629 research outputs found
Evidence for Photoionization Driven Broad Absorption Line Variability
We present a qualitative analysis of the variability of quasar broad
absorption lines using the large multi-epoch spectroscopic dataset of the Sloan
Digital Sky Survey Data Release 10. We confirm that variations of absorption
lines are highly coordinated among different components of the same ion or the
same absorption component of different ions for C IV, Si IV and N V.
Furthermore, we show that the equivalent widths of the lines decrease or
increase statistically when the continuum brightens or dims. This is further
supported by the synchronized variations of emission and absorption line
equivalent width, when the well established intrinsic Baldwin effect for
emission lines is taken into account. We find that the emergence of an
absorption component is usually accompanying with dimming of the continuum
while the disappearance of an absorption line component with brightening of the
continuum. This suggests that the emergence or disappearance of a C IV
absorption component is only the extreme case, when the ionic column density is
very sensitive to continuum variations or the continuum variability amplitude
is larger. These results support the idea that absorption line variability is
driven mainly by changes in the gas ionization in response to continuum
variations, that the line-absorbing gas is highly ionized, and in some extreme
cases, too highly ionized to be detected in UV absorption lines. Due to
uncertainties in the spectroscopic flux calibration, we cannot quantify the
fraction of quasars with asynchronized continuum and absorption line
variations.Comment: 41 pages, 15 figures, accepted to Ap
The clustering of galaxies with pseudo bulge and classical bulge in the local Universe
We investigate the clustering properties and close neighbour counts for
galaxies with different types of bulges and stellar masses. We select samples
of "classical" and "pseudo" bulges, as well as "bulge-less" disk galaxies,
based on the bulge/disk decomposition catalog of SDSS galaxies provided by
Simard et al. (2011). For a given galaxy sample we estimate: the projected
two-point cross-correlation function with respect to a spectroscopic reference
sample, w_p(r_p), and the average background-subtracted neighbour count within
a projected separation using a photometric reference sample, N_neighbour(<r_p).
We compare the results with the measurements of control samples matched in
color, concentration and redshift. We find that, when limited to a certain
stellar mass range and matched in color and concentration, all the samples
present similar clustering amplitudes and neighbour counts on scales above
~0.1h^{-1}Mpc. This indicates that neither the presence of a central bulge, nor
the bulge type is related to intermediate-to-large scale environments. On
smaller scales, in contrast, pseudo-bulge and pure-disk galaxies similarly show
strong excess in close neighbour count when compared to control galaxies, at
all masses probed. For classical bulges, small-scale excess is also observed
but only for M_stars < 10^{10} M_sun; at higher masses, their neighbour counts
are similar to that of control galaxies at all scales. These results imply
strong connections between galactic bulges and galaxy-galaxy interactions in
the local Universe, although it is unclear how they are physically linked in
the current theory of galaxy formation.Comment: 14 pages, 16 figures, accepted for publication in MNRA
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