arXiv subjects

Dieter Reimers

Publications and source records attributed to Dieter Reimers.

25 records · Page 2Linked to original sources

arXiv2002

HE 0435-1223: a wide separation quadruple QSO and gravitational lens

We report the discovery of a new gravitationally lensed QSO, at a redshift z = 1.689, with four QSO components in a cross-shaped arrangement around a bright galaxy. The maximum separation between images is 2.6 arcsec, enabling a reliable decomposition of the system. Three of the QSO components have g = 19.6, while component A is about 0.6 mag brighter. The four components have nearly identical colours, suggesting little if any dust extinction in the foreground galaxy. The lensing galaxy is prominent in the i band, weaker in r and not detected in g. Its spatial profile is that of an elliptical galaxy with a scale length of $\sim$ 12 kpc. Combining the measured colours and a mass model for the lens, we estimate a most likely redshift range of 0.3 < z < 0.4. Predicted time delays between the components are $\la$ 10 days. The QSO shows evidence for variability, with total g band magnitudes of 17.89 and 17.71 for two epochs separated by $\sim 2$ months. However, the relative fluxes of the components did not change, indicating that the variations are intrinsic to the QSO rather than induced by microlensing.

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arXiv2002

Fine-structure diagnostics of neutral carbon toward HE 0515-4414

New high-resolution high signal-to-noise spectra of the $z=1.15$ damped Lyman $α$ (DLA) system toward the quasi-stellar object HE 0515-4414 reveal absorption lines of the multiplets 2 and 3 in \ion{C}{i}. The resonance lines are seen in two components with total column densities of $\log N=13.79\pm0.01$ and $\log N=13.36\pm0.01$, respectively. The comparision of theoretical calculations of the relative fine-structure population with the ratios of the observed column densities suggests that the \ion{C}{i} absorbing medium is either very dense or exposed to very intense UV radiation. The upper limit on the local UV energy density is 100 times the galactic UV energy density, while the upper limit on the \ion{H}{i} number density is 110 cm$^{-3}$. The excitation temperatures of the ground state fine-structure levels of $T=15.7$ and $T=11.1$ K, respectively, are consistent with the temperature-redshift relation predicted by the standard Friedmann cosmology. The cosmic microwave background radiation (CMBR) is only a minor source of the observed fine-structure excitation.

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arXiv2002

Metal abundances and ionization conditions in a possibly dust-free damped Ly-alpha system at z=2.3

We have obtained a high resolution, high S/N UVES spectrum of the bright QSO HE2243-6031 to analyze the damped Ly-alpha system (DLA) observed at z=2.33. The metallicity of this system is 1/12 solar at a neutral hydrogen column density of log N(HI)=20.7. From the observed ratios [Zn/Cr]=-0.01+/-0.05 and [S/Si]=-0.06+/-0.03$ we conclude that dust is very likely absent from the ISM of this protogalaxy. We observe an enhancement of the alpha/Fe-peak ratios of +0.2 dex for various elements, a marked odd-even effect in Mn, and a strong underabundance of N relative to Si and S, [N/Si,S]=-1 at [Si/H]=-0.86. All of these ratios support an environment that is in an early evolutionary stage, where the onset of star formation has begun only shortly before the DLA was observed. We also perform a cloud-by-cloud analysis -- without precedent at high redshift -- and find a tight correlation of all low-ionization species with respect to FeII extending over 2.5 orders of magnitude in N(FeII). We interpret this trend as being due to homogeneous physical conditions (very mild ionization effects, common dust-destruction histories, same chemical composition) and propose that this line of sight encounters absorbing clouds that share a common environment. In addition, photoionization models show that these single clouds are shielded from the external ionizing radiation, so the fraction of ionized gas is small and, except for argon, does not influence the measured metal abundances. The observed AlIII/low-ion ratios suggest the mildly ionized gas occurs in shells surrounding neutral cores of AlII.

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arXiv2001

High-resolution O VI absorption line observations at 1.2 < z < 1.7 in the bright QSO HE 0515-4414

STIS Echelle observations at a resolution of 10 km/s and UVES/VLT spectroscopy at a resolution of 7 km/s of the luminous QSO HE 0515-4414 (z_em = 1.73, B = 15.0) reveal four intervening O VI absorption systems in the redshift range 1.2 < z_abs < 1.7 (1.38503, 1.41601, 1.60175, 1.67359). In addition two associated systems at z = 1.69707 and z = 1.73585 are present. For the first time high resolution observations allow to measure radial velocities of H I, C IV and O VI simultaneously in several absorption systems (1.385, 1.674, 1.697) with the result that significant velocity differences (up to 18 km/s) are observed between H I and O VI, while smaller differences (up to 5 km/s) are seen between C IV and O VI. We tentatively conclude that H I, O VI, and C IV are not formed in the same volumes and that therefore implications on ionization mechanisms are not possible from observed column density ratios O VI/H I or O VI/C IV. The number density of O VI absorbers with W_rest > 25 mA is dN/dz < 10, roughly a factor of 5 less than what has been found by Tripp at al. (2000) at low redshift. An estimate of the cosmological mass-density of the O VI-phase yields Omega_b(O VI) = 0.0003 h^{-1}_{75} for [O/H] = -1 and an assumed ionization fraction O VI/O = 0.2. This corresponds to an increase by roughly a factor of 15 between z = 1.5 (this work) and the value found by Tripp et al. (2000) at z = 0.21, if the same oxygen abundance [O/H] = -1 is assumed. Agreement with the simulations by Dave et al. (2001) can be obtained, if the oxygen abundance increases by a factor of 3 over the same redshift interval.

