63 research outputs found
Molecular hydrogen from z = 0.0963 DLA towards the QSO J1619+3342
We report the detection of H2 in a zabs= 0.0963 Damped Lyman-{\alpha} (DLA)
system towards zem = 0.4716 QSO J1619+3342. This DLA has log N(H I) = 20.55
(0.10), 18.13 < log N(H2) < 18.40, [S/H] = -0.62 (0.13), [Fe/S] = -1.00 (0.17)
and the molecular fraction -2.11 < log f(H2) < -1.85. The inferred gas kinetic
temperature using the rotational level population is in the range 95 - 132 K.
We do not detect C I or C II* absorption from this system. Using R- and V-band
deep images we identify a sub-L* galaxy at an impact parameter of 14 kpc from
the line of sight, having consistent photometric redshift, as a possible host
for the absorber. We use the photoionization code CLOUDY to get the physical
conditions in the H2 component using the observational constrains from H2, C I,
C II* and Mg I. All the observations can be consistently explained if one or
more of the following is true: (i) Carbon is underabundant by more than 0.6 dex
as seen in halo stars with Z ~ 0.1 Z_sun, (ii) H I associated with H2 component
is less than 50% of the H I measured along the line of sight and (iii) the H2
formation rate on the dust grains is at least a factor two higher than what is
typically used in analytic calculations for Milky Way interstellar medium. Even
when these are satisfied, the gas kinetic temperature in the models are much
lower than what is inferred from the ortho-to-para ratio of the molecular
hydrogen. Alternatively the high kinetic temperature could be a consequence of
contribution to the gas heating from non-radiative heating processes seen in
hydrodynamical simulations.Comment: 10 pages, 4 figues, resubmitted to the MNRAS after minor revision
suggested by the refere
Discovery of an HI-rich Gas Reservoir in the Outskirts of SZ-effect Selected Clusters
We report on the detection of three strong HI absorbers originating in the
outskirts (i.e., impact parameter, )
of three massive () clusters of galaxies
at redshift , in the Cosmic
Origins Spectrograph (/COS) spectra of 3 background UV-bright quasars.
These clusters were discovered by the 2500 deg South Pole Telescope
SunyaevZel'dovich (SZ) effect survey. All three COS spectra show partial
Lyman limit absorber with near the
photometric redshifts () of the clusters. The
compound probability of random occurrence of all three absorbers is %,
indicating that the absorbers are most likely related to the targeted clusters.
We find that the outskirts of these SZ-selected clusters are remarkably rich in
cool gas compared to existing observations of other clusters in the literature.
The effective Doppler parameters of the Lyman series lines, obtained using
single cloud curve-of-growth (COG) analysis, suggest a non-thermal/turbulent
velocity of a few in the absorbing gas. We emphasize
the need for uniform galaxy surveys around these fields and for more UV
observations of QSO-cluster pairs in general in order to improve the statistics
and gain further insights into the unexplored territory of the largest
collapsed cosmic structures.Comment: Accepted for publication in ApJ Letters (6 pages
Implications of an updated ultraviolet background for the ionization mechanisms of intervening Ne VIII absorbers
Ne VIII absorbers seen in QSO spectra are useful tracers of warm ionized gas,
when collisional ionization is the dominant ionization process. While
photoionization by the ultraviolet background (UVB) is a viable option, it
tends to predict large line-of-sight thickness for the absorbing gas. Here, we
study the implications of the recently updated UVB at low-z to understand the
ionization mechanisms of intervening Ne VIII absorbers. With the updated UVB,
one typically needs higher density and metallicity to reproduce the observed
ionic column densities under photoionization. Both reduce the inferred
line-of-sight thicknesses of the absorbers. We find a critical density of
cm above which the observed N(Ne VIII)/N(O VI) can
be reproduced by pure collisional processes. If the gas is of near solar
metallicity (as measured for the low ions) then the cooling timescales will be
small (< yrs). Therefore, a continuous injection of heat is required in
order to enhance the detectability of the collisionally ionized gas. Using
photoionization models we find that in almost all Ne VIII systems the inferred
low ion metallicity is near solar or supersolar. If we assume the Ne VIII phase
to have similar metallicities then photoionization can reproduce the observed
N(Ne VIII)/N(O VI) without the line-of-sight thickness being unreasonably large
and avoids cooling issues related to the collisional ionization at these
metallicities. However the indication of broad Ly absorption in a
couple of systems, if true, suggests that the Ne VIII phase is distinct from
the low ion phase having much lower metallicity.Comment: 11 pages, 5 figures, 2 tables. Accepted for publication in MNRA
MUSEQuBES: The relation between Ly emitters and C IV absorbers at
We present a detailed study of the column density and covering fraction
profiles of C IV absorption around 86 redshift Ly
emitters (LAEs) detected in 8 Multi-Unit Spectroscopic Explorer (MUSE) fields
of centered on 8 bright background quasars as part of the
MUSEQuBES survey. Using Voigt profile fitting of all the C IV absorbers
detected along these 8 sightlines, we generated a ``blind'' absorbers' catalog
consisting of 489 C IV absorption components. We cross-matched this blind C IV
catalog with the MUSE-detected LAE catalog and found a significant enhancement
of C IV components within 400 of the systemic
redshifts of the LAEs. Neither the C IV column density () nor the Doppler
parameter () of individual C IV components shows any significant
anti-correlation with impact parameter () of the LAEs in the 68
percentile range of physical kpc (pkpc). We find a
covering fraction of for a threshold (C IV) of , which is roughly twice as high as in random regions. The C IV
covering fraction remains constant at for impact parameters in
the range 150--250~pkpc (). Using the covering fraction
profile, we constrained the LAE--C IV absorber two-point correlation function,
and obtained comoving Mpc (cMpc) and for a
threshold (C IV) of . The C IV covering fraction is
found to be enhanced for the LAEs that are part of a ``pair/group'' compared to
the isolated ones.Comment: 18 (+15 in the appendix) pages, 15 (+2 in the appendix) figures.
Submitted to MNRA
The Extreme Ultraviolet Variability of Quasars
We study the extreme ultraviolet (EUV) variability (rest frame wavelengths
500 - 920 ) of high luminosity quasars using HST (low to intermediate
redshift sample) and SDSS (high redshift sample) archives. The combined HST and
SDSS data indicates a much more pronounced variability when the sampling time
between observations in the quasar rest frame is sec
compared to sec. Based on an excess variance analysis, for
time intervals sec in the quasar rest frame, of the
quasars (4/40) show evidence of EUV variability. Similarly, for time intervals
sec in the quasar rest frame, of the quasars (21/38)
show evidence of EUV variability. The propensity for variability does not show
any statistically significant change between sec and
sec (1 yr). The temporal behavior is one of a threshold
time interval for significant variability as opposed to a gradual increase on
these time scales. A threshold time scale can indicate a characteristic spatial
dimension of the EUV region. We explore this concept in the context of the slim
disk models of accretion. We find that for rapidly spinning black holes, the
radial infall time to the plunge region of the optically thin surface layer of
the slim disk that is responsible for the preponderance of the EUV flux
emission (primarily within 0 - 7 black hole radii from the inner edge of the
disk) is consistent with the empirically determined variability time scale.Comment: To appear in Ap
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