Science with the Low Frequency Bands on Alma: Cmbr, Sze and Cosmological Applications the Cosmic Microwave Background the Sunyaev-zeldovich Eeect

The ALMA receiver suite includes provisions for covering the Ka and Q bands from 30 { 45.5 GHz. This contribution summarizes some of the scienti c drivers for this capability, in particular observations of the Cosmic Microwave Background Radiation anisotropy and scattering of the CMBR from hot gas in massive clusters of galaxies, the Sunyaev-Zeldovich e ect. In addition to its unique capabilities at millimeter and submillimeter wavelengths, ALMA will also be a superb instrument at the smallest centimeter wavelengths. ALMA will complement the VLA with its greater e ective collecting area at high frequency and a full view of the Southern Sky. We use examples from current CMB, SZE, gravitational lensing, and other extragalactic observations along with theoretical models of large scale structure evolution and galaxy formation to extrapolate the capabilities of ALMA for these programs. The Cosmic Microwave Background The Cosmic Microwave Background Radiation (CMBR) is the relic of the time when the universe was ionized and opaque to photons and thus thermalized at temperatures T 3000 K. When the Universe expanded su ciently (at a redshift of z 1100) and the hydrogen was able to recombine, these optical photons were then free to stream to us unimpeded, eventually redshifting into the microwave spectrum at an observed temperature of 2:73 K. Imprinted upon the isotropic 3K background and the large-scale dipole (due to our local peculiar motion with respect to the CMB frame) is a much smaller pattern of ripples | the CMBR anisotropy. These uctuations were produced by matter clustering at the time of recombination, and thus are one of our most important cosmological fossils. There are a number of upcoming and proposed CMBR anisotropy experiments, which cover the parameter space of frequency and angular scale. However, the focus is largely on the angular scales above 0.25 degrees, where the primary cosmological signatures appear in the uctuation power spectrum. As shown in Figure 1, there are few that are able to target the ne scale anisotropies beyond ` > 1000. ALMA will do this. The current state-of-the-art ground-based experiments are using fast-switching single-beam telescopes to scan over several degrees on the sky at good sites. The Mobile Anisotropy Telescope (MAT), with its 1-meter primary mirror, was built by Mark Devlin (UPenn) and Lyman Page (Princeton) and run at Cerro-Toco on the Atacama site in Chile. MAT has measured the so-called Doppler Peak at the 1 degree angular scale in the CMBR anisotropy power spectrum (Miller et al. 1999) as shown in Figure 2. Similar experiments are also being run at the South Pole. In addition to single dish scanning experiments such as MAT, small special-purpose interferometers such as the Cosmic Background Imager (CBI: Readhead et al.) and the Degree Angular Scale Interferometer (DASI: Carlstrom et al.) are soon to be operating at the Atacama and South Pole sites respectively. DASI will probe the degree scales similarly to MAT, and the CBI will image the CMBR on scales down to 4 arcminutes. A signi cant problem a ecting intermediate and small-scale CMBR anisotropy observations is the identi cation and removal of galactic and extragalactic foreground emission (see Figure 3). For example, the OVRO 5-meter telescope has measured the CMBR anisotropy on angular scales of 100 (Leitch et al. 1999) but confusing foreground emission attributed to an anomalous component of the galactic ISM was found and subtracted (Leitch et al. 1996). ALMA, along with the northern CARMA (the combined OVRO and BIMA) are two instruments with the sensitivity, frequency coverage, and angular resolution required to perform accurate foreground assessment. Of course, the nature of these anomalous foregrounds is of astrophysical interest in their own right! The location and amplitude of the rst \Doppler" peaks are controlled by the overall matter and energy density, baryon density and curvature of the Universe. On the other hand, the structure in the CMBR anisotropy power spectrum for multipoles beyond ` > 1000 and angular scales less than 200 are sensitive to the \microphysics" that controls the formation of large-scale structures in the Universe we see today. Roughly, 1 arc-minute corresponds to 1 comoving megaparsec. By measuring the anisotropies on these small scales, we can get a snapshot of galaxy cluster-sized density perturbations when their amplitudes were less than 10 5 of the mean! With its precision 12-meter diameter primary and its fast and accurate switching capabilities, ALMA will be a powerful instrument with which to image the CMBR anisotropy on small angular scales. In particular, when \On-The-Fly" (OTF) total power observations are combined with compact array interferometric data, ALMA will be able to produce maps of the CMBR from sub-arcmintue scales up to one degree, at unprecedented sensitivity levels. As seen in Figure 4, mapping 4 square degrees will not only capture the primary CMB uctuations, but pick out against this background the signatures of massive clusters when they do form. The Sunyaev-Zeldovich E ect The space density of the most massive clusters of galaxies is extremely sensitive