110 research outputs found
Properties of the Dwarf Galaxy Population in Galaxy Clusters
We present the observational properties of the dwarf galaxy population (Mr >
M*+1) corresponding to one of the largest samples of spectroscopically
confirmed galaxy cluster members reported in the literature. We have observed
that red dwarf galaxies (u-r > 2.22) share the same cluster environment as the
brightest cluster members (Mr < -21), but are not in dynamical equilibrium. We
computed the dwarf-to-giant ratio (DGR) using a spectroscopically selected
sample. The DGR was found to vary with clustercentric distance, essentially due
to the blue dwarf population (u-r < 2.22). The u-r color of red dwarf galaxies
was independent of their environment and similar to the color of red isolated
dwarfs. Blue dwarf galaxies located outside r200 show similar u-r colors to
those of the field population, while strong reddening was observed toward the
cluster center. We also present evidence that the fraction of red to blue dwarf
galaxies in clusters is larger in the innermost cluster regions. We conclude
that the present red dwarf population observed in the central regions of nearby
galaxy clusters could be related to the blue dwarf population observed in
clusters at high redshift.Comment: 5 pages, 3 color figures, accepted for publication in the ApJ Letter
A numerical study of interactions and stellar bars
For several decades it has been known that stellar bars in disc galaxies can
be triggered by interactions, or by internal processes such as dynamical
instabilities. In this work, we explore the differences between these two
mechanisms using numerical simulations. We perform two groups of simulations
based on isolated galaxies, one group in which a bar develops naturally, and
another group in which the bar could not develop in isolation. The rest of the
simulations recreate 1:1 coplanar fly-by interactions computed with the impulse
approximation. The orbits we use for the interactions represent the fly-bys in
groups or clusters of different masses accordingly to the velocity of the
encounter. In the analysis we focus on bars' amplitude, size, pattern speed and
their rotation parameter, . The latter is used to
define fast (). Compared with
equivalent isolated galaxies we find that bars affected or triggered by
interactions: (i) remain in the slow regime for longer; (ii) are more boxy in
face-on views; (iii) they host kinematically hotter discs. Within this set of
simulations we do not see strong differences between retrograde or prograde
fly-bys. We also show that slow interactions can trigger bar formation.Comment: 12 pages, 7 figures. Accepted for publication in MNRA
Moving Groups Across Galactocentric Radius with Gaia DR3
The kinematic plane of stars near the Sun has proven an indispensable tool
for untangling the complexities of the structure of our Milky Way (MW). With
ever improving data, numerous kinematic "moving groups" of stars have been
better characterized and new ones continue to be discovered. Here we present an
improved method for detecting these groups using MGwave, a new open-source 2D
wavelet transformation code that we have developed. Our code implements similar
techniques to previous wavelet software; however, we include a more robust
significance methodology and also allow for the investigation of underdensities
which can eventually provide further information about the MW's
non-axisymmetric features. Applying MGwave to the latest data release from Gaia
(DR3), we detect 45 groups of stars with coherent velocities. We reproduce the
majority of the previously detected moving groups in addition to identifying
four additional significant candidates: one near Antoja12-GCSIII-13, one near
GMG 5, and two with very low and similar to Hercules. Finally,
we have followed these associations of stars beyond the solar neighborhood,
from Galactocentric radius of 6.5 to 10~kpc. Most detected groups are extended
throughout radius indicating that they are streams of stars possibly due to
non-axisymmetric features of the MW.Comment: 13 pages, 7 figures, 3 tables. MGwave code available upon request to
the corresponding autho
Evolution along the sequence of S0 Hubble types induced by dry minor mergers. II - Bulge-disk coupling in the photometric relations through merger-induced internal secular evolution
Galaxy mergers are considered as questionable mechanisms for the evolution of
lenticular galaxies (S0's), on the basis that even minor ones induce structural
changes that are difficult to reconcile with the strong bulge-disk coupling
observed in the photometric scaling relations of S0's. We check if the
evolution induced onto S0's by dry intermediate and minor mergers can reproduce
their photometric scaling relations, analysing the bulge-disk decompositions of
the merger simulations presented in Eliche-Moral et al. (2012). The mergers
induce an evolution in the photometric planes compatible with the data of S0's,
even in those ones indicating a strong bulge-disk coupling. The mergers drive
the formation of the observed photometric relation in some cases, whereas they
induce a slight dispersion compatible with data in others. Therefore, this
evolutionary mechanism tends to preserve these scaling relations. In those
photometric planes where the morphological types segregate, the mergers always
induce evolution towards the region populated by S0's. The structural coupling
of the bulge and the disk is preserved or reinforced because the mergers
trigger internal secular processes in the primary disk that induce significant
bulge growth, even although these models do not induce bars. Intermediate and
minor mergers can thus be considered as plausible mechanisms for the evolution
of S0's attending to their photometric scaling relations, as they can preserve
and even strengthen any pre-existing structural bulge-disk coupling, triggering
significant internal secular evolution (even in the absence of bars or
dissipational effects). This means that it may be difficult to isolate the
effects of pure internal secular evolution from those of the merger-driven one
in present-day early-type disks (abridged).Comment: Accepted for publication in Astronomy & Astrophysics, 13 pages, 8
figures. Definitive version after proofs. Added references and corrected
typo
CALIFA reveals Prolate Rotation in Massive Early-type Galaxies: A Polar Galaxy Merger Origin?
