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All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

Cosmic Pathways for Compact Groups in the Milli-Millennium Simulation

We detected 10 compact galaxy groups (CGs) at z=0 in the semianalytic galaxy catalog of Guo et al. for themilli-Millennium Cosmological Simulation (sCGs in mGuo2010a). We aimed to identify potential canonicalpathways for compact group evolution and thus illuminate the history of observed nearby CGs. By constructingmerger trees for z=0 sCG galaxies, we studied the cosmological evolution of key properties and compared themwith z=0 Hickson CGs (HCGs). We found that, once sCG galaxies come within 1 (0.5) Mpc of their mostmassive galaxy, they remain within that distance until z=0, suggesting sCG "birth redshifts." At z=0 stellarmasses of sCG most massive galaxies are within 1010M*/Me1011. In several cases, especially in the twofour- and five-member systems, the amount of cold gas mass anticorrelates with stellar mass, which in turncorrelates with hot gas mass. We define the angular difference between group members' 3D velocity vectors,vel, and note that many of the groups are long-lived because their small values of vel indicate a significantparallel component. For triplets in particular, vel values range between 20° and 40° so that galaxies are comingtogether along roughly parallel paths, and pairwise separations do not show large pronounced changes after closeencounters. The best agreement between sCG and HCG physical properties is for M* galaxy values, but HCGvalues are higher overall, including for star formation rates (SFRs). Unlike HCGs, due to a tail at low SFR and M*and a lack of M*1011Me galaxies, only a few sCG galaxies are on the star-forming main sequence

Tzanavaris, Panayiotis↗
NASA NTRS2004

Over-Luminous Elliptical Galaxies

We have completed a first draft of a paper on the galaxy group ESO3060170, the hottest known fossil group. We have submitted a first draft of the paper but the final completion is delayed due to several issues mentioned by the referee that we wish to revisit and discuss in more detail. The XMM data was combined with Chandra data which allowed a rich set of projects. The paper discusses the north-south elongation which is similar to that of the central dominant galaxy as well as the galaxy distribution. We detect an X-ray 'finger' or small tail emanating from the central galaxy to the north, suggesting motion of the galaxy within the elongated gravitational potential. The overall agreement between XMM and Chandra data are excellent (although the XMM data extend to larger radii). Both data sets show a cool core centered on the dominant galaxy. Surprisingly, - the temperature maps and detailed spectra indicate that the finger of gas is NOT cool, but has the same temperature as the ambient gas. We extracted surface brightness profiles, deprojected gas density profiles, cooling time profiles, and entropy profiles. There is a sharp discontinuity in gas temperature where the surface brightness profile starts to rise rapidly at 10 kpc. This produces a decrease in the cooling time and the gas entropy within 10 kpc. The central cooling time (within 10 kpc) is less than 109 years and falls to almost half that value in the inner 5 kpc. Despite the very short cooling time, we find no evidence (even with the excellent statistics from XMM-Newton) for multi-phased gas, i.e., a cooling flow. We find two 'edges' associated with the gas distribution (common in peaked X-ray groups and galaxies). On large scales, the temperature profile is flat and disagrees with the profile predicted by Loken et al. (2003) from detailed numerical simulations. We studied the galaxy distribution within one virial radius. The galaxy concentration associated with the group is detectable only within 0.3 of the virial radius (450 kpc) given the available depth of the optical galaxy catalogs at present. We have derived total mass and gas mass distributions (from the X-ray data) and find the gas fraction approaches a constant 8% (for H0 = 70).

