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Scientific MotivationMore detailed Scientific motivations of both BCII and the LMT can be found at LMT/GTM Scientific Overview Sub-mm galaxy surveysBolocam II on the LMT will perform deep millimeter continuum surveys of massive starburst galaxies. Dust within such galaxies would absorb most of the UV photons and re-emit at lower frequencies, resulting in a peak luminosity in the far-infrared. At sub-mm and millimeter wavelengths, the SED of the DUST can be approximated by a power law ƒ = a νλ where λ is in the range 3-4. Such a steep slope can result in a constant (or even increasing) observed flux with increasing redshift (i.e. a negative k-correction). This results in these galaxies being equally detectable from z~1 to z~10, should they exist at these redshifts. A large sample over this wide range of redshifts could help us understand how these dusty star-forming galaxies formed and evolved with time. 
Sensitivity of BOLOCAM to dusty starburst galaxies on a 12-m and the LMT as a function of redshift. On the LMT, Bolocam II will have mapping speeds that are three orders of magnitude faster, with three times better resolution, than SCUBA on the JCMT (Figure 1). Bolocam II will produce mm-wave source maps tens of square degrees of size in just a few hundred hours of observation (see section 4). These maps can be used to investigate how these mm-wave sources (dusty galaxies) trace large-scale structure formation in the universe by comparing the observed clustering to model simulations and their coincidence with known optical and x-ray clusters.
Figure 1: Survey speed of BOLOCAM II on the LMT as compared to the original BOLOCAM on the CSO and the SCUBA instrument on the JCMT. Graph courtesy of Min Yun, University of Massachusetts. Observations of the Sunyaev-Zel’dovich effectBolocam II will also be useful in observing small fluctuations in the Cosmic Microwave Background due to interactions with galaxy clusters through the Sunyaev-Zel’dovich (SZ) Effect. The SZ effect has two distinct components. The first is known as the thermal SZ effect and is the distortion of the CMB spectrum through inverse Compton scattering by gravitationally bound hot gas (~108K) in a galaxy cluster. On average, the energies of the scattered photons are increased, distorting the CMB spectrum in a characteristic fashion (figure 2), as originally outlined by Sunyaev and Zel’dovich1. One of the primary uses of Bolocam II on the LMT will be to map these small fluctuations over large areas of the sky. The second component, known as the kinetic SZ effect, is a result of the bulk motion of the galaxy cluster with respect to the CMB rest frame. This net motion of the scattering electrons will result in a Doppler shift being imposed on the scattered CMB photons, which, due to the Hubble flow, is usually a decrement in power. It is, however, possible for the kinetic effect to result in an increment of power if the cluster should be moving towards us. At most frequencies, the kinetic SZ effect on the CMB intensity is very small in comparison to the thermal effect, making it nearly indistinguishable from its counterpart. Fortunately, the kinetic SZ effect reaches a maximum near the null frequency of the thermal effect about 217 GHz (see figure below), thus making a separation of the two effects plausible using high sensitivity, multi-frequency measurements. While Bolocam’s passband is probably too wide to be able to distinguish the two effects, another LMT instrument being developed at CDL, the SPEctral Energy Distribution (SPEED) camera, will be better suited to attempt a separation of the two signals. For more information on the SPEED instrument, refer to SPEED. 
Figure 2: (a)Characteristic change in CMB spectrum. (b) Deviations from blackbody CMB intensity. Measurements of the SZ effect can lay constraints on several key cosmological parameters. Most directly, the Hubble constant and baryon mass fraction can be determined by combining thermal SZ data with x-ray observations of the hot gas within the cluster. The kinetic SZ effect can estimate the peculiar radial velocities of the individual clusters, allowing the velocity field and mass distribution of the universe to be mapped on very large scales. Both forms of the SZ effect work to distort the spectrum of the CMB photons, giving the effect the unique property of being virtually independent of redshift, thus allowing for the detection of clusters at very high z. With the ability to detect these clusters over a wide range of redshifts, number counts from blank sky surveys can be used to examine cluster evolution and formation as well as place restrictions on Ωmatter. 1. Sunyaev, R. A. and Zel’dovich, Y. B. 1970, Ap. & Sp. Sci., 7, 3. Other observational opportunitiesThe true strength of Bolocam II on the LMT comes in its ability to make measurements over a very wide range in scale, making it an ideal instrument for mapping purposes. Bolocam is sensitive to all types of sources exhibiting dust emission and will be used for far more applications than those mentioned above. Several of those projects will include imaging nearby galaxies, surveying the dust emission from our galactic center, mapping the dust emission from star forming regions, studying dusty disks around young stellar objects (YSOs), estimating the dust mass produced by comets, and other galactic sources with dust emission such as evolved stars and planetary nebulae. Back to BOLOCAM II main page. For further information on BOLOCAM II, contact Grant Wilson or Jay Austermann. |