M. K. Kellogg's Journal, 1872

Abstract

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Tracing the Metal-Poor M31 Stellar Halo With Blue Horizontal Branch Stars

“…The result is that the metal-poor fraction has a minimum at 10-20 kpc, and a steep increase toward the galaxy center. These ratios are similar to those found by Gilbert et al (2014), which were ∼0.2-0.7 between 9 and 30 kpc, respectively. We are not able to match the spectroscopic ratios exactly because the difference in power-law index between the two components does not result in the fraction changing that steeply.…”

“…Much work has gone into measuring the stellar density profile of M31. M31 makes an excellent case study because it is very nearby, and its halo has been resolved to 150 kpc (e.g., Ibata et al 2001;Kalirai et al 2006a;Gilbert et al 2007;McConnachie et al 2009;Gilbert et al 2009;Courteau et al 2011;Gilbert et al 2012;Williams et al 2012;Dorman et al 2013;Ibata et al 2014;Gilbert et al 2014). Recently, the Panchromatic Hubble Andromeda Treasury (PHAT Dalcanton et al 2012) has started a new era in the study of M31 by producing homogeneous HST imaging of about 1/3 of the star forming disk.…”

“…Furthermore, recently there have been several relevant and comprehensive studies of the M31 halo structure by Dorman et al (2013), Ibata et al (2014), and Gilbert et al (2014). Dorman et al (2013) decomposed the structure of M31 by simultaneously fitting surface brightness, stellar luminosity function, and stellar velocity data.…”

“…Confirming previous measurements of a metallicity gradient in the M31 halo (Kalirai et al 2006b;Koch et al 2008;Tanaka et al 2010), Ibata et al (2014) found that the different metallicity components of the M31 halo have significantly different profiles outside of 27 kpc, so that measuring the metal-poor component, as we trace with the BHB, does not necessarily tell the whole story. Gilbert et al (2014) quantified the metallicity gradient of the halo with spectroscopically-confirmed members and included radii as small as 9 kpc.…”