JWST Potential for Studies of the Local Group

1. JWST Potential for Studies of the Local Group R. Michael Rich, UCLA

2. The JWST Observatory & Optical Telescope Following slides, thanks to J. Kriss & JWST project (HST website) , Diameter: 6.5 m

3. Observatory Performance Characteristics • Primary mirror is 18 hexagonal segments, 6.5 m in diameter. • Strehl ratio > 0.80 at 2 micrometers • Encircled energy > 0.74 within 0.15 arc sec at 1um • Gold coating  good response at wavelengths > 0.6 micrometers • Field of regard • Sun angles of 85°–135° are permitted, with roll of ±5°. •  >35% sky coverage at any instant • There is a Continuous Viewing Zone (CVZ) of 5° about the ecliptic poles.

4. Overview of JWST Science Instruments • NIRCam (Near Infrared Camera) • 0.6–2.3 m, 2.4–5.0 m. R=4, 10, 100. • Fields of view: 2  2.22.2 0.032, 0.065 “/pix • Lyot-mask coronagraphy; • F070W, F090W, F110W, F150W, F200W (short wavelength) • NIRSpec (Near Infrared Spectrometer) • 0.6–5.0 m for R=100. 1.0–5.0 m for R=1000, 3000. • Micro-shutter array (33), fixed slits, and Integral Field Unit (33) • MIRI (Mid Infrared Instrument) • 5–28 m. R=4, 10, 100, 3000. • Imager (1.91.4), Coronagraphy, Low Resolution Spectrometer, IFU (~55) • FGS-TF (Fine Guidance Sensor-Tunable Filter Imager) • 1.0–2.1 m, 2.1–4.8 m. R=70–150. • Field of view: 2.22.2 • Coronagraphy

5. The JWST Focal Plane

6. JWST Background 106 OTA 105 Sunshield [photon s-1mm-1arcsec-2] 104 Zodiacal Dust 103 5 10 15 20 25 Wavelength [micron] JWST Limiting Sensitivities • Sensitivity is limited by background radiation from the sky and telescope. • The limiting flux (10 ) shown is for a point source at the North Ecliptic Pole (minimum background) in a 100,000 second exposure.

7. Gain in Astronomical Capability with JWST (G. Rieke) JWST=1 Key issues: AB~30.7 at S/N=5 in 10 h (1-2.2um) Images at 0.7-1um may be compromised (~50% enc in 0.1”)

8. The Near Infrared Spectrograph Micro Shutter Array • R=1000 mode • 1.0 - 5.0 µm • Micro-shutter array (MSA) or fixed slits • Covered by three 1st-order gratings: • 1.0 - 1.8 µm • 1.7 - 3.0 µm • 2.9 - 5.0 µm • Sensitivity (10 in 104 s): 5.2 10-19 erg cm-2 s-1 (emission line) • R=3000 mode • 1.0 - 5.0 µm • Fixed slit or integral field unit • Also uses three 1st-order gratings • R=100 mode • 0.6 - 5.0 µm • Micro-shutter array or fixed slits • Covered by single dual-pass prism • Sensitivity (10 in 104 s): 120 nJy at 2 µm • 4 x (384 x 185) Shutters • Slits are 200 mas x 450 mas • 9 arcmin2 of MSA area • IFU is 3x3 arcsec2 • HgCdTe FPA is 2  (2040  2040) • Pixels are 0.1 arcsec

9. Lyot Mask 23mm Lyot coronagraphy 30”x30” Imaging 0.11”/pixel 2.39 arcmin2 4QPM 10.65µm 1.88 arcmin 4-quadrant Phase mask Coronagraphy 26”x26” LRS 5”x0.6” 4QPM 11.4µm 4QPM 15.5µm 1.41 arcmin The Mid Infrared Instrument (MIRI) Imager & Low Resolution Spectrometer MIRI Imager Filters • MIRI Imager uses a single 10241024 Si:As detector • Scale is 0.11 arcsec/pixel, 1.881.41 arcmin2 FOV. • Sensitivity (10 in 104 s): • 10 µm (R=5): 0.7 µJy • 21 µm (R=4.2): 8.7 µJy • LRS uses a fixed slit and a grism at R=100 MIRI Imager, LRS & Coronagraphs:

10. 10 arcseconds Channel 1 (4.9 - 7.7 mm) Channel 2 (7.4 - 11.8 mm) Channel 3 (11.4 - 18.2 mm) Spectral Resolving Power Channel 4 (17.5 - 28.8 mm) Wavelength (mm) MIRI Integral Field Unit (IFU) • The MIRI IFU uses two 10241024 Si:As detectors • One third of each channel’s waveband is dispersed onto one half of a 1k x 1k detector, and the four channels are mapped onto 2 detectors. • A full 5 to 28 mm spectrum requires 3 exposures, with the dichroic/grating wheels moved between each exposure. • 4 channels x 3 exposures = 12 (overlapping) spectral segments • Sensitivity to line emission (10 in 104 s): • 9.2 µm (R=2400): 1.0 10-17 erg cm-2 s-1 • 22.5 µm (R=1200): 5.6 10-17 erg cm-2 s-1

