1,229 research outputs found
The Ages of Elliptical Galaxies from Infrared Spectral Energy Distributions
The mean ages of early-type galaxies obtained from the analysis of optical
spectra, give a mean age of 8 Gyr at z = 0, with 40% being younger than 6 Gyr.
Independent age determinations are possible by using infrared spectra (5-21
microns), which we have obtained with the Infrared Spectrograph on the Spitzer
Observatory. This age indicator is based on the collective mass loss rate of
stars, where mass loss from AGB stars produces a silicate emission feature at
9-12 microns. This feature decreases more rapidly than the shorter wavelength
continuum as a stellar population ages, providing an age indicator. From
observations of 30 nearby early-type galaxies, 29 show a spectral energy
distribution dominated by stars and one has significant emission from the ISM
and is excluded. The infrared age indicators for the 29 galaxies show them all
to be old, with a mean age of about 10 Gyr and a standard deviation of only a
few Gyr. This is consistent with the ages inferred from the values of M/L_B,
but is inconsistent with the ages derived from the optical line indices, which
can be much younger. All of these age indicators are luminosity-weighted and
should be correlated, even if multiple-age components are considered. The
inconsistency indicates that there is a significant problem with either the
infrared and the M/L_B ages, which agree, or with the ages inferred from the
optical absorption lines.Comment: Accepted for publication in Ap
A survey of the properties of early-type galaxies
A compilation of the properties of elliptical and early disk galaxies was completed. In addition to material from the literature, such as Infrared Astronomy Satellite (IRAS) fluxes, the compilation includes recent measurements of HI and CO, as well as a review of the x ray properties by Forman and Jones. The data are used to evaluate the gas content of early systems and to search for correlations with x ray emission. The interstellar medium in early-type galaxies is generally dominated by hot interstellar gas (T approx. 10 to the 7th power K; c.f. the review by Fabbiano 1989 and references therein). In addition, a significant fraction of these galaxies show infrared emission (Knapp, et al., 1989), optical emission lines, and visible dust. Sensitive studies in HI and CO of a number of these galaxies have been completed recently, resulting in several detections, particularly of the later types. Researchers wish to understand the connection among these different forms of the interstellar medium, and to examine the theoretical picture of the fate of the hot gas. To do so, they compiled observations of several forms of interstellar matter for a well-defined sample of early-type galaxies. Here they present a statistical analysis of this data base and discuss the implications of the results
The Closest Damped Lyman Alpha System
A difficulty of studying damped Lyman alpha systems is that they are distant,
so one knows little about the interstellar medium of the galaxy. Here we report
upon a damped Lyman alpha system in the nearby galaxy NGC 4203, which is so
close (v_helio = 1117 km/s) and bright (B_o = 11.62) that its HI disk has been
mapped. The absorption lines are detected against Ton 1480, which lies only
1.9' (12 h_50 kpc) from the center of NGC 4203. Observations were obtained with
the Faint Object Spectrograph on HST (G270H grating) over the 2222-3277
Angstrom region with 200 km/s resolution. Low ionization lines of Fe, Mn, and
Mg were detected, leading to metallicities of -2.29, -2.4, which
are typical of other damped Lyman alpha systems, but well below the stellar
metallicity of this type of galaxy. Most notably, the velocity of the lines is
1160 +- 10 km/s, which is identical to the HI rotational velocity of 1170 km/s
at that location in NGC 4203, supporting the view that these absorption line
systems can be associated with the rotating disks of galaxies. In addition, the
line widths of the Mg lines give an upper limit to the velocity dispersion of
167 km/s, to the 99% confidence level.Comment: 4 pages LaTeX, including 1 figure and 1 table, uses emulateapj.sty.
