Intracluster Planetary Nebulae Research Articles

Planetary Nebulae and their parent stellar populations. Tracing the mass assembly of M87 and Intracluster light in the Virgo cluster core

AbstractThe diffuse extended outer regions of galaxies are hard to study because they are faint, with typical surface brightness of 1% of the dark night sky. We can tackle this problem by using resolved star tracers which remain visible at large distances from the galaxy centers. This article describes the use of Planetary Nebulae as tracers and the calibration of their properties as indicators of the star formation history, mean age and metallicity of the parent stars in the Milky Way and Local Group galaxies. We then report on the results from a deep, extended, planetary nebulae survey in a 0.5 deg2region centered on the brightest cluster galaxy NGC 4486 (M87) in the Virgo cluster core, carried out with SuprimeCam@Subaru and FLAMES-GIRAFFE@VLT. Two planetary nebulae populations are identified out to 150 kpc distance from the center of M87. One population is associated with the M87 halo and the second one with the intracluster light in the Virgo cluster core. They have different line-of-sight velocity and spatial distributions, as well as different planetary nebulae specific frequencies and luminosity functions. The intracluster planetary nebulae in the surveyed region correspond to a luminosity of four times the luminosity of the Large Magellanic Cloud. The M87 halo planetary nebulae trace an older, more metal-rich, parent stellar population. A substructure detected in the projected phase-space of the line-of-sight velocity vs. major axis distance for the M87 halo planetary nebulae provides evidence for the recent accretion event of a satellite galaxy with luminosity twice that of M33. The satellite stars were tidally stripped about 1 Gyr ago, and reached apocenter at a major axis distance of 60–90 kpc from the center of M87. The M87 halo is still growing significantly at the distances where the substructure is detected.

Extended halos and intracluster light using Planetary Nebulae as tracers in nearby clusters

AbstractSince the first detection of intracluster planetary nebulae in 1996, imaging and spectroscopic surveys identified such stars to trace the radial extent and the kinematics of diffuse light in clusters. This topic of research is tightly linked with the studies of galaxy formation and evolution in dense environment, as the spatial distribution and kinematics of planetary nebulae in the outermost regions of galaxies and in the cluster cores is relevant for setting constraints on cosmological simulations. In this sense, extragalactic planetary nebulae play a very important role in the near-field cosmology, in order to measure the integrated mass as function of radius and the orbital distribution of stars in structures placed in the densest regions of the nearby universe.

Extended halos and intracluster light using Planetary Nebulae as tracers in nearby clusters

AbstractSince the first detection of intracluster planetary nebulae in 1996, imaging and spectroscopic surveys identified such stars to trace the radial extent and the kinematics of diffuse light in clusters. This topic of research is tightly linked with the studies of galaxy formation and evolution in dense environment, as the spatial distribution and kinematics of planetary nebulae in the outermost regions of galaxies and in the cluster cores is relevant for setting constraints on cosmological simulations. In this sense, extragalactic planetary nebulae play a very important role in the near-field cosmology, in order to measure the integrated mass as function of radius and the orbital distribution of stars in structures placed in the densest regions of the nearby universe.

The formation of cD Halos: the case of NGC 3311 in the Hydra I Cluster

We have studied the core of the Hydra I cluster, around its central cD galaxy, NGC 3311. We have analyzed the kinematics a sample of 60 intracluster planetary nebulae (PNs), detected using the multi-slit imaging spectroscopy technique (MSIS, Gerhard et al., 2005, Ventimiglia et al., 2008). PNs are good tracers of light (Coccato et al., 2009) and the MSIS allows to measure their velocities and positions at the same time. The histogram of the PN radial velocities presents several discrete components. We are comparing this result with ΛCDM hydro-dynamical simulations and other data in order to interpret it in the framework of the formation of extended halos around cD galaxies. V band photometric data around NGC 3311 have revealed the presence of an excess of light in the North-East part of the galaxy, which is spatially coincident with most of the PNs contributing to the reddest peak in the PNs LOSVD. We have measured, using Long-Slit data, the velocity of HCC26, a dwarf (DW) galaxy in the middle of the excess of light. The reddest peak in the PNs LOSVD is consistent both with the velocity of HCC 26 and of several other DWs in the same region. We are investigating the possibility that the light in excess has been stripped from these galaxies and now incorporated into the halo of NGC 3311.

