arXiv subjects

M. J. Geller

Publications and source records attributed to M. J. Geller.

At least 19 recordsLinked to original sources

arXiv2022

Mass accretion rates of the HectoMAP clusters of galaxies

We estimate the mass accretion rate (MAR) of the 346 clusters of galaxies in the HectoMAP Cluster Survey. The clusters span the redshift range $0.17-0.42$ and the $M_{200}$ mass range $\approx (0.5 - 3.5)\cdot 10^{14} M_\odot$. The MAR estimate is based on the caustic technique along with a spherical infall model. Our analysis extends the measurement of MARs for 129 clusters at $z<0.3$ from the Cluster Infall Regions in the Sloan Digital Sky Survey (CIRS) and the Hectospec Cluster Survey (HeCS) to redshift $z \sim 0.42$. Averaging over redshift, low-mass clusters with $M_{200}\sim 0.7\cdot 10^{14} M_\odot$ accrete $\sim 3\cdot 10^4 M_\odot$yr$^{-1}$; more massive clusters with $M_{200}\sim 2.8\cdot 10^{14} M_\odot$ accrete $\sim 1\cdot 10^5 M_\odot$yr$^{-1}$. Low- and high-mass clusters increase their MAR by $\sim 46\%$ and $\sim 84\%$, respectively, as the redshift increases from $z\sim 0.17-0.29$ to $z\sim 0.34-0.42$. The MARs at fixed redshift increase with mass and MARs at fixed mass increase with redshift in agreement with $Λ$CDM cosmological model for hierarchical structure formation. We consider the extension of MAR measurements to $z \sim 1$.

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arXiv2021

Mass accretion rates of clusters of galaxies: CIRS and HeCS

We use a new spherical accretion recipe tested on N-body simulations to measure the observed mass accretion rate (MAR) of 129 clusters in the Cluster Infall Regions in the Sloan Digital Sky Survey (CIRS) and in the Hectospec Cluster Survey (HeCS). The observed clusters cover the redshift range of $0.01<z<0.30$ and the mass range of $\sim 10^{14}-10^{15} {h^{-1}~\rm{M_\odot}}$. Based on three-dimensional mass profiles of simulated clusters reaching beyond the virial radius, our recipe returns MARs that agree with MARs based on merger trees. We adopt this recipe to estimate the MAR of real clusters based on measurements of the mass profile out to $\sim 3R_{200}$. We use the caustic method to measure the mass profiles to these large radii. We demonstrate the validity of our estimates by applying the same approach to a set of mock redshift surveys of a sample of 2000 simulated clusters with a median mass of $M_{200}= 10^{14} {h^{-1}~\rm{M_{\odot}}}$ as well as a sample of 50 simulated clusters with a median mass of $M_{200}= 10^{15} {h^{-1}~\rm{M_{\odot}}}$: the median MARs based on the caustic mass profiles of the simulated clusters are unbiased and agree within $19\%$ with the median MARs based on the real mass profile of the clusters. The MAR of the CIRS and HeCS clusters increases with the mass and the redshift of the accreting cluster, which is in excellent agreement with the growth of clusters in the $Λ$CDM model.

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arXiv2017

Separating Galaxies from the Cluster Dark Matter Halo in Abell 611

We investigate the mass content of galaxies in the core of the galaxy cluster Abell 611. We perform a strong lensing analysis of the cluster core and use velocity dispersion measurements for individual cluster members as additional constraints. Despite the small number of multiply-imaged systems and cluster members with central velocity dispersions available in the core of A611, the addition of velocity dispersion measurements leads to tighter constraints on the mass associated with the galaxy component, and as a result, on the mass associated with the dark matter halo. Without the spectroscopic velocity dispersions, we would overestimate the mass of the galaxy component by a factor of $\sim1.5$, or, equivalently, we would underestimate the mass of the cluster dark halo by $\sim5\%$. We perform an additional lensing analysis using surface brightness (SB) reconstruction of the tangential giant arc. This approach improves the constraints on the mass parameters of the 5 galaxies close to the arc by up to a factor $\sim10$. The galaxy velocity dispersions resulting from the SB analysis are consistent at the 1$σ$ confidence level with the spectroscopic measurements and with the prediction from the simple pointlike analysis. In contrast the truncation radii for 2-3 galaxies depart significantly from the galaxy scaling relation and suggest differences in the stripping history from galaxy to galaxy.

