Cumulative Luminosity Function Research Articles

X-ray emission from hot gas and XRBs in the NGC 5846 galaxy

Abstract This article presents X-ray emission characteristics of the brightest member of a G50 galaxy group NGC 5846 based on analysis of high resolution of 30 ks and 90 ks Chandra X-ray data. X-ray imaging analysis revealed the presence of 90 discrete X-ray point sources, spectral study of which depicted that the majority of them are LMXBs with a neutron star accretor. Among 90, only one source exhibits an X-ray luminosity greater than 1 0 39 erg s − 1 1{0}^{39}\hspace{0.33em}{\rm{erg}}\hspace{0.33em}{{\rm{s}}}^{-1} , exceeding the Eddington limit for a canonical mass of a neutron star and occupies a position in the hard region of the X-ray color–color plot. The cumulative X-ray luminosity function plot for all resolved XRBs exhibits a knee at L X = 6.6 × 1 0 38 erg s − 1 {L}_{X}=6.6\times \hspace{0.33em}1{0}^{38}\hspace{0.33em}{\rm{erg}}\hspace{0.33em}{{\rm{s}}}^{-1} , corresponding to the Eddington limit of 2.8 solar mass neutron star. The most dominant source of the observed X-ray luminosity of NGC 5846 happens to be the diffusely distributed plasma, making its contribution up to 85% of its total value, while the contribution from resolved and unresolved point sources is up to 15%. The surface brightness distribution of the X-ray emitting gas in this galaxy exhibit structures in the form of discontinuities due to the presence of a pair of cold fronts at ∼ 20 \sim 20 kpc. The presence of these cold fronts were confirmed in the azimuthally averaged surface brightness profile and sectorial temperature profiles and may have formed due to minor mergers. The larger values of emission line flux density ratio log([N II]H α \alpha ) and floor in the entropy profile of the plasma collectively point toward a nonthermal ionization source of gas heating like a low-level AGN activity.

Devouring the Centaurus A Satellites: Modeling Dwarf Galaxies with Galacticus

For the first time, systematic studies of dwarf galaxies are being conducted throughout the Local Volume, including the dwarf satellites of the nearby giant elliptical galaxy Centaurus A (NGC 5128). Given Centaurus A's mass (roughly 10 times larger than that of the Milky Way), AGN activity, and recent major mergers, investigating the dwarf galaxies of Centaurus A and their star formation physics is imperative. However, simulating the faintest dwarfs around a galaxy of Centaurus A's mass with sufficient resolution in a hydrodynamic simulation is computationally expensive and currently infeasible. In this study, we seek to reproduce the properties of Centaurus A dwarfs using the semianalytic model Galacticus to model dwarfs within a 700 kpc region around Centaurus A, corresponding approximately to its splashback radius. We investigate the effects of host halo mass and environment and predict observable properties of Centaurus A dwarfs using astrophysical prescriptions and parameters previously tuned to match properties of the Milky Way’s satellite galaxies. This approach allows us to approximately replicate cumulative luminosity functions, and luminosity–metallicity and luminosity–half-light-radii relations observed in the Centaurus A satellites. We provide predictions for the velocity dispersions, and star formation histories of Centaurus A dwarfs. The agreement between our predicted star formation histories for Centaurus A dwarfs and those of the Milky Way dwarfs implies the presence of universal processes governing star formation in dwarf galaxies. Overall, our findings shed light on the star formation physics of dwarf galaxies in the Centaurus A system, revealing insights into their properties and dependence on the host environment.

