431 research outputs found
X-ray emission from star-forming galaxies
No full textIn this dissertation we study the properties of high-mass X-ray binaries (HMXBs) and hot inter-stellar medium in star-forming galaxies and their relation with the star formation rate (SFR), based on the data from Chandra, Spitzer, GALEX and 2MASS public archives. We constructed a large sample of galaxies for which we collected homogeneous sets of multiwavelength measurements in X-ray, ultraviolet (UV), far-infrared (FIR) and near-infrared (NIR) bands. The sample includes 45 star-forming galaxies in total, divided in two sub-samples: the primary sample, consisting of 29 nearby galaxies, having distance < 40 Mpc, so that Chandra can resolve their X-ray point-like source population; the high-SFR sample, including 16 more distant galaxies that allowed us to extend the dynamical range of SFRs by approximately two orders of magnitude.
In this sample we detected 1057 compact X-ray sources, of which ~300 are expected to be background active galactic nuclei (AGN). The majority of remaining ~700 sources are young systems associated with star-formation in the host galaxy. Based on their high X-ray luminosities and analogy with the X-ray populations in the Milky Way and few other very nearby galaxies, we conclude that they are high-mass X-ray binaries, powered by accretion of matter from a massive donor star onto a compact object - a black hole or a neutron star.
Such a large number of sources allowed us to perform the most detailed study of the population of HMXBs and its dependence on various properties of the host galaxy, as well as to obtain a very accurate calibration of the X-ray luminosity-SFR relation.
The study of the population of HMXBs is based on their X-ray luminosity functions (XLF). To this end, we took a special care to minimize the contamination by LMXBs, background AGN and to control the incompleteness of the Chandra source lists. The shape of the HMXB luminosity function is similar in different galaxies with the power law indexes having rms=0.25 with respect to the average value of ~1.6. The XLF normalizations, on the contrary, show significantly larger dispersion with the rms=0.34 dex around the A-SFR law. Combining the data of all galaxies, which include ~700 X-ray sources, we produced the average XLF of high-mass X-ray binaries in nearby star-forming galaxies. Its statistical accuracy exceeds by far that achieved in any of the previous studies of the HMXB luminosity function. The HMXB XLF has a single power law shape in a broad luminosity range of logLx~35-40 and shows a moderately significant evidence for the high luminosity break or cut-off at logLx~40. We did not find any statistically significant features at the Eddington luminosity limits of neutron stars or a 10 Msun black hole.
With the knowledge of the relation between the number of high-mass X-ray binaries and star formation rate of the host galaxy, we estimated that the fraction of compact objects that went through an X-ray active phase at least once in their lifetime, powered by accretion of matter from a massive donor star in a binary system is fx~0.2. This constrains the mass distribution of the secondary in massive binaries. For an independent mass distribution of the secondary, the power law index must be flatter than 0.3. In particular, an independent mass distribution of a Kroupa or Salpeter type is strongly excluded. Assuming that the masses of components in a binary are not independent, our results are consistent with the flat mass ratio distribution. For comparison, we obtained a similar estimate for the fraction of compact objects that become X-ray sources powered by accretion from a low-mass donor star in an LMXB. Based on the scaling-laws by Gilfanov (2004), the fraction of compact objects, X-ray active in LMXBs, is small, fx~1e-6, demonstrating that LMXBs are extremely rare objects. This result is in line with the conclusions of the binary population studies.
The collective luminosity of high-mass X-ray binaries is a good tracer of the recent star formation activity in the host galaxy:
L_XRB(0.5-8 keV)(erg/s) = 2.5 10^{39} SFR (Msun/yr)
The rms of points around this relation is 0.4 dex. The observed dispersion is unlikely to be caused by any of the obvious contaminating factors such as CXB or LMXB sources and is likely to have a physical origin.
In addition to the emission from XRB population, the X-ray emission from star-forming galaxies includes a hot diffuse gas component with a mean characteristic temperature of 2-3 10^{6} K. We show that its X-ray luminosity correlates with the star formation rate of the host galaxy. Finally we demonstrate that the total X-ray luminosity of a galaxy scales with the star formation rate:
L_tot(0.5-8 keV)(erg/s) = 4.5 10^{39} SFR(Msun/yr)
with a dispersion sigma = 0.32 dex.
