Galactic Structure Heidi Newberg Rensselaer Polytechnic Institute

Overview Overview of results from SDSS (this will go quickly, so I hope most peole have some familiarity with it) SEGUE – Sloan Extension for Galactic Underpinnings and Evolution Galactic Structure in SNAP/Destiny

The Milky Way Galaxy 40,000 square degrees on the sky Composed of stars, gas and dust, dark matter Dark matter: not detected at all (yet) Gas and dust: R v, density, composition Stars: 3D velocities, distances, mass, age, chemical composition The only galaxy for which we can hope to get comprehensive stellar information in the next two decades (RAVE, QUEST, SEGUE, Pan-STARRS, GAIA, etc.). The dark matter is only revealed by the motions of stars. The better we understand the detailed motions of stars in the Galaxy, the better resolution we will have on the spatial distribution of dark matter. How are we going to understand all of that “detail” found in external galaxies if we don’t even know how our own galaxy is put together?

The Standard Galactic Model Radial scale length (kpc) Bulge Spheroid Thick Disk Thin Disk Dark Halo Vertical scale height or c/a kpc 325 kpc 1? Density near Sun (M sol /pc 3 ) Metallicity [Fe/H] V rot at R sol (km/s) ? Allen’s Astrophysical Quantities, 2000

Yanny et al Pal 5 globular cluster

Galactic Center Yanny et al. 2000

Newberg et al Celestial equator

Look at these BHB/A stars at g=20.3 near (l,b)= (190,30) degrees.

NGC2419 right nearby the 80 kpc stream piece! Globular Cluster was perhaps once associated with Sagittarius

Galactic Center Yanny et al. 2000

Newberg et al. 2002

Squashed halo Spherical halo Exponential disk Prolate halo Newberg et al. 2002

Yanny et al. 2003

Disk “Ring” 2MASS M stars from Rocha-Pinto et al.

Disk “Ring” 2MASS M stars from Rocha-Pinto et al. Frinchaboy et al GCs from Crane et al GC from Harris 1996 Open clusters

Martin et al., 2003

Canis Major Southern Arc Northern Arc A A B B

Disk “Ring” 2MASS M stars from Rocha-Pinto et al. Frinchaboy et al GCs from Crane et al GC from Harris 1996 Open clusters

Following Helmi et al (V x, V y, V z ) = (-65, 135, -249), (σ x, σ y, σ z ) = (62, 33, 17)

Density of dark matter in Sagittarius Stream [2, 190] x 10 4 M  /kpc 3 [0.001, 0.07] Gev/cm % of the local density of the isothermal Galactic halo, assumed to be 0.3 GeV/cm 3

Left : z=10, small haloes dominate. Red indicates possible site of star formation at this time (very dense regions). Right: Present time, many of the small haloes have merged into the model Milky Way halo; oldest stars found throughout the Milky Way and in satellites. CDM simulation Moore et al. 2001

Michael Odenkirchen, MPIA

Ibata et al q=1.0

Ibata et al q=0.9

Ibata et al q=0.75

Photometric surveys can: Discover spatial density through statistical photometric parallax Separate stellar populations by turnoff color, metallicity Discover tidal streams from globular clusters and dwarf galaxies in the Galactic halo Contribute to proper motion/parallax measurements Find variable objects

Spectroscopy can be used to Find radial velocities (need < 2 Angstrom resolution to get interesting error bars) Determine individual stellar properties [SDSS spectroscopy produces radial velocities to ±15 km/sec (g~20), Temperatures: ± 200 K, and surface gravities to ± 0.4 dex, and [Fe/H] within 0.3 dex] Stellar populations maintain kinematic coherence long after density coherence is lost, so finer and older structures can be identified this way.

Clearly, we are not yet using all of the information in the data We have found everything so far by looking by eye at two- dimensional parameter plots (color-magnitude, magnitude vs. angle) of sub-selected stellar catalogs (A stars, F stars). Clearly, we want to build up a global model of the Galaxy that fits all of the stars, using colors, magnitude, velocities if available. We want to identify components from the kinematics, age, metallicity, and spatial distribution. I currently have a graduate student working on this problem, and we have a prototype algorithm that has successfully rediscovered the Sagittarius dwarf tidal stream (Purnell et al., in preparation).

Gerson Goldhaber, Professor of Physics at UC Berkeley 1991 winner of the Panofsky prize of the American Physical Society, in recognition of his discovery of charmed mesons

Leonard Searle and Bob Zinn (1978) Eggen, Lynden-Bell, and Sandage (1962) The galaxy was created in a monolithic gravitational collapse The galaxy was created by hierarchical merging

Eggen’s Spaghetti sky

Rigatoni's ridges and holes are perfect with any sauce, from cream or cheese to the chunkiest meat sauces. National Pasta Association.

