Physical Properties of Ly Emitters from z=2 to 3

Caryl Gronwall (Pennsylvania State University)Collaborators:

Eric Gawiser (Rutgers), Lucia Guaita (PUC), Nicholas Bond (Rutgers),

Robin Ciardullo (PSU), John Feldmeier (YSU),

Harold Francke, Nelson Padilla (PUC)

Jean Walker, Michael Berry, Viviana Acquaviva (Rutgers),

Ana Matkovic, Christopher Wolf (PSU)

+ the MUSYC collaboration

6 May 2010

Searches for Primeval Galaxies

• Primeval = “galaxy in the act of formation”• Expect: strong star-formation (hence strong emission-

lines), little dust & metals, high redshift• Search primarily consists of looking for Ly emission-line

galaxies• Understanding the properties of such galaxies can help

with our pictures of galaxy formation• Redshift range of z=2-3 traces peak of star-formation,

allows for direct comparison to LBGs at similar redshifts

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BV-NB5000 selection of z=3.1 LAEs

(Gronwall et al 2007, ApJ 667, 79;Ciardullo et al. 2010, in prep.)

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Observations

• Detected 156 Lyα emitters (LAEs) in λ4990, 158 in λ5015 (96 new) and 250 LAEs in λ3727 in the Extended CDF-S with:– Rest-frame EW > 20 Å – monochromatic flux > 1.5 x 10-17 (2.0 x 10-17 ) ergs-cm-2-s-1 at z=3.1

(2.1)

• These samples are large enough for statistical analysis allowing us to study the evolution of these systems.

• Spectroscopy of ~80 LAEs at z=3.1 finds:– Only one luminous [OII] emitter!– Two interlopers at z=1.6 (via the CIII] 1909 line).– One z=3.1 AGN (with emission from CIV 1550).– Remainder are “normal” star-forming LAEs at z=3.1

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Evolution of Lyα LF

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Rest Frame Equivalent

Widths• Less than 10% of LAEs

have EW0 > 240 Å which would imply a top-heavy IMF

• EW distribution is exponential with scale length of 76 Å

• Extrapolation implies ~20% of LAEs fall below the EW cutoff

• Similar distribution at z=2.1 and 3.1

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(Guaita et al 2010, ApJ, 714, 255)

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UV vs. emission-line SFR @z=3.1

UV SFRs are slightlyhigher than emission-line SFRs==> dust!

Gronwall+ 2007; Ciardullo+ 2010

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Rest-UV colors(Guaita et al 2010, ApJ, 714, 255)

Most LAEs are blue, with B-R<0.5Median continuum magnitude is R=25.5One branch is bright and red, with R<25, B-R>16 May 2010 STScI

Comparison to LBGs @ z=3.1

LAEs primarilyfall in same regionin color-color spaceas LBGs

6 May 2010

Gronwall+ 2007

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Two-population fit to stacked Spectral Energy Distribution (SED) of IRAC-undetected LAEs

(Gawiser et al 2007, ApJ 671, 278)

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LAEs at 2<z<3 evolve into ~L* galaxies at z=0 (Guaita et al. 2010, ApJ, 714, 255; Gawiser et al. 2007, ApJ 671, 278)

Evolution of bias :(dashed tracks are median of conditional mass function)

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Conclusions

• The Lyα emission line allows LAEs to be selected and confirmed spectroscopically to the lowest bolometric luminosity of any high-redshift technique.

• There appears to be little evolution in the observed LAE LF from z=2 to 6.

• With low stellar masses (M<109 M), LAEs have the highest specific SFR of any galaxy population. This is consistent with the young starburst age of 20 Myr inferred for the dominant population not detected by IRAC.

• LAEs at z=3 have dark matter halo masses of ~1011M.

They will evolve into ~L* galaxies today.

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