Are There Local Analogs of Lyman Break Galaxies?
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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)