New dwarf galaxy candidates in the sphere of influence of the Sombrero galaxy

ABSTRACT We report the discovery of 40 new satellite dwarf galaxy candidates in the sphere of influence of the Sombrero Galaxy (M104), the most luminous galaxy in the Local Volume. Using the Subaru Hyper Suprime-Cam, we surveyed 14.4 deg2 of its surroundings, extending to the virial radius. Visual inspection of the deep images and galfit modelling yielded a galaxy sample highly complete down to Mg ∼ −9 ($L_{g}\sim 3\times 10^{5}\ \mathrm{ L}_\odot$) and spanning magnitudes −16.4 < Mg < −8 and half-light radii 50 pc < re < 1600 pc assuming the distance of M104. These 40 new candidates, out of which 27 are group members with high confidence, double the number of potential satellites of M104 within the virial radius, placing it among the richest hosts in the Local Volume. Using a principal component analysis, we find that the entire sample of candidates is consistent with an almost circular on-sky distribution, more circular than any comparable environment found in the Illustris TNG100-1 (The Next Generation) simulation. However, the distribution of the high-probability sample is more oblate and consistent with the simulation. The cumulative satellite luminosity function is broadly consistent with analogues from the simulation, albeit it contains no bright satellite with Mg < −16.4 ($L_{g}\sim 3 \times 10^{8}\ \mathrm{ L}_\odot$), a $2.3\, \sigma$ occurrence. Follow-up spectroscopy to confirm group membership will begin to demonstrate how these systems can act as probes of the structure and formation history of the halo of M104.

Devouring the Milky Way Satellites: Modeling Dwarf Galaxies with Galacticus

Dwarf galaxies are ubiquitous throughout the universe and are extremely sensitive to various forms of internal and external feedback. Over the last two decades, the census of dwarf galaxies in the Local Group and beyond has increased markedly. While hydrodynamic simulations (e.g., FIRE II, Mint Justice League) have reproduced the observed dwarf properties down to the ultrafaints, such simulations require extensive computational resources to run. In this work, we constrain the standard physical implementations in the semianalytic model Galacticus to reproduce the observed properties of the Milky Way satellites down to the ultrafaint dwarfs found in the Sloan Digital Sky Survey. We run Galacticus on merger trees from our high-resolution N–body simulation of a Milky Way analog. We determine the best-fit parameters by matching the cumulative luminosity function and luminosity–metallicity relation from both observations and hydrodynamic simulations. With the correct parameters, the standard physics in Galacticus can reproduce the observed luminosity function and luminosity–metallicity relation of the Milky Way dwarfs. In addition, we find a multidimensional match with half-light radii, velocity dispersions, and mass to light ratios at z = 0 down to M V ≤ −6 (L ≥ 104 L ⊙). In addition to successfully reproducing the properties of the z = 0 Milky Way satellite population, our modeled dwarfs have star formation histories that are consistent with those of the Local Group dwarfs.

Virial Halo Mass Function in the Planck Cosmology

Abstract We study halo mass functions with high-resolution N-body simulations under a ΛCDM cosmology. Our simulations adopt the cosmological model that is consistent with recent measurements of the cosmic microwave backgrounds with the Planck satellite. We calibrate the halo mass functions for 108.5 ≲ M vir/(h −1 M ⊙) ≲ 1015.0–0.45 z , where M vir is the virial spherical-overdensity mass and redshift z ranges from 0 to 7. The halo mass function in our simulations can be fitted by a four-parameter model over a wide range of halo masses and redshifts, while we require some redshift evolution of the fitting parameters. Our new fitting formula of the mass function has a 5%-level precision, except for the highest masses at z ≤ 7. Our model predicts that the analytic prediction in Sheth & Tormen would overestimate the halo abundance at z = 6 with M vir = 108.5–10 h −1 M ⊙ by 20%–30%. Our calibrated halo mass function provides a baseline model to constrain warm dark matter (WDM) by high-z galaxy number counts. We compare a cumulative luminosity function of galaxies at z = 6 with the total halo abundance based on our model and a recently proposed WDM correction. We find that WDM with its mass lighter than 2.71 keV is incompatible with the observed galaxy number density at a 2σ confidence level.