THE CONNECTION BETWEEN DIFFUSE LIGHT AND INTRACLUSTER PLANETARY NEBULAE IN THE VIRGO CLUSTER

We compare the distribution of diffuse intracluster light detected in the Virgo Cluster via broadband imaging with that inferred from searches for intracluster planetary nebulae (IPNe). We find a rough correspondence on large scales (~ 100 kpc) between the two, but with very large scatter (~ 1.3 mag/arcsec^2). On smaller scales (1 -- 10 kpc), the presence or absence of correlation is clearly dependent on the underlying surface brightness. On these scales, we find a correlation in regions of higher surface brightness (mu_V < ~27) which are dominated by the halos of large galaxies such as M87, M86, and M84. In those cases, we are likely tracing PNe associated with galaxies rather than true IPNe. In true intracluster fields, at lower surface brightness, the correlation between luminosity and IPN candidates is much weaker. While a correlation between broadband light and IPNe is expected based on stellar populations, a variety of statistical, physical, and methodological effects can act to wash out this correlation and explain the lack of a strong correlation at lower surface brightness found here. [abridged]

The edge of the M 87 halo and the kinematics of the diffuse light in the Virgo cluster core

We present high resolution FLAMES/VLT spectroscopy of intracluster planetary nebula (ICPN) candidates, targeting three new fields in the Virgo cluster core with surface brightness down to mu_B = 28.5. Based on the projected phase space information we separate the old and 12 newly-confirmed PNs into galaxy and intracluster components. The M87 PNs are confined to the extended stellar envelope of M87, within a projected radius of ~ 160 kpc, while the ICPNs are scattered across the whole surveyed region between M87 and M86. The velocity dispersions determined from the M87 PNs at projected radii of 60 kpc and 144 kpc show that the galaxy's velocity dispersion profile decreases in the outer halo, down to 78 +/- 25 km/s. A Jeans model for the M87 halo stars in the gravitational potential traced by the X-ray emission fits the observed velocity dispersion profile only if the stellar orbits are strongly radially anisotropic (beta ~= 0.4 at r ~= 10 kpc increasing to 0.8 at the outer edge), and if additionally the stellar halo is truncated at ~= 150 kpc average elliptical radius. From the spatial and velocity distribution of the ICPNs we infer that M87 and M86 are falling towards each other and that we may be observing them just before the first close pass. The inferred luminosity-specific PN numbers for the M87 halo and the ICL are in the range of values observed for old (> 10 Gyr) stellar populations (abridged).

Intracluster Planetary Nebulae in the Hydra I cluster

AbstractUsing the Multislit Imaging Spectroscopy (MSIS) technique at the FORS2 spectrograph on VLT‐UT1, we have identified 60 Intracluster Planetary Nebula (ICPN) candidates associated with the Intracluster Light (ICL) in the central region of the Hydra I cluster. Hydra I is a medium compact, relatively near (∼50 Mpc), rich cluster in the southern hemisphere. Here we describe the criteria used to select emission sources and present the evidence for these PN candidates to be associated with the ICL in the Hydra I cluster. We also show, using the luminosity‐specific planetary nebulae number, the α parameter, that the expected number of PNs associated with the stellar population of the central cD galaxy NGC 3311 in the cluster is close to the number of PNs detected. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Multi-Slit Imaging Spectroscopy Technique: Catalog of Intracluster Planetary Nebulae in the Coma Cluster

