Normal Elliptical Galaxies Research Articles

Galaxies at the detection limits of deep X-ray surveys

The great sensitivities of the Chandra X-ray Observatory and XMM-Newton have allowed us to begin to explore the X-ray emission from galaxies at moderate to high redshift. By using the stacking method, we show that we can detect the ensemble emission from normal elliptical, spiral and irregular galaxies out to redshifts approaching unity. The average X-ray luminosity of these galaxy types can then be compared with the results of models of the evolution in the numbers of low-mass and high-mass X-ray binaries and can possibly be used to constrain models of star formation.

Resolving the Stellar Population of the Standard Elliptical Galaxy NGC 3379

Using the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) on board the Hubble Space Telescope, we have obtained F110W (J-band) and F160W (H-band) images of three fields in NGC3379, a nearby normal giant elliptical galaxy. These images resolve individual red giant stars, yielding the first accurate color-magnitude diagrams for a normal luminous elliptical. The photometry reaches 1 magnitude below the red giant branch tip with errors of < 0.2 mags in F110W-F160W. A strong break in the luminosity function at F160W = 23.68 +/- 0.06 is identified as the tip of the red giant branch (RGB); comparison with theoretical isochrones implies a distance of 10.8 +/- 0.6 Mpc, in good agreement with a number of previous estimates using various techniques. The mean metallicity is close to solar, but there is an appreciable spread in abundance, from at least as metal poor as [Fe/H] = -1.5 to as high as +0.8. There is a significant population of stars brighter than the RGB tip by up to about 1 magnitude. The observations of each field were split over two epochs, separated by 2-3 months, allowing the identification of candidate long period variables; at least 40% of the stars brighter than the RGB tip are variable. Lacking period determinations, the exact nature of these variables remains uncertain, but the bright AGB stars and variables are similar to those found in metal rich globular clusters and are not luminous enough to imply an intermediate age population. All of the evidence points to a stellar population in NGC3379 which is very similar to the bulge of the Milky Way, or an assortment of Galactic globular clusters covering a large metallicity spread.

The near-infrared properties of the host galaxies of radio quasars

We present K-band images of 31 radio quasars selected from the B3-VLA quasar sample. A new method has been developed to detect and restore the host galaxies of these quasars. We have detected the host galaxies of 16 of them. Using these data together with previous data from the B3-VLA quasars (Carballo et al. 1998, hereafter Paper I) and literature data from other samples, we have analyzed a sample of 69 hosts of radio quasars, covering a redshift range between 0<z<3. The host galaxies are large (r_e}~15kpc) and luminous elliptical galaxies (~75% of them brighter than L_*), with an evolution similar to that of radio galaxies. A significant fraction (~40%) of them shows evidence of a possible collision/merging process. They follow a mu_e-r_e relation similar to that of normal elliptical galaxies. The morphological and photometric similarities between these galaxies and radio galaxies in this wide range of redshifts is a good test of the reliability of unification schemes. All of them show little evolution from z=3 to the present epoch. Their K-z distribution is consistent with a no-evolution model, with a fraction of the dispersion due to differences in radio power. We have found a correlation between the quasar radio power and the host luminosity. We have also found a correlation between the host and nuclear source luminosities. These correlations could be induced by a physical relation between the central black hole and the bulge mass (Magorrian et al. 1998).

Simulations of Galaxy Formation in a ΛCDM Universe. III. The Dissipative Formation of an Elliptical Galaxy

