environment, halo mass, or other parameters (many of which are inter-related).

25 What parameters drive quenching? Better predictor of passivity Passivity best predicted by quantities that trace the BH and bulge masses. Passivity NOT strongly linked to halo, disk or environment. Teimoorinia et al. (in prep), Bluck et al. (2014)

26 Death is not forever! Salim et al Movement from blue cloud to red sequence is not necessarily a oneway trip! See also Gil de Paz et al. 2005; Cortese & Hughes (2009); Thilker et al. (2010); Fang et al. (2012).

27 Death is not forever! 25% 20% 55% Salim et al. 2012

28 How is the (low z) SFR modulated by galaxy structures? Some conclusions Main sequence dominated by disks. Pure disks appear to have constant star formation efficiency. Mergers/interactions can elevate SFR. No evidence of quenching or gas consumption (at least a few 100 Myr post-merger). Interactions can both trigger and destroy bars. Bars can elevate SFR. Possible evidence of quenching in some barred galaxies due to gas consumption (short t dep and long lived bars) Bars can build bulges (but are not essential) and grow stellar mass Bulges are implicated in both the presence of starbursts, and the mechanism for cessation of SF. Mass build-up followed by quenching? Galaxies might (at least temporarily) return from the dead.

29 What is the spatial distribution of triggered star formation in, for example, mergers and bars? Is the disk largely unaffected? What drives the variations in these enhancements? Gas fractions, mass, internal structure? Do short(er) depletion times in mergers/bars actually lead to gas exhaustion? Different timescales important. Why is the bulge implicated in galaxy quenching? How does the functionality of these mechanisms evolve with redshift? If you want to truly understand star formation, you have to look at the gas. Large IFU surveys are set to be transformative. Further revolution awaits us in the ALMA and SKA era.