Abstract With a new multi-slit imaging spectroscopy (MSIS) technique pioneered at the 8.2 m Subaru telescope and the Faint Object Camera and Spectrograph, we detect and measure the line-of-sight velocities of 40 intracluster planetary nebula candidates associated with the diffuse intracluster population of stars in the Coma cluster core, at nearly 100 Mpc distance. We describe the method for extracting the single two-dimensional spectra from the MSIS image, discuss the criteria for the identification of the emission line objects, and describe the procedure to compute their $\alpha, \delta$ (J2000) coordinates. We present the catalog of the intracluster planetary nebula candidates, their spatial location in the surveyed field, and their distribution in the velocity–magnitude plane. Finally, we comment on possible population effects and the use of these planetary nebulae to confirm the distance to the Coma cluster.

The kinematics of intracluster planetary nebulae and the on-going subcluster merger in the Coma cluster core

Aims. The Coma cluster is the richest and most compact of the nearby clusters, yet there is growing evidence that its formation is still on-going. A sensitive probe of this evolution is the dynamics of intracluster stars, which are unbound from galaxies while the cluster forms, according to cosmological simulations. Methods. With a new multi-slit imaging spectroscopy technique pioneered at the 8.2 m Subaru telescope and FOCAS, we have detected and measured the line-of-sight velocities of 37 intracluster planetary nebulae associated with the diffuse stellar population of stars in the Coma cluster core, at 100 Mpc distance. Results. We detect clear velocity substructures within a 6 arcmin diameter field. A substructure is present at ~5000${\rm\,km\,s^{-1}}$, probably from in-fall of a galaxy group, while the main intracluster stellar component is centered around ~6500${\rm\,km\,s^{-1}}$, ~700${\rm\,km\,s^{-1}}$ offset from the nearby cD galaxy NGC 4874. The kinematics and morphology of the intracluster stars show that the cluster core is in a highly dynamically evolving state. In combination with galaxy redshift and X-ray data this argues strongly that the cluster is currently in the midst of a subcluster merger, where the NGC 4874 subcluster core may still be self-bound, while the NGC 4889 subcluster core has probably dissolved. The NGC 4889 subcluster is likely to have fallen into Coma from the eastern A2199 filament, in a direction nearly in the plane of the sky, meeting the NGC 4874 subcluster arriving from the west. The two inner subcluster cores are presently beyond their first and second close passage, during which the elongated distribution of diffuse light has been created. We predict the kinematic signature expected in this scenario, and argue that the extended western X-ray arc recently discovered traces the arc shock generated by the collision between the two subcluster gas halos. Any preexisting cooling core region would have been heated by the subcluster collision.

Calibrating Type Ia Supernovae Using the Planetary Nebula Luminosity Function. I. Initial Results

We report the results of an [O III] lambda 5007 survey for planetary nebulae (PN) in five galaxies that were hosts of well-observed Type Ia supernovae: NGC 524, NGC 1316, NGC 1380, NGC 1448 and NGC 4526. The goals of this survey are to better quantify the zero-point of the maximum magnitude versus decline rate relation for supernovae Type Ia and to validate the insensitivity of Type Ia luminosity to parent stellar population using the host galaxy Hubble type as a surrogate. We detected a total of 45 planetary nebulae candidates in NGC 1316, 44 candidates in NGC 1380, and 94 candidates in NGC 4526. From these data, and the empirical planetary nebula luminosity function (PNLF), we derive distances of 17.9 +0.8/-0.9 Mpc, 16.1 +0.8/-1.1 Mpc, and 13.6 +1.3/-1.2 Mpc respectively. Our derived distance to NGC 4526 has a lower precision due to the likely presence of Virgo intracluster planetary nebulae in the foreground of this galaxy. In NGC 524 and NGC 1448 we detected no planetary nebulae candidates down to the limiting magnitudes of our observations. We present a formalism for setting realistic distance limits in these two cases, and derive robust lower limits of 20.9 Mpc and 15.8 Mpc, respectively. After combining these results with other distances from the PNLF, Cepheid, and Surface Brightness Fluctuations distance indicators, we calibrate the optical and near-infrared relations for supernovae Type Ia and we find that the Hubble constants derived from each of the three methods are broadly consistent, implying that the properties of supernovae Type Ia do not vary drastically as a function of stellar population. We determine a preliminary Hubble constant of H_0 = 77 +/- 3 (random) +/- 5 (systematic) km/s/Mpc for the PNLF, though more nearby galaxies with high-quality observations are clearly needed.