11. The Tunable Filter Imager • The FGS Tunable Filter imager has short and long-wave channels • Short wavelength channel: 1.0-2.1 µm, R=70–150 • Long wavelength channel: 2.1-4.8 µm, R=70–150 • Optics are reflective except for the dichroic beamsplitter, the Fabry-Perot etalon assemblies, and the order-blocking filters. • Each channel uses a 2048  2048 HgCdTe detector • FOV: 2.22.2 arcmin2 • 0.065 arcsec/pixel • Lyot coronagraphic occulters are similar to NIRCam’s---bars and spots. • Sensitivity (10, R=100, 104 s): • 1.5 m: 357 nJy (continuum), 7.1 10-18 erg cm-2 s-1 (line) • 2.0 m: 325 nJy (continuum), 4.9 10-18 erg cm-2 s-1 (line) • 3.5 m: 368 nJy (continuum), 3.2 10-18 erg cm-2 s-1 (line) • 5.0 m: 504 nJy (continuum), 3.0 10-18 erg cm-2 s-1 (line)

12. Stellar Populations Science Case Design Reference Mission: White dwarf cooling ages of globular clusters, age of Local Group populations, Abundances of intergalactic stars in Virgo. Star Formation History: Age, metallicity, stellar content of streams, structure, and outer disks of M31, M33 and other Local Group galaxies and their globular clusters. Global SF history and gradients for dwarf galaxies. Streams, satellites, metallicity, and age constraints for halos of galaxies to ~10 Mpc Very long integrations: ages of halos, ages of satellites in Virgo cluster.

13. Stellar Populations Goals (cont’d) Are the ages of the oldest stars (~M92) the same in all metal poor systems? Did character of star formation change after reionization? Resolve the stellar populations in low surface brightness galaxies and tidal tails out to ~15 Mpc. Survey low luminosity stars and mass function in the Galactic halo and bulge. Settle problem of white dwarfs as dark matter. Precise relative ages, maybe star formation history reconstruction, from white dwarf cooling sequence. AGB stellar content of galaxies to Virgo

14. Where might we be in 2013? Is science worth doing? Galaxy evolution and formation major science aims. The relative roles of gas accretion, interactions, ingestion of companions will best be sorted out for nearby galaxies. Galaxy evolution and formation in the Local Group may not be representative of either low or high density environments; we will want to conduct detailed studies of stellar populations across the Hubble sequence and across environment.

15. The HR diagram and the Age Ladder AGB 10^7 yr Red Giant Branch (RGB) ~ 5x10^8 yr 100-10^3 Lsun Horizontal Branch (HB) ~10^8 yr (He burning) 100 Lsun UVX? MS turnoff is most reliable age measure. HB can indicate Intermediate age vs. old pops. The AGB tip luminosity still not a reliable indicator of inter- mediate age stars, especially In metal rich populations Main sequence ~10^10 yr H-burning 1 Lsun

16. IR is not as good as optical for measuring age/metallicitybut useful measurements possible

17. Deep IR CMD Simulation by D. Reitzel Simulate field of globular cluster G1 as imaged in J and K bands with realistic errors. Mu_v=24 mag/sq arcsec. Age sensitivity is less than optical but there’s hope for modeling.

18. Optical vs. IR: IR superior for low luminosity stars and obscured populations (e.g. survey of the inner 100pc of the Galaxy). Absolute mag in V and K as a function of stellar mass. Infrared colors have a clear advantage for this problem. At the Galactic Center, one must reach K=27 to get to the end of the hydrogen burning stars, whereas one must reach to V=36 (!) to accomplish the same in optical colors. This problem (and others like it) will be done by JWST. (models from Baraffe et al. 2002)

19. The Fuel Consumption Theorem Renzini & Buzzoni (1986); Renzini 1998 nj is number of stars in evol. stage j B is specific evolutionary flux, 2x10^11 stars/yr L T is the total bolometric luminosity tj is the lifetime in yr, in evol. stage j. nj = B LTtj The fuel consumption equation can be used to predict the number of stars in a given evolutionary stage, per sq. arcsec. We can solve the FCT to find the maximum surface brightness at which A stellar population can be resolved. Surf (V) = distance modulus – mag (for main sequence stars) Surf (V) = distance modulus – 5 mag (HB stars).

