We marginalize over solutions to the spherical Jeans equation to obtain mass profiles for five An... more We marginalize over solutions to the spherical Jeans equation to obtain mass profiles for five Andromeda dwarf spheroidals (dSphs). We analyze stellar kinematics of And I, II, III, X, and XIV, obtained from Keck/DEIMOS spectroscopy, and we compare the mass within 300 parsecs to the Milky Way dSphs.
We summarize recent developments in the study of the origin of halo spin profiles and preliminary... more We summarize recent developments in the study of the origin of halo spin profiles and preliminary implications on disk formation. The specific angular-momentum distributions within halos in N-body simulations match a universal shape, M(<j) ∝ j/(j0+j). It is characterized by a power law over most of the mass, and one shape parameter in addition to the spin parameter lambda. The
We investigate the clustering properties of high-redshift galaxies within three competing scenari... more We investigate the clustering properties of high-redshift galaxies within three competing scenarios for assigning luminous galaxies to dark matter halos from N-body simulations: a one galaxy per massive halo model, a quiescent star formation model, and a collisional starburst model. We compare these models to observations of Lyman-Break galaxies at z~3$ With current data and the simple statistic used here,
We introduce a comprehensive analysis of multi-epoch stellar line-of-sight velocities to determin... more We introduce a comprehensive analysis of multi-epoch stellar line-of-sight velocities to determine the intrinsic velocity dispersion of the ultrafaint satellites of the Milky Way. Our method includes a simultaneous Bayesian analysis of both membership probabilities and the contribution of binary orbital motion to the observed velocity dispersion within a 14-parameter likelihood. We apply our method to the Segue 1 dwarf
Substructure in LCDM provides a number of interesting puzzles. While the missing satellites probl... more Substructure in LCDM provides a number of interesting puzzles. While the missing satellites problem is well-studied, there are suggestions of an opposite problem on the bright end. Subhalos large enough to host luminous satellites are uncommon, so we investigate whether the existence of the Large Magellanic Cloud (LMC) orbiting the Galaxy is a challenge for LCDM. We construct a volume
There is a vast menagerie of plausible candidates for the constituents of dark matter, both withi... more There is a vast menagerie of plausible candidates for the constituents of dark matter, both within and beyond extensions of the Standard Model of particle physics. Each of these candidates may have scattering (and other) cross section properties that are consistent with the dark matter abundance, BBN, and the most scales in the matter power spectrum; but which may have vastly different behavior at sub-galactic "cutoff" scales, below which dark matter density fluctuations are smoothed out. The only way to quantitatively measure the power spectrum behavior at sub-galactic scales at distances beyond the local universe, and indeed over cosmic time, is through probes available in multiply imaged strong gravitational lenses. Gravitational potential perturbations by dark matter substructure encode information in the observed relative magnifications, positions, and time delays in a strong lens. Each of these is sensitive to a different moment of the substructure mass function and ...
We propose to resolve the halo stellar populations of four nearby, massive disk galaxies (NGC 240... more We propose to resolve the halo stellar populations of four nearby, massive disk galaxies (NGC 2403, M81, M83, and NGC 4244) using deep observations with MegaCam on the MMT and IMACS on Magellan-I. These observations will provide star counts and color-magnitude diagrams ~1.5 magnitudes below the tip of the Red Giant Branch (RGB) of the halos of each galaxy. We will measure the metallicity distribution functions and stellar density profiles from star counts down to very low average surface brightnesses, equivalent to ~29.5 V-magnitude per square arcsec. Our targets are part of our HST SNAP program and cover a range in galaxy mass, luminosity, and morphology. As function of these galaxy properties this survey will provide: The first systematic study of the radial and isophotal shapes of diffuse stellar halos. A comprehensive analysis of halo metallicity distributions as a function of galaxy type and position within the galaxy. A sensitive search for tidal streams and halo substructure....
