Terry L. Herter

Observations of Ultraluminous Infrared Galaxies with the Infrared Spectrograph on the Spitzer Space Telescope. II. The IRAS Bright Galaxy Sample

We present spectra taken with the Infrared Spectrograph on Spitzer covering the 5-38 μm region of the 10 ultraluminous infrared galaxies (ULIRGs) found in the IRAS Bright Galaxy Sample (BGS). There is a factor of 50 spread in the rest-frame 5.5-60 μm spectral slopes, and the 9.7 μm silicate optical depths range from at least τ_(9.7) ≤ 0.4 (A_V ~ 8) to τ_(9.7) ≥ 4.2 (A_V ≥ 78). There is evidence for water ice and hydrocarbon absorption and C_2H_2 and HCN absorption features in 4 and possibly 6 of the 10 BGS ULIRGs, indicating shielded molecular clouds and a warm, dense ISM. We have detected [Ne V] emission in 3 of the 10 BGS ULIRGs, at flux levels of 5-18 × 10^(-14) ergs cm^(-2) s^(-1) and [Ne V] 14.3/[Ne II] 12.8 line flux ratios of 0.12-0.85. The remaining BGS ULIRGs have limits on their [Ne V]/[Ne II]line flux ratios, which range from ≤0.15 to ≤0.01. Among the BGS ULIRGs, the AGN fractions implied by either the [Ne V]/[Ne II] or [O IV]/[Ne II] line flux ratios (or their upper limits) are significantly lower than implied by the MIR slope or strength of the 6.2 μm PAH EQW feature. There is evidence for hot (T > 300 K) dust in five of the BGS ULIRGs, with the fraction of hot dust to total dust luminosity ranging from ~1% to 23%, before correcting for extinction. When integrated over the IRAC-8, IRS blue peak-up, and MIPS-24 filter bandpasses, the IRS spectra imply very blue colors for some ULIRGs at z ~ 1.3. The large range in diagnostic parameters among the nearest ULIRGs suggests that matching survey results to a small number of templates may lead to biased results about the fraction of luminous dusty starbursts and AGNs at high z.

A Survey and Analysis of Spitzer Infrared Spectrograph Spectra of T Tauri Stars in Taurus

We present mid-infrared spectra of T Tauri stars in the Taurus star-forming region obtained with the Spitzer Infrared Spectrograph (IRS). For the first time, the 5–36 � m spectra of a large sample of T Tauri stars belonging to the same star-forming region is studied, revealing details of the midinfrared excess due to dust in circumstellar disks. We analyze common features and differences in the mid-IR spectra based on disk structure, dust grain properties, and the presence of companions. Our analysis encompasses spectral energy distributions from the optical to the far-infrared, a morphological sequence based on the IRS spectra, and spectral indices in IRS wave bands representative of continuum emission. By comparing the observed spectra to a grid of accretion disk models, we infer some basic disk properties for our sample of T Tauri stars, and find additional evidence for dust settling. Subject headings: circumstellar matter — planetary systems: protoplanetary disks — stars: pre-main sequence — infrared: stars

Disks in Transition in the Taurus Population: Spitzer IRS Spectra of GM Aurigae and DM Tauri

We present Spitzer Infrared Spectrograph (IRS) observations of two objects of the Taurus population that show unambiguous signs of clearing in their inner disks. In one of the objects, DM Tau, the outer disk is truncated at 3 AU; this object is akin to another recently reported in Taurus, CoKu Tau/4, in that the inner disk region is free of small dust. Unlike CoKu Tau/4, however, this star is still accreting, so optically thin gas should still remain in the inner disk region. The other object, GM Aur, also accreting, has ~0.02 lunar masses of small dust in the inner disk region within ~5 AU, consistent with previous reports. However, the IRS spectrum clearly shows that the optically thick outer disk has an inner truncation at a much larger radius than previously suggested, ~24 AU. These observations provide strong evidence for the presence of gaps in protoplanetary disks.