We examine the dynamical structure of an elliptical galaxy simulated in the ΛCDM scenario. The morphology of the galaxy evolves dramatically over time in response to the mode and timing of mass accretion; smooth deposition of cooled gas leads to the formation of centrifugally supported disks, while major mergers disperse stellar disks into spheroids. In the case we consider here, these two modes of accretion alternate successively until z ~ 0.6, when the galaxy undergoes one last major (1 : 3) merger. The event triggers a starburst that consumes much of the remaining gas into stars. Little gas cools and accretes subsequently, and as a result, most stars at z = 0 are rather old (75% are older than 9 Gyr) and distributed in a spheroidal component that resembles present-day elliptical galaxies. Dynamically, the galaxy is well approximated by an E4 oblate rotator, with rotational support increasing steadily from the center outward. The apparent rotation support, as measured by Vrot/σ, correlates strongly with isophotal deviations from perfect ellipses. Boxy isophotes are obtained when the galaxy is seen face-on and Vrot/σ ≪ 1. On the other hand, disky isophotes are found for inclinations that maximize Vrot/σ. The line-of-sight velocity distribution is nearly Gaussian at all radii, although small but significant deviations are robustly measured. The sign of the Gauss-Hermite skewness parameter h3 is anticorrelated with the apparent sense of rotation, in agreement with observed trends. Despite its relatively recent assembly, the simulated galaxy has much higher effective surface brightness than normal elliptical galaxies of similar luminosity, in a way reminiscent of the less common type of M32-like "compact elliptical galaxies." This is likely a direct consequence of our star formation and feedback algorithm, which allows for efficient transformation of gas into stars in dense, early collapsing progenitors rather than a definitive prediction for the structure of galaxies assembled in this ΛCDM halo. Despite this limitation, our simulation suggests that dark matter plays a minor role in the luminous regions of compact elliptical galaxies, whose dynamical mass-to-light ratios are thus not dissimilar to those of normal elliptical galaxies. This explains the proximity of compact elliptical galaxies to edge-on projections of the fundamental plane, despite their far greater velocity dispersion at given luminosity. Overall, our simulation shows that repeated episodes of dissipational collapse, followed by merger events, lead to stellar spheroids that are only mildly triaxial and of relatively simple kinematic structure. This is in better agreement with observation than earlier models based on dissipationless mergers of stellar disks and a positive step toward reconciling the observed structure of elliptical galaxies with a hierarchical assembly process where mergers play a substantial role.

Keck Spectroscopy of Four Quasi-stellar Object Host Galaxies

We present optical spectroscopy of the host galaxies of four quasi-stellar objects (QSOs)—PG 1444+407, PKS 2349-147, 3C 323.1, and 4C 31.63—having a redshift range 0.1 ≤ z ≤ 0.3. The spectra were obtained at the Keck Observatory with the Low Resolution Imaging Spectrograph instrument offset 2''-4'' from the nucleus at several position angles in each galaxy. The objects close to 3C 323.1 and PKS 2349-147 have the same redshifts as their nearby QSOs and appear to be the nuclei of galaxies in the final states of merging with the host galaxies. The spectra of the hosts show some variety: PKS 2349-147 and 3C 323.1 show strong off-nuclear emission lines plus stellar absorption features, while the other two show only stellar absorption. PKS 2349-147 and PG 1444+407 have a mixture of old and moderately young stars, while 4C 31.63 has the spectrum of a normal giant elliptical galaxy, which is very rare in our larger sample. The spectrum of the host of 3C 323.1 appears to be dominated by older stars, although our data for it are of lower quality. The redshifts of the off-nucleus emission lines and stellar components are very close to those of the associated QSOs.

The Host Galaxies of Optically Bright Quasi-stellar Objects: Molecular Gas in [CLC][ITAL]z[/ITAL][/CLC] ≤ 0.1 Palomar-Green Quasi-stellar Objects

We present results of a CO (1-0) line survey in a complete sample of 12 low-redshift (z ≤ 0.1), optically bright Palomar-Green quasi-stellar objects (PG QSOs with MB ≤ -23 mag). Six new CO detections are reported here at levels exceeding ICO 2 Jy km s-1. Combined with three previously reported detections, we find that nine of the 12 QSOs have abundant, dense interstellar medium (ISM) characteristic of late-type galaxies. In all nine of the detected QSOs, the derived molecular gas masses are M ≥ 1.0 × 109 M☉, with the most massive being 1010 M☉ (PG 0050+124; I Zw 1). In the three sources not yet detected in CO, the upper limits on the gas masses are ~109 M☉, and thus we cannot rule out abundant ISMs even in these objects. Since our sample was chosen entirely on the basis of low redshift and optical luminosity (and not selected for strong infrared emission), we conclude that the majority of luminous, low-redshift QSOs have gas-rich host galaxies and therefore cannot be normal elliptical galaxies.

