Dark matter dominated dwarf disc galaxy Segue 1

There is observational evidence for inside-out growth of elliptical galaxies since $z \gtrsim 2-3$, which is not driven by in-situ star formation. Many systems at high redshift have small sizes $\sim 1kpc$ and surface brightness profiles with low Sersic indices n. The most likely descendants have, on average, grown by a factor of two in mass and a factor of four in size, indicating $r \propto M^{\alpha}$ with $\alpha \gtrsim 2$. They also have surface brightness profiles with $n \gtrsim 5$. This evolution can be qualitatively explained on the basis of two assumptions: compact ellipticals predominantly grow by collisionless minor or intermediate 'dry' mergers, and they are embedded in massive dark matter halos. We draw these conclusions from idealized collisionless mergers spheroidal galaxies - with and without dark matter - with mass ratios of 1:1, 1:5, and 1:10. The sizes evolve as $r \propto M^{\alpha}$ with $\alpha < 2$ for mass-ratios of 1:1. For minor mergers of galaxies embedded in dark matter halos, the sizes grow significantly faster and the profile shapes change more rapidly. Mergers with moderate mass-ratios of 1:5 give $\alpha \sim 2.3$ and a final Sersic index of $n = 9.5$ after doubling the stellar mass. This is accompanied by a significant increase of the dark matter fraction within the stellar half-mass radius, driven by the strong size increase probing larger, dark matter dominated regions. Only a few intermediate mass-ratio mergers of galaxies embedded in massive dark matter halos can result in the observed concurrent inside-out growth and the rapid evolution in profile shapes. Apart from negative stellar metallicity gradients such a 'minor' merger scenario also predicts significantly lower dark matter fractions for $z \sim 2$ compact quiescent galaxies and their rare present day analogues (abbreviated).

We present 2-D stellar kinematics of M87 out to R = 238" taken with the integral field spectrograph VIRUS-P. We run a large set of axisymmetric, orbit-based dynamical models and find clear evidence for a massive dark matter halo. While a logarithmic parameterization for the dark matter halo is preferred, we do not constrain the dark matter scale radius for an NFW profile and therefore cannot rule it out. Our best-fit logarithmic models return an enclosed dark matter fraction of 17.2 +/- 5.0 % within one effective radius (R_e ~ 100"), rising to 49.4 (+7.2,-8.8) % within 2 R_e. Existing SAURON data (R < 13"), and globular cluster kinematic data covering 145" < R < 540" complete the kinematic coverage to R = 47 kpc. At this radial distance the logarithmic dark halo comprises 85.3 (+2.5,-2.4) % of the total enclosed mass of 5.7^(+1.3)_(-0.9) X 10^(12) M_sun making M87 one of the most massive galaxies in the local universe. Our best-fit logarithmic dynamical models return a stellar mass-to-light ratio of 9.1^(+0.2)_(-0.2) (V-band), a dark halo circular velocity of 800^(+75)_(-25) kms, and a dark halo scale radius of 36^(+7)_(-3) kpc. The stellar M/L, assuming an NFW dark halo, is well constrained to 8.20^(+0.05)_(-0.10) (V-band). The stars in M87 are found to be radially anisotropic out to R ~ 0.5 R_e then isotropic or slightly tangentially anisotropic to our last stellar data point at R = 2.4 R_e where the anisotropy of the stars and globular clusters are in excellent agreement. The globular clusters then become radially anisotropic in the last two modeling bins at R = 3.4 R_e and R = 4.8 R_e. As one of the most massive galaxies in the local universe, constraints on both the mass distribution of M87 and anisotropy of its kinematic components strongly informs our theories of early-type galaxy formation and evolution in dense environments.