The i-band tully-fisher relation for cluster galaxies: a template relation, its scatter and bias corrections

Infrared I band photometry and velocity widths for galaxies in 24 clusters, with radial velocities between 1,000 and 10,000 \kms, are used to construct a template Tully--Fisher (TF) relation. The sources of scatter in the TF diagram are analyzed in detail; it is shown that the common practice of referring to a single figure of TF scatter is incorrect and can lead to erroneous bias corrections. Biases resulting from sample incompleteness, catalog inaccuracies, cluster size and other sources, as well as dependences of TF parameters on morphological type and local environment, are discussed and appropriate corrections are obtained. A template TF relation is constructed by combining the data from the 24 clusters, and kinematic cluster offsets from a putative reference frame which well approximates null velocity with respect to the cosmic microwave background, are obtained.

The I band Tully-Fisher relation for cluster galaxies: data presentation.

Observational parameters which can be used for redshift-independent distance determination using the Tully-Fisher (TF) technique are given for 782 spiral galaxies in the fields of 24 clusters or groups. I band photometry for the full sample was either obtained by us or compiled from published literature. Rotational velocities are derived either from 21 cm spectra or optical emission line long--slit spectra, and converted to a homogeneous scale. In addition to presenting the data, a discussion of the various sources of error on TF parameters is introduced, and the criteria for the assignment of membership to each cluster are given. The construction of a TF template, bias corrections and cluster motions are discussed in an accompanying paper.

SPECTROSCOPIC REDSHIFTS TO Z > 2 FOR OPTICALLY OBSCURED SOURCES DISCOVERED WITH THE SPITZER SPACE TELESCOPE

We have surveyed a field covering 9.0 degrees 2 within the NOAO Deep Wide-Field Survey region in Bootes with the Multiband Imaging Photometer on the Spitzer Space Telescope (SST) to a limiting 24 µm flux density of 0.3 mJy. Thirty one sources from this survey with F24 µm > 0.75mJy which are optically very faint (R & 24.5mag) have been observed with the low-resolution modules of the Infrared Spectrograph on SST. Redshifts derived primarily from strong silicate absorption features are reported here for 17 of these sources; 10 of these are optically invisible (R & 26mag), with no counterpart in BW, R, or I. The observed redshifts for 16 sources are 1.7 < z < 2.8. These represent a newly discovered population of highly obscured sources at high redshift with extreme infrared to optical ratios. Using IRS spectra of local galaxies as templates, we find that a majority of the sources have mid-infrared spectral shapes most similar to ultraluminous infrared galaxies powered primarily by AGN. Assuming the same templates also apply at longer wavelengths, bolometric luminosities exceed 10 13 L⊙. Subject headings: dust, extinction — galaxies: high-redshift - infrared: galaxies — galaxies: starburst galaxies: AGN

Infrared spectra of protostars - Composition of the dust shells

Nearly complete 2 to 13 ..mu..m spectra are presented for 13 compact infrared sources associated with molecular clouds, as well as partial spectra of six additional objects. The spectra resemble blackbodies with superposed absorption features from 2.8 to 3.5 ..mu..m, at 6.0 and 6.8 ..mu..m, and in the silicate band centered near 9.7 ..mu..m. Correlations among the features are studied in an attempt to confirm possible identifications. A good correlation between the deepest part of the absorption at 3.1 ..mu..m, its long wavelength wing, and the 6.0 ..mu..m features suggests that all may be due to large amorphous water ice particles. The relatively poor correlation between the 3.4 and 6.8 ..mu..m optical depths adds no evidence to support the suggestion that these bands may be due to CH bonds.

Early science with SOFIA, the stratospheric observatory for infrared astronomy

The Stratospheric Observatory For Infrared Astronomy (SOFIA) is an airborne observatory consisting of a specially modified Boeing 747SP with a 2.7 m telescope, flying at altitudes as high as 13.7 km (45,000 ft). Designed to observe at wavelengths from 0.3 μm to 1.6 mm, SOFIA operates above 99.8% of the water vapor that obscures much of the infrared and submillimeter. SOFIA has seven science instruments under development, including an occultation photometer, near-, mid-, and far-infrared cameras, infrared spectrometers, and heterodyne receivers. SOFIA, a joint project between NASA and the German Aerospace Center Deutsches Zentrum fur Luft und-Raumfahrt, began initial science flights in 2010 December, and has conducted 30 science flights in the subsequent year. During this early science period three instruments have flown: the mid-infrared camera FORCAST, the heterodyne spectrometer GREAT, and the occultation photometer HIPO. This Letter provides an overview of the observatory and its early performance.

