Intracluster Planetary Nebulae Research Articles

Intracluster Planetary Nebulae in Clusters and Groups

We present the results from multiple surveys for intracluster planetary nebulae (IPNe) in nearby galaxy clusters and groups. We find that in the case of clusters, our observations imply: 1) the amount of intracluster starlight is significant, up to 20% of the total starlight, 2) in Virgo, is elongated along our line of sight, and 3) is clustered on the sky, implying ongoing tidal stripping. In contrast, searches for IPNe in groups have found little or no intra-group population, implying there may be something in the cluster environment that significantly enhances intracluster star production. from high-resolution N-body simulations, we find that the IPNe should create observable features in position-velocity space, and that these features may eventually allow us to place limits on the dynamics of galaxy clusters.

Intracluster Stellar Population

I shall review the latest results for the presence of diffuse light in nearby clusters, and the evidence of ongoing star formation in an intracluster Virgo field. I shall discuss how intracluster planetary nebulae (ICPN) can be used as excellent tracers of the diffuse stellar population in nearby clusters. Their number density distribution, density profile and radial velocity distribution provide observational constraints to models for cluster formation and evolution. The preliminary comparison of the available ICPN samples with high resolution N-body models of a Virgo-like cluster in a Lambda CDM cosmology supports “harassment” as the most likely mechanism for the origin of diffuse stellar light in clusters.

The Systematics of Intracluster Starlight

Surveys for intracluster planetary nebulae and red giants have been performed in a variety of cluster environments, from the well-mixed regions of the Virgo and Fornax Clusters, to the low-density areas of the M81 Group. When coupled with the results of Abell Cluster surface photometry and intracluster supernova detections, these surveys provide clues to the systematics of the intracluster light phenomenon. We analyze the results of the intracluster surveys performed to date and show how the fraction of intracluster stars depends on parameters such as cluster richness and rate of galaxy interaction. We also compare our results to numerical predictions and discuss avenues for future research.

Intracluster Stellar Population Properties fromN‐Body Cosmological Simulations. I. Constraints atz= 0

We use a high-resolution collisionless simulation of a Virgo-like cluster in a ΛCDM cosmology to determine the velocity and clustering properties of the diffuse stellar component in the intracluster region at the present epoch. The simulated cluster builds up hierarchically and tidal interactions between member galaxies and the cluster potential produce a diffuse stellar component free-flying in the intracluster medium. Here we adopt an empirical scheme to identify tracers of the stellar component in the simulation and hence study its properties. We find that at z = 0 the intracluster stellar light is mostly unrelaxed in velocity space and clustered in structures whose typical clustering radii are about 50 kpc at R = 400-500 kpc from the cluster center, and we predict the radial velocity distribution expected in spectroscopic follow-up surveys. Finally, we compare the spatial clustering in the simulation with the properties of the Virgo intracluster stellar population, as traced by ongoing intracluster planetary nebula surveys in Virgo. The preliminary results indicate a substantial agreement with the observed clustering properties of the diffuse stellar population in Virgo.

Narrow band survey for intragroup light in the Leo HI cloud

We have observed emission line objects located in a 0.26 deg2 field in the M 96 (Leo) group, coincident with the intergalactic HI cloud. The emission line objects were selected using the same procedure as used for the search for intracluster planetary nebulae in the Virgo cluster. 29 emission line objects were identified, with [OIII] filter magnitudes brighter than . Their m5007 luminosity function has a bright cut-off 1.2 mag fainter than for the luminosity function of the planetary nebulae (PN) associated with the elliptical galaxies in the M 96 group. Therefore the vast majority of these emission line objects are compatible with not being intragroup planetary nebulae at the Leo group distance of 10 Mpc. Spectroscopic follow-up of two emission line objects in this Leo field showed that indeed these do not have the [OIII] Å doublet expected for a real PN. The brighter source is identified as an AGN at redshift , because of a second emission in the near infrared, identified as FeII ( Å). From these data we derive three main results: (i) from the absence of PN we can determine a more stringent upper limit to the surface brightness in any old stellar population associated with the Leo HI cloud at the surveyed position, . (ii) This translates to an upper limit of for the fraction of luminosity in a diffuse intragroup component in the densest area of the Leo group, relative to the light in galaxies. (iii) Using this Leo field as a blank field, we derive an average fraction of 13.6% background emission line objects that enter in surveys of Virgo intracluster PN. This is in agreement with an earlier estimate (15%) obtained from the Ly break galaxy population at . The small fraction confirms the validity of the selection criteria for intracluster PN candidates in Virgo.

