arXiv subjects

Sean L. McGee

Publications and source records attributed to Sean L. McGee.

At least 37 records · Page 2Linked to original sources

arXiv2019

The Rest-frame $H$-band Luminosity Function of Red Sequence Galaxies in Clusters at $1.0 < z < 1.3$

We present results on the rest-frame $H$-band luminosity functions (LF) of red sequence galaxies in seven clusters at 1.0 < z < 1.3 from the Gemini Observations of Galaxies in Rich Early Environments Survey (GOGREEN). Using deep GMOS-z' and IRAC $3.6 μ$m imaging, we identify red sequence galaxies and measure their LFs down to $M_{H} \sim M_{H}^{*} + (2.0 - 3.0)$. By stacking the entire sample, we derive a shallow faint end slope of $ α\sim -0.35^{+0.15}_{-0.15} $ and $ M_{H}^{*} \sim -23.52^{+0.15}_{-0.17} $, suggesting that there is a deficit of faint red sequence galaxies in clusters at high redshift. By comparing the stacked red sequence LF of our sample with a sample of clusters at z~0.6, we find an evolution in the faint end of the red sequence over the ~2.6 Gyr between the two samples, with the mean faint end red sequence luminosity growing by more than a factor of two. The faint-to-luminous ratio of our sample ($0.78^{+0.19}_{-0.15}$) is consistent with the trend of decreasing ratio with increasing redshift as proposed in previous studies. A comparison with the field shows that the faint-to-luminous ratios in clusters are consistent with the field at z~1.15 and exhibit a stronger redshift dependence. Our results support the picture that the build up of the faint red sequence galaxies occurs gradually over time and suggest that faint cluster galaxies, similar to bright cluster galaxies, experience the quenching effect induced by environment already at z~1.15.

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arXiv2019

The case for a 'sub-millimeter SDSS': a 3D map of galaxy evolution to z~10

The Sloan Digital Sky Survey (SDSS) was revolutionary because of the extraordinary breadth and ambition of its optical imaging and spectroscopy. We argue that a 'sub-millimeter SDSS' - a sensitive large-area imaging+spectroscopic survey in the sub-mm window - will revolutionize our understanding of galaxy evolution in the early Universe. By detecting the thermal dust continuum emission and atomic and molecular line emission of galaxies out to z~10 it will be possible to measure the redshifts, star formation rates, dust and gas content of hundreds of thousands of high-z galaxies down to ~L*. Many of these galaxies will have counterparts visible in the deep optical imaging of the Large Synoptic Survey Telescope. This 3D map of galaxy evolution will span the peak epoch of galaxy formation all the way back to cosmic dawn, measuring the co-evolution of the star formation rate density and molecular gas content of galaxies, tracking the production of metals and charting the growth of large-scale structure.

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arXiv2019

Disruption of satellite galaxies in simulated groups and clusters: the roles of accretion time, baryons, and pre-processing

We investigate the disruption of group and cluster satellite galaxies with total mass (dark matter plus baryons) above 10^10 M_sun in the Hydrangea simulations, a suite of 24 high-resolution cosmological hydrodynamical zoom-in simulations based on the EAGLE model. The simulations predict that ~50 per cent of satellites survive to redshift z = 0, with higher survival fractions in massive clusters than in groups and only small differences between baryonic and pure N-body simulations. For clusters, up to 90 per cent of galaxy disruption occurs in lower-mass sub-groups (i.e., during pre-processing); 96 per cent of satellites in massive clusters that were accreted at z < 2 and have not been pre-processed survive. Of those satellites that are disrupted, only a few per cent merge with other satellites, even in low-mass groups. The survival fraction changes rapidly from less than 10 per cent of those accreted at high z to more than 90 per cent at low z. This shift, which reflects faster disruption of satellites accreted at higher z, happens at lower z for more massive galaxies and those accreted onto less massive haloes. The disruption of satellite galaxies is found to correlate only weakly with their pre-accretion baryon content, star formation rate, and size, so that surviving galaxies are nearly unbiased in these properties. These results suggest that satellite disruption in massive haloes is uncommon, and that it is predominantly the result of gravitational rather than baryonic processes.

