Nucleus Of M31 Research Articles

A Search for Molecular Gas in the Nucleus of M87 and Implications for the Fueling of Supermassive Black Holes

Supermassive black holes in giant elliptical galaxies are remarkably faint given their expected accretion rates. This motivates models of radiatively inefficient accretion, due to either ion-electron thermal decoupling, generation of outflows that inhibit accretion, or settling of gas to a gravitationally unstable disk that forms stars in preference to feeding the black hole. The latter model predicts the presence of cold molecular gas in a thin disk around the black hole. Here we report Submillimeter Array observations of the nucleus of the giant elliptical galaxy M87 that probe 230 GHz continuum and CO(J=2--1) line emission. Continuum emission is detected from the nucleus and several knots in the jet, including one that has been undergoing flaring behavior. We estimate a conservative upper limit on the mass of molecular gas within ~100pc and +-400km/s line of sight velocity of the central black hole of ~8x10^6Msun, which includes an allowance for possible systematic errors associated with subtraction of the continuum. Ignoring such errors, we have a 3 sigma sensitivity to about 3x10^6Msun. In fact, the continuum-subtracted spectrum shows weak emission features extending up to 4 sigma above the RMS dispersion of the line-free channels. These may be artifacts of the continuum subtraction process. Alternatively, if they are interpreted as CO emission, then the implied molecular gas mass is ~5x10^6Msun spread out over a velocity range of 700km/s. These constraints on molecular gas mass are close to the predictions of the model of self-gravitating, star-forming accretion disks fed by Bondi accretion (Tan & Blackman 2005).

Hubble Space TelescopeSpace Telescope Imaging Spectrograph Spectroscopy of the Environment in the Starburst Core of M82

We present optical HST STIS observations made with two slits crossing four of the optically brightest starburst clumps near the nucleus of M82. These provide Hα kinematics, extinction, electron density, and emission measures. From the radial velocity curves derived from both slits we confirm the presence of a stellar bar. We derive a new model for the orientation of the bar and disk with respect to the main starburst clumps and the cluster M82-A1. We propose that clump A has formed within the bar region as a result of gas interactions between the bar orbits, whereas region C lies at the edge of the bar and regions D and E are located farther out from the nucleus but heavily obscured. We derive extremely high interstellar densities of 500-900 cm-3, corresponding to ISM pressures of P/k ≈ (0.5-1.0) × 107 cm-3 K, and discuss the implications of the measured gas properties on the production and evolution of the galactic wind. Despite varying pressures, the ionization parameter is uniform down to parsec scales, and we discuss why this might be so. Where the signal-to-noise ratios of our spectra are high enough, we identify multiple emission-line components. Through detailed Gaussian line fitting, we identify a ubiquitous broad (200-300 km s-1) underlying component to the bright Hα line and discuss the physical mechanism(s) that could be responsible for such widths. We conclude that evaporation and/or ablation of material from interstellar gas clouds caused by the impact of high-energy photons and fast flowing cluster winds produce a highly turbulent layer on the surface of the clouds from which the emission arises.

The Origin of the Young Stars in the Nucleus of M31

The triple nucleus of M31 consists of a population of old red stars in an eccentric disk (P1 and P2) and another population of younger A stars in a circular disk (P3) around M31's central supermassive black hole (SMBH). We argue that P1 and P2 determine the maximal radial extent of the younger A star population and provide the gas that fueled the starburst that generated P3. The eccentric stellar disk creates an m = 1 nonaxisymmetric perturbation to the potential. This perturbed potential drives gas into the inner parsec around the SMBH, if the pattern speed of the eccentric stellar disk is Ωp ≲ 3-10 km s-1 pc-1. We show that stellar mass loss from P1 and P2 is sufficient to create a gravitationally unstable gaseous disk of ~105 M☉ every 0.1-1 Gyr, consistent with the 200 Myr age of P3. Similar processes may act in other systems to produce very compact nuclear starbursts.

