The Swift GRB Host Galaxy Legacy Survey

Transcription

1 The Swift GRB Host Galaxy Legacy Survey (Caltech) + the SHOALS collaboration: Antonio de Ugarte Postigo (IAA) Steve Schulze (PUC) Thomas Kruehler (ESO) Tanmoy Laskar (Harvard) Antonino Cucchiara (GSFC) Ranga Chary (Caltech) Jens Hjorth (DARK) Nial Tanvir (Leicester) Javier Gorosabel (IAA) Andrew Levan (Warwick) and many others

2 GRB Hosts as a Cosmological Tool A large sample of GRB redshifts and host properties can constrain... The History of Cosmic Star-Formation (out to very high redshift) The Sites of Stellar Mass Assembly (including the faintest galaxies) Connections between the ISM and Stellar Population (dust, metallicity, kinematics vs. mass, SFR, etc.) The Nature of the GRB Progenitor (formation conditions; single star vs. binary-channel) 2

3 SHOALS : A large, deep, unbiased multiwavelength survey to include all host galaxies of all types at all redshifts. Selection criteria: Occurred between Swift detected; gamma-ray fluence > 10-6 erg/cm2 Swift slewed immediately to the position Far from the Sun at time of explosion (afterglow easily observable) Low Milky Way foreground extinction No nearby bright stars Localized within 2 (Similar procedure to VLT R/K-band host survey; Hjorth+2012) 120 Swift GRBs (out of ~950 to date), 75% with predetermined redshift (usually from afterglow.) (Currently 90% after host galaxy observations.) range 0.03 < z < 6.3 3

4 SHOALS Selection Criteria Swift Host Galaxy Legacy Survey (PI ) Swift detected; gamma-ray fluence > 10-6 erg/cm2 Swift slewed immediately to the position Well-observed or at least well-observable: (a) Autonomously triggered a 2m-class telescope, or (b) >5 hours from Sun and between , or (c) Satisfied TOUGH positional criteria Low Milky Way foreground extinction No nearby bright foreground stars Localized within 2 All Swift bursts Jakobsson+2006 SHOALS TOUGH sample BAT6 sample Total w/redshift completeness % % %* 58 84% 53 91% *before any additional host follow-up 4

5 Spitzer (3.6 μm imaging): Good stellar mass proxy (even with no color information); Sensitive to 1010 M galaxies to z~5 All targets observed to deep limits (1-6 hours/target at z>1) VLA (3 GHz continuum): Dust-unbiased SFRs 90 hours to observe 32 targets (from overlapping TOUGH survey) Keck, Gemini, VLT, GTC Optical/NIR imaging for full SED modeling (age, extinction, improved stellar masses) Spectroscopy to complete redshift distribution Numerous programs ongoing 5

6 Spitzer (3.6 μm imaging): Good stellar mass proxy (even with no color information); Sensitive to 1010 M galaxies to z~5 230-hour large program to observe all SHOALS targets (+ some others of interest) PI D. Perley Keck, Gemini, VLT, GTC Spectroscopy to complete redshift distribution, measure metallicities of some galaxies Multicolor optical/nir imaging for full SED modeling (age, extinction, improved stellar masses) Ongoing, worldwide campaign 6

7 130 GRB Host Galaxies from Spitzer 7

8 130 GRB Host Galaxies from Spitzer 8

9 GRB host NIR luminosities to z~6 9

10 GRB host stellar masses to z~ Mo 109 Mo stellar mass 1011 Mo 108 Mo 10

11 GRB host stellar masses to z~6 Milky Way 1010 Mo LMC 109 Mo SMC 108 Mo stellar mass 1011 Mo 11

12 GRB host stellar masses to z~6 Milky Way LMC SMC 12

13 GRB host stellar masses to z~6 100% complete above m<23.2 Milky Way LMC SMC 13

14 GRB host stellar masses to z~6 97% complete above m<24.4 Milky Way LMC SMC 14

15 GRB host stellar masses to z~6 90% complete to full survey depth 70% of targets are detected; all but a few nondetections have strict upper limits Milky Way LMC SMC 15

16 GRB host stellar masses to z~6 Milky Way LMC SMC 16

17 GRB host redshift evolution Milky Way Median GRB host mass ~7x109 at z=1-4 LMC but less than 109 at z<0.5! SMC cosmic downsizing, but on steroids to be continued... 17

18 GRB host redshift evolution Stellar mass (M ) z = z = z = z = z = z = z = z > 5.0 (includes upper limits) at λ = 3.6/(1+z) 18

19 GRB hosts vs. SFR-selected galaxies Milky Way median mass for GRB hosts LMC SMC 19

20 GRB hosts vs. SFR-selected galaxies Milky Way median mass for GRB hosts LMC Grey points: GOODS-N galaxies from Kajisawa+2011 SMC 20

21 GRB hosts vs. SFR-selected galaxies Milky Way median SFR-weighted mass for galaxies median mass for GRB hosts LMC Grey points: GOODS-N galaxies from Kajisawa+2011 SMC 21