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arXiv2019

LoCuSS: Scaling relations between galaxy cluster mass, gas, and stellar content

We present a simultaneous analysis of galaxy cluster scaling relations between weak-lensing mass and multiple cluster observables, across a wide range of wavelengths, that probe both gas and stellar content. Our new hierarchical Bayesian model simultaneously considers the selection variable alongside all other observables in order to explicitly model intrinsic property covariance and account for selection effects. We apply this method to a sample of 41 clusters at $0.15<z<0.30$, with a well-defined selection criteria based on RASS X-ray luminosity, and observations from Chandra / XMM, SZA, Planck, UKIRT, SDSS and Subaru. These clusters have well-constrained weak-lensing mass measurements based on Subaru / Suprime-Cam observations, which serve as the reference masses in our model. We present 30 scaling relation parameters for 10 properties. All relations probing the intracluster gas are slightly shallower than self-similar predictions, in moderate tension with prior measurements, and the stellar fraction decreases with mass. K-band luminosity has the lowest intrinsic scatter with a 95th percentile of 0.16, while the lowest scatter gas probe is gas mass with a fractional intrinsic scatter of $0.16 \pm 0.03$. We find no distinction between the core-excised X-ray or high-resolution Sunyaev-Zel'dovich relations of clusters of different central entropy, but find with modest significance that higher entropy clusters have higher stellar fractions than their lower entropy counterparts. We also report posterior mass estimates from our likelihood model.

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arXiv2018

The XXL Survey: XXIX. GMRT 610 MHz continuum observations

We present the 25 square-degree GMRT-XXL-N 610 MHz radio continuum survey, conducted at 50~cm wavelength with the Giant Metrewave Radio Telescope (GMRT) towards the XXL Northern field (XXL-N). We combined previously published observations of the XMM-Large Scale Structure (XMM-LSS) field, located in the central part of XXL-N, with newly conducted observations towards the remaining XXL-N area, and imaged the combined data-set using the Source Peeling and Atmospheric Modeling ({\sc SPAM}) pipeline. The final mosaic encompasses a total area of $30.4$ square degrees, with ${\rm rms}<150~μ$Jy/beam over 60\% of the area. The ${\rm rms}$ achieved in the inner 9.6 square degree area, enclosing the XMM-LSS field, is about $200~μ$Jy/beam, while that over the outer 12.66 square degree area (which excludes the noisy edges) is about $45~μ$Jy/beam. The resolution of the final mosaic is 6.5 arcsec. We present a catalogue of 5\,434 sources detected at $\geq7\times {\rm rms}$. We verify, and correct the reliability of, the catalog in terms of astrometry, flux, and false detection rate. Making use of the (to date) deepest radio continuum survey over a relatively large (2 square degree) field, complete at the flux levels probed by the GMRT-XXL-N survey, we also assess the survey's incompleteness as a function of flux density. The radio continuum sensitivity reached over a large field with a wealth of multi-wavelength data available makes the GMRT-XXL-N 610 MHz survey an important asset for studying the physical properties, environments and cosmic evolution of radio sources, in particular radio-selected active galactic nuclei (AGN).

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arXiv2017

LoCuSS: Pre-processing in galaxy groups falling into massive galaxy clusters at z=0.2

We report direct evidence of pre-processing of the galaxies residing in galaxy groups falling into galaxy clusters drawn from the Local Cluster Substructure Survey (LoCuSS). 34 groups have been identified via their X-ray emission in the infall regions of 23 massive ($\rm \langle M_{200}\rangle = 10^{15}\,M_{\odot}$) clusters at $0.15<z<0.3$. Highly complete spectroscopic coverage combined with 24 $\rmμ$m imaging from Spitzer allows us to make a consistent and robust selection of cluster and group members including star forming galaxies down to a stellar mass limit of $\rm M_{\star} = 2\times10^{10}\,M_{\odot}$. The fraction $\rm f_{SF}$ of star forming galaxies in infalling groups is lower and with a flatter trend with respect to clustercentric radius when compared to the rest of the cluster galaxy population. At $\rm R\approx1.3\,r_{200}$ the fraction of star forming galaxies in infalling groups is half that in the cluster galaxy population. This is direct evidence that star formation quenching is effective in galaxies already prior to them settling in the cluster potential, and that groups are favourable locations for this process.

