Mapping the COSMOS at 1 mm using Bolocam

James AguirreUniversity of Colorado, Boulder

H. Aussel (2), A. Blain (3), J. Bock (4), C. Borys (3), S. Eales (5), J. Glenn (1), A. Goldin (4), S. Golwala (3), D. Haig (5), A. Lange (3), G. Laurent (1), P. Maloney (1), P. Mauskopf (5), H. Nguyen (4), P. Rossinot (3), J.

Sayers (3), D. Sanders (2), N. Scoville (3), K. Sheth (3), P. Stover (1), J. Williams (2), M. Yun (6)

(1) CASA, University of Colorado, Boulder; (2) Institute for Astronomy, University of Hawaii; (3) California Institute of Technology; (4) Jet Propulsion Laboratory; (5) University of Wales, Cardiff; (6) University of

Massachusetts, Amherst

Submillimeter Galaxies• Large far-IR to mm-wave (125 mm < l

< 2 mm) luminosities and faint or nonexistent optical counterparts

• Emission due to thermal radiation from star formation (~1000 M_solar/year) and / or AGN (~1/3 of sources, ~20% of luminosity)

• Lie predominantly at z > 1 • Possible progenitors of modern-day

elliptical galaxies and spiral galaxy bulges.

• Most submillimeter galaxies discovered with SCUBA and MAMBO

• In typical blank fields, ~10’s of detections

• Spectroscopic redshifts are trickling in• Typical flux at 1.1 mm is ~few mJy

Bolocam 1.1 mm

• Observes at Caltech Submillimeter Observatory (10.4 m dish)

• Hexagonal array of 144 bolometers

• Array has a 7.5’ field-of-view with individual beam sizes of 30” FWHM

• Public: http://www.cso.caltech.edu/bolocam

Challenges of Millimeter Measurements

• Large beams (Bolocam has ~30” FWHM): no extragalactic sources are resolved

• Best astrometry has RMS error ~few arcseconds• Sensitivity from the ground limited by temporal

water vapor fluctuations • Eddington bias (due to instrument and

atmosphere noise and confusion) is non-negligible

• False detection rate is non-negligible

Current Status of Bolocam-COSMOS

• Data was taken at 1.1 mm in February and May 2004

• RA/Dec raster scans make nearly perfect square 38’ x 38’

• Approximately 1000 arcmin2 was covered with nearly uniform integration time (2% RMS) per 10” x 10” pixel; nearly all observed area is usable

• The data presented here is 8 nights between 2004 February 20 and 2004 February 27

Current Map

• First pass calibrated map produced from February data

• RMS is ~3.3 mJy, in comparison with Lockman Hole East with RMS of 1.4 mJy

• No excess due to sources is evident

Models and Projections for Larger Area Surveys

Probing Cosmological Volumes

Optimizing Survey Area and Depth

• False detection rate grows as area

• 3-sigma threshold produces far too many spurious sources for a large area survey

• Figure of merit for optimizing is number true – number false

Multiwavelength Observations

• Radio: provide precise positions for ~65% of sources, elucidate radio/sub-mm correlation

• Millimeter CO: gas mass, redshifts• Near-to-mid-IR: stellar populations; Spitzer (?)

AGN discrimination• Optical: morphology, stellar population• UV: star formation rates• X-ray: AGN• Keck LRIS spectroscopy for redshifts

Conclusions

• New survey (time granted for February through April) can probe cosmologically interesting volume to sufficient depth in a single season

• Survey will be optimized to minimize contamination from false detections, allowing efficient follow-up

• Existing data has demonstrated scan strategy, sensitivity predictions, and has improved our pointing analysis and systematics tests

• Existing data and future data will be searched for very bright (>10 mJy) non-thermal sources

• Bolocam will constrain the bright end of the submillimeter galaxy luminosity function