We present new evidence for eight early-type galaxies (ETGs) from the CALIFA
Survey that show clear rotation around their major photometric axis ("prolate
rotation"). These are LSBCF560-04, NGC 0647, NGC 0810, NGC 2484, NGC 4874, NGC
5216, NGC 6173 and NGC 6338. Including NGC 5485, a known case of an ETG with
stellar prolate rotation, as well as UGC 10695, a further possible candidate
for prolate rotation, we report ten CALIFA galaxies in total that show evidence
for such a feature in their stellar kinematics. Prolate rotators correspond to
~9% of the volume-corrected sample of CALIFA ETGs, a fraction much higher than
previously reported. We find that prolate rotation is more common among the
most massive ETGs. We investigate the implications of these findings by
studying N-body merger simulations, and show that a prolate ETG with rotation
around its major axis could be the result of a major polar merger, with the
amplitude of prolate rotation depending on the initial bulge-to-total stellar
mass ratio of its progenitor galaxies. Additionally, we find that prolate ETGs
resulting from this formation scenario show a correlation between their stellar
line-of-sight velocity and higher order moment h_3, opposite to typical oblate
ETGs, as well as a double peak of their stellar velocity dispersion along their
minor axis. Finally, we investigate the origin of prolate rotation in polar
galaxy merger remnants. Our findings suggest that prolate rotation in massive
ETGs might be more common than previously expected, and can help towards a
better understanding of their dynamical structure and formation origin.Comment: accepted for publication in A&
Relations among structural parameters in barred galaxies with a direct measurement of bar pattern speed
We investigate the relations between the properties of bars and their host
galaxies in a sample of 77 nearby barred galaxies, spanning a wide range of
morphological types and luminosities, with 34 SB0-SBa and 43 SBab-SBc galaxies.
The sample includes all the galaxies with reliable direct measurement of their
bar pattern speed based on long-slit or integral-field stellar spectroscopy
using the Tremaine-Weinberg method. We limited our analysis to the galaxies
with a relatively small relative error on the bar pattern speed (smaller than
50 per cent) and not hosting an ultrafast bar. For each galaxy, we collected
the radius, strength, pattern speed, corotation radius, and rotation rate for
the bar and we also collected the Hubble type and absolute SDSS r-band
magnitude. We also used literature bulge-to-total luminosity ratio for a
subsample of 53 galaxies with an available photometric decomposition. We
confirmed earlier observational findings that longer bars rotate with lower bar
pattern speeds, shorter bars are weaker, and bars with a small bar rotation
rate rotate with higher bar pattern speeds and have smaller corotation radii.
In addition, we found that stronger bars rotate with lower bar pattern speeds,
as predicted from the interchange of angular momentum during bar evolution,
which in turn may depend on different galaxy properties. Moreover, we report
that brighter galaxies host longer bars, which rotate with lower bar pattern
speeds and have larger corotation radii. This result is in agreement with a
scenario of downsizing in bar formation, if more massive galaxies formed
earlier and had sufficient time to slow down, grow in length, and push
corotation outwards.Comment: revised and accepted for pubblication in Astronomy & Astrophysic
The edge of the M87 halo and the kinematics of the diffuse light in the Virgo cluster core
We present high resolution FLAMES/VLT spectroscopy of intracluster planetary
nebula (ICPN) candidates, targeting three new fields in the Virgo cluster core
with surface brightness down to mu_B = 28.5. Based on the projected phase space
information we separate the old and 12 newly-confirmed PNs into galaxy and
intracluster components. The M87 PNs are confined to the extended stellar
envelope of M87, within a projected radius of ~ 160 kpc, while the ICPNs are
scattered across the whole surveyed region between M87 and M86. The velocity
dispersions determined from the M87 PNs at projected radii of 60 kpc and 144
kpc show that the galaxy's velocity dispersion profile decreases in the outer
halo, down to 78 +/- 25 km/s. A Jeans model for the M87 halo stars in the
gravitational potential traced by the X-ray emission fits the observed velocity
dispersion profile only if the stellar orbits are strongly radially anisotropic
(beta ~= 0.4 at r ~= 10 kpc increasing to 0.8 at the outer edge), and if
additionally the stellar halo is truncated at ~= 150 kpc average elliptical
radius. From the spatial and velocity distribution of the ICPNs we infer that
M87 and M86 are falling towards each other and that we may be observing them
just before the first close pass. The inferred luminosity-specific PN numbers
for the M87 halo and the ICL are in the range of values observed for old (> 10
Gyr) stellar populations (abridged).Comment: Accepted for publication in Astronomy and Astrophysics. 16 pages, 14
figures and 4 table
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