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arXiv2017

Galaxy cluster luminosities and colours, and their dependence on cluster mass and merger state

We study a sample of 19 galaxy clusters in the redshift range $0.15<z<0.30$ with highly complete spectroscopic membership catalogues (to $K < K^{\ast}(\rm z)+1.5$) from the Arizona Cluster Redshift Survey (ACReS); individual weak-lensing masses and near-infrared data from the Local Cluster Substructure Survey (LoCuSS); and optical photometry from the Sloan Digital Sky Survey (SDSS). We fit the scaling relations between total cluster luminosity in each of six bandpasses (${\it grizJK}$) and cluster mass, finding cluster luminosity to be a promising mass proxy with low intrinsic scatter $σ_{\ln L|M}$ of only $\sim 10-20$ per cent for all relations. At fixed overdensity radius, the intercept increases with wavelength, consistent with an old stellar population. The scatter and slope are consistent across all wavelengths, suggesting that cluster colour is not a function of mass. Comparing colour with indicators of the level of disturbance in the cluster, we find a narrower variety in the cluster colours of 'disturbed' clusters than of 'undisturbed' clusters. This trend is more pronounced with indicators sensitive to the initial stages of a cluster merger, e.g. the Dressler Schectman statistic. We interpret this as possible evidence that the total cluster star formation rate is 'standardised' in mergers, perhaps through a process such as a system-wide shock in the intracluster medium.

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arXiv2017

Gemini Observations of Galaxies in Rich Early Environments (GOGREEN) I: Survey Description

We describe a new Large Program in progress on the Gemini North and South telescopes: Gemini Observations of Galaxies in Rich Early Environments (GOGREEN). This is an imaging and deep spectroscopic survey of 21 galaxy systems at $1 10$ in halo mass. The scientific objectives include measuring the role of environment in the evolution of low-mass galaxies, and measuring the dynamics and stellar contents of their host haloes. The targets are selected from the SpARCS, SPT, COSMOS and SXDS surveys, to be the evolutionary counterparts of today's clusters and groups. The new red-sensitive Hamamatsu detectors on GMOS, coupled with the nod-and-shuffle sky subtraction, allow simultaneous wavelength coverage over $λ\sim 0.6$--$1.05μ$m, and this enables a homogeneous and statistically complete redshift survey of galaxies of all types. The spectroscopic sample targets galaxies with AB magnitudes $z^{\prime}<24.25$ and [3.6]$μ$m$<22.5$, and is therefore statistically complete for stellar masses $M_\ast\gtrsim10^{10.3}M_\odot$, for all galaxy types and over the entire redshift range. Deep, multiwavelength imaging has been acquired over larger fields for most systems, spanning $u$ through $K$, in addition to deep IRAC imaging at 3.6$μ$m. The spectroscopy is $\sim 50$ per cent complete as of semester 17A, and we anticipate a final sample of $\sim 500$ new cluster members. Combined with existing spectroscopy on the brighter galaxies from GCLASS, SPT and other sources, GOGREEN will be a large legacy cluster and field galaxy sample at this redshift that spectroscopically covers a wide range in stellar mass, halo mass, and clustercentric radius.

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arXiv2017

The Hydrangea simulations: galaxy formation in and around massive clusters

We introduce the Hydrangea simulations, a suite of 24 cosmological hydrodynamic zoom-in simulations of massive galaxy clusters (M_200c = 10^14-10^15 M_Sun) with baryon particle masses of ~10^6 M_Sun. Designed to study the impact of the cluster environment on galaxy formation, they are a key part of the `Cluster-EAGLE' project (Barnes et al. 2017). They use a galaxy formation model developed for the EAGLE project, which has been shown to yield both realistic field galaxies and hot gas fractions of galaxy groups consistent with observations. The total stellar mass content of the simulated clusters agrees with observations, but central cluster galaxies are too massive, by up to 0.6 dex. Passive satellite fractions are higher than in the field, and at stellar masses Mstar > 10^10 M_Sun this environmental effect is quantitatively consistent with observations. The predicted satellite stellar mass function matches data from local cluster surveys. Normalized to total mass, there are fewer low-mass (Mstar < 10^10 M_Sun) galaxies within the virial radius of clusters than in the field, primarily due to star formation quenching. Conversely, the simulations predict an overabundance of massive galaxies in clusters compared to the field that persists to their far outskirts (> 5r_200c). This is caused by a significantly increased stellar mass fraction of (sub-)haloes in the cluster environment, by up to ~0.3 dex even well beyond r_200c. Haloes near clusters are also more concentrated than equally massive field haloes, but these two effects are largely uncorrelated.

