Measuring the evolution of the star formation rate efficiency of neutral atomic hydrogen gas from z ~1 4 Marc Rafelski Galactic Scale Star Formation August 2012 Collaborators: Harry Teplitz Arthur Wolfe Hsiao-Wen Chen Xavier Prochaska UV UDF team
Relative Flux Damped Lyman Alpha Systems (DLAs) Rest Wavelength (Å) Observed Wavelength (Å) Definition of Damped Lyα System (DLA): N(HI) 2 10 20 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: f H2 ~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] Wolfe et al. 2005 Heidelberg 2012: Marc Rafelski 2 / 30
Kennicutt-Schmidt (KS) Relation The Star Formation Rate (SFR) surface density goes as the total gas surface density to a power law Can rewrite it with column density N: Σ SFR = K (N/N c ) β N c =1.25 10 20 cm 2 β =1.4 ± 0.15 K= 2.5 10 4 M yr 1 kpc 2 Normal Disks Star Forming Kennicutt, 1998 Heidelberg 2012: Marc Rafelski 3 / 30
Tightly Correlated HI and FUV emission in M83 Blue: FUV map (GALEX) Arc Minutes Red: HI contours (THINGS) Bigiel et al. 2010a Arc Minutes Heidelberg 2012: Marc Rafelski 4 / 30
Can we see DLAs in emission at z~3? Gas Density SFR (KS) SFR FUV Lν (Madau Kennicutt Calibration) At z=3 1500 Å 6000 Å - This puts it in the visible! Lν/area Surface Brightness Most DLAs: N ~ 2x10 20 3x10 21 cm -2 Navg ~ 1x10 21 cm -2 Column Density (N) [cm -2 ] 10 23 z = 2.5 z = 3.0 z = 3.5 10 22 10 21 10 20 32 30 28 26 24 Surface Brightness [AB mag/arcsec 2 ] Surface Brightness [mag arcsec -2 ] Only high resolution image sensitive enough is the Hubble Ultra Deep Field (UDF) Heidelberg 2012: Marc Rafelski 5 / 30
Cumulative comoving SFR density for DLAs Σ SFR (N) =K(N/N c ) β Cumulative comoving SFR density log * ( µ V ) [M yr 1 Mpc 3 ] 1 z = 3 2 3 4 5 1% K 10% K K=0.01 K kenn 38 36 34 32 30 28 26 Surface Brightness (µ V ) [mag arcsec 2 ] Wolfe & Chen 2006 K=0.1 K kenn K=K kenn Surface Brightness [mag arcsec -2 ] (A proxy for N HI via the KS relation) Heidelberg 2012: Marc Rafelski 6 / 30
Wolfe & Chen 2006 result: SFR efficiency of DLAs is a factor of 10 below KS relation Caveat: Wolfe & Chen 2006 search excluded objects with high surface-brightness cores (µ V < 26.6 mag/arcsec 2 ) (i.e. LBGS) Another possibility: Lyman Break galaxy cores may be embedded in DLAs, and may themselves exhibit in situ star formation Heidelberg 2012: Marc Rafelski 7 / 30
LBGs embedded in DLA Neutral Gas Reservoirs DLA LBG Dust Heidelberg 2012: Marc Rafelski 8 / 30
In situ star formation in DLAs associated with LBGs In-situ star formation DLA LBG Dust Heidelberg 2012: Marc Rafelski 9 / 30
Solution: Ultra Deep u -band image of UDF with Keck Keck Telescopes 1 σ depth = 30.7 mag/arcsec 2 Detection limit =27.6 mag/arcsec 2 FWHM = 1.3 arcsec Rafelski et al. 2009 Heidelberg 2012: Marc Rafelski Use the u-band image to select 407 z~3 LBGS via their flux decrement from the Lyman break 10 / 30
48 compact, symmetric, and isolated z~3 LBGs in V-band Rafelski et al. 2011 Heidelberg 2012: Marc Rafelski 11 / 30
Stack 48 isolated, compact, symmetric z~3 LBGs in the V-band (rest-frame FUV) Rafelski et al. 2011 Heidelberg 2012: Marc Rafelski 12 / 30
Radial surface brightness profile of stacked image Inner core Outskirts Surface Brightness [mag arcsec -2 ] Surface Brightness (µ V ) [mag arcsec 2 ] Rafelski et al. 2011 Radius [kpc] 0 2 4 6 8 22 Median LBGs PSF 24 1 image sky limit 48 image stack sky limit 26 28 30 32 34 4 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Radius [arcsec] Radius [arcsec] Heidelberg 2012: Marc Rafelski 0 1 2 3 Log SFR [M yr 1 kpc 2 ] 13 / 30
Goal: compare comoving SFR density in outskirts of LBGs to DLAs to obtain a SFR efficiency Column density of gas varies with radius, we need a differential version of the comoving SFR density( ρ ) Previously: Differential: ρ N = Σ SFR(N) H 0 c f(n,x) ρ I Heidelberg 2012: Marc Rafelski 14 / 30
Model differential comoving SFR density for DLAs 24 Surface Brightness [mag arcsec -2 ] 26 28 30 32 34 K=K kenn K=0.1 K kenn K=0.05 K kenn K=0.02 K kenn K=0.01 K kenn 15 16 17 18 19 Differential comoving SFR density per intensity interval Rafelski et al. 2011 Heidelberg 2012: Marc Rafelski 15 / 30