Environmental statistics provide a necessary means of comparing the properties of galaxies in dif... more Environmental statistics provide a necessary means of comparing the properties of galaxies in different environments and a vital test of models of galaxy formation within the prevailing, hierarchical, LCDM cosmological model. We explore counts-in-cylinders, a common statistic defined as the number of companions of a particular galaxy found within a given projected radius and redshift interval. Galaxy distributions with the
We use a volume-limited spectroscopic sample of isolated galaxies in the Sloan Digital Sky Survey... more We use a volume-limited spectroscopic sample of isolated galaxies in the Sloan Digital Sky Survey to investigate the frequency and radial distribution of luminous (M{sub r} â< -18.3) satellites like the Large Magellanic Cloud (LMC) around âL{sub *} Milky Way (MW) analogs and compare our results object-by-object to ÎCDM predictions based on abundance matching in simulations. We show that 12%
Monthly Notices of The Royal Astronomical Society, 2011
We show that dissipationless Lambda cold dark matter simulations predict that the majority of the... more We show that dissipationless Lambda cold dark matter simulations predict that the majority of the most massive subhaloes of the Milky Way are too dense to host any of its bright satellites (LV > 105 L&sun;). These dark subhaloes have peak circular velocities at infall of Vinfall= 30-70 km s-1 and infall masses of (0.2-4) × 1010 M&sun;. Unless the
We use a volume-limited spectroscopic sample of isolated galaxies in the Sloan Digital Sky Survey... more We use a volume-limited spectroscopic sample of isolated galaxies in the Sloan Digital Sky Survey to investigate the frequency and radial distribution of luminous (M{sub r} {approx}< -18.3) satellites like the Large Magellanic Cloud (LMC) around {approx}L{sub *} Milky Way (MW) analogs and compare our results object-by-object to {Lambda}CDM predictions based on abundance matching in simulations. We show that 12% of MW-like galaxies host an LMC-like satellite within 75 kpc (projected), and 42% within 250 kpc (projected). This implies {approx}10% have a satellite within the distance of the LMC, and {approx}40% of L{sub *} galaxies host a bright satellite within the virialized extent of their dark matter halos. Remarkably, the simulation reproduces the observed frequency, radial dependence, velocity distribution, and luminosity function of observed secondaries exceptionally well, suggesting that {Lambda}CDM provides an accurate reproduction of the observed universe to galaxies as fai...
We use a volume-limited spectroscopic sample of isolated galaxies in the Sloan Digital Sky Survey... more We use a volume-limited spectroscopic sample of isolated galaxies in the Sloan Digital Sky Survey (SDSS) to investigate the frequency and radial distribution of luminous (M_r <~ -18.3) satellites like the Large Magellanic Cloud (LMC) around ~L* Milky Way analogs and compare our results object-by-object to LCDM predictions based on abundance matching in simulations. We show that 12% of Milky Way-like galaxies host an LMC-like satellite within 75 kpc (projected), and 42 % within 250 kpc (projected). This implies ~10% have a satellite within the distance of the LMC, and ~40% of L* galaxies host a bright satellite within the virialized extent of their dark matter halos. Remarkably, the simulation reproduces the observed frequency, radial dependence, velocity distribution, and luminosity function of observed secondaries exceptionally well, suggesting that LCDM provides an accurate reproduction of the observed Universe to galaxies as faint as L~10^9 Lsun on ~50 kpc scales. When stacked...
We present five serendipitous spectroscopic interacting Lyman break galaxy (LBG) pairs and six ca... more We present five serendipitous spectroscopic interacting Lyman break galaxy (LBG) pairs and six candidate pairs from our z 3 Keck survey. All galaxies in the pairs exhibit Lyalpha in emission and we show that this is not a selection effect. A complete investigation of all LBG spectroscopic-photometric pairs with at least one spectroscopically confirmed component indicates an abundance of Lyalpha emitting LBGs (eLBGs) with projected separations of < 50 h-1 kpc, physical, with eLBGs comprising all pairs with < 20 h-1 kpc separations. We present a new broadband technique able to select very large numbers of LBGs based on their Lyalpha EW and associated features. We successfully test this technique with CFHTLS Deep data and 200 Keck spectra and show that the Lyalpha emitter (LAE) population is a natural extension of the LBG population. As a result, this technique can efficiently select very large numbers of LAEs over large defined redshift paths using simple broadband criteria. In ...
