Nepal's quake-driven landslide hazards
Large earthquakes can trigger dangerous landslides across a wide geographic region. The 2015
M
w
7.8 Gorhka earthquake near Kathmandu, Nepal, was no exception. Kargal
et al.
used remote observations to compile a massive catalog of triggered debris flows. The satellite-based observations came from a rapid response team assisting the disaster relief effort. Schwanghart
et al.
show that Kathmandu escaped the historically catastrophic landslides associated with earthquakes in 1100, 1255, and 1344 C.E. near Nepal's second largest city, Pokhara. These two studies underscore the importance of determining slope stability in mountainous, earthquake-prone regions.
Science
, this issue p.
10.1126/science.aac8353
; see also p.
147
We investigate the radial velocity difference between the narrow emission‐line components of [O iii]λ5007 and Hβ in a sample of 150 Sloan Digital Sky Survey narrow‐line Seyfert 1 galaxies. Seven ‘blue outliers’ with [O iii] blueshifted by more than 250 km s−1 are found. A strong correlation between the [O iii] blueshift and the Eddington ratio is found for these seven ‘blue outliers’. For the entire sample, we found a modest correlation between the blueshift and the linewidth of the narrow component of the [O iii] line. The reflected profile of [O iii] indicates two kinematically and physically distinct regions. The [O iii] linewidth depends not only on the bulge stellar gravitational potential, but also on the central black hole potential.
To explore the evolutionary connection among red, green, and blue galaxy populations, based on a sample of massive (M * > 10 10 M ⊙ ) galaxies at 0.5 < z < 2.5 in five 3D-HST /CANDELS fields, we investigate the dust content, morphologies, structures, active galactic nucleus (AGN) fractions, and environments of these three galaxy populations. Green valley galaxies are found to have intermediate dust attenuation, and reside in the middle of the regions occupied by quiescent and star-forming galaxies in the U V J diagram. Compared with blue and red galaxy populations at z < 2, green galaxies have intermediate compactness and morphological parameters. The above findings seem to favor the scenario that green galaxies are at a transitional phase when star-forming galaxies are being quenched into quiescent status. The green galaxies at z < 2 show the highest AGN fraction, suggesting that AGN feedback may have played an important role in star formation quenching. For the massive galaxies at 2 < z < 2.5, both red and green galaxies are found to have a similarly higher AGN fraction than the blue ones, which implies that AGN feedback may help to keep quiescence of red galaxies at z > 2. A significant environmental difference is found between green and red galaxies at z < 1.5. Green and blue galaxies at z > 0.5 seem to have similar local density distributions, suggesting that environment quenching is not the major mechanism to cease star formation at z > 0.5. The fractions of three populations as functions of mass support a "downsizing" quenching picture that the bulk of star formation in more massive galaxies is completed earlier than that of lower-mass galaxies.
Using a large sample of 26 623 quasars with redshifts in the range 1.5 ≤ z ≤ 5.1 with C IV λ1549 Å emission line in Fifth Data Release of the Sloan Digital Sky Survey (SDSS), we investigate the cosmological evolution of the Baldwin effect, i.e. the relation between the equivalent width (EW) of the C IV emission line and continuum luminosity. We confirm the earlier result that there exists a strong correlation between the C IV EW and the continuum luminosity, and we find that, up to z ≈ 5, the slope of the Baldwin effect seems to have no effect of cosmological evolution. A subsample of 13 960 quasars with broad C IV λ1549 Å emission line from SDSS is used to explore the origin of the Baldwin effect. We find that C IV EW have a strong correlation with the mass of supermassive black hole (SMBH), and a weak correlation with the Eddington ratio, L Bol /L Edd . This suggests that the SMBH mass is probably the primary drive for the Baldwin effect.
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