Production of TeV Gamma Radiation in the Vicinity of the Supermassive Black Hole in the Giant Radio Galaxy M87

Although the giant radio galaxy M87 harbors many distinct regions of broadband nonthermal emission, the recently reported fast variability of TeV γ-rays from M87, on a timescale of days, strongly constrains the range of speculations concerning the possible sites and scenarios of particle acceleration responsible for the observed TeV emission. A natural production site of this radiation is the immediate vicinity of the central supermassive black hole (BH). Because of its low bolometric luminosity, the nucleus of M87 can be effectively transparent for γ-rays up to an energy of 10 TeV, which makes this source an ideal laboratory for the study of particle acceleration processes close to the BH event horizon. We critically analyze different possible radiation mechanisms in this region and argue that the observed very high energy γ-ray emission can be explained as the inverse Compton emission of ultrarelativistic electron-positron pairs produced through the development of an electromagnetic cascade in the BH magnetosphere. We demonstrate, through detailed numerical calculations of acceleration and radiation of electrons in the magnetospheric vacuum gap, that this pulsar magnetosphere-like scenario can satisfactorily explain the main properties of the TeV γ-ray emission from M87.

CO + in M82: A Consequence of Irradiation by X-Rays

Based on its strong CO+ emission, it is argued that the M82 starburst galaxy is exposed to a combination of FUV and X-ray radiation. The latter is likely to be the result of the starburst superwind, which leads to diffuse thermal emission, and a compact hard source (but not an AGN). Although a photon-dominated region (FUV) component is clearly present in the nucleus of M82, and capable of forming CO+, only X-ray irradiated gas of density 103-105 cm-3 can reproduce the large, ~(1-4) × 1013 cm-2, columns of CO+ that are observed toward the prototypical starburst M82. The total X-ray luminosity produced by M82 is weak, ~1041 ergs s-1, but this is sufficient to drive the formation of CO+.

The Stellar Populations in the Outer Regions of M33. II. Deep ACS Imaging

Studying the stellar populations in the outskirts of spiral galaxies can provide important constraints on their structure, formation, and evolution. To that end, we present VI photometry obtained with the Advanced Camera for Surveys for three fields located ~20'-30' in projected distance southeast of M33's nucleus (corresponding to approximately four to six visual scale lengths or ~9-13 kpc in deprojected radius). The color-magnitude diagrams reveal a mixed stellar population whose youngest constituents have ages no greater than ~100 Myr and whose oldest members have ages of at least several gigayears. The presence of stars as massive as 3-5 M⊙ is consistent with global star formation thresholds in disk galaxies but could argue for a threshold in M33 that is on the low end of observational and theoretical expectations. The metallicity gradient as inferred by comparing the observed red giant branch (RGB) to the Galactic globular clusters is consistent with M33's inner disk gradient traced by several other studies. The surface density of the RGB stars drops off exponentially with a radial scale length of 4.7' ± 0.1'. The scale length increases with age in a manner similar to the vertical scale height of several nearby late-type spirals. Based on the metallicity gradient, density gradient, and mixed nature of the stellar populations, we conclude that these fields are dominated by a disk population, although we cannot rule out the presence of a small halo component.

Detection of CO + in the Nucleus of M82

We present the detection of the reactive ion CO+ towards the prototypical starburst galaxy M82. This is the first secure detection of this short-lived ion in an external galaxy. Values of [CO+]/[HCO+]>0.04 are measured across the inner 650pc of the nuclear disk of M82. Such high values of the [CO+]/[HCO+] ratio had only been previously measured towards the atomic peak in the reflection nebula NGC7023. This detection corroborates that the molecular gas reservoir in the M82 disk is heavily affected by the UV radiation from the recently formed stars. Comparing the column densities measured in M82 with those found in prototypical Galactic photon-dominated regions (PDRs), we need \~20 clouds along the line of sight to explain our observations. We have completed our model of the molecular gas chemistry in the M82 nucleus. Our PDR chemical model successfully explains the [CO+]/[HCO+] ratios measured in the M~82 nucleus but fails by one order of magnitude to explain the large measured CO+ column densities (~1--4x10^{13} cm^{-2}). We explore possible routes to reconcile the chemical model and the observations.

