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We investigate the interaction between a shock-driven hot wind and a cold multi-cloud layer, for conditions commonly found in interstellar and circumgalactic gas. We present a method for identifying distinct clouds using a Friends-of-Friends algorithm. This approach unveils novel detailed information about individual clouds and their collective behaviour. By tracing the evolution of individual clouds, our method provides comprehensive descriptions of cloud morphology, including measures of the elongation and fractal dimension. Combining the kinematics and morphology of clouds, we refine previous models for drag and entrainment processes. Our by-cloud analysis allows to discern the dominant entrainment processes at different times. We find that after the initial shock passage, momentum transfer due to condensation becomes increasingly important, compared to ram pressure, which dominates at early times. We also find that internal motions within clouds act as an effective dynamic pressure that exceeds the thermal pressure by an order of magnitude. Our analysis shows how the highly efficient cooling of the warm mixed gas at temperatures $\sim 10^{5}$ K is effectively balanced by the kinetic energy injected by the hot wind into the warm and cold phases via shocks and shear motions. Compression-driven condensation and turbulence dissipation maintain a multi-phase outflow and can help explain the presence of dense gas in galaxy-scale winds. Finally, we show that applying our Friends-of-Friends analysis to $\rm{H}_\rm{I}$-emitting gas and correcting for beam size and telescope sensitivity can explain two populations of $\rm{H}_\rm{I}$ clouds within the Milky-Way nuclear wind as structures pertaining to the same outflow.

The origin of warm ions in the circum-galactic medium (CGM) surrounding massive galaxies remains a mystery. In this paper, we argue that a significant fraction of the observed warm-ion columns may arise in the intergalactic medium (IGM) surrounding galactic halos. We use a simple spherical collapse model of the dark matter (DM) halos and their baryonic content to compute the evolving ion fractions within and outside virial halos. We show that the photoionized IGM may produce a thick blanket of warm ions around the CGM, thereby contaminating CGM observations. We find that the IGM contributes $> 75\%$ of the total \ion{O}{6} column densities in halos with virial masses exceeding a few times $10^{11}~M_\odot$, and that it may dominate the \ion{O}{6} absorption even for lower mass-halos, depending on the impact parameter. We compare our results with observations and find that our simplified model reproduces the overall \ion{O}{6} columns as well as their trend with the impact parameter and halo mass. We show that observed warm ion columns may be completely dominated by the IGM envelopes, consistent with CGM$^2$ data. We, therefore, suggest that theoretical interpretations of CGM-survey observations must consider the possible contribution of the surrounding IGM. Although our simplified model suggests that it may be possible to kinematically distinguish between CGM and IGM origins through the absorption line profiles, this distinction is likely unfeasible in realistic astrophysical halos, due to the complex velocity structure in the multi-phased CGM., Comment: 12 pages, 6 figures

We present hydrodynamical simulations of galactic winds from star-forming galaxies including non-equilibrium ionization and frequency-dependent radiative transfer, processes that have remained largely unaccounted for in galactic wind studies. We consider radiation from massive stars, the metagalactic UV/X-ray background, and the self-radiation of the supernovae heated gas. We compare our results to classical galactic wind solutions and show the importance of our newly included physical processes toward observations of ions such as O III, O VI, O VII and O VIII plus the observable soft X-ray spectra. Non-equilibrium ionization is reflected in over-ionized gas compared to equilibrium solutions, leading to much enhanced column densities of highly ionized species. The wind produces excess soft X-ray ($E\gtrsim 100$ eV) radiation that is several orders of magnitude higher compared to the metagalactic background. This radiation ionizes the higher ions (such as O VII) somewhat, but affects the lower ions (such as O III) significantly. We predict that the observable X-ray spectra should contain the signatures of such non-equilibrium effects, especially in X-ray lines such as O VII and O VIII. Simple estimates suggest that both the temperature and density of the winds may be overestimated by factors of a few to almost 2 orders of magnitude using simple equilibrium models. We conclude that both the non-equilibrium ionization and the radiation from the wind itself need to be considered for proper modeling of the optical/UV/X-ray emitting plasma in galactic winds., Comment: 19 pages, 11 figures. Accepted for publication in ApJ. Added new estimates and figures for ISM absorption of the wind radiation

