The Quest for Low Metallicity DLA Systems Keck/ESI spectroscopy of SDSS Quasars
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The Quest for Low Metallicity DLA Systems Keck/ESI spectroscopy of SDSS Quasars Bryan E. Penprase (Pomona College) with Wal Sargent (Caltech), Jason X. Prochaska (UCSC) , and students Dan Beeler, and Irene Toro Martinez (Pomona College). (movie by A. Pontzen, I of A, Cambridge).

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Movie by a pontzen i of a cambridge

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)


Our project a summary

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


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Outline of Talk

Overview of DLA Absorption Line Spectroscopy and the context within

other 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 IGM

CIV and SiIV at low metallicity - N(CIV) and N(SiIV) vs [Si/H]


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Observing the High - z universe and metal enrichment -

QSO and GRB lines traverse filaments of newly-enriched IGM

DLAs can sample

small clumps of gas

with low enrichment

lower Z DLAs can study

pre-enriched IGM

Formation of structure after the Big Bang -- the development of the

“Cosmic Web”


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DLA measurements complement existing work on dwarf galaxy

and metal poor MW stars

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.

Stars: EMP, HMP, and other show evidence of [Fe/H] < -4.5,

but interpretation is complicated.


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Quest for low metallicity stars

(from Frebel,

Johnson, and

Bromm 2007)

“forbidden” zone is

at [C/H] = -3.5


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

lower limit for

well-constrained

values

lower limit for

well-constrained

values

Schaye, et al (2003) provide lower

limit of [C/H] > -3.8 from optical depth measurements of Lyman alpha forest.

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

Ryan-Weber (2009;

+ talk later in conference)

constrain Z/H > -4.0 from CIV

buildup at high redshift


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limit of [Fe/H] within

ultra-faint dwarf spheroidals

(Kirby et al 2008; Salvadori + Ferrara (2009)

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


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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.


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New sample of DLAs - 33 low Z systems observed with Keck

ESI spectrograph during 3/07 + 4/08


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Comparison of our low Z sample with overall DLA samples

<[M/H]> = -3.2

= 0.001 of DLAs

Prochaska et al

(2003)

Penprase et al

(2010)

<[M/H]> = -2.2

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


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


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


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

CII and OI lines

both have eqws < 80 mA.

log(N(HI)) = 20.15


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

limiting usable eqw


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Complete set of results from June 2008 (30 DLAs)


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


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

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


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New results showing O/H for sample using AOD columns


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New results showing O/H for sample using AOD columns

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


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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)


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New results extend upturn in [C/O] observed at low

values of [O/H]; indicates nucleosynthetic and enrichment effects

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

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


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

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


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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)


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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)


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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)


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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)


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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)


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Comparison of DLA sample abundances with Heger and

Woosley (2002) Pop III star model; normalized relative to

Carbon abundance.

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


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

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


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

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


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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:

adopt limit of

f (CIV) = 0.3


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CIV from low-Z DLAs

<N(HII)-N(HI)> = -0.3

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

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


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

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


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Conclusions

1). 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!


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