1,687 research outputs found
The optical spectrum of PKS 1222+216 and its black hole mass
We investigate the optical spectral properties of the blazar PKS 1222+216
during a period of 3 years. While the continuum is highly variable the broad
line emission is practically constant. This supports a scenario in which the
broad line region is not affected by jet continuum variations. We thus infer
the thermal component of the continuum from the line luminosity and we show
that it is comparable with the continuum level observed during the phases of
minimum optical activity. The mass of the black hole is estimated through the
virial method from the FWHM of MgII, Hbeta, and Halpha broad lines and from the
thermal continuum luminosity. This yields a consistent black hole mass value of
6x10^8 solar masses.Comment: 7 pages, 4 figures, accepted for publication in MNRA
Search of sub-parsec massive binary black holes through line diagnosis
We investigate on the spectral properties of an active black hole, member of
a massive (10^7 - 10^9 Msun) sub-parsec black hole binary. We work under the
hypothesis that the binary, surrounded by a circum-binary disc, has cleared a
gap, and that accretion occurs onto the secondary black hole fed by material
closer to the inner edge of the disc. Broad line emission clouds orbit around
the active black hole and suffer erosion due to tidal truncation at the Roche
Lobe surface, following gap opening and orbital decay. We consider three of the
most prominent broad emission lines observed in the spectra of AGNs, i.e. CIV,
MgII and H{\beta}, and compute the flux ratios between the lines of MgII and
CIV (FMgII/FCIV) and those of MgII and H{\beta} (FMgII/FH{\beta}). We find that
close black hole binaries have FMgII/FCIV up to one order of magnitude smaller
than single black holes. By contrast FMgII/FH{\beta} may be significantly
reduced only at the shortest separations. Peculiarly low values of line flux
ratios together with large velocity offsets between the broad and narrow
emission lines and/or periodic variability in the continuum (on timescales >=
years) would identify genuine sub-pc binary candidates.Comment: 7 pages, 4 figures. Accepted for publication in MNRA
Oral contraceptive use and the risk of epithelial ovarian cancer.
The relation between the use of combination oral contraceptives (OCs) and the risk of epithelial ovarian cancer was investigated in a case-control study conducted in Milan on 209 women below the age of 60 with histologically confirmed epithelial ovarian cancer, and 418 age-matched controls with a spectrum of acute conditions apparently unrelated to OC use. Combination oral contraceptives were used by 18 (9%) cases, and 59 (14%) controls, giving a relative risk estimate of 0.6 (95% confidence interval = 0.3-1.0, P less than 0.05). The risk of ovarian cancer decreased with increasing duration of use and the point estimate remained below unity long after cessation of use. These results were not accounted for by parity, infertility, or other identified potential confounding factors. Thus, the findings of the present study add further support to the evidence emerging from American data of a reduction of approximately 40% in the risk of epithelial ovarian cancer among women who had used oral contraceptives
The kiloparsec-scale star formation law at redshift 4: wide-spread, highly efficient star formation in the dust-obscured starburst galaxy GN20
We present high-resolution observations of the 880 m (rest-frame FIR)
continuum emission in the z4.05 submillimeter galaxy GN20 from the IRAM
Plateau de Bure Interferometer (PdBI). These data resolve the obscured star
formation in this unlensed galaxy on scales of
0.30.2 (2.11.3 kpc).
The observations reveal a bright (161 mJy) dusty starburst centered on the
cold molecular gas reservoir and showing a bar-like extension along the major
axis. The striking anti-correlation with the HST/WFC3 imaging suggests that the
copious dust surrounding the starburst heavily obscures the rest-frame
UV/optical emission. A comparison with 1.2 mm PdBI continuum data reveals no
evidence for variations in the dust properties across the source within the
uncertainties, consistent with extended star formation, and the peak star
formation rate surface density (1198 M yr kpc)
implies that the star formation in GN20 remains sub-Eddington on scales down to
3 kpc. We find that the star formation efficiency is highest in the central
regions of GN20, leading to a resolved star formation law with a power law
slope of , and that
GN20 lies above the sequence of normal star-forming disks, implying that the
dispersion in the star formation law is not due solely to morphology or choice
of conversion factor. These data extend previous evidence for a fixed star
formation efficiency per free-fall time to include the star-forming medium on
kpc-scales in a galaxy 12 Gyr ago.Comment: 6 pages, 5 figures, accepted to ApJ
The compact, ∼1 kpc host galaxy of a quasar at a redshift of 7.1
We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the [C ii] fine-structure line and the underlying far-infrared (FIR) dust continuum emission in J1120+0641, the most distant quasar currently known (). We also present observations targeting the CO(2–1), CO(7–6), and [C i] 369 μm lines in the same source obtained at the Very Large Array and Plateau de Bure Interferometer. We find a [C ii] line flux of Jy and a continuum flux density of mJy beam−1, consistent with previous unresolved measurements. No other source is detected in continuum or [C ii] emission in the field covered by ALMA (~ 25''). At the resolution of our ALMA observations (0farcs23, or 1.2 kpc, a factor of ~70 smaller beam area compared to previous measurements), we find that the majority of the emission is very compact: a high fraction (~80%) of the total line and continuum flux is associated with a region 1–1.5 kpc in diameter. The remaining ~20% of the emission is distributed over a larger area with radius lesssim4 kpc. The [C ii] emission does not exhibit ordered motion on kiloparsec scales: applying the virial theorem yields an upper limit on the dynamical mass of the host galaxy of , only ~20 × higher than the central black hole (BH). The other targeted lines (CO(2–1), CO(7–6), and [C i]) are not detected, but the limits of the line ratios with respect to the [C ii] emission imply that the heating in the quasar host is dominated by star formation, and not by the accreting BH. The star formation rate (SFR) implied by the FIR continuum is 105–340 , with a resulting SFR surface density of ~100–350 kpc−2, well below the value for Eddington-accretion-limited star formation
Probing the nature of the massive black hole binary candidate SDSS J1536+0441
We present an imaging study of the black hole binary candidate SDSS
J1536+0441 (z=0.3893), based on deep, high resolution VzK images collected at
the ESO/VLT. The images clearly show an asymmetric elongation, indicating the
presence of a companion source at ~1" (~5 kpc projected distance) East from the
quasar. The host galaxy of the quasar is marginally resolved. We find that the
companion source is a luminous galaxy, the light profile of which suggests the
presence of an unresolved, faint nucleus (either an obscured AGN or a compact
stellar bulge). The study of the environment around the quasar indicates the
occurrence of a significant over-density of galaxies with a redshift compatible
with z~0.4. This suggests that it resides in a moderately rich cluster of
galaxies.Comment: 4 figures, 1 table. Accepted for publication in ApJ Letter
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