We present numerical simulations of the evolution of a supernova (SN) remnant expanding into a uniform background medium with density $n_H = 1.0$ cm$^{-3}$ and temperature of $10^4$ K. We include a dynamically evolving non-equilibrium ionisation (NEI) network (consisting of all the ions of H, He, C, N, O, Ne, Mg, Si, S, Fe), frequency dependent radiation transfer (RT), thermal conduction, and a simple dust evolution model, all intra-coupled to each other and to the hydrodynamics. We assume spherical symmetry. Photo-ionisation, radiation losses, photo-heating, charge-exchange heating/cooling and radiation pressure are calculated on-the-fly depending on the local radiation field and ion fractions. We find that the dynamics and energetics (but not the emission spectra) of the SN remnants can be well modelled by collisional equilibrium cooling curves even in the absence of non-equilibrium cooling and radiative transport. We find that the effect of precursor ionising radiation at different stages of SN remnant are dominated by rapid cooling of the shock and differ from steady state shocks. The predicted column densities of different ions such as N II, C IV and N V, can be higher by up to several orders of magnitude compared to steady state shocks. We also present some high esolution emission spectra that can be compared with the observed remnants to obtain important information about the physical and chemical states of the remnant, as well as constrain the background ISM., Comment: 18 pages, accepted by MNRAS. Added implications towards 1D oscillatory instability in SN remnants

We introduce a new general-purpose time-dependent ionisation network (IN) and a radiation transport (RT) module in the magneto-hydrodynamic (MHD) code PLUTO. Our ionisation network is reliable for temperatures ranging from 5e3 to 3e8 K, and includes all ionisation states of H, He, C, N, O, Ne, Mg, Si, S and Fe making it suitable for studying a variety of astrophysical scenarios. Radiation loss for each ion-electron pair is calculated using CLOUDY-17 data on-the-fly. Photo-ionisation and charge exchange are the chemical heating mechanisms. The IN is fully coupled to the radiation transport module over a very large range of opacities at different frequencies. The RT module employs a method of short characteristics assuming spherical symmetry. The radiation module requires the assumption of spherical symmetry, while the IN is compatible with full 3D. We also include a simple prescription for dust opacity, grain destruction, and the dust contribution to radiation pressure. We present numerical tests to show the reliability and limitations of the new modules. We also present a post-processing tool to calculate projected column densities and emission spectra., Comment: 19 pages, accepted by MNRAS. Added error estimates for radiative transfer, and runtime plots for different components of the code. Added late time (>1Myr) dynamics of the HII region

I explore the thermal evolution and ionization states in gas cooling from an initially hot state in the presence of external photoionizing radiation. I compute the equilibrium and nonequilibrium cooling efficiencies, heating rates, and ion fractions for low-density gas cooling while exposed to the ionizing metagalactic background radiation at various redshifts (z=0 - 3), for a range of temperatures (1e8-1e4 K), densities (1e-7 - 1e3 cm^-3) and metallicities (1e-3 - 2 times solar). The results indicate the existence of a threshold ionization parameter, above which the cooling efficiencies are very close to those in photoionization equilibrium (so that departures from equilibrium may be neglected), and below which the cooling efficiencies resemble those in collisional time-dependent gas cooling with no external radiation (and are thus independent of density)

The G2 object has recently passed its pericenter passage in our Galactic Center. While the $Br_\gamma$ emission shows clear signs of tidal interaction, the change in the observed luminosity is only of about a factor of 2, in contention with all previous predictions. We present high resolution simulations performed with the moving mesh code, RICH, together with simple analytical arguments that reproduce the observed $Br_\gamma$ emission. In our model, G2 is a gas cloud that undergoes tidal disruption in a dilute ambient medium. We find that during pericenter passage, the efficient cooling of the cloud results in a vertical collapse, compressing the cloud by a factor of $\sim5000$. By properly taking into account the ionization state of the gas, we find that the cloud is UV starved and are able to reproduce the observed $Br_\gamma$ luminosity. For densities larger than $\approx500\;\mathrm{cm}^{-3}$ at pericenter, the cloud fragments, due to cooling instabilities and the emitted radiation is inconsistent with observations. For lower densities, the cloud survives the pericenter passage intact and its emitted radiation matches the observed lightcurve. From the duration of $Br_\gamma$ emission which contains both redshifted and blueshifted components, we show that the cloud is not spherical but rather elongated with a size ratio of 4 at year 2001. The simulated cloud's elongation grows as it travels towards pericenter and is consistent with observations, due to viewing angles. The simulation is also consistent with having a spherical shape at apocenter.

