Distant galaxies: a future 25-m submm telescope

Transcription

1 Distant galaxies: a future 25-m submm telescope Andrew Blain Caltech 11 th October 2003 Cornell-Caltech Workshop

2 Contents Galaxy populations being probed Modes of investigation Continuum surveys Line surveys Motivation for aperture size Confusion in continuum surveys Advances over existing/proposed capabilities 2

3 Example target: the Antennae Excellent example of distinct opt/uv and IR luminosity Interaction long known, but great luminosity unexpected ~90% energy escapes at far-ir wavelengths Resolved images important Relevant scales ~1 at high redshift CSO/SHARC-2 Dowell et al. ISOCAM HST WFPC2 3

4 Observed far-ir/submm SEDs Non-thermal radio Thermal dust Dominates luminosity Hotter in AGN? Molecular and atomic lines Mm CO / HCN IR: C/N/O/H 2 IR: C=C PAH 4

5 Example Deep Submm Image Ivison et al. (2000) cd galaxy square Abell 1835 Hale 3-color optical 850-micron SCUBA Contrast: Image resolution Visible populations Orthogonal submm and optical views One of 7 images from Smail et al. SCUBA lens survey (97-02) About 25 SCUBA cluster images 5

6 Example IDed submm galaxy Ivison et al (2000, 2001) Unusually bright example May not see most important region in the optical J2 is a Lyman-break galaxy (Adelberger & Steidel 2000) J1n is an Extremely Red Object (ERO; Ivison 2001) Remains red in deeper Keck-NIRC data Both J1n & J2 at z = 2.55 radio and mm from J1n 6

7 Population of submm galaxies Most data at 850 µm New bright limit from Barnard Very few are Galactic contaminating clouds Red star Barnard et al 850-µm upper limit (in prep). * * Blain et al (2002) updated First limit at 2.8 mm (BIMA) Bright 95/175 µm counts (ISO) Also data at 1.2mm (MAMBO); 1.1mm (BOLOCAM) ; 450µm 7

8 Unique access to highest z Redshift the steep submm SED Counteracts inverse square law dimming Detect high-z galaxies as easily as those at z=0 Low-z galaxies do not dominate submm images Unique high-z access in mm and submm 8

9 850-µm redshift distribution Chapman et al. (2003; Nature; augmented) Histogram: sample expanded from Nature list Expected submm & radio redshift distributions from Scott Chapman s model Consistent with studeis of star-formation history that show far-ir domiates optical at z~2, but result now MUCH more robust z~1.5 gap is the spectroscopic desert Bias against highest z is likely modest, but still uncertain 9

10 Signs of large-scale structure HDF field HDF & GOODS frames Circles: all radio-submm galaxies Small empty: no try for z Large empty: tried but no z Black solid: z found Colored: cluster within 1200 km/s Note more clusters than expected unless powerful galaxy-galaxy correlation r 0 ~ 11 Mpc Blain, Chapman et al. (in prep) 10

11 Submm galaxies in CO(3-2),(4-3) Chapman et al. Frayer et al. N4 Smail et al. N2.4 Neri et al. ApJ (2003); IRAM interferometer; source of detections given on individual frames 6 more now have CO measurements 11

12 Confusion noise Model based on SCUBA/ISO populations 1 per beam RMS noise Extragalactic sources dominate When < 500µm ~25- m aperture very important <0.1mJy sure to find submm counterparts to high-z optical galaxies 12

13 Time to reach confusion limit Galactic & extragalactic confusion limits Sensitivity α D -1 Practical limit ~10-100hr in any field At shortest wavelengths need large aperture to allow deep surveys Note speed at 850µm 9 resolution 13

14 Speed vs other instruments ALMA, SCUBA-2, LMT, Herschel, SOFIA Assume 32x32 camera Fastest ~mjy 850µm FOV 30 arcmin 2 1mJy 5σ in 30s 1/2-sky survey in 2.5 yr 10 8 galaxies Confusion limited 0.05mJy 1σ in 600s 2 deg 2 in 40hr 10 6 galaxies CMB foreground map 14

15 Photometric redshifts Combine different bands to estimate T & z together Strongest lever from µm Based on knowledge of galaxies/site, can probably design 2 optimal bands Once z known, get accurate luminosity 15

16 Line emission Optical spectroscopy probably never able to keep up with discoveries Especially the hard cases, deeply enshrouded in dust at z>5 Far-IR emission lines and CO rotational emission reveal astrophysics R~1000 a good start for redshifts Heterodyne R>10 6 can see details: watch ALMA! Short of 500µm ALMA has coherence issues? ALMA can make spatially & spectrally resolved images of the most interesting galaxies found in <1hr Little information on far-ir lines available so far SOFIA will test this science CII and OI pair give redshifts for z~4.5 16

17 Line detection rate Left: 870µm window; 5x10-21 Wm -2 (3hr) Right: 350µm window; 4-10x10-20 Wm -2 (3hr) Long wavelength blind searches ~ 1 / hour Slower than ALMA working at longer wavelengths Concern with unresolved spectroscopy redshift only ALMA image essential for location 17

18 Summary ~25-m telescope needed to overcome source confusion at a great site Need not be circular Much faster to discover new targets than ALMA/Herschel Much better resolution than a space-based submm telescope Wide-area deep continuum surveys a unique feature All of accessible sky in ~10yr Find rarest, most exciting forming clusters Wide field camera allows parallel survey start with SHARC2 Line observations: get redshifts, but unresolved Longer wavelength redshift spectrograph should be very powerful ZSPEC hitchhiker Leverage best science out of ~$600m ALMA 18