174 research outputs found
Evolution induced by dry minor mergers onto fast-rotator S0 galaxies
Tapia, Trinidad et al.[Context] Numerical studies have shown that the properties of the S0 galaxies with kinematics intermediate between fast and slow rotators are difficult to explain by a scenario of major mergers.[Aims] We investigate whether the smoother perturbation induced by minor mergers can reproduce these systems.[Methods] We analysed collisionless N-body simulations of intermediate and minor dry mergers onto S0s to determine the structural and kinematic evolution induced by the encounters. The original primary galaxies represent gas-poor fast-rotator S0b and S0c galaxies with high intrinsic ellipticities. The original bulges are intrinsically spherical and have low rotation. Different mass ratios, parent bulges, density ratios, and orbits were studied.[Results] Minor mergers induce a lower decrease of the global rotational support (as provided by λe) 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 Δe ⌠0.8. 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 0.4 0.9), but exhibit a wide range of triaxialities (0.20 < T < 1.00). In the plane of global anisotropy of velocities (Ύ) vs.? intrinsic ellipticity (Δe,intr), some of our models extend the linear trend found in previous major merger simulations towards higher Δ e,intr values, while others clearly depart from it (depending on the progenitor S0). 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.[Conclusions] The smoother changes induced by minor mergers can explain the existence of S0s with intermediate kinematic properties between fast and slow rotators that are difficult to explain with major mergers. The different trends exhibited by ellipticals and S0 galaxies in the Ύ - Δe diagram may be pointing to the different role played by major mergers in the build-up of each morphological type. © ESO 2014.Supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under projects AYA2006-12955, AYA2009-10368, AYA2009-11137, AYA2012-
30717, AYA2010-21322-C03-02, AYA2010-21887-C04-04, and by the Madrid Regional Government through the AstroMadrid Project (CAM S2009/ESP-1496, http://www.laeff.cab.inta-csic.es/projects/astromadrid/main/index.php). Funded by the Spanish MICINN under the Consolider-Ingenio 2010 Program grant CSD2006-
0070: âFirst Science with the GTCâ (http://www.iac.es/consolider-ingenio-gtc/), and by the Spanish programme of International Campus of Excellence Moncloa (CEI). A.C.G.G. is a RamĂłn y Cajal Fellow of the Spanish MINECO.Peer Reviewe
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
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&
Euclid preparation : XVI. Exploring the ultra-low surface brightness Universe with Euclid/VIS
Context. While Euclid is an ESA mission specifically designed to investigate the nature of dark energy and dark matter, the planned unprecedented combination of survey area (similar to 15000 deg(2)), spatial resolution, low sky-background, and depth also make Euclid an excellent space observatory for the study of the low surface brightness Universe. Scientific exploitation of the extended low surface brightness structures requires dedicated calibration procedures that are yet to be tested. Aims. We investigate the capabilities of Euclid to detect extended low surface brightness structure by identifying and quantifying sky-background sources and stray-light contamination. We test the feasibility of generating sky flat-fields to reduce large-scale residual gradients in order to reveal the extended emission of galaxies observed in the Euclid survey. Methods. We simulated a realistic set of Euclid/VIS observations, taking into account both instrumental and astronomical sources of contamination, including cosmic rays, stray-light, zodiacal light, interstellar medium, and the cosmic infrared background, while simulating the effects of background sources in the field of view. Results. We demonstrate that a combination of calibration lamps, sky flats, and self-calibration would enable recovery of emission at a limiting surface brightness magnitude of mu(lim) = 29.5(-0.27)(+0.08) mag arcsec(-2) (3 sigma, 10 x 10 arcsec(2)) in theWide Survey, and it would reach regions deeper by 2 mag in the Deep Surveys. Conclusions. Euclid/VIS has the potential to be an excellent low surface brightness observatory. Covering the gap between pixel-to-pixel calibration lamp flats and self-calibration observations for large scales, the application of sky flat-fielding will enhance the sensitivity of the VIS detector at scales larger than 1 '', up to the size of the field of view, enabling Euclid to detect extended surface brightness structures below mu(lim) = 31 mag arcsec(-2) and beyond.Peer reviewe
Kinematic Clues to Bar Evolution for Galaxies in the Local Universe: Why the Fastest Rotating Bars are Rotating Most Slowly
We have used Spitzer images of a sample of 68 barred spiral galaxies in the local universe to make systematic measurements of bar length and bar strength. We combine these with precise determinations of the corotation radii associated with the bars, taken from our previous study, which used the phase change from radial inflow to radial outflow of gas at corotation, based on high-resolution two-dimensional velocity fields in Hα taken with a Fabry-Pérot spectrometer. After presenting the histograms of the derived bar parameters, we study their dependence on the galaxy morphological type and on the total stellar mass of the host galaxy, and then produce a set of parametric plots. These include the bar pattern speed versus bar length, the pattern speed normalized with the characteristic pattern speed of the outer disk versus the bar strength, and the normalized pattern speed versus R, the ratio of corotation radius to bar length. To provide guidelines for our interpretation, we used recently published simulations, including disk and dark matter halo components. Our most striking conclusion is that bars with values of R < 1.4, previously considered dynamically fast rotators, can be among the slowest rotators both in absolute terms and when their pattern speeds are normalized. The simulations confirm that this is because as the bars are braked, they can grow longer more quickly than the outward drift of the corotation radius. We conclude that dark matter halos have indeed slowed down the rotation of bars on Gyr timescales. © 2017. The American Astronomical Society. All rights reserved.
