SFR+Project+Glossary

Back to Project Page Here is a list of terms and concepts that are commonly used in our project that will be used as reference


 * Butcher-Oemler effect¹:** describes the tendency of galaxy colors to be bluer at hight redshifts.


 * ESO Distance Cluster Survey (EDisCS)¹:** a European Southern Observatory Large Program aimed at studying galaxy and galaxy evolution; survery is composed of 30 galaxy clusters; it combinces different data from the Very Large Telescope (VLT) :D, New Technology Telescope (NTT), and Focal Reducer Spectrograph (FORS2).


 * Flux:** the energy given off by an object in space over a certain period of time; used to determine age and size [|Definition Link]


 * Gas Stripping¹:** the interaction between galaxies and the intergalactic medium.


 * Harassment¹:** a type of tidal force, describes the cumulative gravitational effect from many cluster galaxies on a galaxy. This is important in the lower end of the galaxy mass spectrum.


 * Infrared:** heat radiaion; form of light wavelength
 * Near-infrared: infrared wavelengths close to visible wavelengths; often behave like visible wavelengths; can be detected using some visble light detectors (Hubble Telescope)
 * Infrared wavelengths (in micrometers)
 * .65 to 1.0: can be detected by all major optical telescopes
 * 1.25 to 3.45: can be detected by most major optical telescopes and most infrared telescopes
 * 3.45 to 10.0: can be detected by most major infrared telescopes and some optical telescopes
 * 10.0 to 20.0: can be detected by some major infrared telescopes and some optical telescopes
 * 20.0 to 450: can be detected by submillimeter telescope

Here is the formula for converting to luminosity at the rest-frame wavelength. I haven't figured out how to just get the formula up! [|sjsrc.doc]
 * Luminosity:** heat energy; measure of the amount of energy per unit time that an object raduates at the source; must be given at rest-frame wavelength and not observed wavelength.


 * Merging galaxies:** galaxies that look like they are close together and exchange gas.

This definition comes from [|Wikipedia].
 * Morphology:** shape of a galaxy
 * **Spiral:** has a define nucleus of old stars; flat with a central bulge; with characteristic spiral arms of dust, clouds, and young stars
 * Different Types of Spiral Galaxies
 * Sa: comprised of older Population II stars or redder stars with low metal content
 * SBa: larger galaxies
 * Sc: contains young, blue Population I stars
 * SBc: smaller, young blue, Population I stars
 * **Elliptical:** "football" shape; lack spiral arms; are large in volume and mass compared to spiral; vary from nearly spherical to flattened ellipsoids [[image:m87trillion.jpg width="280" height="274" align="center" link="http://images.google.com/imgres?imgurl=http://antwrp.gsfc.nasa.gov/apod/image/0406/m87_cfht.jpg&imgrefurl=http://antwrp.gsfc.nasa.gov/apod/ap040616.html&h=480&w=640&sz=75&hl=en&start=12&tbnid=vt5-KBryu1VgUM:&tbnh=103&tbnw=137&prev=/images%3Fq%3Delliptical%2Bgalaxies%26gbv%3D2%26svnum%3D10%26hl%3Den%26safe%3Dactive"]]
 * **Lenticular galaxy:** in-between elliptical and spiral; at a transitional point between being elliptical and spiral; ill-defined spiral arms with elliptical halo of stars [[image:lenticular.jpg width="272" height="246" align="center"]]
 * **Irregular:** galaxies that have irregular patter or doesn't belong to any of the above definitions; an example would be merging galaxies or a galaxy torn apart by larger galaxies

This table of conversions came from [|wikipedia].
 * Parsec:** a unit of length in astronomy.
 * 1 parsec** =||||~ [|SI units] ||
 * 30.857×1015 [|m] || 30.857×1012 [|km] ||
 * ~ Astronomical units ||
 * 206.26×103 [|AU] || 3.2616 [|ly] ||
 * ~ [|US customary] / [|Imperial units] ||
 * 101.24×1015 [|ft] || 19.174×1012 [|mi] ||


 * Redshift:** the farther away an object is from the earth, it is toward the red part of the light spectrum, because the energy of the wavelength loses energy, but not speed; the object appears to be redder; we use this to determine the distance of the object (in this case stars or galaxies)
 * Low Redshift: have a redshift less than or equal to .5414; the time from emission to when it reaches Earth is present to 3.46 billion years ago
 * Intermediate Redshift: have a redshift greater than .5414 and less than .6355; the time from emission to when it reaches Earth is 3.46 billion years to 7.84 billion years ago
 * High Redshift: have a redshift greater than .6355; the time from emission to when it reaches Earth is 7.84 billion years ago
 * Here is a [|link] to a web tool to convert time to redshift and redsift to time and distance using several model


 * Spectral Energy Distributions (SEDs):** the amount of energy emitted by an object at every wavelength
 * To find a further explanation of SED go to this [|Link]
 * One way to determine SED for a galaxy is to plot the energy emitted by stars
 * this only shows the light from stars
 * Another way to determine SED is by the energy not only emitted by light but also by dust
 * Dust absorbes light energy and re-emits the energy in longer wavelengths
 * The wavelengths are typically in the infrared radiation
 * Can be determined using Spitzer
 * Spitzer can only look at one wavelength
 * Scientists have a good idea what the rest of dust SED looks like
 * Can determine the rest of the curve based on the flux of one or more wavelengths
 * Actual SED= light SED + dust SED


 * Spitzer Space Telescope¹:** an infrared telescope in orbit around the sun.


 * Strangulation¹:** the removal of the galactic envelope of hot gas that is responsible for cooling and feuling star formation.


 * Velocity dispersion**²**:** the faster galaxies move, the more massive the cluster must be in order to retain them, so velocity dispersion is proportional to the cube root of the mass of the cluster of the cluster, as well as directly proportional to the virial radius.


 * Virial radius**²**:** radius at which the mean dnesity of the cluster is 200 times the critical density of the universe; the galaxies will be able to resist universla expansion and separation from the cluster.

² "Galaxy Clusters: The Local Effects on Star Synthesis" by Zackery Schroeder
 * ¹** "Star Formation Rate in Three High-Redshift Galaxy Clusters: A Contribution to the Study of Galactic Evolution" by Vinay Patel and Matt Pellegrino