What is Metallicity? Metallicity refers to the proportion of matter made of chemical elements heavier than Hydrogen & Helium. A celestial object’s metallicity can be calculated with the equation:
Metallicity and Age Each generation of stars is enriched with metals that were produced in the preceding generations. Older objects: Lower metal content Younger objects: Higher metal content Mu Arae, a metal-rich star
Gathering Data from Spectra IRAF (image reduction and analysis facility) was a program used to measure Emission Lines such as H-alpha, H-beta, OII, OIII, and NII. How do astronomers get Spectra? The lens from a telescope collects light from a distant object & brings it to a focal point. Diffraction occurs when light passes through thin slits in a metal plate set over the lens, separating the light into various wavelengths. Example Spectra: Wavelength vs. Flux
What do we know from emission lines? Before making calculations... What do we know from emission lines? For Each Galaxy: Observed Center Wavelength and Flux of Emission Lines of: OIII, OII, H-alpha, H-beta, NII Wavelength Rest Wavelength Apparent Magnitude
H_0 = Hubble Constant = 70 km/s/Mpc Finding Redshift Redshift (z) informs us of galaxies that are moving away from us. (Since the objects move away, the light waves are stretched out) (Observed Wavelength - Rest Wavelength) Rest Wavelength z = Finding Distance v c v H_0 z = d = c = speed of light = (3 x 10^8 m/s) H_0 = Hubble Constant = 70 km/s/Mpc
m_Abs = M_apparent - 5log(distance) + 5 Calculating Absolute Magnitude Absolute Magnitude is how intrinsically bright a galaxy is. *The greater the magnitude, the fainter it is. m_Abs = M_apparent - 5log(distance) + 5 Star Formation Rate Luminosity = (Halpha Flux) x 4 π d 2 SFR = Luminosity x (7.9 x 10 ) -42
Calculating Metallicity Metallicity = (12 + Log O/H) – (0.32 x O3N2) If O3N2 is less than 1.9 = (12 + Log O/H) + (0.57 * log N2) If O3N2 is less than 1.9 *Note: O/H, N2, O3N2 refer to the proportion of the flux of one emission line versus another.
WE think this may be because Younger galaxies dont have as many metals because they haven’t had enough time to go through combining process to have more elements, and star formation rate relies on how much halpha is in the galaxy, and since the galaxy is young, it has not yet converted h alpha (hydrogen) to helium
Absolute Magnitude increases (galaxies are getting fainter) as stellar mass is decreasing because the smaller the galaxy, the fainter the star is.
Absolute Magnitude increases (galaxies are getting fainter) as stellar mass is decreasing because the smaller the galaxy, the fainter the star is.
Importance Metallicity of objects allow us to determine: age, composition, relative motion, density, mass, and temperature of a single star or a galaxy. Through emission line measurements of the plasma in galaxies, we calculated information that contributed to general knowledge for the astronomical community. After graphing our information, we discovered many relations and trends within our data.
Further Research We could create a program that, when given an object’s metallicity, can predict different properties. Find relation between a population I star’s metallicity and its potential for hosting planets.
Special Thanks to: Raja GuhaThakurta Meredith Muller John Wright Jessica Werk COSMOS