This project is funded by Scribner-Mellon and Schupf funding for summer research by rising sophomores at Skidmore College, allowing students several years of collaborative research.
Here in the Milky Way Galaxy, space is seeded with chemical elements heavier than hydrogen and helium- elements like carbon, that are necessary for organic life. But most galaxies are smaller than ours, and have very few heavy elements. We propose to examine the properties of a sample of galaxies to test whether their heavy elements are missing because they escaped into intergalactic space, or because they failed to form in the first place.
Our primary goal is to test the extent to which the lack of heavy elements in dwarf galaxies is caused by low star effeciency versus the loss of heavy elements into intergalactic space. (Another possibility is the infall fresh gas.) To do this we need to observationally estimate the total mass and metal abundance for each galaxy (to establish each galaxy's type relative to mass and chemical abundance), as well as the amount of stars and loose gas (to test for the importance of star formation efficiency). The table below summarizes the types of data we will use to estimate each of these properties.
Total mass 21-centimeter width Chemical abundance Spectroscopy Mass in stars Brightness at near-infrared or red wavelengths Amount of HI gas 21-centimeter flux
Very roughly, the star formation efficiency would be the comparison between the amount of loose HI gas that is in a galaxy and the number of stars that have formed from this gas. A low star formation efficiency would indicate that the heavy elements never formed in the first place, whereas a high star formation efficiency would suggest that the heavy elements were forced into intergalactic space due to high energy events such as supernovae. Our current working definition of star formation efficiency is (Abs. I, r, or J band luminosity)/log HI mass.
We are using ALFALFA data for 21-cm rotation curves and fluxes, and combing the literature for chemical abundance and stellar mass. Ideally we would have liked to use our data on the MKW 11 cluster that we recieved for the ALFALFA Groups Project. However, we could not find any published metallicity information about any of those galaxies. Instead we decided to create and use a similar sized region in the center of the much better-studied Virgo Cluster. In our Virgo region there are 111 sources in the ALFALFA catalog. We are currently searching the literature for metallicities and IR or red magnitudes for as many galaxies in this region as possible. One source is Vílchez et al. 2003, which includes metallicities for nine of them (all dwarfs):
Positions for the 102 detections in the MKW 11 four-grid region. The bubble size is proportional to HI mass.Our team at Skidmore is examining the group MKW 11 to determine its properties for comparison the other galaxy groups.
The ALFALFA data for MWK 11 includes four grids. We have used FLAGBB and GRIDVIEW to examine and partially reduce these data. But conveniently, this part of sky is included in the third data release (Kent et al. 2008).
The ALFALFA source catalog for this region (four grids) includes 102 detections. We are in the process of comparing them to other surveys.