Modern models predict that galaxies do not evolve in isolation, but exist in haloes of dark matter and gas, embedded in the large-scale cosmic web. To build a self-consistent model for how galaxies form and evolve, it is vital to understand how galaxies regulate their formation through interaction with the circumgalactic medium that surrounds them, and at present the nature and impact of these interactions is poorly-constrained by both theory and observations. This thesis presents new insights into how galaxies affect their surroundings through feedback processes, the impact of the properties of the CGM on galaxy evolution, and how the properties of galaxy-CGM ecosystems are fundamentally connected to the assembly histories of their dark matter haloes. I begin by examining the origin of scatter in the relationship between the gas fraction and mass of dark matter haloes hosting present-day ~L* central galaxies in the EAGLE simulations. The scatter is uncorrelated with the accretion rate of the central galaxy's black hole (BH), but correlates strongly and negatively with the BH's mass, implicating differences in the expulsion of gas by active galactic nucleus (AGN) feedback, throughout the assembly of the halo, as the main cause of scatter. Haloes whose central galaxies host undermassive BHs also tend to retain a higher gas fraction, and exhibit elevated star formation rates (SFRs). Diversity in the mass of central BHs stems primarily from diversity in the dark matter halo binding energy, as these quantities are strongly and positively correlated at fixed halo mass, such that ~L* galaxies hosted by haloes that are more (less) tightly-bound develop central BHs that are more (less) massive than is typical for their halo mass. Variations in the halo gas fraction at fixed halo mass are reflected in both the soft X-ray luminosity and thermal Sunyaev-Zel'dovich flux, suggesting that the prediction of a strong coupling between the properties of galaxies and their halo gas fractions can be tested with measurements of these diagnostics for galaxies with diverse SFRs but similar halo masses. I then examine the connection between the properties of the CGM and the quenching and morphological evolution of central galaxies in both the EAGLE and IllustrisTNG simulations. The simulations yield very different median CGM mass fractions as a function of halo mass, with low-mass haloes being significantly more gas-rich in IllustrisTNG than in EAGLE. Nonetheless, in both cases the scatter in the CGM mass fraction at fixed halo mass is strongly correlated with the specific star formation rate and the kinematic morphology of central galaxies. This feedback elevates the CGM cooling time, preventing gas from accreting onto the galaxy to fuel star formation, and thus establishing a preference for quenched, spheroidal galaxies to be hosted by haloes with low CGM mass fractions for their mass. In both simulations, the CGM mass fraction correlates negatively with the host halo's intrinsic concentration, and hence with its binding energy and formation redshift, primarily because early halo formation fosters the rapid early growth of the central black hole (BH). This leads to a lower CGM mass fraction at fixed halo mass in EAGLE because the BH reaches high accretion rates sooner, whilst in IllustrisTNG it occurs because the central BH reaches the mass threshold at which AGN feedback is assumed to switch from thermal to kinetic injection earlier. Despite these differences, there is consensus from these state-of-the-art simulations that the expulsion of efficiently-cooling gas from the CGM is a crucial step in the quenching and morphological evolution of central galaxies. The above results suggest a connection between the assembly histories of dark matter haloes and the properties of their galaxy-CGM ecosystems. I clearly demonstrate this connection by performing a controlled and systematic experiment in which I adjust the assembly history of a single EAGLE halo hosting a moderately star-forming Milky Way-like galaxy by ``genetically modifying its initial conditions, keeping all other variables fixed. Shifting the halo assembly history to earlier times increases the integrated feedback injected by the AGN, ejecting a greater fraction of the CGM baryons and leading to the quenching and morphological transformation of the central galaxy. These effects can only have originated from differences in the assembly history of the halo, providing compelling evidence for this novel picture of the self-regulation of galaxy formation.