The luminosity functions and redshift evolution of satellites of low-mass galaxies in the COSMOS survey

ABSTRACT The satellite populations of the Milky Way, and Milky Way mass galaxies in the local Universe, have been extensively studied to constrain dark matter and galaxy evolution physics. Recently, there has been a shift to studying satellites of hosts with stellar masses between that of the Large Magellanic Cloud and the Milky Way, since they can provide further insight on hierarchical structure formation, environmental effects on satellites, and the nature of dark matter. Most work is focused on the Local Volume, and little is still known about low-mass host galaxies at higher redshift. To improve our understanding of the evolution of satellite populations of low-mass hosts, we study satellite galaxy populations as a function of host stellar mass 9.5 < log (M*/M⊙) < 10.5 and redshifts 0.1 < $z$ < 0.8 in the COSMOS survey, making this the first study of satellite systems of low-mass hosts across half the age of the universe. We find that the satellite populations of low-mass host galaxies, which we measure down to satellite masses equivalent to the Fornax dwarf spheroidal satellite of the Milky Way, remain mostly unchanged through time. We observe a weak dependence between host stellar mass and number of satellites per host, which suggests that the stellar masses of the hosts are in the power-law regime of the stellar mass to halo mass relation (M*–Mhalo) for low-mass galaxies. Finally, we test the constraining power of our measured cumulative luminosity function to calculate the low-mass end slope of the M*–Mhalo relation. These new satellite luminosity function measurements are consistent with Lamda cold dark matter predictions.

Using Strong Gravitational Lensing to Identify Fossil Group Progenitors

Abstract Fossil galaxy systems are classically thought to be the end result of galaxy group/cluster evolution, as galaxies experiencing dynamical friction sink to the center of the group potential and merge into a single, giant elliptical that dominates the rest of the members in both mass and luminosity. Most fossil systems discovered lie within z < 0.2, which leads to the question, what were these systems’ progenitors? Such progenitors are expected to have imminent or ongoing major merging near the brightest group galaxy that, when concluded, will meet the fossil criteria within the look forward time. Since strong gravitational lensing preferentially selects groups merging along the line of sight, or systems with a high mass concentration like fossil systems, we searched the CASSOWARY survey of strong-lensing events with the goal of determining whether lensing systems have any predisposition to being fossil systems or progenitors. We find that ∼13% of lensing groups are identified as traditional fossils while only ∼3% of nonlensing control groups are. We also find that ∼23% of lensing systems are traditional fossil progenitors compared to ∼17% for the control sample. Our findings show that strong-lensing systems are more likely to be fossil/pre-fossil systems than comparable nonlensing systems. Cumulative galaxy luminosity functions of the lensing and nonlensing groups also indicate a possible, fundamental difference between strong-lensing and nonlensing systems’ galaxy populations, with lensing systems housing a greater number of bright galaxies even in the outskirts of groups.

The [CII] 158 μm line emission in high-redshift galaxies

Gas is a crucial component of galaxies, providing the fuel to form stars, and it is impossible to understand the evolution of galaxies without knowing their gas properties. The [CII] fine structure transition at 158 μm is the dominant cooling line of cool interstellar gas, and is the brightest of emission lines from star forming galaxies from FIR through metre wavelengths, almost unaffected by attenuation. With the advent of ALMA and NOEMA, capable of detecting [CII]-line emission in high-redshift galaxies, there has been a growing interest in using the [CII] line as a probe of the physical conditions of the gas in galaxies, and as a star formation rate (SFR) indicator at z ≥ 4. In this paper, we have used a semi-analytical model of galaxy evolution (G.A.S.) combined with the photoionisation code CLOUDY to predict the [CII] luminosity of a large number of galaxies (25 000 at z ≃ 5) at 4 ≤ z ≤ 8. We assumed that the [CII]-line emission originates from photo-dominated regions. At such high redshift, the CMB represents a strong background and we discuss its effects on the luminosity of the [CII] line. We studied the L[CII ]–SFR and L[ CII ]–Zg relations and show that they do not strongly evolve with redshift from z = 4 and to z = 8. Galaxies with higher [CII] luminosities tend to have higher metallicities and higher SFRs but the correlations are very broad, with a scatter of about 0.5 and 0.8 dex for L[ CII ]–SFR and L[ CII ]–Zg, respectively. Our model reproduces the L[ CII ]–SFR relations observed in high-redshift star-forming galaxies, with [CII] luminosities lower than expected from local L[ CII ]–SFR relations. Accordingly, the local observed L[ CII ]–SFR relation does not apply at high-z (z ≳ 5), even when CMB effects are ignored. Our model naturally produces the [CII] deficit (i.e. the decrease of L[ CII ]/LIR with LIR), which appears to be strongly correlated with the intensity of the radiation field in our simulated galaxies. We then predict the [CII] luminosity function, and show that it has a power law form in the range of L[ CII] probed by the model (1 × 107–2 × 109 L⊙ at z = 6) with a slope α = −1. The slope is not evolving from z = 4 to z = 8 but the number density of [CII]-emitters decreases by a factor of 20×. We discuss our predictions in the context of current observational estimates on both the differential and cumulative luminosity functions.