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arXiv2014

Constraining the galaxy mass content in the core of A383 using velocity dispersion measurements for individual cluster members

We use velocity dispersion measurements of 21 individual cluster members in the core of Abell 383, obtained with MMT Hectospec, to separate the galaxy and the smooth dark halo (DH) lensing contributions. While lensing usually constrains the overall, projected mass density, the innovative use of velocity dispersion measurements as a proxy for masses of individual cluster members breaks inherent degeneracies and allows us to (a) refine the constraints on single galaxy masses and on the galaxy mass-to-light scaling relation and, as a result, (b) refine the constraints on the DM-only map, a high-end goal of lens modelling. The knowledge of cluster member velocity dispersions improves the fit by 17% in terms of the image reproduction $χ^2$, or 20% in terms of the rms. The constraints on the mass parameters improve by ~10% for the DH, while for the galaxy component, they are refined correspondingly by ~50%, including the galaxy halo truncation radius. For an L$^*$ galaxy with M$^*_B$=-20.96, for example, we obtain best fitting truncation radius r$^*_{tr}=20.5^{+9.6}_{-6.7}$ kpc and velocity dispersion $σ^*=324\pm17 km/s$. Moreover, by performing the surface brightness reconstruction of the southern giant arc, we improve the constraints on r$_{tr}$ of two nearby cluster members, which have measured velocity dispersions, by more than ~30%. We estimate the stripped mass for these two galaxies, getting results that are consistent with numerical simulations. In the future, we plan to apply this analysis to other galaxy clusters for which velocity dispersions of member galaxies are available.

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arXiv2014

The FMOS-Cosmos Survey of Star-Forming Galaxies at z~1.6 II. The Mass-Metallicity Relation and the Dependence on Star Formation Rate and Dust Extinction

We investigate the relationships between stellar mass, gas-phase oxygen abundance (metallicity), star formation rate, and dust content of star-forming galaxies at z$\sim$1.6 using Subaru/FMOS spectroscopy in the COSMOS field. The mass-metallicity relation at $z\sim1.6$ is steeper than the relation observed in the local Universe. The steeper MZ relation at $z\sim1.6$ is mainly due to evolution in the stellar mass where the MZ relation begins to turnover and flatten. This turnover mass is 1.2 dex larger at $z\sim1.6$. The most massive galaxies at $z\sim1.6$ ($\sim 10^{11}M_\odot$) are enriched to the level observed in massive galaxies in the local Universe. The mass-metallicity relation we measure at $z\sim1.6$ supports the suggestion of an empirical upper metallicity limit that does not significantly evolve with redshift. We find an anti-correlation between metallicity and star formation rate for galaxies at a fixed stellar mass at $z\sim1.6$ which is similar to trends observed in the local Universe. We do not find a relation between stellar mass, metallicity and star formation rate that is independent of redshift; our data suggest that there is redshift evolution in this relation. We examine the relation between stellar mass, metallicity and dust extinction. We find that at a fixed stellar mass dustier galaxies tend to be more metal rich. From examination of the stellar masses, metallicities, SFRs and dust extinctions we conclude that stellar mass is most closely related to dust extinction.

