X-ray observations of circumgalactic coronae provide a valuable means by which to test galaxy formation theories. Two primary mechanisms are thought to be responsible for the establishment of such coronae: accretion of intergalactic gas (IGM) and/or
galactic feedback. In this paper, we first compare our Chandra sample of galactic coronae of 53 nearby highly-inclined disc galaxies to an analytical model considering only the accretion of IGM. We confirm the existing conclusion that this pure accretion model substantially over-predicts the coronal emission. We then select 30 field galaxies from our original sample, and correct their coronal luminosities to uniformly compare them to deep X-ray measurements of several massive disc galaxies from the literature, as well as to a comparable sample of simulated galaxies drawn from the Galaxies-Intergalactic Medium Interaction Calculation (GIMIC). These simulations explicitly model both accretion and SNe feedback and yield galaxies exhibit X-ray properties in broad agreement with our observational sample. However, notable and potentially instructive discrepancies exist between the slope and scatter of the Lx-M200 and Lx-SFR relations, highlighting some known shortcomings of GIMIC, e.g., the absence of AGN feedback, and possibly the adoption of constant stellar feedback parameters. The simulated galaxies exhibit a tight Lx-M200 correlation with little scatter. Having inferred M200 for our observational sample via the Tully-Fisher relation, we find a weaker and more scattered correlation. In the simulated and observed samples alike, massive non-starburst galaxies above a typical transition mass of M*~2e11Msun or M200~1e13Msun tend to have higher Lx/M* and Lx/M200 than low-mass counterparts, indicating that the accretion of IGM plays an increasingly important role in establishing the observable hot circumgalactic medium with increasing galaxy mass.
X-ray-emitting coronae of nearby galaxies are expected to be produced either by accretion from the intergalactic medium and/or by various galactic feedback. We herein present a systematical analysis of the Chandra observations of 53 nearby edge-on di
sk galaxies over a range of 3 orders of magnitude in SFR. Various coronal properties, such as the luminosity, vertical/horizontal extent, and other inferred parameters, are characterized for all the sample galaxies. For galaxies with high enough counting statistics, we also examine the thermal and chemical states of the coronal gas. Here we concentrate on the coronal luminosity (Lx), estimated in 0.5-2keV and within 5 times the diffuse X-ray vertical scale height. We find Lx strongly correlates with the SFR for the whole sample. But the inclusion of Ia SNe in the total energy input (E_SN) gives an even tighter correlation, which may be characterized with a linear relation, Lx=0.5%E_SN, and with a dispersion of 0.45dex. Moreover, the coronal radiation efficiency (eta=Lx/E_SN) shows little correlation with either the stellar mass or the gravitational mass (M_TF, inferred from the rotation velocity), but is significantly correlated with their ratio (M_TF/M_*), which may be expressed as a linear scaling relation eta=0.35%M_TF/M_* for the entire ranges of galaxy parameters. This joint scaling relation suggests that the coronae are self-regulated by the combination of gravitational confinement and feedback. But SN appears to be the primary heating source, because about half of our galaxies are not massive enough to allow for the accretion to play a major role. The commonly low eta further suggests that the bulk of the SN energy likely flows out into large-scale galactic halos for essentially all the galaxies. Such ubiquitous outflows could have profound implications for understanding the ecosystem, hence the evolution of galaxies.
Let $M_1$ and $M_2$ be orientable irreducible 3--manifolds with connected boundary and suppose $partial M_1congpartial M_2$. Let $M$ be a closed 3--manifold obtained by gluing $M_1$ to $M_2$ along the boundary. We show that if the gluing homeomorphis
m is sufficiently complicated, then $M$ is not homeomorphic to $S^3$ and all small-genus Heegaard splittings of $M$ are standard in a certain sense. In particular, $g(M)=g(M_1)+g(M_2)-g(partial M_i)$, where $g(M)$ denotes the Heegaard genus of $M$. This theorem is also true for certain manifolds with multiple boundary components.
We study the edge-on galaxy NGC 5775, utilizing a 58.2 ks {sl Chandra} ACIS-S observation together with complementary {sl HST} ACS, {sl Spitzer} IRAC and other multi-wavelength data sets. This edge-on galaxy, with its disk-wide active star formation,
is particularly well-suited for studying the disk/halo interaction on sub-galactic scales. We detect 27 discrete X-ray sources within the $D_{25}$ region of the galaxy, including an ultra-luminous source with a 0.3-7 keV luminosity of $sim7times10^{40}rm ergs s^{-1}$. The source-removed diffuse X-ray emission shows several prominent extraplanar features, including a $sim10rm kpc$ diameter ``shell-like feature and a ``blob reaching a projected distance of $sim25rm kpc$ from the galactic disk. The bulk of the X-ray emission in the halo has a scale height of $sim$1.5 kpc and can be characterized by a two-temperature optically thin thermal plasma with temperatures of $sim$ 0.2 and 0.6 keV and a total 0.3-2 keV luminosity of $sim3.5times10^{39}rm ergs s^{-1}$. The high-resolution, multi-wavelength data reveal the presence of several extraplanar features around the disk, which appear to be associated with the in-disk star formation. We suggest that hot gas produced with different levels of mass loading can have different temperatures, which may explain the characteristic temperatures of hot gas in the halo. We have obtained a sub-galactic scale X-ray-intensity-star formation relation, which is consistent with the integrated version in other star forming galaxies.
We show that given a trivalent graph in $S^3$, either the graph complement contains an essential almost meridional planar surface or thin position for the graph is also bridge position. This can be viewed as an extension of a theorem of Thompson to g
raphs. It follows that any graph complement always contains a useful planar surface.
