469 research outputs found
Formation of S0 galaxies through mergers. Evolution in the Tully-Fisher relation since
(Abridged version) We explore whether a scenario that combines an origin by
mergers at 1.8-1.5 with a subsequent passive evolution of the resulting
S0 remnants since 0.8-1 is compatible with observational data of S0s in
the Tully-Fisher relation (TFR). We studied a set of major and minor merger
experiments from the GalMer database that generate massive S0 remnants. We
analysed the location of these remnants in the photometric and stellar TFRs
assuming that they correspond to galaxies. We then estimated their
evolution in these planes over the last 7 Gyr. The results were compared with
data of real S0s and spirals at different redshifts. We also tested how the use
of Vcirc or Vrot,max affects the results. We found that just after 1-2
Gyr of coalescence, major mergers generate S0 remnants that are outliers of the
local photometric and stellar TFRs at . After 4-7 Gyr of
passive evolution in isolation, the S0 remnants move towards the local TFR,
although the initial scatter among them persists. This scatter is sensitive to
the indicator used for the rotation velocity: Vcirc values yield a lower
scatter than when Vrot,max values are considered instead. In the planes
involving Vrot,max, a clear segregation of the S0 remnants in terms of the
spin-orbit coupling of the model is observed, in which the remnants of
retrograde encounters overlap with local S0s hosting counter-rotating discs.
The location of the S0 remnants at agrees well with the observed
distribution of local S0 galaxies in the -, Vcirc- and
Vrot,max- planes. Thus, massive S0 galaxies may have been formed
through major mergers that occurred at high redshift and have later evolved
towards the local TFR through passive evolution in relative isolation, a
mechanism that would also contribute to the scatter observed in this relation.Comment: 19 pages, 15 figures. Accepted for publication in A&
Formation of S0 galaxies through mergers. Morphological properties: tidal relics, lenses, ovals, and other inner components
Major mergers are popularly considered too destructive to produce the relaxed
regular structures and the morphological inner components (ICs) usually
observed in lenticular (S0) galaxies. We aim to test if major mergers can
produce remnants with realistic S0 morphologies. We have selected a sample of
relaxed discy remnants resulting from the dissipative merger simulations of the
GalMer database and derived their properties mimicking the typical conditions
of current observational data. We compare their global morphologies, visual
components, and merger relics in mock photometric images with their real
counterparts. Only 1-2 Gyr after the full merger, we find that: 1) many
remnants (67 major and 29 minor events) present relaxed structures and typical
S0 or E/S0 morphologies, for a wide variety of orbits and even in gas-poor
cases. 2) Contrary to popular expectations, most of them do not exhibit any
morphological traces of their past merger origin under typical observing
conditions and at distances as nearby as 30 Mpc. 3) The merger relics are more
persistent in minor mergers than in major ones for similar relaxing time
periods. 4) No major-merger S0-like remnant develops a significant bar. 5)
Nearly 58% of the major-merger S0 remnants host visually detectable ICs, such
as embedded inner discs, rings, pseudo-rings, inner spirals, nuclear bars, and
compact sources, very frequent in real S0s too. 6) All remnants contain a lens
or oval, identically ubiquitous in local S0s. 7) These lenses and ovals do not
come from bar dilution in major merger cases, but are associated with stellar
halos or embedded inner discs instead (thick or thin). We conclude that the
relaxed morphologies, lenses, ovals, and other ICs of real S0s do not
necessarily come from internal secular evolution, gas infall or environmental
mechanisms, as traditionally assumed, but they can result from major mergers as
well.Comment: Accepted for publication in A&A, 37 pages, 21 figures, 9 tables.