Massive Elliptical Galaxies at High Redshift: NICMOS Imaging ofz ≈ 1 Radio Galaxies

We present deep, ≈1.6 μm, continuum images of 11 high-redshift (0.811 < z < 1.875) 3CR radio galaxies observed with NICMOS on board the Hubble Space Telescope. Our NICMOS images probe the rest-frame optical light where stars are expected to dominate the galaxy luminosity. The rest-frame ultraviolet light of eight of these galaxies demonstrates the well-known alignment effect, with extended and often complex morphologies elongated along an axis close to that of the Fanaroff-Riley type II (FRII) radio source. As has been previously noted from ground-based near-infrared imaging, most of the radio galaxies have rounder, more symmetric morphologies at rest-frame optical wavelengths. Here we show the most direct evidence that in most cases the stellar hosts are normal elliptical galaxies with r1/4-law light profiles. For a few galaxies, very faint traces (less than 4% of the total H-band light) of the UV-bright aligned component are also visible in the infrared images. We derive both the effective radius and surface brightness for nine of 11 sample galaxies by fitting one- and two-dimensional surface-brightness models to them. We compare the high-redshift radio galaxies to lower redshift counterparts. We find that their sizes are similar to those of local FRII radio source hosts and are in general larger than other local galaxies. The derived host galaxy luminosities are very high and lie at the bright end of luminosity functions constructed at similar redshifts. This indicates that the high-redshift radio galaxies are likely rare, massive sources. The galaxies in our sample are also brighter than the rest-frame size-surface-brightness locus defined by the low-redshift sources. Passive evolution roughly aligns the z ≈ 1 galaxies with the low-redshift samples with a slope equal to 4.7. This value is intermediate between the canonical Kormendy relation (≈3.5) and a constant luminosity line (=5). The optical host is sometimes centered on a local minimum in the rest-frame UV emission, suggesting the presence of substantial dust obscuration. We also see good evidence of nuclear point sources (no brighter than 5% of the total H-band light) in three galaxies. Overall, our results are consistent with the hypothesis that these galaxies have already formed the bulk of their stars at redshifts greater than z ≈ 2 and that the active galactic nucleus phenomenon takes place within otherwise normal, perhaps passively evolving, galaxies.

Maffei 1 with the [ITAL]Hubble Space Telescope[/ITAL

High-resolution R, I, and Hα images of the center of Maffei 1, the nearest normal giant elliptical galaxy (M = -20.9), have been acquired with the Hubble Space Telescope. At its distance of 3.0 Mpc, 1 pixel in the Planetary Camera field covers only 0.66 pc. The observations reveal that Maffei 1 is a type elliptical galaxy, which is typical of intermediate to massive elliptical galaxies. A source of Hα emission has been discovered in the center. It is barely resolved, with a size of 1.2 pc and an ionized gas mass of only 29 M⊙. Dust is very prominent west of the center in a complex irregular pattern. The correlation between the reddening and the deficiency in surface brightness reveals that the dust is most likely Galactic in origin and that the reddening law along the line of sight is typical of that for the diffuse interstellar medium. For the first time, globular clusters have been detected. Twenty field sources show slightly or significantly extended profiles relative to foreground stars. In I the absolute magnitude of the brightest is -9.6, which is comparable to that of M3 in the Milky Way. The spread in R-I colors, as well the mean color, of these objects is greater than that found for Galactic globular clusters, which may be due in part to a metallicity difference compared with Galactic globular clusters and in part to the variable Galactic extinction across the Wide Field Planetary Camera 2 field. Fits of integrated analytic King models to three of the brighter candidates give core radii and concentration parameters that are comparable to those of Galactic globular clusters.

R-band imaging of the host galaxies of RGB BL Lacertae objects

We present optical R-band images of 100 BL Lacertae objects in the ROSAT-Green Bank (RGB) sample obtained at the Nordic Optical Telescope (NOT). For 62 objects we could not find any previously published images in the literature, of these 35 are new BL Lacs discovered during the RGB BL Lac survey. We were able to resolve the host galaxy in 62% of the objects. We analyze the host galaxies using a two-dimensional fitting procedure and tabulate the best-fit core magnitude and host galaxy parameters (magnitude, effective radius, ellipticity, position angle and shape parameter β) for each object. With two exceptions, all objects are better fit by a model representing an elliptical galaxy (β = 0.25) than by a disk galaxy model (β = 1.0). In the two exceptions the disk host fit is only marginally better than the elliptical host fit, however, and we do not find a single clear example of a disk-dominated host galaxy. The host galaxies have an average brightness MR = −23.9 ± 0.8 and average effective radius reff = 13.2 ± 0.8 kpc. Their bulk properties are indistinguishable from normal elliptical and radio galaxies. The median β is 0.18, well below the value 0.25 that is normally used to describe ellipticals. However, the difference may be caused by as election effect due to the dependence of β on host galaxy luminosity.