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arXiv2008

Hypervelocity Stars: From the Galactic Center to the Halo

Hypervelocity stars (HVS) traverse the Galaxy from the central black hole to the outer halo. We show that the Galactic potential within 200 pc acts as a high pass filter preventing low velocity HVS from reaching the halo. To trace the orbits of HVS throughout the Galaxy, we construct two forms of the potential which reasonably represent the observations in the range 5--100,000 pc, a simple spherically symmetric model and a bulge-disk-halo model. We use the Hills mechanism (disruption of binaries by the tidal field of the central black hole) to inject HVS into the Galaxy and compute the observable spatial and velocity distributions of HVS with masses in the range 0.6--4 Msun. These distributions reflect the mass function in the Galactic Center, properties of binaries in the Galactic Center, and aspects of stellar evolution and the injection mechanism. For 0.6--4 Msun main sequence stars, the fraction of unbound HVS and the asymmetry of the velocity distribution for their bound counterparts increases with stellar mass. The density profiles for unbound HVS decline with distance from the Galactic Center approximately as r^{-2} (but are steeper for the most massive stars which evolve off the main sequence during their travel time from the Galactic Center); the density profiles for the bound ejecta decline with distance approximately as r^{-3}. In a survey with a limiting visual magnitude V of 23, the detectability of HVS (unbound or bound) increases with stellar mass.

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arXiv2007

The Representative XMM-Newton Cluster Structure Survey (REXCESS) of an X-ray Luminosity Selected Galaxy Cluster Sample

The largest uncertainty for cosmological studies using clusters of galaxies is introduced by our limited knowledge of the statistics of galaxy cluster structure, and of the scaling relations between observables and cluster mass. To improve on this situation we have started an XMM-Newton Large Programme for the in-depth study of a representative sample of 33 galaxy clusters, selected in the redshift range z=0.055 to 0.183 from the REFLEX Cluster Survey, having X-ray luminosities above 0.4 X 10^44 h_70^-2 erg s^-1 in the 0.1 - 2.4 keV band. This paper introduces the sample, compiles properties of the clusters, and provides detailed information on the sample selection function. We describe the selection of a nearby galaxy cluster sample that makes optimal use of the XMM-Newton field-of-view, and provides nearly homogeneous X-ray luminosity coverage for the full range from poor clusters to the most massive objects in the Universe. For the clusters in the sample, X-ray fluxes are derived and compared to the previously obtained fluxes from the ROSAT All-Sky Survey. We find that the fluxes and the flux errors have been reliably determined in the ROSAT All-Sky Survey analysis used for the REFLEX Survey. We use the sample selection function documented in detail in this paper to determine the X-ray luminosity function, and compare it with the luminosity function of the entire REFLEX sample. We also discuss morphological peculiarities of some of the sample members. The sample and some of the background data given in this introductory paper will be important for the application of these data in the detailed studies of cluster structure, to appear in forthcoming publications.

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arXiv2005

Metallicity and Nuclear Star Formation in Nearby Galaxy Pairs: Evidence for Tidally Induced Gas Flows

We derive the first luminosity-metallicity relation for a large objectively selected sample of local galaxy pairs and we compare the pairs LZ relation with the relation for the Nearby Field Galaxy Survey (NFGS). Galaxy pair members with small projected separations (s<20 kpc/h) have systematically lower metallicities (~0.2 dex on average) than the field galaxies, or than more widely separated pairs at the same luminosity. There is a strong correlation between metallicity and central burst strength in the galaxy pairs. All five galaxies in the pairs sample with strong central bursts have close companions and metallicities lower than the comparable field galaxies. Our results provide strong observational evidence for a merger scenario where galaxy interactions cause gas flows towards the central regions, carrying less enriched gas from the outskirts of the galaxy into the central regions. The less enriched gas dilutes the pre-existing nuclear gas to produce a lower metallicity than would be obtained prior to the interaction. These gas flows trigger central bursts of star formation, causing strong central burst strengths, and possibly aiding the formation of blue bulges. We show that the timescale and central gas dilution required by this scenario are consistent with predictions from hydrodynamic merger models.