Mushotsky, Richard↗
NASA NTRS2004

Over-Luminous Elliptical Galaxies

We have completed a first draft of a paper on the galaxy group ES03060170, the hottest known fossil group. We have submitted a first draft of the paper but the final completion is delayed due to several issues mentioned by the referee that we wish to revisit and discuss in more detail. The XMM data was combined with Chandra data which allowed a rich set of projects. The paper discusses the north-south elongation which is similar to that of the central dominant galaxy as well as the galaxy distribution. We detect an X-ray "finger" or small tail emanating from the central galaxy to the north, suggesting motion of the galaxy within the elongated gravitational potential. The overall agreement between XMM and Chandra data are excellent (although the XMM data extend to larger radii). Both data sets show a cool core centered on the dominant galaxy. Surprisingly, the temperature maps and detailed spectra indicate that the finger of gas is NOT cool, but has the same temperature as the ambient gas. We extracted surface brightness profiles, deprojected gas density profiles, cooling time profiles, and entropy profiles. There is a sharp discontinuity in gas temperature where the surface brightness profile starts to rise rapidly at 10 kpc. This produces a decrease in the cooling time and the gas entropy within 10 kpc. The central cooling time (within 10 kpc) is less than l0(exp 9) years and falls to almost half that value in the inner 5 kpc. Despite the very short cooling time, we find no evidence (even with the excellent statistics from XMM-Newton) for multi-phased gas, i.e., a cooling flow. We find two "edges" associated with the gas distribution (common in peaked X-ray groups and galaxies). On large scales, the temperature profile is flat and disagrees with the profile predicted by Loken et al. (2003) from detailed numerical simulations. We studied the galaxy distribution within one virial radius. The galaxy concentration associated with the group is detectable only within 0.3 of the virial radius (450 kpc) given the available depth of the optical galaxy catalogs at present. We have derived total mass and gas mass distributions (from the X- ray data) and find the gas fraction approaches a constant 8% (for Ho = 70).

Mushotzky, Richard↗
NASA NTRS1983

Photometry of resolved galaxies. II - Sextans A

Luminosity functions and color-magnitude diagrams are given for 652 stars in the Sextans A dwarf irregular galaxy, and they are compared with other Local Group galaxies. The brightest red and blue stars presently determined are in agreement with those of Sandage and Carlson (1982), and a group of red stars is identified which may be analogous to the bright carbon star population recently found in the Magellanic Clouds. While the similarity of Sextans A's luminosity function with those of the LMC and the Milky Way is in keeping with a universal luminosity function, stellar mass function and birthrate resemble those of the SMC. Per unit gas mass, Sextans A has a birthrate almost identical to the SMC, suggesting that the mean age of stars in Sextans A is significantly less than of those in the Magellanic Clouds.

Hoessel, J. G.↗
NASA NTRS1990

Dynamics and configurations of galaxy triplets

The purpose is to infer the probable dynamical states of galaxy triplets by the observed data on their configurations. Two methods are proposed for describing the distributions of the triplet configuration parameters characterizing a tendency to alignment and hierarchy: (1) obtaining a representative sample of configurations and determining its statistical parameters (moments and percentages); and (2) dividing the region of possible configurations of triple systems (Agekian and Anosova, 1967) into a set of segments and finding the probabilities for the configurations to find themselves in each of them. Both these methods allow representation of the data by numerical simulations as well as observations. The effect of projection was studied. It rather overestimates the alignment and hierarchy of the triple systems. Among the parameters of interest there are found some parameters that are least sensitive to projection effects. The samples consist of simulated galaxy triplets (with hidden mass) as well as of 46 probably physical triple galaxies (Karachentseva et al., 1979). The observed triples as well as numerical models show a tendency to alignment. The triple galaxies do not show any tendency to hierarchy (formation of the temporary binaries), but this tendency may be present for simulated triplets without significant dark matter. The significant hidden mass (of order ten times the total mass of a triplet) decreases the probability of forming a binary and so weakens the hierarchy. Small galaxy groups consisting of 3 to 7 members are probably the most prevalent types of galaxy aggregate (Gorbatsky, 1987). Galaxy triplets are the simplest groups, but dynamically nontrivial ones.