We study the formation of fifty-three galaxy cluster-size dark matter halos formed within a pair ... more We study the formation of fifty-three galaxy cluster-size dark matter halos formed within a pair of cosmological LCDM N-body simulations, and track the accretion histories of cluster subhalos with masses large enough to host 0.1L* galaxies. By associating subhalos with cluster galaxies, we find the majority of galaxies in clusters experience no pre-processing in the group environment prior to their accretion into the cluster. On average, ~70% of cluster galaxies fall into the cluster potential directly from the field, with no luminous companions in their host halos at the time of accretion; and less than ~12% are accreted as members of groups with five or more galaxies. Moreover, we find that cluster galaxies are significantly less likely to have experienced a merger in the recent past (~6 Gyr) than a field halo of the same mass. These results suggest that local, cluster processes like ram-pressure stripping, galaxy harassment, or strangulation play the dominant role in explaining t...
Most Galaxy-sized systems (M_host ~ 10^12 M_sun) in the LCDM cosmology are expected to have accre... more Most Galaxy-sized systems (M_host ~ 10^12 M_sun) in the LCDM cosmology are expected to have accreted at least one satellite with a total mass M_sat ~ 10^11 M_sun = 3M_disk in the past 8 Gyr. Analytic and numerical investigations suggest that this is the most precarious type of merger for the survival of thin galactic disks because more massive accretion events are relatively rare and less massive ones preserve thin disk components. We use high-resolution, dissipationless N-body simulations to study the response of an initially-thin, fully-formed Milky-Way type stellar disk to these cosmologically common events and show that the thin disk does not survive. Regardless of orbital configuration, the impacts transform the disks into structures that are roughly three times as thick and more than twice as kinematically hot as the observed dominant thin disk component of the Milky Way. We conclude that if the Galactic thin disk is a representative case, then the presence of a stabilizing ga...
Proceedings of the International Astronomical Union
Disk galaxies are common in our universe and this is a source of concern for hierarchical formati... more Disk galaxies are common in our universe and this is a source of concern for hierarchical formation models like LambdaCDM. Here we investigate this issue as motivated by raw merger statistics derived for galaxy-size dark matter halos from LambdaCDM simulations. Our analysis shows that a majority (~ 70%) of galaxy halos with M0 = 1012 M&sun; at z = 0 should have accreted at least one object with mass m > 1011 M&sun; ~= 3 Mdisk over the last 10 Gyr. Mergers involving larger objects m ≳ 3 × 1011 M&sun; should have been very rare for Milky-Way size halos today, and this pinpoints m/M ~ 0.1 mass-ratio mergers as the most worrying ones for the survival of thin galactic disks. Motivated by these results, we use use high-resolution, dissipationless N-body simulations to study the response of stellar Milky-Way type disks to these common mergers and show that thin disks do not survive the bombardment. The remnant galaxies are roughly three times as thick and twice as kinematically hot...
Massive satellite accretions onto early galactic disks can lead to the deposition of dark matter ... more Massive satellite accretions onto early galactic disks can lead to the deposition of dark matter in disk-like configurations that co-rotate with the galaxy. This phenomenon has potentially dramatic consequences for dark matter detection experiments. We utilize focused, high-resolution simulations of accretion events onto disks designed to be Galaxy analogues, and compare the resultant disks to the morphological and kinematic properties of the Milky Way's thick disk in order to bracket the range of co-rotating accreted dark matter. We find that the Milky Way's merger history must have been unusually quiescent compared to median LCDM expectations and therefore its dark disk must be relatively small: the fraction of accreted dark disk material near the Sun is about 20% of the host halo density or smaller and the co-rotating dark matter fraction near the Sun, defined as particles moving with a rotational velocity lag less than 50 km/s, is enhanced by about 30% or less compared t...
Minor accretion events with mass ratio M_sat : M_host ~ 1:10 are common in the context of LCDM co... more Minor accretion events with mass ratio M_sat : M_host ~ 1:10 are common in the context of LCDM cosmology. We use high-resolution simulations of Galaxy-analogue systems to show that these mergers can dynamically eject disk stars into a diffuse light component that resembles a stellar halo both spatially and kinematically. For a variety of orbital configurations, we find that ~3-5e8 M_sun of primary stellar disk material is ejected to a distance larger than 5 kpc above the galactic plane. This ejected contribution is similar to the mass contributed by the tidal disruption of the satellite galaxy itself, though it is less extended. If we restrict our analysis to the approximate solar neighborhood in the disk plane, we find that ~1% of the initial disk stars in that region would be classified kinematically as halo stars. Our results suggest that the inner parts of galactic stellar halos contain ancient disk stars and that these stars may have been liberated in the very same events that ...
