An Over-Massive Black Hole in the Compact Lenticular Galaxy NGC1277

All massive galaxies likely have supermassive black holes at their centers, and the masses of the black holes are known to correlate with properties of the host galaxy bulge component. Several explanations have been proposed for the existence of these locally-established empirical relationships; they include the non-causal, statistical process of galaxy-galaxy merging, direct feedback between the black hole and its host galaxy, or galaxy-galaxy merging and the subsequent violent relaxation and dissipation. The empirical scaling relations are thus important for distinguishing between various theoretical models of galaxy evolution, and they further form the basis for all black hole mass measurements at large distances. In particular, observations have shown that the mass of the black hole is typically 0.1% of the stellar bulge mass of the galaxy. The small galaxy NGC4486B currently has the largest published fraction of its mass in a black hole at 11%. Here we report observations of the stellar kinematics of NGC 1277, which is a compact, disky galaxy with a mass of 1.2 x 10^11 Msun. From the data, we determine that the mass of the central black hole is 1.7 x 10^10 Msun, or 59% its bulge mass. Five other compact galaxies have properties similar to NGC 1277 and therefore may also contain over-sized black holes. It is not yet known if these galaxies represent a tail of a distribution, or if disk-dominated galaxies fail to follow the normal black hole mass scaling relations.Comment: 7 pages. 6 figures. Nature. Animation at http://www.mpia.de/~bosch/blackholes.htm

An extreme magneto-ionic environment associated with the fast radio burst source FRB 121102

Fast radio bursts are millisecond-duration, extragalactic radio flashes of unknown physical origin(1-3). The only known repeating fast radio burst source(4-6)-FRB 121102-has been localized to a star-forming region in a dwarf galaxy(7-9) at redshift 0.193 and is spatially coincident with a compact, persistent radio source(7,10). The origin of the bursts, the nature of the persistent source and the properties of the local environment are still unclear. Here we report observations of FRB 121102 that show almost 100 per cent linearly polarized emission at a very high and variable Faraday rotation measure in the source frame (varying from + 1.46 x 10(5) radians per square metre to + 1.33 x 10(5) radians per square metre at epochs separated by seven months) and narrow (below 30 microseconds) temporal structure. The large and variable rotation measure demonstrates that FRB 121102 is in an extreme and dynamic magneto-ionic environment, and the short durations of the bursts suggest a neutron star origin. Such large rotation measures have hitherto been observed(11,12) only in the vicinities of massive black holes (larger than about 10,000 solar masses). Indeed, the properties of the persistent radio source are compatible with those of a low-luminosity, accreting massive black hole(10). The bursts may therefore come from a neutron star in such an environment or could be explained by other models, such as a highly magnetized wind nebula(13) or supernova remnant(14) surrounding a young neutron star.</p

A direct localization of a fast radio burst and its host

Fast radio bursts are astronomical radio flashes of unknown physical nature with durations of milliseconds. Their dispersive arrival times suggest an extragalactic origin and imply radio luminosities orders of magnitude larger than any other kind of known short-duration radio transient. Thus far, all FRBs have been detected with large single-dish telescopes with arcminute localizations, and attempts to identify their counterparts (source or host galaxy) have relied on contemporaneous variability of field sources or the presence of peculiar field stars or galaxies. These attempts have not resulted in an unambiguous association with a host or multi-wavelength counterpart. Here we report the sub-arcsecond localization of FRB 121102, the only known repeating burst source, using high-time-resolution radio interferometric observations that directly image the bursts themselves. Our precise localization reveals that FRB 121102 originates within 100 mas of a faint 180 uJy persistent radio source with a continuum spectrum that is consistent with non-thermal emission, and a faint (25th magnitude) optical counterpart. The flux density of the persistent radio source varies by tens of percent on day timescales, and very long baseline radio interferometry yields an angular size less than 1.7 mas. Our observations are inconsistent with the fast radio burst having a Galactic origin or its source being located within a prominent star-forming galaxy. Instead, the source appears to be co-located with a low-luminosity active galactic nucleus or a previously unknown type of extragalactic source. [Truncated] If other fast radio bursts have similarly faint radio and optical counterparts, our findings imply that direct sub-arcsecond localizations of FRBs may be the only way to provide reliable associations.Comment: Nature, published online on 4 Jan 2017, DOI: 10.1038/nature2079

