Abstract
We present observations from the First Light Infrared TEst CAMera (FLITECAM) on board the Stratospheric Observatory for Infrared Astronomy, the Spitzer Infrared Array Camera (IRAC), and the ...Spitzer Infrared Spectrograph SH mode in three well-known photodissociation regions, the reflection nebulae (RNe) NGC 7023 and NGC 2023 and to the southeast of the Orion Bar, which are well suited to probe emission from polycyclic aromatic hydrocarbon molecules (PAHs). We investigate the spatial behavior of the FLITECAM 3.3
μ
m filter as a proxy for the 3.3
μ
m PAH band, the integrated 11.2
μ
m PAH band, and the IRAC 8.0
μ
m filter as a proxy for the sum of the 7.7 and 8.6
μ
m PAH bands. The resulting ratios of 11.2/3.3 and IRAC 8.0/11.2 provide an approximate measure of the average PAH size and PAH ionization, respectively. In both RNe, we find that the relative PAH ionization and the average PAH size increase with decreasing distance to the illuminating source. The average PAH sizes derived for NGC 2023 are greater than those found for NGC 7023 at all points. Both results indicate that PAH size is dependent on the radiation field intensity. These results provide additional evidence of a rich carbon-based chemistry driven by the photochemical evolution of the omnipresent PAH molecules within the interstellar medium. In contrast, we did not detect a significant variation in the average PAH size found in the region southeast of the Orion Bar and report a peculiar PAH ionization radial profile.
ABSTRACT
We present 5–14 $\mu$m spectra at two different positions across the Orion Bar photodissociation region (PDR) obtained with the Infrared Spectrograph onboard the Spitzer Space Telescope and ...3.3 $\mu$m PAH observations obtained with the Stratospheric Observatory for Infrared Astronomy (SOFIA). We aim to characterize emission from Polycyclic Aromatic Hydrocarbon (PAH), dust, atomic and molecular hydrogen, argon, sulfur, and neon as a function of distance from the primary illuminating source. We find that all the major PAH bands peak between the ionization front and the PDR front, as traced by H2, while variations between these bands become more pronounced moving away from this peak into the face-on PDRs behind the PDR front and at the backside of the H ii region. While the relative PAH intensities are consistent with established PAH characteristics, we report unusual behaviours and attribute these to the PDR viewing angle and the strength of the FUV radiation field impinging on the PDRs. We determine the average PAH size which varies across the Orion Bar. We discuss subtle differences seen between the cationic PAH bands and highlight the photochemical evolution of carbonaceous species in this PDR environment. We find that PAHs are a good tracer of environmental properties such as the strength of the FUV radiation field and the PAH ionization parameter.
We present a 0.6-4.1 mu m spectroscopic sequence of M, L, and T dwarfs. The spectra have R identical with lambda / Delta lambda approximately 2000 from 0.9 to 2.4 mu m and R = 2500-200 from 2.9 to ...4.1 mu m. These new data nearly double the number of L and T dwarfs that have reported L-band spectra. The near-infrared spectra are combined with previously published red-optical spectra to extend the wavelength coverage to similar to 0.6 mu m. Prominent atomic and molecular absorption features are identified including neutral lines of Al, Fe, Mg, Ca, Ti, Na, and K and 19 new weak CH sub(4) absorption features in the H-band spectra of mid- to late-type T dwarfs. In addition, we detect for the first time the 0-0 band of the A super(4) capital pi -X super(4) capital sigma super(-) transition of VO at similar to 1.06 mu m in the spectra of L dwarfs and the P- and R-branches of the v sub(3) band of CH sub(4) in the spectrum of a T dwarf. The equivalent widths of the refractory atomic features all decrease with increasing spectral type and are absent by a spectral type of similar to L0, except for the 1.189 mu m Fe I line, which persists to at least similar to L3. We compute the bolometric luminosities of the dwarfs in our sample with measured parallaxes and find good agreement with previously published results that use L'-band photometry to account for the flux emitted from 2.5 to 3.6 mu m. Finally, 2MASS J2224381-0158521 (L4.5) has an anomalously red spectrum and the strongest Delta v = +2 CO bands in our sample. This may be indicative of unusually thick condensate clouds and/or low surface gravity.
The isophotal wavelengths, flux densities, and AB magnitudes for Vega (α Lyr) are presented for the Mauna Kea Observatories near‐infrared filter set. We show that the near‐infrared absolute ...calibrations for Vega as determined by Cohen et al. and Mégessier are consistent within the uncertainties, so that either absolute calibration can be used.
We present SOFIA/FIFI-LS observations of the C ii 158 m cooling line across the nearby spiral galaxy NGC 6946. We combine these with UV, IR, CO, and H i data to compare C ii emission to dust ...properties, star formation rate (SFR), H2, and H i at 560 pc scales via stacking by environment (spiral arms, interarm, and center), radial profiles, and individual, beam-sized measurements. We attribute 73% of the C ii luminosity to arms, and 19% and 8% to the center and interarm region, respectively. C ii/TIR, C ii/CO, and C ii/PAH radial profiles are largely constant, but rise at large radii ( 8 kpc) and drop in the center ("C ii deficit"). This increase at large radii and the observed decline with the 70 m/100 m dust color are likely driven by radiation field hardness. We find a near proportional C ii-SFR scaling relation for beam-sized regions, though the exact scaling depends on methodology. C ii also becomes increasingly luminous relative to CO at low SFR (interarm or large radii), likely indicating more efficient photodissociation of CO and emphasizing the importance of C ii as an H2 and SFR tracer in such regimes. Finally, based on the observed C ii and CO radial profiles and different models, we find CO to increase with radius, in line with the observed metallicity gradient. The low CO (galaxy average 2 M pc−2 (K km s−1)−1) and low C ii/CO ratios (∼400 on average) imply little CO-dark gas across NGC 6946, in contrast to estimates in the Milky Way.