Hubble Space TelescopeImaging of the Outburst Site of M31 RV

M31 RV is a luminous red variable star that appeared for several months in the bulge of M31 during 1988. Unlike classical novae, M31 RV was cool throughout its outburst. Interest in this object has been revived recently because of its strong resemblance to V838 Mon, a luminous Galactic variable star that appeared in 2002 and is illuminating a spectacular light echo, and has evolved to ever cooler surface temperatures. (V4332 Sgr is a third object that was also a red supergiant throughout its eruption.) We have examined archival Hubble Space Telescope (HST) images of the site of M31 RV, obtained fortuitously in 1999 with the WFPC2 camera in parallel mode during spectroscopic observations of the nucleus of M31. We located the site of M31 RV in the HST frames precisely through astrometric registration with ground-based CCD images, including several taken during the outburst. No light echo is seen at the M31 RV site, implying either that M31 RV is not surrounded by circumstellar (or interstellar) dust similar to that around V838 Mon, or that its extent is less than ~1.7 pc. The stellar population at the outburst site consists purely of old red giants; there is no young population, such as that seen around V838 Mon. There are no stars of unusual color at the site, suggesting either that M31 RV had faded below HST detectability in the 11 years since outburst, that it is an unresolved companion of one of the red giants in the field, or that it is one of the red giants. We suggest future observations that may help decide among these possibilities.

The Wendelstein Calar Alto Pixellensing Project (WeCAPP): the M 31 variable star catalogue

In this paper we present the WeCAPP variable star catalogue towards the bulge of M31. The observations of the WeCAPP microlensing survey (optical R and I bands) during three years (2000-2003) result in a database with unprecedented time coverage for an extragalactic variable star study. We detect 23781 variable sources in a 16.1' x 16.6' field centered on the nucleus of M31. The catalogue of variable stars contains the positions, the periods and the variations in the R and I bands. We classify the variables according to their position in the R-band period-amplitude plane. Three groups can be distinguished; while the first two groups can be mainly associated with Cepheid-like variables (population I Cepheids in group I, type II Cepheids and RV Tauri stars in group II), the third one consists of Long Period Variables (LPVs). We detect 37 RV Tauri stars and 11 RV Tauri candidates which is one of the largest collections of this class of stars to date. The classification scheme is supported by Fourier decomposition of the light curves. Our data shows a correlation of the low-order Fourier coefficients Phi_21 with Phi_31 for classical Cepheids, as well for type II Cepheids and RV Tauri stars. Correlating our sample of variable stars with the X-ray based catalogues of Kaaret (2002) and Kong et al. (2002) results in 23 and 31 coincidences, 8 of which are M31 globular clusters. The number density of detected variables is clearly not symmetric, which has to be included in the calculations of the expected microlensing event rate towards M31. This asymmetry is due to the enhanced extinction in the spiral arms superimposed on the bulge of M31 which reduces the number of sources to about 60%, if compared to areas of equivalent bulge brightness (without enhanced extinction being present).

HSTSTIS Spectroscopy of the Triple Nucleus of M31: Two Nested Disks in Keplerian Rotation around a Supermassive Black Hole

We present Hubble Space Telescope (HST) spectroscopy of the nucleus of M31 obtained with the Space TelescopeImagingSpectrograph(STIS).SpectrathatincludetheCaiiinfraredtriplet(k ’ 85008)seeonlythered giant stars in the double brightness peaks P1 and P2. In contrast, spectra taken atk ’ 3600 51008 are sensitive to thetinybluenucleusembeddedinP2,thelowersurfacebrightnessnucleusofthegalaxy.P2 hasaK-typespectrum, but we find that the blue nucleus has an A-type spectrum: it shows strong Balmer absorption lines. Hence, the blue nucleus is blue not because of AGN light but rather because it is dominated by hot stars. We show that the spectrum is well described by A0 giant stars, A0 dwarf stars, or a 200 Myr old, single-burst stellar population. White dwarfs, in contrast, cannot fit the blue nucleus spectrum. Given the small likelihood for stellar collisions, recent star formation appears to be the most plausible origin of the blue nucleus. In stellar population, size, and velocity dispersion, the blue nucleus is so different from P1 and P2 that we call it P3 and refer to the nucleus of M31 as triple. Because P2 and P3 have very different spectra, we can make a clean decomposition of the red and blue stars and hence measure the light distribution and kinematics of eachuncontaminated by the other. The line-of-sight velocity distributions of the red stars near P2 strengthen the support for Tremaine’s eccentric disk model. Their wings indicate the presence of stars with velocities of up to 1000 km s � 1 on the anti-P1 side of P2. The kinematics of P3 are consistent with a circular stellar disk in Keplerian rotation around a supermassive black hole.If the P3 diskis perfectlythin,thentheinclination anglei ’ 55 � isidentical withinthe errorsto theinclination of the eccentric disk models for P1+P2 by Peiris & Tremaine and by Salow & Statler. Both disks rotate in the same sense and are almost coplanar. The observed velocity dispersion of P3 is largely caused by blurred rotation and has a maximum value of � ¼ 1183 � 201 km s � 1 . This is much larger than the dispersion � ’ 250 km s � 1 of the red stars along the same line of sight and is the largest integrated velocity dispersion observed in any galaxy. The rotation curve of P3 is symmetric around its center. It reaches an observed velocity of V ¼ 618 � 81 km s � 1 at radius 0B05 ¼ 0:19 pc, where the observed velocity dispersion is � ¼ 674 � 95 km s � 1 . The corresponding circular rotation velocity at this radius is � 1700 km s � 1 . We therefore confirm earlier suggestions that the central dark object

