Diffuse Gas and LMXBs in the Chandra Observation of the S0 Galaxy NGC 1553

We have spatially and spectrally resolved the sources of X-ray emission from the X-ray faint S0 galaxy NGC 1553 using an observation from the Chandra X-ray Observatory. The majority (70%) of the emission in the 0.3 - 10.0 keV band is diffuse, and the remaining 30% is resolved into 49 discrete sources. Most of the discrete sources associated with the galaxy appear to be low mass X-ray binaries (LMXBs). The luminosity function of the LMXB sources is well-fit by a broken power-law with a break luminosity comparable to the Eddington luminosity for a 1.4 solar mass neutron star. It is likely that those sources with luminosities above the break are accreting black holes and those below are mostly neutron stars in binary systems. Spectra were extracted for the total emission, diffuse emission, and sum of the resolved sources; the spectral fits for all require a model including both a soft and hard component. The diffuse emission is predominately soft while the emission from the sources is mostly hard. Approximately 24% of the diffuse emission arises from unresolved LMXBs, with the remainder resulting from thermal emission from hot gas. There is a very bright source at the projected position of the nucleus of the galaxy. The spectrum and luminosity derived from this central source are consistent with it being an AGN; the galaxy also is a weak radio source. Finally, the diffuse emission exhibits significant substructure with an intriguing spiral feature passing through the center of the galaxy. The X-ray spectrum and surface brightness of the spiral feature are consistent with adiabatic or shock compression of ambient gas, but not with cooling. This feature may be due to compression of the hot interstellar gas by radio lobes or jets associated with the AGN.Comment: 23 pages using emulateapj.sty; ApJ, in press; revised version includes correction to error in the L_X,src/L_B ratio as well as other revision

Variegate galaxy cluster gas content: Mean fraction, scatter, selection effects and covariance with X-ray luminosity

We use a cluster sample selected independently of the intracluster medium content with reliable masses to measure the mean gas mass fraction and its scatter, the biases of the X-ray selection on gas mass fraction, and the covariance between the X-ray luminosity and gas mass. The sample is formed by 34 galaxy clusters in the nearby ($0.050<z<0.135$) Universe, mostly with $14<\log M_{500}/M_\odot \lesssim 14.5$, and with masses calculated with the caustic technique. First, we found that integrated gas density profiles have similar shapes, extending earlier results based on subpopulations of clusters such as those that are relaxed or X-ray bright for their mass. Second, the X-ray unbiased selection of our sample allows us to unveil a variegate population of clusters; the gas mass fraction shows a scatter of $0.17\pm0.04$ dex, possibly indicating a quite variable amount of feedback from cluster to cluster, which is larger than is found in previous samples targeting subpopulations of galaxy clusters, such as relaxed or X-ray bright clusters. The similarity of the gas density profiles induces an almost scatterless relation between X-ray luminosity, gas mass, and halo mass, and modulates selection effects in the halo gas mass fraction: gas-rich clusters are preferentially included in X-ray selected samples. The almost scatterless relation also fixes the relative scatters and slopes of the $L_X-M$ and $M_{gas}-M$ relations and makes core-excised X-ray luminosities and gas masses fully covariant. Therefore, cosmological or astrophysical studies involving X-ray or SZ selected samples need to account for both selection effects and covariance of the studied quantities with X-ray luminosity/SZ strength.Comment: A&A, in press, minor language changes from previous versio

A multi-wavelength study of the evolution of Early-Type Galaxies in Groups: the ultraviolet view

ABRIDGED- The UV-optical color magnitude diagram (CMD) of rich galaxy groups is characterised by a well developed Red Sequence (RS), a Blue Cloud (BC) and the so-called Green Valley (GV). Loose, less evolved groups of galaxies likely not virialized yet may lack a well defined RS. This is actually explained in the framework of galaxy evolution. We are focussing on understanding galaxy migration towards the RS, checking for signatures of such a transition in their photometric and morphological properties. We report on the UV properties of a sample of ETGs galaxies inhabiting the RS. The analysis of their structures, as derived by fitting a Sersic law to their UV luminosity profiles, suggests the presence of an underlying disk. This is the hallmark of dissipation processes that still must have a role in the evolution of this class of galaxies. SPH simulations with chemo-photometric implementations able to match the global properties of our targets are used to derive their evolutionary paths through UV-optical CDM, providing some fundamental information such as the crossing time through the GV, which depends on their luminosity. The transition from the BC to the RS takes several Gyrs, being about 3-5 Gyr for the the brightest galaxies and more long for fainter ones, if it occurs. The photometric study of nearby galaxy structures in UV is seriously hampered by either the limited FoV of the cameras (e.g in HST) or by the low spatial resolution of the images (e.g in the GALEX). Current missions equipped with telescopes and cameras sensitive to UV wavelengths, such as Swift-UVOT and Astrosat-UVIT, provide a relatively large FoV and better resolution than the GALEX. More powerful UV instruments (size, resolution and FoV) are obviously bound to yield fundamental advances in the accuracy and depth of the surface photometry and in the characterisation of the galaxy environment.Comment: 12 pages, 6 figures: accepted for publication in Astrophysics & Space Science as contributions to the workshop: "UV astronomy, the needs and the means