Formation of S0 galaxies through mergers Explaining angular momentum and concentration change from spirals to S0s
The CALIFA team has recently found that the stellar angular momentum and concentration of late-type spiral galaxies are incompatible with those of lenticular galaxies (S0s), concluding that fading alone cannot satisfactorily explain the evolution from spirals into S0s. Here we explore whether major mergers can provide an alternative way to transform spirals into S0s by analysing the spiral-spiral major mergers from the GalMer database that lead to realistic, relaxed S0-like galaxies. We find that the change in stellar angular momentum and concentration can explain the differences in the λ_Re-R_90/R_50 plane found by the CALIFA team. Major mergers thus offer a feasible explanation for the transformation of spirals into S0s
Extragalactic magnetism with SOFIA (SALSA Legacy Program). VI. The magnetic fields in the multi-phase interstellar medium of the Antennae galaxies
Mergers are thought to be a fundamental channel for galaxy growth, perturbing
the gas dynamics and the magnetic fields (B-fields) in the interstellar medium
(ISM). However, the mechanisms that amplify and dissipate B-fields during a
merger remain unclear. We characterize the morphology of the ordered B-fields
in the multi-phase ISM of the closest merger of two spiral galaxies, the
Antennae galaxies. We compare the inferred B-fields using m thermal
dust and cm radio synchrotron emission polarimetric observations. We find
that the m B-fields are more ordered across the Antennae galaxies than
the cm B-fields. The turbulent-to-ordered m B-field increases at
the galaxy cores and star-forming regions. The relic spiral arm has an ordered
spiral m B-field, while the cm B-field is radial. The m
B-field may be dominated by turbulent dynamos with high CO(1-0) velocity
dispersion driven by star-forming regions, while the cm B-field is
cospatial with high HI velocity dispersion driven by galaxy interaction. This
result shows the dissociation between the warm gas mainly disturbed by the
merger, and the dense gas still following the dynamics of the relic spiral arm.
We find a kpc scale ordered B-field connecting the two galaxies. The
base of the tidal tail is cospatial with the HI and CO(1-0) emission and
has compressed and/or sheared m and cm B-fields driven by the
merger. We suggest that amplify B-fields, with respect to the rest of the
system and other spiral galaxies, may be supporting the gas flow between both
galaxies and the tidal tail.Comment: 11 pages, 5 figures, Accepted for publication in ApJ Letter
Extragalactic magnetism with SOFIA (SALSA Legacy Program) -- V: First results on the magnetic field orientation of galaxies
We present the analysis of the magnetic field (-field) structure of
galaxies measured with far-infrared (FIR) and radio (3 and 6 cm) polarimetric
observations. We use the first data release of the Survey on extragALactic
magnetiSm with SOFIA (SALSA) of 14 nearby ( Mpc) galaxies with resolved (5
arcsec-18 arcsec; pc-- kpc) imaging polarimetric observations using
HAWC+/SOFIA from to \um. We compute the magnetic pitch angle
() profiles as a function of the galactrocentric radius. We introduce
a new magnetic alignment parameter () to estimate the
disordered-to-ordered -field ratio in spiral -fields. We find FIR and
radio wavelengths to not generally trace the same -field morphology in
galaxies. The profiles tend to be more ordered with galactocentric
radius in radio () than in FIR
(). For spiral galaxies, FIR -fields
are \% more turbulent than the radio -fields. For starburst galaxies,
we find that FIR polarization is a better tracer of the -fields along the
galactic outflows than radio polarization. Our results suggest that the
-fields associated with dense, dusty, turbulent star-forming regions, those
traced at FIR, are less ordered than warmer, less-dense regions, those traced
at radio, of the interstellar medium. The FIR -fields seem to be more
sensitive to the activity of the star-forming regions and the morphology of the
molecular clouds within a vertical height of few hundred pc in the disk of
spiral galaxies than the radio -fields.Comment: 26 pages, 13 figure
Extragalactic Magnetism with SOFIA (SALSA Legacy Program). VII. A tomographic view of far infrared and radio polarimetric observations through MHD simulations of galaxies
The structure of magnetic fields in galaxies remains poorly constrained,
despite the importance of magnetism in the evolution of galaxies. Radio
synchrotron and far-infrared dust polarization (FIR) polarimetric observations
are the best methods to measure galactic scale properties of magnetic fields in
galaxies beyond the Milky Way. We use synthetic polarimetric observations of a
simulated galaxy to identify and quantify the regions, scales, and interstellar
medium (ISM) phases probed at FIR and radio wavelengths. Our studied suite of
magnetohydrodynamical cosmological zoom-in simulations features
high-resolutions (10 pc full-cell size) and multiple magnetization models. Our
synthetic observations have a striking resemblance to those of observed
galaxies. We find that the total and polarized radio emission extends to
approximately double the altitude above the galactic disk (half-intensity disk
thickness of kpc)
relative to the FIR total and polarized emission that are concentrated in the
disk midplane ( kpc).
Radio emission traces magnetic fields at scales of pc, whereas
FIR emission probes magnetic fields at the smallest scales of our simulations.
These scales are comparable to our spatial resolution and well below the
spatial resolution ( pc) of existing FIR polarimetric measurements.
Finally, we confirm that synchrotron emission traces a combination of the warm
neutral and cold neutral gas phases, whereas FIR emission follows the densest
gas in the cold neutral phase in the simulation. These results are independent
of the ISM magnetic field strength. The complementarity we measure between
radio and FIR wavelengths motivates future multiwavelength polarimetric
observations to advance our knowledge of extragalactic magnetism.Comment: Submitted to ApJ. 32 pages, 15 figure
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