The Dragonfly Nearby Galaxies Survey. III. The Luminosity Function of the M101 Group

Abstract We obtained follow-up HST observations of the seven low surface brightness galaxies discovered with the Dragonfly Telephoto Array in the field of the massive spiral galaxy M101. Out of the seven galaxies, only three were resolved into stars and are potentially associated with the M101 group at D = 7 Mpc. Based on HST ACS photometry in the broad F606W and F814W filters, we use a maximum likelihood algorithm to locate the Tip of the Red Giant Branch in galaxy color–magnitude diagrams. Distances are and and we confirm that they are members of the M101 group. Combining the three confirmed low-luminosity satellites with previous results for brighter group members, we find the M101 galaxy group to be a sparsely populated galaxy group consisting of seven group members, down to M V = −9.2 mag. We compare the M101 cumulative luminosity function to that of the Milky Way and M31. We find that they are remarkably similar; in fact, the cumulative luminosity function of the M101 group gets even flatter for fainter magnitudes, and we show that the M101 group might exhibit the two known small-scale flaws in the ΛCDM model, namely “the missing satellite” problem and the “too big to fail” problem. Kinematic measurements of M101's satellite galaxies are required to determine whether the “too big to fail” problem does in fact exist in the M101 group.

CHANDRAAND VERY LARGE ARRAY OBSERVATIONS OF THE NEARBY Sd GALAXY NGC 45

We present an analysis of high angular resolution observations made in the X-ray and the radio with the Chandra X-ray Observatory and the Karl Jansky Very Large Array (VLA), respectively, of the nearby spiral galaxy NGC 45. This galaxy is the third that we have considered in a study of the supernova remnant (SNR) populations of nearby spiral galaxies and the present work represents the first detailed analysis of the discrete X-ray and radio source populations of this galaxy. We analyzed data sets from the three pointed observations made of this galaxy with Chandra along with a merged data set obtained from combining these data sets: the total effective exposure time of the merged data set is 63515 s. A total of 25 discrete X-ray sources are found in the entire field of view of the ACIS-S3 chip, with 16 sources found within the visual extent of the galaxy. We estimate that as many as half of the sources detected in the entire field of view of the ACIS-S3 chip and seven of the sources detected in the optical extent of NGC 45 may be background sources. We analyzed the spectral properties of the discrete X-ray sources within the galaxy and conclude that the majority of these sources are X-ray binaries. We have searched for counterparts at different wavelengths to the discrete X-ray sources and we find two associations: one with a star cluster and the other with a background galaxy. We have found one source that is clearly variable within one observation and seven that are seen to vary from one observation to another. We also conduct a photometric analysis to determine the near-infrared fluxes of the discrete X-ray sources in Spitzer Infrared Array Camera channels. We constructed a cumulative luminosity function of the discrete X-ray sources seen toward NGC 45: taking into account simultaneously the luminosity function of background sources, the fitted slope of the cumulative luminosity function Γ = –1.3_(-1.6)^(+0.7) (all error bounds correspond to 90% confidence intervals). The VLA observations reveal seven discrete radio sources: we find no overlaps between these sources and the X-ray detected sources. Based on their measured spectral indices and their locations with respect to the visible extent of NGC 45, we classify one source as a candidate radio SNR associated with the galaxy and the others as likely background galaxies seen in projection toward NGC 45. Finally, we discuss the properties of a background cluster of galaxies (denoted as CXOU J001354.2–231254.7) seen in projection toward NGC 45 and detected by the Chandra observations. The fit parameters to the extracted Chandra spectra of this cluster are a column density N_H = 0.07(<0.14) × 10^(22) cm^(−2), a temperature kT = 4.22_(-1.42)^(+2.08) keV, an abundance Z = 0.30(<0.75) relative to solar and a redshift z = 0.28 ± 0.14. From the fit parameters we derive an electron number density n_e = 4(±1) × 10^(−3) cm^(−3), an unabsorbed X-ray luminosity L_(0.5-7.0keV) ~ 8.77(±0.96) × 10^(43) erg s^(−1) for the cluster and an X-ray emitting mass M = 2.32(±1.75) × 10^(12)M_☉.