Accepted for publication by Astrophysical Journal Letter
Infrared spectra of WC10 planetary nebulae nuclei
The 5.2 to 8.0 micron spectra are presented for two planetary nebulae nuclei Hen1044 (He2-113) and CPD-56 8032. The unidentified infrared (UIR) emission bands at 6.2 microns, 6.9 microns, 7.7 microns are present in the spectra of Hen1044 and in CPD-56 8032, and the 8.6 micron band is present in the long wavelength shoulder of the 7.7 micron band in the spectrum of CPD-56 8032. The 8 to 13 micron spectra of these two stars by Aitken et. al. clearly show the presence of the 8.6 micron band in He2-113 while weakly resolving this feature in the spectra of CPD-56 8032. In their spectra the 11.3 micron band is also clearly detected in both objects. The 6.2 micron and 7.7 micron bands are characteristic of the infrared active C-C stretching modes in polycyclic aromatic hydrocarbons (PAHs); the 3.3 micron, 8.6 micron, and 11.3 micron bands are respectively assigned to the in-plane stretching mode, the in-plane bending mode, and the out-of-plane bending mode of the aromatic CH bond. The weak 6.9 micron emission feature is attributed to the UIR spectrum by Bregman et. al. The IRAS LRS spectra of He2-113 (IRAS 14562-5406) and CPD-56 8032 (IRAS 17047-5650) are presented. Cohen et. al. identify the broad plateau from 11.3 to 13.0 microns in the spectrum of He2-113 with increased hydrogenation of PAHs. This broad plateau is not seen in the LRS spectrum of CPD-56 8032. Also, He2-113 has greater infrared excess emission in the 17-22 micron region than does CPD-56 8032
Airborne observations of the infrared emission bands
Earlier airborne studies of the infrared bands between 5 and 8 microns have now been extended to a sample of southern sources selected from the IRAS Low Resolution Spectra (LRS) atlas. The correlation between the strongest bands at 6.2 and 7.7 microns is now based on a total sample of 40 sources and is very strong. A new emission band at 5.2 microns, previously predicted for polycyclic aromatic hydrocarbons (PAHs), is recognized in 27 sources; it too correlates with the dominant 7.7 micron band, showing that the 5.2 micron feature also belongs to the generic spectrum of PAH features at 3.3, 5.6, 6.2, 6.2, 7.7, 8.7, 11.3, and 12.7 microns. Sufficient sources are had now to define the relative strengths of most of these bands in three separate nebular environments: planetaries, H II regions, and reflection nebulae. Significant variations are detected in the generic spectra of PAHs in these different environments which are echoed by variations in the exact wavelength of the strong 7.7 micron peak. The earlier suggestion that, in planetaries, the fraction of total emission observed by IRAS that is carried by the PAH emissions is correlated with nebular gas-phase C/O ratio is supported by the addition of newly-observed southern planetaries, including the unusually carbon-rich (WC10) nebular nuclei. These (WC10) nuclei also exhibit a strong plateau of emission linking the 6.2 and 7.7 micron features
Some 5-13 micrometer airborne observations of Comet Wilson 1986l: Preliminary results
Comet Wilson was observed from the Kuiper Airborne Observatory approximately 23.6 and 25.7 Apr. 1987, UT (approx. 3 to 5 days after perihelion) using the NASA-Ames Faint Object Grating Spectrometer. Spectrophotometric data were observed with a 21 inch aperture between 5 and 13 micrometer and with a spectral resolution of 50 to 100. Spectra of the inner coma and nucleus reveal a fairly smooth continuum with little evidence of silicate emission. The 5 to 8 micrometer color temperature of the comet was 300 + or - 15 K, approx. 15 percent higher than the equilibrium blackbody temperature. All three spectra of the nucleus show a new emission feature at approx. 12.25 micrometer approx. two channels (.22 micrometer) wide. Visual and photographic observations made during the time of these observations showed a broad faint, possible two component tail. No outburst activity was observed
Spectral structure near the 11.3 micron emission feature
If the 11.3 micron emission feature seen in the spectra of many planetary nebulae, H II regions, and reflection nebulae is attributable to polycyclic aromatic hydrocarbons (PAHs), then additional features should be present between 11.3 and 13.0 microns. Moderate resolution spectra of NGC 7027, HD 44179, BD+30 deg 3639, and IRAS 21282+5050 are presented which show evidence for new emission features centered near 12.0 and 12.7 microns. These are consistent with an origin from PAHs and can be used to constrain the molecular structure of the family of PAHs responsible for the infrared features. There is an indication that coronene-like PAHs contribute far more to the emission from NGC 7027 than to the emission from HD 44179. The observed asymmetric profile of the 11.3 micron band in all the spectra is consistent with the slight anharmonicity expected in the C-H out-of-plane bending mode in PAHs. A series of repeating features between 10 and 11 microns in the spectrum of HD 44179 suggests a simple hydride larger than 2 atoms is present in the gas phase in this object
Radiation survival of murine and human melanoma cells utilizing two assay systems: monolayer and soft agar.
The radiation response of murine and human melanoma cells assayed in bilayer soft agar and monolayer was examined. Cells from the murine melanoma Cloudman S91 CCL 53.1 cell line and three human melanoma cell strains (C8146C, C8161, and R83-4) developed in our laboratory were irradiated by single dose X-rays and plated either in agar or on plastic. D0 values were the same within 95% confidence intervals for cells from the human melanoma cell strains C8146C, C8161, and R83-4 but were dissimilar for the murine cell line CCL 53.1 Dq values were different for all cells studied. The shape of the survival curve for all four melanomas was not identical for cells assayed in soft agar versus cells grown on plastic. This would indicate that apparent radiosensitivity was influenced by the method of assay although there were no apparent consistent differences between the curves generated by monolayer or bilayer soft agar assays
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