The near-IR window to study mysteries of the Milky Way disk

1. The near-IR window to study mysteries of the Milky Way disk Noriyuki Matsunaga (The University of Tokyo, Japan)

2. Acknowledgement • To J. Baba (TiTEC) and M. Fujii (NAOJ) • General discussions on the Galactic evolution • To N. Gouda (NAOJ) • Showing his talk slides in advance • Section 2.11 in the last Japanese WISH book, prepared by J. Baba et al., is dedicated to a proposal of the Galactic disk survey (for spiral-arm dynamics and stellar cluster evolution).

3. Contents • Why we want WISH to observe the Galaxy. • Useful tracers and possible projects with WISH (1) Pulsating stars (Cepheids, Miras, RR Lyrs, …) (2) Stellar clusters • What should be kept in mind when we use WISH for studying the Galactic objects.

4. The Galaxy: the nearest spiral • Detailed information within reach. • A lot of the information needs to be collected yet. • Details are necessary for the comprehensive understanding of the galactic evolution. • Bridging individual stars, clouds, and the whole galaxy Dame et al. (2001)

5. Motivations • What does the Galaxy look like? How did it evolve? • Almost all kinds of objects gather in the bulge/disk. • But, these are difficult regions to observe in the optical. • An example of big questions to study • Are spiral arms predicted in density-wave theory or transient as suggested in recent simulations? Baba et al. (2009) suggested that spiral arms are transient in a short time scale of 100 Myr based on their cutting-edge N-body/SPH simulations.

6. Gaia to reveal the Galaxy • To be launched by ESA on 19th Dec 2013 • The final catalogue with astrometric (parallaxes & proper motions) as well as photometric and velocity data will be released in 2021. • G-band: 0.33-1.0 micron, 6 mag < G < 20 mag • Parallax accuracy: 7μas (G<12) down to 100μas (G~18) • 109 stars at almost the whole Galaxy to be observed.

7. The Galactic disk behind the veil • The disk, the main body of the Galaxy, is obscured by the interstellar extinction. • Infrared (astrometric) observations are necessary. Reyle et al. (2008) Stellar density of the bulge seen down to G=20 Absolute magnitude MV just reached at G=20

8. Tracers of the Galactic disk/bulge • Normal stars • Statistically large samples; but errors tend to be large. • Red clump giants • Useful, but necessary to be treated statistically • Pulsating variable stars • Distances and ages can be easily/accurately estimated. • Stellar clusters • Distances and ages can be easily/accurately estimated. • Star forming regions • Good tracers (especially with VLBI data). • Complementary to our optical/near-IR tracers, but tracing only star-forming sites.

9. Two kinds of possible projects • Survey of pulsating stars and their proper motions • Some dense and obscured regions remain to be discovered. • Deep photometry of stellar clusters and their proper motions • Many interesting targets will be available until the WISH days. • Both projects would provide us with valuable information on individual objects with distances and 3D velocities as well as ages. (x, v, t).

10. Why WISH is good for our purpose? • High spatial resolution • Diff. Limits = 0.3arcsec, 0.4arcsec in filters 2 and 3. • Significantly better than 0.8arcsec in the VVV survey. • In many cases, the crowding effect limits our surveys. • Efficient survey ability • Wide-field(0.23 deg2). Deep with a short exposure. • Multi-color photometry • Need to make the CMD and correct for reddenings. • Astrometry • Proper motions (even without parallaxes) would be very useful to constrain the kinematic model.

11. Remarks on our requirements • High signal-to-noise ratio needed • Almost nothing can do with 3-σ detection! • Photometric errors on individual distance tracers should be less than 0.1 mag. • To estimate distances, we need S/N=30 at least. The CMD must go down well below the feature we try to determine.

12. Usefulness and possible WISH projects (1) Pulsating stars

13. Pulsating stars as tracers Classical Cepheid • Distance indicators • Population indicators • Kinematic tracers • Chemical tracers Type II Cepheid Mira RR Lyr Gautchy & Saio (1995)

14. Variable stars as distance indicators Period-Luminosity relations (from Matsunaga et al. 2009, 2011) Classical Cepheid Mira Ks [mag] For Miras, P-L relations are narrow only in the IR (not in the optical) Type II Cepheid log(Period/day)

15. Variable stars as population indicators log (Age/yr) 8.5 300Myr 8.0 100Myr 30Myr 7.5 Period-Age relation of classical Cepheids (Bono et al. 2005) 10Myr 7.0 0 1 2 log (Period/day)

16. The earlier status of Cepheid surveys • Cepheids distant in the Galactic disk are obscured. • Many remain to be discovered (by infrared surveys). GC Sun The distribution of ~500 Cepheids from DDO database: http://www.astro.utronto.ca/DDO/research/cepheids/ overlaid on the illustration by GLIMPSE project (2008)

17. Recent and the expected progress • Near-infrared surveys in progress • VISTA/VVV (K-band): Bulge 300 deg2, Disk 220 deg2 • OGLE (I-band), Pan-STARRS (optical) • and LSST in the future • Our works • IRSF/SIRIUS (South Africa), Galactic center, etc. • the first near-IR (JHKs) survey of pulsating stars which successfully discovered Cepheids • KWFC (Kiso), northern Galactic disk

18. IRSF variable survey of the Galactic Center • With 8 year survey using the IRSF/SIRIUS in South Africa, we detected 3 classical Cepheids, 16 type II Cepheids, and >500 Miras towards 30min ×20min around the GC (Matsunaga et al. 2009, 2011, 2013). • We discussed the GC distance and star formation there. >500 Miras 3 Classical Cepheids 16 Type II Cepheids

19. WISH and pulsating stars • Fainter pulsating stars in the obscured and dense regions probably remain elusive for a decade. • The bulge survey presented by Gouda-san would also provide us with a good dataset. • Some additional fields towards the disk (eg. towards spiral arms) A plan of the bulge survey from Gouda-san’s slides.

