Intracluster Red Giant Stars in the Virgo Cluster

Abstract

We have used the WFPC2 camera of the Hubble Space Telescope to obtain deep F814W images of a blank field in the Virgo Cluster located 41 arcmin northwest of M87. We perform star counts in that field, and in another Virgo field observed by Ferguson, Tanvir & von Hippel (1998), and show that, when compared to the Hubble Deep Field North and South, the Virgo Cluster contains an excess of objects with magnitudes I > 27. We attribute this excess to a population of intracluster red-giant branch (IC-RGB) stars. By modeling the luminosity function of these stars, we show that the tip of the Virgo RGB is at I = 27.31 +0.27/-0.17 and that the cluster contains a small, but significant, excess of stars that are up to ~1 mag brighter than this tip. If this luminous component is due entirely to stars on the asymptotic giant branch (AGB), it implies an age for the population of > 2 Gyr; if foreground RGB stars contribute to the luminous tail, then the derived age for the stars is older still. The luminosity function also suggests that most of the intracluster stars are moderately metal-rich (-0.8 < [Fe/H] <-0.2), a result consistent with that expected from stars that have been tidally stripped from intermediate luminosity galaxies. Additionally, a comparison with the planetary nebulae in our field also supports this view, although the existence of a more metal-poor population (from stripped dwarfs) cannot be ruled out. Our derived average surface brightness, mu_I = 27.9 +0.3/-0.5 mag/arcsec^2 for Virgo's diffuse component suggests that intracluster stars contribute 10% to 20% of the cluster's total I-band luminosity.Comment: 21 pages, 8 figures included, accepted for publication in the Astrophysical Journa

Deep CCD Surface Photometry of Galaxy Clusters. II. Searching for Intracluster Starlight in Non‐cD clusters

“…Once simply another curiosity of Zwicky (1951), individual intracluster stars have been clearly detected in several nearby galaxy clusters (Arnaboldi et al 1996;Ferguson et al1998;Durrell et al 2002;Feldmeier et al 2004), and through deep imaging this diffuse light has been detected in many more distant clusters (Uson et al 1991;Vílchez-Gómez et al 1994;Bernstein et al 1995;Gonzalez et al 2000). From the results to date, it is clear that intracluster light (ICL) is a common component of galaxy clusters and contains between 10% and 50% of the total stellar luminosity of the cluster, albeit with large uncertainties due to the intrinsic low surface brightness of the component (less than 1% of the night-sky background).…”

“…Ultracompact dwarf galaxies (Drinkwater et al 2003), the formation of S0 galaxies (Quilis et al 2000 and references therein), and tidal debris in nearby clusters (Trentham & Mobasher 1998;Gregg & West 1998;Calcáneo-Roldán et al 2000) may all be closely related to the ICL phenomenon. Since searches for individual intracluster stars in nearby galaxy clusters can be influenced by metallicity effects (Durrell et al 2002;Feldmeier et al 2004), knowing the dominant progenitor population is critical to avoid underestimating the true fraction of intracluster light. However, observational constraints on the ICL are still extremely poor, owing largely to the scarcity of quantitative measurements of the ICL in clusters, especially over a range of cluster properties.…”

Efficiency of Stripping Mechanisms

“…Although CCD images are now able to reveal ICL in most clusters, a large sensitivity for this diffuse component is gained from Planetary Nebulae tracers, without the problems of flat fielding, etc, since they are detected by emission lines (Feldmeier et al 1998, Arnaboldi et al 2002 The intra-cluster stars have moderate metallicity (Durrell et al 2002), which supports the scenario of their stripping from intermediate mass galaxies. These tidal debris and plumes are expected from simulations of galaxy clusters (cf Dubinski 1998) It has been known for a long time that there exists in clusters a larger fraction of blue galaxies at increasing redshift (Butcher & Oemler 1978, 1984.…”

The Survival of Planetary Nebulae in the Intracluster Medium

“…From our lifetime estimate we find that α 1.0 is between 2.4 and 4.8 ×10 −9 PN L −1 ⊙ depending on whether we assume that the IC PN fades in 5 000 or 10 000 yr. For the longer fading time the stars in the Virgo core IC contribute about 7% to the total starlight, as derived by Aguerri et al (2005) using α 1.0 from Durrell et al (2002). We are inclined to believe that a better estimate of the duration of the IC PN life is 5 000 yr, thus the fraction of the IC starlight in the Virgo core would rise to ∼15% of the total starlight.…”

“…In the last few years, quantitative estimates of the diffuse IC stellar population have been inferred from the study of Red Giants and Asymptotic Giant Branch (AGB) stars in the Virgo cluster (Ferguson, Tanvir, & von Hippel 1998;Durrell et al 2002), Planetary Nebulae (PNe) in the Virgo and Fornax clusters and the Leo I group (Mendez, et al 1997;Feldmeier, Ciardullo, Jacoby, & Durrell 2003;Ciardullo, Jacoby, Feldmeier, & Bartlett 1998;Arnaboldi et al 1996Arnaboldi et al , 2002Arnaboldi et al , 2003Castro-Rodríguez et al 2003), Supernovae (SNe) type Ia in the Virgo cluster (Smith 1981;Gal-Yam, Maoz, & Sharon 2002;Gal-Yam, Maoz, Guhathakurta, & Filippenko 2003), and Novae in the Fornax cluster (Neill et al 2005).…”