GOODS K-band mosaic

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Making Sense of Restframe Mid-UV Spectra of
Galaxies Using Hubbles Next Generation Spectral
Library Sally Heap, NASA/Goddard Granada, 3
Oct 2007
BC03
GOODS K-band mosaic
Daddi et al. 2005
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The major spectral diagnostics, MgUV, D4000, and
Hd are all visible in the spectra of galaxies at
z0.4-1.0
z
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Age(z, zf) Age(MSTO Teff,
Fe/H)
MgUV lgt3500lt8000
logZ
-2.0
-1.5
-1.0
-0.5
0.5
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• z1 galaxies
• oldest stars lt6 Gyr
• wide spread in restframe B-V
• restframe near-UV comes into view

De Lucia Blaizot 2006, astro-ph
z0.36 z0.62 z1.0 z1.7
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The Mid-UV (2000-3000 Å) flux is produced
mainly by MSTO stars, the clock for stellar
evolution
Hottest stars MSTO

• Dealing with MSTO stars simplifies things
  greatly
• Observed spectrum looks like that of a single
  F-type MS star
• Modeling of the atmosphere and spectrum is
  easier for MS F-type stars
• Modeling of the interior structure is easier for
  F-type MS stars.

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Except that blue HB stars may contaminate the
UV spectrum of very old, metal-poor stellar
populations
Blue HB
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At z1, blue HB stars should not be a problem
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The spread in Teff increases with lower
metallicities
Fe/H0 Fe/H-1.01 a/Fe0.3
Isochrone log g
Teff
V-R isochrones
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The primary mid-UV feature is MgUV (composed of
MgII, FeI, FeII, etc.)
BC03 models Kurucz library
HST UDF
Daddi et al. 2005
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The MgUV feature can distinguish between a dusty,
star-forming galaxy and an older, passively
evolving galaxy but it cannot tell its age
because of the age-metallicity degeneracy. Can
we do better?
BC03 Models of the Evolution of MgUV
Adapted from Daddi et al. 2005
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Line blanketing, especially in the UV,
distinguishes high-metallicity stars Can UV
colors help?
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Problems with Spectral Models Assumption of LTE,
Missing Opacities
B2640 MgII
2800 MgI 2850
Munari Castelli
Chromospheric Emission
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Next Generation Spectral Library
HD 16031
HD 2665 (G5 IIIw) Teff5004 log g2.27 log
Z -1.96 ELODIE
Teff log g log Z
6341 4.19 -1.12 (this
study) 6114 4.07 -1.79 (Clem et al.
2004)
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• Estimating the Stellar Parameters Teff, logg,
  logZ, E(B-V)
• Set up
• Resample STIS spectrum to resolution of
  Castellis models
• Normalize observed model spectra over 0.4-0.7
  m
• Make c2 fit to spectrum (Dl0.20 -1.00 m) for
  Teff, logZ, and E(B-V)
• Determine Lv range corresponding to V, p, ep
• Calculate Lbol from BCv(Teff, logZ, E(B-V))
• Derive possible ilogg from comparison with
• V-R evolutionary models
• Make c2 fit for Teff, logg, logZ, and E(B-V)
  with
• wt 1 for l0.2-1.0 m, and wt 10 for Mgb
• wt 0 for MgII and CaII resonance
  lines

ilogg cube (DT x DL x DZ)
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The most important stars for the UV-blue spectrum
have Teff5000-8000 K, log g 3.8-4.5
Flux Contributions to stellar population at 6
Gyr, Fe/H0
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Mid-UV colors are good distinguishers of
metallicity among MSTO stars having similar
line spectra
2500 2600 2700
2800 2900 3000
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BC03 Predictions
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Even fine spectral analyses have their
uncertainties! (1)
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Even fine spectral analyses have their
uncertainties! (2)
Valenti Fischer 2005
Log gSME iso log g 0.1
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MSTO stars can have the same Teff and log g but
very different ages if they have different
metallicities
log g
Teff
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MSTO
MSTO
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0.1 0.3 1 3 10 Gyr
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