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-Spiral arms in our Galaxy. Optical arms (black squares) and K-band arms (open squares). Continuous line: is our fit to a four-armed locus. The third locus we considered is composed by the two locus joined, our fit to K-band arms (shown in the previous figure) and the four-armed locus presented in this Figure.
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With the aim of studying the nonlinear stellar and gaseous response to the gravitational potential of a galaxy such as the Milky Way, we have modeled 3D galactic spiral arms as a superposition of inhomogeneous oblate spheroids and added their contribution to an axisymmetric model of the Galactic mass distribution. Three spiral loci are proposed her...
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Context 1
... (2002) shows in his Fig. 2 his fit to these optical arms, taking a pitch angle of 12 • and R 0 = 7.2 kpc for the Sun's galactocentric distance. Figure 3 shows our fit with N = 100, i p = 12 • , and R s = 3.54 kpc in Eq. (2), and R 0 = 8.5 kpc. Drimmel (2000) has suggested that the four optical arms in our Galaxy trace the response of the gas to the two-armed, K-band, stellar spiral arms in Figure 2. Thus, we take the third spiral locus for the spiral arms in our Galaxy as the superposition of the two-armed, K-band and four-armed, optical spiral loci. ...
Context 2
... studied several models with a two-armed spiral pattern, taking combinations of Ω p (15 or 20 km s −1 kpc −1 ), i p (11 • or 15.5 • ), M S /M D (0.0175, 0.03, or 0.05), and the function p 0 (linear or exponential). Also, we studied models with the six spiral arms in Figure 3, taking combinations of Ω p = 20, 60 km s −1 kpc −1 , M S /M D = 0.0175, 0.05, and an exponential function p 0 . In all cases the orbits were computed with a Bulirsch-Stoer algorithm ( Press et al. 1992), with a mean maximum error |(E J f inal − E J initial )/E J initial | of order 10 −12 , in runs with elapsed physical times of 10 9 to 10 11 years. ...
Context 3
... boundary of the permitted region begins to open at the value E J of the island around the corotation distance (see Figure 10) to which the x ′ axis is tangent. This value of E J is the maximum of the curve in Figure 11. Figure 13 gives four Poincaré diagrams for a model with the six spiral arms in Figure 3, and again Ω p = 20 km s −1 kpc −1 . In this example the mass ratio for the two, K-band, spiral arms is M S /M D = 0.0175, and the total mass in the four optical arms has this same ratio; i.e. the total mass in the four optical arms is equal to the total mass in the two K-band arms. ...
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... On the contrary, local spiral arms contain stellar masses ∼1%-5% of the disk (e.g., Pichardo et al. 2003), significantly smaller than the substructures we have identified. The 2× asymmetry of the stellar mass between the northern and southern ridges of UDF2 is another departure from classical spiral arms and bears a resemblance to the lopsided stellar disk reported by Kalita et al. (2022), who proposed that mass lopsidedness in the stellar disk could be a remnant indicating the "impact point" of the cold gas accretion stream (also in a cluster environment). ...
We present an identification of dust-attenuated star-forming galactic-disk substructures in a typical star-forming galaxy (SFG), UDF2, at z = 2.696. To date, substructures containing significant buildup of stellar mass and actively forming stars have yet to be found in typical (i.e., main-sequence) SFGs at z > 2. This is due to the strong dust attenuation common in massive galaxies at the epoch and the scarcity of high-resolution, high-sensitivity extinction-independent imaging. To search for disk substructures, we subtracted the central stellar-mass disk from the JWST/NIRCam rest-frame 1.2 μ m image (0.″13 resolution) and subtracted, in the visibility plane, the central starburst disk from Atacama Large Millimeter/submillimeter Array (ALMA) rest-frame 240 μ m observations (0.″03 resolution). The residual images revealed substructures at rest-frame 1.2 μ m colocated with those found at rest-frame 240 μ m, ≃2 kpc away from the galactic center. The largest substructure contains ≃20% of the total stellar mass and ≃5% of the total star formation rate of the galaxy. While UDF2 exhibits a kinematically ordered velocity field of molecular gas consistent with a secularly evolving disk, more sensitive observations are required to characterize the nature and the origin of this substructure (spiral arms, minor merger, or other types of disk instabilities). UDF2 resides in an overdense region ( N ≥ 4 massive galaxies within 70 kpc projected distance at z = 2.690–2.697) and the substructures may be associated with interaction-induced instabilities. Importantly, a statistical sample of such substructures identified with JWST and ALMA could play a key role in bridging the gap between the bulge-forming starburst and the rest of the galaxy.