We discuss recent improvements in the calculation of the radiative cooling in both collisionally and photo ionized plasmas. We are extending the spectral simulation code Cloudy so that as much as possible of the underlying atomic data is taken from external databases, some created by others, some developed by the Cloudy team. This paper focuses on recent changes in the treatment of many stages of ionization of iron, and discusses its extensions to other elements. The H-like and He-like ions are treated in the iso-electronic approach described previously. Fe II is a special case treated with a large model atom. Here we focus on Fe III through Fe XXIV, ions which are important contributors to the radiative cooling of hot, 1e5 to 1e7 K, plasmas and for X-ray spectroscopy. We use the Chianti atomic database to greatly expand the number of transitions in the cooling function. Chianti only includes lines that have atomic data computed by sophisticated methods. This limits the line list to lower excitation, longer wavelength, transitions. We had previously included lines from the Opacity Project database, which tends to include higher energy, shorter wavelength, transitions. These were combined with various forms of the g-bar approximation, a highly approximate method of estimating collision rates. For several iron ions the two databases are almost entirely complementary. We adopt a hybrid approach in which we use Chianti where possible, supplemented by lines from the Opacity Project for shorter wavelength transitions. The total cooling including the lightest thirty elements differs significantly from some previous calculations.

Cold gas streaming along the dark-matter filaments of the cosmic web is predicted to be the major provider of resources for disc buildup, violent disk instability and star formation in massive galaxies in the early universe. We study to what extent these cold streams are traceable in the extended circum-galactic environment of galaxies via Ly alpha absorption and selected low ionisation metal absorption lines. We model the expected absorption signatures using high resolution zoom-in AMR cosmological simulations. In the postprocessing, we distinguish between self-shielded gas and unshielded gas. In the self-shielded gas, which is optically thick to Lyman continuum radiation, we assume pure collisional ionisation for species with an ionisation potential greater than 13.6 eV. In the optically thin, unshielded gas these species are also photoionised by the meta-galactic radiation. In addition to absorption of radiation from background quasars, we compute the absorption line profiles of radiation emitted by the galaxy at the centre of the same halo. We predict the strength of the absorption signal for individual galaxies without stacking. We find that the Ly alpha absorption profiles produced by the streams are consistent with observations of absorption and emission Ly alpha profiles in high redshift galaxies. Due to the low metallicities in the streams, and their low covering factors, the metal absorption features are weak and difficult to detect., Comment: 26 pages, 25 figures, 3 tables, final version accepted for publication in MNRAS

It is widely recognized that nucleosynthetic output of the first, Population III supernovae was a catalyst defining the character of subsequent stellar generations. Most of the work on the earliest enrichment was carried out assuming that the first stars were extremely massive and that the associated supernovae were unusually energetic, enough to completely unbind the baryons in the host cosmic minihalo and disperse the synthesized metals into the intergalactic medium. Recent work, however, suggests that the first stars may in fact have been somewhat less massive, with a characteristic mass scale of a few tens of solar masses. We present a cosmological simulation following the transport of the metals synthesized in a Population III supernova assuming that it had an energy of 1e51 ergs, compatible with standard Type II supernovae. A young supernova remnant is inserted in the first star's relic HII region in the free expansion phase and is followed for 40 Myr employing adaptive mesh refinement and Lagrangian tracer particle techniques. The supernova remnant remains partially trapped within the minihalo and the thin snowplow shell develops pronounced instability and fingering. Roughly half of the ejecta turn around and fall back toward the center of the halo, with 1% of the ejecta reaching the center in 30 kyr and 10% in 10 Myr. The average metallicity of the combined returning ejecta and the pristine filaments feeding into the halo center from the cosmic web is 0.001 - 0.01 Z_sun, but the two remain unmixed until accreting onto the central hydrostatic core that is unresolved at the end of the simulation. We conclude that if Population III stars had less extreme masses, they promptly enriched the host minihalos with metals and triggered Population II star formation., Comment: 13 pages, 8 figures

We present ion-by-ion cooling efficiencies for low-density gas. We use Cloudy (ver. 08.00) to estimate the cooling efficiencies for each ion of the first 30 elements (H-Zn) individually. We present results for gas temperatures between 1e4 and 1e8K, assuming low densities and optically thin conditions. When nonequilibrium ionization plays a significant role the ionization states deviate from those that obtain in collisional ionization equilibrium (CIE), and the local cooling efficiency at any given temperature depends on specific non-equilibrium ion fractions. The results presented here allow for an efficient estimate of the total cooling efficiency for any ionic composition. We also list the elemental cooling efficiencies assuming CIE conditions. These can be used to construct CIE cooling efficiencies for non-solar abundance ratios, or to estimate the cooling due to elements not explicitly included in any nonequilibrium computation. All the computational results are listed in convenient online tables., Comment: Submitted to ApJS. Electronic data available at http://wise-obs.tau.ac.il/~orlyg/ion_by_ion/

