Chandra Survey of Nearby Galaxies: A Significant Population of Candidate Central Black Holes in Late-type Galaxies

Based on the Chandra data archive as of March 2016, we have identified 314 candidate active galactic nuclei in 719 galaxies located closer than 50 Mpc, among them late-type (Hubble types Sc and later) galaxies that previously had been classified from optical observations as containing star-forming (H II) nuclei. These late-type galaxies comprise a valuable subsample to search for low-mass (<~ 10^6 solar masses) central black holes. For the sample as a whole, the overall dependence of the fraction of active nuclei on galaxy type and nuclear spectral classification is consistent with previous results based on optical surveys. We detect 51 X-ray cores among the 163 H II nuclei and estimate that, very conservatively, ~74% of them with luminosities above 10^38 erg/s are not contaminated by X-ray binaries; the fraction increases to ~92% for X-ray cores with a luminosity of 10^39 erg/s or higher. This allows us to estimate a black hole occupation fraction of >~ 21% in these late-type, many bulgeless, galaxies.Comment: ApJ to appea

Chandra Survey of Nearby Galaxies: The Catalog

We searched in the public archive of the Chandra X-ray Observatory as of March 2016 and assembled a sample of 719 galaxies within 50 Mpc with ACIS observations available. By cross-correlation with the optical or near-infrared nuclei of these galaxies, 314 of them are identified to have an X-ray active galactic nucleus (AGN). The majority of them are low-luminosity AGNs and are unlikely X-ray binaries based upon their spatial distribution and luminosity functions. The AGN fraction is around 60% for elliptical galaxies and early-type spirals, but drops to roughly 20% for Sc and later types, consistent with previous findings in the optical. However, the X-ray survey is more powerful in finding weak AGNs, especially from regions with active star formation that may mask the optical AGN signature. For example, 31% of the H II nuclei are found to harbor an X-ray AGN. For most objects, a single power-law model subject to interstellar absorption is adequate to fit the spectrum, and the typical photon index is found to be around 1.8. For galaxies with a non-detection, their stacked Chandra image shows an X-ray excess with a luminosity of a few times 10^37 erg/s on average around the nuclear region, possibly composed of faint X-ray binaries. This paper reports on the technique and results of the survey; in-depth analysis and discussion of the results will be reported in forthcoming papers.Comment: Accepted for publication in the Astrophysical Journa

Regulation of the stability and transcriptional activity of NFATc4 by ubiquitination

AbstractNuclear factor of activated T cells (NFATc4) has been implicated as a critical regulator of the cardiac development and hypertrophy. However, the mechanisms for regulating NFATc4 stability and transactivation remain unclear. We showed that NFATc4 protein was predominantly ubiquitinated through the formation of Lysine 48-linked polyubiquitin chains, and this modification decreased NFATc4 protein levels and its transcriptional activity. Furthermore, activation of GSK3β markedly enhanced NFATc4 ubiquitination and decreased its transactivation, whereas inhibition of GSK3β had opposite effects. Importantly, ubiquitination and phosphorylation induced by GSK3β repressed NFATc4-dependent cardiac-specific gene expression. These results demonstrate that the ubiquitin–proteasome system plays an important role in regulating NFATc4 stability and transactivation.Structured summaryMINT-6798349:NFATc4 (uniprotkb:Q14934) physically interacts (MI:0218) with Ubiquitin (uniprotkb:P62988) by anti bait coimmunoprecipitation (MI:0006)MINT-6798334:NFATc4 (uniprotkb:Q14934) physically interacts (MI:0218) with Ubiquitin (uniprotkb:P62988) by anti tag coimmunoprecipitation (MI:0007)MINT-6798321:Ubiquitin (uniprotkb:P62988) physically interacts (MI:0218) with NFATc4 (uniprotkb:Q14934) by pull down (MI:0096

Di-μ-sulfato-bis­[diaqua­(1H-imidazo[4,5-f][1,10]phenanthroline)nickel(II)] dihydrate

In the title compound, [Ni2(SO4)2(C13H8N4)2(H2O)4]·2H2O, the complete dimeric complex is generated by an inversion center. The NiII atoms are octa­hedrally coordinated by two N atoms from one 1H-imidazo[4,5-f][1,10]phenanthroline (IP) ligand and two O atoms from two adjacent sulfate ions forming the equatorial plane, with two coordinated water mol­ecules in the axial sites. Both of the sulfate ions act as bidentate-bridging ligands connecting the two NiII ions, thus generating a binuclear complex. In the crystal structure, O—H⋯O and O—H⋯N hydrogen bonds involving the coordinated and uncoordinated water mol­ecules and N—H⋯O links lead to the formation of a two-dimensional sheet structure developing parallel to (010). Weak π–π stacking inter­actions [centroid–centroid separation = 3.613 (2) Å] between the IP ligands also occur