Observations of submillimeter galaxies and of the Sunyaev-Zeldovich effect toward clusters of galaxies

• This thesis describes observations of a population of high-redshift, dusty star-forming galaxies: thesubmillimeter (submm) galaxies. The submm galaxies detected so far are very massive and lumi-nous systems, with huge star-formation-rates (SFR>100Myr−1), large reservoirs of moleculargas (Mgas∼1×1010M) and large dynamical masses (Mdyn>1010M). The median redshiftof detected submm galaxies isz∼2.2, which corresponds to a look-back time of 10 Gyr.We have used the LABOCA bolometer camera mounted on the APEX telescope in Chile tosearch for gravitationally lensed submm galaxies behind massive galaxy clusters (with a total massMclust>5×1014M). The gravitational magnification induced by the galaxy clusters boosts theobserved flux densities of the background submm galaxies and allows us to probe deeper intothe faint galaxy population. The number counts of submm galaxies show that there are manymore faint galaxies than bright ones, and thus the properties of the bright submm galaxies mainlystudied so far may not be representative of the bulk of the population.In two papers we present our results of the observations toward galaxy clusters. In paperI, we discuss a merging galaxy cluster: the Bullet Cluster at redshiftz∼0.3. The huge massconcentration provides large magnification factors, and one of the background galaxies detectedwith LABOCA is gravitationally magnified∼100times. The number of galaxies detected towardthe Bullet Cluster is consistent with previously published number counts, and we probed thenumber counts to some of the lowest flux density levels so far. Paper I also includes a studyof the multi-wavelength-properties of the LABOCA galaxies, where we identified counterparts ininfrared Spitzer maps.In paper II the study of submm galaxies lensed by clusters was extended with four additionalclusters. The number of detected galaxies was more than doubled compared to paper I. A more so-phisticated method was used to determine the magnification factors for each galaxy, and to correctthe number counts for the effect of magnification differences across the map. The number countsagree with previous work but may indicate a flattening towards low flux densities. A study of thefaint, unresolved background population was also included, via the stacking technique. We usedthe positions of all sources detected in Spitzer 24μmmaps across the observed LABOCA fields.The LABOCA flux was extracted at each 24μmposition and when added together this yieldeda14.5σdetection, and a signal 5 to 10 times lower than the adopted flux limit for extraction ofsignificant sources in the maps. In combination with gravitational magnification, stacking makesit possible to probe deeper into the submm population, although only mean properties of the faintgalaxies can be derived.Having studied the observational properties of a sample of submm galaxies in paper III wefocused on one particular galaxy behind the Bullet Cluster, SMMJ0658, gravitationally magnifiedup to 100 times in total. The strong lensing caused by the total cluster potential and an ellipticalgalaxy within the cluster gives rise to three images of the same background galaxy. In ouriobservations with a radio/mm interferometer, the Australia Telescope Compact Array (ATCA),we detected two rotational transitions of the carbon monoxide (CO) molecule in SMMJ0658.CO is commonly used as a tracer of the more abundant moleculeH2, which constitutes a largefraction of the molecular gas in galaxies. Because of the large magnification factor of this galaxyit is possible to probe the physical conditions in a system with ten times less molecular gas anda lower star formation rate than the bright submm galaxy population studied so far.Finally, I have participated in the APEX-SZ project. APEX-SZ is a bolometer camera oper-ating at 2 mm wavelength, designed with the aim of detecting the Sunyaev–Zeldovich decrementin clusters of galaxies. The Sunyaev–Zeldovich effect is a secondary anisotropy to the Cosmic Mi-crowave Background (CMB) radiation. It is due to inverse Compton scattering of CMB photonsby hot electrons in the cluster gas. At 2 mm the SZ effect gives rise to a lower temperature whencompared to the 2.7 K radiation. I participated in six observing runs in Chile between 2008 and2010. The scientific studies with APEX-SZ focus on the physical state of the intra-cluster gasin galaxy clusters. In two of the papers summarized in this thesis the APEX-SZ detection wasused together with XMM-Newton X-ray observations to constrain non-parametric models for thedistribution and temperature of the hot gas. The existence of dusty galaxies within high-redshiftgalaxy clusters is a possible explanation as to why several high-redshift galaxy clusters have eludeddetection in Sunyaev–Zeldovich experiments.

Ämnesord

NATURVETENSKAP  -- Fysik -- Astronomi, astrofysik och kosmologi (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Astronomy, Astrophysics and Cosmology (hsv//eng)

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