Are There Local Analogs of Are There Local Analogs of Lyman Break Galaxies?Lyman Break Galaxies?

James D. Lowenthal (Smith College/FCAD)R. Nick Durham (Smith College)Brian Lyons (Amherst College)David C. Koo (UCO/Lick Obs.)

Matt A. Bershady (U. Wisconsin)Rafael Guzmán (U. Florida)

Jesús Gallego (Universidad Complutense de Madrid)

See also: Jason Melbourne (AO)Matt Bershady (internal kinematics)David Koo (z~1)Drew Phillips ([O/H])Kai Noeske (UDF profiles)

Big question: How do Lyman break galaxies fit into galaxy formation/evolution?

Specific motivating questions: •What are detailed characteristics of LBGs? •Range of LBG masses?•Do LBGs reside in much larger, more massive halos, or is it “what-you-see-is-what-you-get”, i.e., dwarf starburst galaxies?•What constraints can we place on LBG “host galaxy” type?

One approach: find local analogs -- easier to study in detail. Then compare to LBGs.

Basic parameters of Lyman break galaxies

Sizes r1/2~3 kpc

Luminosities L~L* and up (L<L* hard to study)

ColorsVery blue (except for Lyman/Lyα breaks)

B-V(rest)<0.4

MorphologiesDiverse: multiple knots, halos, chains, compact

Star Formation Rates

1<SFR<1000 M yr-1

Masses109 < M < 1012 M from stellar populations, emission line widths, spatial kinematics

Clustering r0~5 Mpc

Lyman Break Galaxy Examples

Lowenthal et al. 1997

10”

Possible best local analogs to LBGs: HII galaxies and luminous blue compact galaxies (LBCGs)

Sizes r1/2<3 kpc

Luminosities 0.1<L/L*<2

Colors Very blue: B-V~0.5

Morphologies Diverse: small disks, irregulars

Star Formation Rates

0.5<SFR<25 M yr-1

Masses1010 < M < 1011 M from stellar populations, emission line widths

Clustering r0~5 Mpc

LCB Galaxy Examplesz<0.05 z~0.75

WIYN R-band (Pisano et al. 2001) HDF-FF I814 (Phillips et al. 1997)

6”

10 kpc

HST/STIS images in rest-UV of HII Galaxies and LCBGs

Goal: Compare local starburst and high-redshift LBG samples at same rest-UV wavelength

• 12 (HII) galaxies from UCM survey (z~0): STIS/FUV images

• 14 LCBGs from Kitt Peak Galaxy Redshift Survey (z~0.5): STIS/NUV images

STIS FUV images

Morphologies: VERY diverse, disturbed, multiple knots

z~0 sample

6.5”

STIS NUV images

Morphologies: more disturbed, multiple knot systems

z~0.75 sample

3.75”

Rest-UV AsymmetriesMeasure image asymmetry A following Conselice et al. (2000)

Rest-UV Asymmetries

Large range in A; spans median for LBGs

LBG median

What would LCBGs and HII galaxies look like at z~3?

• Simulate z=3 HDF view:– Rebin STIS images– Add noise to match S/N at z=3

• Low redshift sample not visible at z=3 (but barely visible in ACS/GOODS/UDF)

• z~0.75 sample all visible at z=3; morphologies much simpler, more compact; low-SB structure lost.

True z STIS vs. simulated HDF

True zSimulated HDF

z=3

Rest-UV Asymmetries of simulated z=3 view

Asymmetry affected by z?

Asymmetries drop with redshift as faint outer regions fade

True z vs. simulated z=3 asymmetries

Median asymmetry in z=3 simulation:

Amed<0.1 (vs. 0.3 for original images)

Conclusions

• HIIGs and LCBGs are smaller, lower-L than LBGs, but with similar morphologies, asymmetries, colors, star formation properties.

• Masses of HIIGs and LCBGs are small, M<1010 M; many LBGs may be too.

• Caveats: Fate of LBGs not known; difficult to constrain masses of LBGs for comparison

• Still to come: better morphological analysis (e.g., Gini coefficient, Lotz et al. 2004)