We explore the environment of 36 nearby galaxies in neutral hydrogen (H I) as part of the MeerKAT H I Observations of Nearby Galactic Objects; Observing Southern Emitters (MHONGOOSE) survey with the Robert C. Byrd Green Bank Telescope (GBT), and the Imaging Galaxies Intergalactic and Nearby En- vironment (IMAGINE) survey with the Parkes Radio Telescope. We obtained deep observations of each of these galaxies, reaching column density detection sensitivities as low as NHI ∼ 1e17 cm^−2, which allowed us to quantify the amount of diffuse H I in both samples of galaxies. This allows us to search for evidence of gas that could be accreting onto galaxies via filamentary structures from the cosmic web. These structures are predicted to be low column density gas flows, which should be seen within the dark matter halo of a galaxy. With our sample of 18 MHONGOOSE galaxies, we are able to make comparisons to environmental factors that are associated with cold accretion. Our GBT observations of diffuse H I in these galaxies do reveal trends in properties associated with this accretion, such as higher amounts of diffuse H I in galaxies with baryonic masses below a threshold of 1e10.3 M⊙. Our data also revealed trends when looking at the dark matter halo masses and rotation velocities of these MHONGOOSE galaxies. We take a deep look into one of the IMAGINE galaxies, ESO 214-17, revealing a new low column density H I bridge connecting the central galaxy to a companion. We also present a look at the first data sample from the IMAGINE survey with the Parkes telescope. These 18 galaxies were mapped to extremely low H I column densities (NHI ∼ 1e17 cm−2), and extend out to or beyond the virial radius of each galaxy. Encompassing the entire dark matter halo allows us to quantify the amount of HI throughout the halo, and subsequently the circumgalactic medium of each galaxy. Our environmental comparisons with properties associated with cold accretion do not reveal strong trends in the IMAGINE sample, however when combining all 36 galaxies discussed here we do see trends consistent with cold mode accretion. These trends are revealed when we look at baryonic masses, galaxy densities, and to a lesser degree with dark matter halo masses and rotation velocities.

Recent observations have discovered star formation activities in the extreme outer regions of disk galaxies. However, it remains unclear what physical mechanisms are responsible for triggering star formation in such low-density gaseous environments of galaxies. In order to understand the origin of these outer star-forming regions, we numerically investigate how the impact of dark matter subhalos orbiting a gas-rich disk galaxy embedded in a massive dark matter halo influences the dynamical evolution of the outer H I gas disk of the galaxy. We find that if the masses of the subhalos (Msb) in a galaxy with an extended H I gas disk are as large as 10-3Mh, where Mh is the total mass of the galaxy's dark halo, local fine structures can be formed in the extended H I disk. We also find that the gas densities of some apparently filamentary structures can exceed a threshold gas density for star formation and thus be likely to be converted into new stars in the outer part of the H I disk in some models with larger Msb. These results thus imply that the impact of dark matter subhalos (dark impact) can be important for better understanding the origin of recent star formation discovered in the extreme outer regions of disk galaxies. We also suggest that characteristic morphologies of local gaseous structures formed by the dark impact can indirectly prove the existence of dark matter subhalos in galaxies. We discuss the origin of giant H I holes observed in some gas-rich galaxies (e.g., NGC 6822) in the context of the dark impact.

Theories of structure formation in a cold dark matter dominated universe predict that massive clusters of galaxies assemble from the hierarchical merging of lower mass subhalos. Exploiting strong and weak gravitational lensing signals inferred from panoramic Hubble Space Telescope imaging data, we present a high-resolution reconstruction of the mass distribution in the massive, lensing cluster Cl 0024+16 at z = 0.39. Applying galaxy–galaxy lensing techniques we track the fate of dark matter subhalos as a function of projected cluster-centric radius out to 5 Mpc, well beyond the virial radius. We report the first detection of the statistical lensing signal of dark matter subhalos associated with late-type galaxies in clusters. The mass of a fiducial dark matter halo that hosts an early-type L* galaxy varies from M = 6.3+2.7−2.0 × 1011 M☉ within r < 0.6 Mpc, 1.3+0.8−0.6 × 1012 M☉ within r < 2.9 Mpc, and increases further to M = 3.7+1.4−1.1 × 1012 M☉ in the outskirts. The mass of a typical dark matter subhalo that hosts an L* galaxy increases with projected cluster-centric radius in line with expectations from the tidal stripping hypothesis. The mass of a dark matter subhalo that hosts a late-type L* galaxy is 1.06+0.52−0.41 × 1012 M☉. Early-type galaxies appear to be hosted on average in more massive dark matter subhalos compared to late-type galaxies. Early-type galaxies also trace the overall mass distribution of the cluster whereas late-type galaxies are biased tracers. We interpret our findings as evidence for the active assembly of mass via tidal stripping in galaxy clusters. The mass function of dark matter subhalos as a function of projected cluster-centric radius is compared with an equivalent mass function derived from clusters in the Millennium Run simulation populated with galaxies using semianalytic models. The shape of the observationally determined mass functions based on an I-band-selected sample of cluster members and lensing data are in agreement with the shapes of the subhalo mass functions derived from the Millennium Run simulation. However, simulated subhalos appear to be more efficiently stripped than lensing observations suggest. This is likely an artifact of comparison with a dark matter only simulation. Future simulations that simultaneously follow the detailed evolution of the baryonic component during cluster assembly will be needed for a more detailed comparison.

