UV and FIR properties of galaxies from
combined GALEX-IRAS data
Jorge Iglesias Páramo
V. Buat
T. Takeuchi
K. Xu
& the GALEX team
Motivation
To understand the differential properties
observational biases of UV and FIR selections.
●
and
To consistently calibrate physical quantities estimated
from the samples.
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To provide observables for models of statistical
properties of galaxies.
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The data
NUV selected sample: from GALEX AIS (615 deg2).
● m
NUV < 16 ABmag
● FIR counterparts from IRAS FSC (SCANPI)
● Detection at 60µm of all galaxies with A
NUV > 0.3 mag
94 galaxies
FIR selected sample: from IRAS PSCz (509 deg2).
● f
60 > 0.6 Jy
● UV counterparts from GALEX AIS
● Detection at NUV of all galaxies with A
NUV < 4.4 mag
163 galaxies
log F60 (erg s-1 cm-2)
FNUV vs. F60µm
GALEX AIS
mNUV=16
IRAS PSCz
IRAS FSC
log FNUV (erg s-1 cm-2)
The FIR selected sample is drawn from a larger
volume than the NUV selected one.
Vel. (km s-1)
Representativity of the Samples
Wyder et al. (2005)
Takeuchi et al. (2003)
log LNUV (Lsun)
UV and FIR luminosities
log L60 (Lsun)
In order to improve the quality of the FIR/UV flux
association some objets of both samples were
discarded...
IRAS 60µ
NUV
NVSS
Also discarded for the FIR/UV analysis:
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Ellipticals and S0s
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AGNs
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Galaxies for which Cirrus > 2
Finally we end up with:
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NUV selected subsample: 62 galaxies
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FIR selected subsample: 118 galaxies
Dust attenuation
ANUV directly from FFIR/FNUV (Buat et al. 2005)
〈ANUV〉 ~ 0.8 mag
〈ANUV〉 ~ 2.1 mag
ANUV (mag)
No such relation
is observed for
the FIR selected
galaxies.
ANUV (mag)
ANUV
correlated
with LH for NUV
selected galaxies.
log LH (Lsun)
Star Formation Rates
Comparison between SFRNUV and SFRdust
Scenario:
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Constant SFR over the last 108 yr
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Salpeter IMF with 0.1M⊙ < M✮ < 100M⊙
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Solar metallicity
From Starburst99:
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log SFRNUV (M⊙ yr-1) = log LNUV,corr (L⊙) – 9.33
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log SFRdust (M⊙ yr-1) = log Ldust (L⊙) - 9.75
SFRNUV vs. SFRdust
log SFRdust (Msun yr-1)
Quite good agreement on average but...
log SFRNUV (Msun yr-1)
Two different trends are observed:
At low values of ANUV,
the
dust
emission
underestimates
the
total SFR because of
the non negligible NUV
emission.
At high values of ANUV,
the
NUV
emission
underestimates
the
total SFR.
Problem with ANUV?
●
log SFRNUV/SFRdust
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log SFRNUV (Msun yr-1)
Star Formation Activity: F60µm/F100µm
log F60/F100
Birthrate parameter
Following Boselli et
al. (2001):
b = SFR0/〈SFR〉
b ∝ SFRNUV/LH
We obtain values
typical of Sb - Sbc
galaxies (Kennicutt
et al. 1994).
log b
Fdust/FFUV vs. β
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.
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Starbursts
beta
Fdust/FFUV vs. β
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).
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Starbursts
beta
SFR per unit area
log SFRNUV/Area (Msun yr-1 kpc-2)
Lower than local starbursts for both samples.
Meurer et al. (1999)
log SFRNUV (Msun yr-1)
log SFRNUV/SFRdust
The SFRNUV vs. SFRdust discrepancy is mainly related to
the star formation activity.
log SFRNUV/Area (Msun yr-1 kpc-2)
Starburst
Normal SF
UV Structural Properties
Concentration index: 5 × log r80/r20
Concentration index
No obvious correlation between concentration index and
morphological type.
Different morphological patterns...
UV Bright Galaxies
We find 8 galaxies with LFUV ≥ 2 × 1010 L⊙, all of them
FIR selected and 3 also NUV selected.
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Redshift range: z < 0.10
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Co-moving spatial density: ~ 5.3 ± 3.1 × 10-6 Mpc-3
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Dust attenuation: 1.3 < AFUV < 3.5 mag
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Low surface brightness: ∑FUV < 1.32 × 108 L⊙ kpc-2
For all of them: L60µm > LFUV
objects!
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⇒ Very luminous