1. Do Luminous Infrared Galaxies -LIRGs- follow Hubble’s Law? Harrison Rivera Colon and Yesenia M. Rivera Lopez; Antonio Lucchetti Voc. H.S., Arecibo, Puerto Rico Mentor: Dr. Tapasi Ghosh; Arecibo Observatory, Arecibo Puerto Rico Ana G. Mendez University System AGMUS Institute of MathematicsCaribbean Computing Center for Excellence LIRGs: -Discovered three decades ago. -Compared to normal galaxies, brighter in the infrared area of the electro-magnetic spectrum. -Star forming rate is 100 times more than that in a normal galaxy. Hubble’s Law: -Proposed by Edwin Hubble 1929. -He notice that the further away a galaxy was, the faster it was moving away from us. -This can be expressed as: V=H 0 D. All of the galaxies in the Universe emit some kind of light, some more or less than others. In this research, those galaxies that emit their most intense light in the infrared band were studied. These are called Luminous Infrared Galaxies (LIRGs). The goal of this research was to inquire if, like normal galaxies, LIRGs also follows Hubble’s law. In 1929, Edwin Hubble noted that the further away a galaxy was, the faster it was moving away. This can be expressed as V=H 0 D and is called Hubble's Law. The recessional velocities of the galaxies in the sample of LIRGs in this study were derived from the observations of (redshifted) neutral hydrogen (HI) spectra, and the application of the Doppler Effect. An independent indication of their distances was obtained from their apparent angular sizes, as gathered from the literature. The velocities obtained from the HI spectra were plotted against the angular sizes of these Galaxies, and an exploration was made whether or not the Hubble law is followed by the galaxies in this sample. In this graphic, we see that velocities increase when angular sizes decrease. For small angular sizes we see many deviant points that show much higher velocities. We think that those are due to intrinsically bigger galaxies (larger linear sizes) that are much further away, and hence with higher velocity. So, our conclusion is that the LIRGs do follow Hubble’s Law. LIRGs do participate in the general expansion of the universe regardless of their spectral behavior. As the universe gets old, it grows and expands its spatial dimension. Edwin Hubble made one of the biggest discoveries in modern science: the universe’s expansion. The Hubble’s Law proclaims that the farther a galaxy is, the faster it moves away from us. If that is due to the expansion of the universe as a whole, then LIRGs should not be any different just because they emit more IR radiation. Abstract A galaxy is a collection of stars, gas, and dust bound together by gravity. There are billion of galaxies in the observable universe. They can be smaller with hundred thousand stars or much larger containing thousands of billion stars. Also, they can be classified by their form in to spirals and elliptical. Our solar system is in a normal spiral galaxy named the Milky Way. The experiment is based on data that the telescope receives via its L-band wide receiver. The CIMA (Control Interface Module of Arecibo) controls the telescope. In this program, radio spectra of 21-cm neutral hydrogen transition (HI-line) were recorded for 33 LIRGs. If the galaxies were at rest relative to the Earth, the HI-line would be seen at 1420.4058 MHz. Instead, we found that the HI line was visible at much lower frequencies (ν). This is due to Doppler Effect where the radio signal emitting galaxy is moving away from the observer. Measuring the shift in the frequency of the HI-line from its rest-frequency, (ν 0 ) o f 1420.405 MHz, we derived the redshift (z) of the galaxy using the equation, z= (ν 0 -ν)/ν Next, the velocity of the galaxy (away from us) was derived using the equation, V = z C (where, C = the velocity of light = 299792.485 km/s) As an independent measure of the distance (D) to the galaxy, we obtained the angular sizes of all 33 LIRGs from an online database (NED). Angular size reflects how large an object actually appears to an observer; expressed in words as: the apparent size of an object decreases linearly as you get further away from the object. The farther is a galaxy the smaller is the angular size (for a fixed linear size). The angular size is inversely proportional to distance. Introduction HypothesisResult and Conclusion Observational and Analytical Method Background Information Acknowledgments References Thanks to this Saturday Academy, we can be involved in new science areas that sometimes we only dream about it, like Astronomy. Thanks to Dr. Tapasi Ghosh, our mentor, and to Aida Albó for taking care of us. Thanks to Dr. Arratia, for setting students’ achievement goals in science and math areas. Special thanks to Ana G. Méndez University System, AGMUS Institute of Mathematics and Caribbean Computing Center for Excellence for making this possible and developing student programs in these areas of studies. Gribbin, J. (2008). Galaxies, A Very Short Introduction. United States: Oxford University Press Inc., New York. Roberts,M. S. & Haynes.M.P.,1994 Annu. Rev. Astron. Astrophys., 32: 115 Haynes, M.P. & Giovanelli,R. Astron. J. 1984, 89, 758 http://ned.ipac.caltech.edu/ http://www.sdss.org/ http://www.gemini.edu//www.gemini.edu/