We make predictions for the metallicity of diffuse stellar components in systems ranging from sma... more We make predictions for the metallicity of diffuse stellar components in systems ranging from small spiral galaxies to rich galaxy clusters. We extend the formalism of Purcell et al. (2007), in which diffuse stellar mass is produced via galaxy disruption, and we convolve this result with the observed mass-metallicity relation for galaxies in order to analyze the chemical abundance of intrahalo light (IHL) in host halos with virial mass 10^10.5 M_sun < M_host < 10^15 M_sun. We predict a steep rise of roughly two dex in IHL metallicity from the scales of small to large spiral galaxies. In terms of the total dynamical mass M_host of the host systems under consideration, we predict diffuse light metallicities ranging from Z_IHL < -2.5 for M_host ~ 10^11 M_sun, to Z_IHL ~ -1.0 for M_host ~ 10^12 M_sun. In larger systems, we predict a gradual flattening of this trend with Z_IHL ~ -0.4 for M_host ~ 10^13 M_sun, increasing to Z_IHL ~ 0.1 for M_host ~ 10^15 M_sun. This behavior is c...
Recently, Widrow and collaborators announced the discovery of vertical density waves in the Milky... more Recently, Widrow and collaborators announced the discovery of vertical density waves in the Milky Way disk. Here we investigate a scenario where these waves were induced by the Sagittarius dwarf galaxy as it plunged through the Galaxy. Using numerical simulations, we find that the Sagittarius impact produces North-South asymmetries and vertical wave-like behavior that qualitatively agrees with what is observed. The extent to which vertical modes can radially penetrate into the disc, as well as their amplitudes, depend on the mass of the perturbing satellite. We show that the mean height of the disc is expected to vary more rapidly in the radial than in the azimuthal direction. If the observed vertical density asymmetry is indeed caused by vertical oscillations, we predict radial and azimuthal variations of the mean vertical velocity, correlating with the spatial structure. These variations can have amplitudes as large as 8 km/s.
We marginalize over solutions to the spherical Jeans equation to obtain mass profiles for five An... more We marginalize over solutions to the spherical Jeans equation to obtain mass profiles for five Andromeda dwarf spheroidals (dSphs). We analyze stellar kinematics of And I, II, III, X, and XIV, obtained from Keck/DEIMOS spectroscopy, and we compare the mass within 300 parsecs to the Milky Way dSphs.
We summarize recent developments in the study of the origin of halo spin profiles and preliminary... more We summarize recent developments in the study of the origin of halo spin profiles and preliminary implications on disk formation. The specific angular-momentum distributions within halos in N-body simulations match a universal shape, M(<j) ∝ j/(j0+j). It is characterized by a power law over most of the mass, and one shape parameter in addition to the spin parameter lambda. The
We investigate the clustering properties of high-redshift galaxies within three competing scenari... more We investigate the clustering properties of high-redshift galaxies within three competing scenarios for assigning luminous galaxies to dark matter halos from N-body simulations: a one galaxy per massive halo model, a quiescent star formation model, and a collisional starburst model. We compare these models to observations of Lyman-Break galaxies at z~3$ With current data and the simple statistic used here,
We introduce a comprehensive analysis of multi-epoch stellar line-of-sight velocities to determin... more We introduce a comprehensive analysis of multi-epoch stellar line-of-sight velocities to determine the intrinsic velocity dispersion of the ultrafaint satellites of the Milky Way. Our method includes a simultaneous Bayesian analysis of both membership probabilities and the contribution of binary orbital motion to the observed velocity dispersion within a 14-parameter likelihood. We apply our method to the Segue 1 dwarf
Substructure in LCDM provides a number of interesting puzzles. While the missing satellites probl... more Substructure in LCDM provides a number of interesting puzzles. While the missing satellites problem is well-studied, there are suggestions of an opposite problem on the bright end. Subhalos large enough to host luminous satellites are uncommon, so we investigate whether the existence of the Large Magellanic Cloud (LMC) orbiting the Galaxy is a challenge for LCDM. We construct a volume
There is a vast menagerie of plausible candidates for the constituents of dark matter, both withi... more There is a vast menagerie of plausible candidates for the constituents of dark matter, both within and beyond extensions of the Standard Model of particle physics. Each of these candidates may have scattering (and other) cross section properties that are consistent with the dark matter abundance, BBN, and the most scales in the matter power spectrum; but which may have vastly different behavior at sub-galactic "cutoff" scales, below which dark matter density fluctuations are smoothed out. The only way to quantitatively measure the power spectrum behavior at sub-galactic scales at distances beyond the local universe, and indeed over cosmic time, is through probes available in multiply imaged strong gravitational lenses. Gravitational potential perturbations by dark matter substructure encode information in the observed relative magnifications, positions, and time delays in a strong lens. Each of these is sensitive to a different moment of the substructure mass function and ...