Merging of low-mass systems and the origin of the fundamental plane

We present the preliminary results of a study of how small stellar systems merge to form larger ones. As we display the families of galaxies in the μe - Re plane (effective surface brightness versus effective radius) we realize that different morphological types occupy different loci, evidencing the different physical mechanisms operating in each family. As proposed by Capaccioli et al. (1992) this diagram is the logical equivalent of the HR diagram for stars. Here we take some initial steps in understanding of how we can establish the evolutionary tracks, solely due to dynamical processes, in the μe - Re plane, ultimately making a dwarf elliptical to turn into a normal elliptical galaxy.

Galaxies at the Detection Limits of Deep X-ray Surveys

The great sensitivities of the Chandra X-ray Observatory and XMM-Newton are allowing us to explore the X-ray emission from galaxies at moderate to high redshift. By using the stacking method, we show that we can detect the ensemble emission from normal elliptical, spiral and irregular galaxies out to redshifts approaching one. The average X-ray luminosity can then be compared with the results of models of the evolution in the numbers of X-ray binaries and can possibly be used to constrain models of star formation.

Galaxies at the detection limits of deep X-ray surveys

The great sensitivities of the Chandra X-ray Observatory and XMM-Newton are allowing us to explore the X-ray emission from galaxies at moderate to high redshift. By using the stacking method, we show that we can detect the ensemble emission from normal elliptical, spiral and irregular galaxies out to redshifts approaching one. The average X-ray luminosity can then be compared with the results of models of the evolution in the numbers of X-ray binaries and can possibly be used to constrain models of star formation.

Internal Dynamics, Structure, and Formation of Dwarf Elliptical Galaxies. I. A Keck/[ITAL]Hubble Space Telescope[/ITAL] Study of Six Virgo Cluster Dwarf Galaxies

Spectroscopy with the Keck II 10 m telescope and Echelle Spectrograph and Imager is presented for six Virgo Cluster dwarf elliptical (dE) galaxies in the absolute magnitude range -15.7 ? MV ? -17.2. The mean line-of-sight velocity and velocity dispersion are resolved as a function of radius along the major axis of each galaxy, nearly doubling the total number of dEs with spatially resolved stellar kinematics. None of the observed objects shows evidence of strong rotation; upper limits on vrot/?, the ratio of the maximum rotational velocity to the mean velocity dispersion, are well below those expected for rotationally flattened objects. Such limits place strong constraints on dE galaxy formation models. Although these galaxies continue the trend of low rotation velocities observed in Local Group dEs, they are in contrast to recent observations of large rotation velocities in slightly brighter cluster dEs. Using surface photometry from Hubble Space Telescope Wide Field Planetary Camera 2 images and spherically symmetric dynamical models, we determine global mass-to-light ratios 3 ? V ? 6. These ratios are comparable to those expected for an old to intermediate-age stellar population and are broadly consistent with the observed V-I colors of the galaxies. These dE galaxies therefore do not require a significant dark matter component inside an effective radius. We are able to rule out central black holes more massive than ~107 M?. For the five nucleated dEs in our sample, kinematic and photometric properties were determined for the central nucleus separately from the underlying host dE galaxy. These nuclei are as bright or brighter than the most luminous Galactic globular clusters and lie near the region of fundamental plane space occupied by globular clusters. In this space, the Virgo dE galaxies lie in the same general region as Local Group and other nearby dEs, although nonrotating dEs appear to have a slightly higher mean mass and mass-to-light ratio than rotating dEs; the dE galaxies occupy a plane parallel to, but offset from, that occupied by normal elliptical galaxies.

Witnessing the Hierarchical Assembly of the Brightest Cluster Galaxy in a Cluster at [CLC][ITAL]z[/ITAL][/CLC] = 1.26

We have obtained a new high-resolution K'-band image of the central region of the rich X-ray cluster RX J0848.9+4452 at z = 1.26. We found that the brightest cluster galaxy (BCG) in the cluster is clearly separated into two distinct objects. Whereas the optical to near-infrared colors of the objects are consistent with the predictions of passive evolution models for galaxies formed at high redshift, the luminosities of the two galaxies are both considerably fainter than predicted by passive evolution of BCGs in low- and intermediate-redshift clusters. We argue that this is evidence of an ongoing merger of normal cluster elliptical galaxies to form the dominant galaxy in the core of RX J0848.9+4452. The two galaxies appear to point toward the nearby cluster ClG J0848+4453 and are aligned with the outer X-ray contour of their parent cluster, supporting a model of BCG formation by collimated infall along the surrounding large-scale structure.