Intracluster Planetary Nebulae in the Virgo Cluster. II. Imaging Catalog

Intracluster stars—stars outside of individual galaxies—are a sensitive measure of the poorly understood processes of galactic mergers, cluster accretion, and tidal stripping that occur in galaxy clusters. In particular, intracluster planetary nebulae are a useful probe of intracluster light as a whole. We present a catalog of 318 intracluster planetary nebula candidates in the nearby Virgo Cluster of galaxies, taken with the Kitt Peak National Observatory 4 m telescope. We detail the automated detection routines developed to search for these candidates and discuss the routines' strengths and weaknesses. We discuss the importance of contamination in the catalog, and the likely causes. We present magnitudes and positions of these candidates, suitable for spectroscopic follow-up observations. Analyses of these candidates are presented in other papers of this series.

Narrowband Imaging in [O [CSC]iii[/CSC]] and Hα to Search for Intracluster Planetary Nebulae in the Virgo Cluster

We have identified intracluster planetary nebulae (PNs) in a Virgo Cluster core field by imaging with the Subaru Suprime-Cam through two narrowband filters centered at the redshifted wavelengths of the [O III] λ5007 and the Hα 6563 A lines; broadband images in V and R were acquired to check for emission in the adjacent continuum. Emission-line objects in Virgo are then selected from the two-color diagram [O III]-Hα versus [O III]-(V+R), which is calibrated using PNs in M84 (Jacoby et al.). Using both [O III] and Hα allows us to distinguish bona fide planetary nebulae from high-redshift emission-line galaxies at the bright end of the [O III] luminosity function. Spectroscopic observations of a subsample of these objects were made at the Telescopio Nazionale Galileo and at the Very Large Telescope in a region around M84 and in an intracluster field, respectively. The observations confirm the efficiency of the combined [O III]+Hα imaging to identify true PNs. We also obtained the first spectrum of an intracluster PN that shows the [O III] doublet with a signal-to-noise ratio greater than 10 and its Hα emission. From the results based on the spectroscopic follow-up, we derive a lower limit to the fraction of the Virgo Cluster light contributed by the intracluster stars at the surveyed position in the cluster core: it amounts to 10%.

Intracluster Planetary Nebulae

We review the progress of research on intracluster planetary nebulae (IPN). In the past five years, hundreds of IPN candidates have been detected in the Virgo and Fornax galaxy clusters and searches are also underway in poorer galaxy groups. From the observations to date, and applying the known properties of extragalactic planetary nebulae, the intracluster light in Virgo and Fornax: 1) is significant, at least 20% of the total cluster stellar luminosity, 2) is elongated in Virgo along our line of sight, and 3) may derive from lower-luminosity galaxies, consistent with some models of intracluster star production. A fraction of IPN candidates are not true IPN, but emission-line sources of very large observed equivalent width (≥ 200 Å). The most likely source for these contaminating objects are Lyman-α galaxies at z ≈ 3.1. Follow-up spectroscopy of the IPN candidates will be crucial to discriminate against high red-shift galaxies and to derive the velocity field of the intracluster stellar population.

Candidates for Intracluster Planetary Nebulae in the Virgo Cluster Based on the Suprime-Cam Narrow-Band Imaging in [O III] and $\mathrm{H}\alpha$

Abstract We have identified 38 candidates of intracluster planetary nebulae (ICPNe) in a $34^\prime\times27^\prime$ field in the core of the Virgo cluster based on Suprime-Cam imaging through two narrow-band filters centered at redshifted wavelengths of the [O III] $\lambda=5007 \,$$\,{Å}$ and the $\mathrm{H}\alpha \lambda = 6563 \,$$\,{Å}$ lines. Broad-band images in the $V$ and $R$ bands are used to check for any emissions in the adjacent continuum. We describe the method briefly and present a list of the intracluster planetary nebula candidates, together with their finding charts. The ICPN candidates show a highly inhomogeneous distribution, which may suggest an association with the M 86–M 84 subcluster. The fraction of diffuse intracluster light with respect to the total light in galaxies is estimated to be about 10%, leading to an estimate of about 20% for the baryon fraction. A spectroscopic follow up and a wider survey are critical to reveal the nature of the intracluster stellar population.

