953 research outputs found
The Multi-Wavelength Tully-Fisher relation with spatially resolved HI kinematics
In this paper we investigate the statistical properties of the Tully-Fisher
relation for a sample of 32 galaxies with measured distances from the Cepheid
period-luminosity relation and/or TRGB stars.
We take advantage of panchromatic photometry in 12 bands (from FUV to 4.5
m) and of spatially resolved HI kinematics. We use these data together
with three kinematic measures (, and )
extracted from the global HI profiles or HI rotation curves, so as to construct
36 correlations allowing us to select the one with the least scatter. We
introduce a tightness parameter of the TFr, in order to obtain
a slope-independent measure of the goodness of fit. We find that the tightest
correlation occurs when we select the 3.6 m photometric band together with
the parameter extracted from the HI rotation curve.Comment: 16 pages, 16 figures, accepted for publication in MNRAS, minor
changes due to proof correction
A subarcsecond resolution near-infrared study of Seyfert and `normal' galaxies: II. Morphology
We present a detailed study of the bar fraction in the CfA sample of Seyfert
galaxies, and in a carefully selected control sample of non-active galaxies, to
investigate the relation between the presence of bars and of nuclear activity.
To avoid the problems related to bar classification in the RC3, e.g.,
subjectivity, low resolution and contamination by dust, we have developed an
objective bar classification method, which we conservatively apply to our new
sub-arcsecond resolution near-infrared imaging data set (Peletier et al. 1999).
We are able to use stringent criteria based on radial profiles of ellipticity
and major axis position angle to determine the presence of a bar and its axial
ratio. Concentrating on non-interacting galaxies in our sample for which
morphological information can be obtained, we find that Seyfert hosts are
barred more often (79% +/- 7.5%) than the non-active galaxies in our control
sample (59% +/- 9%), a result which is at the 2.5 sigma significance level. The
fraction of non-axisymmetric hosts becomes even larger when interacting
galaxies are taken into account. We discuss the implications of this result for
the fueling of central activity by large-scale bars. This paper improves on
previous work by means of imaging at higher spatial resolution and by the use
of a set of stringent criteria for bar presence, and confirms that the use of
NIR is superior to optical imaging for detection of bars in disk galaxies.Comment: Latex, 3 figures, includes aaspptwo.sty, accepted for publication in
the Astrophysical Journa
Star formation associated with neutral hydrogen in the outskirts of early-type galaxies
About 20 percent of all nearby early-type galaxies ( M) outside the Virgo cluster are surrounded by a disc
or ring of low-column-density neutral hydrogen (HI) gas with typical radii of
tens of kpc, much larger than the stellar body. In order to understand the
impact of these gas reservoirs on the host galaxies, we analyse the
distribution of star formation out to large radii as a function of HI
properties using GALEX UV and SDSS optical images. Our sample consists of 18
HI-rich galaxies as well as 55 control galaxies where no HI has been detected.
In half of the HI-rich galaxies the radial UV profile changes slope at the
position of the HI radial profile peak. To study the stellar populations, we
calculate the FUV-NUV and UV-optical colours in two apertures, 1-3 and 3-10
R . We find that HI -rich galaxies are on average 0.5 and 0.8 mag bluer
than the HI-poor ones, respectively. This indicates that a significant fraction
of the UV emission traces recent star formation and is associated with the HI
gas. Using FUV emission as a proxy for star formation, we estimate the
integrated star formation rate in the outer regions (R > 1R) to be on
average M yr for the HI-rich galaxies. This
rate is too low to build a substantial stellar disc and, therefore, change the
morphology of the host. We find that the star formation efficiency and the gas
depletion time are similar to those at the outskirts of spirals.Comment: 27 pages (13 without appendices). 9 figures, 5 tables, 2 appendix
tables and 12 appendix figures. Accepted for publication in MNRA
Young stellar populations in early-type dwarf galaxies; occurrence, radial extent and scaling relations
To understand the stellar population content of dwarf early-type galaxies
(dEs) and its environmental dependence, we compare the slopes and intrinsic
scatter of color-magnitude relations (CMRs) for three nearby clusters, Fornax,
Virgo and Coma. Additionally we present and compare internal color profiles of
these galaxies to identify central blue regions with younger stars.
We use the imaging of the HST/ACS Fornax cluster in the magnitude range of
-18.7 <= M_g' <= -16.0, to derive magnitudes, colors and color profiles, which
we compare with literature measurements.