... We consider a model where all DNSs are born in the spiral arms, henceforth the Spiral model. We use the same radial stellar density as the Fiducial model but place the binaries along the two-armed bared spiral following Pichardo et al. ( 2003 ). The initial angle of a DNS in the Fiducial model is changed to : ...
Observations of binaries containing pairs of neutron stars using the upcoming space-based gravitational wave observatory, LISA, have the potential to improve our understanding of neutron star physics and binary evolution. In this work we assess the effect of changing the model of the Milky Way’s kinematics and star formation history on predictions of the population of double neutron stars that will be detected and resolved by LISA. We conclude that the spatial distribution of these binaries is insensitive to the choice of galactic models, compared to the stochastic variation induced by the small sample size. In particular, the time-consuming computation of the binaries’ Galactic orbits is not necessary. The distributions of eccentricity and gravitational-wave frequency are, however, affected by the choice of star-formation history. Binaries with eccentricities e > 0.1, which can be measured by LISA observations, are mostly younger than 100 Myr. We caution that comparisons between different predictions for LISA observations need to use consistent star formation histories, and that the Galactic star formation history should be taken into account in the analysis of the observations themselves. The lack of strong dependency on Galactic models means that LISA detection of double neutron star binaries may provide a relatively clean probe of massive binary star evolution.
... We consider a model where all DNSs are born in the spiral arms, henceforth the Spiral model. We use the same radial stellar density as the Fiducial model but place the binaries along the two-armed bared spiral following Pichardo et al. (2003). The initial angle of a DNS in the Fiducial model is changed to; ...
The upcoming space-based gravitational wave observatory, LISA, will detect binaries containing pairs of neutron stars. LISA observations of double neutron stars, particularly in combination with electromagnetic observations, have the potential to improve our understanding of neutron star physics and binary evolution. In this work we assess the effect of changing the model of the Milky Way on predictions of the population of double neutron star binaries that will be detected and resolved by LISA. We conclude that the spatial and gravitational-wave frequency distributions of these binaries are insensitive to the choice of galactic models, compared to the stochastic variation induced by the small sample size. In particular, the time-consuming computation of the binaries' Galactic orbits is not necessary. However, the distribution of eccentricities is strongly affected by the choice of star-formation history. Binaries with eccentricities e>0.1 that can be measured by LISA observations are all younger than 100 Myr. We caution that comparisons between different predictions for LISA observations need to use consistent star formation histories, and that the Galactic star formation history should be taken into account in the analysis of the observations themselves.
... Self-consistent spiral models using such potential have been presented by Contopoulos and Grosbol (1986), Contopoulos and Grosbol (1988), Patsis et al. (1991), and Amaral and Lepine (1997). Departing from this approach, the more recent spiral models of Pichardo et al. (2003) and Junqueira et al. (2013) were derived from the modeling of the stellar spiral density in the Galactic disk and the self-consistency were calculated to define their physical parameters. As pointed out by Junqueira et al. (2013), the brightness profiles observed in galactic disks in circles around the center are not simple sine functions. ...
... As a natural consequence of this dynamical process, a ring-shaped void of gas should form at the corotation radius (Lacey and Fall, 1985;Mishurov, 2000;Lépine et al., 2001). From recent magnetohydrodynamic simulations, Gómez et al. (2013) and Pérez-Villegas et al. (2015) verified the presence of instabilities at the corotation radius in the gas response to a self-gravitating spiral-arms model, the PERLAS model (Pichardo et al., 2003), and such instabilities led to a decrease in the gas density at corotation. By investigating the H I gas distribution in the Galactic disk, using the H I LAB survey data base (Kalberla et al., 2005), Amôres et al. (2009) evidenced the existence of a ring-like gap in the gas density distribution. ...
