3,045 research outputs found
The role of stellar radial motions in shaping galaxy surface brightness profiles
Aims. The physics driving features such as breaks observed in galaxy surface brightness (SB) profiles remains contentious. Here, we assess the importance of stellar radial motions in shaping their characteristics. Methods. We use the simulated Milky Way-mass cosmological discs from the Ramses Disc Environment Study (RaDES) to characterise the radial redistribution of stars in galaxies displaying type-I (pure exponentials), II (downbending), and III (upbending) SB profiles. We compare radial profiles of the mass fractions and the velocity dispersions of different sub-populations of stars according to their birth and current location. Results. Radial redistribution of stars is important in all galaxies regardless of their light profiles. Type-II breaks seem to be a consequence of the combined effects of outward-moving and accreted stars. The former produce shallower inner profiles (lack of stars in the inner disc) and accumulate material around the break radius and beyond, strengthening the break; the latter can weaken or even convert the break into a pure exponential. Further accretion from satellites can concentrate material in the outermost parts, leading to type-III breaks that can coexist with type-II breaks, but situated further out. Type-III galaxies would be the result of an important radial redistribution of material throughout the entire disc, as well as a concentration of accreted material in the outskirts. In addition, type-III galaxies display the most efficient radial redistribution and the largest number of accreted stars, followed by type-I and II systems, suggesting that type-I galaxies may be an intermediate case between types-II and III. In general, the velocity dispersion profiles of all galaxies tend to flatten or even increase around the locations where the breaks are found. The age and metallicity profiles are also affected, exhibiting different inner gradients depending on their SB profile, being steeper in the case of type-II systems (as found observationally). The steep type-II profiles might be inherent to their formation rather than acquired via radial redistribution
Substructure in the stellar halo near the Sun:I. Data-driven clustering in integrals-of-motion space
Aims: Develop a data-driven and statistically based method for finding such
clumps in Integrals of Motion space for nearby halo stars and evaluating their
significance robustly. Methods: We use data from Gaia EDR3 extended with radial
velocities from ground-based spectroscopic surveys to construct a sample of
halo stars within 2.5 kpc from the Sun. We apply a hierarchical clustering
method that uses the single linkage algorithm in a 3D space defined by the
commonly used integrals of motion energy , together with two components of
the angular momentum, and . To evaluate the statistical
significance of the clusters found, we compare the density within an
ellipsoidal region centered on the cluster to that of random sets with similar
global dynamical properties. We pick out the signal at the location of their
maximum statistical significance in the hierarchical tree. We estimate the
proximity of a star to the cluster center using the Mahalanobis distance. We
also apply the HDBSCAN clustering algorithm in velocity space. Results: Our
procedure identifies 67 highly significant clusters (), containing
12\% of the sources in our halo set, and in total 232 subgroups or individual
streams in velocity space. In total, 13.8\% of the stars in our data set can be
confidently associated to a significant cluster based on their Mahalanobis
distance. Inspection of our data set reveals a complex web of relationships
between the significant clusters, suggesting that they can be tentatively
grouped into at least 6 main structures, many of which can be associated to
previously identified halo substructures, and a number of independent
substructures. This preliminary conclusion is further explored in an
accompanying paper by Ruiz-Lara et al., where we also characterize the
substructures in terms of their stellar populations. Conclusions: We find...
(abridged version)Comment: 16 pages, 14 figures, 2 tables. Accepted for publication in A&A. This
is the first in a series of papers, the second (Ruiz-Lara et al.) can be
found in https://ui.adsabs.harvard.edu/abs/2022arXiv220102405R/abstract Code
of the clustering algorithm can be found in
https://github.com/SofieLovdal/IOM_clusterin
Spectroscopic characterisation of the stellar content of ultra diffuse galaxies
Understanding the peculiar properties of Ultra Diffuse Galaxies (UDGs) via
spectroscopic analysis is a challenging task requiring very deep observations
and exquisite data reduction. In this work we perform one of the most complete
characterisations of the stellar component of UDGs to date using deep optical
spectroscopic data from OSIRIS at GTC. We measure radial and rotation
velocities, star formation histories (SFH) and mean population parameters, such
as ages and metallicities, for a sample of five UDG candidates in the Coma
cluster. From the radial velocities, we confirm the Coma membership of these
galaxies. We find that their rotation properties, if detected at all, are
compatible with dwarf-like galaxies. The SFHs of the UDG are dominated by old
(~ 7 Gyr), metal-poor ([M/H] ~ -1.1) and alpha-enhanced ([Mg/Fe] ~ 0.4)
populations followed by a smooth or episodic decline which halted ~ 2 Gyr ago,
possibly a sign of cluster-induced quenching. We find no obvious correlation
between individual SFH shapes and any UDG morphological properties. The
recovered stellar properties for UDGs are similar to those found for DDO44, a
local UDG analogue resolved into stars. We conclude that the UDGs in our sample
are extended dwarfs whose properties are likely the outcome of both internal