Based on analysis of the color profiles, we report a large number of dEs with
young stellar populations in their center in all three clusters. While for
Virgo and Coma the number of blue-cored dEs is found to be 85 +/- 2% and 53 +/-
3% respectively, for Fornax, we find that all galaxies have a blue core. We
show that bluer cores reside in fainter dEs, similar to the trend seen in
nucleated dEs. We find no correlation between the luminosity of the galaxy and
the size of its blue core. Moreover, a comparison of the CMRs of the three
clusters shows that the scatter in Virgo's CMR is considerably larger than in
the Fornax and Coma clusters. Presenting adaptive smoothing we show that the
galaxies on the blue side of the CMR often show evidence for dust extinction,
which strengthens the interpretation that the bluer colors are due to young
stellar populations. We also find that outliers on the red side of the CMR are
more compact than expected for their luminosity. We find several of these red
outliers in Virgo, often close to more massive galaxies. No red outlying
compact early-types are found in Fornax and Coma in this magnitude range while
we find three in the Virgo cluster. We suggest that the large number of
outliers and larger scatter found for the Virgo cluster CMR is a result of
Virgo's different assembly history.Comment: 24 pages, accepted for publication in Astronomy and Astrophysic
Short range correlations and the isospin dependence of nuclear correlation functions
Pair densities and associated correlation functions provide a critical tool
for introducing many-body correlations into a wide-range of effective theories.
Ab initio calculations show that two-nucleon pair-densities exhibit strong spin
and isospin dependence. However, such calculations are not available for all
nuclei of current interest. We therefore provide a simple model, which involves
combining the short and long separation distance behavior using a single
blending function, to accurately describe the two-nucleon correlations inherent
in existing ab initio calculations. We show that the salient features of the
correlation function arise from the features of the two-body short-range
nuclear interaction, and that the suppression of the pp and nn pair-densities
caused by the Pauli principle is important. Our procedure for obtaining
pair-density functions and correlation functions can be applied to heavy nuclei
which lack ab initio calculations.Comment: 5 pages, 4 figure
Star formation in the outer regions of the early type galaxy NGC 4203
NGC 4203 is a nearby early-type galaxy surrounded by a very large,
low-column-density HI disc. In this paper we study the star formation
efficiency in the gas disc of NGC 4203 by using the UV, deep optical imaging
and infrared data. We confirm that the HI disc consists of two distinct
components: an inner star forming ring with radius from 1 to 3
R, and an outer disc. The outer HI disc is 9 times more massive than
the inner HI ring. At the location of the inner HI ring we detect spiral-like
structure both in the deep image and in the 8 m -IRAC
image, extending in radius up to 3 R. These two gas components
have a different star formation efficiency likely due to the different
metallicity and dust content. The inner component has a star formation
efficiency very similar to the inner regions of late-type galaxies. Although
the outer component has a very low star formation efficiency, it is similar to
that of the outer regions of spiral galaxies and dwarfs. We suggest that these
differences can be explained with different gas origins for the two components
such as stellar mass loss for the inner HI ring and accretion from the inter
galactic medium (IGM) for the outer HI disc. The low level star formation
efficiency in the outer HI disc is not enough to change the morphology of NGC
4203, making the depletion time of the HI gas much too long.Comment: Accepted for publication in MNRAS. 12 pages, 7 figure
Approaching the Coverability Problem Continuously
The coverability problem for Petri nets plays a central role in the
verification of concurrent shared-memory programs. However, its high
EXPSPACE-complete complexity poses a challenge when encountered in real-world
instances. In this paper, we develop a new approach to this problem which is
primarily based on applying forward coverability in continuous Petri nets as a
pruning criterion inside a backward coverability framework. A cornerstone of
our approach is the efficient encoding of a recently developed polynomial-time
algorithm for reachability in continuous Petri nets into SMT. We demonstrate
the effectiveness of our approach on standard benchmarks from the literature,
which shows that our approach decides significantly more instances than any
existing tool and is in addition often much faster, in particular on large
instances.Comment: 18 pages, 4 figure
The number of globular clusters around the iconic UDG DF44 is as expected for dwarf galaxies
There is a growing consensus that the vast majority of ultra-diffuse galaxies
(UDGs) are dwarf galaxies. However, there remain a few UDGs that seem to be
special in terms of their globular cluster (GC) systems. In particular,
according to some authors, certain UDGs exhibit large GC populations when
compared to expectations from their stellar (or total) mass. Among these
special UDGs, DF44 in the Coma cluster is one of the better-known examples.
DF44 has been claimed to have a relatively high number of GCs,
, for a stellar mass of only which would indicate a much larger dark halo mass than dwarfs of similar
stellar mass. In this paper we revisit this number and, contrary to previous
results, find assuming that the distribution of the GCs
follows the same geometry as the galaxy. If we assume that the GCs around DF44
are distributed in a (projected) circularly symmetric way and, if we use a less
strict criterion for the selection of the GCs, we find .
Making use of the relation, this number of GCs
suggests a dark matter halo mass of , a value which is consistent with the expected total mass for DF44
based on its velocity dispersion, km s. We
conclude that the number of GCs around DF44 is as expected for regular dwarf
galaxies of similar stellar mass and DF44 is not extraordinary in this respect.Comment: 16 pages, 13 figures, accepted for publication in MNRAS, minor
changes on the text to match the accepted versio
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