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arXiv2016

The origin of the enhanced metallicity of satellite galaxies

Observations of galaxies in the local Universe have shown that both the ionized gas and the stars of satellites are more metal-rich than of equally massive centrals. To gain insight into the connection between this metallicity enhancement and other differences between centrals and satellites, such as their star formation rates, gas content, and growth history, we study the metallicities of >3600 galaxies with M_star > 10^10 M_sun in the cosmological hydrodynamical EAGLE 100 Mpc `Reference' simulation, including ~1500 in the vicinity of galaxy groups and clusters (M_200 >= 10^13 M_sun). The simulation predicts excess gas and stellar metallicities in satellites consistent with observations, except for stellar metallicities at M_star <~ 10^10.2 M_sun where the predicted excess is smaller than observed. The exact magnitude of the effect depends on galaxy selection, aperture, and on whether the metallicity is weighted by stellar mass or luminosity. The stellar metallicity excess in clusters is also sensitive to the efficiency scaling of star formation feedback. We identify stripping of low-metallicity gas from the galaxy outskirts, as well as suppression of metal-poor inflows towards the galaxy centre, as key drivers of the enhancement of gas metallicity. Stellar metallicities in satellites are higher than in the field as a direct consequence of the more metal-rich star forming gas, whereas stripping of stars and suppressed stellar mass growth, as well as differences in accreted vs. in-situ star formation between satellites and the field, are of secondary importance.

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arXiv2015

Evidence for a change in the dominant satellite galaxy quenching mechanism at z=1

We present an analysis of galaxies in groups and clusters at $0.8 10^{10.3}M_\odot$, we find $f_{\rm convert}\sim 0.4$ in the groups and $\sim 0.6$ in the clusters, similar to comparable measurements at $z=0$. This means the time between first accretion into a more massive halo and final star formation quenching is $t_p\sim 2$ Gyr. This is substantially longer than the estimated time required for a galaxy's star formation rate to become zero once it starts to decline, suggesting there is a long delay time during which little differential evolution occurs. In contrast with local observations we find evidence that this delay timescale may depend on stellar mass, with $t_p$ approaching $t_{\rm Hubble}$ for $M_{\rm star}\sim 10^{9.5}M_\odot$. The result suggests that the delay time must not only be much shorter than it is today, but may also depend on stellar mass in a way that is not consistent with a simple evolution in proportion to the dynamical time. Instead, we find the data are well-matched by a model in which the decline in star formation is due to "overconsumption", the exhaustion of a gas reservoir through star formation and expulsion via modest outflows in the absence of cosmological accretion. Dynamical gas removal processes, which are likely dominant in quenching newly accreted satellites today, may play only a secondary role at $z=1$.

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arXiv2015

Evidence for the inside-out growth of the stellar mass distribution in galaxy clusters since z~1

We study the radial number density and stellar mass density distributions of satellite galaxies in a sample of 60 massive clusters at 0.04<z<0.26 selected from the Multi-Epoch Nearby Cluster Survey (MENeaCS) and the Canadian Cluster Comparison Project (CCCP). In addition to ~10,000 spectroscopically confirmed member galaxies, we use deep ugri-band imaging to estimate photometric redshifts and stellar masses, and then statistically subtract fore-, and background sources using data from the COSMOS survey. We measure the galaxy number density and stellar mass density distributions in logarithmically spaced bins over 2 orders of magnitude in radial distance from the BCGs. For projected distances in the range 0.1<R/R200<2.0, we find that the stellar mass distribution is well-described by an NFW profile with a concentration of c=2.03+/-0.20. However, at smaller radii we measure a significant excess in the stellar mass in satellite galaxies of about $10^{11}$ Msun per cluster, compared to these NFW profiles. We do obtain good fits to generalized NFW profiles with free inner slopes, and to Einasto profiles. To examine how clusters assemble their stellar mass component over cosmic time, we compare this local sample to the GCLASS cluster sample at z~1, which represents the approximate progenitor sample of the low-z clusters. This allows for a direct comparison, which suggests that the central parts (R<0.4 Mpc) of the stellar mass distributions of satellites in local galaxy clusters are already in place at z~1, and contain sufficient excess material for further BCG growth. Evolving towards z=0, clusters appear to assemble their stellar mass primarily onto the outskirts, making them grow in an inside-out fashion.

