Submm observations of Spitzer selected galaxies Ongoing research at the CSO using SHARC-II

1. Submm observations of Spitzer selected galaxies Ongoing research at the CSO using SHARC-II Colin Borys (Caltech) Andrew Blain (Caltech) Darren Dowell (JPL) Duncan Farrah (IPAC) Carol Lonsdale (UCSD) Tom Soifer (Caltech) Vicki Barnard (JAC) and many many others…. IRAC 8 micron image of GOODSN Submillimeter Astronomy: Cambridge MA, June 13, 2005

2. SHARC-II and the obligatory picture SHARC-II array SCUBA • The second Sub-mm High Angular Resolution Camera (SHARC-II) was commissioned in November 2002 at the CSO. • 12x32 fully sampled array (CCD style) • Operates in `Total Power’ mode (no chopping). • Optimized for use at short wavelengths (350/450 micron), takes advantage of the DSOS system. • Suitable for observing all of the usual submm luminous objects. See posters by Darren Dowell and Sean Andrews.

3. Sub-mm/Spitzer synergy SHARC/SCUBA/Bolocam/MAMBO • Sensitive to the thermal peak of the dust emission, and hence T,L • “High” resolution. Ground MIPS: shortward of peak at high-z • Surrogate to sub-mm cross-IDs • Selecting z=1.5 dropouts • FIR SEDs for application to phot-z’s Spitzer Space Telescope IRAC: Rest-frame NIR data at high-z • Evolved stellar mass estimation • AGN vs Starburst discrimination • Photometric redshift estimation IRS: New diagnostics • PAH emission • Silicate absorption

4. Which are SMGs? • MIPS and IRAC are able to detect almost all submm galaxies known (e.g. Egami et al. 2004, Ivison et al. 2004) • But is there a way to preselect which Spitzer sources are IR luminous at high redshift? • For instance, the 10’x16’ image to the left has 1200 sources in it detected at 24 micron, while the deep SCUBA map from Borys et al. 2004 has at best 40 850 micron detections. MIPS 24 micron image of GOODSN.

5. MIPS waters the redshift desert? • LBGs and Sub-mm galaxies tell us about starformation at z~3, and observations at z<1 are relatively straightforward. But determining how galaxies evolved between these two epochs is challenging in part due to the so-called “redshift desert” • MIPS offers a way to select large statistical samples of starforming galaxies at intermediate redshifts via a Silicate absorption feature at 9.7 micron.

6. Silicate Dropout (SiDs) selection

7. Cool technique, but who cares? Massive galaxies • Objects are selected to have high lumis, and at the brightest end are the same as SCUBA galaxies. • Such objects are expected to trace out the more massive dark matter halos at any given epoch. (SHADES justification) Large samples • The SWIRE fields + FLS + GTO Boötes contains ~70 square degrees of MIPS+IRAC imaging from which to draw samples. • Each has a plethora of multi-wavelength data. • We expect 1000 candidates at redshift 1.5, compared with 300 from SHADES between 1<z<4.

8. Boötes-59 Hyperlirg • GTO MIPS observations of the NDWFS region provided the initial catalog for which to obtain submm followup. • First target observed with SHARC-II yielded a detection in just 10 minutes. S(350) = 0.25 Jy. • Observation inspired further efforts with SCUBA, IRS, Keck, and Palomar, allowing us to trace out the SED from X-ray to radio. Borys et al. 2005

9. Boötes-59 Hyperlirg Boötes-59 has one of the best sampled SEDs of any z>1 ULIRG.

10. Boötes-59 Hyperlirg Desai et al. 2005 z=1.325+/-0.002

11. Boötes-59 Hyperlirg Physical properties • A fit to the far-IR SED reveals that the object is very luminous: L=1013.5±0.1 L. Its dust is a lukewarm 42K. • 20cm emission is slightly quieter than expected from the radio/far-IR correlation, but still within the scatter. • PAH lines, small velocity dispersion (~250 km/s), lack of X-ray emission, and lack of any high excitation diagnostic lines in the optical spectra all suggest that the source is STARBURST dominated, with no hint of an AGN. • Using radio or FIR SFR estimators, we find that the source is very prolific, forming stars at a rate of >5000 M/yr. • Fitting the rest-frame UV-NIR SED, we estimate that the object is over 1011M. It also seems very young, with an age < 100Myr. (also note the lack of a significant Balmer break). Lensed??It seems unlikely…The high resolution SMA observation does constrain the position of the submm emission, which is coincident with the optically detected galaxy. See Allison’s poster!

12. SiD status • ~400 selected so far from Legacy surveys. Source density of luminous objects is low…typically 10/square degree. (SCUBA detectable ULIRGS) • Objects seem to demonstrate clustering (Farrah et al. 2005) • Followup program at CSO is ongoing, and Spitzer GO2 IRS observations of 15 candidates are approved. The class of object discussed here is only one of many, and Spitzer will continue to feed targets to submm observatories for years to come.

14. Mid-IR SEDs of ULIRGs • Given the difficulty in obtaining UV spectra for these objects, and since NIR spectrometers are too narrow for “blind” redshift determination, ground-based spectroscopic followup is challenging. • The IRS spectrometer on IRS offers the ability to measure a broad range of lines unaccessible from the ground. Armus et al. 2004 (ApJ special supplement)

15. Sub-mm photometric redshifts • Only 75% of the bright SCUBA galaxies have a radio ID for which a redshift estimate can be attempted, hence only a very small fraction of the “SCUBA counts” have a spec-z. • The radio surrogate method is time intensive, requiring deep exposures from optical imaging, optical spectroscopy, and radio imaging. • Such arguments motivate a photo-z approach, but in the sub-mm the template spectra are not well known. The above plot from Aretxaga et al. 2003 shows a sample of SEDs that fit the radio +available sub-mm data on LH850.1. The redshift estimate is derived from the mean and dispersion of all models that fit the data.

16. T-z degeneracy/L-T breaker • Phot-z’s in the sub-mm have met with considerable debate over Temperature and redshift degeneracy. • Luminosity-Temperature relation can break it (if it exists), but SCUBA can’t measure temperatures. Blain, Barnard, Chapman (2004)