I present computations of the integrated column densities produced in the post-shock cooling layers and in the radiative precursors of partially-cooled fast shocks as a function of the shock age. The results are applicable to the shock-heated warm/hot intergalactic medium (WHIM) which is expected to be a major baryonic reservoir, and contain a large fraction of the so-called "missing baryons". My computations indicate that readily observable amounts of intermediate and high ions, such as CIV, NV, and OVI are created in the precursors of young shocks, for which the shocked gas remains hot and difficult to observe. I suggest that such precursors may provide a way to identify and estimate the "missing" baryonic mass associated with the shocks. The absorption-line signatures predicted here may be used to construct ion-ratio diagrams, which will serve as diagnostics for the photoionized gas in the precursors. In my numerical models, the time-evolution of the shock structure, self-radiation, and associated metal-ion column densities are computed by a series of quasi-static models, each appropriate for a different shock age. The shock code used in this work calculates the nonequilibrium ionization and cooling, follows the radiative transfer of the shock self-radiation through the post-shock cooling layers, takes into account the resulting photoionization and heating rates, follows the dynamics of the cooling gas, and self-consistently computes the photoionization states in the precursor gas. I present a complete set of the age-dependent post-shock and precursor columns for all ionization states of the elements H, He, C, N, O, Ne, Mg, Si, S, and Fe, as functions of the shock velocity, gas metallicity, and magnetic field. I present my numerical results in convenient online tables., Comment: Submitted to ApJ. Comments welcomed. Electronic data available at: http://wise-obs.tau.ac.il/~orlyg/partial_shocks/

We present numerical computations of the equilibrium configurations of tidally-locked homogeneous binaries, rotating in circular orbits. Unlike the classical Roche approximations, we self-consistently account for the tidal and rotational deformations of both components, and relax the assumptions of ellipsoidal configurations and Keplerian rotation. We find numerical solutions for mass ratios q between 1e-3 and 1, starting at a small angular velocity for which tidal and rotational deformations are small, and following a sequence of increasing angular velocities. Each series terminates at an appropriate ``Roche limit'', above which no equilibrium solution can be found. Even though the Roche limit is crossed before the ``Roche lobe'' is filled, any further increase in the angular velocity will result in mass-loss. For close, comparable-mass binaries, we find that local deviations from ellipsoidal forms may be as large as 10-20%, and departures from Keplerian rotation are significant. We compute the light curves that arise from our equilibrium configurations, assuming their distance is >>1 AU (e.g. in the Kuiper Belt). We consider both backscatter (proportional to the projected area) and diffuse (Lambert) reflections. Backscatter reflection always yields two minima of equal depths. Diffuse reflection, which is sensitive to the surface curvature, generally gives rise to unequal minima. We find detectable intensity differences of up to 10% between our light curves and those arising from the Roche approximations. Finally, we apply our models to Kuiper Belt binary 2001 QG298, and find a nearly edge-on binary with a mass ratio q = 0.93 ^{+0.07}_{-0.03}, angular velocity Omega^2/G rho = 0.333+/-0.001 (statistical errors only), and pure diffuse reflection. For the observed period of 2001 QG298, these parameters imply a bulk density, rho = 0.72 +/- 0.04 g cm^-3., Comment: Accepted to ApJ

We present computations of the ionization structure and metal-absorption properties of thermally conductive interface layers that surround evaporating warm spherical clouds, embedded in a hot medium. We rely on the analytical formalism of Dalton & Balbus to calculate the temperature profile in the evaporating gas, and explicitly solve the time-dependent ionization equations for H, He, C, N, O, Si, and S in the interface. We include photoionization by an external field. We estimate how departures from equilibrium ionization affect the resonance-line cooling efficiencies in the evaporating gas, and determine the conditions for which radiative losses may be neglected in the solution for the evaporation dynamics and temperature profile. Our results indicate that non-equilibrium cooling significantly increases the value of the saturation parameter at which radiative losses begin to affect the flow dynamics. As applications we calculate the ion fractions and projected column densities arising in the evaporating layers surrounding dwarf-galaxy-scale objects that are also photoionized by metagalactic radiation. We compare our results to the UV metal-absorption column densities observed in local highly-ionized metal-absorbers, located in the Galactic corona or intergalactic medium. Conductive interfaces significantly enhance the formation of high-ions such as C^3+, N^4+, and O^5+ relative to purely photoionized clouds, especially for clouds embedded in a high-pressure corona. However, the enhanced columns are still too low to account for the O VI columns (~1e14 cm^-2) observed in the local high-velocity absorbers. We find that O VI columns larger than ~1e13 cm^-2 cannot be produced in evaporating clouds. Our results do support the conclusion of Savage & Lehner, that absorption due to evaporating O VI likely occurs in the local interstellar medium, with characteristic columns of ~1e13 cm^-2., Comment: Accepted for Publication in ApJ

