Measuring the evolution of the star formation rate efficiency of neutral atomic hydrogen gas from z ~1– 4
Marc RafelskiGalactic Scale Star Formation
August 2012
Collaborators: Harry Teplitz
Arthur WolfeHsiao-Wen ChenXavier ProchaskaUV UDF team
/ 30Heidelberg 2012: Marc Rafelski
• Definition of Damped Lyα System (DLA): N(HI)≥ 2×1020 cm-2
• Distinguishing characteristics of DLAs : (1) Gas is Neutral (2) Metallicity is low: [M/H]=-1.3 (more on this later) (3) Molecular fraction is low: fH2~10-5
• DLAs dominate the neutral-gas content of the Universe out to z~4.5• DLAs cover 1/3 of the sky at z=[2.5,3.5]
2Wolfe et al. 2005
Damped Lyman Alpha Systems (DLAs)
Observed Wavelength (Å)
Rel
ativ
e Fl
ux
Rest Wavelength (Å)
/ 30Heidelberg 2012: Marc Rafelski 3
Kennicutt-Schmidt (KS) Relation
The Star Formation Rate (SFR) surface density goes as the total
gas surface density to a power law
Normal Disks
Star Forming
Kennicutt, 1998
β = 1.4± 0.15
Can rewrite it with column density N:
Nc=1.25×1020 cm−2
K= 2.5×10−4M⊙ yr−1 kpc−2
ΣSFR = K × (N/Nc)β
/ 30Heidelberg 2012: Marc Rafelski 4
Bigiel et al. 2010a
Tightly Correlated HI and FUV emission in M83
Blue: FUV map (GALEX)
Red: HI contours (THINGS)
Arc Minutes
Arc
Min
utes
/ 30Heidelberg 2012: Marc Rafelski
Col
umn
Den
sity
(N
) [c
m-2]
32 30 28 26 24Surface Brightness [AB mag/arcsec2]
1020
1021
1022
1023
Obs
erve
d Co
lum
n De
nsity
(N) [
cm2 ] z = 2.5
z = 3.0z = 3.5
Surface Brightness [mag arcsec-2]
5
Can we see DLAs in emission at z~3?• Gas Density ↔ SFR (KS)
• SFR ↔ FUV Lν
(Madau Kennicutt Calibration)
Only high resolution image sensitive enough is the Hubble Ultra Deep Field (UDF)
• Most DLAs:N ~ 2x1020 →3x1021 cm-2 Navg ~ 1x1021 cm-2
At z=3 1500 Å → 6000 Å- This puts it in the visible!
• Lν/area↔ Surface Brightness
/ 30Heidelberg 2012: Marc Rafelski 6
Cumulative comoving SFR density for DLAs
Wolfe & Chen 2006
(A proxy for NHI via the KS relation)
ΣSFR(N) = K(N/Nc)β
38 36 34 32 30 28 26Surface Brightness (µV) [mag arcsec 2]
5
4
3
2
1
log
*˙ (
µV)
[M �• y
r1 Mpc
3 ]
z = 3K=Kkenn
K=0.1 × Kkenn
K=0.01 × Kkenn
38 36 34 32 30 28 26Surface Brightness (µV) [mag arcsec 2]
5
4
3
2
1
log
*˙ (
µV)
[M �• y
r1 Mpc
3 ]
z = 3K=Kkenn
K=0.1 × Kkenn
K=0.01 × Kkenn
10% K
1% K
Cum
ulat
ive
com
ovin
g SF
R d
ensi
ty
Surface Brightness [mag arcsec-2]
/ 30Heidelberg 2012: Marc Rafelski 7
Wolfe & Chen 2006 result:• SFR efficiency of DLAs is a factor of ≥10 below KS relation
Another possibility:• Lyman Break galaxy cores may be embedded in DLAs, and may themselves exhibit in situ star formation
Caveat:• Wolfe & Chen 2006 search excluded objects with high surface-brightness cores (µV < 26.6 mag/arcsec2) (i.e. LBGS)
/ 30Heidelberg 2012: Marc Rafelski 8
LBGs embedded in DLA Neutral Gas Reservoirs
DLA
LBG
Dust
/ 30Heidelberg 2012: Marc Rafelski 9
In situ star formation in DLAs associated with LBGs
DLA
LBG
Dust
In-situ star formation
/ 30Heidelberg 2012: Marc Rafelski
Solution: Ultra Deep u’-band image of UDF with Keck
Keck Telescopes
1 σ depth = 30.7 mag/arcsec2
Detection limit =27.6 mag/arcsec2
FWHM = 1.3 arcsec
10
Rafelski et al. 2009
Use the u-band image to select 407 z~3 LBGS via their flux
decrement from the Lyman break
/ 30Heidelberg 2012: Marc Rafelski 11
48 compact, symmetric, and isolated z~3 LBGs in V-band
Rafelski et al. 2011
/ 30Heidelberg 2012: Marc Rafelski
Stack 48 isolated, compact, symmetric z~3 LBGs in the V-band (rest-frame FUV)
12Rafelski et al. 2011
/ 30Heidelberg 2012: Marc Rafelski
0.0 0.2 0.4 0.6 0.8 1.0 1.2Radius [arcsec]
