A Deprojection Analysis of Abell 1650 with XMM-Newton

We revisit the XMM-Newton observation of the galaxy cluster Abell 1650 with a deprojection technique. We find that the radial deprojected spectra of Abell 1650 can be marginally fitted by a single-temperature model. In order to study the properties of the central gas, we fit the spectra of the central two regions with a two-temperature model. The fits then become significantly better and the cool gas about 1-2keV can be connected with the gas cooling. Fitting the central spectrum (r ≤ 1') by using a cooling flow model with an isothermal component yields a small mass deposition rate of 10-7 11 M⊙ yr-1, while the standard cooling flow model can not fit this spectrum satisfactorily except that there exists a cut-off temperature having a level of about 3 keV. From the isothermal model we derive the deprojected electron density profile ne(r), and then together with the deprojected temperature profile the total mass and gas mass fraction of cluster are also determined. We compare the properties of Abell 1650 with those of Abell 1835 (a large cooling flow cluster) and some other clusters, to explore the difference in properties between large and small cooling flow cluster, and what causes the difference in the cooling flow of different clusters. It has been shown that Abell 1835 has a steeper potential well and thus a higher electron density and a lower temperature in its center, indicating that the shape of the gravitational potential well in central region determines the cooling flow rates of clusters. We calculate the potential, internal and radiated energies of these two clusters, and find that the gas energies in both clusters are conserved during the collapsing stage.     

Statistical Cluster-QSO Weak Lensing in the Sloan Digital Sky Survey

We investigate the cross-correlation between galaxy clusters and QSOs using Sloan Digital Sky Survey (SDSS) DR4 - 5000 deg2 data. With photometric redshifts of galaxies, we select galaxy clusters based on the local projected densities of LRGs brighter than Mr' = -22. The QSOs are from the main sample of SDSS QSO spectroscopic survey to i' - 19. A significant positive correlation is found between the clusters and QSOs. Under the assumption that the signal is caused by gravitational leasing, we fit the signal with singular isothermal sphere (SIS) model and NFW profile halo model. The velocity dispersionσv = 766 km s-1 is derived for the best-fit of SIS model. Best-fit for the NFW model requires the dark matter halo mass within 1.5 h-1 Mpc to be 4.6×1014 h-1 M⊙. The mass parameterΩcl of the cluster sample is deduced as 0.077 with the SIS model and 0.083 with the NFW model. Our results ofΩcl are smaller than those given by Croom & Shanks and by Myers et al.     

An empirical model to form and evolve galaxies in dark matter halos

Based on the star formation histories of galaxies in halos with different masses, we develop an empirical model to grow galaxies in dark matter halos. This model has very few ingredients, any of which can be associated with observational data and thus be efficiently assessed. By applying this model to a very high resolution cosmological N-body simulation, we predict a number of galaxy properties that are a very good match to relevant observational data. Namely, for both centrals and satellites, the galaxy stellar mass functions up to redshift z ≈ 4 and the conditional stellar mass functions in the local universe are in good agreement with observations. In addition, the two point correlation function is well predicted in the different stellar mass ranges explored by our model. Furthermore, after applying stellar population synthesis models to our stellar composition as a function of redshift, we find that the luminosity functions in the 0.1_u,0.1_g,0.1_r,0.1_i and 0.1_z bands agree quite well with the SDSS observational results down to an absolute magnitude at about –17.0. The SDSS conditional luminosity function itself is predicted well. Finally, the cold gas is derived from the star formation rate to predict the HI gas mass within each mock galaxy. We find a remarkably good match to observed HI-to-stellar mass ratios. These features ensure that such galaxy/gas catalogs can be used to generate reliable mock redshift surveys.     

Chandra Studies of the X-ray gas properties of fossil systems

We study ten galaxy groups and clusters suggested in the literature to be "fossil systems(FSs)"based on Chandra observations. According to the M_(500)- T and L_X- T relations, the gas properties of FSs are not physically distinct from ordinary galaxy groups or clusters. We also first study the f_(gas, 2500)- T relation and find that the FSs exhibit the same trend as ordinary systems. The gas densities of FSs within 0.1_(r200) are ~ 10~(-3)cm~(-3), which is the same order of magnitude as galaxy clusters. The entropies within 0.1_(r200)(S_(0.1r200)) of FSs are systematically lower than those in ordinary galaxy groups, which is consistent with previous reports, but we find their S_(0.1r200)- T relation is more similar to galaxy clusters. The derived mass profiles of FSs are consistent with the Navarro, Frenk and White model in(0.1- 1)_(r200), and the relation between scale radius r_s and characteristic mass density δ_c indicates self-similarity of dark matter halos of FSs. The ranges of r_s and δ_c for FSs are also close to those of galaxy clusters. Therefore, FSs share more common characteristics with galaxy clusters. The special birth place of the FS makes it a distinct type of galaxy system.     

