Coma Intracluster Plumes

Ten to forty percent of the total light in a galaxy cluster comes from stars that have been stripped from their parent galaxies and are now bound to the cluster potential.  In order to answer interesting questions of galaxy evolution within clusters and intracluster light formation, we require high resolution, multi-band photometry.  To achieve this, we propose to analyze archival ACS data of two giant intracluster light plumes in the Coma and Centaurus clusters along with ancillary GALEX, Spitzer, Arecibo, and IRAS archival data.  With this rich dataset we will study the colors of these ICL features as an indication of the ongoing formation proceses of the ICL.  We will also generate an optical to infrared SED to determine ICL age, metallicity, and mass by fitting the SED to stellar population templates.  Such information will inform cosmological simulations.  This project represents the forefront in ICL research while using all archival data.

 Virgo Intracluster Light

We study 3.6 and 4.5 μm Spitzer IRAC imaging over 0.77 square degrees at the Virgo cluster core for the purpose of understanding the formation mecha- nisms of the low surface brightness intracluster light features. Instrumental and astrophysical backgrounds that are hundreds of times higher than the signal were carefully characterized and removed. We examine both intracluster light plumes as well as the outer halo of the giant elliptical M87. For two intracluster light plumes, we use optical colors to constrain their ages to be greater than 3 & 5 Gyr, respectively. Upper limits on the IRAC fluxes constrain the upper limits to the masses, and optical detections constrain the lower limits to the masses. In this first measurement of mass of intracluster light plumes we find masses in the range of 5.5×108 −4.5×109 and 2.1×108 −1.5×109 M⊙ for the two plumes for which we have coverage. Given their expected short lifetimes, and a constant production rate for these types of streams, integrated over Virgo’s lifetime, they can account for the total ICL content of the cluster implying that we do not need to invoke ICL formation mechanisms other than gravitational mechanisms leading to bright plumes. We also examined the outer halo of the giant elliptical M87. The color profile from the inner to outer halo of M87 (160 Kpc) is con- sistent with either a flat or optically blue gradient, where a blue gradient could be due to younger or lower metallicity stars at larger radii. The similarity of the age predicted by both the infrared and optical colors (> few Gyr) indicates that the optical measurements are not strongly affected by dust extinction.

o   Krick, J.E. et al., 2011, ApJ submitted

 

 Spitzer IRAC Dark Field

The dark current for the near-IR camera on Spitzer is calibrated by observing a  ~20 arcminute diameter field near the north ecliptic pole roughly every three weeks throughout the mission duration of Spitzer.  The field is unique for its extreme depth, low background, high quality imaging, time-series information, and accompanying photometry including data taken with Palomar, MMT, Akari, KPNO, Chandra, and HST.  This serendipitous survey contains the deepest mid-IR data taken to date.  The science goals of acquiring this dataset are the study of high redshift galaxy clusters (z=1), characterizing high redshift galaxies (z > 6), compton thick AGN, the lowest mass brown dwarfs, population III Sne, the reddest objects in the universe from their 24 micron - r colors, and other interesting phenomenon, the study of which is uniquely suited to this field.  As this is the only mid-IR dataset with time domain information on a 5+ year timeline, we are exploring the variable objects in the field, from stars to AGN

o   Krick, J.E. et al., 2009 ApJS, 185, 85

o   Krick, J.E. et al., 2009 ApJ, 700, 123

o   Krick, J.E. et al., 2009 AAS, 21344826

o   Frost, M. et al., 2009 ApJ, 698L, 68

o   Krick, J.E. et al., 2008 ApJ, 686, 918

o   Krick, J.E. et al., 2008 ASPC 399 365

o   Krick, J.E. et al., 2007 AAS, 2101204

o   Surace, J.A. et al., 2007 AAS 2100205

Intracluster Light

When counting up the mass in clusters of galaxies, the obvious sources of baryons are the galaxies themselves and the hot gas between the galaxies.  There are also stars between the galaxies that are not bound to any particular galaxy but to the potential well of the cluster.  These intracluster stars are a product of galaxy mergers and interactions between the galaxies and the cluster potential. The main goal in studying the intracluster light (ICL) is to use its total flux, color, and substructure to constrain models of galaxy evolution and galaxy interactions in clusters.  Another product of the study of the ICL is a more complete census of the baryons in the universe. This project aims to study clusters with different masses and morphologies at a range of redshifts, to obtain the fraction of total light as well as the color of  the ICL.  This will allow us to test models of galaxy evolution and inform cosmological simulations.   

o   J.E. Krick, and R.A. Bernstein, 2007, AJ, 134, 466

o   J.E. Krick, R.A. Bernstein, & K.A. Pimbblet 2006, AJ, 131, 168