The Quest for Low Metallicity DLA Systems Keck/ESI spectroscopy of SDSS

QuasarsBryan E. Penprase (Pomona College)

withWal Sargent (Caltech), Jason X. Prochaska

(UCSC), and students Dan Beeler, and Irene Toro Martinez (Pomona

College)

(movie by A. Pontzen, I of A, Cambridge)

Keck ESI Spectroscopy of 33 SDSS DR5 quasars (based on reducing SDSS DR5 from 77,289 quasars to 458 candidates with DLAs).

Quasars Selected for DLA systems with large HI columns, (log N(HI) > 20.3) and weak lines of CI.

SDSS Spectra with DLA + weakest lines chosen for further study with Keck; our sample represents the lowest metallicity group possible for observation with R < 19.5.

Observations Constrain the “floor” of metallicity in IGM; possible indication of “mini-halos” (Bromm et al) and can test “threshold” of metallicity for star formation (Frebel, Johnson and Bromm (2007)) where [C/H] > -3.5 and [O/H] > -3.1.

Abundances provide some information on nucleosynthesis and enrichment of IGM (Wise, Cen et al) which predict minimum metallicities of [M/H] ~ -3.0.

Our Project - a Summary

Outline of Talk

Overview of DLA Absorption Line Spectroscopy and the context withinother studies of enrichment, and metallicity. Our sample -- an overview of the basic parameters

Trends in metal abundances with redshift

Limitations of our ESI sample - effects of correcting for possible saturation effects

Resulting trends in abundances of [C/O], [O/H], [Si/H], comparison with [Fe/H], and implications for nucleosynthesis and enrichment of the IGMCIV and SiIV at low metallicity - N(CIV) and N(SiIV) vs [Si/H]

Formation of structure after the Big Bang -- the development of the “Cosmic Web”

Observing the High - z universe and metal enrichment -QSO and GRB lines traverse filaments of newly-enriched IGM

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

DLAs can samplesmall clumps of gaswith low enrichment

lower Z DLAs can studypre-enriched IGM

Pros: QSO measurements are in situ, with no complicated mixing in stellar atmospheres

Cons: QSO measurements have fewer available transitions,have blending, dust, and possible saturation effects in our ESI sample; also QSOs are faint.

DLA measurements complement existing work on dwarf galaxyand metal poor MW stars

Stars: EMP, HMP, and other show evidence of [Fe/H] < -4.5,but interpretation is complicated.

Quest for low metallicity stars(from Frebel,Johnson, and Bromm 2007)

“forbidden” zone is at [C/H] = -3.5

Simcoe, et al (2004) detect lower limits of [C/H] > -3.4 based on Ly-alpha forest components of CIV and SiIV.

Our low-Z DLA measurements complement work with pixel optical depths and measurements of CIV/H and SiIV/H for “floor” of metallicity

Schaye, et al (2003) provide lower limit of [C/H] > -3.8 from optical depth measurements of Lyman alpha forest. lower limit for

well-constrained values

lower limit forwell-constrained values

Ryan-Weber (2009; + talk later in conference)constrain Z/H > -4.0 from CIVbuildup at high redshift

“Pre-enrichment” at levels of [Fe/H] = -3.5 in ultra-faint dwarf galaxies

limit of [Fe/H] withinultra-faint dwarf spheroidals(Kirby et al 2008; Salvadori + Ferrara (2009)

Quest for low metallicity in the ISM and IGM: known DLA systems

New DLA and sub-DLA results from Pettini, Steidel, et al (2008); DLA systems seen down to [O/H] = -2.42.

Of the 3 low metallicity DLAs observed, -2.04 < [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.