This article discusses the effects of the spiral-arm corotation on the stellar dynamics in the Solar Neighborhood (SN). All our results presented here rely on: (1) observational evidence that the Sun lies near the corotation circle, where stars rotate with the same angular velocity as the spiral-arm pattern; the corotation circle establishes domains of the corotation resonance (CR) in the Galactic disk; (2) dynamical constraints that put the spiral-arm potential as the dominant perturbation in the SN, comparing with the effects of the central bar in the SN; (3) a long-lived nature of the spiral structure, promoting a state of dynamical relaxing and phase-mixing of the stellar orbits in response to the spiral perturbation. With an analytical model for the Galactic potential, composed of an axisymmetric background deduced from the observed rotation curve, and perturbed by a four-armed spiral pattern, numerical simulations of stellar orbits are performed to delineate the domains of regular and chaotic motions shaped by the resonances. Such studies show that stars can be trapped inside the stable zones of the spiral CR, and this orbital trapping mechanism could explain the dynamical origin of the Local arm of the Milky Way (MW). The spiral CR and the near high-order epicyclic resonances influence the velocity distribution in the SN, creating the observable structures such as moving groups and their radially extended counterpart known as diagonal ridges. The Sun and most of the SN stars evolve inside a stable zone of the spiral CR, never crossing the main spiral-arm structure, but oscillating in the region between the Sagittarius-Carina and Perseus arms. This orbital behavior of the Sun brings insights to our understanding of questions concerning the solar system evolution, the Earth environment changes, and the preservation of life on Earth.
... Self-consistent spiral models using such potential have been presented by [55,56,57,11]. Departing from this approach, the more recent spiral models of [58] and [59] were derived from the modelling of the stellar spiral density in the Galactic disk and the self-consistency were calculated to define their physical parameters. As pointed out by [59], the brightness profiles observed in galactic disks in circles around the center are not simple sine functions. ...
... As a natural consequence of this dynamical process, a ring-shaped void of gas should form at the corotation radius ( [95,96,12]). From recent magnetohydrodynamic simulations, [94] and [97] verified the presence of instabilities at the corotation radius in the gas response to a self-gravitating spiral-arms model, the PERLAS model ( [58]), and such instabilities led to a decrease in the gas density at corotation. ...
This article discusses the effects of the spiral-arm corotation on the stellar dynamics in the Solar Neighborhood (SN). All our results presented here rely on: 1) observational evidence that the Sun lies near the corotation circle, where stars rotate with the same angular velocity as the spiral-arm pattern; the corotation circle establishes domains of the corotation resonance (CR) in the Galactic disk; 2) dynamical constraints that put the spiral-arm potential as the dominant perturbation in the SN, comparing with the effects of the central bar in the SN; 3) a long-lived nature of the spiral structure, promoting a state of dynamical relaxing and phase-mixing of the stellar orbits in response to the spiral perturbation. With an analytical model for the Galactic potential, composed of an axisymmetric background deduced from the observed rotation curve, and perturbed by a four-armed spiral pattern, numerical simulations of stellar orbits are performed to delineate the domains of regular and chaotic motions shaped by the resonances. Such studies show that stars can be trapped inside the stable zones of the spiral CR, and this orbital trapping mechanism could explain the dynamical origin of the Local arm of the Milky Way (MW). The spiral CR and the near high-order epicyclic resonances influence the velocity distribution in the SN, creating the observable structures such as moving groups and their radially extended counterpart known as diagonal ridges. The Sun and most of the SN stars evolve inside a stable zone of the spiral CR, never crossing the main spiral-arm structure, but oscillating in the region between the Sagittarius-Carina and Perseus arms. This orbital behavior of the Sun brings insights to our understanding of questions concerning the solar system evolution, the Earth environment changes, and the preservation of life on Earth.
... 5.3.1. The 3D spiral model is the PERLAS spiral arms from Pichardo et al. (2003, hereafter new A&S + spiral arms (P03)). The locus is the one following Drimmel and Spergel (2001) and has a pitch angle of 15.5 • . ...
