arXiv subjects

G. Neugebauer

Publications and source records attributed to G. Neugebauer.

44 records · Page 3Linked to original sources

arXiv1998

Near Infrared Observations of a Redshift 5.34 Galaxy: Further Evidence for Dust Absorption in the Early Universe

Imaging at 1.25 and 2.20 microns has been obtained of the field containing the galaxy (RD1) found at redshift 5.34 by Dey et al.(1998). This galaxy has been detected at 1.25 microns, while the lower redshift (z=4.02) galaxy also found in the same field by Dey et al. was detected at both 1.25 and 2.20 microns. Comparison to stellar population synthesis models indicates that if RD1 is a young (< 100 Myr old) galaxy, significant reddening (A(V) > 0.5 mag) is indicated. Combined with observations of other high redshift systems, these data show that dust is likely to be an important component of young galaxies even at redshifts of z > 5. The extinction-corrected monochromatic luminosity of RD1 at 1500 angstroms is then a factor of about three larger than L(1500)* as determined by Dickinson (1998) for z ~ 3 starburst galaxies. The implied star formation rate in RD1, corrected for extinction, is ~ 50-100 solar masses per year.

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arXiv1998

Near Infrared Observations of a Redshift 4.92 Galaxy: Evidence for Significant Dust Absorption

Near-infrared imaging and spectroscopy have been obtained of the gravitationally lensed galaxy at z=4.92 discovered in HST images by Franx et al. (1997). Images at 1.2, 1.6 and 2.2 microns show the same arc morphology as the HST images. The spectrum with resolution λ/ Δλ~ 70 shows no emission lines with equivalent width stronger than 100 A in the rest frame wavelength range 0.34 to 0.40 microns. In particular, [OII]3727 A and [NeIII]3869 A are not seen. The energy distribution is quite blue, as expected for a young stellar population with the observed Ly alpha flux. The spectral energy distribution can be fit satisfactorily for such a young stellar population when absorption by dust is included. The models imply a reddening 0.1 mag < E(B-V) < 0.4 mag. The stellar mass of the lensed galaxy lies in the range of 2 to 16 x 10^9 Msun. This is significantly higher than estimates based on the HST data alone. Our data imply that absorption by dust is important to redshifts of ~5.

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arXiv1997

The [OIII] Emission-line Nebula of the z=3.594 Radio Galaxy 4C +19.71

We have imaged the z=3.594 radio galaxy 4C +19.71 in the light of the redshifted [OIII] 5007 angstrom emission line, using a narrow-band filter centered at 2.3 microns with the Near Infrared Camera on the Keck Telescope. The [OIII] nebula of 4C +19.71 has a size of 74 x 9 kpc, and a luminosity of 3 x 10^37 W. The rest frame equivalent width of the 5007 line, averaged over the entire nebula, is 560 angstroms. The length of the major axis of the [OIII] emission is nearly identical to the separation of the radio lobes seen at 1465 MHz (Rottgering, et al. 1994), and the position angle of the nebula is the same as that of the two radio lobes. In addition, 4C +19.71 follows the optical emission line vs. radio power correlation seen in other powerful radio galaxies. The [OIII] and Lyman alpha emission line luminosities suggest that the ionized gas mass lies in the range of 2 x 10^8 - 10^9 solar masses. The O/H ratio in the nebula is at least a few tenths solar, and may be as high as a factor of three above solar, indicating a previous phase of star formation in 4C +19.71. Thirty five percent of the total K-band flux is contributed by the 5007 angstrom emission line, and the continuum of 4C +19.71 has a K=19.6 mag. This places 4C +19.71 along the K-z relation found for other radio galaxies and radio loud quasars. If the continuum is dominated by starlight, the host galaxy has a rest frame visual luminosity of about 40L*. There are no candidate emission-line objects at the redshift of 4C +19.71 having [OIII] rest frame equivalent widths of more than about 2% that of the radio galaxy itself within a volume of 212 cubic Mpc.

