Evolution of macromolecular dust: Far-ultraviolet spectral dust extinction and gas absorption of stellar light as measured with the Hopkins Ultraviolet Telescope

Buss, Richard H.; Allen, Marsha; McCandliss, Stephan R.; Kruk, J. W.; Liu, Jicheng; Brown, Thomas M.

doi:10.1086/174437

Cited by 23 publications

(20 citation statements)

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“…This results in a foreground extinction of 0.29 mag in our far-UV window (centered at ∼940Å) using an extrapolation of the parameterized extinction law of Cardelli et al (1989) shortward of 1000Å. Such an extrapolation is supported by the measurements of Buss et al (1994). We therefore have to account for a factor of 1.306 absorption that does not occur in Mrk 54; our upper limit on the f (900) flux of Mrk 54 is increased to 6.15 × 10 −16 erg cm…”

Section: Correction To the Upper Limitsupporting

confidence: 70%

Constraints on the Lyman continuum radiation from galaxies: First results with FUSE on Mrk 54

Deharveng

Buat

Brun

et al. 2001

A&A

101

104

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Abstract. We present Far Ultraviolet Spectroscopic Explorer observations of the star-forming galaxy Mrk 54 at z = 0.0448. The Lyman continuum radiation is not detected above the H i absorption edge in our Galaxy. An upper limit is evaluated by comparison with the background measured in regions of the detector adjacent to the observed spectrum. A spectral window of 16Å, reasonably free of additional H i Lyman series line absorption, is used. No correction is needed for molecular hydrogen absorption in our Galaxy but a foreground extinction of 0.29 mag is accounted for. An upper limit of 6.15 × 10 −16 erg cm −2 s −1 A −1 is obtained for the flux at ≈900Å in the rest frame of Mrk 54. By comparison with the number of ionizing photons derived from the Hα flux, this limit translates into an upper limit of fesc < 0.062 for the fraction of Lyman continuum photons that escape the galaxy without being absorbed by interstellar material. This limit compares with the limits obtained in three other nearby galaxies and is compatible with the escape fractions predicted by models. The upper limits obtained in nearby galaxies contrasts with the detection of Lyman continuum flux in the composite spectrum of Lyman-break galaxies at z ≈ 3.4. The difficulties and implications of a comparison are discussed.

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Section: Correction To the Upper Limitsupporting

confidence: 70%

Constraints on the Lyman continuum radiation from galaxies: First results with FUSE on Mrk 54

Deharveng

Buat

Brun

et al. 2001

A&A

101

104

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“…Such variations cannot be interpreted as the result of different emission temperature Buss et al 1994, (b) Lang 1991 Rubin et al 1991, (d) van der Werf et al 1996, (e) Felli et al 1984 distributions of PAHs (obtained with different size distributions and/or radiation field effective temperature). In fact, the 3.3 µm-band is dominated by the emission of small (hot) PAHs while the 11.3 µm-band is contributed to by larger (cold) PAHs (Schutte et al 1993): thus, changing the PAH temperature distribution cannot explain why the 11.3 µm-band varies along with the 3.3 µm-band.…”

