a steep faint-end slope of the uv lf at z~2-3: implications for the missing stellar problem
DESCRIPTION
A Steep Faint-End Slope of the UV LF at z~2-3: Implications for the Missing Stellar Problem. Naveen Reddy (Hubble Fellow, NOAO). C. Steidel ( Caltech ). Galaxies in Real Life and Simulations, Leiden, Netherlands, 16 September 2008. Luminosity/Redshift Evolution of Dust; - PowerPoint PPT PresentationTRANSCRIPT
A Steep Faint-End Slope of the UV LF at z~2-3: Implications for the Missing Stellar Problem
C. Steidel ( CaltechC. Steidel ( Caltech))
Naveen Reddy (Hubble Fellow, NOAO)
Galaxies in Real Life and Simulations, Leiden, Netherlands, 16 September 2008
Are There Problems with Stellar Mass/ Star Formation Rate Measurements?
• SFR / stellar mass calibrations
• IMF evolution?
• Dust extinction
• Incompleteness
Luminosity/Redshift Evolution of Dust;
Incompleteness of Stellar Mass Density Measurements
Reddy & Steidel (2008b)
Quantifying Number Densities via the UV Luminosity Function
Advantages of UV:
- direct tracer of massive star formation, modulo the effects of dust
- deepest observations up to 2000 times more sensitive than those at IR and longer wavelengths
- accessibility over almost the entire age of the Universe
Need for Spectroscopy:
- assess contamination
- quantify perturbing effects of line emission and consequence for sample completeness
- color corrections for IGM opacity
- physical state of the ISM (stellar population; outflows)
Going Beyond the Spectroscopic Limit
Reddy et al 2008a
?Use spectroscopic trends as a zeropoint for determining how galaxy properties depend on UV luminosity
Preferential Scattering due to Lya:
- contribution of high Ly EW systems at UV-faint magnitudes; ~10% (>50 A) at M ~ -17
Change in mean dust attenuation:
- no variance with UV luminosity?
- evolution of dust with UV luminosity; UV-faint galaxies less dusty than UV-bright ones?
Upshot: these systematics modulate the inferred faint-end slope of the UV LF by up to ~10%, with a tendency to steepen
Advantages of our analysis
- > 2000 spectroscopic redshifts at the bright-end
- modeling of systematic effects
- maximum-likelihood constraints on LF that are robust to non-uniform sources of scatter
- 31000 LBGs in 31 independent fields
Results on the UV LF at z~2-3
Reddy et al 2008b
Steep faint-end slope of ~ -1.73, similar to that measured at z~4-6
0.1L*0.07L*
• z=2:
N(0.07L*<L<L*)~0.98N(>0.07L*)
(0.07L*<L<L*)~0.84(>0.07L*)
z=3:
N(0.1L*<L<L*)~0.97N(>0.1L*)
(0.1L*<L<L*)~0.82(>0.1L*)
Make use of UGR+JK+IRAC photometry for several hundred galaxies
- spectroscopic redshifts remove a key degeneracy from this analysis!
- independent monochromatic indicators constrain SFRs and reddening
Stellar Population Modeling
R<25.5
Reddy et al 2008b
Trends between UV luminosity and SFR with Stellar Mass
Sawicki et al. 2007
Dust Corrections as a Function of UV Luminosity
~4-5 dust correction
~2 dust correction
Mean Correction of ~2-3 for Total UV
Luminosity Density
For >0.083L* galaxies
Estimate of the Stellar Mass Function at z~2
Reddy et al 2008b
Integral of the Star Formation History
z
L>0.083L*(z>2)
[L>0.083L*(z=2)]
Integrated to L=0.083L*(z=6)
What about contribution from massive galaxies?
Contributions to the Stellar Mass Density at z~2
For >0.083L* galaxies
(R<25.5;<10^11 M*) ~ 3.7 +/- 0.2 crit
(R>25.5;<10^11 M*) ~
2.0 +/- 0.2 crit
(>10^11 M*) ~
1.6 +/- 0.4 crit
Comparisons with the Integrated Star Formation History
>0.083L* R<25.5; M<10^11 Msun
R>25.5; M<10^11 Msun
M>10^11 Msun
WRONG!
Redshift Evolution of the Faint-End Slope
Reddy et al 2008b
Slope roughly constant at z>2, with ~ -1.73
- but, strong evolution in UV LF implies sub-L* galaxies at z~6 are different from sub-L* galaxies at z~2
- evolution of faint-end slope may have less to do with delayed feedback and more to do with the availability of low mass halos with cold gas below z~2
Conclusions
Constraints on the faint-end slope of the UV LF:
- UV LF evolves strongly between z~6 and z~2
- very steep faint-end slope of the UV LF of ~ -1.73 at z~2 and z~3, remarkably similar to those derived at higher redshifts (z~4-6)
-but, faint-end population evolves between z~6 and z~2, so evolution of faint-end slope may have less to do with feedback and more to do with the availability of low mass halos with cold gas below z~2
- dust corrections depend on how far one integrates to obtain the UV LD
Combining the stellar masses of star-forming galaxies at z~2-3 with the luminosity function:
- significant stellar mass density in UV-faint galaxies (R>25.5) as in UV-bright ones
- appears to resolve the supposed discrepancy between stellar mass density estimates and the integrated star formation history up to z~2
ADDITIONAL SLIDES
Infrared Luminosity Function at z~2
Total IR LD ~ 1.3e09 Lo/Mpc3
Total IR LD (Caputi et al. 2006) ~ 6.6e08 Lo/Mpc3
Limit of MIPS observations without prior information