Anosova, Joanna P.↗
NASA NTRS2020

A Catalog of Emission-line Galaxies from the Faint Infrared Grism Survey: Studying Environmental Influence on Star Formation

We present a catalog of 208 0.3 < z < 2.1 emission-line galaxies (ELGs) selected from 1D slitless spectroscopy obtained using Hubble's WFC3 G102 grism, as part of the Faint Infrared Grism Survey. We identify ELG candidates by searching for significant peaks in all continuum-subtracted G102 spectra and, where possible, confirm candidates by identifying consistent emission lines in other available spectra or with published spectroscopic redshifts. We provide derived emission-line fluxes and errors, redshifts, and equivalent widths for Hα λ6563, [O iii] λλ4959, 5007, and [O ii] λ3727 emission lines, for ELGs down to AB(F105W) >28 and >10^(−17) erg/ sq. cms line flux. We use the resulting line catalog to investigate a possible relationship between line emission and a galaxy's environment. We use seventh-nearest-neighbor distances to investigate the typical surroundings of ELGs compared to non-ELGs, and we find that [O iii] emitters are preferentially found at intermediate galaxy densities near galaxy groups. We characterize these ELGs in terms of the galaxy specific star formation rate (SFR) versus stellar mass and find no significant influence of environment on that relation. We calculate SFRs and find no dependence of SFR on local galaxy surface density for 0.3 < z < 0.8 Hα emitters and for 0.8 < z < 1.3 [O iii] emitters. We find similar rates of close-pair interaction between ELGs and non-ELGs. For galaxy surface densities Σ ≤ 30 Mp/sq.c, we find no consistent effect of environment on star formation.

John Pharo↗
NASA NTRS1995

The least-action method, cold dark matter, and omega

Peebles has suggested an interesting technique, called the least-action method, to trace positions of galaxies back in time. This method applied on the Local Group galaxies seems to indicate that we live in an omega approximately = 0.1 universe. We have studied a cold dark matter (CDM) N-body simulation with omega = 0.2 and H = 50 km/s/Mpc and compared trajectories traced back by the least-action method with the ones given by the center of mass of the CDM halos. We show that the agreement between these sets of trajectories is at best qualitative. We also show that the line-of-sight peculiar velocities of halos are underestimated. This discrepancy is due to orphans, i.e., CDM particles which do not end up in halos. We vary the value of omega in the least-action method until the line-of-sight velocities agree with the CDM ones. The best value for this omega underestimates one of the CDM simulations by a factor of 4-5.

Dunn, A. M.↗
NASA NTRS1979

The luminosity function of galaxy systems - From single galaxies and small groups to rich clusters

The luminosity function (LF) of galaxy systems is determined, from single galaxies and small groups to rich clusters. The LF of rich (Abell) clusters is found to be a steeply decreasing function of cluster number density with cluster luminosity, and the groupings LF (that is, groups to rich clusters) can be well represented by a Schechter-type (1976) analytic form. The general LF of all galaxy systems is also found to be a smooth and steeply decreasing function of number density with luminosity, exhibiting an exponential cutoff in the rich-cluster luminosity domain, a power law dependence over most of the intermediate luminosity range, and a flattening of slope below the characteristic galactic luminosity. Comparisons of the LF with the LF of galaxies and X-ray clusters of galaxies are also discussed.

Bahcall, N. A.↗
NASA NTRS2018

ALMA Observations of Molecular Clouds in Three Group-centered Elliptical Galaxies:NGC 5846, NGC 4636, and NGC 5044

We present new ALMA CO(2–1) observations of two well-studied group-centered elliptical galaxies: NGC 4636 and NGC 5846. In addition, we include a revised analysis of Cycle 0 ALMA observations of the central galaxy in the NGC 5044 group. We find evidence that molecular gas is a common presence in bright group-centered galaxies (BGG). CO line widths are broader than Galactic molecular clouds, and using the reference Milky Way XCO, the total molecular mass ranges from 2.6 x 10(exp 5)M(☉) in NGC 4636 to 6.1 x 10(exp 7) M(☉) in NGC 5044. Complementary observations using the ALMA Compact Array do not exhibit any detection of a CO diffuse component at the sensitivity level achieved by current exposures. The origin of the detected molecular features is still uncertain, but these ALMA observations suggest that they are the end product of the hot gas cooling process and not the result of merger events. Some of the molecular clouds are associated with dust features as revealed by HST dust extinction maps, suggesting that these clouds formed from dust-enhanced cooling. The global nonlinear condensation may be triggered via the chaotic turbulent field or buoyant uplift. The large virial parameter of the molecular structures and correlation with the warm (10(exp 3)–10(exp 5) K)/hot (≥ 10(exp 6)) phase velocity dispersion provide evidence that they are unbound giant molecular associations drifting in the turbulent field, consistent with numerical predictions of the chaotic cold accretion process. Alternatively, the observed large CO line widths may be generated by molecular gas flowing out from cloud surfaces due to heating by the local hot gas atmosphere.