Galaxy luminosity functions in WINGS clusters

Using V band photometry of the WINGS survey, we derive galaxy luminosity functions (LF) in nearby clusters. This sample is complete down to Mv=-15.15, and it is homogeneous, thus allowing the study of an unbiased sample of clusters with different characteristics. We constructed the photometric LF for 72 out of the original 76 WINGS clusters, excluding only those without a velocity dispersion estimate. For each cluster we obtained the LF for galaxies in a region of radius=0.5 x r200, and fitted them with single and double Schechter's functions. We also derive the composite LF for the entire sample, and those pertaining to different morphological classes. Finally we derive the spectroscopic cumulative LF for 2009 galaxies that are cluster members. The double Schechter fit parameters are neither correlated with the cluster velocity dispersion, nor with the X-ray luminosity. Our median values of the Schechter's fit slope are, on average, in agreement with measurements of nearby clusters, but are less steep that those derived from large surveys, such as the SDSS. Early--type galaxies outnumber late-types at all magnitudes, but both early and late types contribute equally to the faint end of the LF. Finally, the spectroscopic LF is in excellent agreement with the ones derived for A2199, A85 and Virgo, and with the photometric one at the bright magnitudes (where both are available). There is a large spread in the LF of different clusters. However, this spread is not caused by correlation of the LF shape with cluster characteristics such as X--ray luminosity or velocity dispersions. The faint end is flatter than what previously derived (alpha_f=-1.7) at odds with what predicted from numerical simulations.

A DEEP CHANDRA ACIS SURVEY OF M83

We have obtained a series of deep X-ray images of the nearby galaxy M83 using Chandra, with a total exposure of 729 ks. Combining the new data with earlier archival observations totaling 61 ks, we find 378 point sources within the D25 contour of the galaxy. We find 80 more sources, mostly background active galactic nuclei (AGNs), outside of the D25 contour. Of the X-ray sources, 47 have been detected in a new radio survey of M83 obtained using the Australia Telescope Compact Array. Of the X-ray sources, at least 87 seem likely to be supernova remnants (SNRs), based on a combination of their properties in X-rays and at other wavelengths. We attempt to classify the point source population of M83 through a combination of spectral and temporal analysis. As part of this effort, we carry out an initial spectral analysis of the 29 brightest X-ray sources. The soft X-ray sources in the disk, many of which are SNRs, are associated with the spiral arms, while the harder X-ray sources, mostly X-ray binaries (XRBs), do not appear to be. After eliminating AGNs, foreground stars, and identified SNRs from the sample, we construct the cumulative luminosity function (CLF) of XRBs brighter than 8 × 1035 erg s−1. Despite M83's relatively high star formation rate, the CLF indicates that most of the XRBs in the disk are low mass XRBs.