The Black Hole Masses and Host Galaxies of BL Lacertae Objects

We have measured the central stellar velocity dispersion in the host galaxies of 11 BL Lac objects with redshifts z ≤ 0.125. The range of velocity dispersions, ~170-370 km s-1, is similar to that of nearby radio galaxies. Using the correlation between stellar velocity dispersion and black hole mass defined for nearby galaxies, we derive estimates of the black hole masses in the range 107.9-109.2 M☉. We do not find any significant difference between the black hole masses in high-frequency-peaked and low-frequency-peaked BL Lac objects. Combining the velocity dispersions with previously measured host galaxy structural parameters, we find that the host galaxies lie on the fundamental plane of elliptical galaxies. This supports the conclusions of imaging studies that the majority of BL Lac hosts are normal giant elliptical galaxies.

Tidal Interaction of M32 and NGC 205 with M31: Surface Photometry and Numerical Simulations

We investigate the interaction history of the M31 subgroup by comparing surface photometry of two of its satellites, M32 and NGC 205, with N-body simulations of satellite destruction. The recent discovery of a giant stream in the outer halo of M31, apparently pointed in the direction of M32 and NGC 205, makes such an investigation particularly relevant. The observational component of this study is based on 17 × 5° B- and I-band CCD mosaic images centered on M31 and covering both satellites. Standard ellipse-fitting techniques are used to model and remove M31 disk light and to perform surface photometry on the satellites to limiting brightness levels of (μB, μI) = (27, 25) mag arcsec-2, corresponding to isophotal semimajor axis lengths of r = 420'' (1.6 kpc) and r = 720'' (2.7 kpc). A hint of excess light in the outer parts of M32 noted in earlier studies is confirmed; in particular, clear evidence is seen for a sharp (upward) break in the surface brightness profile at r = 150'' relative to a r1/4 law that fits the inner region of M32. This break is accompanied by a steep increase in isophotal ellipticity , as well as position angle ' twisting. In addition to this excess, evidence is seen for an inner downward break in the surface brightness profile at r = 50''. The robustness of the M32 isophotal features is demonstrated through their (1) insensitivity to the details of background subtraction, (2) symmetry about M32's center, and (3) narrow range of B-I color that is consistent with the interior regions of M32 but not with M31 residual spiral arm/dust lane features. The study of NGC 205 reveals pronounced isophote twisting at r ~ 300'' that is coincident with a subtle downward break in the surface brightness profile, relative to an exponential law fitted to the inner region. The simulation component of this project is based on the analysis of single-component, spherical satellites that are being tidally disrupted through interactions with their parent galaxy. Generic features of the simulations include an excess in the surface brightness profile at large radii, a depletion zone at intermediate radii, and isophotal elongation and twists that are coincident with breaks in the brightness profile. The two satellites, M32 and NGC 205, display most of these features consistently across the B and I bands, which is strongly suggestive of tidal interaction and probable stripping by M31. We discuss what these observed features can tell us about the satellites' orbital parameters and histories. Specifically, M32 is found to be on a highly eccentric orbit and away from pericenter. Investigating M32's unusual combination of high surface brightness and low luminosity (the hallmark of compact ellipticals), we make empirical estimates of the galaxy's intrinsic properties and conclude that it is not likely to be the residual core of a tidally stripped normal elliptical galaxy, as has been suggested, but rather that its precursor was intrinsically compact.

X-Ray Binaries and Globular Clusters in Elliptical Galaxies

The X-ray emission from normal elliptical galaxies has two major components: soft emission from diffuse gas and harder emission from populations of accreting (low-mass) stellar X-ray binaries (LMXB). If LMXB populations are tied to the field stellar populations in galaxies, their total X-ray luminosities should be proportional to the optical luminosities of galaxies. However, recent ASCA and Chandra X-ray observations show that the global luminosities of LMXB components in ellipticals exhibit significant scatter at a given optical luminosity. This scatter may reflect a range of evolutionary stages among LMXB populations in ellipticals of different ages. If so, the ratio of the global LMXB X-ray luminosity to the galactic optical luminosity, L_LMXB/L_opt, may be used to determine when the bulk of stars were formed in individual ellipticals. To test this, we compare variations in L_LMXB/L_opt for LMXB populations in ellipticals to optically-derived estimates of stellar ages in the same galaxies. We find no correlation, implying that L_LMXB/L_opt variations are not good age indicators for ellipticals. Alternatively, LMXBs may be formed primarily in globular clusters (through stellar tidal interactions), rather than in the stellar fields of galaxies. Since elliptical galaxies exhibit a wide range of globular cluster populations for a given galaxian luminosity, this may induce a dispersion in the LMXB populations of ellipticals with similar optical luminosities. Indeed, we find that L_LMXB/L_opt ratios for LMXB populations are strongly correlated with the specific globular cluster frequencies in elliptical galaxies. This suggests that most LMXBs were formed in globular clusters.

