Diapositiva 1

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UV and FIR properties of galaxies from combined
GALEX-IRAS data
Jorge Iglesias Páramo V. Buat T. Takeuchi K. Xu
the GALEX team
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Motivation

• To understand the differential properties and
  observational biases of UV and FIR selections.

• To consistently calibrate physical quantities
  estimated from the samples.

• To provide observables for models of statistical
  properties of galaxies.

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The data

• NUV selected sample from GALEX AIS (615 deg2).
• mNUV lt 16 ABmag
• FIR counterparts from IRAS FSC (SCANPI)
• Detection at 60µm of all galaxies with ANUV gt
  0.3 mag
• 94 galaxies

• FIR selected sample from IRAS PSCz (509 deg2).
• f60 gt 0.6 Jy
• UV counterparts from GALEX AIS
• Detection at NUV of all galaxies with ANUV lt 4.4
  mag
• 163 galaxies

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FNUV vs. F60µm
log F60 (erg s-1 cm-2)
log FNUV (erg s-1 cm-2)
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The FIR selected sample is drawn from a larger
volume than the NUV selected one.
Vel. (km s-1)
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Representativity of the Samples
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L60µm vs. Redshift
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LNUV vs. Redshift
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UV and FIR luminosities
log LNUV (Lsun)
log L60 (Lsun)
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In order to improve the quality of the FIR/UV
flux association some objets of both samples were
discarded...
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• Also discarded for the FIR/UV analysis
• Ellipticals and S0s
• AGNs
• Galaxies for which Cirrus gt 2

• Finally we end up with
• NUV selected subsample 62 galaxies
• FIR selected subsample 118 galaxies

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Dust attenuation
ANUV directly from FFIR/FNUV (Buat et al. 2005)
ltANUVgt 0.8 mag ltANUVgt 2.1 mag
ANUV (mag)
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ANUV correlated with LH for NUV selected galaxies.
ANUV (mag)
No such relation is observed for the FIR selected
galaxies.
log LH (Lsun)
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Star Formation Rates
Comparison between SFRNUV and SFRdust

• Scenario
• Constant SFR over the last 108 yr
• Salpeter IMF with 0.1M? lt M? lt 100M?
• Solar metallicity

• From Starburst99
• log SFRNUV (M? yr-1) log LNUV,corr (L?) 9.33
• log SFRdust (M? yr-1) log Ldust (L?) - 9.75

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SFRNUV vs. SFRdust
Quite good agreement on average but...
log SFRdust (Msun yr-1)
log SFRNUV (Msun yr-1)
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Two different trends are observed

• At low values of ANUV, the dust emission
  underestimates the total SFR because of the non
  negligible NUV emission.

log SFRNUV/SFRdust

• At high values of ANUV, the NUV emission
  underestimates the total SFR.
• Problem with ANUV?

log SFRNUV (Msun yr-1)
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Star Formation Activity F60µm/F100µm
log F60/F100
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Birthrate parameter
Following Boselli et al. (2001) b ? SFRNUV/LH
b SFR0/ltSFRgt
We obtain values typical of Sb - Sbc galaxies
(Kennicutt et al. 1994).
log b
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Fdust/FFUV vs. ß

• To the left of the starburst sequence of Meurer
  et al. (1995).

log Fdust/FFUV

• The distance to the sequence is not related to
  the birthrate parameter.

beta
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Fdust/FFUV vs. ß

• Some of them follow the same trend as the NUV
  selected.

log Fdust/FFUV

• The rest, to the left of the starburst sequence,
  below the ULIRGS of (Goldader et al. 2002).

beta
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SFR per unit area
Lower than local starbursts for both samples.
log SFRNUV/Area (Msun yr-1 kpc-2)
log SFRNUV (Msun yr-1)
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The SFRNUV vs. SFRdust discrepancy is mainly
related to the star formation activity.
log SFRNUV/SFRdust
log SFRNUV/Area (Msun yr-1 kpc-2)
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UV Structural Properties
Concentration index 5 log r80/r20
Concentration index
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No obvious correlation between concentration
index and morphological type.
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Different morphological patterns...
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UV Bright Galaxies

• We find 8 galaxies with LFUV 2 1010 L?, all
  of them FIR selected and 3 also NUV selected.

• Redshift range z lt 0.10

• Co-moving spatial density 5.3 3.1 10-6
  Mpc-3

• Dust attenuation 1.3 lt AFUV lt 3.5 mag

• Low surface brightness ?FUV lt 1.32 108 L?
  kpc-2

• For all of them L60µm gt LFUV ? Very luminous
  objects!