SDSS Contributions to Galactic Structure (1)Measurement of the scale height of the thick disk (2)Discovery of the Sagittarius tidal stream in A-type stars (3)Discovery of additional tidal debris in the Galactic halo, including a stream of debris in the Galactic plane (Monoceros, GASS, Canis Major) (4)Discovery and analysis of the tidal tails of Pal 5 (5)Discovery that the Sagittarius tidal stream extends to a distance of 90 kpc from the Galactic center (6)Found globular cluster in Sagittarius tidal stream (7)Draco dwarf galaxy has no tidal tails (8)Tidal tail discovered in Andromeda (9)Tracing the Sagittarius tidal stream in RR Lyrae stars From a survey that was designed to avoid as many Galactic stars as possible

SEGUE

Sloan Extension for Galactic Underpinnings and Evolution (SEGUE) Segue (v.) – to proceed to what follows without pause Heidi Newberg 1, Kurt Anderson 2,3, Timothy Beers 4, Jon Brinkmann 3, Bing Chen 5, Eva Grebel 6, Jim Gunn 7, Hugh Harris 8, Greg Hennessy 9, Zeljko Ivezic 7, Jill Knapp 7, Alexei Kniazev 6, Steve Levine 8, Robert Lupton 7, David Martinez-Delgado 6, Peregrine McGehee 2,10, Dave Monet 8, Jeff Munn 8, Michael Odenkirchen 6, Jeff Pier 8, Connie Rockosi 11, Regina Schulte-Ladbeck 12, J. Allyn Smith 10, Paula Szokody 11, Alan Uomoto 13, Rosie Wyse 13, Brian Yanny 14 1 Rensselaer Polytechnic Inst. 2 New Mexico State University 3 Apache Point Observatory 4 Michigan State University 5 ESA/Vilspa, Madrid, Spain 6 Max-Planck Heidelberg 7 Princeton University 8 US Naval Observatory, Flagstaff 9 US Naval Observatory, DC 10 Los Alamos National Laboratory 11 University of Washington 12 University of Pittsburgh 13 The Johns Hopkins University 14 Fermi National Accelerator Laboratory

Legacy – complete spectroscopy in the contiguous area of the N. Galactic Cap SEGUE – new survey (4000 square degrees of low latitude imaging + 250,000 stellar spectra) for Galactic structure Supernovae – light curves for ~200 Type Ia supernovae (on the south celestial equator, two or three three three-month photometry campaigns) Elements of the SDSS extension Three years, $15 million dollars

Legacy fills in spectroscopy in this region

Designed to sample the galaxy every degrees, with ~10 distance bins per blue dot

l b SDSS + SEGUE Sky Coverage Test Stripe at l=110 deg:

Turnoffs and Giant Branches visible, even at low latitudes b = E(B-V)=

Spectroscopic Samples (1) 20,000 stars within 2 kpc of the Sun. This and the next category will be valuable to normalize Galactic components at the solar position. (2) 40,000 stars within 4 kpc of the Sun. (3) 20,000 BHB stars, from 6 kpc to 70 kpc from the Sun (A nearer sample of BS stars will also be obtained.) (4) 15,000 K giant stars, to distances of 80 kpc from the Sun (5) 4800 local white dwarf stars (6) 50,000 G dwarfs from 3 to 12 kpc from the Sun, which will sample birth rate of stars, in each component, since these stars are selected to be redder than the turnoff of all Galactic components. (7) 55,000 stars which sample all areas of color space, primarily low metallicity, in search of unusual things we did not expect - in search of those rare low metallicity stars that can tell us about the heavy element production in the very first generation of stars.

Current Status of SEGUE Sloan Foundation has promised $5.2 million Negotiations for institutional support underway Proposal for ~$5 million NSF funding will be submitted in June A few hundred square degrees already obtained

M(V)D(20)D(27)D(30) O5V Mpc35 Mpc140 Mpc B5V kpc4 Mpc17 Mpc A5V kpc1.0 Mpc4.1 Mpc F5V3.520 kpc500 kpc2.0 Mpc G5V5.110 kpc240 kpc950 kpc K5V kpc85 kpc340 kpc M5V kpc8.7 kpc35 kpc G5III0.966 kpc1.7 Mpc6.6 Mpc K5III kpc2.8 Mpc11 Mpc M5III kpc2.9 Mpc11 Mpc Distance at which we can see individual stars Radius of Galactic disk: 15 kpc Distance to Virgo galaxy cluster: 19 Mpc Known Extent of stellar halo: 100 kpc The Great Wall: 100 Mpc Dist. to Andromeda 700 kpc Distance to edge of visible Universe: 4000 Mpc

Galactic structure projects RAVE – eventually (starting 2006 if funded) 5 x 10 7 stellar spectra to V=16 and R~ 10,000. Currently running pilot to get 10 5 stars to V=12 with R~4000. RVS on GAIA (Launch 2010??) – All sky. Imaging to V=20, distance and space motion to V~18, spectra of everything to V~16 with R=11,500. Pan-STARRS – deeper repeated photometry of northern sky for variability and better astrometry UKIDSS/VISTA – deeper 2MASS to K~18.5

Galactic Structure and SN Spectroscopy The spectra are too low resolution to get interesting radial velocities. They are probably too low resolution to learn anything interesting about stellar properties, beyond what we would get from photometry. The DESTINY survey would allow us to use synthetic magnitudes in passbands that we understand, by convolving the spectra, but only the long wavelength bands that are less important for discriminating stellar properties.

Parallax 0.1” pixels If you centroid to 1/10 th of a pixel, then we have 10 mas astrometry (parallaxes to 100 pc). Parallaxes for very nearby brown dwarfs. Proper motions for intrinsically faint, solar neighborhood stars (depends on time between repeat images).

Directions that could be explored (1)Looking through many magnitudes of extinction in the Galactic plane. (2)Looking at stellar populations in external galaxies. (3)Mapping main sequence stars in our galaxy, understanding the IMF. (4)Study extremely faint red “stars” in the solar neighborhood.