Mass-Temperature Relation of X-ray Clusters in Triaxial Halo

We investigate the mass-temperature relation of clusters for both the spherical NFW halo model and a concentric triaxial halo model. We study the temperature and density distributions of both an isothermal and a polytropic intra-cluster gas in hydrostatic equilibrium. We find that both the uncertainties in the concentration parameter and in the eccentricities (in case of the triaxial halo) lead to a greater scatter in the emission-weighted temperature at a given halo mass for less massive clusters. This may be helpful when determining the intrinsic statistical error of the σ8 normalization of the linear power spectrum from cluster abundance.     

Integrated HI emission in galaxy groups and clusters

The integrated HI emission from hierarchical structures such as groups and clusters of galaxies can be detected by FAST at intermediate redshifts. Here we propose to use FAST to study the evolution of the global HI content of clusters and groups over cosmic time by measuring their integrated HI emissions. We use the Virgo Cluster as an example to estimate the detection limit of FAST, and have estimated the integration time to detect a Virgo type cluster at different redshifts(from z = 0.1 to z = 1.5). We have also employed a semi-analytic model(SAM) to simulate the evolution of HI contents in galaxy clusters. Our simulations suggest that the HI mass of a Virgo-like cluster could be 2–3 times higher and the physical size could be more than 50% smaller when redshift increases from z = 0.3 to z = 1. Thus the integration time could be reduced significantly and gas rich clusters at intermediate redshifts can be detected by FAST in less than 2 hours of integration time. For the local Universe, we have also used SAM simulations to create mock catalogs of clusters to predict the outcomes from FAST all sky surveys. Comparing with the optically selected catalogs derived by cross matching the galaxy catalogs from the SDSS survey and the ALFALFA survey, we find that the HI mass distribution of the mock catalog with 20 s of integration time agrees well with that of observations. However, the mock catalog with 120 s of integration time predicts many more groups and clusters that contain a population of low mass HI galaxies not detected by the ALFALFA survey. A future deep HI blind sky survey with FAST would be able to test such prediction and set constraints on the numerical simulation models. The observational strategy and sample selections for future FAST observations of galaxy clusters at high redshifts are also discussed.     

Braking PSR J1734–3333 with a possible fall-back disk

The very small braking index of PSR J1734–3333,n=0.9±0.2,challenges the current theories of braking mechanisms in pulsars.We present a possible interpretation that this pulsar is surrounded by a fall-back disk and braked by it.A modified braking torque is proposed based on the competition between the magnetic energy density of the pulsar and the kinetic energy density of the fall-back disk.With this torque,a self-similar disk can fit all the observed parameters of PSR J1734–3333with natural initial values of parameters.In this regime,the star will evolve to the region having anomalous X-ray pulsars and soft gamma repeaters in the P˙P diagram in about 20 000 years and stay there for a very long time.The mass of the disk around PSR J1734–3333 in our model is about 10M⊕,similar to the observed mass of the disk around AXP 4U 0142+61.     

Stellar and HI Mass Functions Predicted by a Simple Preheating Galaxy Formation Model

According to the new preheating mechanism of galaxy formation suggested by Mo et al., we construct a simple model of formation of disk galaxies within the current paradigm of galaxy formation. It incorporates preheating, gas cooling, bulge formation and star for-mation. The predicted stellar and HI mass functions of galaxies are discussed and compared with the observations. It is found that our model can roughly match both the observed galaxy luminosity function and the observed HI-mass function.     

The non-Gaussian distribution of galaxy gravitational fields

We perform a theoretical analysis of the observational dependence between angular momentum of galaxy clusters and their mass(richness), based on the method introduced in our previous paper.For that we obtain the distribution function of gravitational fields for astronomical objects(like galaxies and/or smooth halos of different kinds) due to their tidal interaction. By applying the statistical method of Chandrasekhar, we are able to show that the distribution function is determined by the form of interaction between objects and for multipole(tidal) interaction it is never Gaussian. Our calculation permits demonstrating how the alignment of galaxy angular momenta depends on cluster richness. The specific form of the corresponding dependence is due to assumptions made about cluster morphology. Our approach also predicts the time evolution of stellar object angular momenta within CDM and ΛCDM models. Namely, we have shown that angular momentum of galaxies increases with time.     

