STACKED STAR FORMATION RATE PROFILES OF BURSTY GALAXIES EXHIBIT - PowerPoint PPT Presentation

STACKED STAR FORMATION RATE PROFILES OF BURSTY GALAXIES EXHIBIT ‘COHERENT’ STAR FORMATION GalFresca 2017, Pasadena, CA August 25, 2017 Matt Orr Dr. Philip F. Hopkins TAPIR | California Institute of Technology

At high z (~1), observations are difficult. Stellar Continuum H α Emission Nelson et al. 2016 Low signal-to-noise makes it difficult to say if star formation appears coherent spatially, or is bursty in time.

At high z (~1), observations are difficult. Stellar Continuum H α Emission What can we do about it? Nelson et al. 2016 Low signal-to-noise makes it difficult to say if star formation appears coherent spatially, or is bursty in time.

Observers stack galaxies. H α Emission SFR Radius I n d i v i d u a l M a p s Stacking similar sized/massed galaxies produces ‘high’ signal- Stacked Map to-noise radial SFR profiles… Nelson et al. 2016

Observers stack galaxies. H α Emission SFR Radius I n d i v i d u a l M a p s Stacking similar sized/massed galaxies produces ‘high’ signal- Stacked Map to-noise radial SFR profiles… Nelson et al. 2016 …at the expense of losing information from individual galaxies.

Where we come in: Simulations FIRE: Feedback In Realistic Environments GIZMO/Gadget 2 SPH Code Includes all the feedback we need! Cosmological, 10 9 -10 12 M � halos Mass resolution ~10 2 -10 4 M � Multiphase ISM —> Consequential Feedback Physics Collaboration Site: http://fire.northwestern.edu/

(Maps from: arXiv:1701.01788) We have Galaxy Maps! Face-on projection Halos from: (Not FIRE.. NCG 1232) Hopkins et al. 2014, Chan et al. 2015. M. Orr

(Maps from: arXiv:1701.01788) We have Galaxy Maps! Pixel sizes 100 pc - 5 kpc Mock observational maps of various quantities (Gas, SFR, Ω dyn ) M. Orr

We can stack them too! Stack clumpy, ‘incomplete’ maps to make radial SFR profiles Radius M. Orr

How does the FIRE look? − 0 . 6 1 3 . 0 SFR Maps 10 z = 1 . 42 z = 1 . 42 − 0 . 9 z = 1 . 38 log ( Σ SFR [M � yr � 1 kpc � 2 ]) z = 1 . 38 0 2 . 5 z = 1 . 36 z = 1 . 36 − 1 . 2 log ( Σ ? [M � pc � 2 ]) 5 m12v ( z ≈ 1 . 4 ) − 1 2 . 0 y [kpc] − 1 . 5 0 − 1 . 8 − 2 1 . 5 − 5 − 2 . 1 − 3 1 . 0 − 2 . 4 − 10 − 2 . 7 − 4 0 . 5 − 10 − 5 0 5 10 0 2 4 6 8 10 0 2 4 6 8 10 SFR Profiles 𝚻 ★ Profiles x [kpc] R [kpc] R [kpc] 0 . 0 1 3 . 0 205 snapshots 10 − 0 . 8 log ( Σ SFR [M � yr � 1 kpc � 2 ]) 0 2 . 5 5 − 1 . 6 log ( Σ ? [M � pc � 2 ]) Stacked Map − 1 2 . 0 y [kpc] − 2 . 4 0 − 3 . 2 − 2 1 . 5 − 5 − 4 . 0 − 3 1 . 0 − 4 . 8 − 10 − 5 . 6 − 4 0 . 5 − 10 − 5 0 5 10 0 2 4 6 8 10 0 2 4 6 8 10 x [kpc] R [kpc] R [kpc] All M ★ ~ 10 10 M ⊙ M. Orr

Stacks and the main sequence Star formation ‘main sequence’ relates SFR and Stellar Mass. Do stacks of galaxies 205 snapshots above/on/below the MS have characteristic differences? Nelson et al. 2016

Stacks and the main sequence 205 snapshots Nelson et al. 2016

Stacks and the main sequence 205 snapshots Stacks of galaxies above/below the MS appear to just Nelson et al. 2016 have uniformly elevated/ depressed SFRs.