Mid-Infrared Spectra of Polycyclic Aromatic Hydrocarbon Emission in Herbig Ae/Be Stars

We present spectra of four Herbig Ae/Be stars obtained with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope. All four of the sources show strong emission from polycyclic aromatic hydrocarbons (PAHs), with the 6.2 μm emission feature shifted to 6.3 μm and the strongest C–C skeletal-mode feature occurring at 7.9 μm instead of at 7.7 μm, as is often seen. Remarkably, none of the four stars has silicate emission. The strength of the 7.9 μm feature varies with respect to the 11.3 μm feature among the sources, indicating that we have observed PAHs with a range of ionization fractions. The ionization fraction is higher for systems with hotter and brighter central stars. Two sources, HD 34282 and HD 169142, show emission features from aliphatic hydrocarbons at 6.85 and 7.25 μm. The spectrum of HD 141569 shows a previously undetected emission feature at 12.4 μm that may be related to the 12.7 μm PAH feature. The spectrum of HD 135344, the coolest star in our sample, shows an unusual profile in the 7-9 μm region, with the peak emission to the red of 8.0 μm and no 8.6 μm PAH feature.We present spectra of four Herbig AeBe stars obtained with the Infrared Spectrograph (IRS) 1 on the Spitzer Space Telescope. All four of the sources show strong emission from polycyclic aromatic hydrocarbons (PAHs), with the 6.2 µm emission feature shifted to 6.3 µm and the strongest C C skeletal-mode feature occuring at 7.9 µm instead of at 7.7 µm as is often seen. Remarkably, none of the four stars have silicate emission. The strength of the 7.9 µm feature varies with respect to the 11.3 µm feature among the sources, indicating that we have observed PAHs with a range of ionization fractions. The ionization fraction is higher for systems with hotter and brighter central stars. Two sources, HD 34282 and HD 169142, show emission features from aliphatic hydrocarbons at 6.85 and 7.25 µm. The spectrum of HD 141569 shows a previously undetected emission feature at 12.4 µm which may be related to the 12.7 µm PAH feature. The spectrum of HD 135344, the coolest star in our sample, shows an unusual profile in the 7–9 µm region, with the peak emission to the red of 8.0 µm and no 8.6 µm PAH feature. Subject headings: stars: chemically peculiar — infrared: stars

OBSERVATIONS OF ULTRALUMINOUS INFRARED GALAXIES WITH THE INFRARED SPECTROGRAPH (IRS) ON THE SPITZER SPACE TELESCOPE: EARLY RESULTS ON MARKARIAN 1014, MARKARIAN 463, AND UGC 5101

We present spectra taken with the Infrared Spectrograph on the Spitzer Space Telescope covering the 5-38 μm region of three ultraluminous infrared galaxies (ULIRGs): Mrk 1014 (z = 0.163), Mrk 463 (z = 0.051), and UGC 5101 (z = 0.039). The continua of UGC 5101 and Mrk 463 show strong silicate absorption suggesting significant optical depths to the nuclei at 10 μm. UGC 5101 also shows the clear presence of water ice in absorption. Polycyclic aromatic hydrocarbon (PAH) emission features are seen in both Mrk 1014 and UGC 5101, including the 16.4 μm line in UGC 5101. The fine-structure lines are consistent with dominant active galactic nucleus (AGN) power sources in both Mrk 1014 and Mrk 463. In UGC 5101 we detect the [Ne V] 14.3 μm emission line, providing the first direct evidence for a buried AGN in the mid-infrared. The detection of the 9.66 μm and 17.03 μm H2 emission lines in both UGC 5101 and Mrk 463 suggest that the warm molecular gas accounts for 22% and 48% of the total molecular gas masses in these galaxies.