20. Reach of large space telescopes to image the Sun (Mv=+5). JWST gets a wider range of Hubble types. (courtesy Tom Brown, STScI)

21. Applying the White Dwarf Cooling Sequence to determine Precision relative ages for the Milky Way and LMC/SMC Globular Clusters and the Galactic Bulge New cooling models by Hansen (1998) show that the oldest DA white dwarfs become bluer at the end of their cooling tracks, due to H_2 molecular opacity, and may be observed at M_V=+18 HST+ACS will likely observe 3-4 clusters (needs 2 epochs for proper motion cleaning of CMD; 10-50 orbits per epoch) JWST can do this problem if it can reach the R band, but old wd suffer the H_2 opacity in the IR. JWST can reach M_1um ~34, placing the bulge (m-M)_V=16 and intermediate age LMC/SMC clusters in reach. The technique has the potential for relative age dating to +/- 1 Gyr

22. Color-magnitude diagram of M4 HST/WFPC2 Richer et al. 2002 Full Sample Cluster Field 120 Orbits with WFPC2 -- ~ 1 Hr with JWST

23. Constraining the Age of the Globular Cluster M4 (Hansen et al. 2001) A powerful age constraint, insensitive to 0.5 mag distance/reddening error. Detail of proper-motion cleaned cooling sequence with selection function and DB cooling track (red). Note the hint of a blueward hook (DA track in blue). Fit of cooling models (including incomplete- ness, and the wd counts from M4. The best fit is for 12.5 Gyr. Data in grey area ignored in fit. Chi-square insensitive to +/-0.5 mag error in distance/reddening.

24. Best fit age and formation redshift for M4 and the disk (constrained from models of WD luminosity function) Hansen et al. 2001; LDM=Liebert Dahn Monet Hansen et al. 2004

25. New results: 126 orbits (ACS) on NGC 6397 Richer et al. 2006, Hansen et al. 2006 (in prep) Potentially can date ages to before/after reionization

26. ACS imaging of M31 halo field (vs. 5 old globular Clusters spanning -2<[Fe/H]<-0.2) Brown et al.2003

27. Brown et al. 2005 astro-ph/0512001 Kalirai et al. 2005 Rich et al. 06 Rich et al. 2006 STREAM HALO stream halo Stellar populations in halo and giant stream identical

28. RED ALL Ferguson et al. 2002 SNAP could map With actual MS Turnoff ages! Int. Age AGB Blue/Red

29. Turnoff Photometry of a large sample of M31 Globular clusters presently impossible with HST (100 orbits/cluster). JWST will do this in 5hr per cluster. Rich et al. 2004 (WFPC2 4 orbits) Jablonka 1999

30. The Andromeda dwarfs range from [Fe/H]=-2 to -1, and show internal age ranges, but RR Lyrae stars and BHB demand some old component. They look like Galactic dwarf spheroidals. Da Costa et al. 1996, 2000, 2002

31. For Local Group, possible to work in the outer M31, M33 disks; measure star formation history to the main sequence turnoff. Contrast SFH of disks, halos, dwarf galaxies. Kent 1989

32. Detailed star formation histories and Population gradients in dwarf galaxies: Did star formation change before/after reionization? Mighell&Rich 1996 Fornax Buonnano et al.

33. One would like to map age, star formation history of dwarf galaxies - was there a transition in SF before/after reionization? SF history vs radius? Fornax Dwarf Galaxy Coleman et al. 2004

34. Survey of Omega Cen - Ferraro et al. 2004 ApJ L; Bedin et al.

35. Extend studies of metallicities of halo populations Haris, Harris, Poole 2001

36. Wide field surveys of Local Group halos could reach to below the horizontal branch and allow structural and relative star formation history studies.

37. Galaxy halos can be resolved to 10 Mpc. Could make maps of interaction streamers and dwarf galaxies over wide range Hubble type and luminosity

38. Spiral Galaxy halos Mouhcine, Ferguson, Rich, Brown, Smith (2005 ApJ 633, 821) Implication: How can halos be accretion of low mass low metallicity satellites ? MW

39. Intergalactic Stars in Virgo Virgo IntraCluster Stars (VICS) Ciardullo & Williams 2006 An ideal low surface brightness stellar population Likely tidal streams, possibly new (very ancient) stellar population formed in a high density region JWST can measure the age of this population, easily reach the HB; age will need ~100 hrs (equivalent to M31 halo)

40. Antennae Hibbard + Galex Team 2005

41. Saviane et al. 2004 HST image of “tidal dwarf”

42. A SNAP could do detailed studies of unusual stellar populations, such as those found in interacting galaxies, tidal tails, etc. The CMDs at left from WFPC/2 Imagery of the tidal dwarf Galaxy candidate in NGC 4038/9 SNAP could map over whole Field of Antennae. 8 associations in the tidal dwarf galaxy candidate In the Antennae (NGC 4038/9) Saviane. Hibbard, & Rich 2004

43. M31 nucleus with resolved stars and PAH emission (Spitzer/IRAC Ch4 8um Rich et al. 2006 MIRI will produce ~0.5” diffraction limited images; Virgo Possible since AGB stars are short lived, luminous, rare.

44. M32 with resolved AGB stars ~200 resolved stars > lifetime ~ 104 yrs

45. CONCLUSIONS JWST will have ~10x HST sensitivity, but must work in IR. Resolution like HST but worse in optical. mid-IR is diffraction limited. JWST will be powerful in the study of resolved populations. However, deep photometry will be possible only in regions of very low surface brightness. Major progress likely in white dwarf cooling ages, resolved populations of halos and satellites, AGB content of major galaxies in the Local Group.