We propose to resolve the halo stellar populations of four nearby, massive disk galaxies (NGC 240... more We propose to resolve the halo stellar populations of four nearby, massive disk galaxies (NGC 2403, M81, M83, and NGC 4244) using deep observations with MegaCam on the MMT and IMACS on Magellan-I. These observations will provide star counts and color-magnitude diagrams ~1.5 magnitudes below the tip of the Red Giant Branch (RGB) of the halos of each galaxy. We will measure the metallicity distribution functions and stellar density profiles from star counts down to very low average surface brightnesses, equivalent to ~29.5 V-magnitude per square arcsec. Our targets are part of our HST SNAP program and cover a range in galaxy mass, luminosity, and morphology. As function of these galaxy properties this survey will provide: The first systematic study of the radial and isophotal shapes of diffuse stellar halos. A comprehensive analysis of halo metallicity distributions as a function of galaxy type and position within the galaxy. A sensitive search for tidal streams and halo substructure....
Environmental statistics provide a necessary means of comparing the properties of galaxies in dif... more Environmental statistics provide a necessary means of comparing the properties of galaxies in different environments and a vital test of models of galaxy formation within the prevailing, hierarchical, LCDM cosmological model. We explore counts-in-cylinders, a common statistic defined as the number of companions of a particular galaxy found within a given projected radius and redshift interval. Galaxy distributions with the
We use a volume-limited spectroscopic sample of isolated galaxies in the Sloan Digital Sky Survey... more We use a volume-limited spectroscopic sample of isolated galaxies in the Sloan Digital Sky Survey to investigate the frequency and radial distribution of luminous (M{sub r} â< -18.3) satellites like the Large Magellanic Cloud (LMC) around âL{sub *} Milky Way (MW) analogs and compare our results object-by-object to ÎCDM predictions based on abundance matching in simulations. We show that 12%
Monthly Notices of The Royal Astronomical Society, 2011
We show that dissipationless Lambda cold dark matter simulations predict that the majority of the... more We show that dissipationless Lambda cold dark matter simulations predict that the majority of the most massive subhaloes of the Milky Way are too dense to host any of its bright satellites (LV > 105 L&sun;). These dark subhaloes have peak circular velocities at infall of Vinfall= 30-70 km s-1 and infall masses of (0.2-4) × 1010 M&sun;. Unless the
We use a volume-limited spectroscopic sample of isolated galaxies in the Sloan Digital Sky Survey... more We use a volume-limited spectroscopic sample of isolated galaxies in the Sloan Digital Sky Survey to investigate the frequency and radial distribution of luminous (M{sub r} {approx}< -18.3) satellites like the Large Magellanic Cloud (LMC) around {approx}L{sub *} Milky Way (MW) analogs and compare our results object-by-object to {Lambda}CDM predictions based on abundance matching in simulations. We show that 12% of MW-like galaxies host an LMC-like satellite within 75 kpc (projected), and 42% within 250 kpc (projected). This implies {approx}10% have a satellite within the distance of the LMC, and {approx}40% of L{sub *} galaxies host a bright satellite within the virialized extent of their dark matter halos. Remarkably, the simulation reproduces the observed frequency, radial dependence, velocity distribution, and luminosity function of observed secondaries exceptionally well, suggesting that {Lambda}CDM provides an accurate reproduction of the observed universe to galaxies as fai...