processes, such as bursty SFHs and/or high-spin haloes, as well as
environmental effects within the Coma cluster.Comment: Accepted for publication in MNRA
The bursty star formation history of the Fornax dwarf spheroidal galaxy revealed with the HST
We present a new derivation of the star formation history (SFH) of the dSph
galaxy Fornax in two central regions, characterised by unprecedented precision
and age resolution. It reveals that star formation has proceeded in sharp
bursts separated by periods of low-level or quiescent activity. The SFH was
derived through colour-magnitude diagram (CMD) fitting of two extremely deep
Hubble Space Telescope CMDs, sampling the centre and one core radius. The
attained age resolution allowed us to single out a major star formation episode
at early times, a second strong burst Gyr ago and recent
intermittent episodes Gyr ago. Detailed testing with mock stellar
populations was used to estimate the duration of the main bursts and study the
occurrence of low-level star formation between them. The SFHs in both regions
show common features, with activity at the same epochs and similar
age-metallicity relationship. However, clear indications of a spatial gradient
were also found, with mean age increasing with radius and star formation
episodes being more prolonged in the centre. While some galaxy evolution models
predict bursty SFHs in dwarf galaxies and thus a secular origin of the observed
SFH cannot be excluded in Fornax, other evidence points to possible mergers or
interactions as the cause of its bursty SFH. In particular, we calculated the
Fornax orbit relative to the closest dwarfs and the Milky Way and observed a
correspondence between the main intermediate-age and young events and
peri-passages of Fornax around the Milky Way, possibly indicating
tidally-induced star formation.Comment: 20 pages, 12+3 figures, accepted for publication in MNRAS; corrected
error estimation (Figure 5, Sec. 3.3), added Sec. 4.3, appendices, more
references, moderate revision of text and figure
Evidence of ongoing radial migration in NGC 6754: Azimuthal variations of the gas properties
Understanding the nature of spiral structure in disk galaxies is one of the
main, and still unsolved questions in galactic astronomy. However, theoretical
works are proposing new testable predictions whose detection is becoming
feasible with recent development in instrumentation. In particular, streaming
motions along spiral arms are expected to induce azimuthal variations in the
chemical composition of a galaxy at a given galactic radius. In this letter we
analyse the gas content in NGC 6754 with VLT/MUSE data to characterise its 2D
chemical composition and H line-of-sight velocity distribution. We find
that the trailing (leading) edge of the NGC 6754 spiral arms show signatures of
tangentially-slower, radially-outward (tangentially-faster, radially-inward)
streaming motions of metal-rich (poor) gas over a large range of radii. These
results show direct evidence of gas radial migration for the first time. We
compare our results with the gas behaviour in a -body disk simulation
showing spiral morphological features rotating with a similar speed as the gas
at every radius, in good agreement with the observed trend. This indicates that
the spiral arm features in NGC 6754 may be transient and rotate similarly as
the gas does at a large range of radii.Comment: 8 pages, 4 figures, accepted for publication in ApJL 2016 September
2
Recovering star formation histories: Integrated-light analyses vs stellar colour-magnitude diagrams
Accurate star formation histories (SFHs) of galaxies are fundamental for
understanding the build-up of their stellar content. However, the most accurate
SFHs - those obtained from colour-magnitude diagrams (CMDs) of resolved stars
reaching the oldest main sequence turnoffs (oMSTO) - are presently limited to a
few systems in the Local Group. It is therefore crucial to determine the
reliability and range of applicability of SFHs derived from integrated light
spectroscopy, as this affects our understanding of unresolved galaxies from low
to high redshift.
To evaluate the reliability of current full spectral fitting techniques in
deriving SFHs from integrated light spectroscopy by comparing SFHs from
integrated spectra to those obtained from deep CMDs of resolved stars.
We have obtained a high signal--to--noise (S/N 36.3 per \AA)
integrated spectrum of a field in the bar of the Large Magellanic Cloud (LMC)
using EFOSC2 at the 3.6 meter telescope at La Silla Observatory. For this same
field, resolved stellar data reaching the oMSTO are available. We have compared
the star formation rate (SFR) as a function of time and the age-metallicity
relation (AMR) obtained from the integrated spectrum using {\tt STECKMAP}, and
the CMD using the IAC-star/MinnIAC/IAC-pop set of routines. For the sake of
completeness we also use and discuss other synthesis codes ({\tt STARLIGHT} and
{\tt ULySS}) to derive the SFR and AMR from the integrated LMC spectrum.
We find very good agreement (average differences 4.1 ) between the
SFR(t) and the AMR obtained using {\tt STECKMAP} on the integrated light
spectrum, and the CMD analysis. {\tt STECKMAP} minimizes the impact of the
age-metallicity degeneracy and has the advantage of preferring smooth solutions
to recover complex SFHs by means of a penalized . [abridged]Comment: 23 pages, 24 figures. Accepted for publication in A&A (6 Sep 2015
Observational constraints to boxy/peanut bulge formation time
Boxy/peanut bulges are considered to be part of the same stellar structure as
bars and both could be linked through the buckling instability. The Milky Way
is our closest example. The goal of this letter is determining if the mass
assembly of the different components leaves an imprint in their stellar
populations allowing to estimate the time of bar formation and its evolution.