We obtained consistent scale factors for nearby galaxies from the resolved sample and galaxies from the high-SFR sample. Among the latter (eight out of 16) are Chandra Deep Field North galaxies, located at the red-shifts of z~0.2-1.3. This proves that the total X-ray luminosity of a galaxy is a powerful tool to measure the star formation rate in distant galaxies
Hot X-ray coronae around massive spiral galaxies: a unique probe of structure formation models
No full textLuminous X-ray gas coronae in the dark matter halos of massive spiral
galaxies are a fundamental prediction of structure formation models, yet
only a few such coronae have been detected so far. In this paper, we
study the hot X-ray coronae beyond the optical disks of two ''normal''
massive spirals, NGC 1961 and NGC 6753. Based on XMM-Newton X-ray
observations, hot gaseous emission is detected to \~{60 kpc\mdashwell
beyond their optical radii. The hot gas has a best-fit temperature of kT
\~{} 0.6 keV and an abundance of \~{}0.1 Solar, and exhibits a fairly uniform
distribution, suggesting that the quasi-static gas resides in
hydrostatic equilibrium in the potential well of the galaxies. The
bolometric luminosity of the gas in the (0.05-0.15)r
region (r is the virial radius) is \~{}6 \times
10 erg s for both galaxies. The baryon
mass fractions of NGC 1961 and NGC 6753 are f \~{}
0.11 and f \~{} 0.09, which values fall short of the
cosmic baryon fraction. The hot coronae around NGC 1961 and NGC 6753
offer an excellent basis to probe structure formation simulations. To
this end, the observations are confronted with the moving mesh code
AREPO and the smoothed particle hydrodynamics code GADGET. Although
neither model gives a perfect description, the observed luminosities,
gas masses, and abundances favor the AREPO code. Moreover, the shape and
the normalization of the observed density profiles are better reproduced
by AREPO within \~{}0.5r . However, neither model
incorporates efficient feedback from supermassive black holes or
supernovae, which could alter the simulated properties of the X-ray
coronae. With the further advance of numerical models, the present
observations will be essential in constraining the feedback effects in
structure formation simulations.
Can AGN and galaxy clusters explain the surface brightness fluctuations of the cosmic X-ray background?
No full textFluctuations of the surface brightness of cosmic X-ray background (CXB) carry unique information about faint and low-luminosity source populations, which is inaccessible for conventional large-scale structure (LSS) studies based on resolved sources. We used XBOOTES (5ks deep Chandra X-rayObservatoryACIS-I maps of the similar to 9 deg(2) Bootes field of the NOAO Deep Wide-Field Survey) to conduct the most accurate measurement to date of the power spectrum of fluctuations of the unresolved CXB on the angular scales of 3 arcsec-17 arcmin. We find that at sub-arcmin angular scales, the power spectrum is consistent with the active galactic nucleus ( AGN) shot noise, without much need for any significant contribution from their onehalo term. This is consistent with the theoretical expectation that low-luminosity AGN reside alone in their dark matter haloes. However, at larger angular scales, we detect a significant LSS signal above the AGN shot noise. Its power spectrum, obtained after subtracting the AGN shot noise, follows a power law with the slope of -0.8 +/- 0.1 and its amplitude is much larger than what can be plausibly explained by the two-halo term of AGN. We demonstrate that the detected LSS signal is produced by unresolved clusters and groups of galaxies. For the flux limit of the XBOOTES survey, their flux-weighted mean redshift equals z similar to 0.3, and the mean temperature of their intracluster medium (ICM), T approximate to 1.4 keV, corresponds to the mass of M500 similar to 10(13.5) M-circle dot. The power spectrum of CXB fluctuations carries information about the redshift distribution of these objects and the spatial structure of their ICM on the linear scales of up to similar to Mpc, i. e. of the order of the virial radius.International Max Planck Research School (IMPRS) on Astrophysics at the Ludwig-Maximilians University of Munich (LMU); China Postdoctoral Science Foundation [2016M590012]; Russian Scientific Foundation (RNF) [14-22-00271]SCI(E)ARTICLE33035-305946
Radio sources in the Chandra Galactic Bulge Survey
No full textWe discuss radio sources in the Chandra Galactic Bulge Survey region. By cross-matching the X-ray sources in this field with the NRAO VLA Sky Survey archival data, we find 12 candidate matches. We present a classification scheme for radio/X-ray matches in surveys taken in or near the Galactic plane, taking into account other multiwavelength data. We show that none of the matches found here is likely to be due to coronal activity from normal stars because the radio to X-ray flux ratios are systematically too high. We show that one of the source could be a radio pulsar, and that one could be a planetary nebula, but that the bulk of the sources are likely to be background active galactic nuclei (AGN), with many confirmed through a variety of approaches. Several of the AGN are bright enough in the near-infrared (and presumably in the optical) to use as probes of the interstellar medium in the inner Galaxy
The Hot Interstellar Medium
No full textThe interstellar medium (ISM) of galaxies very often contains a gas component
that reaches the temperature of several million degrees, whose physical and
chemical properties can be investigated through imaging and spectroscopy in the
X-rays. We review the current knowledge on the origin and retention of the hot
ISM in star-forming and early-type galaxies, from a combined theoretical and
observational standpoint. As a complex interplay between gravitational
processes, environmental effects, and feedback mechanisms contributes to its
physical conditions, the hot ISM represents a key diagnostic of the evolution
of galaxies.Comment: Chapter to appear in the Section "Galaxies" (eds. G. Fabbiano & M.