We use a volume-limited spectroscopic sample of isolated galaxies in the Sloan Digital Sky Survey... more We use a volume-limited spectroscopic sample of isolated galaxies in the Sloan Digital Sky Survey (SDSS) to investigate the frequency and radial distribution of luminous (M_r <~ -18.3) satellites like the Large Magellanic Cloud (LMC) around ~L* Milky Way analogs and compare our results object-by-object to LCDM predictions based on abundance matching in simulations. We show that 12% of Milky Way-like galaxies host an LMC-like satellite within 75 kpc (projected), and 42 % within 250 kpc (projected). This implies ~10% have a satellite within the distance of the LMC, and ~40% of L* galaxies host a bright satellite within the virialized extent of their dark matter halos. Remarkably, the simulation reproduces the observed frequency, radial dependence, velocity distribution, and luminosity function of observed secondaries exceptionally well, suggesting that LCDM provides an accurate reproduction of the observed Universe to galaxies as faint as L~10^9 Lsun on ~50 kpc scales. When stacked...
We present five serendipitous spectroscopic interacting Lyman break galaxy (LBG) pairs and six ca... more We present five serendipitous spectroscopic interacting Lyman break galaxy (LBG) pairs and six candidate pairs from our z 3 Keck survey. All galaxies in the pairs exhibit Lyalpha in emission and we show that this is not a selection effect. A complete investigation of all LBG spectroscopic-photometric pairs with at least one spectroscopically confirmed component indicates an abundance of Lyalpha emitting LBGs (eLBGs) with projected separations of < 50 h-1 kpc, physical, with eLBGs comprising all pairs with < 20 h-1 kpc separations. We present a new broadband technique able to select very large numbers of LBGs based on their Lyalpha EW and associated features. We successfully test this technique with CFHTLS Deep data and 200 Keck spectra and show that the Lyalpha emitter (LAE) population is a natural extension of the LBG population. As a result, this technique can efficiently select very large numbers of LAEs over large defined redshift paths using simple broadband criteria. In ...
We study the formation of fifty-three galaxy cluster-size dark matter halos formed within a pair ... more We study the formation of fifty-three galaxy cluster-size dark matter halos formed within a pair of cosmological LCDM N-body simulations, and track the accretion histories of cluster subhalos with masses large enough to host 0.1L* galaxies. By associating subhalos with cluster galaxies, we find the majority of galaxies in clusters experience no pre-processing in the group environment prior to their accretion into the cluster. On average, ~70% of cluster galaxies fall into the cluster potential directly from the field, with no luminous companions in their host halos at the time of accretion; and less than ~12% are accreted as members of groups with five or more galaxies. Moreover, we find that cluster galaxies are significantly less likely to have experienced a merger in the recent past (~6 Gyr) than a field halo of the same mass. These results suggest that local, cluster processes like ram-pressure stripping, galaxy harassment, or strangulation play the dominant role in explaining t...
Most Galaxy-sized systems (M_host ~ 10^12 M_sun) in the LCDM cosmology are expected to have accre... more Most Galaxy-sized systems (M_host ~ 10^12 M_sun) in the LCDM cosmology are expected to have accreted at least one satellite with a total mass M_sat ~ 10^11 M_sun = 3M_disk in the past 8 Gyr. Analytic and numerical investigations suggest that this is the most precarious type of merger for the survival of thin galactic disks because more massive accretion events are relatively rare and less massive ones preserve thin disk components. We use high-resolution, dissipationless N-body simulations to study the response of an initially-thin, fully-formed Milky-Way type stellar disk to these cosmologically common events and show that the thin disk does not survive. Regardless of orbital configuration, the impacts transform the disks into structures that are roughly three times as thick and more than twice as kinematically hot as the observed dominant thin disk component of the Milky Way. We conclude that if the Galactic thin disk is a representative case, then the presence of a stabilizing ga...
Proceedings of the International Astronomical Union
Disk galaxies are common in our universe and this is a source of concern for hierarchical formati... more Disk galaxies are common in our universe and this is a source of concern for hierarchical formation models like LambdaCDM. Here we investigate this issue as motivated by raw merger statistics derived for galaxy-size dark matter halos from LambdaCDM simulations. Our analysis shows that a majority (~ 70%) of galaxy halos with M0 = 1012 M&sun; at z = 0 should have accreted at least one object with mass m > 1011 M&sun; ~= 3 Mdisk over the last 10 Gyr. Mergers involving larger objects m ≳ 3 × 1011 M&sun; should have been very rare for Milky-Way size halos today, and this pinpoints m/M ~ 0.1 mass-ratio mergers as the most worrying ones for the survival of thin galactic disks. Motivated by these results, we use use high-resolution, dissipationless N-body simulations to study the response of stellar Milky-Way type disks to these common mergers and show that thin disks do not survive the bombardment. The remnant galaxies are roughly three times as thick and twice as kinematically hot...