Intracluster Planetary Nebulae

I review the progress in research on intracluster planetary nebulae over the last five years. Hundreds more intracluster planetary nebulae have been detected in the nearby Virgo and Fornax galaxy clusters, searches of several galaxy groups have been made, and intracluster planetary candidates have been detected in the distant Coma cluster. The first theoretical studies of intracluster planetaries have also been completed, studying their utility as tracers of the intracluster light as a whole, and also as individual objects.From the results to date, it appears that intracluster planetaries are common in galaxy clusters (10-20% of the total amount of starlight), but thus far, none have been detected in galaxy groups, a result which currently is not well understood. Limited spectroscopic follow-up of intracluster planetaries in Virgo indicate that they have a complex velocity structure, in agreement with numerical models of intracluster light. Hydrodynamic simulations of individual intracluster planetaries predict that their morphology is significantly altered by their intracluster environment, but their emission-line properties appear to be unaffected.

Kinematic Substructures in the Coma Cluster Core as traced by Intracluster Planetary Nebulae

The Coma cluster is the richest and most compact of the nearby clusters, yet there is growing evidence that its formation is still on-going. A sensitive probe of this evolution is the dynamics of intracluster stars, which are unbound from galaxies while the cluster forms, according to cosmological simulations. With a new multi-slit imaging spectroscopy technique pioneered at the 8.2 m Subaru telescope and FOCAS, we can now detect and measure the line-of-sight velocities of the intracluster planetary nebulae which are associated with the diffuse stellar population of stars, at 100 Mpc distance. We detect significant velocity substructures within a 6 arcmin diameter field, centred on the Coma X-ray cluster emission. One substructure is present at $\sim $ 5000 km s $^{-1}$ , probably from infall of a galaxy group, while the main intracluster stellar component moves at $\sim $ 6500 km s $^{-1}$ . Hence the ICPNs associated with the diffuse light at the position of the MSIS field are not bound to the nearby cD galaxy NGC 4874, whose radial velocity is $\sim $ 700 km s $^{-1}$ higher.

Intracluster stars tracing motions in nearby clusters

Cosmological simulations of structure formation predict that galaxies are dramatically modified by galaxy harassment during the assembly of galaxy clusters, losing a substantial fraction of their stellar mass which today must be in the form of intracluster stars. Simulations predict non-uniform spatial and radial velocity distributions for these stars. Intracluster planetary nebulae are the only abundant component of the intracluster light whose kinematics can be measured at this time. Comparing these velocity distributions with simulations will provide a unique opportunity to investigate the hierarchical cluster formation process as it takes place in the nearby universe.

The Survival of Planetary Nebulae in the Intracluster Medium

The stellar population stripped from galaxies in clusters evolves under the extreme conditions imposed by the intracluster (IC) medium. Intracluster stars generally suffer very high systemic velocities moving through a rarefied and extremely hot IC medium. We present numerical simulations that aim to explore the evolution and survival of IC asymptotic giant branch (AGB) envelopes and planetary nebula (PN) shells. Our models reflect the evolution of a low-mass star under the observed conditions in the Virgo IC medium. We find that the integrated hydrogen-recombination line emission of a PN is dominated by the inner dense shell, whose evolution is unaffected by the environment. Ram pressure stripping mainly affects the outermost IC PN shell, which hardly influences the emission when the PN is observed as a point source. More importantly, we find that a PN with progenitor mass of 1 M☉ fades to ~30% and ~10% of its maximum emission in 5000 and 10,000 yr, respectively, disclosing an actual PN lifetime (tPN) several times shorter than what is usually adopted (25,000 yr). This result affects the theoretical calculation of the luminosity-specific density of IC PNe, which scales with tPN. For tPN = 10,000 yr, our more conservative estimate, we obtain that the luminosity-specific density of PNe is in fair agreement with the value obtained from red giants. With our more realistic PN lifetime, we infer a fraction of IC starlight in the Virgo core of above 15%, which is higher than current estimates.

