Tidal Disruption Event Host Galaxies

K. Decker French (Hubble Fellow, Carnegie Obs) with: Iair Arcavi, Ann Zabludof, Or Graur Tidal Disruption Event Host Galaxies

• What kinds of galaxies host TDEs?

• What galaxy properties infuence the

TDE rate?

K. Decker French (Hubble Fellow, Carnegie Obs) with: Iair Arcavi, Ann Zabludof, Or Graur What kinds of galaxies host TDEs?

• Only answerable with sample of TDEs • Sample of 8 UV/ optical bright TDEs

from ASASSN, PTF, subtracted) (continuum Pan-Starrs, SDSS

Arcavi+ 2014 Decker French (Carnegie) What kinds of galaxies host TDEs? Arcavi+ 2014

Decker French (Carnegie) Large # of E+A galaxies! What kinds of galaxies host TDEs?

20 Star-forming galaxies 15

5 Early-type galaxies

EW Emission [Å] (Current SFR) 0 α

H −6 −4 −2 0 2 4 6 8 Lick HδA Absorption [Å] (SFR over past Gyr) French+2016 Decker French (Carnegie) What kinds of galaxies host TDEs?

EW Emission [Å] (Current SFR) 0

α Post-starburst/ E+A “spur” H −6 −4 −2 0 2 4 6 8 Lick HδA Absorption [Å] (SFR over past Gyr) French+2016 Decker French (Carnegie) What kinds of galaxies host TDEs?

25 TDE hosts 20

EW Emission [Å] (Current SFR) 0 α

H −6 −4 −2 0 2 4 6 8 Lick HδA Absorption [Å] (SFR over past Gyr) French+2016 Decker French (Carnegie) TDEs Occur at Higher Rates in Post-Starburst Galaxies

100 Myr burst 25 200 Myr burst 3 Gyr decline 0.2% 2.3% SDSS Galaxies 20 Optical TDE hosts Swift J1644 15 33x rate enhancement 190x rate enhancement 10

EW Emission [Å] (Current SFR) 0 α

H −6 −4 −2 0 2 4 6 8 Lick HδA Absorption [Å] (SFR over past Gyr) French+2016 Decker French (Carnegie) TDEs Occur at Higher Rates` in Post-Starburst Galaxies

X-ray TDEs from Auchettl+17a may have lower post-starburst rate enhancement ~20-40x Decker French (Carnegie) (Graur, KDF, et al. 2017; Law-Smith+17) What galaxy properties infuence the TDE rate? Why is the TDE Rate High in Post-Starburst Galaxies?

Why do the pc-scale stellar dynamics care about the kpc-scale star formation history?

Decker French (Carnegie) What galaxy properties infuence the TDE rate? Why is the TDE Rate High in Post-Starburst Galaxies?

Most post-starburst galaxies appear to have had a recent major merger Yang+2008: ubiquitous tidal features Decker French (Carnegie) What galaxy properties infuence the TDE rate? Why is the TDE Rate High in Post-Starburst Galaxies?

Most post-starburst galaxies have concentrated young stellar populations Yang+2008

Decker French (Carnegie) What galaxy properties infuence the TDE rate? Why is the TDE Rate High in Post-Starburst Galaxies?

Merger -> starburst: • Central concentration of stars? (Stone+16 Law-Smith+17, Graur+17) • Unusual central dynamics: • Eccentric disk? (Madigan+17) Radial anisotropies? (Stone+17) • SMBH binary? (e.g., Chen+09,11; Li+15) • Related to circumnuclear gas? (Kennedy+16)

Decker French (Carnegie) What galaxy properties infuence the TDE rate?

Central concentration of stars?

TDE rate ~ 1e-3/yr

Stone & Van Velzen 2016 (see later talk!) Decker French (Carnegie) What galaxy properties infuence the TDE rate?

Central concentration of stars?

Stellar Surface Density Graur, KDF, et al. 2017

Decker French (Carnegie) What galaxy properties infuence the TDE rate?

Central concentration of stars?

Law-Smith+ 2017

Decker French (Carnegie) (see later talk!) What galaxy properties infuence the TDE rate?