Recent observations have revealed that some Type Ia supernovae exhibit narrow, time-variable Na I D absorption features. The origin of the absorbing material is controversial, but it may suggest the presence of circumstellar gas in the progenitor system prior to the explosion, with significant implications for the nature of the supernova progenitors. We present the third detection of such variable absorption, based on six epochs of high-resolution spectroscopy of the Type Ia supernova SN 2007le from Keck and the HET. The data span ~3 months, from 5 days before maximum light to 90 days after maximum. We find that one component of the Na D absorption lines strengthened significantly with time, indicating a total column density increase of ~2.5 x 10^12 cm^-2. The changes are most prominent after maximum light rather than at earlier times when the UV flux from the SN peaks. As with SN 2006X, we detect no change in the Ca II H&K lines over the same time period, rendering line-of-sight effects improbable and suggesting a circumstellar origin for the absorbing material. Unlike the previous two SNe exhibiting variable absorption, SN 2007le is not highly reddened (E_B-V = 0.27 mag), also pointing toward circumstellar rather than interstellar absorption. Photoionization models show that the data are consistent with a dense (10^7 cm^-3) cloud or clouds of gas located ~0.1 pc from the explosion. These results broadly support the single-degenerate scenario previously proposed to explain the variable absorption, with mass loss from a nondegenerate companion star responsible for providing the circumstellar gas. We also present tentative evidence for narrow Halpha emission associated with the SN, which will require followup observations at late times to confirm. [abridged], Comment: 16 pages, 10 figures (8 in color), 5 tables. Accepted for publication in ApJ

In this paper we present computations of the integrated metal-ion column densities produced in the post-shock cooling layers behind fast, radiative shock-waves. For this purpose, we have constructed a new shock code that calculates the non-equilibrium ionization and cooling; follows the radiative transfer of the shock self-radiation through the post-shock cooling layers; takes into account the resulting photoionization and heating rates; follows the dynamics of the cooling gas; and self-consistently computes the initial photoionization state of the precursor gas. We discuss the shock structure and emitted radiation, and study the dependence on the shock velocity, magnetic field, and gas metallicity. We present a complete set of integrated post-shock and precursor metal-ion column densities of all ionization stages of the elements H, He, C, N, O, Ne, Mg, Si, S, and Fe, for shocks with velocities of 600 and ~2000 km/s, corresponding to initial post-shock temperatures of 5e6 and 5e7 K, cooling down to 1000 K. We consider shocks in which the magnetic field is negligible (B=0) so that the cooling occurs at approximately constant pressure ("isobaric"), and shocks in which the magnetic pressure dominates everywhere such that the cooling occurs at constant density (isochoric). We present results for gas metallicities Z ranging from 1e-3 to twice the solar abundance of heavy elements, and we study how the observational signatures of fast radiative shocks depend on Z. We present our numerical results in convenient online figures and tables, available at http://wise-obs.tau.ac.il/~orlyg/shocks/, Comment: 32 pages, 29 figures. ApJ in press. Electronic data available at http://wise-obs.tau.ac.il/~orlyg/shocks/

We establish a simple model for the distribution of cold gas around L* galaxies using a large set of observational constraints on the properties of strong MgII absorber systems. Our analysis suggests that the halos of L* galaxies are filled with cool gaseous clouds having sizes of order 1kpc and densities of ~10^{-2} cm^{-3}. We then investigate the physical effects of cloud irradiation by a quasar and study the resulting spectral signatures. We show that quasar activity gives rise to (i) extended narrow-line emission on ~100kpc scales and (ii) an anisotropy in the properties of the absorbing gas arising from the geometry of the quasar radiation field. Provided that quasars reside in halos several times more massive than those of L* galaxies, our model predictions appear to be in agreement with observations of narrow emission-line nebulae around quasars and the recent detections of ~100kpc cold gaseous envelopes around those objects, suggesting a common origin for these phenomena. We discuss the implications of our results for understanding absorption systems, probing quasar environments at high redshifts, and testing the quasar unification scheme., Comment: 15 pages, 13 figures (ApJ submitted)