Dynamical models allow us to connect the motion of a set of tracers to the underlying gravitational potential, and thus to the total (luminous and dark) matter distribution. They are particularly useful for understanding the mass and spatial distribution of dark matter (DM) in a galaxy. Globular clusters (GCs) are an ideal tracer population in dynamical models, since they are bright and can be found far out into the halo of galaxies. We aim to test how well Jeans-Anisotropic-MGE (JAM) models using GCs (positions and line-of-sight velocities) as tracers can constrain the mass and radial distribution of DM haloes. For this, we use the E-MOSAICS suite of 25 zoom-in simulations of L* galaxies. We find that the DM halo properties are reasonably well recovered by the JAM models. There is, however, a strong correlation between how well we recover the mass and the radial distribution of the DM and the number of GCs in the galaxy: the constraints get exponentially worse with fewer GCs, and at least 150 GCs are needed in order to guarantee that the JAM model will perform well. We find that while the data quality (uncertainty on the radial velocities) can be important, the number of GCs is the dominant factor in terms of the accuracy and precision of the measurements. This work shows promising results for these models to be used in extragalactic systems with a sample of more than 150 GCs.

We compute the mass function of galactic dark matter halos for different values of the warm dark matter (WDM) particle mass m X and compare it with the number density of ultra-faint galaxies derived from the deepest UV luminosity function available so far at redshift z ≈ 2. The magnitude limit M UV = −13 reached by such observations allows us to probe the WDM mass functions down to scales close to or smaller than the half-mass mode mass scale ∼109 M ⊙. This allowed for an efficient discrimination among predictions for different m X which turn out to be in practice independent of the star formation efficiency η adopted to associate the observed UV luminosities of galaxies to the corresponding dark matter halo masses. Adopting a conservative approach to take into account the existing theoretical uncertainties in the galaxy halo mass function, we obtain a robust limit m X ≥ 1.8 keV for the mass of thermal relic WDM particles when comparing with the measured abundance of the faintest galaxies, while m X ≥ 1.5 keV is obtained when we compare with the Schechter fit to the observed luminosity function. The corresponding lower limit for sterile neutrinos depends on the modeling of the production mechanism; for instance m sterile ≳ 4 keV holds for the Shi–Fuller mechanism. We discuss the impact of observational uncertainties on the above bound on m X . In the cold dark matter (CDM) limit m X &Gt; 1 keV ?> we recover the generic CDM result that very inefficient star formation efficiency is required to match the observed galaxy abundances. As a baseline for comparison with forthcoming observational results from the Hubble Space Telescope Frontier Field project, we provide predictions for the number density of faint galaxies with M UV = −13 for different values of the WDM particle mass and of the star formation efficiency η, which are valid up to z ≈ 4.

The velocity anisotropy of particles inside dark matter (DM) haloes is an important physical quantity, which is required for the accurate modelling of mass profiles of galaxies and clusters of galaxies. It is typically measured using the ratio of the radial-to-tangential velocity dispersions at a given distance from the halo centre. However, this measure is insufficient to describe the dynamics of realistic haloes, which are typically quite elongated. Studying the velocity distribution in massive DM haloes in cosmological simulations, we find that in the inner parts of the haloes the local velocity ellipsoids are strongly aligned with the major axis of the halo, the alignment being stronger for more relaxed haloes. In the outer regions of the haloes, the alignment becomes gradually weaker and the orientation is more random. These two distinct regions of different degree of the alignment coincide with two characteristic regimes of the DM density profile: shallower and steeper than \rho r^{-2}. This alignment of the local velocity ellipsoids requires reinterpretation of features found in measurements based on the spherically averaged ratio of the radial-to-tangential velocity dispersions. In particular, we show that the velocity distribution in the central halo regions is highly anisotropic. For cluster-size haloes with mass 10^{14}-10^{15} h^-1 Msun, the velocity anisotropy along the major axis is nearly independent of radius and is equal to \beta=1-\sigma^2_{perp}/\sigma^2_{radial}=0.4, which is significantly larger than the previously estimated spherically averaged velocity anisotropy. The alignment of density and velocity anisotropies, and the radial trends may also have some implications for the mass modelling based on kinematical data of such objects as galaxy clusters or dwarf spheroidals, where the orbital anisotropy is a key element in an unbiased mass inference.