New Technology Telescope (NTT)/Son of Isaac (SOFI) imaging and spectroscopy of the Wolf-Rayet population in the massive cluster Westerlund 1 are presented. Narrow-band near-infrared (IR) imaging ...together with follow up spectroscopy reveals four new Wolf-Rayet stars, of which three were independently identified recently by Groh et al., bringing the confirmed Wolf-Rayet content to 24 (23 excluding source S) - representing 8 per cent of the known Galactic Wolf-Rayet population - comprising eight WC stars and 16 (15) WN stars. Revised coordinates and near-IR photometry are presented, whilst a quantitative near-IR spectral classification scheme for Wolf-Rayet stars is presented and applied to members of Westerlund 1. Late subtypes are dominant, with no subtypes earlier than WN5 or WC8 for the nitrogen and carbon sequences, respectively. A qualitative inspection of the WN stars suggests that most (∼75 per cent) are highly H deficient. The Wolf-Rayet binary fraction is high (≥62 per cent), on the basis of dust emission from WC stars, in addition to a significant WN binary fraction from hard X-ray detections according to Clark et al. We exploit the large WN population of Westerlund 1 to reassess its distance (∼5.0 kpc) and extinction (A
We present Keck/NIRSPEC near-IR images and Magellan/IMACS optical spectroscopy of the host galaxy of GRB 031203. The host is an actively star-forming galaxy at z = 0.1055 plus or minus 0.0001. This ...is the lowest redshift GRB to date, aside from GRB 980425. From the hydrogen Balmer lines, we infer an extinction of A sub(V) = 3.62 plus or minus 0.25 or a total reddening E sub(T)(B-V) = 1.17 plus or minus 0.1 toward the sight line to the nebular regions. After correcting for reddening, we perform an emission-line analysis and derive an ISM temperature of T = 13400 plus or minus 2000 K and electron density of n sub(e) = 300 cm super(-3). These imply a metallicity O/H =-0.72 plus or minus 0.15 dex and a roughly solar abundance pattern for N, Ne, S, and Ar. Integrating Halpha, we infer a dust-corrected star formation rate (SFR) of more than 11 M sub(o) yr super(-1). These observations have the following implications: (1) The galaxy has a low Karcmin-band luminosity L ~ Limage/5, typical of GRB host galaxies. (2) The low redshift indicates GRB 031203 had an isotropic-equivalent gamma-ray energy release smaller than all previous confirmed GRB events. The burst discovery raises the likelihood of identifying many additional low-z, low-flux events with Swift. (3) The large SFR, low metallicity, and inferred hard radiation field are suggestive of massive star formation, supporting the collapsar model. (4) Several lines of evidence argue against the identification of GRB 031203 as an X-ray flash event.
The formation processes and the exact appearance of the dust torus and broad line region (BLR) of active galactic nuclei (AGN) are under debate. Theoretical studies show a possible connection between ...the dust torus and BLR through a common origin in the accretion disk. However observationally the dust torus and BLR are typically studied separately. NGC 4151 is possibly one of the best suited Seyfert 1 galaxies for simultaneous examinations because of its high number of both photometric and spectroscopic observations in the past. Here we compare changes of the dust radius to shape variations of broad emission lines (BEL). While the radius of the dust torus decreased by almost a factor of two from 2004 to 2006 shape variations can be seen in the red wing of BELs of NGC 4151. These simultaneous changes are discussed in a dust and BEL formation scheme. We also use the BEL shape variations to assess possible cloud distributions, especially in azimuthal direction, which could be responsible for the observed variations. Our findings can best be explained in the framework of a dust inflated accretion disk. The changes in the BELs suggest that this dusty cloud formation does not happen continuously, and over the whole accretion disk, but on the contrary in spatially confined areas over rather short amount of times. We derive limits to the azimuthal extension of the observed localized BEL flux enhancement event.
Abstract
SOFIA is an airborne observatory for far-infrared astronomy. Although SOFIA flies at altitudes of ∼41,000 feet, any far-infrared observations from within the Earth’s atmosphere are ...nevertheless hampered by water vapor absorbing the astronomical signal. The atmospheric parameter governing absorption is the total upward precipitable water vapor, PWV. In this paper we investigated if data of the Earth’s atmosphere provided by the European Centre for Medium-Range Weather Forecasts, ECMWF, can be used to determine spatially and time-resolved PWV data to allow a more precise calibration of far-infrared data taken with SOFIA along its flight path. We found that PWV values obtained from ECMWF correlate extremely well with independently determined PWV values obtained with the FIFI-LS instrument onboard SOFIA. We determined maximum observing time intervals (depending on the pressure altitude SOFIA is flying at) within which the upward PWV value changes inflight by less than a certain amount. We also present a new calibration method which enhances data quality and observing efficiency with FIFI-LS significantly. Furthermore our new method is universal and may be applied to data from all of SOFIA's instruments.
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