Limits on [OIII] 5007 emission from NGC4472's globular clusters: constraints on planetary nebulae and ultraluminous black hole X-ray binaries in globular clusters

We have searched for [OIII] 5007 emission in high resolution spectroscopic data from Flames/Giraffe VLT observations of 174 massive globular clusters (GCs) in NGC4472. No planetary nebulae (PNe) are observed in these clusters, constraining the number of PNe per bolometric luminosity, \alpha<0.8*10^{-7}PN/L_{\odot}. This is significantly lower than the rate predicted from stellar evolution, if all stars produce PNe. Comparing our results to populations of PNe in galaxies, we find most galaxies have a higher \alpha than these GCs (more PNe per bolometric luminosity - though some massive early-type galaxies do have similarly low \alpha). The low \alpha required in these GCs suggests that the number of PNe per bolometric luminosity does not increase strongly with decreasing mass or metallicity of the stellar population. We find no evidence for correlations between the presence of known GC PNe and either the presence of low mass X-ray binaries (LMXBs) or the stellar interaction rates in the GCs. This, and the low \alpha observed, suggests that the formation of PNe may not be enhanced in tight binary systems. These data do identify one [OIII] emission feature, this is the (previously published) broad [OIII] emission from the cluster RZ 2109. This emission is thought to originate from the LMXB in this cluster, which is accreting at super-Eddington rates. The absence of any similar [OIII] emission from the other clusters favors the hypothesis that this source is a black hole LMXB, rather than a neutron star LMXB with significant geometric beaming of its X-ray emission.Comment: 10 pages, 3 figures, accepted for publication in Ap

Some Constraints On the Effects of Age and Metallicity on the Low Mass X-ray Binary Formation Rate

We have studied the low mass X-ray binary (LMXB) populations within and outside globular clusters (GC) in NGC 4365 and NGC 3115. Using published age and metallicity constraints from optical and IR observations of their GCs, we do not find any evidence for an increase in the LMXB formation rate in the intermediate age cluster population of NGC 4365, as has been proposed in some scenarios of dynamical LMXB formation in GCs. The old, metal-rich, red population of GCs in NGC 3115 on the other hand is {\it at least} three times as efficient at creating LMXBs as the old, metal-poor, blue clusters. These data suggest that the higher formation efficiency of LMXBs in the red GC subsystems of many galaxies is largely a consequence of their higher metallicity. A comparison of the densities of field LMXBs in different galaxies does not reveal an obvious correlation with the age of the field stars as predicted by models in which the LMXB formation rate in the field drops monotonically with time after an initial burst. This suggests that either a significant fraction of the field LMXBs are created in GCs and subsequently injected into the field, or the LMXB formation rate has a more complex time evolution pattern.Comment: Accepted for publication in ApJ Letters. 7 pages including 5 figure

A new globular cluster black hole in NGC 4472

We discuss CXOU~1229410+075744, a new black hole candidate in a globular cluster in the elliptical galaxy NGC~4472. By comparing two Chandra observations of the galaxy, we find a source that varies by at least a factor of 4, and has a peak luminosity of at least $2\times10^{39}$ ergs/sec. As such, the source varies by significantly more than the Eddington luminosity for a single neutron star, and is a strong candidate for being a globular cluster black hole. The source's X-ray spectrum also evolves in a manner consistent with what would be expected from a single accreting stellar mass black hole. We consider the properties of the host cluster of this source and the six other strong black hole X-ray binary candidates, and find that there is suggestive evidence that black hole X-ray binary formation is favored in bright and metal rich clusters, just as is the case for bright X-ray sources in general.Comment: 6 pages, one 2-panel figure, 2 tables; accepted to MNRA

Velocity Structure and Variability of [O III] Emission in Black Hole Host Globular Cluster RZ2109

We present a multi-facility study of the optical spectrum of the extragalactic globular cluster RZ2109, which hosts a bright black hole X-ray source. The optical spectrum of RZ2109 shows strong and very broad [O III]\lambda \lambda 4959,5007 emission in addition to the stellar absorption lines typical of a globular cluster. We use observations over an extended period of time to constrain the variability of these [O III] emission lines. We find that the equivalent width of the lines is similar in all of the datasets; the change in L[O III]\lambda 5007 is \ltsim 10% between the first and last observations, which were separated by 467 days. The velocity profile of the line also shows no significant variability over this interval. Using a simple geometric model we demonstrate that the observed [O III]\lambda 5007 line velocity structure can be described by a two component model with most of the flux contributed by a bipolar conical outflow of about 1,600 km/s, and the remainder from a Gaussian component with a FWHM of several hundred km/s.Comment: 20 pages, 6 figures, 1 table. ApJ accepte

The faint 2005 hard state outburst of Aquila X-1 seen by INTEGRAL and RXTE

We report on the spectral analysis of RXTE and INTEGRAL data of the 2005 April outburst of the transient Atoll source Aql X-1. Although this outburst is one of the faintest ever detected for this source in the soft X-rays (RXTE/ASM), one of our INTEGRAL observations, taken close to the soft X-ray peak, shows that the source flux was quite high, with a 20-200 keV flux of 2.05 x 10^-9 erg cm^-2 s^-1. On this occasion we detect the source up to 150 keV for the first time. We compare and discuss the similarity of the source behavior with that of black hole transients especially XTE J1550-564.Comment: 4 pages 2 figures, Accepted for publication in A&A as a RESEARCH NOT

Limits on the quiescent radio emission from the black hole binaries GRO J1655-40 and XTE J1550-564

We present the results of radio observations of the black hole binaries GRO J1655-40 and XTE J1550-564 in quiescence, with the upgraded Australia Telescope Compact Array. Neither system was detected. Radio flux density upper limits (3 sigma) of 26 micro Jy (at 5.5 GHz), 47 micro Jy (at 9 GHz) for GRO J1655-40, and 1.4 mJy (at 1.75 GHz), 27 micro Jy (at 5.5 GHz), 47 micro Jy (at 9 GHz) for XTE J1550-564 were measured. In conjunction with quasi-simultaneous Chandra X-ray observations (in the case of GRO J1655-40) and Faulkes Telescope optical observations (XTE J1550-564) we find that these systems provide the first evidence of relatively `radio quiet' black hole binaries at low luminosities; indicating that the scatter observed in the hard state X-ray:radio correlation at higher luminosities may also extend towards quiescent levels.Comment: Accepted for publication in MNRA

From Supermassive Black Holes to Dwarf Elliptical Nuclei: a Mass Continuum

Considerable evidence suggests that supermassive black holes reside at the centers of massive galactic bulges. At a lower galactic mass range, many dwarf galaxies contain extremely compact nuclei that structurally resemble massive globular clusters. We show that both these types of central massive objects (CMO's) define a single unbroken relation between CMO mass and the luminosity of their host galaxy spheroid. Equivalently, M_CMO is directly proportional to the host spheroid mass over 4 orders of magnitude. We note that this result has been simultaneously and independently identified by Cote et al. (2006), see also Ferrarese et al. (2006). We therefore suggest that the dE,N nuclei may be the low-mass analogs of supermassive black holes, and that these two types of CMO's may have both developed starting from similar initial formation processes. The overlap mass interval between the two types of CMO's is small, and suggests that for M_CMO > 10^7 M_sun, the formation of a black hole was strongly favored, perhaps because the initial gas infall to the center was too rapid and violent for star formation to occur efficiently.Comment: 4 pages, 2 figures, submitted to ApJ