Heating of the IGM

Using the cosmic virial theorem, Press-Schechter analysis and numerical simulations, we compute the expected X-ray background (XRB) from the diffuse IGM with the clumping factor expected from gravitational shock heating. The predicted fluxes and temperatures are excluded from the observed XRB. The predicted clumping can be reduced by entropy injection. The required energy is computed from the two-point correlation function, as well as from Press-Schechter formalisms. The minimal energy injection of 1 keV/nucleon excludes radiative or gravitational heating as a primary energy source. We argue that the intergalactic medium (IGM) must have been heated through violent processes such as massive supernova bursts. If the heating proceeded through supernova explosions, it likely proceeded in bursts which may be observable in high redshift supernova searches. Within our model we reproduce the observed cluster luminosity-temperature relation with energy injection of 1 keV/nucleon if this injection is assumed to be uncorrelated with the local density. These parameters predict that the diffuse IGM soft XRB has a temperature of ~1 keV with a flux near 10 keV/cm^2 s str keV, which may be detectable in the near future.Comment: to appear in ApJ Lett., 11 pages incl 1 figur

The Multiphase Intracluster Medium in Galaxy Groups Probed by the Lyman Alpha Forest

The case is made that the intracluster medium (ICM) in spiral-rich galaxy groups today probably has undergone much slower evolution than that in elliptical-rich groups and clusters. The environments of proto-clusters and proto-groups at z > 2 are likely similar to spiral-rich group environments at lower redshift. Therefore, like the ICM in spiral-rich groups today, the ICM in proto-groups and proto-clusters at z > 2 is predicted to be significantly multiphased. The QSO Lyman alpha forest in the vicinity of galaxies is an effective probe of the ICM at a wide range of redshift. Two recent observations of Lyman alpha absorption around galaxies by Adelberger et al. and by Pascarelle et al are reconciled, and it is shown that observations support the multiphase ICM scenario. Galaxy redshifts must be very accurate for such studies to succeed. This scenario can also explain the lower metallicity and lower hot gas fraction in groups.Comment: 4 pages, 1 figure, replaced with the version after proo

Distance to G14.33-0.64 in the Sagittarius Spiral Arm: H2O Maser Trigonometric Parallax with VERA

We report on trigonometric parallax measurements for the Galactic star forming region G14.33-0.64 toward the Sagittarius spiral arm. We conducted multi-epoch phase-referencing observations of an H2O maser source in G14.33-0.64 with the Japanese VLBI array VERA. We successfully detected a parallax of 0.893+/-0.101 mas, corresponding to a source distance of 1.12+/-0.13 kpc, which is less than half of the kinematic distance for G14.33-0.64. Our new distance measurement demonstrates that the Sagittarius arm lies at a closer distance of ~1 kpc, instead of previously assumed ~2-3 kpc from kinematic distances. The previously suggested deviation of the Sagittarius arm toward the Galactic center from the symmetrically fitted model (Taylor & Cordes 1993) is likely due to large errors of kinematic distances at low galactic longitudes. G14.33-0.64 most likely traces the near side of the Sagittarius arm. We attempted fitting the pitch angle of the arm with other parallax measurements along the arm, which yielded two possible pitch angles of i=34.7+/-2.7 degrees and i=11.2+/-10.5 degrees. Our proper motion measurements suggest G14.33-0.64 has no significant peculiar motion relative to the differential rotation of the Galaxy (assumed to be in a circular orbit), indicating that the source motion is in good agreement with the Galactic rotation.Comment: 14 pages, 7 figures, to appear in PASJ Vol. 62, No.

Dark Matter Halo Models of Stellar Mass-Dependent Galaxy Clustering in PRIMUS+DEEP2 at 0.2<z<1.2

We utilize $\Lambda$CDM halo occupation models of galaxy clustering to investigate the evolving stellar mass dependent clustering of galaxies in the PRIsm MUlti-object Survey (PRIMUS) and DEEP2 Redshift Survey over the past eight billion years of cosmic time, between $0.2<z<1.2$. These clustering measurements provide new constraints on the connections between dark matter halo properties and galaxy properties in the context of the evolving large-scale structure of the universe. Using both an analytic model and a set of mock galaxy catalogs, we find a strong correlation between central galaxy stellar mass and dark matter halo mass over the range $M_\mathrm{halo}\sim10^{11}$-$10^{13}~h^{-1}M_\odot$, approximately consistent with previous observations and theoretical predictions. However, the stellar-to-halo mass relation (SHMR) and the mass scale where star formation efficiency reaches a maximum appear to evolve more strongly than predicted by other models, including models based primarily on abundance-matching constraints. We find that the fraction of satellite galaxies in haloes of a given mass decreases significantly from $z\sim0.5$ to $z\sim0.9$, partly due to the fact that haloes at fixed mass are rarer at higher redshift and have lower abundances. We also find that the $M_1/M_\mathrm{min}$ ratio, a model parameter that quantifies the critical mass above which haloes host at least one satellite, decreases from $\approx20$ at $z\sim0$ to $\approx13$ at $z\sim0.9$. Considering the evolution of the subhalo mass function vis-\`{a}-vis satellite abundances, this trend has implications for relations between satellite galaxies and halo substructures and for intracluster mass, which we argue has grown due to stripped and disrupted satellites between $z\sim0.9$ and $z\sim0.5$.Comment: 17 pages, 9 figures and 4 tables; Astrophysical Journal, publishe