100 Myr burst 25 200 Myr burst 3 Gyr decline 0.2% 2.3% SDSS Galaxies 20 Optical TDE hosts Swift J1644 15 33x rate enhancement 190x rate enhancement 10

EW Emission [Å] (Current SFR) 0 α Weaker starburst H −6 −4 −2 0 2 4 6 8 LickOlder HδA Absorpost-starburstption [Å] (SFR over past Gyr) French+2016 Decker French (Carnegie)Longer duration starburst What galaxy properties infuence the TDE rate? Highest mass of stars evolving off Main Sequence (MO • ) 10.0 5.0 4.0 3.0 2.5 2.3 2.2 1.000

0.100

0.010 Burst Mass Fraction

0.001 a −1.0 −0.5 0.0 0.5 1.0 1.5 Age Since Starburst Ended (Gyr) French+2017 •0.5-10% of current stellar mass from burst for most •Most (6/8) have short (<200 Myr) starbursts •(not long >1 Gyr decline) •Post-burst ages range from ~1 Gyr (except for one star-forming galaxy) Decker French (Carnegie) What galaxy properties infuence the TDE rate?

Li+2017 •SMBH binaries can substantially increase TDE rate for a short time (e.g., Chen+09,11; Li+15) •Expect SMBH after merger

Decker French (Carnegie) What galaxy properties infuence the TDE rate? Highest mass ratio merger with time to coalesce 12:1 20:1 33:1 1.000

0.100

0.010 Burst Mass Fraction

0.001 b 0.0 0.5 1.0 1.5 Age Since Starburst Began (Gyr) French+2017 •SMBH binary? •Only most equal-mass mergers have had time to coalesce •Timescales too short for SMBHB enhancement (Stone+17)

Decker French (Carnegie) What galaxy properties infuence the TDE rate? BPT WHAN 1.5 2.5 Seyfert SDSS Quiescent Balmer−strong Seyfert TDE Hosts (data before TDE) 2.0 TDE Hosts (data after TDE) 1.0 4681) λ

β 1.5 0.5 [Å] α

H 1.0 Star−Forming 5007)/(H λ 0.0 Star−Forming LINER−like LINER log W 0.5

0.0 −0.5 SDSS log([O III] Quiescent Balmer−strong TDE Hosts (data before TDE) TDE Hosts (data after TDE) −0.5 −1.0 −2.0 −1.5 −1.0 −0.5 0.0 0.5 1.0 −2.0 −1.5 −1.0 −0.5 0.0 0.5 1.0 log([N II] λ 6583)/(Hα λ 6563) log([N II] λ 6583)/(Hα λ 6563) •Circumnuclear gas? Kennedy+16: Can increase TDE rate by ~10x (not enough) •But, what is the relation between TDEs and LINER-like emission from hosts? Decker French (U. Arizona) French+2017 What galaxy properties infuence the TDE rate? Why is the TDE Rate High in Post-Starburst Galaxies?

•Central concentration of stars? (Stone+16 Law-Smith+17, Graur+17) Possible in at least one case (pc scale), hints at kpc-scale over densities •Unusual central dynamics: Eccentric disk? (Madigan+17) Radial

anisotropies? (Stone+17) Possible, evidence from timing after starburst (see talks by Stone & Madigan) •SMBH binary? (e.g., Chen+09,11; Li+15) Unlikely, if TDE rate scales weakly with SMBH mass ratio •Related to circumnuclear gas? (Kennedy+16) Not enough to explain TDE rate in PSBs, other connections unknown Decker French (Carnegie) What galaxy properties infuence the TDE rate?

12 •Any of these Engel+2011 Av mechanisms would Arp 220 10 Extinction map also increase TDE 8 rate in starburst 6 galaxies •But, heavy 4 extinction 2

Decker French (Carnegie) What galaxy properties infuence the TDE rate?

•Any of these mechanisms would also increase TDE rate in starburst galaxies •But, heavy extinction •Nonetheless, one TDE candidate in ULIRG discovered (Tadhunter+17) •Implies rate ~0.01-0.1/yr

Decker French (Carnegie) Conclusions

• TDEs occur at a high rate in post-starburst galaxies

• Central stellar concentration and/or dynamics likely

infuence the TDE rate

• Future surveys will enable better analysis of host

galaxies of full TDE population

Decker French (Carnegie)