LUMINOUS SATELLITES. II. SPATIAL DISTRIBUTION, LUMINOSITY FUNCTION, AND COSMIC EVOLUTION

We infer the normalization and the radial and angular distributions of the number density of satellites of massive galaxies ($\log_{10}[M_{h}^*/M\odot]>10.5$) between redshifts 0.1 and 0.8 as a function of host stellar mass, redshift, morphology and satellite luminosity. Exploiting the depth and resolution of the COSMOS HST images, we detect satellites up to eight magnitudes fainter than the host galaxies and as close as 0.3 (1.4) arcseconds (kpc). Describing the number density profile of satellite galaxies to be a projected power law such that $P(R)\propto R^{\rpower}$, we find $\rpower=-1.1\pm 0.3$. We find no dependency of $\rpower$ on host stellar mass, redshift, morphology or satellite luminosity. Satellites of early-type hosts have angular distributions that are more flattened than the host light profile and are aligned with its major axis. No significant average alignment is detected for satellites of late-type hosts. The number of satellites within a fixed magnitude contrast from a host galaxy is dependent on its stellar mass, with more massive galaxies hosting significantly more satellites. Furthermore, high-mass late-type hosts have significantly fewer satellites than early-type galaxies of the same stellar mass, likely a result of environmental differences. No significant evolution in the number of satellites per host is detected. The cumulative luminosity function of satellites is qualitatively in good agreement with that predicted using subhalo abundance matching techniques. However, there are significant residual discrepancies in the absolute normalization, suggesting that properties other than the host galaxy luminosity or stellar mass determine the number of satellites.

Ensemble properties of comets in the Sloan Digital Sky Survey

We present the ensemble properties of 31 comets (27 resolved and 4 unresolved) observed by the Sloan Digital Sky Survey (SDSS). This sample of comets represents about 1 comet per 10million SDSS photometric objects. Five-band (u,g,r,i,z) photometry is used to determine the comets’ colors, sizes, surface brightness profiles, and rates of dust production in terms of the Afρ formalism. We find that the cumulative luminosity function for the Jupiter Family Comets in our sample is well fit by a power law of the form N(<H)∝10(0.49±0.05)H for H<18, with evidence of a much shallower fit N(<H)∝10(0.19±0.03)H for the faint (14.5<H<18) comets. The resolved comets show an extremely narrow distribution of colors (0.57±0.05 in g−r for example), which are statistically indistinguishable from that of the Jupiter Trojans. Further, there is no evidence of correlation between color and physical, dynamical, or observational parameters for the observed comets.

Simulations of the Hyades

Context: Using the recent observational data of R\"oser et al. we present $N$-body simulations of the Hyades open cluster. Aims: We make an attempt to determine initial conditions of the Hyades cluster at the time of its formation in order to reproduce the present-day cumulative mass profile, stellar mass and luminosity function (LF). Methods: We performed direct $N$-body simulations of the Hyades in an analytic Milky Way potential that account for stellar evolution and include primordial binaries in a few models. Furthermore, we applied a Kroupa (2001) IMF and used extensive ensemble-averaging. Results: We find that evolved single-star King initial models with King parameters $W_0 = 6-9$ and initial particle numbers $N_0 = 3000$ provide good fits to the observational present-day cumulative mass profile within the Jacobi radius. The best-fit King model has an initial mass of $1721\ M_\odot$ and an average mass loss rate of $-2.2 \ M_\odot/\mathrm{Myr}$. The K-band LFs of models and observations show a reasonable agreement. Mass segregation is detected in both observations and models. If 33% primordial binaries are included the initial particle number is reduced by 5% as compared to the model without primordial binaries. Conclusions: The present-day properties of the Hyades can be well reproduced by a standard King or Plummer initial model when choosing appropriate initial conditions. The degeneracy of good-fitting models can be quite high due to the large dimension of the parameter space. More simulations with different Roche-lobe filling factors and primordial binary fractions are required to explore this degeneracy in more detail.