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arXiv1997

The Unusual Near-Infrared Morphology of the Radio Loud Quasar 4C+09.17

Near-infrared images of the luminous, high redshift (z=2.1108) radio loud quasar 4C+09.17 reveal a complex structure. The quasar (K=15.76 mag) is surrounded by three "companion" objects having 17.9< K < 20.2 mag at radii of 1.7" < r < 2.9", as well as bright, diffuse emission. The brightest companion has a redshift of z=0.8384 (Lehnert & Becker 1997) and its optical-infrared colors (Lehnert et al. 1997) are consistent with a late-type spiral galaxy at this redshift with a luminosity of about 2L*. This object is likely the galaxy responsible for the strongest MgII absorption line system seen in the spectrum of 4C+09.17 by Barthel et al. (1990). Redshifts are not available for the remaining two companions. The red colors of the second brightest companion appear most consistent with a high redshift star-forming galaxy at z > 1.5. If this object is at the redshift of 4C +09.17 it has a luminosity of about 7L*. The faintest companion has colors which are unlike those expected from either a spiral or an E/S0 galaxy at any redshift associated with the 4C+09.17 system. Since this object lies along the same direction as the radio jet/lobe of 4C+09.17, as well as the extended Ly-alpha emission mapped by Heckman et al. (1991) we suggest that this component can be explained as a combination of strong line emission and scattered QSO light. The resolved, diffuse emission surrounding 4C+09.17 is bright, K~17.0 mag, and about one magnitude redder in J-K than the quasar. If this emission is starlight, a very luminous elliptical host galaxy is implied for 4C+09.17. Scattered and reddened AGN light, emission line gas, and flux from absorbing galaxies along the line of sight may all contribute to this emission.

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arXiv1997

Near Infrared Imaging of the Hubble Deep Field with The Keck Telescope

Two deep K-band ($2.2 μm$) images, with point-source detection limits of $K=25.2$ mag (one sigma), taken with the Keck Telescope in subfields of the Hubble Deep Field, are presented and analyzed. A sample of objects to K=24 mag is constructed and $V_{606}-I_{814}$ and $I_{814}-K$ colors are measured. By stacking visually selected objects, mean $I_{814}-K$ colors can be measured to very faint levels; the mean $I_{814}-K$ color is constant with apparent magnitude down to $V_{606}=28$ mag.

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arXiv1995

HST Observations of the Luminous IRAS Source FSC10214+4724: A Gravitationally Lensed Infrared Quasar

We present an image of the redshift 2.3 IRAS source FSC10214+4724 at 0.8 microns obtained with the HST WFPC2 Planetary Camera. The source appears as an unresolved (< 0.06") arc 0.7" long, with significant substructure along its length. The arc is centered near an elliptical galaxy 1.18" to the north. An unresolved component 100 times fainter than the arc is clearly detected on the opposite side of this galaxy. The most straightforward interpretation is that FSC 10214+4724 is gravitationally lensed by the foreground elliptical galaxy, with the faint component a counterimage of the IRAS source. The brightness of the arc in the HST image is then magnified by ~100 and the intrinsic source diameter is ~0.01" (80 pc) at 0.25 microns rest wavelength. The bolometric luminosity is probably amplified by a smaller factor (~30), yielding an intrinsic luminosity ~2E13 solar luminosities. A detailed lensing model is presented which reproduces the observed morphology and relative flux of the arc and counterimage, and correctly predicts the position angle of the lensing galaxy. The model also predicts reasonable values for the velocity dispersion, mass, and mass-to-light ratio of the lensing galaxy. A redshift for the lensing galaxy of ~0.9 is consistent with the measured surface brightness profile from the image, as well as with the galaxy's SED.

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arXiv1995

A Luminous Companion to SGR 1806-20

We have obtained infrared spectra of the star suggested to be the counterpart of the soft gamma-ray repeater (SGR) 1806-20. We found strong emission lines similar to those seen in the spectra of the rare Luminous Blue Variables and B[e] stars. A He I absorption line is also seen, from which we infer a spectral type O9--B2. This classification, in combination with the minimum distance of $\simgt6$ kpc inferred from its extinction, makes the star one of the most luminous in the Galaxy. We infer that it is a companion to SGR 1806-20, and suggest that the presence of a companion is somehow related to the SGR phenomenon.

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arXiv1994

Optical and Infrared Observations of SGR 1806-20

The soft gamma-ray repeater (SGR) 1806$-$20 is associated with the center-brightened non-thermal nebula G~10.0$-$0.3, thought to be a plerion. As in other plerions, a steady \Xray\ source, AX~1805.7$-$2025, has been detected coincident with the peak of the nebular radio emission. Vasisht et al.\ have shown that the radio peak has a core-jet appearance, and argue that the core marks the true position of the SGR. At optical wavelengths, we detect three objects in the vicinity of the radio core. Only for the star closest to the core, barely visible in the optical but bright in the infrared ($K=8.4\,$mag.), the reddening is consistent with the high extinction ($A_V\simeq30\,$mag.) that has been inferred for AX~1805.7$-$2025. From the absence of CO band absorption, we infer that the spectral type of this star is earlier than late~G/early~K. The large extinction probably arises in a molecular cloud located at a distance of 6$\,$kpc, which means that the star, just like AX~1805.7$-$2025, is in or behind this cloud. This implies that the star is a supergiant. Since supergiants are rare, a chance coincidence with the compact radio core is very unlikely. To our knowledge, there are only three other examples of luminous stars embedded in non-thermal radio nebulae, SS~433, \mbox{Cir X-1} and G~70.7+1.2. Given this and the low coincidence probability, we suggest that the bright star is physically associated with SGR~1806$-$20, making it the first stellar identification of a high-energy transient.

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