Version with better resolution and language edited. A version with full
Appendices is available at:
https://www.researchgate.net/publication/325905181_Formation_of_S0_galaxies_through_mergers_Morphological_properties_tidal_relics_lenses_ovals_and_other_inner_components_-_Version_of_the_corresponding_AA_paper_with_full_Appendice
Formation of S0 galaxies through mergers. Bulge-disc structural coupling resulting from major mergers
Observations reveal a strong structural coupling between bulge and disc in S0
galaxies, which seems difficult to explain if they have formed from supposedly
catastrophic events such as major mergers. We face this question by quantifying
the bulge-disc coupling in dissipative simulations of major and minor mergers
that result in realistic S0s. We have studied the dissipative N-body binary
merger simulations from the GalMer database that give rise to realistic,
relaxed E/S0 and S0 remnants (67 major and 29 minor mergers). We simulate
surface brightness profiles of these S0-like remnants in the K-band, mimicking
typical observational conditions, to perform bulge-disc decompositions
analogous to those carried out in real S0s. The global bulge-disc structure of
these remnants has been compared with real data, and they distribute in the B/T
- r_e - h_d parameter space consistently with real bright S0s, where B/T is the
bulge-to-total luminosity ratio, r_e is the bulge effective radius, and h_d is
the disc scalelength. Major mergers can rebuild a bulge-disc coupling in the
remnants after having destroyed the structures of the progenitors, whereas
minor mergers directly preserve them. Remnants exhibit B/T and r_e/h_d spanning
a wide range of values, and their distribution is consistent with observations.
Many remnants have bulge Sersic indices ranging 1<n<2, flat appearance, and
contain residual star formation in embedded discs, a result which agrees with
the presence of pseudobulges in real S0s. Contrary to the popular view, mergers
(and in particular, major events) can result in S0 remnants with realistically
coupled bulge-disc structures in less than ~3 Gyr. In conclusion, the
bulge-disc coupling and the presence of pseudobulges in real S0s cannot be used
as an argument against the possible major-merger origin of these galaxies.Comment: 23 pages, accepted for publication in Astronomy and Astrophysics
(version after minor language corrections
Creating lenticular galaxies with major mergers
Lenticular galaxies (S0s) represent the majority of early-type galaxies in the local Universe, but their formation channels are still poorly understood. While galaxy mergers are obvious pathways to suppress star formation and increase bulge sizes, the marked parallelism between spiral and lenticular galaxies (e.g. photometric bulge-disc coupling) seemed to rule out a potential merger origin. Here, we summarise our recent work in which we have shown, through N-body numerical simulations, that disc-dominated lenticulars can emerge from major mergers of spiral galaxies, in good agreement with observational photometric scaling relations. Moreover, we show that mergers simultaneously increase the light concentration and reduce the angular momentum relative to their spiral progenitors. This explains the mismatch in angular momentum and concentration between spirals and lenticulars recently revealed by CALIFA observations, which is hard to reconcile with simple fading mechanisms (e.g. ram-pressure stripping)
Evolution induced by dry minor mergers onto fast-rotator S0 galaxies
We analysed collisionless N-body simulations of intermediate and minor dry
mergers onto S0s to test whether these mergers can generate S0 galaxies with
kinematics intermediate between fast and slow rotators. We find that minor
mergers induce a lower decrease of the global rotational support than
encounters of lower mass ratios, which results in S0s with properties
intermediate between fast and slow rotators. The resulting remnants are
intrinsically more triaxial, less flattened, and span the whole range of
apparent ellipticities up to . They do not show
lower apparent ellipticities in random projections than initially; on the
contrary, the formation of oval distortions and the disc thickening increase
the percentage of projections at . In the
experiments with S0b progenitor galaxies, minor mergers tend to spin up the
bulge and to decrease slightly its intrinsic ellipticity, whereas in the cases
of primary S0c galaxies they keep the rotational support of the bulge nearly
constant and decrease significantly its intrinsic ellipticity. The remnant
bulges remain nearly spherical (), but exhibit a wide range
of triaxialities (). In the plane of global anisotropy of
velocities () vs. intrinsic ellipticity (),
some of our models extend the linear trend found in previous major merger
simulations towards higher values, while others
depart from it. This is consistent with the wide dispersion exhibited by real
S0s in this diagram compared with ellipticals, which follow the linear trend