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arXiv2005

XMM-Newton and Gemini Observations of Eight RASSCALS Galaxy Groups

We study the distribution of gas pressure and entropy in eight groups of galaxies belonging to the ROSAT All-Sky Survey / Center for Astrophysics Loose Systems (RASSCALS). We use archival and proprietary XMM-Newton observations, supplementing the X-ray data with redshifts derived from the literature; we also list 127 new redshifts measured with the Gemini North telescope. The groups show remarkable self-similarity in their azimuthally averaged entropy and temperature profiles. The entropy increases with radius; the behavior of the entropy profiles is consistent with an increasing broken power law with inner and outer slope 0.92+0.04-0.05 and 0.42+0.05-0.04 (68% confidence), respectively. There is no evidence of a central, isentropic core, and the entropy distribution in most of the groups is flatter at large radii than in the inner region, challenging earlier reports as well as theoretical models predicting large isentropic cores or asymptotic slopes of 1.1 at large radii. The pressure profiles are consistent with a self-similar decreasing broken power law in radius; the inner and outer slopes are -0.78+0.04-0.03 and -1.7+0.1-0.3, respectively. The results suggest that the larger scatter in the entropy distribution reflects the varied gasdynamical histories of the groups; the regularity and self-similarity of the pressure profiles is a sign of a similarity in the underlying dark matter distributions.

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arXiv2005

Aperture effects on Star Formation Rate, Metallicity and Reddening

(Abridged) We use 101 galaxies selected from the Nearby Field Galaxy Survey (NFGS) to investigate the effect of aperture size on the star formation rate, metallicity and reddening determinations for galaxies. We compare the star formation rate, metallicity and reddening derived from nuclear spectra to those derived from integrated spectra. For apertures capturing <20% of the B(26) light, the differences between nuclear and global metallicity, extinction and star formation rate are substantial. We calculate an `expected' star formation rate using our nuclear spectra and apply the commonly-used aperture correction method. The expected star formation rate overestimates the global value for early type spirals, with large scatter for all Hubble types, particularly late types. The differences between the expected and global star formation rates probably result from the assumption that the distributions of the emission-line gas and the continuum are identical. We discuss the implications of these results for metallicity-luminosity relations and star formation history studies based on fiber spectra. To reduce systematic and random errors from aperture effects, we recommend selecting samples with fibers that capture >20% of the galaxy light. For the Sloan Digital Sky Survey and the 2dFGRS, redshifts z>0.04 and z>0.06 are required, respectively, to ensure a covering fraction >20% for galaxies similar to the average size, type, and luminosity observed in our sample. Higher luminosity samples and samples containing many late-type galaxies require a larger minimum redshift to ensure that >20% of the galaxy light is enclosed by the fiber.

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arXiv2004

K-band Properties of Well-Sampled Groups of Galaxies

We use a sample of 55 groups and 6 clusters of galaxies ranging in mass from 7 x 10^11 Msun to 1.5 x 10^15 Msun to examine the correlation of the Ks-band luminosity with mass discovered by Lin et al. (2003). We use the 2MASS catalog and published redshifts to construct complete magnitude limited redshift surveys of the groups. From these surveys we explore the IR photometric properties of groups members including their IR color distribution and luminosity function. Although we find no significant difference between the group Ks luminosity function and the general field, there is a difference between the color distribution of luminous group members and their counterparts (generally background) in the field. There is a significant population of luminous galaxies with H-Ks > 0.35 which are rarely, if ever, members of the groups in our sample. The most luminous galaxies which populate the groups have a very narrow range of IR color. Over the entire mass range covered by our sample, the Ks luminosity increases with mass as L ~ M^(0.64 +/- 0.06) implying that the mass-to-light ratio in the Ks-band increases with mass. The agreement between this result and earlier investigations of essentially non-overlapping sets of systems shows that this window in galaxy formation and evolution is insensitive to the selection of the systems and to the details of the mass and luminosity computations.

