131 research outputs found
On the Lengths, Colours and Ages of Bars
In an effort to obtain further observational evidences for secular evolution
processes in galaxies, as well as observational constraints to current
theoretical models of secular evolution, we have used BVRI and Ks images of a
sample of 18 barred galaxies to measure the lengths and colours of bars, create
colour maps and estimate global colour gradients. In addition, applying a
method we developed in a previous article, we could distinguish for 7 galaxies
in our sample those whose bars have been recently formed from the ones with
already evolved bars. We estimated an average difference in the optical colours
between young and evolved bars that may be translated to an age difference of
the order of 10 Gyr, meaning that bars may be long standing structures.
Moreover, our results show that, on average, evolved bars are longer than young
bars. This seems to indicate that, during its evolution, a bar grows longer by
capturing stars from the disk, in agreement with recent numerical and
analytical results.Comment: To appear in Galaxy Evolution Across the Hubble Time, proceedings of
the IAU Symp. 235, F. Combes and J. Palous (eds.); 1 page; the poster can be
found at http://www.mpa-garching.mpg.de/~dimitri/iauga.pd
Peanut-shaped metallicity distributions in bulges of edge-on galaxies: the case of NGC 4710
Bulges of edge-on galaxies are often boxy/peanut-shaped (B/PS), and unsharp masks reveal the presence of an X shape. Simulations show that these shapes can be produced by dynamical processes driven by a bar which vertically thickens the centre. In the Milky Way, which contains such a B/PS bulge, the X-shaped structure is traced by the metal-rich stars but not
by the metal-poor ones. Recently, Debattista et al. interpreted this property as a result of the varying effect of the bar on stellar populations with different starting kinematics. This kinematic fractionation model predicts that cooler populations at the time of bar formation go on to trace the X shape, whereas hotter populations are more uniformly distributed. As this
prediction is not specific to the Milky Way, we test it with Multi Unit Spectroscopic Explorer (MUSE) observations of the B/PS bulge in the nearby galaxy NGC 4710. We show that the metallicity map is more peanut-shaped than the density distribution itself, in good agreement with the prediction. This result indicates that the X-shaped structure in B/PS bulges is formed of relatively metal-rich stars that have been vertically redistributed by the bar, whereas the metal-poor stars have more uniform, box-shaped distribution
Peanut-shaped metallicity distributions in bulges of edge-on galaxies: the case of NGC 4710
Bulges of edge-on galaxies are often boxy/peanut-shaped (B/PS), and unsharp masks reveal the presence of an X shape. Simulations show that these shapes can be produced by dynamical processes driven by a bar which vertically thickens the centre. In the Milky Way, which contains such a B/PS bulge, the X-shaped structure is traced by the metal-rich stars but not
by the metal-poor ones. Recently, Debattista et al. interpreted this property as a result of the varying effect of the bar on stellar populations with different starting kinematics. This kinematic fractionation model predicts that cooler populations at the time of bar formation go on to trace the X shape, whereas hotter populations are more uniformly distributed. As this
prediction is not specific to the Milky Way, we test it with Multi Unit Spectroscopic Explorer (MUSE) observations of the B/PS bulge in the nearby galaxy NGC 4710. We show that the metallicity map is more peanut-shaped than the density distribution itself, in good agreement with the prediction. This result indicates that the X-shaped structure in B/PS bulges is formed of relatively metal-rich stars that have been vertically redistributed by the bar, whereas the metal-poor stars have more uniform, box-shaped distribution
Training telescope operators and support astronomers at Paranal
The operations model of the Paranal Observatory relies on the work of
efficient staff to carry out all the daytime and nighttime tasks. This is
highly dependent on adequate training. The Paranal Science Operations
department (PSO) has a training group that devises a well-defined and
continuously evolving training plan for new staff, in addition to broadening
and reinforcing courses for the whole department. This paper presents the
training activities for and by PSO, including recent astronomical and quality
control training for operators, as well as adaptive optics and interferometry
training of all staff. We also present some future plans.Comment: Paper 9910-123 presented at SPIE 201
Kinematical Signatures of Disc Instabilities and Secular Evolution in the MUSE TIMER Survey
The MUSE TIMER Survey has obtained high signal and high spatial resolution
integral-field spectroscopy data of the inner kpc of 21 nearby
massive disc galaxies. This allows studies of the stellar kinematics of the
central regions of massive disc galaxies that are unprecedented in spatial
resolution. We confirm previous predictions from numerical and hydrodynamical
simulations of the effects of bars and inner bars on stellar and gaseous
kinematics, and also identify box/peanuts via kinematical signatures in mildly
and moderately inclined galaxies, including a box/peanut in a face-on inner
bar. In 20/21 galaxies we find inner discs and show that their properties are
fully consistent with the bar-driven secular evolution picture for their
formation. In addition, we show that these inner discs have, in the region
where they dominate, larger rotational support than the main galaxy disc, and
discuss how their stellar population properties can be used to estimate when in
cosmic history the main bar formed. Our results are compared with photometric
studies in the context of the nature of galaxy bulges and we show that inner
discs are identified in image decompositions as photometric bulges with
exponential profiles (i.e., S\'ersic indices near unity).Comment: 4 pages, 5 figures, to appear in Galactic Dynamics in the Era of
Large Surveys, M. Valluri & J. A. Sellwood (eds.