Understanding how stars form is one of the fundamental questions which astronomy aims to answer. Currently, it is well accepted that the majority of stars form in groups and that their predominant mechanism of formation is the core-collapse. However, several mechanisms have been suggested to explain the formation of substellar objects, and their contribution is still under debate. The main goal of this thesis is to determine the initial mass function, the mass distribution of stars at birth time, in different associations and star-forming regions. The mass function constitutes a fundamental observational parameter to constrain stellar and substellar formation theories since different formation mechanisms predict different fraction of stellar and substellar objects. We used the Gaia Data Release 2 catalogue together with ground-based observations from the COSMIC-DANCe project to look for high probability members via a probabilistic model of the distribution of the observable quantities in both the cluster and background populations. We applied this method to the 30 Myr open cluster IC 4665 and the 1 - 10 Myr star-forming region Upper Scorpius (USC) and r Ophiuchi (r Oph). We found very rich populations of substellar objects which largely exceed the numbers predicted by core-collapse models. In USC, where our sensitivity is best, we found a large number of free-floating planets and we suggest that ejection from planetary systems must have a similar contribution than core-collapse in their formation. The age is a fundamental parameter to study the formation and evolution of stars and is essential to accurately convert luminosities to masses. For that, we also presented a strategy to study the dynamical traceback age of young local associations through an orbital traceback analysis. We applied this method to determine the age of the b Pictoris moving group and in the future, we plan to apply it to other regions such as USC. The members we identified with the membership analysis are excellent targets for follow-up studies such as a search for discs, exoplanets, characterisation of brown dwarfs and free-floating planets. I this thesis, we presented a search for discs hosted by members of IC 4665 and we found six excellent candidates to be imaged with ALMA or the JWST. The tools we developed, are ready to be used in other regions such as USC and r Oph, where we expect to find a larger number of disc-host stars.
... We estimate the effect a spiral arm potential would have had by implementing a modified version of the potential presented in Pichardo et al. (2003). In their work, they construct the spiral arm potential by superpositioning oblate spheroids along the arm. ...
... It should be noted that for computational efficiency the number of trajectories in the runs with the spiral potential are reduced by a factor of 10 This lead to large amounts of noise at large V z for R > 6 kpc and bins with R > 8.5 kpc have been excluded as they were too noisy. the oblate spheroids in Pichardo et al. (2003) and with the mass of the Plummer spheres following the same radial distribution as the gas. We find that the effect on the number of GMC hits is small, as the gravitational focusing by the arms is limited. ...
Giant molecular clouds (GMCs) are believed to affect the biospheres of planets as their host star passes through them. We simulate the trajectories of stars and GMCs in the Galaxy and determine how often stars pass through GMCs. We find a strong decreasing dependence with Galactocentric radius, and with the velocity perpendicular to the Galactic plane, V$\mathrm{ z}$. The XY-component of the kinematic heating of stars was shown to not affect the GMC hit rate, unlike the Z-dependence (V$\mathrm{ z}$) implies that stars hit fewer GMCs as they age. GMCs are locations of star formation, therefore we also determine how often stars pass near supernovae. For the supernovae the decrease with V$\mathrm{ z}$ is steeper as how fast the star passes through the GMC determines the probability of a supernova encounter. We then integrate a set of Sun-like trajectories to see the implications for the Sun. We find that the Sun hits 1.6 ± 1.3 GMCs per Gyr which results in 1.5 ± 1.1 or (with correction for clustering) 0.8 ± 0.6 supernova closer than 10 pc per Gyr. The different the supernova frequencies are from whether one considers multiple supernovae per GMC crossing (few Myr) as separate events. We then discuss the effect of the GMC hits on the Oort cloud, and the Earth’s climate due to accretion, we also discuss the records of distant supernova. Finally, we determine Galactic Habitable Zone using our model. For the thin disc, we find it to lie between 5.8 and 8.7 kpc and for the thick disc to lie between 4.5 and 7.7 kpc.
... "Wild" (Martinet 1974) or ergotic ( Athanassoula et al. 1983) behavior associated with resonant overlap can be identified in regions of a surface of section (SoS) diagram by irregularly distributed consequents (see Binney & Tremaine 2008, Section 3.7.3). Pichardo et al. (2003) combined SoS and Lyapunov analyses to show that for a sufficiently strong perturbation, orbits in these regions exhibit chaotic behavior. SoS analysis can have limited utility since, in order to to resolve a chaotic signature, it necessitates a significant number of orbits in order to populate the phase space within a given energy slice, and these are best evolved over several dynamical periods. ...