The Centers of Early-Type Galaxies withHubble Space Telescope. V. New WFPC2 Photometry

We present observations of 77 early-type galaxies imaged with the PC1 CCD of the Hubble Space Telescope (HST) WFPC2. "Nuker-law" parametric fits to the surface brightness profiles are used to classify the central structure into "core" or "power-law" forms. Core galaxies are typically rounder than power-law galaxies. Nearly all power-law galaxies with central ellipticities ≥ 0.3 have stellar disks, implying that disks are present in power-law galaxies with < 0.3 but are not visible because of unfavorable geometry. A few low-luminosity flattened core galaxies also have disks; these may be transition forms from power-law galaxies to more luminous core galaxies, which lack disks. Several core galaxies have strong isophote twists interior to their break radii, although power-law galaxies have interior twists of similar physical significance when the photometric perturbations implied by the twists are evaluated. Central color gradients are typically consistent with the envelope gradients; core galaxies have somewhat weaker color gradients than power-law galaxies. Nuclei are found in 29% of the core galaxies and 60% of the power-law galaxies. Nuclei are typically bluer than the surrounding galaxy. While some nuclei are associated with active galactic nuclei (AGNs), just as many are not; conversely, not all galaxies known to have a low-level AGN exhibit detectable nuclei in the broadband filters. NGC 4073 and 4382 are found to have central minima in their intrinsic starlight distributions; NGC 4382 resembles the double nucleus of M31. In general, the peak brightness location is coincident with the photocenter of the core to a typical physical scale of <1 pc. Five galaxies, however, have centers significantly displaced from their surrounding cores; these may be unresolved asymmetric double nuclei. Finally, as noted by previous authors, central dust is visible in about half of the galaxies. The presence and strength of dust correlates with nuclear emission; thus, dust may outline gas that is falling into the central black hole. The prevalence of dust and its morphology suggest that dust clouds form, settle to the center, and disappear repeatedly on ∼108 yr timescales. We discuss the hypothesis that cores are created by the decay of a massive black hole binary formed in a merger. Apart from their brightness profiles, there are no strong differences between core galaxies and power-law galaxies that demand this scenario; however, the rounder shapes of core, their lack of disks, and their reduced color gradients may be consistent with it.

Formation of Massive Black Holes in Globular Clusters

The hydrodynamic formation of massive black holes (BHs) in globular clusters is considered. In particular, we examine the possibility of BH formation induced by the radiation drag that is exerted on the interstellar matter by stellar radiation in globular clusters. The radiation drag extracts angular momentum from interstellar gas and thus allows the gas to accrete onto the cluster center. By incorporating the realistic chemical evolution of globular clusters, we scrutinize the efficiency of the radiation drag to assess the total accreted mass. As a result, we find that if a globular cluster is more massive than ≈6 × 106 M☉ in the present-day stellar component, a massive BH with >260 M☉ can form within it. But the BH-to-cluster mass ratio is considerably smaller than the BH-to-bulge mass ratio (≈10-3) found in galactic bulges. The results are not sensitive to the assumed stellar initial mass function and star formation rate in the cluster, as long as the resulting color-magnitude relation, metallicity, and mass-to-luminosity ratio satisfy those observed in globular clusters. Hence, the putative linear relation between BH mass and bulge mass (MBH-Mbulge relation) cannot be extrapolated to globular cluster systems. In the present regime, we discuss the BH formation in M15, G1, ω Cen, the M33 nucleus, and the compact X-ray sources in M82. Finally, we discuss observational indications of the formation process of massive BHs in globular clusters. We find that the final phase of BH growth due to the radiation drag can be observed as ultraluminous X-ray sources (ULXs) with ~1041 ergs s-1.