Lyman Break Galaxies: Are They Young Spheroids?

We have compared the results from a model for the chemical evolution of an elliptical galaxy with initial luminous mass of 2x10^10 M_sun and effective radius of 2 kpc with the recent abundance determinations for the Lyman-break galaxy MS 1512-cB58 at a redshift z=2.7276. After correcting the iron abundance determination for the presence of dust we concluded that the observed [Si/Fe], [Mg/Fe], [N/Fe] are consistent with our model when a galactic age between 20 and 35 Myr is assumed. Moreover, the [N/O] ratio also suggests the same age. This age is in very good agreement with other independent studies based on the analysis of the spectral energy distribution suggesting that this object is younger than 35 Myr. Therefore, we suggest that MS 1512-cB58 is a truly young normal elliptical galaxy experiencing its main episode of star formation and galactic wind.

Globular Cluster Systems in Elliptical Galaxies of Coma

Globular cluster systems of 17 elliptical galaxies have been studied in the Coma cluster of galaxies. Surface-brightness fluctuations have been used to determine total populations of globular clusters and specific frequency (S_N) has been evaluated for each individual galaxy. Enormous differences in S_N between similar galaxies are found. In particular, S_N results vary by an order of magnitude from galaxy to galaxy. Extreme cases are the following: a) at the lower end of the range, NGC 4673 has S_N = 1.0 +/- 0.4, a surprising value for an elliptical galaxy, but typical for spiral and irregular galaxies; b) at the upper extreme, MCG +5 -31 -063 has S_N = 13.0 +/- 4.2 and IC 4051 S_N = 12.7 +/- 3.2, and are more likely to belong to supergiant cD galaxies than to normal elliptical galaxies. Furthermore, NGC 4874, the central supergiant cD galaxy of the Coma cluster, also exhibits a relatively high specific frequency (S_N = 9.0 +/- 2.2). The other galaxies studied have S_N in the range [2, 7], the mean value being S_N = 5.1. No single scenario seems to account for the observed specific frequencies, so the history of each galaxy must be deduced individually by suitably combining the different models (in situ, mergers, and accretions). The possibility that Coma is formed by several subgroups is also considered. If only the galaxies of the main subgroup defined by Gurzadyan & Mazure (2001) are used, a trend in S_N arises in the sense of S_N being bigger in higher density regions. This result needs further confirmation.

The Chandra Deep Field North Survey. X. X-Ray Emission from Very Red Objects

The multi-wavelength properties of Very Red Objects (VROs; I-K>=4) are largely unknown as many of these sources are optically faint (I>=24) and undetected at most wavelengths. Here we provide constraints on the X-ray properties of VROs using the 1 Ms Chandra exposure of an 8.4'x8.4' region within the Hawaii Flanking-Field area containing the HDF-N. We find that VROs detected in the hard band (2-8 keV) have flat X-ray spectral slopes (Gamma ~ 0.9) and X-ray properties consistent with those expected from luminous obscured AGN. The fraction of such sources in the K 1.4), and the X-ray emission from these sources is consistent with that expected from less energetic processes (i.e., star formation, low-luminosity AGN activity, normal elliptical galaxy emission); star-formation and low-luminosity AGN activity scenarios are favored in those sources with irregular optical morphologies. Stacking analyses of the X-ray emission from VROs not individually detected at X-ray energies yield significant detections (>=99% confidence) in the soft band and the full band (0.5-8 keV). We find this X-ray emission is produced predominantly by the optically brightest VROs. The simplest explanation of this result is that we have detected the average X-ray emission from non-active VROs with low X-ray-to-optical flux ratios [log(FX/FI) ~ -2]; this is consistent with that expected if the majority of these VROs are ~ M* elliptical galaxies. A number of VROs are also detected with mid-IR (15um) and radio emission, and we provide constraints on the nature of this emission.