34
32
30
28
26
24
22
Surfa
ce B
right
ness
(µV)
[mag
arc
sec
2 ]
4
3
2
1
0
Log
SFR [M
�• y
r1 kpc
2 ]
0 2 4 6 8Radius [kpc]
Median LBGsPSF
1 image sky limit48 image stack sky limit
13
Radial surface brightness profile of stacked image
Inner core OutskirtsSu
rfac
e Br
ight
ness
[m
ag a
rcse
c-2]
Radius [arcsec]Rafelski et al. 2011
/ 30Heidelberg 2012: Marc Rafelski 14
Previously:
Column density of gas varies with radius, we need a differential version of the comoving SFR density(ρ̇∗)
Goal: compare comoving SFR density in outskirts of LBGs to DLAs to obtain a SFR efficiency
Differential:
∆ρ̇∗∆N
= �ΣSFR(N)�H0
cf(N,X) ⇒ ∆ρ̇∗
∆I
/ 30Heidelberg 2012: Marc Rafelski 15
15 16 17 18 19log *˙ /< I 0
obs > [M �• yr 1 Mpc 3 / ergs cm 2 sec 1 Hz 1]
34
32
30
28
26
24Su
rface
Brig
htne
ss (µ
V) [m
ag a
rcse
c2 ]
K=0.01 × Kkenn
K=0.02 × Kkenn
K=0.05 × Kkenn
K=0.1 × Kkenn
K=Kkenn
Model differential comoving SFR density for DLAs
Differential comoving SFR density per intensity interval
Surf
ace
Brig
htne
ss [
mag
arc
sec-2
]
Rafelski et al. 2011
/ 30Heidelberg 2012: Marc Rafelski 16
Determine efficiency for each point
Comparison of model to data to determine efficiency
Differential comoving SFR density per intensity interval15 16 17 18 19
log *˙ / I [M �• yr 1 Mpc 3 / ergs cm 2 sec 1 Hz 1]
34
32
30
28
26
24Su
rface
Brig
htne
ss (µ
V) [m
ag a
rcse
c2 ]
Overlapping Average LBGAverage LBGLBG Uncertainty (1 )LBG R/H rangeK=0.01 × Kkenn
K=0.02 × Kkenn
K=0.05 × Kkenn
K=0.1 × Kkenn
K=Kkenn
Surf
ace
Brig
htne
ss [
mag
arc
sec-2
]
Rafelski et al. 2011
/ 30Heidelberg 2012: Marc Rafelski
10 100gas [M �• pc 2]
0.0001
0.0010
0.0100
0.1000SF
R [M
�• y
r1 kpc
2 ]
KS relationKS relation, K=0.1 × KkennLBG R/H rangeLBG Uncertainty (1 )LBG outskirtsDLAs
17
The KS relation for atomic dominated gas at z~3Σ
SFR[M
⊙yr
−1kp
c−2]
Σgas [M⊙pc−2]
Rafelski et al. 2011
/ 30Heidelberg 2012: Marc Rafelski 18
3.0
2.5
2.0
1.5
1.0
Log
Cov
erin
g Fr
actio
n
22.5 22.0 21.5 21.0Log N [cm 2] with K=0.1×KKenn
26 27 28 29 30 31 32Surface Brightness (µV) [mag arcsec 2]
LBG outskirtsCorrected LBG outskirtsDLAs with K=KkennDLAs with K=0.1×KkennDLAs with K=0.02×Kkenn
atomic-dominated gas
The covering fraction of the outskirts of LBGs is consistent with the DLA covering fraction
Log
Cov
erin
g Fr
actio
n
The emission unlikely to be from molecular-dominated gas
Surface Brightness [mag arcsec-2]
molecular-dominated gas
3.0
2.5
2.0
1.5
1.0
Log
Cov
erin
g Fr
actio
n
21.5 21.0 20.5 20.0Log N [cm 2] with K=KBigiel
26 27 28 29 30 31 32Surface Brightness (µV) [mag arcsec 2]
LBGs with coresCorrected LBGs with coresextrapolated upper limit
Surface Brightness [mag arcsec-2]
Rafelski et al. 2011
/ 30Heidelberg 2012: Marc Rafelski
gas [M �• pc 2]
SFR [M
�• y
r1 kpc
2 ]
1 10 102 103 10 4
10 3
10 2
0.1
1
10KS relationKS relation, K=0.1 × KkennLBG R/H rangeLBG Uncertainty (1 )LBG outskirtsDLAsG&K 2010 total gasG&K 2010 atomic gasG&K 2010 molecular gas
All Metals
19
Comparisons to predictions from simulations (Gnedin & Kravtsov 2010)
LBG Metallicity
gas [M �• pc 2]
SFR [M
�• y
r1 kpc
2 ]
1 10 102 103 10 4
10 3
10 2
0.1
1
10KS relationKS relation, K=0.1 × KkennLBG R/H rangeLBG Uncertainty (1 )LBG outskirtsDLAsG&K 2010 total gas Z<0.1Z �•
G&K 2010 atomic gas Z<0.1Z �•
G&K 2010 molecular gas Z<0.1Z �•
Metals with Z<0.1Z �•
DLA Metallicity
Σgas [M⊙pc−2]Σgas [M⊙pc
−2]
ΣSFR[M
⊙yr−
1kpc−
2]
Rafelski et al. 2011
/ 30Heidelberg 2012: Marc Rafelski 20
What is responsible for the reduced SFR efficiency?