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arXiv2014

The GEEC2 spectroscopic survey of Galaxy Groups at $0.8<z<1$

We present the data release of the Gemini-South GMOS spectroscopy in the fields of 11 galaxy groups at $0.8 50$ per cent complete for galaxies within the virial radius, and with stellar mass $M_{\rm star}>10^{10.3}M_\odot$. Including galaxies with photometric redshifts we have an effective sample size of $\sim 400$ galaxies within the virial radii of these groups. We present group velocity dispersions, dynamical and stellar masses. Combining with the GCLASS sample of more massive clusters at the same redshift we find the total stellar mass is strongly correlated with the dynamical mass, with $\log{M_{200}}=1.20\left(\log{M_{\rm star}}-12\right)+14.07$. This stellar fraction of $~\sim 1$ per cent is lower than predicted by some halo occupation distribution models, though the weak dependence on halo mass is in good agreement. Most groups have an easily identifiable most massive galaxy (MMG) near the centre of the galaxy distribution, and we present the spectroscopic properties and surface brightness fits to these galaxies. The total stellar mass distribution in the groups, excluding the MMG, compares well with an NFW profile with concentration $4$, for galaxies beyond $\sim 0.2R_{200}$. This is more concentrated than the number density distribution, demonstrating that there is some mass segregation.

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arXiv2014

Overconsumption, outflows and the quenching of satellite galaxies

The baryon cycle of galaxies is a dynamic process involving the intake, consumption and ejection of vast quantities of gas. In contrast, the conventional picture of satellite galaxies has them methodically turning a large gas reservoir into stars until this reservoir is forcibly removed due to external ram pressure. This picture needs revision. Our modern understanding of the baryon cycle suggests that in some regimes the simple interruption of the fresh gas supply may quench satellite galaxies long before stripping events occur, a process we call overconsumption. We compile measurements from the literature of observed satellite quenching times at a range of redshifts to determine if satellites are principally quenched through orbit-based gas stripping events -- either direct stripping of the disk (ram pressure stripping) or the extended gas halo (strangulation) -- or from internally-driven star formation outflows via overconsumption. The observed timescales show significant deviation from the evolution expected for gas stripping mechanisms and suggest that either ram pressure stripping is much more efficient at high redshift, or that secular outflows quench satellites before orbit-based stripping occurs. Given the strong redshift evolution of star formation rates, at high redshift (z > 1.5) even moderate outflow rates will lead to extremely short quenching times with the expectation that such satellites will be quenched almost immediately following the cessation of cosmological inflow, regardless of stripping events. Observations of high redshift satellites give an indirect but sensitive measure of the outflow rate with current measurements suggesting that outflows are no larger than 2.5 times the star formation rate for galaxies with a stellar mass of 10^{10.5} solar masses.

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arXiv2014

The Phase Space and Stellar Populations of Cluster Galaxies at z ~ 1: Simultaneous Constraints on the Location and Timescale of Satellite Quenching

We investigate the velocity vs. position phase space of z ~ 1 cluster galaxies using a set of 424 spectroscopic redshifts in 9 clusters drawn from the GCLASS survey. Dividing the galaxy population into three categories: quiescent, star-forming, and poststarburst, we find that these populations have distinct distributions in phase space. Most striking are the poststarburst galaxies, which are commonly found at small clustercentric radii with high clustercentric velocities, and appear to trace a coherent ``ring" in phase space. Using several zoom simulations of clusters we show that the coherent distribution of the poststarbursts can be reasonably well-reproduced using a simple quenching scenario. Specifically, the phase space is best reproduced if satellite quenching occurs on a rapid timescale (0.1 < tau_{Q} < 0.5 Gyr) after galaxies make their first passage of R ~ 0.5R_{200}, a process that takes a total time of ~ 1 Gyr after first infall. We compare this quenching timescale to the timescale implied by the stellar populations of the poststarburst galaxies and find that the poststarburst spectra are well-fit by a rapid quenching (tau_{Q} = 0.4^{+0.3}_{-0.4} Gyr) of a typical star-forming galaxy. The similarity between the quenching timescales derived from these independent indicators is a strong consistency check of the quenching model. Given that the model implies satellite quenching is rapid, and occurs well within R_{200}, this would suggest that ram-pressure stripping of either the hot or cold gas component of galaxies are the most plausible candidates for the physical mechanism. The high cold gas consumption rates at z ~ 1 make it difficult to determine if hot or cold gas stripping is dominant; however, measurements of the redshift evolution of the satellite quenching timescale and location may be capable of distinguishing between the two.