Section: The Observed Aib Profilesmentioning

confidence: 99%

The Aromatic Infrared Bands as seen by ISO-SWS: Probing the PAH model

Verstraete

Pech

Moutou³

et al. 2001

A&A

185

224

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Abstract. We discuss the Aromatic Infrared Band (AIB) profiles observed by ISO-SWS towards a number of bright interstellar regions where dense molecular gas is illuminated by stellar radiation. Our sample spans a broad range of excitation conditions (exciting radiation fields with effective temperature, T ef f , ranging from 23,000 to 45,000 K). The SWS spectra are decomposed coherently in our sample into Lorentz profiles and a broadband continuum. We find that the individual profiles of the main AIBs at 3.3, 6.2, 8.6 and 11.3 µm are well represented with at most two lorentzians. The 7.7 µm-AIB has a more complex shape and requires at least three Lorentz profiles. Furthermore, we show that the positions and widths of these AIBs are remarkably stable (within a few cm −1 ) confirming, at higher spectral resolution, the results from ISOCAM-CVF and ISOPHOT-S. This spectral decomposition with a small number of Lorentz profiles implicitly assumes that most of the observed bandwidth arises from a few, large carriers. Boulanger et al. (1998b) recently proposed that the AIBs are the intrinsic profiles of resonances in small carbon clusters. This interpretation can be tested by comparing the AIB profile parameters (band position and width) given in this work to laboratory data on relevant species when it becomes available. Taking advantage of our decomposition, we extract the profiles of individual AIBs from the data and compare them to a state-of-the-art model of Polycyclic Aromatic Hydrocarbon (PAH) cation emission. In this model, the position and width of the AIBs are rather explained by a redshift and a broadening of the PAH vibrational bands as the temperature of the molecule increases (Joblin et al. 1995). In this context, the present similarity of the AIB profiles requires that the PAH temperature distribution remains roughly the same whatever the radiation field hardness. Deriving the temperature distribution of interstellar PAHs, we show that its hot tail, which controls the AIB spectrum, sensitively depends on N min (the number of C-atoms in the smallest PAH) and T ef f . Comparing the observed profiles of the individual AIBs to our model results, we can match all the AIB profiles (except the 8.6 µm-AIB profile) if N min is increased with T ef f . This increase is naturally explained in a picture where small PAHs are more efficiently photodissociated in harsher radiation fields. The observed 8.6 µm-profile, both intensity and width, is not explained by our model. We then discuss our results in the broader context of ISO observations of fainter interstellar regions where PAHs are expected to be in neutral form. A&A manuscript no. (will be inserted by hand later)Your thesaurus codes are: missing; you have not inserted them

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Section: Chemical Modelingmentioning

confidence: 99%

“…, and the ultraviolet extinction curve (CCM89; Buss et al 1994), information on τ uv can be derived. For the direction toward HD 37903, τ uv was set at 2A v , with an R v somewhat larger than average (Buss et al 1994). Since the extinction curve for HD 147009 is similar to that seen for ρ Oph, τ uv toward ρ Oph ) was scaled by E(B − V ) to obtain the value for the sight line to HD 147009.…”

Section: Chemical Modelingmentioning

confidence: 99%

Physical Conditions in the Foreground Gas of Reflection Nebulae: NGC 2023, vdB 102, and NGC 7023

Knauth

Federman

Pan

et al. 2001

ASTROPHYS J SUPPL S

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1 Guest Observer, McDonald Observatory, University of Texas at Austin.High resolution optical spectra of HD 37903 and HD 147009, which illuminate the reflection nebulae, NGC 2023 and vdB 102, were obtained for comparison with our results for HD 200775 and NGC 7023. Ground-based measurements of the molecules, CH, C 2 , and CN, and the atoms, Na I and K I, were analyzed to extract physical conditions in the foreground cloud. Estimates of the gas density, gas temperature and flux of ultraviolet radiation were derived and were compared with the results from infrared and radio studies of the main molecular cloud. The conditions are similar to those found in studies of diffuse clouds. The foreground material is less dense than the gas in the molecular cloud behind the star(s). The gas temperature was set at 40 K, the temperature determined for the foreground gas in NGC 7023. The flux of ultraviolet radiation was found to be less intense than in the molecular material behind the star(s). The column densities of Na I and K I were reproduced reasonably well when the extinction curve for the specific line of sight was adopted. We obtained NEWSIPS data from the IUE archive for HD 37903 and HD 200775. The ultraviolet data on C I and CO allow extraction of the physical conditions by alternate methods. General agreement among the various diagnostics was found, leading to self-consistent pictures of the foreground photodissociation regions.An Appendix describes checks on the usefulness of IUE NEWSIPS data for interstellar studies. Equivalent widths are compared with a previous analysis of IUE observations for interstellar gas toward 20 Aquilae. Excellent agreement is found with NEWSIPS results having smaller errors. A comparison of NEWSIPS data for C I toward X Per with data acquired with the Hubble Space Telescope shows similar levels of agreement in equivalent widths and that the derived column densities from IUE results are accurate to better than a factor of 2 for absorption lines of moderate strength.

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Evolution of macromolecular dust: Far-ultraviolet spectral dust extinction and gas absorption of stellar light as measured with the Hopkins Ultraviolet Telescope

Cited by 23 publications

References 0 publications

Constraints on the Lyman continuum radiation from galaxies: First results with FUSE on Mrk 54

Constraints on the Lyman continuum radiation from galaxies: First results with FUSE on Mrk 54

The Aromatic Infrared Bands as seen by ISO-SWS: Probing the PAH model

Physical Conditions in the Foreground Gas of Reflection Nebulae: NGC 2023, vdB 102, and NGC 7023

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