Dean C. Hines

We present ATCA interferometric observations of the old (13 Myr), nearby (86pc) classical T Tauri star, PDS 66. Unresolved 3 and 12 mm continuum emission is detected towards PDS 66, and upper limits are derived for the 3 and 6 cm flux densities. The mm-wave data show a spectral slope flatter than that expected for ISM-sized dust particles, which is evidence of grain growth. We also present HST/NICMOS 1.1 micron PSF-subtracted coronagraphic imaging of PDS 66. The HST observations reveal a bilaterally symmetric circumstellar region of dust scattering about 0.32% of the central starlight, declining radially in surface brightness. The light-scattering disk of material is inclined 32 degrees from face-on, and extends to a radius of 170 AU. These data are combined with published optical and longer wavelength observations to make qualitative comparisons between the median Taurus and PDS 66 spectral energy distributions (SEDs). By comparing the near-infrared emission to a simple model, we determine that the location of the inner disk radius is consistent with the dust sublimation radius (1400 K at 0.1 AU). We place constraints on the total disk mass using a flat-disk model and find that it is probably too low to form gas giant planets according to current models. Despite the fact that PDS 66 is much older than a typical classical T Tauri star (< 5 Myr), its physical properties are not much different.

We have determined the mineralogical composition of dust in the Broad Absorption Line (BAL) quasar PG 2112+059 using mid-infrared spectroscopy obtained with the Spitzer Space Telescope. From spectral fitting of the solid state features, we find evidence for Mg-rich amorphous silicates with olivine stoichiometry, as well as the first detection of corundum (Al_2O_3) and periclase (MgO) in quasars. This mixed composition provides the first direct evidence for a clumpy density structure of the grain forming region. The silicates in total encompass 56.5% of the identified dust mass, while corundum takes up 38 wt.%. Depending on the choice of continuum, a range of mass fractions is observed for periclase ranging from 2.7% in the most conservative case to 9% in a less constrained continuum. In addition, we identify a feature at 11.2 micron as the crystalline silicate forsterite, with only a minor contribution from polycyclic aromatic hydrocarbons. The 5% crystalline silicate fraction requires high temperatures such as those found in the immediate quasar environment in order to counteract rapid destruction from cosmic rays.

We present the stellar calibrator sample and the conversion from instrumental to physical units for the 24 μm channel of the Multiband Imaging Photometer for Spitzer (MIPS). The primary calibrators are A stars, and the calibration factor based on those stars is 4.54 × 10^-2 MJy sr⁻¹ (DN s⁻¹)⁻¹, with a nominal uncertainty of 2%. We discuss the data reduction procedures required to attain this accuracy; without these procedures, the calibration factor obtained using the automated pipeline at the Spitzer Science Center is 1.6% ± 0.6% lower. We extend this work to predict 24 μm flux densities for a sample of 238 stars that covers a larger range of flux densities and spectral types. We present a total of 348 measurements of 141 stars at 24 μm. This sample covers a factor of ~460 in 24 μm flux density, from 8.6 mJy up to 4.0 Jy. We show that the calibration is linear over that range with respect to target flux and background level. The calibration is based on observations made using 3 s exposures; a preliminary analysis shows that the calibration factor may be 1% and 2% lower for 10 and 30 s exposures, respectively. We also demonstrate that the calibration is very stable: over the course of the mission, repeated measurements of our routine calibrator, HD 159330, show a rms scatter of only 0.4%. Finally, we show that the point‐spread function (PSF) is well measured and allows us to calibrate extended sources accurately; Infrared Astronomy Satellite (IRAS) and MIPS measurements of a sample of nearby galaxies are identical within the uncertainties.

We report MIPS photometry of 20 radio-loud quasars and galaxies at 24 and 70 μm (and of five at 160 μm). We combine this sample with additional sources detected in the far-infrared by IRAS and ISO for a total of 47 objects, including 23 steep-spectrum type I AGNs: radio-loud quasars and broad-line radio galaxies; and 24 type II AGNs: narrow-line and weak-line FR II radio galaxies. Of this sample, the far-infrared emission of all but 3C 380 appears to be dominated by emission by dust heated by the AGN and by star formation. The AGN appears to contribute more than 50% of the far-infrared luminosity in most of the sources. It is also expected that the material around the nucleus is optically thin in the far-infrared. Thus, the measurements at these wavelengths can be used to test the orientation-dependent unification model. As predicted by the model, the behavior of the sources is consistent with the presence of an obscuring circumnuclear torus; in fact, we find that it may still have significant optical depth at 24 μm. In addition, as expected for the radio-loud quasars, there is a significant correlation between the low-frequency radio (178 MHz) and the 70 μm emission, two presumably isotropic indicators of nuclear activity. This result is consistent with the simple unified scheme. However, there is a population of radio galaxies that are underluminous at 70 μm compared with the radio-loud quasars and hence are a challenge to the simple unified model.