Pasquale Temi↗
NASA NTRS2015

The X-Ray Surveyor Mission: A Concept Study

NASA's Chandra X-ray Observatory continues to provide an unparalleled means for exploring the high-energy universe. With its half-arcsecond angular resolution, Chandra studies have deepened our understanding of galaxy clusters, active galactic nuclei, galaxies, supernova remnants, neutron stars, black holes, and solar system objects. As we look beyond Chandra, it is clear that comparable or even better angular resolution with greatly increased photon throughput is essential to address ever more demanding science questions-such as the formation and growth of black hole seeds at very high redshifts; the emergence of the first galaxy groups; and details of feedback over a large range of scales from galaxies to galaxy clusters. Recently, we initiated a concept study for such a mission, dubbed X-ray Surveyor. The X-ray Surveyor strawman payload is comprised of a high-resolution mirror assembly and an instrument set, which may include an X-ray microcalorimeter, a high-definition imager, and a dispersive grating spectrometer and its readout. The mirror assembly will consist of highly nested, thin, grazing-incidence mirrors, for which a number of technical approaches are currently under development-including adjustable X-ray optics, differential deposition, and new polishing techniques applied to a variety of substrates. This study benefits from previous studies of large missions carried out over the past two decades and, in most areas, points to mission requirements no more stringent than those of Chandra.

Astronomy↗
NASA NTRS2015

Beyond Chandra - the X-ray Surveyor

Over the past 16 years, NASA's Chandra X-ray Observatory has provided an unparalleled means for exploring the high energy universe with its half-arcsecond angular resolution. Chandra studies have deepened our understanding of galaxy clusters, active galactic nuclei, galaxies, supernova remnants, planets, and solar system objects addressing most, if not all, areas of current interest in astronomy and astrophysics. As we look beyond Chandra, it is clear that comparable or even better angular resolution with greatly increased photon throughput is essential to address even more demanding science questions, such as the formation and subsequent growth of black hole seeds at very high redshift; the emergence of the first galaxy groups; and details of feedback over a large range of scales from galaxies to galaxy clusters. Recently, NASA Marshall Space Flight Center, together with the Smithsonian Astrophysical Observatory, has initiated a concept study for such a mission now named the X-ray Surveyor. This concept study starts with a baseline payload consisting of a high resolution X-ray telescope and an instrument set which may include an X-ray calorimeter, a wide-field imager and a dispersive grating spectrometer and readout. The telescope would consist of highly nested thin shells, for which a number of technical approaches are currently under development, including adjustable X-ray optics, differential deposition, and modern polishing techniques applied to a variety of substrates. In many areas, the mission requirements would be no more stringent than those of Chandra, and the study takes advantage of similar studies for other large area missions carried out over the past two decades. Initial assessments indicate that such an X-ray mission is scientifically compelling, technically feasible, and worthy of a high prioritization by the next American National Academy of Sciences Decadal Survey for Astronomy and Astrophysics.

