Low-Metallicity DLAs

The Development of the “Cosmic Web” - the First Galaxies! Observing the High - z universe and metal enrichment - QSO and GRB lines traverse filaments of newly-enriched IGM First stars inject C,N,O, Fe early after forming and blowing up DLA/ Smaller galaxies coalesce near star formation sites (too faint to study in emission!)

Simulations of Temperature of Universe from Big Bang to 5 Gyr “warming trend” + C, N, O, Si, and other elements from the first stars!

E Simulations of “Metal” production and Reionization (Abel, et al 2011) DLA/ Smaller galaxies coalesce near star formation sites (too faint to study in emission!) First stars inject C,N,O, Fe early after forming and blowing up

Nucleosynthesis and Yields - Deuterium, C, N, O Four Key Facts: 1.Mass of Star determines “yields” of elements and “remnant.” 2.Early Universe favors high Mass (“Population III”) stars. 3.Primordial Abundances include ONLY H, He, D and trace amounts of Li, Be, B - no C, N, O, Fe, Ni, Elements in gas phase of Early Universe can be measured from absorption lines, but also can be hidden by dust.

Where your elements come from

With some uncertainty about exact demarcations, one can delineate four kinds of deaths for non-rotating helium stars. (For rotation decrease main sequence mass %) He Core Main Seq. Mass Supernova Mechanism (from Woosley, 2007)

approximate E expl 56 Ni Fe-rich Fe-poor Heger and Woosley (2002)

Vanbeveren and DeDonder (2006) Stars from 140 and 200 solar masses are allowed but stars from 200 to 260 solar masses would overproduce iron in metal deficient stars.``` Theory and data from Stellar Spectroscopy low metallicity Early Universe Now High O/Fe solar abundances (Now) are a mix with Pop III SN and lower mass stars

Low neutron excess from CNO -> 22 Ne in helium burning No extended stable period of carbon and oxygen burning where weak interactions might increase the neutron excess Elements we can measure in DLA spectra

note: N(O) / N(C) > 1

Q Examples of some of Universe’s first C, O, and Si in Quasar Absorption Lines!

Q

Typical Quasar DLA “protogalaxy” contains C and O atoms spread out over 1 kpc (3200 light years) By comparison - one breath of air (2-3 liters) contains about Oxygen atoms! Mean separation of atoms in early universe is 30,000 km!

Question - What are the nuclear abundances in a “pristine sample” of intergalactic medium and how would we find this? Answer 1: A huge survey of quasar DLAs should produce some low-Z systems - what are their abundances? Largest survey - Prochaska, Wolfe, et al 2007: ~100 Keck DLA systems; lowest [C/H] ~ - 2.8; only a weak correlation between z and Z (Age-Metallicity relation from Prochaska et al 2003)

Other surveys and low-Z DLA systems New DLA and sub-DLA results from Pettini, Steidel, et al (2008); DLA systems seen down to [O/H] = Of the 3 low metallicity DLAs observed, < [O/H] < -2.42, High resolution UVES spectra show a median b value of ~ 7.5 km/s within components; with b ranging from 3 < b < 20 km/s.

Evidence of enrichment of Si, Fe, and Zn and Dust formation at z~2! (from work with Sargent DLA HIRES database, Penprase et al) Zn Cr Si Fe Ni Evolution of Zn/Cr

typical cutoff of metallicity near [Fe/H] = -3.5 Answer 2: A large survey of halo stars should show this primordial metallicity - what are their abundances? Survey by Frebel et al (2007) shows a few HMP stars, but a typical cutoff around [Fe/H] = -3.5

Answer 3: Dwarf Spheroidal Galaxies (dSphs) should trace primordial material - what are their metallicities? “Pre-enrichment” of dSphs at levels of [Fe/H] = -3.5 seen in ultra-faint dwarf galaxies; however measurements are difficult limit of [Fe/H] within ultra-faint dwarf spheroidals (Kirby et al 2008; Salvadori + Ferrara (2009)

Question - What are the nuclear abundances in a “pristine sample” of intergalactic medium and how would we find this? Answer 4: Why not take spectra of the highest redshift DLAs - what are their metallicities? Problem- high-z DLA systems typically have “black” Ly-alpha forest, and so measuring HI column is nearly impossible; best work is by Becker et al (2012) and can measure C/O, Si/O, and alpha/Fe - from sample of quasars with 4.7 < z < 6.3 (Becker, Sargent, Rauch, Carswell, 2012)

Question - What are the nuclear abundances in a “pristine sample” of intergalactic medium and how would we find this? Answer 4: Why not take spectra of the highest redshift DLAs - what are their metallicities? Problem- high-z DLA systems typically have “black” Ly-alpha forest, and so measuring HI column is nearly impossible; best work is by Becker et al (2012) and can measure C/O, Si/O, and alpha/Fe - from sample of quasars with 4.7 < z < 6.3 (Becker, Sargent, Rauch, Carswell, 2012)

Our Program: Finding the “Floor” of metallicity among quasar DLAs Search the entire SDSS quasar database (up to DR6) for new quasars (from 80,000) with R < 19. Find DLA systems within this sample of quasars (see Prochaska Herbert-Forte, Wolfe (2005), Prochaska et al (2008) - this produces about 1000 DLA systems Within the DLA systems, do a preliminary measurement of metallicity using the CII (1334) line and DLA Ly-Alpha fits from damping wings (Prochaska, with some help by Penprase) Choose the best candidate systems with preliminary [C/H] < -3.0 and observe them with the Keck ESI spectrograph (Penprase, Sargent + students Beeler, Toro-Martinez and Wilka) Analyze systems using AOD fitting to derive abundances (Penprase, Prochaska, Sargent et al 2010, Ap. J. 721, 1.)

New sample of DLAs - 33 low Z systems observed with Keck ESI spectrograph during 3/07 + 4/08

Properties of our low-Z DLA sample - N(HI) and z histograms

Example of ESI spectrum with [C/H] = and [O/H] = CII and OI lines both have eqws < 80 mA. log(N(HI)) = 20.15

limiting usable eqw AOD Column density corrections assuming b = 6.5, 7.5, 8.5 km/s

Complete set of results from June 2008 (30 DLAs)

Example of ESI low-Z spectrum with [C/H] = (from Penprase, Prochaska, Sargent, Toro-Martinez*, Beeler* 2010)

New results showing “floor” of [C/H] for sample of ~ 35 Keck low-Z ESI DLA systems

New results showing “floor” of O/H for same sample

New results extend upturn in C/O from prompt Type II supernova enrichment of IGM (from Penprase, Prochaska, Sargent, Toro-Martinez*, Beeler* 2010) low metallicity Early Universe Now High C/O in early universe Now mixing of yields of mid-size SN

Trends in C,O enhancement at low Z from prompt nucleosynthesis by Pop III stars low metallicity Early Universe Now High O/Si

Observed yields of C,O (a process elements) vs Fe-peak in the DLA sample

Comparison of DLA sample abundances with Heger and Woosley (2002) pair production Supernova model. note - deficit of Oxygen and Silicon, excess of Aluminum compared to nucleosynthesis model!

Our data (Penprase et al 2010)

Low neutron excess from CNO -> 22 Ne in helium burning No extended stable period of carbon and oxygen burning where weak interactions might increase the neutron excess Our data (Penprase et al 2010) Pair Production SN

Others Confirm the C/O reversal - Cooke et al 2011, 2012

Models of how low-mass galaxy formation can produce observed Abundances Salvadori and Ferrara, 2012, MNRAS