NOAO >   Observing Info >   Approved Programs >   2007B-0194

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Proposal Information for 2007B-0194


PI: Kimberly A. Herrmann, Penn State University, herrmann@astro.psu.edu
Address: Dept. of Astronomy and Astrophysics, 525 Davey Lab, University Park, PA 16802, USA

CoI: Robin Ciardullo, Penn State University

Title: The Planetary Nebula Systems of M74 and IC 342

Abstract: Our understanding of galaxy formation is severely limited by our lack of knowledge about the mass profiles of galaxies. Rotation curves reveal the presence of dark matter halos around spiral galaxies, but the mass profiles of these halos cannot be decoupled from the visible disk mass using rotation curves alone. Most analyses therefore rely on the ``maximal disk'' hypothesis wherein the disk mass-to-light ratio (M/L) is assumed to be \bf constant with radius. Absorption-line spectroscopy has shown that the constant M/L hypothesis is reasonable in a galaxy's \em inner regions. However, only recently have rotation curves \em farther out been decomposed into baryonic and dark matter components. Planetary nebula (PN) velocity measurements over the central ~6 disk scale lengths in M33 and M83 reveal flattened dispersion, indicating that the disks' M/L_Ks \bf increase by a factor of ~10 radially outward. PN velocity measurements over ~4 disk scale lengths in M31 are also consistent with a flattened dispersion (Merrett \etal 2006). We propose to continue studying the disk mass distribution by measuring the vertical motions of PNe in nearby, face-on spirals. In the past year, we used WIYN+Hydra to measure velocities of ~54 PNe in M74 and ~87 PNe in IC 342 with (Delta) v < 10 km s^-1. For a detailed study, we need a sample larger than 54 PNe. We now propose to use Hydra to obtain some velocities more precisely and target additional PNe so we may have a large enough sample to trace the systems' disk surface mass density over ~5 disk scale lengths, and thereby better constrain models of galactic dark halos. We will see if the M/L versus distance in scale lengths continues to follow the same curve for M74 and IC 342 as for both M33 and M83. (Might this be a universal property?) We also plan to test color-M/L relations that have recently been used to decompose rotation curves.


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