1,706 research outputs found
A huge reservoir of ionized gas around the Milky Way: Accounting for the Missing Mass?
Most of the baryons from galaxies have been "missing" and several studies
have attempted to map the circumgalactic medium (CGM) of galaxies in their
quest. Recent studies with the Hubble Space Telescope have shown that many
galaxies contain a large reservoir of ionized gas with temperatures of about
10^5 K. Here we report on X-ray observations made with the Chandra X-ray
Observatory probing an even hotter phase of the CGM of our Milky Way at about
10^6 K. We show that this phase of the CGM is massive, extending over a large
region around the Milky Way, with a radius of over 100 kpc. The mass content of
this phase is over ten billion solar masses, many times more than that in
cooler gas phases and comparable to the total baryonic mass in the disk of the
Galaxy. The missing mass of the Galaxy appears to be in this warm-hot gas
phase.Comment: 15 pages, 3 figures; http://stacks.iop.org/2041-8205/756/L
A view of PKS 2155-304 with XMM-Newton Reflection Grating Spectrometers
We present the high resolution X-ray spectrum of the BL Lac object PKS
2155-304 taken with the RGS units onboard XMM-Newton in November 2000. We
detect a OVII Kalpha resonant absorption line from warm/hot local gas at 21.59A
(~4.5 sigma detection). The line profile is possibly double peaked. We do not
confirm the strong 20.02 A absorption line seen with Chandra and interpreted as
z~0.05 OVIII Kalpha. A 3sigma upper limit of 14 mA on the equivalent width is
set. We also detect the ~23.5 A interstellar OI 1s-->2p line and derive a
factor <=1.5 subsolar O/H ratio in the ISM along PKS 2155-304 line of sight.Comment: 13 pages, 5 figures, 3 tables, emulateapj style. Accepted by Ap
Studying the WHIM Content of the Galaxy Large-Scale Structures along the Line of Sight to H 2356-309
We make use of a 500ks Chandra HRC-S/LETG spectrum of the blazar H2356-309,
combined with a lower S/N spectrum of the same target, to search for the
presence of warm-hot absorbing gas associated with two Large-Scale Structures
(LSSs) crossed by this sightline at z=0.062 (the Pisces-Cetus Supercluster,
PCS) and at z=0.128 ("Farther Sculptor Wall", FSW). No statistically
significant (>=3sigma) individual absorption is detected from any of the strong
He- or H-like transitions of C, O and Ne at the redshifts of the structures.
However we are still able to constrain the physical and geometrical parameters
of the associated putative absorbing gas, by performing joint spectral fit of
marginal detections and upper limits of the strongest expected lines with our
self-consistent hybrid ionization WHIM spectral model. At the redshift of the
PCS we identify a warm phase with logT=5.35_-0.13^+0.07 K and log N_H
=19.1+/-0.2 cm^-2 possibly coexisting with a hotter and less significant phase
with logT=6.9^+0.1_-0.8 K and log N_H=20.1^+0.3_-1.7 cm^-2 (1sigma errors). For
the FSW we estimate logT=6.6_-0.2^+0.1 K and log N_H=19.8_-0.8^+0.4 cm^-2. Our
constraints allow us to estimate the cumulative number density per unit
redshifts of OVII WHIM absorbers. We also estimate the cosmological mass
density obtaining Omega_b(WHIM)=(0.021^+0.031_-0.018) (Z/Z_sun)^-1, consistent
with the mass density of the intergalactic 'missing baryons' for high
metallicities.Comment: 29 pages, 8 figures, 4 tables. Accepted for publication in Ap
Broad band spectral properties of Seyfert 1 galaxies observed with BeppoSAX
We will present some results on the broad--band observations of BeppoSAX of
the bright Seyfert galaxies NGC 4151 and NGC 5548.Comment: 5 pages, 4 figures, Proc. of the 32 COSPAR Ass., Session E1.1 "Broad
Band X-Ray Spectra of Cosmic Sources, ed.s K. Makishima, L. Piro, T.
Takahashi, Advances in Space Research, in pres
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