578 research outputs found
The NGC 4013 tale: a pseudo-bulged, late-type spiral shaped by a major merger
Many spiral galaxy haloes show stellar streams with various morphologies when
observed with deep images. The origin of these tidal features is discussed,
either coming from a satellite infall or caused by residuals of an ancient,
gas-rich major merger. By modelling the formation of the peculiar features
observed in the NGC 4013 halo, we investigate their origin. By using GADGET -2
with implemented gas cooling, star formation, and feedback, we have modelled
the overall NGC 4013 galaxy and its associated halo features. A gas-rich major
merger occurring 2.7-4.6 Gyr ago succeeds in reproducing the NGC 4013 galaxy
properties, including all the faint stellar features, strong gas warp,
boxy-shaped halo and vertical 3.6 mum luminosity distribution. High gas
fractions in the progenitors are sufficient to reproduce the observed thin and
thick discs, with a small bulge fraction, as observed. A major merger is able
to reproduce the overall NGC 4013 system, including the warp strength, the red
colour and the high stellar mass density of the loop, while a minor merger
model cannot. Because the gas-rich model suffices to create a pseudo-bulge with
a small fraction of the light, NGC 4013 is perhaps the archetype of a late-type
galaxy formed by a relatively recent merger. Then late type, pseudo-bulge
spirals are not mandatorily made through secular evolution, and the NGC 4013
properties also illustrate that strong warps in isolated galaxies may well
occur at a late phase of a gas-rich major merger.Comment: 11 pages,9 figures,accepted for publication in MNRA
Towards a robust estimate of the merger rate evolution using near-IR photometry
We use a combination of deep, high angular resolution imaging data from the
CDFS (HST/ACS GOODS survey) and ground based near-IR images to derive the
evolution of the galaxy major merger rate in the redshift range . We select galaxies on the sole basis of their J-band rest-frame,
absolute magnitude, which is a good tracer of the stellar mass. We find steep
evolution with redshift, with the merger rate for
optically selected pairs, and for pairs selected
in the near-IR. Our result is unlikely to be affected by luminosity evolution
which is relatively modest when using rest-frame J band selection. The
apparently more rapid evolution that we find in the visible is likely caused by
biases relating to incompleteness and spatial resolution affecting the ground
based near IR photometry, underestimating pair counts at higher redshifts in
the near-IR. The major merger rate was 5.6 times higher at
than at the current epoch. Overall 41%(0.5\gyr/) of all
galaxies with have undergone a major merger in the last \sim8
\gyr, where is the merger timescale. Interestingly, we find no effect
on the derived major merger rate due to the presence of the large scale
structure at in the CDFS.Comment: Accepted for Publication in ApJ. 9 Figure
FALCON: a concept to extend adaptive optics corrections to cosmological fields
FALCON is an original concept for a next generation spectrograph at ESO VLT
or at future ELTs. It is a spectrograph including multiple small integral field
units (IFUs) which can be deployed within a large field of view such as that of
VLT/GIRAFFE. In FALCON, each IFU features an adaptive optics correction using
off-axis natural reference stars in order to combine, in the 0.8-1.8 \mu m
wavelength range, spatial and spectral resolutions (0.1-0.15 arcsec and
R=10000+/-5000). These conditions are ideally suited for distant galaxy
studies, which should be done within fields of view larger than the galaxy
clustering scales (4-9 Mpc), i.e. foV > 100 arcmin2. Instead of compensating
the whole field, the adaptive correction will be performed locally on each IFU.
This implies to use small miniaturized devices both for adaptive optics
correction and wavefront sensing. Applications to high latitude fields imply to
use atmospheric tomography because the stars required for wavefront sensing
will be in most of the cases far outside the isoplanatic patch.Comment: To appear in the Backaskog "Second Workshop on ELT" SPIE proceeding
Reproducing properties of MW dSphs as descendants of DM-free TDGs
The Milky Way (MW) dwarf spheroidal (dSph) satellites are known to be the
most dark-matter (DM) dominated galaxies with estimates of dark to baryonic
matter reaching even above one hundred. It comes from the assumption that
dwarfs are dynamically supported by their observed velocity dispersions.