Near-infrared properties of metal-poor globular clusters in the Galactic bulge direction

Aims. J, H, and K' images obtained from the near-infrared imager CFHTIR on the Canada-France-Hawaii Telescope are used to derive the morphological parameters of the red giant branch (RGB) in the near-infrared color-magnitude diagrams for 12 metal-poor globular clusters in the Galactic bulge direction. Using the compiled data set of the RGB parameters for the observed 12 clusters, in addition to the previously studied 5 clusters, we discuss the properties of the RGB morphology for the clusters and compare them with the calibration relations for the metal-rich bulge clusters and the metal-poor halo clusters. Methods. The photometric RGB shape indices such as colors at fixed magnitudes of MK = MH = (-5.5, -5, -4, and -3), magnitudes at fixed colors of (J - K)o = (J - H)o = 0.7, and the RGB slope are measured from the fiducial normal points defined in the near- infrared color-magnitude diagrams for each cluster. The magnitudes of RGB bump and tip are also estimated from the differential and cumulative luminosity functions of the selected RGB stars. The derived RGB parameters have been used to examine the overall behaviors of the RGB morphology as a function of cluster metallicity. Results. The correlations between the near-infrared photometric RGB shape indices and the cluster metallicity for the programme clusters compare favorably with the previous observational calibration relations for metal-rich clusters in the Galactic bulge and the metal-poor halo clusters. The observed near-infrared magnitudes of the RGB bump and tip for the investigated clusters are also in accordance with the previous calibration relations for the Galactic bulge clusters.

CHANDRAOBSERVATIONS OF THE X-RAY POINT SOURCE POPULATION IN NGC 4636

We present the X-ray point-source population in the nearby Virgo elliptical galaxy NGC 4636 from three Chandra X-ray observations. These observations, totaling ~193 ks after time filtering, were taken with the Advanced CCD Imaging Camera (ACIS) over a three-year period. Using a wavelet decomposition detection algorithm, we detect 318 individual point sources. For our analysis, we use a subset of 277 detections with ≥ net 10 counts (a limiting luminosity of approximately 1.2 × 1037 erg s–1 in the 0.5-2 keV band, outside the central 15 bright galaxy core). We present a radial distribution of the point sources. Between 15 and 6' from the center, 25% of our sources are likely to be background sources (active galactic nuclei (AGNs)) and 75% are low-mass X-ray binaries (LMXBs) within the galaxy, while at radial distances greater than 6', background sources (AGN) will dominate the point sources. We explore short and long-term variability (over timescales of 1 day to three years) for X-ray point sources in this elliptical galaxy. 54 sources (24%) in the common ACIS fields of view show significant variability between observations. Of these, 37 are detected with at least 10 net counts in only one observation and thus may be transient. In addition, ~10% of the sources in each observation show significant short-term variability; we present an example light curve for a variable bright source. The cumulative luminosity function (LF) for the point sources in NGC 4636 can be represented as a power law of slope α = 1.14 ± 0.03. We do not detect, but estimate an upper limit of ~4.5 × 1037 erg s–1 to the current X-ray luminosity of the historical supernova SN1939A. We find 77 matches between X-ray point sources and globular cluster (GC) candidates found in deep optical images of NGC 4636. In the annulus from 15 to 6' of the galaxy center, 48 of the 129 X-ray point sources (37%) with ≥10 net counts are matched with GC candidates. Since we expect 25% of these sources to be background AGN, the percentage matched with GCs could be as high as 50%. Of these matched sources, we find that ~70% are associated with the redder GC candidates, those that are thought to have near-solar metal abundance. The fraction of GC candidates with an X-ray point source match decreases with decreasing GC luminosity. We do not find a correlation between the X-ray luminosities of the matched point sources and the luminosity or color of the host GC candidates. The LFs of the X-ray point sources matched with GCs and those that are unmatched have similar slopes over 1.8 × 1037 erg s–1 ≤ Lx ≤ 1 × 1038 erg s–1. Finally, we present a color-color diagram based on ratios of X-ray flux rather than source counts, which yields a much tighter source distribution, and shows a large population of sources which are likely LMXBs and a small population of black hole candidates.

