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
STACKED STAR FORMATION RATE PROFILES OF BURSTY GALAXIES EXHIBIT ‘COHERENT’ STAR FORMATION
Matt Orr
GalFresca 2017, Pasadena, CA August 25, 2017
TAPIR | California Institute of Technology
Nelson et al. 2016
Low signal-to-noise makes it difficult to say if star formation appears coherent spatially, or is bursty in time.
Stellar Continuum Hα 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.
Stellar Continuum Hα Emission What can we
Nelson et al. 2016
Hα Emission Radius SFR I n d i v i d u a l M a p s Stacked Map
Stacking similar sized/massed galaxies produces ‘high’ signal- to-noise radial SFR profiles…
…at the expense of losing information from individual galaxies.
Nelson et al. 2016
Stacking similar sized/massed galaxies produces ‘high’ signal- to-noise radial SFR profiles…
Hα Emission Radius SFR I n d i v i d u a l M a p s Stacked Map
Where we come in: Simulations FIRE: Feedback In Realistic Environments
Collaboration Site: http://fire.northwestern.edu/
GIZMO/Gadget 2 SPH Code Includes all the feedback we need! Cosmological, 109-1012 M halos Mass resolution ~102-104 M Multiphase ISM —> Consequential Feedback Physics
Halos from: Hopkins et al. 2014, Chan et al. 2015.
Face-on projection (Not FIRE.. NCG 1232) (Maps from: arXiv:1701.01788)
(Maps from: arXiv:1701.01788)
Mock observational maps
(Gas, SFR, Ωdyn)
Pixel sizes 100 pc - 5 kpc
Stack clumpy, ‘incomplete’ maps to make radial profiles
SFR Radius
−10 −5 5 10
x [kpc]
−10 −5 5 10
y [kpc]
Stacked Map −5.6 −4.8 −4.0 −3.2 −2.4 −1.6 −0.8 0.0 2 4 6 8 10 R [kpc] −4 −3 −2 −1 1 log (ΣSFR[M yr1 kpc2]) 2 4 6 8 10 R [kpc] 0.5 1.0 1.5 2.0 2.5 3.0 log (Σ?[M pc2]) −10 −5 5 10
x [kpc]
−10 −5 5 10
y [kpc]
m12v (z ≈ 1.4)
z = 1.42 z = 1.38 z = 1.36
−2.7 −2.4 −2.1 −1.8 −1.5 −1.2 −0.9 −0.6 2 4 6 8 10 R [kpc] −4 −3 −2 −1 1 log (ΣSFR[M yr1 kpc2]) 2 4 6 8 10 R [kpc] 0.5 1.0 1.5 2.0 2.5 3.0 log (Σ?[M pc2])
z = 1.42 z = 1.38 z = 1.36
205 snapshots All M★ ~ 1010 M⊙ SFR Profiles SFR Maps
𝚻★ Profiles
205 snapshots
Nelson et al. 2016
Star formation ‘main sequence’ relates SFR and Stellar Mass. Do stacks of galaxies above/on/below the MS have characteristic differences?
205 snapshots
Nelson et al. 2016
205 snapshots
Nelson et al. 2016
Stacks of galaxies above/below the MS appear to just have uniformly elevated/ depressed SFRs.
Nelson et al. 2016
−4 −3 −2 −1
log(ΣSFR [M yr1 kpc2]) 8.4 < log(M⇤/M) < 9.4 9.6 < log(M⇤/M) < 10.2
Below MS On MS Above MS
5 6 7 8 9
log(Σ⇤ [M kpc2])
2 4 6 8 10
R [kpc]
−11.5 −11.0 −10.5 −10.0 −9.5 −9.0 −8.5
log(ΣSFR/Σ⇤ [yr1])
2 4 6 8 10
R [kpc]
Our z~1 MS - why things look different?
−4 −3 −2 −1
log(ΣSFR [M yr1 kpc2]) 8.4 < log(M⇤/M) < 9.4 9.6 < log(M⇤/M) < 10.2
Below MS On MS Above MS
5 6 7 8 9
log(Σ⇤ [M kpc2])
2 4 6 8 10
R [kpc]
−11.5 −11.0 −10.5 −10.0 −9.5 −9.0 −8.5
log(ΣSFR/Σ⇤ [yr1])
2 4 6 8 10
R [kpc]
Self-consistent MS has large spray to low SFRs
8.5 9.0 9.5 10.0 log M [M] −4 −3 −2 −1 1 2 log ˙ M? [M yr1]
log M [M] log ˙ M? [M yr1]
But still, stacking is ‘hacking’
8.5 9.0 9.5 10.0 log M [M] −4 −3 −2 −1 1 2 log ˙ M? [M yr1]
log M [M] log ˙ M? [M yr1]
−4 −3 −2 −1 log(ΣSFR [M yr1 kpc2]) Below MS On MS Above MS 2 4 6 8 10 R [kpc] −
No real difference between above/on/ below MS galaxy profiles.. only normalization of total SFR
−4 −3 −2 −1 log(ΣSFR [M yr1 kpc2]) Below MS On MS Above MS 2 4 6 8 10 R [kpc] − 2 4 6 8 10 R [kpc] −4 −3 −2 −1 log(ΣSFR [M yr1 kpc2]) m12v Profiles
An individual galaxy exhibits the same behavior in time… crossing the MS often, with messy SFR profiles
Driving this home.. m12v, disk-y now - messy around z~1.
star formation - but masks the incoherent nature of star formation on galactic scales (~kpc scales).
depression relative to the MS) can be explained by very bursty (varying on 10’s of Myrs) star formation (in FIRE)
star formation - but masks the incoherent nature of star formation on galactic scales (~kpc scales).
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