Galaxy+Clusters

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Galaxy Clusters: The Local Effects on Star Synthesis by: Zackery Schroeder


 * immediate redshifts have yet to be observed closely
 * in his experiment, he observed three redshift galaxy clusters of differing masses and states of equilibrium with the Spitzer Space Telescope and the Hubble Space Telescope
 * these three galaxies were picked based on their differences in mass, degree of relaxation, and virial radius
 * after studying the "24-micron flux," he was able to derive the SFR for each galaxy and the entire cluster
 * 24-micron data was taken with the Spitzer Space Telescope's "Multiband Imaging Photometer for Spitzer" (MIPS) for wide-field, broadband imaging, and this flux was used for
 * deriving the SFR
 * Schroeder went to the Spitzer Space Telescope Center on the Caltech campus in Passadena, CA
 * There he had access to...
 * MIPS and Hubble Space Telescope data
 * photometric and spectroscopic membership flags
 * model SED curves
 * HST types
 * 24-micron flux
 * velocity dispersions of the individual galaxies
 * EdisCS database
 * routine on how to derive SFR from 24-micron flux
 * 3 Clusters
 * SIDE NOTE: Galaxies within the cluster are moving, so the faster they go, the more massive the cluster.
 * CL 1037.9-1243
 * least massive of the three clusters
 * has a virial radius of .57 megaparsecs (Mpc)
 * lowest velocity dispersion: the faster the galaxies move, the more massive the cluster must be in order to retain them
 * there are 206 star-forming galaxies in the field, but only 45 of them are members of the cluster
 * this is determined by their spectroscopic and photometric membershipflags
 * this makes this cluster the second least populated
 * cigar-like shape, so it is least relaxed (its galaxies have not yet entered equilibrium and the velocity dispersions are not completely accurate in determining the mass of the cluster)
 * CL 1227.9-1138
 * medium mass, velocity dispersion, and virial radius of 1.00 Mpc
 * 145 galaxies present, but only 26 of those are members of this cluster
 * it is less populated than the CL 1037.9-1243
 * it is however, more spread out, so it is larger
 * middle state of relaxation
 * CL 1232.5-1250
 * most massive of all three clusters
 * highest velocity dispersion and virial radius of 1.99 Mpc
 * most populated of three clusters
 * 162 HST galaxies in the image, with 54 of those as part of the cluster
 * most relaxed cluster, with most uniform shape
 * SFR from Flux and Ltir (total infrared luminosity)
 * light emitted by newly formed stars
 * most star formation happens in areas of high conentrations of dust and cool gas--light is absorbed by the dust and is re-emitted at infrared wavelengths
 * averaged 5 different SFRs to determine the average SFR for the clusters
 * Equation that he used: SFR(Msolyr^-1)=4.5x10^-44Ltir(ergs s^-1)^3
 * Normalizing SFR
 * normalize in order to account for the clusters having different masses
 * to do this, SFR must be calculated within half the virial radius because the number of star-forming galaxies is related to the distance from the cluster center
 * this was then used to calculate the sum SFR per cluster mass per 1e14 solar masses (these formulas discussed can be further explained on the Formulas page)
 * Data and Results
 * Shroeder included tables and pictures to display his findings
 * he compared his SFR calculations to those of the different galaxy types that represented his three galaxies
 * these results, however, were inconclusive
 * Elliptical galaxies seem to have a rather low average SFR,