Intracluster Stars in the Virgo Cluster Core

We have investigated the properties of the diffuse light in the Virgo Cluster core region, based on the detection of intracluster planetary nebulae (PNs) in four fields. We eliminate the bias from misclassified faint continuum objects, using improved Monte Carlo simulations, and the contaminations by high-redshift Lyα galaxies, using the Lyα luminosity function in blank fields. Recent spectroscopic observations confirm that our photometric PN samples are well understood. We find that the diffuse stellar population in the Virgo core region is inhomogeneous on scales of 30'–90': there exist significant field-to-field variations in the number density of PNs and the inferred amount of intracluster light, with some fields empty, some fields dominated by extended Virgo galaxy halos, and some fields dominated by the true intracluster component. There is no clear trend with distance from M87. The mean surface luminosity density, its rms variation, and the mean surface brightness of diffuse light in our four fields are ΣB = 2.7 × 106 LB⊙ arcmin-2, rms = 2.1 × 106 LB⊙ arcmin-2, and B = 29.0 mag arcsec-2, respectively. Our results indicate that the Virgo Cluster is a dynamically young environment and that the intracluster component is associated partially with local physical processes like galaxy interactions or harassment. We also argue, based on kinematic evidence, that the so-called over-luminous PNs in the halo of M84 are dynamically associated with this galaxy and must thus be brighter than, and part of a different stellar population from, the normal PN population in elliptical galaxies.

Detection of Intracluster Planetary Nebulae in the Coma Cluster

[OIII] lambda 5007AA emission lines of 16 intracluster planetary nebulae candidates in the Coma cluster were detected with a Multi-Slit Imaging Spectroscopy (MSIS) technique using FOCAS on the Subaru telescope. The identification of these faint emission sources as PNe is supported by (i) their point-like flux distribution in both space and wavelength, with tight limits on the continuum flux; (ii) the identification of the second [OIII] lambda 4959 line in the only object at high enough velocity that this line too falls into the filter bandpass; (iii) emission line fluxes consistent with PNe at 100 Mpc distance, in the range 2.8 x 10^{-19} - 1.7 x 10^{-18} erg/s/cm^2; and (iv) a narrow velocity distribution approximately centered on the systemic velocity of the Coma cluster. Comparing with the velocities of galaxies in our field, we conclude that the great majority of these candidates would be intracluster PNe, free floating in the Coma cluster core. Their velocity dispersion is ~760 km/s, and their mean velocity is lower than that of the galaxies. The velocity distribution suggests that the intracluster stellar population has different dynamics from the galaxies in the Coma cluster core.

Tramp Novae between Galaxies in the Fornax Cluster: Tracers of Intracluster Light

We report the results of a survey for novae in and between the galaxies of the Fornax Cluster. Our survey provides strong evidence that intracluster novae exist and that they provide a useful, independent measure of the intracluster light in Fornax. We discovered six strong nova candidates in six distinct epochs spanning 11 yr from 1993 to 2004. The data were taken with the 4 m and the 1.5 m telescopes at Cerro Tololo Inter-American Observatory. The spatial distribution of the nova candidates is consistent with ~16%-41% of the total light in the cluster being in the intracluster light, based on the ratio of the number of novae we discovered in intracluster space over the total number of novae discovered plus a simple completeness correction factor. This estimate is consistent with independent measures of intracluster light in Fornax and Virgo using intracluster planetary nebulae. The accuracy of the intracluster light measurement improves with each survey epoch as more novae are discovered.