drawn by major merger simulations. The different trends exhibited by
ellipticals and S0 galaxies in the - diagram may
be pointing to the different role played by major mergers in the build-up of
each morphological type.Comment: Corrected typos. 20 pages, 14 figures. Accepted for publishing in A&
Screening of Indigenous Microorganisms as Potential Biofertilisers for Periurban Horticulture Areas
In Buenos Aires periurban area, horticultural practices are one of the most important activities. Pesticides and fertilisers are used without any control to cover the farmers’ needs, obtaining high crop yields at short terms and modifying soil ecosystem in the long term. The aim of this work was to isolate indigenous strains from periurban horticultural units with pesticide degrading capacity and to evaluate their plant growth-promoting properties in order to design biofertilisers to be applied in the restoration of these exploited soils. After the screening, eight strains were isolated and identified. They showed not only the capacity to produce indole-3- acetic acid, to fix nitrogen, to secrete siderophores and to solubilise calcium phosphate but also tolerated the mixture of pesticides usually used for horticultural practices. By their behaviour in mixed cultures and plant growth-promoting properties, these autochthonous isolates represent a promising alternative as biofertilisers according to soil type and activity
Plant’s gypsum affinity shapes responses to specific edaphic constraints without limiting responses to other general constraints
Aims: Harsh edaphic environments harbor species with different soil affinities. Plant’s responses to specific edaphic constraints may be compromised against responses to prevalent stresses shared with other semi-arid environments. We expect that species with high edaphic affinity may show traits to overcome harsh soil properties, while species with low affinity may respond to environmental constraints shared with arid environments. Methods: We quantified the edaphic affinity of 12 plant species co-occurring in gypsum outcrops and measured traits related to plant responses to specific gypsum constraints (rooting and water uptake depth, foliar accumulation of Ca, S and Mg), and traits related to common constraints of arid environments (water use efficiency, macronutrients foliar content). Results: Plants in gypsum outcrops differed in their strategies to face edaphic limitations. A phylogenetic informed PCA segregated species based on their foliar Ca and S accumulation and greater water uptake depths, associated with plant responses to specific gypsum limitations. Species’ gypsum affinity explained this segregation, but traits related to water or nutrient use efficiency did not contribute substantially to this axis. Conclusions: Plant’s specializations to respond to specific edaphic constraints of gypsum soils do not limit their ability to deal with other non-specific environmental constraints
A Portrait of Cold Gas in Galaxies at 60pc Resolution and a Simple Method to Test Hypotheses That Link Small-Scale ISM Structure to Galaxy-Scale Processes
The cloud-scale density, velocity dispersion, and gravitational boundedness
of the interstellar medium (ISM) vary within and among galaxies. In turbulent
models, these properties play key roles in the ability of gas to form stars.
New high fidelity, high resolution surveys offer the prospect to measure these
quantities across galaxies. We present a simple approach to make such
measurements and to test hypotheses that link small-scale gas structure to star
formation and galactic environment. Our calculations capture the key physics of
the Larson scaling relations, and we show good correspondence between our
approach and a traditional "cloud properties" treatment. However, we argue that
our method is preferable in many cases because of its simple, reproducible
characterization of all emission. Using, low-J 12CO data from recent surveys,
we characterize the molecular ISM at 60pc resolution in the Antennae, the Large
Magellanic Cloud, M31, M33, M51, and M74. We report the distributions of
surface density, velocity dispersion, and gravitational boundedness at 60pc
scales and show galaxy-to-galaxy and intra-galaxy variations in each. The
distribution of flux as a function of surface density appears roughly lognormal
with a 1sigma width of ~0.3 dex, though the center of this distribution varies
from galaxy to galaxy. The 60pc resolution line width and molecular gas surface
density correlate well, which is a fundamental behavior expected for virialized
or free-falling gas. Varying the measurement scale for the LMC and M31, we show
that the molecular ISM has higher surface densities, lower line widths, and
more self-gravity at smaller scales.Comment: Accepted for publication in the Astrophysical Journal, 36 pages
(24+appendix), 21 figures (12+appendix), until publication high resolution
version at http://www.astronomy.ohio-state.edu/~leroy.42/cloudscale.pd
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