Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aspc..375...34y&link_type=abstract
From Z-Machines to ALMA: (Sub)Millimeter Spectroscopy of Galaxies ASP Conference Series, Vol. 375, proceedings of the conference
Astronomy and Astrophysics
Astronomy
Scientific paper
I discuss Spitzer GO programs aimed at studying the mid-IR spectral properties of IR-luminous galaxies at high z. I present the IRS low-resolution, mid-IR spectra of a sample of 52 sources from our GO1 medium size program. We found that ˜ 75% of the sample are at z ˜ 1.5 - 2.6, with redshifts determined based on features including PAH emission and silicate absorption in the mid-IR spectra. This dataset revealed the first direct evidence that PAH features are already a significant component of a dusty galaxy's spectrum as early as z=2. Among the 52 targets, one third are starbursts at z˜2 with strong PAH emission, and two thirds are AGN-dominated systems with strong silicate absorption and weak or no PAH emission. The bulk of the sample are dusty, infrared-luminous galaxies at z ˜ 1-3 with estimated Lbol ˜ 1013 L_&sun;. At such a high luminosity, a significant fraction of our sample have dust-obscured, strong AGN components. I will discuss the implication for 24 μm-selected, 1 mJy or brighter samples. I also present the ground-based near-IR/optical spectroscopy and 1.2 mm continuum followup observations of this sample. The Keck spectroscopic redshifts confirm the redshift measurements based on the mid-IR spectra. Since half of our sample are optically faint sources with R ≥ 25.5 mag (Vega), our results demonstrate the potential of using mid-infrared spectroscopy, especially the aromatic and silicate features produced by dust grains, to directly probe optically faint and infrared-luminous populations at high redshift.
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