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….

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….

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

Submillimeter Astronomy: Cambridge MA, June 13, 2005Submillimeter Astronomy: Cambridge MA, June 13, 2005

IRAC 8 micron image of GOODSN

SHARC-II and the obligatory pictureSHARC-II and the obligatory picture

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.

SHARC-II array SCUBA

IRAC: Rest-frame NIR data at high-z

MIPS: shortward of peak at high-z

Evolved stellar mass estimation AGN vs Starburst discrimination Photometric redshift estimation

Surrogate to sub-mm cross-IDs Selecting z=1.5 dropouts FIR SEDs for application to phot-z’s

IRS: New diagnostics PAH emission Silicate absorption

Sub-mm/Spitzer synergySub-mm/Spitzer synergy

SHARC/SCUBA/Bolocam/MAMBO Sensitive to the thermal peak of the dust emission, and hence T,L “High” resolution.

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Which are SMGs?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.

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.

MIPS waters the redshift desert?MIPS waters the redshift desert?

Silicate Dropout (SiDs) selectionSilicate Dropout (SiDs) selection

Cool technique, but who cares?Cool technique, but who cares?Massive galaxiesMassive 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 samplesLarge 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.

Boötes-59 HyperlirgBoötes-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

Boötes-59 HyperlirgBoötes-59 Hyperlirg

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

Boötes-59 HyperlirgBoötes-59 Hyperlirg

z=1.325+/-0.002z=1.325+/-0.002

Desai et al. 2005

Boötes-59 HyperlirgBoötes-59 HyperlirgPhysical propertiesPhysical 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 opticallydetected galaxy. See Allison’s poster!

Lensed?? It seems unlikely…The high resolution SMA observation does constrain the position of the submm emission, which is coincident with the opticallydetected galaxy. See Allison’s poster!

~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.

SiD statusSiD status

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.

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.

Mid-IR SEDs of ULIRGsMid-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)

Sub-mm photometric redshifts Sub-mm photometric redshifts

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.

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.

T-z degeneracy/L-T breaker 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.

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Blain, Barnard, Chapman (2004)