Stacks, the main sequence, and FIRE 8 . 4 < log( M ⇤ /M � ) < 9 . 4 9 . 6 < log( M ⇤ /M � ) < 10 . 2 log( Σ SFR [M � yr � 1 kpc � 2 ]) Below MS 0 On MS − 1 Above MS − 2 − 3 − 4 9 log( Σ ⇤ [M � kpc � 2 ]) 8 7 6 5 − 8 . 5 log( Σ SFR / Σ ⇤ [yr � 1 ]) − 9 . 0 − 9 . 5 − 10 . 0 − 10 . 5 − 11 . 0 − 11 . 5 0 2 4 6 8 10 0 2 4 6 8 10 R [kpc] R [kpc] Nelson et al. 2016

Our z~1 MS - why things look different? 8 . 4 < log( M ⇤ /M � ) < 9 . 4 9 . 6 < log( M ⇤ /M � ) < 10 . 2 log( Σ SFR [M � yr � 1 kpc � 2 ]) Below MS 0 On MS − 1 Above MS 2 − 2 − 3 1 − 4 M ? [M � yr � 1 ] 9 0 log( Σ ⇤ [M � kpc � 2 ]) M ? [M � yr � 1 ] 8 Self-consistent MS − 1 7 has large spray to log ˙ 6 log ˙ − 2 5 low SFRs − 8 . 5 log( Σ SFR / Σ ⇤ [yr � 1 ]) − 3 − 9 . 0 − 9 . 5 − 10 . 0 − 4 8 . 5 9 . 0 9 . 5 10 . 0 − 10 . 5 log M [M � ] log M [M � ] − 11 . 0 − 11 . 5 0 2 4 6 8 10 0 2 4 6 8 10 R [kpc] R [kpc] M. Orr

But still, stacking is ‘hacking’ 2 Below MS 0 1 log( Σ SFR [M � yr � 1 kpc � 2 ]) On MS M ? [M � yr � 1 ] Above MS 0 − 1 M ? [M � yr � 1 ] − 1 − 2 log ˙ log ˙ No real difference − 2 − 3 between above/on/ − 3 below MS galaxy − 4 − profiles.. only − 4 0 2 4 6 8 10 8 . 5 9 . 0 9 . 5 10 . 0 log M [M � ] log M [M � ] R [kpc] normalization of total SFR M. Orr

An individual galaxy exhibits the same behavior in time… crossing the MS often, with messy SFR profiles Below MS m12v Profiles 0 0 log( Σ SFR [M � yr � 1 kpc � 2 ]) log( Σ SFR [M � yr � 1 kpc � 2 ]) On MS Above MS − 1 − 1 − 2 − 2 − 3 − 3 − 4 − 4 − 0 2 4 6 8 10 0 2 4 6 8 10 R [kpc] R [kpc] M. Orr

Driving this home.. m12v, disk-y now - messy around z~1. M. Orr

Summary: Caution while Stacking! • Stacking recovers a time-averaged spatial coherence of star formation - but masks the incoherent nature of star formation on galactic scales (~kpc scales). • Spatially coherent star formation (+ elevation/ depression relative to the MS) can be explained by very bursty (varying on 10’s of Myrs) star formation (in FIRE) M. Orr

Summary: Caution while Stacking! • Stacking recovers a time-averaged spatial coherence of star formation - but masks the incoherent nature of star formation on galactic scales (~kpc scales). • Spatially coherent star formation (+ elevation/ depression relative to the MS) can be explained by very bursty (varying on 10’s of Myrs) star formation (in FIRE) Observers: take care when interpreting stacked observations… you may be glossing over the physical conditions in the galaxies M. Orr

What a week! THANKS FOR LISTENING