Extended ir emission from lirgs
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Extended IR Emission from LIRGs. V. Charmandaris, T. Diaz-Santos, (Univ. of Crete) L. Armus & A. Petric (SSC/Caltech). Motivation. A number of the observational properties of SMGs such as: cold infrared colors energy production dominated by star formation ( > 100 Msun/yr)

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Extended IR Emission from LIRGs

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Extended ir emission from lirgs

Extended IR Emission from LIRGs

V. Charmandaris, T. Diaz-Santos, (Univ. of Crete)

L. Armus & A. Petric (SSC/Caltech)


Motivation

Motivation

  • 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)

      … 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.


The sample

The Sample

  • 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.


The method

  • 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)

The Method


Extended emission fraction type 1

Extended Emission Fraction Type (1)

Follow the green curve…

No Extended Emission


Extended emission fraction type 2

Extended Emission Fraction Type (2)

Constant Extended Emission

Follow the green curve…


Extended emission fraction type 3

PAHs

[ArII]

Extended Emission Fraction Type (3)

Wavelength Depended

Extended Emission


Mean fraction of mid ir extended emission

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%)


Fraction of mid ir extended emission

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


Are pahs more extended than neii 1

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


Are pahs more extended than neii 2

Are PAHs more extended than [NeII] ? (2)

  • “Ionized” PAHs such as the 6.2μm and 7.7μm are not…


Agn dependence of mid ir extended emission

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


Conclusions perspectives

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 extended emission and mid-IR AGN classification nor IR luminosity

  • To do: - Explore the correlations with merging stage

    - Increase the range of IR luminosity to include some ULIRGs.


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