Metallicity of gas?
Background radiation field?
Role of molecular vs. atomic hydrogen gas?
Other possibilities?
To better answer this question, would like to measure SFR efficiency for a range of redshifts
/ 30Heidelberg 2012: Marc Rafelski
0 1 2 3 4 5Redshift (z)
3
2
1
0
[M/H
] 0Gyr 7.7Gyr 10.3Gyr 11.4Gyr 12Gyr 12.3Gyr
LiteratureESI
HIRES<Z>
<Z> best fit
21Rafelski et al. 2012 in press
Metal Abundances versus redshift
<Z>= -(0.22±0.03) z - (0.65±0.09)Typical uncertainty
/ 30Heidelberg 2012: Marc Rafelski 22Haardt & Madau 2012
QuasarsGalaxies
combined
Evolution of Background Radiation Field
/ 30Heidelberg 2012: Marc Rafelski 23
Comparison of z~3 outskirts with z=0 outskirts
ΣSFR[M
⊙yr
−1kp
c−2]
Σgas [M⊙pc−2]
Rafelski et al. 2011
/ 30Heidelberg 2012: Marc Rafelski 24
The Ultraviolet Hubble Ultra Deep Field
Measure SFR efficiency at z~1 and z~2Improve z~3 measurement with larger sample of LBGs
90 HST orbits:30 F336W30 F275W30 F225W
2000 2500 3000 3500Wavelength (Å)
0.00
0.05
0.10
0.15
0.20
0.25
Thro
ughp
ut
F225W F275W F336W
Use existing i’ band UDF data for measurement at z~4
/ 30Heidelberg 2012: Marc Rafelski
Epoch1
Epoch3Epoch2
IR UDF 09
Epoch 1:March 2 - March 116 Orbits / 12 exposures per filter
Epoch 2:May 28 - June 410 Orbits / 20 exposures per filter
Epoch 3:August 4 - September 1914 Orbits / 28 exposures per filter+ 2 failed orbits from above
Total:30 Orbits / 60 exposures per filter90 Orbits in total by mid September
25
NUV Coverage of UDF with WFC3
29th mag 10 sigma point source limit
25
/ 3026
/ 30Heidelberg 2012: Marc Rafelski
F225W F275W F336W B I
F336Wdropouts
F275Wdropouts
F225Wdropouts
27
UV dropout galaxies at z~1-3
/ 30Heidelberg 2012: Marc Rafelski 28
Radial surface brightness profile of stacked LBGs at z~4
0.0 0.2 0.4 0.6 0.8 1.0 1.2Radius [arcsec]
34
32
30
28
26
24
22
Surfa
ce B
right
ness
(µV)
[mag
arc
sec
2 ]
3
2
1
0
Log
SFR [M
�• y
r1 kpc
2 ]
0 2 4 6 8Radius [kpc]
Median LBGsPSF
1 image sky limit73 image stack sky limit
Inner core Outskirts
/ 30Heidelberg 2012: Marc Rafelski
10 100gas [M �• pc 2]
0.0001
0.0010
0.0100
0.1000SF
R [M
�• y
r1 kpc
2 ]
KS relationKS relation, K=0.1 × KkennLBG R/H rangeLBG Uncertainty (1 )LBG outskirtsDLAs
29
How do things change at z~4?Σ
SFR[M
⊙yr
−1kp
c−2]
Σgas [M⊙pc−2]
10 100gas [M �• pc 2]
0.0001
0.0010
0.0100
0.1000SF
R [M
�• y
r1 kpc
2 ]
KS relationKS relation, K=0.1 × KkennLBG outskirts
LBG outskirts z~4
/ 30Heidelberg 2012: Marc Rafelski 30
Summary
• Measured extended rest-frame FUV emission in outskirts of z~3 LBGs
• Star formation rate efficiency of atomic-dominated gas at z~3 is a factor of ~10 lower than predicted by Kennicutt-Schmidt relation for local galaxies at z=0
• Covering fraction of DLA gas consistent with LBG outskirts, while molecular gas insufficient to cover the LBG outskirts.
• Consistent with predictions from Gnedin and Kravtsov 2010 suggesting the metallicity could be the driver for the lower SFR efficiency
• Measured the metallicity evolution of neutral hydrogen gas out to z~5
• Obtaining NUV data with HST to measure the SFR effiency at z~1 & 2
• Preliminary measurement of the SFR efficiency at z~4
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