Massive satellite accretions onto early galactic disks can lead to the deposition of dark matter ... more Massive satellite accretions onto early galactic disks can lead to the deposition of dark matter in disk-like configurations that co-rotate with the galaxy. This phenomenon has potentially dramatic consequences for dark matter detection experiments. We utilize focused, high-resolution simulations of accretion events onto disks designed to be Galaxy analogues, and compare the resultant disks to the morphological and kinematic properties of the Milky Way's thick disk in order to bracket the range of co-rotating accreted dark matter. We find that the Milky Way's merger history must have been unusually quiescent compared to median LCDM expectations and therefore its dark disk must be relatively small: the fraction of accreted dark disk material near the Sun is about 20% of the host halo density or smaller and the co-rotating dark matter fraction near the Sun, defined as particles moving with a rotational velocity lag less than 50 km/s, is enhanced by about 30% or less compared t...
Minor accretion events with mass ratio M_sat : M_host ~ 1:10 are common in the context of LCDM co... more Minor accretion events with mass ratio M_sat : M_host ~ 1:10 are common in the context of LCDM cosmology. We use high-resolution simulations of Galaxy-analogue systems to show that these mergers can dynamically eject disk stars into a diffuse light component that resembles a stellar halo both spatially and kinematically. For a variety of orbital configurations, we find that ~3-5e8 M_sun of primary stellar disk material is ejected to a distance larger than 5 kpc above the galactic plane. This ejected contribution is similar to the mass contributed by the tidal disruption of the satellite galaxy itself, though it is less extended. If we restrict our analysis to the approximate solar neighborhood in the disk plane, we find that ~1% of the initial disk stars in that region would be classified kinematically as halo stars. Our results suggest that the inner parts of galactic stellar halos contain ancient disk stars and that these stars may have been liberated in the very same events that ...
We make predictions for the metallicity of diffuse stellar components in systems ranging from sma... more We make predictions for the metallicity of diffuse stellar components in systems ranging from small spiral galaxies to rich galaxy clusters. We extend the formalism of Purcell et al. (2007), in which diffuse stellar mass is produced via galaxy disruption, and we convolve this result with the observed mass-metallicity relation for galaxies in order to analyze the chemical abundance of intrahalo light (IHL) in host halos with virial mass 10^10.5 M_sun < M_host < 10^15 M_sun. We predict a steep rise of roughly two dex in IHL metallicity from the scales of small to large spiral galaxies. In terms of the total dynamical mass M_host of the host systems under consideration, we predict diffuse light metallicities ranging from Z_IHL < -2.5 for M_host ~ 10^11 M_sun, to Z_IHL ~ -1.0 for M_host ~ 10^12 M_sun. In larger systems, we predict a gradual flattening of this trend with Z_IHL ~ -0.4 for M_host ~ 10^13 M_sun, increasing to Z_IHL ~ 0.1 for M_host ~ 10^15 M_sun. This behavior is c...
Recently, Widrow and collaborators announced the discovery of vertical density waves in the Milky... more Recently, Widrow and collaborators announced the discovery of vertical density waves in the Milky Way disk. Here we investigate a scenario where these waves were induced by the Sagittarius dwarf galaxy as it plunged through the Galaxy. Using numerical simulations, we find that the Sagittarius impact produces North-South asymmetries and vertical wave-like behavior that qualitatively agrees with what is observed. The extent to which vertical modes can radially penetrate into the disc, as well as their amplitudes, depend on the mass of the perturbing satellite. We show that the mean height of the disc is expected to vary more rapidly in the radial than in the azimuthal direction. If the observed vertical density asymmetry is indeed caused by vertical oscillations, we predict radial and azimuthal variations of the mean vertical velocity, correlating with the spatial structure. These variations can have amplitudes as large as 8 km/s.
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Papers by James Bullock