view Abstract Citations (4) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Mass Segregation in Dark Matter Models Campos, A. ; Yepes, G. ; Klypin, A. ; Murante, G. ; Provenzale, A. ; Borgani, S. Abstract We use the moments of counts of neighbors as given by the generalized correlation integrals, to study the clustering properties of dark matter halos (DHs) in cold dark matter (CDM) and cold + hot dark matter (CHDM) models. We compare the results with those found in the CfA and SSRS galaxy catalogs. We show that if we apply the analysis in redshift space, both models reproduce equally well the observed clustering of galaxies. Mass segregation is also found in the models: more massive DHs are more clustered compared with less massive ones. For example, at 3h-1 Mpc in real space, the number of neighbors in excess of random increases ∼3 times when the mass of halos increases by ∼100. In redshift space, this mass segregation is reduced by a factor ∼2-3 due to the peculiar velocities. Observational catalogs give an indication of luminosity and size segregation, which is consistent with the predictions of the models. Because the mass segregation is smaller in redshift space, it is suggestive that the real luminosity or size segregation of galaxies could be significantly larger than what it is found in redshift catalogs. Publication: The Astrophysical Journal Pub Date: June 1995 DOI: 10.1086/175766 arXiv: arXiv:astro-ph/9502018 Bibcode: 1995ApJ...446...54C Keywords: COSMOLOGY: DARK MATTER; COSMOLOGY: LARGE-SCALE STRUCTURE OF UNIVERSE; COSMOLOGY: THEORY; GALAXIES: CLUSTERS: GENERAL; Astrophysics E-Print: 13 pages including 9 figures (220 KB) in uuencoded compressed Postscript format. To appear in The Astrophysical Journal, June 10. Latex file and figures available at ftp://astrohp.ft.uam.es/pub/preprints/masseg full text sources arXiv | ADS |

We use the Delaunay Tessellation Field Estimator (DTFE) to study the one-point density distribution functions of the Millennium (MS) and Millennium-II (MS-II) simulations. The DTFE technique is based directly on the particle positions, without requiring any type of smoothing or analysis grid, thereby providing high sensitivity to all non-linear structures resolved by the simulations. In order to identify the detailed origin of the shape of the one-point density probability distribution function (PDF), we decompose the simulation particles according to the mass of their host FoF halos, and examine the contributions of different halo mass ranges to the global density PDF. We model the one-point distribution of the FoF halos in each halo mass bin with a set of Monte Carlo realizations of idealized NFW dark matter halos, finding that this reproduces the measurements from the N-body simulations reasonably well, except for a small excess present in simulation results. This excess increases with increasing halo mass. We show that its origin lies in substructure, which becomes progressively more abundant and better resolved in more massive dark matter halos. We demonstrate that the high density tail of the one-point distribution function in less massive halos is severely affected by the gravitational softening length and the mass resolution. In particular, we find these two parameters to be more important for an accurate measurement of the density PDF than the simulated volume. Combining our results from individual halo mass bins we find that the part of the one-point density PDF originating from collapsed halos can nevertheless be quite well described by a simple superposition of a set of NFW halos with the expected cosmological abundance over the resolved mass range. The transition region to the low-density unbound material is however not well captured by such an analytic halo model.

Constraints on the masses of dark matter haloes associated with galaxies in the field and in clusters have been successfully obtained used galaxy-galaxy lensing techniques. Weak lensing thus provides important information on the mass distribution in galaxies at large radii in a statistical fashion. Current work suggests that all galaxies possess extended dark matter haloes, however those that host galaxies in clusters are less extended and less massive.