To this aim we use integral field spectroscopy to derive the stellar age
distributions, SADs, along the bar and disc of NGC 6032. The analysis shows
clearly different SADs for the different bar areas. There is an underlying old
(>=12 Gyr) stellar population for the whole galaxy. The bulge shows star
formation happening at all times. The inner bar structure shows stars of ages
older than 6 Gyrs with a deficit of younger populations. The outer bar region
presents a SAD similar to that of the disc. To interpret our results, we use a
generic numerical simulation of a barred galaxy. Thus, we constrain, for the
first time, the epoch of bar formation, the buckling instability period and the
posterior growth from disc material. We establish that the bar of NGC 6032 is
old, formed around 10 Gyr ago while the buckling phase possibly happened around
8 Gyr ago. All these results point towards bars being long-lasting even in the
presence of gas.Comment: Accepted for publication in MNRAS Letter
The shape of oxygen abundance profiles explored with MUSE: evidence for widespread deviations from single gradients
We characterised the oxygen abundance radial distribution of a sample of 102 spiral galaxies observed with VLT/MUSE using the O3N2 calibrator. The high spatial resolution of the data allowed us to detect 14345 H ii regions with the same image quality as with photometric data, avoiding any dilution effect. We developed a new methodology to automatically fit the abundance radial profiles, finding that 55 galaxies of the sample exhibit a single negative gradient. The remaining 47 galaxies also display, as well as this negative trend, either an inner drop in the abundances (21), an outer flattening (10), or both (16), which suggests that these features are a common property of disc galaxies. The presence and depth of the inner drop depends on the stellar mass of the galaxies with the most massive systems presenting the deepest abundance drops, while there is no such dependence in the case of the outer flattening. We find that the inner drop appears always around 0.5 r, while the position of the outer flattening varies over a wide range of galactocentric distances. Regarding the main negative gradient, we find a characteristic slope in the sample of α =-0.10 ± 0.03 dex /r. This slope is independent of the presence of bars and the density of the environment. However, when inner drops or outer flattenings are detected, slightly steeper gradients are observed. This suggests that radial motions might play an important role in shaping the abundance profiles. We define a new normalisation scale (>the abundance scale length>, r) for the radial profiles based on the characteristic abundance gradient, with which all the galaxies show a similar position for the inner drop (~0.5 r) and the outer flattening (~1.5 r). Finally, we find no significant dependence of the dispersion around the negative gradient with any property of the galaxies, with values compatible with the uncertainties associated with the derivation of the abundances.© ESO, 2018.This study is based on observations made with ESO Telescopes at the Paranal Observatory (programmes 60.A-9329(A), 095.D-0172(A), 95.D-0091(A), 95.D-0091(B), 096.D-0263(A), 96.D-0296(A), 97.D-0408(A) and 98.D-0115(A)) and has also made use of the services of the ESO Science Archive Facility (programmes 60.A-9319(A), 60.A-9100(B), 60.A-9329(A), 60.A-9339(A), 60.A-9301(A), 196.B-0578(A) and 094.B-0733(B)). We would like to thank the anonymous referee for comments which helped to improve the content of the paper. We acknowledge financial support from the Spanish Ministerio de Economia y Competitividad (MINECO) via grants AYA2012-31935, and from the >Junta de Andalucia> local government through the FQM-108 project. We also acknowledge support to the ConaCyt funding programme 180125 and DGAPA IA100815. L.G. is supported in part by the US National Science Foundation under Grant AST-1311862. T.K. acknowledges support through the Sofja Kovalevskaja Award to P. Schady from the Alexander von Humboldt Foundation of Germany. We acknowledge the usage of the HyperLeda database (http://leda.univ-lyon1.fr).This research also makes use of python (http://www.python.org),of Matplotlib (Hunter 2007), a suite of open-source python modules that provides a framework for creating scientific plots, and Astropy, a community-developed core Python package for Astronomy (Astropy Collaboration et al. 2013).Peer reviewe
Methodology for Olive Pruning Windrow Assessment Using 3D Time-of-Flight Camera
The management of olive pruning residue has shifted from burning to shredding, laying residues on soil, or harvesting residues for use as a derivative. The objective of this research is to develop, test, and validate a methodology to measure the dimensions, outline, and bulk volume of pruning residue windrows in olive orchards using both a manual and a 3D Time-of-Flight (ToF) camera. Trees were pruned using trunk shaker targeted pruning, from which two different branch sizes were selected to build two separate windrow treatments with the same pruning residue dose. Four windrows were built for each treatment, and four sampling points were selected along each windrow to take measurements using both manual and 3D ToF measurements. Windrow section outline could be defined using a polynomial or a triangular function, although manual measurement required processing with a polynomial function, especially for high windrow volumes. Different branch sizes provided to be significant differences for polynomial function coefficients, while no significant differences were found for windrow width. Bigger branches provided less bulk volume, which implied that these branches formed less porous windrows that smaller ones. Finally, manual and 3D ToF camera measurements were validated, giving an adequate performance for olive pruning residue windrow in-field assessment
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