The two Ultraluminous X-ray sources in the galaxy NGC 925

NGC 925 ULX-1 and ULX-2 are two ultraluminous X-ray sources in the galaxy NGC 925, at a distance of 8.5 Mpc. For the first time, we analyzed high quality, simultaneous XMM-Newton and NuSTAR data of both sources. Although at a first glance ULX-1 resembles an intermediate mass black hole candidate (IMBH) because of its high X-ray luminosity ($(2$$-$$4)\times10^{40}$ erg s$^{-1}$) and its spectral/temporal features, a closer inspection shows that its properties are more similar to those of a typical super-Eddington accreting stellar black hole and we classify it as a `broadened disc' ultraluminous X-ray source. Based on the physical interpretation of this spectral state, we suggest that ULX-1 is seen at small inclination angles, possibly through the evacuated cone of a powerful wind originating in the accretion disc. The spectral classification of ULX-2 is less certain, but we disfavour an IMBH accreting at sub-Eddington rates as none of its spectral/temporal properties can be associated to either the soft or hard state of Galactic accreting black hole binaries.Comment: Accepted on MNRAS with very minor comments, 7 pages, 5 figures, 1 tabl

Decoupled and inhomogeneous gas flows in S0 galaxies

A recent analysis of the "Einstein" sample of early-type galaxies has revealed that at any fixed optical luminosity Lb S0 galaxies have lower mean X-ray luminosity Lx per unit Lb than ellipticals. Following a previous analytical investigation of this problem (Ciotti & Pellegrini 1996), we have performed 2D numerical simulations of the gas flows inside S0 galaxies in order to ascertain the effectiveness of rotation and/or galaxy flattening in reducing the Lx/Lb ratio. The flow in models without SNIa heating is considerably ordered, and essentially all the gas lost by the stars is cooled and accumulated in the galaxy center. If rotation is present, the cold material settles in a disk on the galactic equatorial plane. Models with a time decreasing SNIa heating host gas flows that can be much more complex. After an initial wind phase, gas flows in energetically strongly bound galaxies tend to reverse to inflows. This occurs in the polar regions, while the disk is still in the outflow phase. In this phase of strong decoupling, cold filaments are created at the interface between inflowing and outflowing gas. Models with more realistic values of the dynamical quantities are preferentially found in the wind phase with respect to their spherical counterparts of equal Lb. The resulting Lx of this class of models is lower than in spherical models with the same Lb and SNIa heating. At variance with cooling flow models, rotation is shown to have only a marginal effect in this reduction, while the flattening is one of the driving parameters for such underluminosity, in accordance with the analytical investigation.Comment: 32 pages LaTex file, plus 5 .ps figures and macro aasms4.sty -- Accepted on Ap

Galaxy Halo Masses from Galaxy-Galaxy Lensing

We present measurements of the extended dark halo profiles of bright early type galaxies at redshifts 0.1 to 0.9 obtained via galaxy-galaxy lensing analysis of images taken at the CFHT using the UH8K CCD mosaic camera. Six half degree fields were observed for a total of 2 hours each in I and V, resulting in catalogs containing ~20 000 galaxies per field. We used V-I color and I magnitude to select bright early type galaxies as the lens galaxies, yielding a sample of massive lenses with fairly well determined redshifts and absolute magnitudes M ~ M_* \pm 1. We paired these with faint galaxies lying at angular distances 20" to 60", corresponding to physical radii of 26 to 77 kpc (z = 0.1) and 105 to 315 kpc (z = 0.9), and computed the mean tangential shear of the faint galaxies. The shear falls off with radius roughly as expected for flat rotation curve halos. The shear values were weighted in proportion to the square root of the luminosity of the lens galaxy. Our results give a value for the average mean rotation velocity of an L_* galaxy halo at r~50-200 kpc of v_* = 238^{+27}_{-30} km per sec for a flat lambda (Omega_m0 = 0.3, Omega_l0 = 0.7) cosmology (v_* = 269^{+34}_{-39} km per sec for Einstein-de Sitter), and with little evidence for evolution with redshift. We compare to halo masses measured by other groups/techniques. We find a mass-to-light ratio of ~121\pm28h(r/100 kpc) and these halos constitute Omega ~0.04 \pm 0.01(r/100 kpc) of closure density. (abridged)Comment: Accepted for publication in ApJ (minor modifications) - 32 pages, 11 figs, 5 table

Thermo‐economic analysis of a hybrid ejector refrigerating system based on a low grade heat source

The rising of the global energy demand requires the use of alternative energy conversion systems employing renewable sources. In the refrigeration and air conditioning fields, heat driven ejector systems represent a promising way to produce the cooling effect by using available low-grade temperature sources. In this paper, a thermo‐economic analysis of a waste heat recovery hybrid ejector cycle (WHRHEC) was carried out. A thermodynamic model was firstly developed to simulate a WHRHEC able to obtain chilled water with a cooling load of 20 kW, by varying the working fluids and the pinch point values in the heat exchangers. Specific single‐ and two‐phase heat transfer correlations were used to estimate the heat transfer surface and therefore the investment costs. The operative ranges that provide a reasonable compromise between the set‐up costs and the cycle performances were then defined and compared to the current waste heat‐driven technologies, such as absorption chillers and organic Rankine cycles (ORCs) coupled with vapor compression cycles (VCCs). The last part of the paper presents an economic analysis providing the map of the design (plant size) and contingent (specific cost of energy, waste heat availability) variables that lead to the economic convenience of a WHRHEC system when integrated to a conventional VCC plant