Once thought to be devoid of warm and cold interstellar matter, elliptical galaxies are now commonly observed to host extended regions of neutral and ionized gas. Outside of the innermost nuclear regions of these galaxies, the favoured candidate ioni
zing source remains some component of the stellar population, with mounting evidence suggesting post-asymptotic-giant-branch stars (pAGBs). In a recent paper, we demonstrated that observations of recombination lines of He II (or upper limits thereof) may provide a strong constraint on the presence of any other, higher temperature ionizing sources, in particular nuclear-burning white dwarfs in the context of the single degenerate (SD) scenario for type Ia supernovae. The sensitivity of the HeII test is greatest for WD effective temperatures ~ 2 x 10^5 K. Here we extend our analysis to include predictions for all of the classical strong optical lines, as well as UV, optical, and infra-red lines of neutral Oxygen, Nitrogen, and singly-ionized Carbon. This allows us to extend the temperature range over which we can meaningfully constrain the collective luminosity of nuclear-burning WDs to 10^5 K <~ T <~ 10^6 K. We then demonstrate how observations of nearby early-type and post-starburst galaxies can place strong limits on the origin of type Ia supernovae.
We study the emission from the hot interstellar medium in a sample of nearby late type galaxies defined in Paper I. Our sample covers a broad range of star formation rates, from ~0.1 Msun/yr to ~17 Msun/yr and stellar masses, from ~3x10^8 Msun to ~6x
10^10 Msun. We take special care of systematic effects and contamination from bright and faint compact sources. We find that in all galaxies at least one optically thin thermal emission component is present in the unresolved emission, with the average temperature of <kT>= 0.24 keV. In about ~1/3 of galaxies, a second, higher temperature component is required, with the <kT>= 0.71 keV. Although statistically significant variations in temperature between galaxies are present, we did not find any meaningful trends with the stellar mass or star formation rate of the host galaxy. The apparent luminosity of the diffuse emission in the 0.5-2 keV band linearly correlates with the star formation rate with the scale factor of Lx/SFRapprox 8.3x10^38 erg/s per Msun/yr, of which in average ~30-40% is likely produced by faint compact sources of various types. We attempt to estimate the bolometric luminosity of the gas and and obtained results differing by an order of magnitude, log(Lbol/SFR)sim39-40, depending on whether intrinsic absorption in star-forming galaxies was allowed or not. Our theoretically most accurate, but in practice the most model dependent result for the intrinsic bolometric luminosity of ISM is Lbol/SFRsim 1.5x10^40 erg/s per Msun/yr. Assuming that core collapse supernovae are the main source of energy, it implies that epsilon_SNsim5x10^-2 (E_SN/10^51)^-1 of mechanical energy of supernovae is converted into thermal energy of ISM.
Observations of local star forming galaxies have revealed a correlation between the rate at which galaxies form stars and their X-Ray luminosity. We combine this correlation with the most recent observational constraints on the integrated star format
ion rate density, and find that star forming galaxies account for 5-20% of the total soft and hard X-ray backgrounds, where the precise number depends on the energy band and the assumed average X-ray spectral energy distribution of the galaxies below ~20 keV. If we combine the L_X-SFR relation with recently derived star formation rate function, then we find that star forming galaxies whose X-ray flux falls well (more than a factor of 10) below the detection thresholds of the Chandra Deep Fields, can fully account for the unresolved soft X-ray background, which corresponds to ~6% of its total. Motivated by this result, we put limits on the allowed redshift evolution of the parameter c_X equiv L_X/SFR, and/or its evolution towards lower and higher star formation rates. If we parametrize the redshift evolution of c_X ~ (1+z)^b, then we find that b leq 1.3 (95% CL). On the other hand, the observed X-ray luminosity functions (XLFs) of star forming galaxies indicate that c_X may be increasing towards higher redshifts and/or higher star formation rates at levels that are consistent with the X-ray background, but possibly at odds with the locally observed L_X-SFR relation.