Powerful quasars can be seen out to large distances. As they reside in massive dark matter haloes, they provide a useful tracer of large scale structure. We stack Herschel-SPIRE images at 250, 350 and 500 microns at the location of 11,235 quasars in ten redshift bins spanning $0.5 \leq z \leq 3.5$. The unresolved dust emission of the quasar and its host galaxy dominate on instrumental beam scales, while extended emission is spatially resolved on physical scales of order a megaparsec. This emission is due to dusty star-forming galaxies clustered around the dark matter haloes hosting quasars. We measure radial surface brightness profiles of the stacked images to compute the angular correlation function of dusty star-forming galaxies correlated with quasars. We then model the profiles to determine large scale clustering properties of quasars and dusty star-forming galaxies as a function of redshift. We adopt a halo model and parameterize it by the most effective halo mass at hosting star-forming galaxies, finding $\log(M_\mathrm{eff}/M_{\odot}) = 13.8^{+0.1}_{-0.1}$ at $z=2.21-2.32$, and, at $z=0.5-0.81$, the mass is $\log(M_\mathrm{eff}/M_{\odot}) = 10.7^{+1.0}_{-0.2}$. Our results indicate a downsizing of dark matter haloes hosting dusty star-forming galaxies between $0.5 \leq z \leq 2.9$. The derived dark matter halo masses are consistent with other measurements of star-forming and sub-millimeter galaxies. The physical properties of dusty star-forming galaxies inferred from the halo model depend on details of the quasar halo occupation distribution in ways that we explore at $z>2.5$, where the quasar HOD parameters are not well constrained.

Observations with the Five-hundred-meter Aperture Spherical Telescope recently detected H i 21 cm emission near M94, revealing an intriguing object, Cloud-9, without an optical counterpart. Subsequent analysis suggests that Cloud-9 is consistent with a gas-rich (M H I ≈ 106 M ⊙), starless, dark matter (DM) halo of mass M 200 ≈ 5 × 109 M ⊙. Using the Karl G. Jansky Very Large Array in D-array configuration, we present interferometric observations of Cloud-9, revealing it as a dynamically cold (W 50 ≈ 12 km s−1), nonrotating, and spatially asymmetric system, exhibiting gas compression on one side and a tail-like structure toward the other—features likely originating from ram pressure. Our observations suggest Cloud-9 is consistent with a starless ΛCDM DM halo if the gas is largely isothermal. If interpreted as a faint dwarf, Cloud-9 is similar to Leo T, a nearby gas-rich galaxy that would fall below current optical detection limits at Cloud-9's distance (d ≈ 5 Mpc). Further observations with the Hubble Space Telescope reaching magnitudes m g ≈ 30 would help identify such a galaxy or dramatically lower the current limits on its stellar mass (M gal ≲ 105 M ⊙). Cloud-9 thus stands as the firmest starless DM halo candidate to date or the faintest galaxy known at its distance.

We present an in-depth analysis of gas morphologies for a sample of 25 Milky Way–like galaxies from the IllustrisTNG TNG50 simulation. We constrain the morphology of cold, warm, hot gas, and gas particles as a whole using a local shell iterative method and explore its observational implications by computing the hard-to-soft X-ray ratio, which ranges between 10−3 and 10−2 in the inner ∼50 kpc of the distribution and 10−5–10−4 at the outer portion of the hot gas distribution. We group galaxies into three main categories: simple, stretched, and twisted. These categories are based on the radial reorientation of the principal axes of the reduced inertia tensor. We find that a vast majority (77%) of the galaxies in our sample exhibit twisting patterns in their radial profiles. Additionally, we present detailed comparisons between (i) the gaseous distributions belonging to individual temperature regimes, (ii) the cold gas distributions and stellar distributions, and (iii) the gaseous distributions and dark matter (DM) halos. We find a strong correlation between the morphological properties of the cold gas and stellar distributions. Furthermore, we find a correlation between gaseous distributions with a DM halo that increases with gas temperature, implying that we may use the warm–hot gaseous morphology as a tracer to probe the DM morphology. Finally, we show gaseous distributions exhibit significantly more prolate morphologies than the stellar distributions and DM halos, which we hypothesize is due to stellar and active galactic nucleus feedback.