GALACTIC STRUCTURE, EVOLUTION AND MERGER REMNANTS The Role that Astrometry Plays
Blackwell, Jennifer, News Director/Producer has reference to this Academic Journal, PHwiki organized this Journal GALACTIC STRUCTURE, EVOLUTION AND MERGER REMNANTS The Role that Astrometry Plays in Underst in addition to ing the Kinematical Structure of the Galaxy Dana I. Dinescu (Yale University) SDSS Perturbed Spiral Galaxies
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The Milky Way as a Growing System G. Gilmore in addition to R. Sword Majewski et al. 2003 2MASS The Sagittarius Dwarf Galaxy: Tidal Streams Mapped from 2MASS (Majewski et al. 2003)
The Science Goals 1) Better describe in addition to underst in addition to the accretion process in our Galaxy, in addition to its contribution to the as long as mation of the halo, bulge, in addition to disk. 2) Kinematically characterize the main components of the Milky Way in order to describe the Galactic potential: i.e., measure mean velocities in addition to velocity dispersions over the relevant size of the Galaxy. Requirements Absolute proper motions of: 1) Globular clusters, MW satellites, stars in known streams, in addition to anonymous stars in deep, survey-type programs. 2) Tracers of the main Galactic components: stars, open in addition to globular clusters. Absolute Proper Motions By means of an inertial reference frame defined by: 1) galaxies, QSOs (many pencil beam surveys, clusters in addition to MW satellites programs, NPM, SPM, USNO-B-SDSS, etc.) 2) Stars with already determined absolute proper motions: Hipparcos, Tycho2, UCAC2, NPM, SPM 3) Stars with modeled or assumed known kinematics, e.g., disk stars in the case of Sgr, (Ibata et al. 1997), SMC stars as long as 47 Tuc (Anderson & King 2003), bulge stars as long as NGC 6522, 6528, 6553 (Terndrup et al. 1998, Feltzing & Johnson 2002, Zoccali et al. 2001), kinematic Galactic model as long as 14 globular clusters (Cudworth & Hanson 1993). Millisecond pulsars in globular clusters: From timing data, very accurate absolute positions are obtained. These can be used to determine absolute proper motions over a relatively short time baseline (e.g., Freire et al. 2003). Required proper-motion uncertainty
Most notable systematics found in proper-motion determinations 1) Magnitude-dependent: practically all photographic plates have guiding-induced positional biases of image centroids that occur due to long exposures combined with the non-linear response of the photographic plate. Kohzurina-Platais et al. 1995 NGC 3680 SPM Girard et al. 1998; grating images were used to correct magnitude equation in positions: proper-motion differences between blue in addition to visual plate pairs SPM cluster program, Dinescu et al. 1999; field of M4 after magnitude equation correction based on grating images. 2) Color-dependent: due to color dependence of atmospheric refraction. Observations taken at different hour angles, in addition to with different filter-plate combinations in addition to telescopes are affected by color terms. This is why QSOs in addition to galaxies may give different answers when determining absolute proper motions. Dinescu et al. 2004; Fornax field: galaxies in addition to QSOs
3) Position-dependent: mainly due to optical distortion. Most notable as long as wide field, short f/ratio telescopes (e.g., Schmidt telescopes that were used as long as deep, all-sky surveys). Other: field rotation, coma. Distortion can be modeled (e.g. Chiu 1976, Cudworth & Rees 1991, Zacharias et al. 2004 UCAC1, UCAC2, Anderson & King 2003). However, position-dependent systematics may remain in the proper motions. These can be overcome by defining local plate solutions around objects of interest- clusters, extragalactic objects- through reference stars of the same kinematical population. Dinescu et al. 2001, NGC 7006 Proper-motion Results: Globular Clusters M 4 -12.26 (0.54) -18.95 (0.54) Kalirai et al. 2004 HST, ~12 galaxies -13.21 (0.35) -19.28 (0.35) Bedin et al. 2003 HST, 1 QSO -12.50 (0.36) -19.92 (0.49) Dinescu et al. 1999 – SPM, ~100 Hipparcos stars Proper-motion Results: MW Satellites Sagittarius Dwarf – Ibata et al. 1997 in addition to Dinescu et al. 2005, proper-motion measurements agree in addition to produce an orbit that agrees with the location of tidal debris. LMC Kroupa et al. 1994 (PPM), Jones et al. 1994, Kroupa & Bastian 1997 (Hipparcos), Pedreros et al. 2002, Drake et al. 2002 (MACHO), Momany & Zaggia 2005 (UCAC2); basically limited in precision in addition to accuracy as long as the purpose of detailed dynamical modeling of the system (see van de Marel et al. 2002). SMC Kroupa & Bastian 1997 (Hipparcos), Irwin 1999 (galaxies) More distant dwarf spheroidals (Sculptor, Ursa Minor, Draco, Carina in addition to Fornax) – there are: 1) ground-based, long time-baseline studies (Scholz & Irwin 1994, Schweitzer et al. 1995,1997, Dinescu et al. 2004, in addition to 2) space-based (HST), short time-baseline measurements (Piatek et al. 2002, 2003, 2005). For overlapping measurements (UMi in addition to Fornax), results disagree. Space-based observations produce more energetic, more eccentric orbits than ground-based ones.