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arXiv2000

HST spectroscopy of the double QSO HS 1216+5032 AB

(Abridged) We report on HST FOS observations of the double QSO HS 1216+5032 AB (z(A)=1.455; z(B)=1.451, and angular separation theta=9 arcsec). An unusual broad-absorption-line (BAL) system is observed only in the B component: maximum outflow velocity of ~5000 km/s; probably a mixture of broad and narrow components. Observed ions are: HI, CII, CIII, NIII, NV, OVI, and possibly SIV and SVI. We also discuss two outstanding intervening systems: (1) a complex CIV system at z=0.72 of similar strength in A and B, with a velocity span of 1500 km/s; and (2) a possible strong MgII system at z=0.04 observed in B only. Assuming HS 1216+5032 is a binary QSO, the size of Ly-alpha forest clouds is constrained using S~ 80 /h_50 kpc at redshifts between z=1.15 and 1.45. Four Ly-alpha systems not associated with metal lines and producing lines with W_0>0.17 AA are observed in both spectra, while five appear in only one spectrum. This sample, although scarce due to the redshift path blocked out by the BALs in B, allows us to place upper limits on the transverse cloud sizes. Modelling the absorbers as non-evolving spheres, a maximum-likelihood analysis yields a most probable cloud diameter D=256 /h_50 kpc and 2 sigma bounds of 172<D<896 /h_50 kpc. If the clouds are modelled as filamentary structures, the same analysis yields lower transverse dimensions by a factor of two. Independently of the maximum-likelihood approach, the equivalent width differences provide evidence for coherent structures. The suggestion that the size of Ly-alpha forest clouds increases with decreasing redshift is not confirmed.

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arXiv1998

First Comparison of Ionization and Metallicity in Two Lines of Sight Toward HE 1104-1805 AB at z=1.66

Using new HST/FOS, NTT/EMMI, and Keck/HIRES spectra of the gravitationally-lensed double QSO HE 1104-1805 AB (z=2.31, θ=3.2), and assuming UV photoionization by a metagalactic radiation field, we derive physical conditions (ionization levels, metal abundances and cloud sizes along the lines of sight) in five CIV+MgII absorption systems clustered around z=1.66 along the two lines of sight. Three of these systems are associated with a damped Ly-alpha (DLA) system with logN(HI)=20.85, which is observed in A. The other two systems are associated with a Lyman-limit system with logN(HI)=17.57 (B). The CIV and MgII line profiles in A resemble those in the B spectra, and span Δv=360 km/s. Assuming that the relative metal abundances in these absorption systems are the same as observed in the DLA system, we find that the observed N(CIV)/N(MgII) ratios imply ionization parameters of logΓ=-2.95 to -2.35. Consequently, these clouds should be small (0.5-1.6 kpc with a hydrogen density n_H<=0.01 cm-3) and relatively highly ionized. The absorption systems to B are found to have a metallicity 0.63 times lower than the metallicity of the gas giving rise to the DLA system, Z(DLA)= 0.1*Z(solar). We detect OVI at z=1.66253 in both QSO spectra, but no associated NV. Our model calculations lead us to conclude that the CIV clouds should be surrounded by large (>= 100 kpc) highly ionized low-density clouds (n_H\sim e-4 cm-3), in which OVI, but only weak CIV absorption occurs. In this state, logΓ>=-1.2 reproduces the observed ratio of N(OVI)/N(NV)>60. These results are discussed in view of the disk/halo and hierarchical structure formation models.

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arXiv1998

An Automated Search for Metal-Poor Halo Stars in the Hamburg/ESO Objective-Prism Survey

An automated search for metal-poor stars is carried out in the course of the Hamburg/ESO objective-prism survey (HES), which covers the full southern sky at Galactic latitudes |b| \gtrsim 30 degrees. As the HES reaches approx. 1 magnitude deeper and covers areas of the sky which have not been touched by the HK Survey of Beers and collaborators, the total survey volume of the HES represents an increase by a factor of 4.5 compared to the HK Survey. Because of the limited availability of telescope time for spectroscopic follow-up observations, we will focus on a search for the most metal-poor, unevolved stars. We present a simulation study of the HES selection function P(B_J, T_eff, [Fe/H], log g) for metal-poor stars, and results from a first follow-up campaign at the ESO-NTT.

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