A Measurement of the Contamination in [Oiii] λ5007 Surveys of Intracluster Stars and the Surface Density ofz = 3.13 Lyα Galaxies

We present two pieces of evidence supporting the hypothesis that the bright [O III] λ5007 sources found in Virgo's intracluster space are intracluster planetary nebulae rather than [O II] λ3727 galaxies at z ~ 0.35 or Lyα sources at z ~ 3.13. First, we confirm the nature of five overluminous [O III] sources that are postulated to lie in front of M87: by examining the composite spectrum of these objects, we show that the weaker [O III] line at λ4959 is definitely present at a strength ~ that of [O III] λ5007. The ratio demonstrates that, at most, only one of the five objects is a background galaxy. We then estimate the surface density of background emission-line objects by conducting a wide-field (0.13 deg2) search at λ5019 for faint emission-line sources in a blank field located well away from any galaxy or cluster. We show that the density of blank-field emission-line sources is significantly lower than the density of sources detected between the galaxies of Virgo but in good agreement with the density of Lyα galaxies found by Hu, Cowie, & McMahon. The implication is that background galaxies account for only ~20% of the planetary nebula candidates in Virgo's intracluster fields.

Intracluster Planetary Nebulae in Virgo: Photometric Selection, Spectroscopic Validation, and Cluster Depth

We have imaged an empty area of 34 × 34 arcmin2 15 north of the Virgo Cluster core to survey for intracluster planetary nebula (PN) candidates. We have implemented and tested a fully automatic procedure for the selection of emission-line objects in wide-field images, based on the on-off technique from Ciardullo and Jacoby. Freeman et al. have spectroscopically confirmed a sample of intracluster planetary nebulae in one Virgo field. We use the photometric and morphological properties of this sample to test our selection procedure. In our newly surveyed Virgo field, 75 objects were identified as best candidates for intracluster PNe. The luminosity function of the spectroscopically confirmed PNe shows a brighter cutoff than the planetary nebula luminosity function for the inner regions of M87. Such a brighter cutoff is also observed in the newly surveyed field and indicates a smaller distance modulus, implying that the front end of the Virgo Cluster is closer to us by a significant amount: 14% closer (2.1 Mpc) than M87 for the spectroscopic field, using the PN luminosity function distance of 14.9 Mpc to M87, and 18% closer (2.8 Mpc) than M87 for the newly surveyed field. Independent distance indicators (Tully-Fisher relation for Virgo spirals and surface brightness fluctuations for Virgo ellipticals) agree with these findings. From these two Virgo Cluster fields there is no evidence that the surface luminosity density for the diffuse stellar component in the cluster decreases with radius. The luminosity surface density of the diffuse stellar population is comparable to that of the galaxies.

Discovery of Nine Lyα Emitters at Redshiftz ∼ 3.1 Using Narrowband Imaging and VLT Spectroscopy