Radial Age and Metal Abundance Gradients in the Stellar Content of M32

We present long-slit spectroscopy of the elliptical galaxy M32, obtained with the 8-m Subaru telescope at Mauna Kea, the 1.5-m Tillinghast telescope at the F. L. Whipple Observatory, and the 4-m Mayall telescope at the Kitt Peak National Observatory. The spectra cover the Lick index red spectral region as well as higher order Balmer lines in the blue. Spectra have been taken with the slit off-set from the nucleus to avoid scattered light contamination from the bright nucleus of M32. An analysis of numerous absorption features, particularly involving the H$\gamma$ and H$\beta$ Balmer lines, reveals that systematic radial trends are evident in the integrated spectrum of M32. Population synthesis models indicate a radial change in both the age and chemical composition of the light-weighted mean stellar population in M32, from the nucleus out to 33, i.e., approximately 1.0 effective radius, R_e. Specifically, the light-weighted mean stellar population at 1 R_e is older, by \~3 Gyr, and more metal-poor, by ~-0.25 dex in [Fe/H], t han the central value of ~4 Gyr and [Fe/H]~0.0. We show that this apparent population trend cannot be attributed to a varying contribution from either hot stars or emission line contamination. The increase in age and decrease in metal-abundance with radius are sufficiently well-matched to explain the flat radial color profiles previously observed in M32. In addition, the ratio of Mg to Fe abundance, [Mg/Fe], increases from ~-0.25 in the nucleus to ~-0.08 at 1 R_e. Finally, we find spuriously pronounced line strength gradients in the Mayall data that are an artifact of scattered light from the bright nucleus. Scattered light issues may explain the lack of consistency among previously published studies of radial line strength gradients in M32.

Photon-dominated Chemistry in the Nucleus of M82: Widespread HOC + Emission in the Inner 650 Parsec Disk

The nucleus of M82 has been mapped in several 3 and 1 mm lines of CN, HCN, C2H, c-C3H2, CH3C2H, HC3N, and HOC+ using the IRAM 30 m telescope. These species have been purposely selected as good tracers of photon-dominated chemistry. We have measured [CN]/[HCN] ~ 5 in the inner 650 pc galaxy disk. Furthermore, we have detected the HOC+ 1 → 0 line with an intensity similar to that of the H13CO+ 1 → 0 line. This implies an [HCO+]/[HOC+] ratio of ~40. These results corroborate the existence of a giant photodissociation region (PDR) in the nucleus of M82. In fact, the low [HCO+]/[HOC+] ratio can only be explained if the nucleus of M82 is formed by small (r < 0.02-0.2 pc) and dense (n ~ a few times 104-105 cm-3) clouds immersed in an intense UV field (G0 ~ 104 in units of the Habing field). The detection of the hydrocarbons c-C3H2 and CH3C2H in the nucleus of M82 suggests that a complex carbon chemistry is developing in this giant PDR.

High resolution Chandra X-ray imaging of the nucleus of M 33

We show with a short Chandra HRC-S exposure that the powerful X-ray source coincident with the nucleus of M33 is unresolved at the highest spatial resolution available to date (04). The source flux is variable, doubling during the 5 ks exposure. The combination of properties exhibited by M33 X-8 establishes the source as the nearest example of the ultra-luminous X-ray sources that have been uncovered in other nearby galaxies. On short timescales, we set limits of 9% r.m.s. variability for pulsations in the 0.01-1000 Hz range.

X-Ray Triple Rings around the M87 Jets in the Central Virgo Cluster

The Chandra X-ray data of the central Virgo Cluster are reexamined to reveal a triple-ring structure around the galaxy M87, reminiscent of the spectacular triple-ring pattern of the supernova SN 1987A in the Large Magellanic Cloud. In the sky plane, the two apparent smaller ellipses are roughly aligned along the M87 jets; the larger ring centers at the M87 nucleus and is likely a circle roughly perpendicular to the M87 jet. Certain similarities of these two triple-ring structures might hint at similar processes that operate in these two systems with entirely different sizes and mass scales. We suspect that a major merging event of two galaxies with nuclear supermassive black holes (SMBHs) might create such a triple-ring structure and drove acoustic and internal gravity waves far and near. The M87 jets are perhaps powered by a spinning SMBH resulting from this catastrophic merging event.