Intracluster Planetary Nebulae in the Virgo Cluster. III. Luminosity of the Intracluster Light and Tests of the Spatial Distribution

Intracluster planetary nebulae are a useful tracer of the evolution of galaxies and galaxy clusters. We analyze our catalog of 318 intracluster planetary nebulae candidates found in 0.89 deg-2 of the Virgo Cluster. We give additional evidence for the great depth of the Virgo Cluster's intracluster stellar population, which implies that the bulk of the intracluster stars come from late-type galaxies and dwarfs. We also provide evidence that the intracluster stars are clustered on the sky on arcminute scales, in agreement with tidal-stripping scenarios of intracluster star production. Although significant systematic uncertainties exist, we find that the average fraction of intracluster starlight in the Virgo Cluster is 15.8% ± 3.0% (statistical) ± 5.0% (systematic) and may be higher if the intracluster stars have a large spatial line-of-sight depth. We find that the intracluster star density changes little with radius or projected density over the range surveyed. These results, along with other intracluster star observations, imply that intracluster star production in Virgo is ongoing and consistent with the cluster's known dynamical youth.

The origin and properties of intracluster stars in a rich cluster

We use a multimillion particle N‐body + smooth particle hydrodynamics (SPH) simulation to follow the formation of a rich galaxy cluster in a Λ‐cold dark matter (ΛCDM) cosmology, with the goal of understanding the origin and properties of intracluster stars. The simulation includes gas cooling, star formation, the effects of a uniform ultraviolet background and feedback from supernovae. Haloes that host galaxies as faint as MR=−19.0 are resolved by this simulation, which includes 85 per cent of the total galaxy luminosity in a rich cluster. We find that the accumulation of intracluster light (ICL) is an ongoing process, linked to infall and stripping events. The unbound star fraction varies with time between 10 and 22 per cent of the total amount of cluster stars, with an overall trend to increase with time. The fraction is 20 per cent at z= 0, consistent with observations of galaxy clusters. The surface brightness profile of the cD galaxy shows an excess compared with a de Vaucouleur profile near 200 kpc, which is also consistent with observations. Both massive and small galaxies contribute to the formation of the ICL, with stars stripped preferentially from the outer, lower‐metallicity parts of their stellar distributions. Simulated observations of planetary nebulae (PNe) show significant substructure in velocity space, tracing separate streams of stripped intracluster stars. Despite an unrelaxed distribution, individual intracluster PNe might be useful mass tracers if more than five fields at a range of radii have measured line‐of‐sight velocities, where an accurate mass calculation depends more on the number of fields than the number of PNe measured per field. However, the orbits of intracluster stars are more anisotropic than those of galaxies or dark matter, which leads to a systematic underestimate of cluster mass relative to that calculated with galaxies, if not accounted for in dynamical models. Overall, the properties of ICL formed in a hierarchical scenario are in good agreement with current observations, supporting a model where ICL originates from the dynamical evolution of galaxies in dense environments. ICL should thus be ubiquitous in galaxy clusters.

The Line-of-Sight Velocity Distributions of Intracluster Planetary Nebulae in the Virgo Cluster Core

Radial velocities of 40 intracluster planetary nebulae (ICPNs) in the Virgo Cluster were obtained with the new multifiber FLAMES spectrograph on UT2 at the Very Large Telescope. For the first time, the λ4959 line of the [O III] doublet is seen in a large fraction (50%) of ICPNs spectra, and a large fraction of the photometric candidates with m(5007) ≲ 27.2 is spectroscopically confirmed. ICPNs with the velocity dispersion of the Virgo Cluster are found in our CORE field 12 from M87. These may have originated from tidal mass loss of smaller galaxies in the M87 subcluster halo. In a field 025 from M87, we see an extended stellar halo of M87 in approximate dynamical equilibrium but with few ICPNs. Finally, in a field near M84/M86, the ICPN velocities are highly correlated with the galaxy velocities, showing that any well-mixed intracluster population is yet to form. Overall, the measured velocity distributions confirm the nonuniform dynamical structure and ongoing assembly of the Virgo Cluster.