1,394 research outputs found
Multiple origins for the DLA at toward PKS 1127145 indicated by a complex dust depletion pattern of Ca, Ti, and Mn
We investigate the dust depletion properties of optically thick gas in and
around galaxies and its origin we study in detail the dust depletion patterns
of Ti, Mn, and Ca in the multi-component damped Lyman- (DLA) absorber
at toward the quasar PKS 1127145.} We performed a
detailed spectral analysis of the absorption profiles of CaII, MnII, TiII, and
NaI associated with the DLA toward PKS 1127145, based on optical
high-resolution data obtained with the UVES instrument at the Very Large
Telescope (VLT). We obtained column densities and Doppler-parameters for the
ions listed above and determine their gas-phase abundances, from which we
conclude on their dust depletion properties. We compared the Ca and Ti
depletion properties of this DLA with that of other DLAs. One of the six
analyzed absorption components shows a striking underabundance of Ti and Mn in
the gas-phase, indicating the effect of dust depletion for these elements and a
locally enhanced dust-to-gas ratio. In this DLA and in other similar absorbers,
the MnII abundance follows that of TiII very closely, implying that both ions
are equally sensitive to the dust depletion effects. Our analysis indicates
that the DLA toward PKS 1127145 has multiple origins. With its narrow line
width and its strong dust depletion, component 3 points toward the presence of
a neutral gas disk from a faint LSB galaxy in front of PKS 1127145, while
the other, more diffuse and dust-poor, absorption components possibly are
related to tidal gas features from the interaction between the various,
optically confirmed galaxy-group members. In general, the Mn/CaII ratio in
sub-DLAs and DLAs possibly serves as an important indicator to discriminate
between dust-rich and dust-poor in neutral gas in and around galaxies.Comment: 10 pages, 8 figures, accepted for A&
A population of high-velocity absorption-line systems residing in the Local Group
Aims. We aim to investigate the ionisation conditions and distances of
Galactic high-velocity clouds (HVCs) in the Galactic halo and beyond in the
direction of the Local Group (LG) barycentre and anti-barycentre, by studying
spectral data of 29 extragalactic background sources obtained with Cosmic
Origins Spectropgraph (COS) installed on the Hubble Space Telescope (HST).
Methods. We model column-densities of low, intermediate, and high ions, such as
Si II, C II, Si III, Si IV, and C IV and use this to construct a set of Cloudy
ionisation models. Results. In total, we found 69 high-velocity absorption
components along the 29 lines of sight. The ones in the direction of the LG
barycentre span the entire range of studied velocities, 100 \lesssim
|v_{LSR}|\lesssim 400 km s^-1, while the anti-barycentre sample has velocities
up to about 300 km s^-1. For 49 components, we infer the gas densities. In the
direction of the LG barycentre, the gas densities exhibit a large range between
log n_H=-3.96 to -2.55, while in the anti-barycentre direction the densities
are systematically higher, log n_H>-3.25. The barycentre absorbers can be split
into two groups based on their density: a high density group with log
n_H>-3.54, which can be affected by the Milky Way radiation field, and a low
density group (log n_H \leq -3.54). The latter has very low thermal pressures
of P/k<7.3 K cm^-3. Conclusions. Our study shows that part of the absorbers in
the LG barycentre direction trace gas at very low gas densities and thermal
pressures. Such properties indicate that these absorbers are located beyond the
virial radius of the Milky Way. Our study also confirms results from earlier,
single-sightline studies, suggesting the presence of a metal-enriched
intragroup medium filling the LG near its barycentre.Comment: Accepted for publication in A&A. 12 pages, 11 figure
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