It is widely accepted that stars in a spiral disk, like the Milky Way’s, can radially migrate on the order of a scale length over the disk’s lifetime. With the exception of cold torquing, also known as “churning,” processes that contribute to the radial migration of stars are necessarily associated with kinematic heating. Additionally, it is an open question as to whether or not an episode of cold torquing is kinematically cold over long radial distances. This study uses a suite of analytically based simulations to investigate the dynamical response when stars are subject to cold torquing and are also resonant with an ultraharmonic. Model results demonstrate that these populations are kinematically heated and have rms changes in orbital angular momentum around corotation that can exceed those of populations that do not experience resonant overlap. Thus, kinematic heating can occur during episodes of cold torquing. In a case study of a Milky Way-like disk with an exponential surface density profile and flat rotation curve, up to 40% of cold torqued stars in the solar cylinder experience resonant overlap. This fraction increases toward the galactic center. To first approximation, the maximum radial excursions from cold torquing depend only on the strength of the spiral pattern and the underlying rotation curve. This work places an upper limit to these excursions to be the distance between the ultraharmonics, otherwise radial migration near corotation can kinematically heat. The diffusion rate for kinematically cold radial migration is thus constrained by limiting the step size in the random walk approximation.
... (JRDL) are small perturbations in the gravitational potential of the disc, like gravitational potential grooves or valleys, produced by the crowding of stellar orbits in some regions of the disc. The orbits of the stars constituting the arms are closed ones, which repeat themselves after each turn (in the rotating frame of reference of the arms), and this guarantees a relatively long lifetime to the spiral structure (Pichardo et al. 2003;Junqueira et al. 2013). ...
In this work we revisit the issue of the rotation speed of the spiral arms and the location of the corotation radius of our Galaxy. This research was performed using homogeneous data set of young open clusters (age < 50 Myr) determined from Gaia Data Release 2 (DR2) data. The stellar astrometric membership was determined using proper motions and parallaxes, taking into account the full covariance matrix. The distance, age, reddening, and metallicity of the clusters were determined by our non-subjective multidimensional global optimization tool to fit theoretical isochrones to Gaia DR2 photometric data. The rotation speed of the arms is obtained from the relation between age and angular distance of the birthplace of the clusters to the present-day position of the arms. Using the clusters belonging to the Sagittarius–Carina, Local, and Perseus arms, and adopting the Galactic parameters R0 = 8.3 kpc and V0 = 240 km s⁻¹, we determine a pattern speed of 28.2 ± 2.1 km s⁻¹ kpc⁻¹, with no difference between the arms. This implies that the corotation radius is Rc = 8.51 ± 0.64 kpc, close to the solar Galactic orbit (Rc/R0 = 1.02 ± 0.07).
... The Milky Way model follows Gustafsson et al. (2016) and consists of a axisymmetric potential (Binney 2012), two spiral arms (Pichardo et al. 2003), a Galactic bar (Pichardo et al. 2012) and a distribution of GMCs along the spiral arms (Gustafsson et al. 2016). ...
... The spiral pattern consists of two spiral arms with a pitch angle of 15.5 • described by Pichardo et al. (2003). Each arm is represented by 100 inhomogenous oblate spheroids with semi-major and minor axes of 1000 pc and 500 pc, respectively. ...
... with a radial scale height, R L , of 3.9 kpc. ρ 02 is given in Pichardo et al. (2003) by ...
We investigate the possibility that the Sun could have been born in M67 by carrying out $N$-body simulations of M67-like clusters in a time-varying Galactic environment, and following the galactic orbits of stars that escape from them. We find that model clusters that occupy similar orbits to M67 today can be divided up into three groups. Hot clusters are born with a high initial $z$-velocity, depleted clusters are born on cold orbits but are destroyed by GMC encounters in the Galactic disc, and scattered clusters are born on cold orbits and survive with more than 1000 stars at an age of 4.6 Gyr. We find that all cluster models in all three cluster groups have stellar escapers that are kinematicaly similar to the Sun. Hot clusters having the lowest such fraction $f_{\odot} = 0.06$ %, whilst depleted clusters have the highest fraction, $f_{\odot} = 6.61$ %. We calculate that clusters that are destroyed in the Galactic disc have a specific frequency of escapers that end up on solar-like orbits that is $\sim$ 2 times that of escapers from clusters that survive their journey.
