22 December 2011

A Next-Generation Survey to Count Low Mass Dark Matter Halos in Nearby Galaxy Groups

M.P. Haynes, R. Giovanelli, D.B. Campbell, G. Cortés-Medellín, R.A. Koopmann and the ALFALFA Extragalactic HI Survey Team

Questions: How do baryons cycle in and out of galaxies?
What is dark matter?
Approach: Counting the Leo T analogs in nearby groups by detecting their atomic gas cores via the HI 21cm line
Context: Outside the virial radii of large galaxies, low mass halos may either retain their baryons post-reionization or re-accrete gas at recent epochs. Most of the baryons would reside in a warm ionized envelope surrounding a cooler core of atomic gas, and few, if any, stars. Leo T serves as the prototype of such objects. The robust counting of low mass dwarfs in groups could potentially constrain dark matter decay models (decay injects kinetic energy that can unbind dwarfs).
Needs: Arecibo's collecting area and survey capability, enhanced by a cooled 40-beam phased array feed ("AO40"; in development), will enable a survey of Leo T analogs out to 7-10 Mpc. No other survey previous, on-going or planned for this decade will achieve comparable capability to detect such a population of low mass dwarfs beyond the Local Group.

Overview:     One of the Astro2010 science frontier questions related to "Understanding the Cosmic Order" asks how baryons cycle in and out of galaxies. Dark matter halos of mass below log Mtot/Msun < 10 (e.g. Hoeft+ 2006) are baryon-poor. Studying the process(es) which impose this depletion requires advances in (g)astrophysics (reionization, feedback, etc) and better observational constraints on the baryon content of low mass dwarfs. Exploiting a cooled 40-beam focal plane phased array feed (PAF) now in development, an Arecibo survey of several hundred square degrees around 2-3 nearby groups of galaxies would detect and catalog their population of HI-bearing dwarfs with log MHI > 5, comparable to the HI mass of the Local Group dwarf Leo T. The combination of sensitivity, modest resolution and survey speed made possible by a 40-beam PAF on the Arecibo antenna ("AO40") will enable such a survey in <2000 hours of telescope time starting in 2014. The observing program and software pipeline will rely on the extension of the infrastructure already developed for the ALFALFA survey (to be completed in 2012) using the 7-beam feed horn array (ALFA). A PAF on a single dish can be cooled, and its data reduction requires greatly reduced computational power than does an antenna array. In addition, a drift scan survey conducted with a PAF on a single dish employs a simple, extremely efficient technique that, as demonstrated clearly by ALFALFA, delivers high quality data with >97% "open shutter" time and can be easily and intuitively understood by students at all levels, making it an excellent platform for the active engagement of a broad collaborative team.

What We Know Today about Gas-Bearing Low Mass Dark Matter Halos:
Design of a Survey for Low Mass Dark Matter Halos in Nearby Groups:
The ALFALFA survey as a paradigm for a future AO40 survey:

Last modified: Thu Dec 22 10:12:04 EST 2011 by martha