Based on a homogeneous set of X-ray, infrared and ultraviolet observations from Chandra, Spitzer, GALEX and 2MASS archives, we study populations of high-mass X-ray binaries (HMXBs) in a sample of 29 nearby star-forming galaxies and their relation wit
h the star formation rate (SFR). In agreement with previous results, we find that HMXBs are a good tracer of the recent star formation activity in the host galaxy and their collective luminosity and number scale with the SFR, in particular, Lx~2.6 10^{39} SFR. However, the scaling relations still bear a rather large dispersion of ~0.4 dex, which we believe is of a physical origin. We present the catalog of 1057 X-ray sources detected within the $D25$ ellipse for galaxies of our sample and construct the average X-ray luminosity function (XLF) of HMXBs with substantially improved statistical accuracy and better control of systematic effects than achieved in previous studies. The XLF follows a power law with slope of 1.6 in the logLx~35-40 luminosity range with a moderately significant evidence for a break or cut-off at Lx~10^{40} erg/s. As before, we did not find any features at the Eddington limit for a neutron star or a stellar mass black hole. We discuss implications of our results for the theory of binary evolution. In particular we estimate the fraction of compact objects that once upon their lifetime experienced an X-ray active phase powered by accretion from a high mass companion and obtain a rather large number, fx~0.2 (0.1 Myr/tau_x) (tau_x is the life time of the X-ray active phase). This is ~4 orders of magnitude more frequent than in LMXBs. We also derive constrains on the mass distribution of the secondary star in HMXBs.
We study the X-ray luminosity function (XLF) of low mass X-ray binaries (LMXB) in the nearby early-type galaxy Centaurus A, concentrating primarily on two aspects of binary populations: the XLF behavior at the low luminosity limit and comparison betw
een globular cluster and field sources. The 800 ksec exposure of the deep Chandra VLP program allows us to reach a limiting luminosity of 8e35 erg/s, about 2-3 times deeper than previous investigations. We confirm the presence of the low luminosity break in the overall LMXB XLF at log(L_X)=37.2-37.6 below which the luminosity distribution follows a constant dN/d(ln L). Separating globular cluster and field sources, we find a statistically significant difference between the two luminosity distributions with a relative underabundance of faint sources in the globular cluster population. This demonstrates that the samples are drawn from distinct parent populations and may disprove the hypothesis that the entire LMXB population in early type galaxies is created dynamically in globular clusters. As a plausible explanation for this difference in the XLFs, we suggest that there is an enhanced fraction of helium accreting systems in globular clusters, which are created in collisions between red giants and neutron stars. Due to the 4 times higher ionization temperature of He, such systems are subject to accretion disk instabilities at approximately 20 times higher mass accretion rate, and therefore are not observed as persistent sources at low luminosities.
We study the origin of unresolved X-ray emission from the bulge of M31 based on archival Chandra and XMM-Newton observations. We demonstrate that three different components are present: (i) Broad-band emission from a large number of faint sources --
mainly accreting white dwarfs and active binaries, associated with the old stellar population, similar to the Galactic Ridge X-ray emission of the Milky Way. The X-ray to K-band luminosity ratios are compatible with those for the Milky Way and for M32, in the 2 - 10 keV band it is (3.6 +/- 0.2) x 10^27 erg/s/L_sun. (ii) Soft emission from ionized gas with temperature of about ~ 300 eV and mass of ~ 2 x 10^6 M_sun. The gas distribution is significantly extended along the minor axis of the galaxy suggesting that it may be outflowing in the direction perpendicular to the galactic disk. The mass and energy supply from evolved stars and type Ia supernovae is sufficient to sustain the outflow. We also detect a shadow cast on the gas emission by spiral arms and the 10-kpc star-forming ring, confirming significant extent of the gas in the ``vertical direction. (iii) Hard extended emission from spiral arms, most likely associated with young stellar objects and young stars located in the star-forming regions. The L_X/SFR ratio equals ~ 9 x 10^38 (erg/s)/(M_sun/yr) which is about ~ 1/3 of the HMXBs contribution, determined earlier from Chandra observations of other nearby galaxies.
