Prof. Dimitra Rigopoulou

Abstract:

A Spitzer Space Telescope survey in the NOAO Deep Wide Field in Bootes provides a complete, 8 μm-selected sample of galaxies to a limiting (Vega) magnitude of 13.5. In the 6.88 deg2 field sampled, 79% of the 4867 galaxies have spectroscopic redshifts, allowing an accurate determination of the local (z < 0.3) galaxy luminosity function. Stellar and dust emission can be separated on the basis of observed galaxy colors. Dust emission (mostly PAH) accounts for 80% of the 8 μm luminosity, stellar photospheres account for 19%, and AGN emission accounts for roughly 1%. A subsample of the 8 μm-selected galaxies have blue, early-type colors, but even most of these have significant PAH emission. The luminosity functions for the total 8 μm luminosity and for the dust emission alone are both well fit by Schechter functions. For the 8 μm luminosity function, the characteristic luminosity is νLν*;(8.0 μm) = 1.8 × 1010 L ⊙, while for the dust emission alone it is 1.6 × 10 10 L⊙. The average 8 μm luminosity density at z < 0.3 is 3.1 × 107 L⊙ Mpc-3, and the average luminosity density from dust alone is 2.5 × 107 L⊙ Mpc-3. This luminosity arises predominantly from galaxies with 8 μm luminosities (νLν) between 2 × 109 and 2 × 1010 L⊙, i.e., normal galaxies, not luminous or ultraluminous infrared galaxies (LIRGs/ULIRGs). © 2007. The American Astronomical Society. All rights reserved.

Abstract:

We study 87 extremely red objects (EROs), selected both to have color redder than R - [3.6] = 4.0 and to have confirmed spectroscopic redshifts. Together, these two constraints result in this sample populating a fairly narrow redshift range at 0.76 < z < 1.42. The key new ingredient included here is deep Spitzer Space Telescope Infrared Array Camera (IRAC) data. Based on [3.6] - [8.0] color, we demonstrate that it is possible to classify EROs as early-type galaxies, dusty starburst galaxies, or active galactic nuclei (AGNs; power-law types). We present ultraviolet-to-mid-infrared spectral energy distributions (SEDs) and Advanced Camera for Surveys (ACS) images, both of which support our simple IRAC color classification. © 2007. The American Astronomical Society. All rights reserved.

Abstract:

We report the detection of rest-frame 6.2 and 7.7 μm emission features arising from polycyclic aromatic hydrocarbons (PAHs) in the Spitzer IRS spectrum of an infrared-luminous Lyman break galaxy at z = 3.01. This is currently the highest redshift galaxy where these PAH emission features have been detected. The total IR luminosity inferred from the MIPS 24 μm and radio flux density is 2 × 1013 L⊙, which qualifies this object as a so-called hyperluminous infrared galaxy (HyLIRG). However, unlike local HyLIRGs, which are generally associated with QSO/AGNs and have weak or absent PAH emission features, this HyLIRG has very strong 6.2 and 7.7 μm PAH emission. We argue that intense star formation dominates the IR emission of this source, although we cannot rule out the presence of a deeply obscured AGN. This LBG appears to be a distorted system in the HST ACS F606W and F814W images, possibly indicating that a significant merger or interaction is driving the large IR luminosity. © 2007. The American Astronomical Society. All rights reserved.