20. RR Lyrs in the Galactic Center • K=17～18magincluding the foreground extinction. • The best measurement of the GC distance based on a photometric distance indicator. • Considering their confusion limit, VISTA is not expected to be good enough to detect them. > 500 Miras 3 Classical Cepheids RRLyr 16 Type II Cepheids

21. How far can we reach? • RR Lyr stars (MK=-1mag) across the disk are within the reach. • Limig mag. 20 Vega mag (@S/N=30; with 300sec) • VVV’s limit: Ks=15.5 mag(@S/N=30) • K(AB)=K(Vega)+1.9 RR Lyrs in the far-side disk WISH (20 mag) GC Curves show the limits to detect RR Lyrs (MK=-1mag) on the (AK, D) diagram. VISTA (17 mag)

22. Story about IR surveys of pulsating stars • Our surveys have been demonstrating that infrared surveys are important to study pulsating stars across the Galaxy. • Large-scale surveys like VISTA/VVV will find a lot of (bright) pulsating stars in 5 years. • WISH will be able to • Add proper motions which are crucial to study the kinematic model • Expand our census to fainter (and more numerous) pulsating stars like RR Lyrs.

23. Usefulness and possible WISH projects (2) Stellar Clusters

24. Stellar clusters • See the section by Baba-san in the WISH book • Distances and ages can be estimated based on the CMD. Certainly useful tracers of the disk. • New deep photometric data will give us a chance to use a new distance indicator, a faint kink of the MS. The faint kink of the MS appears in the infrared CMD and is useful to determine distances and reddenings accurately.

25. New clusters being found by IR surveys • Massive and young (and obscured) stellar clusters have been discovered with various IR data (2MASS, Spitzer-GLIMPSE, VISTA-VVV, etc). Sun Davies et al. (2012) Added a new massive (≥104Msun) young (a few Myr) clusters to others discovered in recent infrared surveys. GC

26. WISH and stellar clusters • Many interesting targets will be available. • Measuring distances (mainly based on the CMD) and proper motions. • Accurate measurements of proper motions may be useful to find runaway stars in young clusters (Fujii-san’s works; egFujii & PortegiesZwart, 2011, Science, 334, 1380). Fujii+11 (Illustration by 4D2U)

27. How far can we reach? • The faint MS kinks (MJ=+6 mag) of many clusters can be detected for the first time. • Still challenging, but a great jump with WISH. • Also useful for more distance clusters with bright stars. • Limig mag. 20 Vega mag (@S/N=100, with 900 sec) 23 Vega mag (@S/N=50, with 3.3 hr) • VVV’s limit: Ks=15.5 mag(@S/N=30) • J(AB)=J(Vega)+0.9 WISH (23mag) WISH (20mag) GC Curves show the limits to study the MS kink (MJ=+6mag) on the (AK, D) diagram. VISTA (17 mag)

28. On the system and what we need • Filters and the photometric system • Self photometric calibrations needed. • Otherwise, systematic errors can be sticky. • Efficiency and overhead • Observing objects in the Galaxy tend to require relatively short exposure times. • Visibility: The Galactic Center is near the Ecliptic equator, but 20 day monitoring would good enough.

29. Summary • WISH surveys of the Galaxy will be important: • Infrared—Severe interstellar extinction • WideFOV—Need for a wide coverage of sky • Highresolution—Crowding towards the Milky Way • Depth—More interests in fainter features • Useful tracers of the Galactic disk: • Pulsating stars: RR Lyrs will be within reach. • Stellar clusters: More distant and obscured clusters. • Time-series observations required: • Each integration time is relatively short.

30. End

32. KISOGP survey of the northern disk • Using Kiso Schmidt telescope (1.05m) and KWFC camera (4 deg2 FOV) to survey variable stars. • We are around the middle of 3 year survey plan and have found hundreds of new variables. 10kpc α~21.2h δ~+24deg 4kpc α~23.9h δ~+48deg α~0.4h δ~+63deg α~6.8h δ~+03deg α~4.1h δ~+52deg α~5.8h δ~+29deg

33. WFIRST-2.4 Science Cases seemingly under consideration • from A collection of one page science programs (Version 1.0; Mar 2013) • Proper motions and parallaxes of disk and bulge stars (by S. Gaudi, OSU) • The most distant star-­forming regions in the Milky Way (by J. Stauffer, IPAC) • The infrared color-magnitude relation (by J. Kalirai, STScI)

34. The Galaxy: some interesting features • Bulge: boxy and barred structure, X shape, … • Disk: warp, flare, large peculiar motions of SFRs, … • Halo: streams, ultra-faint dwarfs, … Reid et al. (2009) Finding large motions of SFRs based on VLBI data Levine et al. (2006) investigated the warp of the disk with revised datasets

35. 変光星研究：可視から赤外へ 可視光の周期光度関係 赤外線の周期光度関係 赤色変光星 赤色変光星 セファイド セファイド Ita et al. (2004) RRライリ 横軸・周期、縦軸・明るさ Soszynski et al. (2011)

36. Period-luminosity relations of RR Lyrs • 可視と赤外のそれぞれの指標 24,000 RR Lyrs in the LMC (Soszynski et al. 2004) Cluster “Reticulum” In the LMC (Dall’Ora et al. 2004) V band K band σ＝±0.3 mag WVI=I-(V-I) σ＝±0.03 mag σ＝±0.2 mag 古典的セファイドは±0.1 mag

37. Classical Cepheids • 3 classical Cepheids discovered near the GC. • The first discovery in this important region. (Matsunaga et al., 2013, Nature, 477, 188)