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

Comparison of our low Z sample with overall DLA samples

Prochaska et al (2003)

Penprase et al (2010)

<[M/H]> = -1.52, = 0.52

<[M/H]> = -2.2

<[M/H]> = -3.2= 0.001 of DLAs

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

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

Example of ESI spectrum with [C/H] = -2.85 and [O/H] = -2.93

CII and OI linesboth 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)

New results showing [C/H] for sample using AOD columns

New results showing [C/H] for sample using AOD columns(corrected for saturation, and excluding DLAs with eqws > 125 mA)

New results showing O/H for sample using AOD columns

New results showing O/H for sample using AOD columns(corrected for saturation, and excluding DLAs with eqws > 125 mA)

New results extend upturn in [C/O] observed at low values of [O/H]; indicates nucleosynthetic and enrichment effects

(from Penprase, Sargent, Prochaska, et al 2009)

New results extend upturn in [C/O] observed at low values of [O/H]; indicates nucleosynthetic and enrichment effects

(from Penprase, Sargent, Prochaska, et al, Ap. J. (submitted) 2010

(corrected for saturation, and excluding DLAs with eqws > 125 mA)

alpha/Fe vs metallicity -- [Si/Fe] (red); and [O/Fe] (green)

(corrected for saturation, and excluding DLAs with eqws > 125 mA)

histograms of low-metallicity DLA sample for various elements -- evidence for a floor of [X/H] in the IGM ~ -3.0

limit of [C/H] within DLA sample (-2.9)

histograms of low-metallicity DLA sample for various elements -- evidence for a floor of [X/H] in the IGM ~ -3.0

limit of [O/H] within DLA sample (-3.2)

histograms of low-metallicity DLA sample for various elements -- evidence for a floor of [X/H] in the IGM ~ -3.0

limit of [Si/H] within DLA sample (-2.9)

histograms of low-metallicity DLA sample for various elements -- evidence for a floor of [X/H] in the IGM ~ -3.0

limit of [Al/H] within DLA sample (-2.9)

histograms of low-metallicity DLA sample for various elements -- evidence for a floor of [X/H] in the IGM ~ -3.0

limit of [Fe/H] within DLA sample (-3.2)

Comparison of DLA sample abundances with Heger andWoosley (2002) Pop III star model; normalized relative toCarbon abundance.

not a good match --> suggests enrichment not from pair production Pop III stars

Nucleosynthetic models vs low-Z DLA sample : [C/O]

Becker, et al (2006) high redshift OI system average

Nucleosynthetic models vs low-Z DLA sample : [O/Si]

Becker, et al (2006) high redshift OI system average

CIV and constraints on N(HII) within low metallicity DLA gas

Fox, Petitjean, et al (2008) - results of CIV within large UVES DLA sample

can also estimate N(HII)associated with CIV phase: f (CIV) = 0.3adopt limit of

CIV and constraints on N(HII) within low metallicity DLA gasCIV and constraints on N(HII) within low metallicity DLA gas

CIV from low-Z DLAs<N(HII)-N(HI)> = -0.3

Trend in N(CIV) (a tracer of vel) vs [Si/H]

Correlation could indicate lower metallicity systems have lower velocity dispersion and arise in lower mass regions (perhaps proto-dwarf galaxies)

Conclusions1). low-metallicity systems are rare, and our sample suggests that [M/H] of -3.2 comprises approximately 0.1% of all DLA systems.

2). Results confirm enhancement of [C/O] at low [O/H], which also correlates with redshift. Indicates possible nucleosynthetic effects within DLA sample.

3). Evidence for decrease in [alpha/Fe] as a function of [Fe/H], consistent with a scenario early type II supernovae, followed by enrichment from Type Ia stars.

4). Lowest metallicity DLAs do not match standard Pop III nucleosynthesis predictions of Heger and Woosley (2002) or others for most massive Pop III stars.

5). Results demonstrate existence of a “floor” of metallicity within our DLA sample (culled from 854 DLAs) in which DLA values of [C/H] > -2.9, [O/H] > -3.2, [Al/H] > -2.9, [Fe/H] > -3.2 .

6). Detection of CIV and SiIV shows that warm gas present with lowZ DLAs, and that the low [M/H] has may exist in lower mass regions (akin to dwarf galaxies perhaps?)

thank you!