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arXiv2004

CAIRNS: The Cluster And Infall Region Nearby Survey II. Environmental Dependence of Infrared Mass-to-Light Ratios

CAIRNS (Cluster And Infall Region Nearby Survey) is a spectroscopic survey of the infall regions surrounding nine nearby rich clusters of galaxies. In Paper I, we used redshifts within $\sim 10\Mpc$ of the centers of the clusters to determine the mass profiles of the clusters based on the phase space distribution of the galaxies. Here, we use 2MASS photometry and an additional \ncziinew redshifts to investigate the environmental dependence of near-infrared mass-to-light ratios. In the virial regions, the halo occupation function is non-linear; the number of bright galaxies per halo increases more slowly than the mass of the halo. On larger scales, the light contained in galaxies is less clustered than the mass in rich clusters. Specifically, the mass-to-light ratio inside the virial radius is a factor of $1.8\pm0.3$ larger than that outside the virial radius. This difference could result from changing fractions of baryonic to total matter or from variations in the efficiency of galaxy formation or disruption with environment. The average mass-to-light ratio $M/L_K = 53\pm 5 h$ implies $Ω_m = 0.18\pm 0.03$ (statistical) using the luminosity density based on 2dFGRS data. These results are difficult to reconcile with independent methods which suggest higher $Ω_m$. Reconciling these values by invoking bias requires that the typical value of $M/L_K$ changes significantly at densities of $\lesssim3ρ_c$.

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arXiv2004

A Redshift Survey of Nearby Galaxy Groups: the Shape of the Mass Density Profile

We constrain the mass profile and orbital structure of nearby groups and clusters of galaxies. Our method yields the joint probability distribution of the density slope n, the velocity anisotropy beta, and the turnover radius r0 for these systems. The measurement technique does not use results from N-body simulations as priors. We incorporate 2419 new redshifts in the fields of 41 systems of galaxies with z < 0.04. The new groups have median velocity dispersion sigma=360 km/s. We also use 851 archived redshifts in the fields of 8 nearly relaxed clusters with z < 0.1. Within R < 2 r200, the data are consistent with a single power law matter density distribution with slope n = 1.8-2.2 for systems with sigma < 470 km/s, and n = 1.6-2.0 for those with sigma > 470 km/s (95% confidence). We show that a simple, scale-free phase space distribution function f(E,L^2) ~ (-E)^(alpha-1/2) L^(-2 β) is consistent with the data as long as the matter density has a cusp. Using this DF, matter density profiles with constant density cores (n=0) are ruled out with better than 99.7% confidence.

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arXiv2003

Surveying the Inner Halo of the Galaxy with 2MASS-Selected Horizontal Branch Candidates

We use 2MASS photometry to select blue horizontal branch (BHB) candidates covering the sky |b|>15 deg. A 12.5 50 deg. We insert simulated star streams into the data and conclude that the high Galactic latitude BHB candidates are consistent with having no ~5 deg wide star stream with density greater than 0.33 objects deg^-2 at the 95% confidence level. The absence of structure suggests there have been no major accretion events in the inner halo in the last few Gyr. However, at low Galactic latitudes a two-point angular correlation analysis reveals structure on angular scales <1 deg. This structure is apparently associated with stars in the thick disk, and has a physical scale of 10-100 pc. Interestingly, such structures are expected by cosmological simulations that predict the majority of the thick disk may arise from accretion and disruption of satellite mergers.

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arXiv2003

CAIRNS: The Cluster And Infall Region Nearby Survey I. Redshifts and Mass Profiles

The CAIRNS (Cluster And Infall Region Nearby Survey) project is a spectroscopic survey of the infall regions surrounding eight nearby, rich, X-ray luminous clusters of galaxies. We collect 15665 redshifts (3471 new or remeasured) within \sim 5-10 Mpc of the centers of the clusters, making it the largest study of the infall regions of clusters. We determine cluster membership and the mass profiles of the clusters based on the phase space distribution of the galaxies. All of the clusters display decreasing velocity dispersion profiles. The mass profiles are fit well by functional forms based on numerical simulations but exclude an isothermal sphere. Specifically, NFW and Hernquist models provide good descriptions of cluster mass profiles to their turnaround radii. Our sample shows that the predicted infall pattern is ubiquitous in rich, X-ray luminous clusters over a large mass range. The caustic mass estimates are in excellent agreement with independent X-ray estimates at small radii and with virial estimates at intermediate radii. The mean ratio of the caustic mass to the X-ray mass is 1.03\pm0.11 and the mean ratio of the caustic mass to the virial mass (when corrected for the surface pressure term) is 0.93\pm0.07. We further demonstrate that the caustic technique provides reasonable mass estimates even in merging clusters.

