Relating the host galaxies of type-2 quasars to their infrared properties

One small change from Phase 1 - we'd like to observe target SST171831.6+595317 through F775W and F555W instead of F775W and F475W to better match the rest-wavelengths of the observations of the other targets. There are orientation constraints on some targets to avoid bleeding and ghosts from bright field stars. ----- Submission 1 (Fri May 12 18:19:13 GMT 2006) ----- Assigned ID: 348 ----- Submission 1 (Fri Jan 27 19:29:33 GMT 2006) ----- Relating the host galaxies of type-2 quasars to their infrared properties The obscured quasar population has been found to consist of a wide variety of objects. In this proposal, we wish to study the host galaxies of six z~0.6 type-2 quasars selected via their mid-infrared emission. Infrared spectra and photometry of these objects show that they include both actively star-forming and non-starforming galaxies, and have dust columns to the AGN ranging from moderate to high. We will relate the host galaxy properties to the infrared properties of these type-2 quasars, and to the host galaxies of type-1 quasars of similar redshift and bolometric luminosity. These observations will thus help us to understand how the different types of obscured quasars are related to each other, and to the normal quasar population.

The hosts of our type-2 quasars have i-magnitudes ranging from 18.7-20.7. Most of our imaging will be performed through the F775W and F475W filters (SDSS i and g), sampling each object either side of the 4000A break in the rest frame. For our two highest-redshift objects we will use F814W and F555W, both to keep the rest-wavelength approximately the same, and to help compensate for cosmological surface brightness dimming by using wider bandpasses. Our lowest-redshift object will be observed through F625W and F435W. In some cases our filters will include emission lines such as [OII]3727 and [OIII]5007, however, AGN-powered extended emission line nebulae on scales of kpc are rare in radio-quiet quasars, and we can include any contributions from low equivalent width [OII] and [OIII] emission from star formation in our spectral modeling. For our faintest, highest redshift host galaxies, we want to ensure a high enough signal-to-noise to be able to detect faint features and measure an accurate host galaxy magnitude. The i=20.7 magnitude host galaxy of our most distant quasar-2, if it has an effective radius or 0.5'' (i.e. ~5kpc), will have a surface brightness of approx 23 mag/arcsec^2 at a radius of 0.5''. Using the ACS ETC, we can achieve a 6-sigma detection of this in a 2x2-pixel box in 4x500s of integration through the F814W filter, so a single orbit will suffice to obtain sufficiently deep, well-dithered data. The type-2 host galaxies to be observed through the F775W filter are at least 0.5 mag brighter, so will have similar or better signal-to-noise despite the smaller filter bandwidth. Because of the approx 4x increased sensitivity of the ACS WFC compared to WFPC2, we can achieve similar rest-frame surface brightness limits as, e.g., Dunlop et al. (2003) in their study of z~0.3 quasar hosts for our <z_med>=0.6 sample, despite cosmological surface brightness dimming. We therefore expect to be similarly-sensitive to low surface brightness tidal features and other evidence galaxy interactions. In the shorter wavelength band, our worst case is a g=21.9 host galaxy observed through F475W, but even here we will be able to obtain a 3-sigma detection 0.5'' from the nucleus in a 2x2-pixel box in 4x500s of integration assuming the same host galaxy scale size, so again one orbit per object should suffice in the short wavelength filter. With the resolution of ACS, we will be probing kpc-scale structures in the host galaxies. If, as expected, our host galaxies show star-forming knots and other discrete features, such as secondary nuclei, these will be even easier to detect than the diffuse stellar light of the older stellar population. AGN/QUASARS 12 false 0.0 false false false false false SUPPORTED GALAXY QSO J2000 17 11 6.8500 +59 04 36.50 J2000 GALAXY QSO J2000 17 11 47.4000 +58 58 39.50 J2000 GALAXY QSO J2000 17 13 24.3000 +58 55 49.50 J2000 GALAXY QSO J2000 17 18 31.6000 +59 53 17.00 J2000 GALAXY QSO J2000 17 21 23.1000 +60 12 14.50 J2000 GALAXY QSO J2000 17 24 58.3000 +59 15 45.50 J2000 ACS/WFC Imaging No No F775W ACS/WFC Imaging No No F475W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F555W ACS/WFC Imaging No No F775W ACS/WFC Imaging No No F475W ACS/WFC Imaging No No F775W ACS/WFC Imaging No No F475W ACS/WFC Imaging No No F625W ACS/WFC Imaging No No F435W ACS/WFC Imaging No No F775W ACS/WFC Imaging No No F475W POS-TARG DITHER 0.265 LINE 0.187 false false 69.05 4 20.67 ACS-WFC-DITHER-BOX 1

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