Coevolution of Supermassive Black Holes and Circumnuclear Disks

We propose a new evolutionary model of a supermassive black hole (SMBH) and a circumnuclear disk (CND), taking into account the mass-supply from a host galaxy and the physical states of CND. In the model, two distinct accretion modes depending on gravitational stability of the CND play a key role on accreting gas to a SMBH. (i) If the CMD is gravitationally unstable, energy feedback from supernovae (SNe) supports a geometrically thick, turbulent gas disk. The accretion in this mode is dominated by turbulent viscosity, and it is significantly larger than that in the mode (ii), i.e., the CMD is supported by gas pressure. Once the gas supply from the host is stopped, the high accretion phase ($\sim 0.01- 0.1 M_{\odot} {\rm yr}^{-1}$) changes to the low one (mode (ii), $\sim 10^{-4} M_{\odot} {\rm yr}^{-1}$), but there is a delay with $\sim 10^{8}$ yr. Through this evolution, the gas-rich CND turns into the gas poor stellar disk. We found that not all the gas supplied from the host galaxy accrete onto the SMBH even in the high accretion phase (mode (i)), because the part of gas is used to form stars. As a result, the final SMBH mass ($M_{\rm BH,final}$) is not proportional to the total gas mass supplied from the host galaxy ($M_{\rm sup}$); $M_{\rm BH,final}/M_{\rm sup}$ decreases with $M_{\rm sup}$.This would indicate that it is difficult to form a SMBH with $\sim 10^{9} M_{\odot}$ observed at high-$z$ QSOs. The evolution of the SMBH and CND would be related to the evolutionary tracks of different type of AGNs.Comment: 11 pages, 11 figures, accepted for publication in Ap

The Possible White Dwarf-Neutron Star Connection

The current status of the problem of whether neutron stars can form, in close binary systems, by accretion-induced collapse (AIC) of white dwarfs is examined. We find that, in principle, both initially cold C+O white dwarfs in the high-mass tail of their mass distribution in binaries and O+Ne+Mg white dwarfs can produce neutron stars. Which fractions of neutron stars in different types of binaries (or descendants from binaries) might originate from this process remains uncertain.Comment: 6 pages. To appear in "White Dwarfs", ed. J. Isern, M. Hernanz, and E. Garcia-Berro (Dordrecht: Kluwer

Hubble Space Telescope Imaging in the Chandra Deep Field South: III. Quantitative Morphology of the 1Ms Chandra Counterparts and Comparison with the Field Population

We present quantitative morphological analyses of 37 HST/WFPC2 counterparts of X-ray sources in the 1 Ms Chandra Deep Field-South (CDFS). We investigate: 1) 1-D surface brightness profiles via isophotal ellipse fitting; 2) 2-D, PSF- convolved, bulge+disk+nucleus profile-fitting; 3) asymmetry and concentration indices compared with all ~3000 sources in our three WFPC2 fields; and 4) near- neighbor analyses comparing local environments of X-ray sources versus the field control sample. Significant nuclear point-source optical components appear in roughly half of the resolved HST/WFPC2 counterparts, showing a narrow range of F_X/F_{opt,nuc} consistent with the several HST-unresolved X-ray sources (putative type-1 AGN) in our fields. We infer roughly half of the HST/WFPC2 counterparts host unobscured AGN, which suggests no steep decline in the type-1/type-2 ratio out to the redshifts z~0.5-1 typical of our sources. The concentration indices of the CDFS counterparts are clearly larger on average than those of the field distribution, at 5-sigma, suggesting that the strong correlation between central black hole mass and host galaxy properties (including concentration index) observed in nearby galaxies is already evident by z~0.5-1. By contrast, the asymmetry index distribution of the 21 resolved CDFS sources at I<23 is indistinguishable from the I<23 field. Moreover, the frequency of I<23 near neighbors around the CDFS counterparts is not significantly different from the field sample. These results, combined with previous similar findings for local samples, suggest that recent merger/ interaction history is not a good indicator of AGN activity over a substantial range of look-back time.Comment: 30 pages, incl. 8 figures; accepted for publication in the Astrophysical Journa

The North Ecliptic Pole Supercluster

We have used the ROSAT All-Sky Survey to detect a known supercluster at z=0.087 in the North Ecliptic Pole region. The X-ray data greatly improve our understanding of this supercluster's characteristics, approximately doubling our knowledge of the structure's spatial extent and tripling the cluster/group membership compared to the optical discovery data. The supercluster is a rich structure consisting of at least 21 galaxy clusters and groups, 12 AGN, 61 IRAS galaxies, and various other objects. A majority of these components were discovered with the X-ray data, but the supercluster is also robustly detected in optical, IR, and UV wavebands. Extending 129 x 102 x 67 (1/h50 Mpc)^3, the North Ecliptic Pole Supercluster has a flattened shape oriented nearly edge-on to our line-of-sight. Owing to the softness of the ROSAT X-ray passband and the deep exposure over a large solid angle, we have detected for the first time a significant population of X-ray emitting galaxy groups in a supercluster. These results demonstrate the effectiveness of X-ray observations with contiguous coverage for studying structure in the Universe.Comment: Accepted for publication in The Astrophysical Journal; 5 pages with 2 embedded figures; uses emulateapj.sty; For associated animations, see http://www.ifa.hawaii.edu/~mullis/nep3d.html; A high-resolution color postscript version of the full paper is available at http://www.ifa.hawaii.edu/~mullis/papers/nepsc.ps.g