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arXiv2003

The Century Survey Galactic Halo Project I: Stellar Spectral Analysis

The Century Survey Galactic Halo Project is a photometric and spectroscopic survey from which we select relatively blue stars (V-R<0.30 mag) as probes of the Milky Way halo. The Survey strip spans the range of Galactic latitude 35<b<88 deg, allowing us to study the nature of populations of stars and their systematic motions as a function of Galactic latitude. One of our primary goals is to use blue horizontal-branch stars to trace potential star streams in the halo, and to test the hierarchical model for the formation of the Galaxy. In this paper we discuss spectroscopy and multi-passband photometry for a sample of 764 blue stars in the Century Survey region. Our sample consists predominantly of A- and F-type stars. We describe our techniques for determination of radial velocities, effective temperatures, metallicities, and surface gravities. Based on these measurements, we derive distance estimates by comparison with a set of calibrated isochrones. We devote special attention to the classification of blue horizontal-branch stars, and compare the results obtained from the application of the techniques of Kinman et al., Wilhelm et al., and Clewley et al. We identify 55 blue horizontal-branch stars. Our large sample of stars also uncovers a number of unusual objects, including three carbon-enhanced stars, a late B-type star located 0.8 kpc above the Galactic plane, and a DZ white dwarf.

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arXiv2002

The H-alpha and Infrared Star Formation Rates for the Nearby Field Galaxy Survey

We investigate the H-alpha and infrared star formation rate (SFR) diagnostics for galaxies in the Nearby Field Galaxy Survey (NFGS). For the 81 galaxies in our sample, we derive H-alpha fluxes (included here) from integrated spectra. There is a strong correlation between the ratio of far-infrared to optical luminosities L(FIR)/L(H-alpha) and the extinction E(B-V) measured with the Balmer decrement. Before reddening correction, the SFR(IR) and SFR(H-alpha) are related to each other by a power-law. Correction of the SFR(H-alpha) for extinction using the Balmer decrement and a classical reddening curve both reduces the scatter in the SFR(IR)-SFR(H-alpha) correlation and results in a much closer agreement (within ~10%) between the two SFR indicators. This SFR relationship spans 4 orders of magnitude and holds for all Hubble types with IRAS detections in the NFGS. A constant ratio between the SFR(IR) and SFR(H-alpha) for all Hubble types, including early types (S0-Sab), suggests that the IR emission in all of these objects results from a young stellar population.

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arXiv2002

Mass Profile of the Infall Region of the Abell 2199 Supercluster

Using a redshift survey of 1323 galaxies (1092 new or remeasured) in a region of 95 square degrees centered on the nearby galaxy cluster Abell 2199, we analyze the supercluster containing A2199, A2197, and an X-ray group. The caustic technique accurately reproduces the true mass profiles of simulated simple superclusters (i.e., superclusters where the virial mass of one cluster is 2-10 times the virial mass of all other clusters in the supercluster). We calculate the masses of the two main components of A2197 (A2197W and A2197E) using archival X-ray observations and demonstrate that the A2199 supercluster is simple and thus that the caustic technique should yield an accurate mass profile. The mass profile is uncertain by ~30% within 3 Mpc/h and by a factor of two within 8 Mpc/h and is one of only a few for a supercluster on such large scales. Independent X-ray mass estimates agree with our results at all radii where they overlap. The mass profile strongly disagrees with an isothermal sphere profile but agrees with profiles suggested by simulations. We discuss the interplay of the supercluster dynamics and the dynamics of the bound subclusters. The agreement between the infall mass profile and other techniques shows that the caustic technique is surprisingly robust for simple superclusters (abridged).

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