However their spatial distributions around the MW is not at random and this
could challenge their origin, previously assumed to be residues of primordial
galaxies accreted by the MW potential. Here we show that alternatively, dSphs
could be the residue of tidal dwarf galaxies (TDGs), which would have
interacted with the Galactic hot gaseous halo and disk. TDGs are gas-rich and
have been formed in a tidal tail produced during an ancient merger event at the
M31 location, and expelled towards the MW. Our simulations show that low-mass
TDGs are fragile to an interaction with the MW disk and halo hot gas. During
the interaction, their stellar content is progressively driven out of
equilibrium and strongly expands, leading to low surface brightness feature and
mimicking high dynamical M/L ratios. Our modeling can reproduce the properties,
including the kinematics, of classical MW dwarfs within the mass range of the
Magellanic Clouds to Draco. An ancient gas-rich merger at the M31 location
could then challenge the currently assumed high content of dark matter in dwarf
galaxies. We propose a simple observational test with the coming GAIA mission,
to follow their expected stellar expansion, which should not be observed within
the current theoretical framework.Comment: 17 pages, 11 figures, accepted by the Monthly Notices of the Royal
Astronomical Society (MNRAS
An extended stellar halo discovered in the Fornax dwarf spheroidal using Gaia EDR3
We have studied the extent of the Red Giant Branch stellar population in the
Fornax dwarf spheroidal galaxy using the spatially extended and homogeneous
data set from Gaia EDR3. Our preselection of stars belonging to Fornax is based
on their proper motions, parallaxes and color-magnitude diagram. The latter
criteria provide a Fornax star sample, which we further restrict by color and
magnitude to eliminate contaminations due to either Milky Way stars or QSOs.
The precision of the data has been sufficient to reach extremely small
contaminations (0.02 to 0.3%), allowing us to reach to a background level 12
magnitudes deeper than the central surface brightness of Fornax. We discover a
break in the density profile, which reveals the presence of an additional
component that extents 2.1 degree in radius, i.e. 5.4 kpc, and almost seven
times the half-light radius of Fornax. The extended new component represents
10% of the stellar mass of Fornax, and behaves like an extended halo. The
absence of tidally elongated features at such an unprecedented depth
(equivalent to mag in V-band) rules out a
possible role of tidal stripping. We suggest instead that Fornax is likely at
first infall, and has lost its gas very recently, which consequently leads to a
lack of gravity implying that residual stars have spherically expanded to form
the newly discovered stellar halo of Fornax.Comment: 15 pages, 10 figures, 4 tables, MNRAS, in press, version based on
proof
Developing an integrated concept for the E-ELT Multi-Object Spectrograph (MOSAIC): design issues and trade-offs
We present a discussion of the design issues and trade-offs that have been
considered in putting together a new concept for MOSAIC, the multi-object
spectrograph for the E-ELT. MOSAIC aims to address the combined science cases
for E-ELT MOS that arose from the earlier studies of the multi-object and
multi-adaptive optics instruments. MOSAIC combines the advantages of a
highly-multiplexed instrument targeting single-point objects with one which has
a more modest multiplex but can spatially resolve a source with high resolution
(IFU). These will span across two wavebands: visible and near-infrared
Revisiting mass estimates of the Milky Way
We use the rotation curve from Gaia data release (DR) 3 to estimate the mass
of the Milky Way. We consider an Einasto density profile to model the dark
matter component. We extrapolate and obtain a dynamical mass
at kpc. This lower-mass
Milky Way is consistent with the significant declining rotation curve, and can
provide new insights into our Galaxy and halo inhabitants.Comment: 4 pages, 2 figures, Accepted for publication in proceedings of IAU
Symposium 379: Dynamical Masses of Local Group Galaxies, Potsdam, March
20-24, 202
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