The distance duality relation test from the ACT cluster and type Ia supernova data

The validity of the cosmic distance-duality(DD) relation is investigated by using 91 measurements of the gas mass fraction of galaxy clusters recently reported by the Atacama Cosmology Telescope(ACT) and the luminosity distance from the Union2.1 type Ia supernova(SNIa) sample independent of any cosmological models and the value of the Hubble constant. We consider four different approaches to derive the gas mass function and two different parameterizations of the DD relation, and find that they have very slight influences on the DD relation test and the relation is valid at the 1σ confidence level. We also discuss the constraints on α and β, which represent the effects of the shapes and colors of the light curves of SNIa,respectively. Our results on α and β are different from those obtained from the ΛCDM model and the galaxy cluster plus SNIa data.     

X-Ray Properties of the Point Source Population in the Spiral Galaxy NGC 5055 （M63） with Chandra

Using Chandra ACIS S3 data we studied the X-ray properties of low-and high- mass X-ray binary populations in the nearby spiral galaxy NGC 5055. A total of 43 X-ray point sources were detected within two effective radii, with 31 sources located on the disk and the rest 12 sources in the bulge. The resolved point sources dominate the X-ray emission of the galaxy, accounting for about 80% of the total counts in 0.3–10keV. From spectral fittings we calculated the 0.3–10.0keV luminosities of all the detected X-ray point sources and found that they span a wide range from a few times 1037 erg s-1 to over 1039 erg s-1. After compensating for incompleteness at the low luminosity end, we found that the corrected XLF of the bulge populationis well fitted with a brokenpower-law with a break at 1.57 - 00..2210× 1038 erg s-1, while the profile of the disk population’s XLF agrees with a single power- law distribution of slope 0.93 -00..0076. The disk population is significantly richer at >～ 2 × 1038 erg s-1 than the bulge population, indicating that the disk may have undergonerelatively recent, strong starbursts that significantly increased the HMXB population, although ongoing starbursts are also observed in the nuclear region. Similar XLF profiles of the bulge and disk populations were found in M81. However, in most other spiral galaxies different patterns of spatial variation of the XLF profiles from the bulge to the disk have been observed, indicating that the star formation and evolution history may be more complex than we have expected.     

SDSS J012119.10 001949.9:a very short period M dwarf contact binary from SDSS stripe 82

We present the first multicolor photometric observations of the short period low-mass eclipsing binary SDSS J012119.10–001949.9.By using the 2013 version of the Wilson-Devinney code,the photometric solutions are derived.It is found that the system is in a contact configuration(f=18.9±6.0%)with a moderate mass ratio of 0.5±0.01.A third light contributing about 6.1±1.3%of the total luminosity in the V band was found,which may come from a cool tertiary component.The derived high orbital inclination(i=83.9?±0.5?)and the almost symmetric three light curves suggest that the determined parameters are reliable.Both the color class and spectral class of the system correspond to a spectral type of M0,which may indicate that SDSS J012119.10–001949.9 belongs to a very rare class of M dwarf contact binaries that are below the theoretical short period limit.     

Constraining the Spatial Curvature of the Local Universe with Deep Learning

We use the distance sum rule method to constrain the spatial curvature of the Universe with a large sample of 161strong gravitational lensing systems,whose distances are calibrated from the Pantheon compilation of type Ⅰa supernovae using deep learning.To investigate the possible influence of mass model of the lens galaxy on constraining the curvature parameter Ω_k,we consider three different lens models.Results show that a flat Universe is supported in the singular isothermal sphere(S...     

ISO-SWS Observations of NGC 1068

We present a first analysis of 2.4-45μm spectra of NGC 1068 obtained with the Short Wavelength Spectrometer SWS on board the Infrared Space Observatory ISO. The measured fine-structure line fluxes can be fit successfully by a simple photoionization model invoking an EUV bump in the ionizing continuum, similar to the case of the Circinus galaxy. Difference are observed between the [OIV] 26μm NLR line profile and optical NLR line profiles which may indicate significant extinction to part of the NLR. We detect pure rotational transitions of molecular hydrogen that must be emitted by molecular gas spanning a wide range of temperatures. The unusual strength of the fundamental S(0) 28μm rotational transition is evidence for a large (> 1.5 × 109 M⊙) gas mass at temperatures nea r 100 K. Either most of the gas in the circumnuclear region of NGC 1068 is warm or previous molecular mass estimates based on CO observations were too low. Strong mid-infrared continuum from the circumnuclear warm dust is prominent in our spectrum. The weak PAH emission detected at the edges of the 9.7μm silicate absorption should be considered in interpretations of the silicate feature. This revised version was published online in July 2006 with corrections to the Cover Date.     