We examine the 24 μm 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^-15 ergs s^-1 cm^-2. A deep 24 μm mosaic obtained with Spitzer provides mid-infrared fluxes for the sample. Since obscured AGNs locally have higher 24 μm/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 μm 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 μm 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 μm to X-ray flux ratios.

We present preliminary results on 24 μm detections of luminous infrared galaxies at z 1 with the Multiband Imaging Photometer for Spitzer (MIPS). Observations were performed in the Lockman Hole and the Extended Groth Strip (EGS) and were supplemented by data obtained with the Infrared Array Camera (IRAC) between 3 and 9 μm. The positional accuracy of 2'' for most MIPS/IRAC detections provides unambiguous identifications of their optical counterparts. Using spectroscopic redshifts from the Deep Extragalactic Evolutionary Probe survey, we identify 24 μm sources at z 1 in the EGS, while the combination of the MIPS/IRAC observations with BVRIJHK ancillary data in the Lockman Hole also shows very clear cases of galaxies with photometric redshifts at 1 z 2.5. The observed 24 μm fluxes indicate infrared luminosities greater than 10¹¹ L_⊙, while the data at shorter wavelengths reveal rather red and probably massive ( *) galaxy counterparts. It is the first time that this population of luminous objects is detected up to z ~ 2.5 in the infrared. Our work demonstrates the ability of the MIPS instrument to probe the dusty universe at very high redshift and illustrates how the forthcoming Spitzer deep surveys will offer a unique opportunity to illuminate a dark side of cosmic history not explored by previous infrared experiments.

We present observations of the spiral galaxy M33 with Spitzer at 24, 70, and 160 μm. The excellent resolution and mapping capabilities of Spitzer combined with the proximity of M33 result in observations that enable a detailed study of the distribution of star formation (SF) and dust in the galaxy. We compare the morphology of M33 at far-infrared wavelengths with other standard SF indicators such as Hα and radio continuum using a Fourier filtering technique to separate the diffuse emission components from compact sources. We find that the infrared emission at 24 and 70 μm follows closely the structure of the ionized gas, indicating that it is heated largely by hot, ionizing stars. At 160 μm a diffuse cold dust component matches only approximately the structure of the old red stellar population or the distribution of blue light. It is, however, very similar to the structure of the diffuse nonthermal radio emission.

We present Spitzer observations of the young cluster NGC 2547, obtaining photometry at 3.6, 4.5, 5.8, 8.0, and 24 μm, reaching significantly fainter infrared sensitivities than previous studies. With these observations, we investigate the disk frequency in this cluster. A total of 3770, 2408, 1988, 1238, and 1123 sources were detected in the common region of the five respective bands. The detection limits were 14.9, 14.0, 13.5, 13.3, and 12.0 mag, respectively. The large majority of sources are associated with 2MASS objects. From this large ensemble, we utilize the criteria of Naylor et al. to identify 184 likely members of the cluster. The analyses in this paper are focused on these likely members. Of the 184 candidates, 162 were detected in at least one Infrared Array Camera (IRAC) band. These objects form a well-defined family in the J-K,K-[3.6] color-color diagram. There is no evidence for excess emission at 3.6 μm for cluster candidates with J-K < 0.8, corresponding to spectral types earlier than late K. For later type stars, only 12 have evidence for a 3.6 μm excess. Hence, we derive a 3.6 μm emitting disk fraction of less than 7%. The lack of excess for the more massive stars may indicate a difference in the disk dissipation timescales for different mass stars. At 24 μm, 32 of the sources are detected. Most of them have photospheric K-[3.6] and K-[24] colors, but approximately a quarter show an excess at 24 μm. This observation may be evidence for cool disks with central holes.

We present submillimeter statistical detections of galaxies discovered in the 5^' × 5^' Spitzer Early Release Observations (to ~4-15 μJy 5 σ at 3.6-8 μm, 170 μJy at 24 μm) through a stacking analysis of our reanalyzed SCUBA 8 mJy survey maps and a Spitzer identification of a new submillimeter point source in the 8 mJy survey region. For sources detected at 5.8 or 8 μm (154 and 111 sources, respectively), we detect positive skews in the submillimeter flux distributions at 99.2%-99.8% confidence using Kolmogorov-Smirnov tests, at both 850 and 450 μm. We also marginally detect the Spitzer 24 μm galaxies at 850 μm at 97% confidence and place limits on the mean submillimeter fluxes of the 3.6 and 4.5 μm sources. Integrating the submillimeter fluxes of the Spitzer populations, we find the 5.8 μm galaxies contribute 0.12 ± 0.05 nW m^-2 sr^-1 to the 850 μm background and 2.4 ± 0.7 nW m^-2 sr^-1 to the 450 μm background; similar contributions are made by the 8 μm-selected sample. We infer that the populations dominating the 5.8 and 8 μm extragalactic background light also contribute around a quarter of the 850 μm background and the majority of the 450 μm background.