22 GRB hosts vs. SFR-selected galaxies Milky Way median SFR-weighted mass for galaxies ey v r u s d fiel LMC mit i l ss e n te e l p m o c SMC 22

23 GRB hosts vs. SFR-selected galaxies median SFR-weighted mass for m<24.25 galaxies MW LMC mit i l ss e n median mass for te e l p m<24.25 hosts m o yc e v ur s d fiel SMC 23

24 GRB hosts vs. SFR-selected galaxies Median luminosities consistent at z>2 MW ey v r u s d fiel LMC mit i l ss e n te e l p m o c SMC 24

25 GRB hosts vs. SFR-selected galaxies MW Galaxy cosmic downsizing ey v r u s d fiel LMC mit i l ss e n te e l p m o c GRB cosmic downsizing SMC 25

26 GRB hosts vs. SFR-selected galaxies GRBs almost totally absent in M > 1010 galaxies since z~1 ( but not at z~2 or z~3) MW ey v r u s d fiel LMC mit i l ss e n te e l p m o c SMC 26

27 Luminosity Distribution vs. Galaxies z = z = z = z = z = z = z > 5.0 SF Rwe igh ted ts hos GR B ga lax ies z <

28 Luminosity Distribution vs. Galaxies z = GR B hos ts z < 0.5 SF R (lum -wei ino ghte s ity d g cut alax off) ies x1010 z = z = z = z = z = z >

29 Sharp Metallicity Cutoff? z~0.1 z~0.3 KK04 scale z~1.6 z~2 z~0.8 z~3 z~1.2 (interpolated) Zahid et al Kewley et al Erb et al Maiolino et al. 2008,

30 Sharp Metallicity Cutoff? x KK04 scale z~0.8 z~1.2 (interpolated) z~ Zahid et al

31 Sharp Metallicity Cutoff? x KK04 scale z~0.8 z~1.2 (interpolated) z~ Zahid et al

32 Sharp Metallicity Cutoff? x1010 z~ z~0.3 KK04 scale z~1.6 z~2 z~0.8 z~3 z~1.2 (interpolated) Zahid et al Kewley et al Erb et al Maiolino et al. 2008,

33 GRB hosts vs. SFR-selected galaxies MW median mass for GRB hosts LMC SMC 33

34 GRB hosts vs. SFR-selected galaxies Stifled due to metal buildup in massive galaxies MW median mass for GRB hosts LMC ~ M galaxies dominate cosmic SFR at every epoch from 1 < z < 6 SMC But probably not at z>6; Tanvir et al

35 Stellar mass and dust obscuration MW LMC SMC 35

36 Stellar mass and dust obscuration red: dark or dusty bursts MW LMC SMC 36

37 Stellar mass and dust obscuration High-mass galaxies are usually dusty 13/18 heavily obscured MW LMC Low-mass galaxies are rarely dusty 3/32 heavily obscured SMC 37

38 Conclusions GRBs probe typical star-forming galaxies at high redshift (z>1.5) Median host mass is ~6 109 M, intermediate between LMC and MW. Host mass distribution agrees with SFR-weighted galaxy population; weak dependence on environment at these redshifts. Very little evolution in host mass distribution between 1.5 < z < 5. No large, unseen population of low-mass galaxies. Deep mass-selected surveys see most cosmic SFR out to z~6. GRB host properties significantly diverge from cosmic SFR at z<1 They strongly avoid high-mass galaxies ( cosmic downsizing on steroids ) Suggests strong suppression above ~ Z. Possible additional dependencies (ssfr?) GRBs provide novel constraints on high-z dust. Low-mass galaxies contain very little dust and are optically thin; high-mass galaxies have lots of dust with high covering fraction. No strong connection between dust and galaxy properties outside Local Group. GRBs support a significant (but non-dominant) contribution to cosmic SFR from ULIRGs at z>1. 38

39 39

40 Dust and Selection Bias See if adding enough of these events makes a difference! ~20% of GRBs are systematically missing from optical afterglow searches as a result of dust. Av ~ 1 mag underrepresented Observed Av distribution Av ~ 5 mag missing completely (optically bright events) (Compiled from data in Kann et al & 2010, Cenko et al. 2009, Perley et al. 2009, Greiner et al. 2011) 40

41 Different Host Morphologies GRBs SNe 41

42 Lower Host Metallicities Metallicity Core-collapse supernova hosts (z<0.5): Type II Type Ic/bl GRB hosts Graham & Fruchter 2013 (Levesque+2010, Modjaz+2008) Luminosity 42

43 Lower Host Metallicities Core-collapse supernova hosts (z<0.5): Type II Type Ic/bl GRB hosts Metallicity GRBs rare (~1 per 106 SN) ~0.7 Z GRBs common (~1 per 105 SN) Graham & Fruchter 2013 (Levesque+2010, Modjaz+2008) Luminosity 43