Scientific Results 1) Characterizing the Globular-Cluster System: Age, Metallicity, Orbit Shape Mackey & Gilmore 2004 with orbits from Dinescu et al. 1999, 2000, 2001, ages from De Angeli et al. 2005 2) Detecting/Characterizing Accretion Signatures Sagittarius in addition to its tidal debris Pal 12 proper motion – Dinescu et al. 2000 Martinez-Delgado et al. 2002 Cohen 2004 Majewski et al. 2004 Sagittarius in addition to its tidal debris (cont.) SA 71 – Dinescu et al. 2002 Putman et al. 2004
w Centauri Bedin et al. 2004 Lee et al. 2001 Self-enriched system with a complex chemical pattern w Cens Orbit Retrograde; Rp = 1.6 kpc, Ra = 6.0 kpc, z = 2.0 kpc, ecc = 0.57, Pr = 80 mill. years, plane crossing ~ 22 mill. years (Dinescu et al. 1999) On the current orbit, w Cen couldnt have chemically enriched itself (Gnedin et al. 2002) N-body modeling of the disruption of w Cens parent galaxy w Cens parent system: a massive system of 8 109 Mo in addition to half-mass radius of 1.4 kpc. It has a radial, low-inclination orbit that starts at ~ 60 kpc from the Galactic center in addition to decays in ~ 2 Gyr to the current orbit of w Cen (Tsuchiya et al. 2004, 2003). The debris as long as m a disklike structure within 6 kpc from the Galactic center. Kinematical in addition to chemical surveys within 1-2 kpc of the Sun should be able to detect such a structure (Dinescu 2002, Meza et al. 2005). The thin disk of the Galaxy is potentially strongly affected by such a massive satellite. Very likely, other globular clusters may originate from this satellite (Dinescu 2002).
Searching as long as debris from w Cens parent galaxy Dinescu 2002, use Beers et al. 2000 cat., in addition to highlight RR Lyrae Meza et al. 2005 The Monoceros tidal stream Pennarubia et al. 2005; proper motions from Munn et al. 2004 (USNOB-SDSS) of 3-4 mas/yr precision per star. These allow the distinction between pro in addition to retrograde orbits of the parent satellite. 3) Milky Way Satellites: Interactions, Orbit Alignments Fornax crossed the Magellanic plate ~200 Myr ago, a time that coincides with the termination of the SF process in Fornax. The excess, anomalous clouds within the SGP region of the Magellanic stream (Putman et al. 2003), whose origin has long been debated in the literature as constituents of either the MS or of the extragalactic Sculptor group, are found to lie along the orbit of Fornax. Cloud orientations differ from those in the MS, in addition to their radial velocities are well below those of galaxies in the Sculptor group. These clouds may be stripped material from Fornax as the dwarf crosses the orbit of the Magellanic clouds. Fornax dwarf Dinescu et al. 2004
3) Galactic Structure: Characterizing the Main Components Thin disk Solar neighborhood samples with proper motions from e.g. Hipparcos, Tycho2, UCAC2, NPM/SPM aim to describe the disk in terms of: 8Galactic potential via surface density as a function of z (e.g. Korchagin et al 2003, Galactic rotation (Oort coefficients, e.g., Ollig & Dehnen 2003), bars signature in local velocity groups (Dehnen 2000, Fux 2001). 8 Disks heating mechanism via velocity dispersion as a function of age (e.g., Nordstrom et al 2004). More distant tracers (OB stars, possibly open clusters) can be used to describe/underst in addition to the disk on a larger scale: 8 The spiral pattern in addition to the warp: (Fern in addition to ez et al. 2001, Drimmel et al. 2000) 3) Galactic Structure: Characterizing the Main Components (cont.) Thick disk There are numerous studies that use particular tracers to measure the thick disks mean velocity in addition to dispersion. It was found that these numbers do not necessarily agree, in addition to that there appears to be a variation with distance from the Galactic plane (Majewski 1994). This dependence is now being quantified from homogeneous data sets: e.g., Chiba & Beers 2000 (Hipparcos, NPM, SPM, the rotation velocity gradient) in addition to Girard et al. 2005 (SPM, velocity in addition to velocity dispersion gradients). Chiba & Beers 2000 Thick disk (cont.) Girard et al. (2004 in addition to work in progress); SPM + 2MASS toward SGP
3) Galactic Structure: Characterizing the Main Components (cont.) The Bulge/Bar A very complex system where a LOT is happening. Current studies (HST in addition to ground based, e.g. Kuijken 2002, 2004, Zoccali et al 2004, Feltzing & Johnson 2002, Terndrup et al. 1998, Spaenhauer et al. 2002) have focused on determining proper-motion dispersions that are to be matched with dynamical models of the bulge. Currently, there are too few directions sampled in the bulge to allow robust constraints on the models, in addition to there are very few absolute proper-motion studies. Two ongoing programs that can probe a large area of the bulge are: the OGLE proper motion catalog (Sumi et al. 2004, has a 4-yr time baseline!), in addition to absolute proper motions of globular clusters in the bulge (Dinescu et al. 2003). 3) Galactic Structure: Characterizing the Main Components (cont.) Halo See above discussion as long as the accreted component. For the traditional stellar halo – as in the case of the thick disk there are many localized studies that have provided mean velocities in addition to velocity dispersions (most of these are towards the Galactic poles!). Hints that the halo has an inner, dissipational-collapse component in addition to an accreted component are already found in the globular-cluster data in addition to field-star data (Chiba & Beers 2000). However, we lack a satisfactory global kinematical description of the stellar halo, i.e. , velocity means in addition to dispersions as a function of galactocentric distance. Chiba & Beers 2000 CONCLUDING REMARKS 8In light of the complex picture of the Galaxy that has emerged from all-sky photometric surveys, velocities are key quantities to underst in addition to the present structure in addition to the active, dynamical history of the Galaxy. Velocities combined with chemical abundances are the most powerful tool to map out the as long as mation process of the Galaxy. This kind of study is possible only in our Galaxy in addition to perhaps the Local Group, in addition to astrometry has a crucial part to play. 8When using proper-motion catalogs/data, it is imperative that the limitations are understood. Search through the descriptions as long as various tests as long as systematics!
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