Beyond Chandra↗
NASA NTRS2016

Evidence for the Kinematic Sunyaev-Zel'dovich Effect with the Atacama Cosmology Telescope and Velocity Reconstruction from the Baryon Oscillation Spectroscopic Survey

We use microwave temperature maps from two seasons of data from the Atacama Cosmology Telescope at 146 GHz, together with the "Constant Mass" CMASS galaxy sample from the Baryon Oscillation Spectroscopic Survey to measure the kinematic Sunyaev-Zel'dovich (kSZ) effect over the redshift range z1/4 0.4-0.7. We use galaxy positions and the continuity equation to obtain a reconstruction of the line-of-sight velocity field. We stack the microwave temperature at the location of each halo, weighted by the corresponding reconstructed velocity. We vary the size of the aperture photometry filter used, thus probing the free electron profile of these halos from within the virial radius out to three virial radii, on the scales relevant for investigating the missing baryons problem. The resulting best fit kSZ model is preferred over the no-kSZ hypothesis at 3.3 and 2.9 sigma for two independent velocity reconstruction methods, using 25,537 galaxies over 660 square degrees. The data suggest that the baryon profile is shallower than the dark matter in the inner regions of the halos probed here, potentially due to energy injection from active galactic nucleus or supernovae. Thus, by constraining the gas profile on a wide range of scales, this technique will be useful for understanding the role of feedback in galaxy groups and clusters. The effect of foregrounds that are uncorrelated with the galaxy velocities is expected to be well below our signal, and residual thermal Sunyaev-Zel'dovich contamination is controlled by masking the most massive clusters. Finally, we discuss the systematics involved in converting our measurement of the kSZ amplitude into the mean free electron fraction of the halos in our sample.

Schaan, Emmanuel S.↗
NASA NTRS2006

Precision Astrometry with SIM PlanetQuest: Science and Mission Update

This viewgraph presentation gives a science and mission update of precision Astrometry with the Space Interferometry Mission (SIM) PlanetQuest. The topics include: 1) SIM PlanetQuest - the World s First Long- Baseline Optical Interferometer in Space; 2) National Academy of Sciences / NRC endorses SIM PlanetQuest; 3) Astrometry with an Interferometer; 4) Overall Configuration (deployed); 5) SIM Planet Finding Capabilities; 6) Planet detection with SIM - minimum masses; 7) Searching for Terrestrial Planets with SIM; 8) Planets around Young Stars; 9) SIM PlanetQuest Science Team; 10) SIM Astrophysics; 11) SIM's Reach Extends Across our Entire Galaxy to do Precision Astrophysics; 12) Dynamics of Galaxy Groups within 5 Mpc; 13) Galactic tidal tails; 14) Dark Halo of our Galaxy; 15) Probing Active Galactic Nuclei with Astrometry; 16) Sample tile for relative astrometry; 17) Astrometric signatures of AGN; 18) Snapshot Observing Mode: Astrometry for the masses; and 19) SIM Technology Development is Complete.

space interferometry mission (SIM)↗
NASA NTRS1990

A 1.4 GHz source survey in an area without nearby rich galaxy clusters

The paper reports on 1.4 GHz continuum observations for 56 contiguous VLA fields, using the D configuration, in a region devoid of nearby, rich galaxy clusters (at z less than 0.4). 354 continuum sources are tabulated, with fluxes down to about 1.5 mJy, in an area of about 12 sq deg. Only about seven of the 354 radio sources are associated with known rich galaxy clusters at z greater than 0.4 (tabulated by Gunn, Hoessel, and Oke, 1986). Source positions are compared with those from an optical catalog and mild correlations on angular scales of order 1 arcmin are found. This suggests some association of radio sources with galaxy groups (sizes of order 200 kpc) at redshifts of order z = 0.1, even though there are no rich galaxy clusters in this redshift range.

