No abstract

We present observations of the star formation region NGC 7129 taken with the Multiband Imaging Photometer for Spitzer (MIPS). A significant population of sources, likely pre-main sequence members of the young stellar cluster, is revealed outside the central photoionization region. Combining with Infrared Array Camera (IRAC) and ground-based near-infrared images, we have obtained colors and spectral energy distributions for some 60 objects. The [3.6]-[4.5] vs.[8]- [24] color-color plane shows sources clustered at several different loci, which roughly correspond to the archetypal evolutionary sequence Class 0, I, II, and III. We obtain preliminary classifications for 36 objects, and find significant numbers of both Class I and II objects. Most of the pre-main sequence candidates are associated with the densest part of the molecular cloud surrounding the photoionization region, indicating active star formation over a broad area outside the central cluster. We discuss three Class II candidates that exhibit evidence of inner disk clearing, which would be some of the youngest known examples of a transition from accretion to optically thin quiescent disks.

We present Spitzer observations in five wavebands between 3.6 and 24 µm of an unbiased sample of nine luminous, dusty galaxies selected at 1200 µm by the MAMBO camera on the IRAM 30-m telescope, a population akin to the wellknown submillimeter (submm) or 'SCUBA' galaxies (hereafter SMGs). Owing to the coarse resolution of submm/mm instrumentation, SMGs have traditionally been difficult to identify at other wavelengths. We compare our multi-wavelength catalogs to show that the overlap between 24 and 1200 µm must be close to complete at these flux levels. We find that all (4/4) of the most secure ≥4σ SMGs have robust ≥4σ counterparts at 1.4 GHz, while the fraction drops to 7/9 using all ≥3σ SMGs. We show that combining mid-infrared (mid-IR) and marginal (≥3σ) radio detections provides plausible identifications in the remaining cases,

We use the source counts measured with the Multiband Imaging Photometer for Spitzer (MIPS) at 24, 70, and 160 µm to determine the 5-σ confusion limits due to extragalactic sources: 56µJy, 3.2 and 40 mJy at 24, 70 and 160 µm, respectively. We also make predictions for confusion limits for a number of proposed far infrared missions of larger aperture (3.5 to 10m diameter).

We examine the 24 m to X-ray color of 157 X-ray-selected active galactic nuclei (AGNs) as a function of X-ray obscuration and optical classification in the Chandra Deep Field-South. The sample consists of the Chandra hard-band detections with 2-8 keV flux above 10 À15 ergs s À1 cm À2 . A deep 24 m mosaic obtained with Spitzer provides mid-infrared fluxes for the sample. Since obscured AGNs locally have higher 24 m/2-8 keV flux ratios than unobscured AGNs, and since X-ray background models predict a large population of obscured AGNs, we expect to find many X-ray-hard, IR-bright AGNs. Instead, we find that the 24 m to X-ray flux ratio does not depend on X-ray hardness in the full sample, nor does it differ between narrow-and broad-line AGNs. We identify five nearly Compton-thick AGNs and find they have similar 24 m to X-ray flux ratios compared to the full sample. We consider AGNs in the narrow redshift spikes at z $ 0:7; for these AGNs, there is some evidence that the flux ratio increases with X-ray hardness. The redshift slice also shows an odd trend that is also prominent in the full sample: a group of X-ray-hard AGNs with very low 24 m to X-ray flux ratios.