NGC 5746:Formation history of a massive disc-dominated galaxy
The existence of massive galaxies lacking a classical bulge has often been proposed as a challenge to ΛCDM. However, recent simulations propose that a fraction of massive disc galaxies might have had very quiescent merger histories, and also that mergers do not necessarily build classical bulges. We test these ideas with deep MUSE observations of NGC 5746, a massive (~1011 M⊙) edge-on disc galaxy with no classical bulge. We analyse its stellar kinematics and stellar populations, and infer that a massive and extended disc formed very early: 80 per cent of the galaxy's stellar mass formed more than 10 Gyr ago. Most of the thick disc and the bar formed during that early phase. The bar drove gas towards the centre and triggered the formation of the nuclear disc followed by the growth of a boxy/peanut-shaped bulge. Around ~8 Gyr ago, a ~1:10 merger happened, possibly on a low-inclination orbit. The satellite did not cause significant vertical heating, did not contribute to the growth of a classical bulge, and did not destroy the bar and the nuclear disc. It was however an important event for the galaxy: by depositing its stars throughout the whole galaxy it contributed ~30 per cent of accreted stars to the thick disc. NGC 5746 thus did not completely escape mergers, but the only relatively recent significant merger did not damage the galaxy and did not create a classical bulge. Future observations will reveal if this is representative of the formation histories of massive disc galaxies
On the accretion of a new group of galaxies onto Virgo – III. The stellar population radial gradients of dEs
Using MUSE data, we investigate the radial gradients of stellar population properties (namely age, [M/H], and the abundance ratio of α elements [α/Fe]) for a sample of nine dwarf early-type (dE) galaxies with log(M/M) ∼ 9.0 and an infall time onto the Virgo cluster of 2–3 Gyr ago. We followed a similar approach as in Bidaran et al. to derive their stellar population properties and star formation histories (SFHs) through fitting observed spectral indices and full spectral fitting, respectively. We find that these nine dE galaxies have truncated [Mg/Fe] versus [Fe/H] profiles than equally massive Virgo dE galaxies with longer past infall times. Short profiles of three dE galaxies are the result of their intense star formation which has been quenched long before their accretion onto the Virgo cluster, possibly as a result of their group environment. In the remaining six dE galaxies, profilesmainly trace a recent episode of star burst within 0.4Re which results in higher light-weighted [α/Fe] values. The latter SFH peak can be due to ram pressure exerted by the Virgo cluster at the time of the accretion of the dE galaxies. Also, we show that younger, more metal-rich, and less α-enhanced stellar populations dominate their inner regions (i.e. < 0.4Re) resulting in mainly flat ∇age, negative ∇[M/H], and positive ∇[α/Fe]. We find that with increasing log(σ Re) of dE galaxies, ∇age and ∇[α/Fe] flatten, and the latter correlation persists even after including early-type galaxies up to log(σ Re ∼ 2.5), possibly due to the more extended star formation activity in the inner regions of dEs, as opposed to more massive early-type galaxies
On the accretion of a new group of galaxies onto Virgo: III. The stellar population radial gradients of dEs
Using MUSE data, we investigate the radial gradients of stellar population
properties (namely age, [M/H], and the abundance ratio of elements
[/Fe]) for a sample of nine dwarf early-type (dE) galaxies with
log(M/M) 9.0 and an infall time onto the Virgo
cluster of 2-3Gyr ago. We followed a similar approach as in Bidaran et al.
(2022) to derive their stellar population properties and star formation
histories (SFHs) through fitting observed spectral indices and full spectral
fitting, respectively. We find that these nine dE galaxies have truncated
[Mg/Fe]vs.[Fe/H] profiles than equally-massive Virgo dE galaxies with longer
past infall times. Short profiles of three dE galaxies are the result of their
intense star formation which has been quenched long before their accretion onto
the Virgo cluster, possibly as a result of their group environment. In the
remaining six dE galaxies, profiles mainly trace a recent episode of star burst
within 0.4R which results in higher light-weighted [/Fe]
values. The latter SFH peak can be due to ram pressure exerted by the Virgo
cluster at the time of the accretion of the dE galaxies. Also, we show that
younger, more metal-rich and less -enhanced stellar populations
dominate their inner regions (i.e., < 0.4R) resulting in mainly flat
, negative and positive . We find that with increasing log() of dE
galaxies, and flatten, and the
latter correlation persists even after including early-type galaxies up to
log( 2.5), possibly due to the more extended star
formation activity in the inner regions of dEs, as opposed to more massive
early-type galaxies.Comment: 18 pages, 8 figures, accepted in MNRA
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