to cosmological parameters such as the matter density 0, cosmological constant 0, baryon density B, and \shape parameter" or the Large-Scale Structure related 8, the current rms density uctuation amplitude in spheres of radius 8 h 1Mpc (eg. Bond & Myers 1992b, Bond & Myers 1996, Mohr et al. 1999, Holder & Carlstrom 1999). For example, \wedges" of the universe for four di erent cosmologies look very di erent, as shown in Figure 5. Because clusters can be detected at any redshift using the SZE, without the cosmological dimming that attenuates the X-ray and optical emission, the SZE \sky" looks very di erent for di ering cosmologies, as depicted in Figure 6. The SZE in nearby clusters (Myers et al. 1997) and intermediate redshift clusters (Carlstrom et al. 1996) has been clearly measured by single dishes and imaged by interferometers respectively. In the near future, the CBI will provide SZE images of nearby clusters with 40 resolution at 32 GHz. ALMA, and CARMA in the north, will provide high-sensitivity images of the SZE in the most distant clusters as well as survey regions of the sky for the \ambient" SZE to test cosmological models. Figure 7 grapically demonstrates the utility of intermerometer measurements of the SZE for intermediate redshift clusters observed by Carlstrom et al. using the existing California millimeter arrays out tted with 30 GHz receivers. ALMA will be able to extend this to higher redshifts, while the addition of the total-power scans to the interferometer data will improve the image delity, especially for probing the low level SZE pro le in the outskirts of the clusters. While the primary anisotropies allow us to peer directly at the linear matter density uctuations at z 1100, the Sunyaev Zeldovich e ect shows us these same uctuations in the nonlinear stage as they evolve and collapse to form massive clusters of galaxies. Other Applications ALMA as a centimeter-wave telescope will be an important addition to the world radio astrophysical arsenal, especially considering that the SKA and ATCA will not operate with signi cant e ciency at these short wavelengths. There are a number of scienti c programs that su er from the lack of a sensitive high-frequency array in the Southern hemisphere. ALMA with 64 12-meter antennas will have an e ective collecting area greater than the VLA at 30 GHz and 43 GHz above. For example, at 43 GHz, the VLA has an e ective area of 4640 m2 (for 27 25-m at a = 0:35), while ALMA has 5720 m2 (assuming 64 12-m at a = 0:79). Cosmological applications such as the survey for and monitoring of gravitational lenses (eg. Myers 1999) will greatly bene t from ALMA. Studies of the central engines of radio-loud AGN require high-frequency observations to probe deep within the jet. In particular, ALMA will be an important addition to global (and space) VLBI at 7mm. Finally, although the redshifted FIR thermal dust emission from forming galaxies can be detected in the sub-mm and mm (eg. Bond & Myers 1992a), reshifted molecular line emission will be observable at centimeter wavelengths, as well as nonthermal continuum emission from H II regions and the cosmic ray electrons. SummaryAnisotropy in the Cosmic Microwave Background on scales below 200 probes the lineardensity eld and gravitational potential on cluster and supercluster scales at the timeof last scattering (z 1100).ALMA can e ciently make images of CMB anisotropy temperature and polarizationuctuations at 10mm, 7mm and 3mm.On angular scales less than 40 ALMA will be able to separate out anisoropies due tothe primary CMBR uctuations and those due to the Sunyaev-Zeldovich e ect.The total power stability and fast switching capability are critical for the meshing ofthe ALMA interferometric and single-dish data for imaging of extended astronomicaltargets such as the CMBR, SZE as well as galactic molecular cloud studies.A signi cant problem facing large-scale CMBR and SZE surveys is the identi cationand removal of galactic and extragalactic foreground emission. Observations at thewavelength of interest (15mm 3mm) but at higher angular resolution are required.The VLA and GBT will perform this service in the North, but ALMA will be criticalfor all-sky surveys such as those done by MAP and Planck.Probing the very high-redshift Universe beyond a redshift of 6 out to recombinationwill be the \ nal frontier". The capability for observing highly redshifted molecularlines will be critical for shedding light on these \Dark Ages" of cosmology.There are a number of other important contributions to extragalactic and galacticastronomy that ALMA at 10mm and 7mm will be critical to, such as VLBI (in con-junction with the VLBA and the Southern Hemisphere VLBI telescopes), surveys forand monitoring of gravitational lenses, disentangling star formation and AGN contri-butions to the radio spectrum of distant galaxies, and the mapping of the small-scaledi use anomalous galactic emission seen in CMBR observations.Conclusion: The 10mm and 7mm receiver suite proposed for ALMA will add signi -cant new astronomical capabilities to the array, and moreover these capabilites will beunique in the Southern Hemisphere. References[1] \Primaeval Galaxies in the Sub-mm and mm"; Bond, J.R. & Myers, S.T. 1992a, inThe Evolution of Galaxies and Their Environment, proceedings of the Third TetonSummer School July 5-1