X-RAY DETECTED ACTIVE GALACTIC NUCLEI IN DWARF GALAXIES AT 0 < z < 1

We present a sample of accreting supermassive black holes (SMBHs) in dwarf galaxies at z < 1. We identify dwarf galaxies in the NEWFIRM Medium Band Survey with stellar masses of M-star < 3 x 10(9) M-circle dot that have spectroscopic redshifts from the DEEP2 survey and lie within the region covered by deep ( flux limit of similar to 5 x 10(-17)-6 x 10(-16) erg cm(-2) s(-1)) archival Chandra X-ray data. From our sample of 605 dwarf galaxies, 10 exhibit X-ray emission consistent with that arising from active galactic nucleus (AGN) activity. If black-hole mass scales roughly with stellar mass, then we expect that these AGNs are powered by SMBHs with masses of similar to 10(5)-10(6) M-circle dot and typical Eddington ratios of similar to 5%. Furthermore, we find an AGN fraction consistent with extrapolations of other searches of similar to 0.6%-3% for 10(9) M-circle dot. M-star <= 3 x 10(9) M-circle dot and 0.1 < z < 0.6. Our AGN fraction is in good agreement with a semi-analytic model, suggesting that, as we search larger volumes, we may use comparisons between observed AGN fractions and models to understand seeding mechanisms in the early universe

Structure of a new nucleic-acid-binding motif in eukaryotic transcriptional elongation factor TFIIS

Transcriptional elongation involves dynamic interactions among RNA polymerase and single-stranded and double stranded nucleic acids in the ternary complex1–4. In prokaryotes its regulation pro-vides an important mechanism of genetic control1. Analogous eukaryotic mechanisms are not well understood5, but may control expression of proto-oncogenes6,7 and viruses, including the human immunodeficiency virus HIV-1 (ref. 8). The highly conserved euk-aryotic transcriptional elongation factor TFIIS9 enables RNA polymerase II (RNAPII) to read though pause or termination sites, nucleosomes and sequence-specific DNA-binding proteins10–14. Two distinct domains of human TFIIS, which bind RNAPII and nucleic acids, regulate read-through10 and possibly nascent transcript cleavage11–15. Here we describe the three-dimensional NMR16 structure of a Cys4 nucleic-acid-binding domain from human TFIIS9,10. Unlike previously characterized zinc modules17–21, which contain an α-helix, this structure consists of a three-stranded β-sheet. Analogous Cys4 structural motifs may occur in other proteins involved in DNA or RNA trans-actions22–24, including RNAPII itself25. This new structure, desig-nated the Zn ribbon, extends the repertoire of Zn-mediated peptide architectures26 and highlights the growing recognition of the β-sheet as a motif of nucleic-acid recognition27,28.Accepted versio

Transcript cleavage factors GreA and GreB act as transient catalytic components of RNA polymerase

Prokaryotic transcription elongation factors GreA and GreB stimulate intrinsic nucleolytic activity of RNA polymerase (RNAP). The proposed biological role of Gre-induced RNA hydrolysis includes transcription proofreading, suppression of transcriptional pausing and arrest, and facilitation of RNAP transition from transcription initiation to transcription elongation. Using an array of biochemical and molecular genetic methods, we mapped the interaction interface between Gre and RNAP and identified the key residues in Gre responsible for induction of nucleolytic activity in RNAP. We propose a structural model in which the C-terminal globular domain of Gre binds near the opening of the RNAP secondary channel, the N-terminal coiled-coil domain (NTD) protrudes inside the RNAP channel, and the tip of the NTD is brought to the immediate vicinity of RNAP catalytic center. Two conserved acidic residues D41 and E44 located at the tip of the NTD assist RNAP by coordinating the Mg(2+) ion and water molecule required for catalysis of RNA hydrolysis. If so, Gre would be the first transcription factor known to directly participate in the catalytic act of RNAP