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arXiv2013

Star Formation and Environmental Quenching of GEEC2 Group Galaxies at z~1

We present new analysis from the GEEC2 spectroscopic survey of galaxy groups at $0.8<z<1$. Our previous work revealed an intermediate population between the star-forming and quiescent sequences and a strong environmental dependence in the fraction of quiescent galaxies. Only $\sim5$ per cent of star-forming galaxies in both the group and field sample show a significant enhancement in star formation, which suggests that quenching is the primary process in the transition from the star-forming to the quiescent state. To model the environmental quenching scenario, we have tested the use of different exponential quenching timescales and delays between satellite accretion and the onset of quenching. We find that with no delay, the quenching timescale needs to be long in order to match the observed quiescent fraction, but then this model produces too many intermediate galaxies. Fixing a delay time of 3 Gyr, as suggested from the local universe, produces too few quiescent galaxies. The observed fractions are best matched with a model that includes a delay that is proportional to the dynamical time and a rapid quenching timescale ($\sim0.25$ Gyr), but this model also predicts intermediate galaxies Hδ strength higher than that observed. Using stellar synthesis models, we have tested other scenarios, such as the rejuvenation of star formation in early-type galaxies and a portion of quenched galaxies possessing residual star formation. If environment quenching plays a role in the GEEC2 sample, then our work suggests that only a fraction of intermediate galaxies may be undergoing this transition and that quenching occurs quite rapidly in satellite galaxies ($\lesssim0.25$ Gyr).

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arXiv2013

The stellar mass function and efficiency of galaxy formation with a varying initial mass function

Several recent observational studies have concluded that the initial mass function (IMF) of stars varies systematically with galaxy properties such as velocity dispersion. In this paper, we investigate the effect of linking the circular velocity of galaxies, as determined from the Fundamental Plane and Tully-Fisher relations, to the slope of the IMF with parameterizations guided by several of these studies. For each empirical relation, we generate stellar masses of ~600,000 SDSS galaxies at z ~ 0.1, by fitting the optical photometry to large suites of synthetic stellar populations that sample the full range of galaxy parameters. We generate stellar mass functions and examine the stellar-to-halo mass relations using sub-halo abundance matching. At the massive end, the stellar mass functions become a power law, instead of the familiar exponential decline. As a result, it is a generic feature of these models that the central galaxy stellar-to-halo mass relation is significantly flatter at high masses (slope ~ -0.3 to -0.4) than in the case of a universal IMF (slope ~ -0.6). We find that regardless of whether the IMF varies systematically in all galaxies or just early types, there is still a well-defined peak in the central stellar-to-halo mass ratio at halo masses of ~ 10E12 solar masses. In general, the IMF variations explored here lead to significantly higher integrated stellar densities if the assumed dependence on circular velocity applies to all galaxies, including late-types; in fact the more extreme cases can be ruled out, as they imply an unphysical situation in which the stellar fraction exceeds the universal baryon fraction.

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arXiv2013

The strong environmental dependence of black hole scaling relations

We investigate how the scaling relations between central black hole mass (Mbh) and host galaxy properties (velocity dispersion, bulge stellar mass and bulge luminosity) depend on the large scale environment. For each of a sample of 69 galaxies with dynamical black hole measurements we compile four environmental measures (nearest neighbor distance, fixed aperture number density, total halo mass, and central/satellite). We find that central and satellite galaxies follow distinctly separate scalings in each of the three relations we have examined. The Mbh - sigma relation of central galaxies is significantly steeper (6.38 +/- 0.49) than that of satellite galaxies (4.91 +/- 0.49), but has a similar intercept. This behavior remains even after restricting to a sample of only early type galaxies or after removing the 8 brightest cluster galaxies. The Mbh - sigma relation shows more modest differences when splitting the sample based on the other environmental indicators, suggesting that they are driven by the underlying satellite/central fractions. Separate relations for centrals and satellites are also seen in the power law scaling between black hole mass and bulge stellar mass or bulge luminosity. We suggest that gas rich, low mass galaxies undergo a period of rapid black hole growth in the process of becoming satellites. If central galaxies on the current Mbh - sigma relation are representative progenitors of the satellite population, the observations imply that a sigma = 120 km/s galaxy must nearly triple its central black hole mass. The elevated black hole masses of massive central galaxies are then a natural consequence of the accretion of satellites.

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