Gilfanov) of Springer's "Handbook of X-ray and Gamma-ray Astrophysics" (eds.
C. Bambi & A. Santangelo
Discovery of an optical counterpart to the hyperluminous X-ray source in ESO 243-49
No full textThe existence of black holes of masses similar to 10(2)-10(5)M(circle dot) has important implications for the formation and evolution of star clusters and supermassive black holes. One of the strongest candidates to date is the hyperluminous X-ray source (HLX1), possibly located in the S0- a galaxy ESO 243-49, but the lack of an identifiable optical counterpart had hampered its interpretation. Using the Magellan telescope, we have discovered an unresolved optical source with R = 23.80 +/- 0.25 mag and V = 24.5 +/- 0.3 mag within HLX1's positional error circle. This implies an average X-ray/optical flux ratio similar to 500. Taking the same distance as ESO 243-49, we obtain an intrinsic brightness M-R = -11.0 +/- 0.3 mag, comparable to that of a massive globular cluster. Alternatively, the optical source is consistent with a main-sequence M star in the Galactic halo (for example an M4.4 star at approximate to 2.5 kpc). We also examined the properties of ESO 243-49 by combining Swift/Ultraviolet/Optical Telescope (UVOT) observations with stellar population modelling. We found that the overall emission is dominated by a similar to 5-Gyr-old stellar population, but the UV emission at approximate to 2000 angstrom is mostly due to ongoing star formation at a rate of similar to 0.03M(circle dot) yr(-1). The UV emission is more intense (at least a 9 sigma enhancement above the mean) north-east of the nucleus, in the same quadrant as HLX1. With the combined optical and X-ray measurements, we put constraints on the nature of HLX1. We rule out a foreground star and a background AGN. Two alternative scenarios are still viable. HLX1 could be an accreting intermediate mass black hole in a star cluster, which may itself be the stripped nucleus of a dwarf galaxy that passed through ESO 243-49, an event which might have caused the current episode of star formation. Or, it could be a neutron star in the Galactic halo, accreting from an M4-M5 donor star
Accretion and Nuclear Activity of Quiescent Supermassive Black Holes. II. Optical Study and Interpretation
No full textOur X-ray study of the nuclear activity in a new sample of six quiescent early-type galaxies, as well as in a larger sample from the literature, confirmed (Paper I) that the Bondi accretion rate of diffuse hot gas is not a good indicator of the SMBH X-ray luminosity. Here we suggest that a more reliable estimate of the accretion rate must include the gas released by the stellar population inside the sphere of influence of the SMBH, in addition to the Bondi inflow of hot gas across that surface. We use optical surface brightness profiles to estimate the mass-loss rate from stars in the nuclear region: we show that for our sample of galaxies it is an order of magnitude higher (~10-4 to 10-3 Msolar yr-1) than the Bondi inflow rate of hot gas, as estimated from Chandra (Paper I). Only by taking into account both sources of fuel can we constrain the true accretion rate, the accretion efficiency, and the power budget. Radiatively efficient accretion is ruled out, for quiescent SMBHs. For typical radiatively inefficient flows, the observed X-ray luminosities of the SMBHs imply accretion fractions ~1%-10% (i.e., ~90%-99% of the available gas does not reach the SMBH) for at least five of our six target galaxies and most of the other galaxies with known SMBH masses. We discuss the conditions for mass conservation inside the sphere of influence, so that the total gas injection is balanced by accretion plus outflows. We show that a fraction of the total accretion power (mechanical plus radiative) would be sufficient to sustain a self-regulating, slow outflow that removes from the nuclear region all the gas that does not sink into the BH (``BH feedback''). The rest of the accretion power may be carried out in a jet or advected. We also discuss scenarios that would lead to an intermittent nuclear activity
Far-Infrared and Submillimetre Lighthouses
No full textEvidence is discussed which strongly suggests that the sources discovered in deep submillimetre (submm) surveys form a major population of distant dusty galaxies. These sources can account for the background radiation observed in these wavebands. Three sources are identified with certainty with distant galaxies with measured redshifts. They are all hyperluminous, and are likely to be massive galaxies in which a significant fraction of their stellar populations has already been formed. It is a challenge to account for such a large population of high-redshift luminous galaxies. The relation of these observations to the problem of accounting for the evolution of the cosmic star formation rate is discussed
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