Stellar Populations in the Outer Reaches of M31 and M32 from WFPC2 Photometry11Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5‐26555.

ABSTRACTHubble Space Telescope Wide Field Planetary Camera 2 photometry in a field 7 effective radii from the nucleus of M32 and a comparison field in the outer disk of M31, already examined for the presence of RR Lyrae variable stars, are further compared. No relative distance difference between the two fields could be measured using the luminosity of red clump stars. Since M32 is projected on the half of the M31 disk inclined away from us, we argue that M32 most likely lies beyond M31. The color‐magnitude diagrams of the two fields are similar and yield abundance distributions that are similar, with the exception that M32 appears to have a narrower abundance distribution than the comparison field in M31. This conclusion is unlikely to be compromised by age effects. M32 has far fewer metal‐poor stars than the simple one‐zone model of chemical evolution predicts. The deepest combined image shows no trace of a main sequence younger than about 1 Gyr.

Eccentric‐Disk Models for the Nucleus of M31

We construct dynamical models of the nucleus of M31 in which the nucleus consists of an eccentric disk of stars orbiting a central black hole. The principal approximation in these models is that the disk stars travel in a Keplerian potential; i.e., we neglect the mass of the disk relative to the black hole. We consider both aligned models, in which the eccentric disk lies in the plane of the large-scale M31 disk, and models, in which the orientation of the eccentric disk is fitted to the data. Both types of model can reproduce the double structure and overall morphology seen in Hubble Space Telescope photometry. In comparison with the best available ground-based spectroscopy, the models reproduce the asymmetric rotation curve, the peak height of the dispersion profile, and the qualitative behavior of the Gauss-Hermite coefficients h(3) and h(4). Aligned models fail to reproduce the observation that the surface brightness at P1 is higher than at P2 and yield significantly poorer fits to the kinematics; thus, we favor nonaligned models. Eccentric-disk models fitted to ground-based spectroscopy are used to predict the kinematics observed at much higher resolution by the Space Telescope Imaging Spectrograph on the Hubble Space Telescope, and we find generally satisfactory agreement.

Self‐Gravitating Eccentric Disk Models for the Double Nucleus of M31

We present new dynamical models of weakly self-gravitating, finite dispersion eccentric stellar disks around central black holes for the double nucleus of M31. The disk is fixed in a frame rotating at constant precession speed and is populated by stars on quasi-periodic orbits whose parents are numerically integrated periodic orbits in the total potential. A distribution of quasi-periodic orbits about a given parent is approximated by a distribution of Kepler orbits dispersed in eccentricity and orientation, using an approximate phase-space distribution function written in terms of the integrals of motion in the Kepler problem. We use these models, along with an optimization routine, to fit available published kinematics and photometry in the inner 2'' of the nucleus. A grid of 24 best-fit models is computed to accurately constrain the mass of the central black hole and nuclear disk parameters. We find that the supermassive black hole in M31 has mass MBH = 5.62 ± 0.66 × 107 M☉, which is consistent with the observed correlation between the central black hole mass and the velocity dispersion of its host spheroid. Our models precess rapidly, at Ω = 36.5 ± 4.2 km s-1 pc-1, and possess a characteristic radial eccentricity distribution, which gives rise to multimodal line-of-sight velocity distributions along lines of sight near the black hole. These features can be used as sensitive discriminants of disk structure.

Detection of the “Active” Nucleus of M32

M32 hosts a 2.5 × 106 M☉ central black hole, but signs of nuclear activity in this galaxy have long eluded detection. We report the first conclusive detection of the nucleus of M32 in X-rays, based on high-resolution, sensitive observations made with Chandra. The 2-10 keV luminosity is merely 9.4 × 1035 ergs s-1, ~3 × 10-9 times the Eddington luminosity of the black hole. Weak diffuse emission, consistent with thermal gas at a temperature of 0.37 keV, is seen in an annular region ~100 pc from the center. We also present a deep, moderately high-resolution (09) radio continuum observation obtained with the Very Large Array, which places a tight upper bound on the nuclear radio power at 8.4 GHz. We combine these new measurements with upper limits at other wavelengths to discuss implications for the nature of accretion onto the central black hole.