An X-ray spectral survey of the disc of M 31 with XMM-Newton

<i>Aims. <i/>We present the results of a complete spectral survey of the X-ray point sources detected in five XMM-Newton observations along the major axis of M 31 but avoiding the central bulge, aimed at establishing the population characteristics of X-ray sources in this galaxy.<i>Methods. <i/>We obtained background subtracted spectra and lightcurves for each of the 335 X-ray point sources detected across the five observations from 2002. We also correlate our source list with those of earlier X-ray surveys and radio, optical and infra-red catalogues. Sources with more than 50 source counts are individually spectrally fit in order to create the most accurate luminosity functions of M 31 to date.<i>Results. <i/>Based on the spectral fitting of these sources with a power law model, we observe a broad range of best fit photon index. From this distribution of best fit index, we identify 16 strong high mass X-ray binary system candidates in M 31. We show the first cumulative luminosity functions created using the best fit spectral model to each source with more than 50 source counts in the disc of M 31. The cumulative luminosity functions show a distinct flattening in the X-ray luminosity <i>L<i/><sub>X<sub/> interval 37.0 <i>≲<i/> log <i>L<i/><sub>X<sub/> erg s<sup>-1<sup/> <i>≲<i/> 37.5. Such a feature may also be present in the X-ray populations of several other galaxies, but at a much lower statistical significance. We investigate the number of AGN present in our source list and find that above <i>L<i/><sub>X<sub/>~1.410<sup>36<sup/> erg s<sup>-1<sup/> the observed population is statistically dominated by the point source population of M 31.

Population synthesis for the luminosity functions of X-ray binaries made using the “Scenario Machine”

Using the ``Scenario Machine'' we have carried out a population synthesis of X-ray binaries for the purpose of modelling of X-ray luminosity functions (XLFs) in different types of galaxies: star burst, spiral, and elliptical. This computer code allows to calculate, by using Monte Carlo simulations, the evolution of a large ensemble of binary systems, with proper accounting for the spin evolution of magnetized neutron stars. We show that the XLF has no universal type. It depends on the star formation rate in the galaxy. Also it is of importance to take into account the evolution of binary systems and life times of X-ray stages in theoretical models of such functions. We have calculated cumulative and differential XLFs for the galaxy with the constant star formation rate. Also we have calculated cumulative luminosity functions for different intervals of time after the star formation burst in the galaxy and curves depicting the evolution of the X-ray luminosity after the star formation burst in the galaxy.

Mass-to-light ratio of Lyα emitters: implications of Lyα surveys at redshifts z = 5.7, 6.5, 7 and 8.8

We present a simple, relatively model‐independent method to interpret the galaxy number count data at z>6. The only free parameter is a mass‐to‐“observed light” ratio, Mh/Lband, where Mh refers to the total mass of the host halo, and Lband refers to the observed luminosity of the source. For narrow‐band surveys, Lband is simply related to the intrinsic Lyα luminosity with a survival fraction of Lyα photons, αesc. The mass‐to‐“bolometric light”, Mh/Lbol, can also be found, once the metallicity and initial mass function of stellar populations are given. We find constraints on the mass‐to‐light ratio of Ly‐alpha emitters from 5.7<z<8.8 of (Mh/Lbol) (αesce1/γ)−1 = 21–38, 14–26, and 9–17 for Z = 0, 1/50, and 1Z⊙, respectively, where e is the duty cycle and γ∼2 is the local shape of the cumulative luminosity function. Therefore, Lyα emitters are consistent with either starburst galaxies (Mh/Lbol∼0.1–1) for reasonable values of the Lyα survival fraction, αesce1/γ∼0.01–0.05, or normal populations (Mh/Lbol∼10) if ...