We present new computations of the equilibrium and non-equilibrium cooling efficiencies and ionization states for low-density radiatively cooling gas containing cosmic abundances of the elements H, He, C, N, O, Ne, Mg, Si, S, and Fe. We present results for gas temperatures between 1e4 and 1e8 K, assuming dust-free and optically thin conditions, and no external radiation. For non-equilibrium cooling we solve the coupled time-dependent ionization and energy loss equations for a radiating gas cooling from an initially hot, >5e6K equilibrium state, down to 1e4K. We present results for heavy element compositions ranging from 1e-3 to 2 times the elemental abundances in the Sun. We consider gas cooling at constant density (isochoric) and at constant pressure (isobaric). We calculate the critical column densities and temperatures at which radiatively cooling clouds make the dynamical transition from isobaric to isochoric evolution. We construct ion ratio diagnostics for the temperature and metallicity in radiatively cooling gas. We provide numerical estimates for the maximal cloud column densities for which the gas remains optically thin to the cooling radiation. We present our computational results in convenient on-line figures and tables (see http://wise-obs.tau.ac.il/~orlyg/cooling/)., Comment: 20 pages, 12 figures. ApJS in press. Electronic data available at http://wise-obs.tau.ac.il/~orlyg/cooling/

(Abridged) We present computations of the metals photoionization structures of pressure supported gas clouds in gravitationally dominant DM minihalos in the extended Galactic halo or LG environment. We consider low-metallicity (0.1-0.3 solar) clouds that are photoionized by the metagalactic radiation field, and which are pressure-confined by a hot external medium. We study the properties of LCDM Burkert (and NFW) minihalos with circular velocities 12-30 km/s. We present results for the volume densities and projected column densities of low-ions, CII, NI, OI, SiII and SII, produced in the neutral cores, and high-ions, CIV, NV, OVI, SiIII, SiIV, and SIII produced in the ionized envelopes. We examine the possible relationships between the compact HI high-velocity clouds (CHVCs), dwarf galaxies, and high-velocity ionized CIV absorbers, within the context of photoionized minihalo models. In pressure-confined (P/k ~50 K/cm^3) mini-halo models for the CHVCs the photoionization states are much lower than in the CIV absorbers. However, for lower bounding pressures (<~1 K/cm^3) in more massive dwarf galaxy scale halos, the photoionization states in the outer envelopes resemble those observed in the CIV HVCs. An important exception is OVI for which our photoionization models underpredict the relative abundances by about an order-of-magnitude, suggesting that additional processes are at play as concluded by Sembach et al. For the cloud size-scales expected in median LCDM Burkert halos, a metallicity of 0.3 solar is required to produce absorption-line strengths comparable to those in the CIV HVCs. We argue that fully ionized and starless "dark galaxies" could be detectable in the local universe as UV metal line absorbers with ionization states similar to the CIV absorbers., Comment: 35 pages, 12 figures. To appear in the Astrophysical Journal

We present a radial-velocity study of the triple-lined system Gliese 644 and derive spectroscopic elements for the inner and outer orbits with periods of 2.9655 and 627 days. We also utilize old visual data, as well as modern speckle and adaptive optics observations, to derive a new astrometric solution for the outer orbit. These two orbits together allow us to derive masses for each of the three components in the system: M_A = 0.410 +/- 0.028 (6.9%), M_Ba = 0.336 +/- 0.016 (4.7%), and $M_Bb = 0.304 +/- 0.014 (4.7%) M_solar. We suggest that the relative inclination of the two orbits is very small. Our individual masses and spectroscopic light ratios for the three M stars in the Gliese 644 system provide three points for the mass-luminosity relation near the bottom of the Main Sequence, where the relation is poorly determined. These three points agree well with theoretical models for solar metallicity and an age of 5 Gyr. Our radial velocities for Gliese 643 and vB 8, two common-proper-motion companions of Gliese 644, support the interpretation that all five M stars are moving together in a physically bound group. We discuss possible scenarios for the formation and evolution of this configuration, such as the formation of all five stars in a sequence of fragmentation events leading directly to the hierarchical configuration now observed, versus formation in a small N cluster with subsequent dynamical evolution into the present hierarchical configuration., Comment: 17 pages, 9 figures, Accepted for publication in MNRAS