Condon, J. J.↗
NASA NTRS1994

Cold dark matter. 2: Spatial and velocity statistics

We examine high-resolution gravitational N-body simulations of the omega = 1 cold dark matter (CDM) model in order to determine whether there is any normalization of the initial density fluctuation spectrum that yields acceptable results for galaxy clustering and velocities. Dense dark matter halos in the evolved mass distribution are identified with luminous galaxies; the most massive halos are also considered as sites for galaxy groups, with a range of possibilities explored for the group mass-to-light ratios. We verify the earlier conclusions of White et al. (1987) for the low-amplitude (high-bias) CDM model-the galaxy correlation function is marginally acceptable but that there are too many galaxies. We also show that the peak biasing method does not accurately reproduce the results obtained using dense halos identified in the simulations themselves. The Cosmic Background Explorer (COBE) anisotropy implies a higher normalization, resulting in problems with excessive pairwise galaxy velocity dispersion unless a strong velocity bias is present. Although we confirm the strong velocity bias of halos reported by Couchman & Carlberg (1992), we show that the galaxy motions are still too large on small scales. We find no amplitude for which the CDM model can reconcile simultaneously and galaxy correlation function, the low pairwise velocity dispersion, and the richness distribution of groups and clusters. With the normalization implied by COBE, the CDM spectrum has too much power on small scales if omega = 1.

Gelb, James M.↗
NASA NTRS2004

The Chandra Large Area Synoptic X-ray Survey (CLASXS) of the Lockman Hole-Northwest: The X-ray Catalog

We present the X-ray catalog and basic results from our Chandra Large Area Synoptic X-ray Survey (CLASXS) of the Lockman Hole-Northwest field. Our 9 ACIS-I fields cover a contiguous solid angle of approx. 0.4 sq deg and reach fluxes of 5 x 10(exp -16) ergs/sq cm/s (0.4-2 keV) and 3 x 10(exp -15) ergs/sq cm/s (2-8 keV). Our survey bridges the gap between ultradeep pencil-beam surveys, such as the Chandra Deep Fields (CDFs), and shallower, large area surveys, allowing a better probe of the X-ray sources that contribute most of the 2-10 keV cosmic X-ray background (CXB). We find a total of 525 X-ray point sources and 4 extended sources. At approx. 10(exp -14)ergs/sq cm/s (2-8 keV), our number counts are significantly higher than those of several non-contiguous, large area surveys. Such a large difference is an indication of clustering in the X-ray sources. On the other hand, the integrated flux from the CLASXS field, combined with ASCA and Chandra ultradeep surveys, is consistent with results from other large area surveys, within the variance of the CXB. We see spectral evolution in the hardening of the sources at fluxes below 10(exp -14) ergs/sq cm/s, which agrees with previous observations from Chandra and XMM-Newton. About 1/3 of the sources in the CLASXS field have multiple observations, allowing variability tests. Above 4 x 10(exp -14) ergs/sq cm/s (0.4-8 keV), approx. 61% of the sources are variable. We also investigated the spectral variability of the variable sources. While most show spectral softening with increasing flux, or no significant spectral change, there are a few sources that show a different trend. Four extended sources in CLASXS is consistent with the previously measured LogN-LogS of galaxy clusters. Using X-ray spectra and optical colors, we argue that 3 of the 4 extended sources are galaxy clusters or galaxy groups. We report the discovery of a gravitational lensing arc associated with one of these sources. Using red sequence and brightest cluster galaxy methods, we find that the redshifts of the extended sources are in the range z approx. 0.5 - 1. The inferred masses within the Einstein radii are consistent with the mass profiles of local groups scaled to the same virial radii.

Yang, Y.↗
NASA NTRS1984

Photometry of resolved galaxies. IV - Holmberg I and Holmberg II

Colors and magnitudes are presented for 279 resolved stars in the Holmberg I dwarf galaxy and 468 resolved stars in Holmberg II. Both systems are Magellanic type dwarf members of the M81-NGC 2403 Group, which lies at approximately 3 Mpc from the Local Group. The photometry was done in the GRI passbands using CCD detectors. Color-magnitude diagrams and luminosity functions are constructed; these are compared with results for several Local Group galaxies and with theoretical work. Holmberg I is found to have a low present star formation rate, while Holmberg II is very active at present.

Hoessel, J. G.↗
NASA NTRS1996

The Milky Way, the Local Group & the IR Tully-Fisher Diagram

Using the near infrared fluxes of local group galaxies derived from Cosmic Background Explorer/Diffuse Infrared Background Experiment band maps and published Cepheid distances, we construct Tully-Fisher diagrams for the Local Group.

Milky Way↗