4,956 research outputs found
Comparing data distribution using fading histograms
The emergence of real temporal applications under non-stationary scenarios has drastically altered the ability to generate and gather information. Nowadays, under dynamic scenarios, potentially unbounded and massive amounts of information are generated at high-speed rate, known as data streams. Dealing with evolving data streams imposes the online monitoring of data in order to detect changes. The contribution of this paper is to present the advantage of using fading histograms to compare data distribution for change detection purposes. In an windowing scheme, data distributions provided by the fading histograms are compared using the Kullback-Leibler divergence. The experimental results support that the detection delay time is smaller when using fading histograms to represent data instead of standard histograms
A Search for Low Surface Brightness Structure Around Compact Narrow Emission Line Galaxies
As the most extreme members of the rapidly evolving faint blue galaxy
population at intermediate redshift, the compact narrow emission line galaxies
(CNELGs) are intrinsically luminous (-22 < M_B < -18) with narrow emission
linewidths (30 < \sigma < 125 km/s). Their nature is heavily debated: they may
be low-mass starbursting galaxies that will fade to present-day dwarf galaxies
or bursts of star formation temporarily dominating the flux of more massive
galaxies, possibly related to in situ bulge formation or the formation of cores
of galaxies. We present deep, high-quality (~0.6 - 0.8 arcsec) images with CFHT
of 27 CNELGs. One galaxy shows clear evidence for a tidal tail; the others are
not unambiguously embedded in galactic disks. Approximately 55% of the CNELGS
have sizes consistent with local dwarfs of small-to-intermediate sizes, while
45% have sizes consistent with large dwarfs or disks galaxies. At least 4
CNELGs cannot harbor substantial underlying disk material; they are
low-luminosity galaxies at the present epoch (M_B > -18). Conversely, 15 are
not blue enough to fade to low-luminosity dwarfs (M_B > -15.2). The majority of
the CNELGs are consistent with progenitors of intermediate-luminosity dwarfs
and low-luminosity spiral galaxies with small disks. CNELGs are a heterogeneous
progenitor population with significant fractions (up to 44%) capable of fading
into today's faint dwarfs (M_B > -15.2), while 15 to 85% may only experience an
apparently extremely compact CNELG phase at intermediate redshift but remain
more luminous galaxies at the present epoch.Comment: 16 pages, 14 figures, emulateapj, published in Ap
Star Cluster Formation and Disruption Time-Scales -- I. An empirical determination of the disruption time of star clusters in four galaxies
We present a new method to derive the cluster disruption time in selected
regions of galaxies from the mass or age distribution of magnitude-limited
cluster samples. If the disruption time of clusters in a region of a galaxy
depends on their initial mass as t_4 x (M_cluster/10^4 M_sun)^gamma and if the
cluster formation rate is constant, then the mass and age distributions of the
observed clusters will each show two powerlaw relations. The values of t_4 and
gamma can be derived from these relations. We used this method to derive the
cluster disruption time in specific regions in four galaxies: the inner region
of M51, a region of M33, the SMC and the solar neighbourhood. The values of
gamma are the same in the four galaxies within the uncertainty and the mean
value is gamma= 0.62 +- 0.06. However the disruption time t_4 of a cluster of
10^4 M_sun is very different in the different galaxies. The clusters in the SMC
have the longest disruption time, t_4 = 8 Gyr, and the clusters at 1 to 3 kpc
from the nucleus of M51 have the shortest disruption time of t_4 = 0.04 Gyr.
The disruption time of clusters 1 to 5 kpc from the nucleus of M33 is t_4 =
0.13 Gyr and for clusters within 1 kpc from the Sun we find t_4 = 1.0 Gyr.Comment: 18 pages, 18 figures. Accepted for publication by Monthly Notice
Two Conditions for Galaxy Quenching: Compact Centres and Massive Haloes
We investigate the roles of two classes of quenching mechanisms for central
and satellite galaxies in the SDSS (): those involving the halo and
those involving the formation of a compact centre. For central galaxies with
inner compactness ,
the quenched fraction is strongly correlated with
with only weak halo mass dependence. However, at higher and lower
, sSFR is a strong function of and mostly
independent of . In other words, divides galaxies into those with high sSFR
below and low sSFR above this range. In both the upper and lower regimes,
increasing shifts the entire sSFR distribtuion to lower sSFR
without a qualitative change in shape. This is true even at fixed , but
varying at fixed adds no quenching information. Most of the
quenched centrals with are dense (), suggesting compaction-related
quenching maintained by halo-related quenching. However, 21% are diffuse,
indicating only halo quenching. For satellite galaxies in the outskirts of
halos, quenching is a strong function of compactness and a weak function of
host . In the inner halo, dominates quenching, with
of the satellites being quenched once . This regional effect is greatest for the least massive
satellites. As demonstrated via semi-analytic modelling with simple
prescriptions for quenching, the observed correlations can be explained if
quenching due to central compactness is rapid while quenching due to halo mass
is slow.Comment: 16 pages, 11 figures, MNRAS accepte
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