Download Extended Infrared Emission from LIRGs

Extended IR Emission from LIRGs
V. Charmandaris, T. Diaz-Santos, (Univ. of Crete)
L. Armus & A. Petric (SSC/Caltech)
Motivation
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A number of the observational properties of SMGs such as:
 cold infrared colors
 energy production dominated by star formation ( > 100 Msun/yr)
 mid-IR spectral features (ie PAH strength)
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… resemble those of local LIRGs rather than ULIRGs.
Kinematical evidence from ionized (Hα) and molecular (CO) gas are
consistent the presence of extended (~5kpc) star forming disks
There is a “broad” connection between mid-IR emission and star
formation rates (with some caveats…)
We wish to quantify the extended extranuclear emission in local LIRGs
in the 5-15μm range to contribute additional evidence in the analogy
between the physics of the ISM excitation in LIRGs and the conditions
seen in SMGs at z>1.
Heidelberg - 23 Feb 2010
The Sample
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The Sample is drawn from the Great Observatory Allsky LIRG Survey
(GOALS; Armus et al. 2009) of 202 systems (181 of which are LIRGs)
All systems are observed with all four Spitzer/IRS modules (5-37μm)
Apply an upper limit on distance (<85 Mpc) in order for the IRS slit size
to correspond to a projected distance < 1.5kpc (best case is 0.26kpc)
A total of 93 galaxies are selected.
Heidelberg - 23 Feb 2010
The Method
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Use the 2D images of all LIRGs and re-extract total 5-15μm spectrum
using the SSC pipeline algorithms
Use a standard star (HR7341) as our unresolved point source (PSF)
Scale the spatial profile of the standard star along the slit at every
wavelength and subtract it from the corresponding profile of each
source.
Define as fraction of Extended Emission (EE):
Total LIRG flux (λ) - PSF (λ)
Fraction of EE (λ) =
Total LIRG flux (λ)
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Heidelberg - 23 Feb 2010
Extended Emission Fraction Type (1)
Follow the green curve…
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No Extended Emission
Heidelberg - 23 Feb 2010
Extended Emission Fraction Type (2)
Follow the green curve…
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Constant Extended Emission
Heidelberg - 23 Feb 2010
Extended Emission Fraction Type (3)
PAHs
Wavelength Depended
Extended Emission
[ArII]
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Heidelberg - 23 Feb 2010
Mean Fraction of mid-IR Extended Emission
 For 90% of the
sample, at least 20%
of the mid-IR flux is
extended
 For more than 35%
of the sample, the EE
fraction is larger than
0.5 (= 50%)
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Heidelberg - 23 Feb 2010
Fraction of mid-IR Extended Emission
 LIRGs with EE
fractions larger than
0.5 are detected up to
80 Mpc!
 The EE fraction is
not correlated with
the IR luminosity =>
the most luminous
LIRGS are not
necessarily the most
compact
Limits to identifying a source with
intrinsic EE=0.75 due to distance
VC
Heidelberg - 23 Feb 2010
Are PAHs more extended than [NeII] ? (1)
 “Neutral” PAHs
such as the 11.3μm
are…
… possibly because
they do not require a
strong ionizing
radiation field
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Heidelberg - 23 Feb 2010
Are PAHs more extended than [NeII] ? (2)
 “Ionized” PAHs
such as the 6.2μm
and 7.7μm are not…
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Heidelberg - 23 Feb 2010
AGN dependence of mid-IR Extended Emission
We can calculate the
mid-IR AGN fraction
using the EW of the
6.2μm PAH (Petric et al.
2010)…
We find no obvious
dependence of
Extended Emission on
mid-IR AGN strength
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Heidelberg - 23 Feb 2010
Conclusions / Perspectives
Even though the spatial resultion of IRS is ~3.6arcsecs..
 LIRGs display large fraction of extended mid-IR emission in both continuum
and 5-15μm features
 For at least 90% of the sample more than 20% of the mid-IR flux originates
outside the nuclear unresolved region.
 For at least 35% of the sample more than 50% of the mid-IR flux is
extranuclear (possibly also their star formation?)
 The extended emission varies as a function of wavelength.
 The 11.3μm PAH displays the larger extended emission, consistent with it
being a “neutral” PAH.
 No clear correlation between
classification nor IR luminosity
 To do:
extended
emission
and
mid-IR
AGN
- Explore the correlations with merging stage
- Increase the range of IR luminosity to include some ULIRGs.
VC
Heidelberg - 23 Feb 2010