Narrowband imaging surveys aimed at detecting the faint emission from the 5007 A [O III] line of intracluster planetary nebulae in Virgo also probe high-redshift z ~ 3.1 Lyα emitters. Here we report on the spectroscopic identification of nine Lyα emitters at z = 3.13 with fluxes between 2 × 10-17 and 2 × 10-16 ergs cm-2 s-1 obtained with the FORS spectrograph at Unit 1 of the ESO Very Large Telescope (VLT UT1). The spectra of these high-redshift objects show a narrow, isolated Lyα emission with very faint (frequently undetected) continuum, indicating a large equivalent width. No other features are visible in our spectra. Our Lyα emitters are quite similar to those found by Hu, Cowie, and colleagues in 1998. For a flat universe with H0 = 70 km s-1 Mpc-1 and q0 = 0.5 (ΩΛ = 0), the Lyα luminosity of the brightest source is 1.7 × 109 L☉, and the comoving space density of the Lyα emitters in the searched volume is 5 × 10-3 Mpc-3. Using simple population synthesis models, on the assumption that these sources are regions of star formation, we conclude that the nebulae are nearly optically thick and must have a very low dust content in order to explain the high observed Lyα equivalent widths. For the cosmological and star formation parameters we adopted, the total stellar mass produced would seem to correspond to the formation of rather small galaxies, some of which are perhaps destined to merge. However, one of our sources might become a serious candidate for a protogiant spheroidal galaxy if we assumed continuous star formation, a low mass cutoff of 0.1 M☉ in the initial mass function (IMF), and a flat accelerating universe with Ω0 = 0.2 and ΩΛ = 0.8. The implied star formation density in our sampled comoving volume is probably somewhat smaller than, but of the same order of magnitude as, the star formation density at z ~ 3 derived by other authors from Lyman break galaxy surveys. This result agrees with the expectation that the Lyα emitters are a low-metallicity (or low-dust) tail in a distribution of star-forming regions at high redshifts. Finally, the Lyα emitters may contribute as many H-ionizing photons as QSOs at z ~ 3. They are therefore potentially significant for the ionization budget of the early universe.

Intracluster Planetary Nebulae in the Virgo Cluster. I. Initial Results

We report the initial results of a survey for intracluster planetary nebulae in the Virgo Cluster. In two 16' × 16' fields, we identify 69 and 16 intracluster planetary nebula candidates, respectively. In a third 16' × 16' field near the central elliptical galaxy M87, we detect 75 planetary nebula candidates, of which a substantial fraction are intracluster in nature. By examining the number of the planetaries detected in each field and the shape of the planetary nebula luminosity function, we show that (1) the intracluster starlight of Virgo is distributed nonuniformly and varies between subclumps A and B, (2) the Virgo Cluster core extends ~3 Mpc in front of M87, and thus is elongated along the line of sight, and (3) a minimum of 22% of Virgo's stellar luminosity resides between the galaxies in our fields, and the true number may be considerably larger. We also use our planetary nebula data to argue that the intracluster stars in Virgo are likely derived from a population that is of moderate age and metallicity.

The Planetary Nebula Luminosity Function of M87 and the Intracluster Stars of Virgo

We present the results of a wide-field [O III] $\lambda 5007$ survey for planetary nebulae (PN) in M87 and its surrounding halo. We show that the planetary nebula luminosity function (PNLF) of M87's halo is unlike any PNLF observed to date, with a shape that differs from that of the empirical law at the 99.9% confidence level. In addition, we find that the PNLF of M87's outer halo differs from that of the galaxy's inner regions at a high degree of certainty ($\sim 92%$). We show that both these effects are most likely due to the existence of intracluster PN, many of which are foreground to M87. These intracluster objects explain the ``overluminous'' [O III] $\lambda 5007$ sources previously identified by Jacoby, Ciardullo, & Ford (1990), and present us with a new tool with which to probe the morphological and dynamical properties of the cluster. By modifying the maximum likelihood procedures of Ciardullo et al (1989a) and using an assumed M31 distance of 770 Kpc (Freedman & Madore 1990), we derive a distance modulus to M87 of $30.79 \pm 0.16$ ($14.4 \pm 1.1$ Mpc).

More Evidence for a Population of Intracluster Planetary Nebulae in the Virgo Cluster

We surveyed a 50 arcmin2 region in the Virgo cluster core to search for intergalactic planetary nebulae and found 11 candidates in the surveyed area. The measured fluxes of these unresolved sources are consistent with these objects being planetary nebulae from an intergalactic population of stars, although we cannot exclude some minor contamination of our sample by redshifted starburst galaxies. We compute the cumulative luminosity function of these 11 planetary nebula candidates. If we assume that they belong to the Virgo cluster, their cumulative luminosity function is in good agreement with planetary nebula luminosity-function simulations for a typical stellar population of ellipticals or spiral bulges. This comparison allows us to estimate the surface mass density of the intergalactic stellar population at the surveyed field in the cluster core.