1. A Mid-infrared Spectroscopic Study of LINERS
Rachel Dudik
Now I am going to tell you about some of the mid-infrared observations of LINERS from the ISO short wavelength spectrometer (SWS) that I have been working on for the past few weeks. This work is not completed and represents just some preliminary results.

2. Why Mid-Infrared?
Low extinction in the infrared – can find buried (highly obscured) AGN that are not seen in the optical
Presence of high excitation lines – AGN Diagnostics
Why study LINERs in the mid-infrared?
First of all, many galaxies contain lots of dust that obscures the light at optical and ultraviolet wavelengths. Therefore, deeply buried AGNs may not be seen at these wavelengths. Infrared light, however, can penetrate through the obscuring material.
Secondly, there exists many spectral lines in the mid-infrared from very highly ionized atoms. This can be a very powerful AGN diagnostic

3. Spectral Lines from Ions with a wide range of Ionization Potentials
Lines from Highly Ionized Ions:
Here is an example of some of the spectral lines from such highly ionized atoms. Listed (column 1) is the ion, the transition (point to column 2), the wavelength of the spectral line (column 3) and the ionization potential required to create the ion listed. As you can see, the ionization potential can be as high as about 350 electron volts.

4. Lines from Ions with lower Ionization Potentials:
In addition, there are spectral lines from lower ionization potentials such as [Ar II] which requires only about 28 electron volts.

5. Cooler Stars
How can these lines be used to determine the presence of an AGN?
Stars emit basically like blackbodies. The hottest can be up to 50,000 K. Show here is the Planck curve for such a star. As stars get cooler they emit less of their light at shorter wavelengths (click) In order to ionize some of the highly ionized atoms shown in the previous table,(click—such as SiIX) we need photons with energy in the soft x-rays (shown above). As you can see, even the hottest stars don’t produce enough high energy photons to ionize the atoms to the level of ionization shown in the previous table.
350 eV

6. Even the hottest stars do not produce light with high enough energy to ionize the atoms to the highest ionization levels shown in table 1!!!
AGN??
This suggests the presences of something capable of producing lots of high energy photons such as an AGN.

7. An Example of a High Excitation Line in M51
Here is an example of a high ionization line detected in the galaxy M51 suggesting the possible presence of an AGN

8. Of the ~500 LINERs, 28 were studied by the SWS
Of these, I have looked at 14 so far. These are the results
Of the 500 LINERs, 28 were studied by SWS. Of these I have looked at 14 so far. These are the results. The yellow cells are galaxies viewed by both Chandra and ISO and John will talk about those results. As you can see five high ionization lines were detected as well as many other ions with lower ionization potentials.

9. Conclusions: I found high ionization lines in 5 galaxies so far
Will reduce the data on the remaining galaxies
Will model the detected lines to infer the properties of the potential AGNs
I will eventually model the data for all of the galaxies to infer the properties of the potential AGNs.