Comparison of model to data to determine efficiency Surface Brightness [mag arcsec -2 ] 24 26 28 30 32 34 K=K kenn K=0.1 K kenn K=0.05 K kenn K=0.02 K kenn K=0.01 K kenn LBG R/H range LBG Uncertainty (1 ) Average LBG Overlapping Average LBG Determine efficiency for each point 15 16 17 18 19 1 3 2 1 1 Differential comoving SFR density per intensity interval Rafelski et al. 2011 Heidelberg 2012: Marc Rafelski 16 / 30
The KS relation for atomic dominated gas at z~3 ΣSFR [M yr 1 kpc 2 ] SFR 0.1000 0.0100 0.0010 KS relation KS relation, K=0.1 K kenn LBG R/H range LBG Uncertainty (1 ) LBG outskirts DLAs Rafelski et al. 2011 0.0001 10 100 [M pc 2 ] Σ gas [M pc 2 ] Heidelberg 2012: Marc Rafelski 17 / 30
The covering fraction of the outskirts of LBGs is consistent with the DLA covering fraction The emission unlikely to be from molecular-dominated gas atomic-dominated gas molecular-dominated gas Log Log Covering Fraction Fraction 1.0 1.5 2.0 2.5 3.0 Log N [cm 2 ] with K=0.1 K Kenn 22.5 22.0 21.5 21.0 LBG outskirts Corrected LBG outskirts DLAs with K=K kenn DLAs with K=0.1 K kenn DLAs with K=0.02 K kenn Log N [cm 2 ] with K=K Bigiel 21.5 21.0 20.5 20.0 LBGs with cores Corrected LBGs with cores extrapolated upper limit 26 27 28 29 30 31 32 Surface Brightness (µ V ) [mag arcsec 2 ] Rafelski et al. 2011 Surface Brightness [mag arcsec -2 ] 26 27 28 29 30 31 32 Surface Brightness (µ V ) [mag arcsec 2 ] Surface Brightness [mag arcsec -2 ] Heidelberg 2012: Marc Rafelski 18 / 30
Comparisons to predictions from simulations (Gnedin & Kravtsov 2010) ΣSFR [M yr 1 kpc 2 ] SFR [M yr 1 kpc 2 ] 10 1 0.1 10 2 10 3 10 4 LBG Metallicity KS relation KS relation, K=0.1 K kenn LBG R/H range LBG Uncertainty (1 ) LBG outskirts DLAs G&K 2010 total gas G&K 2010 atomic gas G&K 2010 molecular gas All Metals 1 10 10 2 10 3 gas [M pc 2 ] Σ gas [M pc 2 ] DLA Metallicity KS relation KS relation, K=0.1 K kenn LBG R/H range LBG Uncertainty (1 ) LBG outskirts DLAs G&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 1 10 10 2 10 3 gas [M pc 2 ] Σ gas [M pc 2 ] Rafelski et al. 2011 Heidelberg 2012: Marc Rafelski 19 / 30
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 Heidelberg 2012: Marc Rafelski 20 / 30
Metal Abundances versus redshift 0Gyr 7.7Gyr 10.3Gyr 11.4Gyr 12Gyr 12.3Gyr 0 Literature ESI HIRES <Z> <Z> best fit 1 [M/H] 2 3 Typical uncertainty <Z>= -(0.22±0.03) z - (0.65±0.09) 0 1 2 3 4 5 Redshift (z) Rafelski et al. 2012 in press Heidelberg 2012: Marc Rafelski 21 / 30
Evolution of Background Radiation Field combined Galaxies Quasars Haardt & Madau 2012 Heidelberg 2012: Marc Rafelski 22 / 30
Comparison of z~3 outskirts with z=0 outskirts ΣSFR [M yr 1 kpc 2 ] Rafelski et al. 2011 Σ gas [M pc 2 ] Heidelberg 2012: Marc Rafelski 23 / 30
The Ultraviolet Hubble Ultra Deep Field 0.25 0.20 Throughput 0.15 0.10 F225W F275W F336W 90 HST orbits: 30 F336W 0.05 30 F275W 0.00 2000 2500 3000 3500 Wavelength (Å) 30 F225W Measure SFR efficiency at z~1 and z~2 Improve z~3 measurement with larger sample of LBGs Use existing i band UDF data for measurement at z~4 Heidelberg 2012: Marc Rafelski 24 / 30
NUV Coverage of UDF with WFC3 Epoch1 Epoch2 Epoch3 Epoch 1: March 2 - March 11 6 Orbits / 12 exposures per filter Epoch 2: May 28 - June 4 10 Orbits / 20 exposures per filter Epoch 3: August 4 - September 19 14 Orbits / 28 exposures per filter + 2 failed orbits from above IR UDF 09 Total: 30 Orbits / 60 exposures per filter 90 Orbits in total by mid September 29th mag 10 sigma point source limit Heidelberg 2012: Marc Rafelski 25 / 30
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UV dropout galaxies at z~1-3 F225W F275W F336W B I F336W dropouts F275W dropouts F225W dropouts Heidelberg 2012: Marc Rafelski 27 / 30
Radial surface brightness profile of stacked LBGs at z~4 Inner core Outskirts Surface Brightness (µ V ) [mag arcsec 2 ] Radius [kpc] 0 2 4 6 8 22 Median LBGs PSF 24 1 image sky limit 73 image stack sky limit 26 28 30 32 0 1 2 3 Log SFR [M yr 1 kpc 2 ] 34 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Radius [arcsec] Heidelberg 2012: Marc Rafelski 28 / 30
How do things change at z~4? ΣSFR [M yr 1 kpc 2 ] SFR 0.1000 0.0100 0.0010 KS relation KS relation, K=0.1 K kenn LBG R/H range LBG Uncertainty (1 ) LBG outskirts DLAs LBG outskirts z~4 0.0001 10 100 [M pc 2 ] Σ gas [M pc 2 ] Heidelberg 2012: Marc Rafelski 29 / 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 Heidelberg 2012: Marc Rafelski 30 / 30