Metal enrichment via ram pressure stripping in the IGM of the compact galaxy group RGH 80

By creating and analyzing two dimensional gas temperature and abundance maps of the RGH 80 compact galaxy group with high-quality Chandra data,we detect a high-abundance (■0.7 Z⊙) arc,where the metal abundance is significantly higher than the surrounding regions by ■0.3Z⊙.This structure shows tight spatial correlations with the member galaxy PGC 046529,as well as with the arm-like feature identified on the X-ray image in the previous work of Randall et al.(2009).Since no apparent signature of AGN activity i...     

Re-Identification of the ''''Enigmatic'''' X-ray Source 1RXS J114003.0+124112

The ROSAT X-ray source 1RXS J114003.0 124112 was identified as a starburst galaxy at redshift 0.177 by He et al. The authors also noted that the source is almost two orders of magnitude brighter in X-ray than the X-ray-brightest starburst galaxy and it seems to be in a merging system, making this source an enigmatic system demanding further observations. Here we report a re-identification of 1RXS J114003.0 124112 using observations on the 2.6m telescope at Byurakan Astrophysical Observatory, Armenia and the SDSS data. The results indicate that the starburst activity is associated with the brighter object of the system, while the fainter object is a typical Seyfert 1 galaxy at a different redshift (0.282). Therefore, the two objects are not in a merging system, and the Seyfert 1 galaxy naturally accounts for the high X-ray flux. Three more objects reside in the vicinity, but they are all too faint to be responsible for the high X-ray flux.     

Molecular Gas and Dust in the Massive Star Forming Region S 233 IR

The massive star forming region S 233 IR is observed in the molecular lines CO J = 2-1, 3-2, NH3 (1,1), (2,2) and the 870#m dust continuum. Four submillimeter continuum sources, labelled SMM 1-4, are revealed in the 870μm dust emission. The main core, SMM1, is found to be associated with a deeply embedded near infrared cluster in the northeast; while the weaker source SMM2 coincides with a more evolved cluster in the southwest. The best fit spectral energy distribution of SMM1 gives an emissivity of β = 1.6, and temperatures of 32 K and 92 K for the cold- and hot-dust components. An SMM1 core mass of 246 M⊙ and a total mass of 445 M⊙ are estimated from the 870μm dust continuum emission.SMM1 is found to have a temperature gradient decreasing from inside out, indicative of the presence of interior heating sources. The total outflow gas mass as traced by the CO J = 3-2 emission is estimated to be 35 M⊙. Low velocity outflows are also found in the NH3 (1,1) emission. The non-thermal dominant NH3 line width as well as the substantial core mass suggest that the SMM1 core is a “turbulent,massive dense core”, in the process of forming a group or a cluster of stars. The much higher star formation efficiency found in the southwest cluster supports the suggestion that this cluster is more evolved than the northeast one. Large near infrared photometric variations found in the source PCS-IR93, a previously found highly polarized nebulosity, indicate an underlying star showing the FU Orionis type of behavior.     

Weak Merging Scenario of CLASH Cluster A209

We study the structural and dynamical properties of A209 based on Chandra and XMM-Newton observations. We obtain detailed temperature, pressure, and entropy maps with the contour binning method, and find a hot region in the NW direction. The X-ray brightness residual map and corresponding temperature profiles reveal a possible shock front in the NW direction and a cold front feature in the SE direction. Combined with the galaxy luminosity density map we propose a weak merger scenario. A young su...     

An Analytic Model of Galactic Winds and Mass Outflows

Galactic winds and mass outflows are observed both in nearby starburst galaxies and in high-redshift star-forming galaxies. We develop a simple analytic model to understand the observed superwind phenomenon with a discussion of the model uncertainties. Our model is built upon the model of McKee & Ostriker for the interstellar medium. It allows one to predict how properties of a superwind, such as wind velocity and mass outflow rate, are related to properties of its starforming host galaxy, such as size, gas density and star formation rate. The model predicts a threshold of star formation rate density for the generation of observable galactic winds. Galaxies with more concentrated star formation activities produce superwinds with higher velocities. The predicted mass outflow rates are comparable to (or slightly larger than) the corresponding star formation rates. We apply our model to both local starburst galaxies and high-redshift Lyman break galaxies, and find its predictions to be in good agreement with current observations. Our model is simple and so can be easily incorporated into numerical simulations and semi-analytical models of galaxy formation.     

Quantifying the Tension between Cosmological Models and JWST Red Candidate Massive Galaxies

We develop a Python tool to estimate the tail distribution of the number of dark matter halos beyond a mass threshold and in a given volume in a light-cone. The code is based on the extended Press–Schechter model and is computationally efficient, typically taking a few seconds on a personal laptop for a given set of cosmological parameters. The high efficiency of the code allows a quick estimation of the tension between cosmological models and the red candidate massive galaxies released by the J...