An Accreting Black Hole in the Nuclear Star Cluster of the Bulgeless Galaxy NGC 1042

We present spectroscopic evidence for a low-luminosity, low-excitation active galactic nucleus (AGN) in NGC 1042, powered by an intermediate-mass black hole. These findings are significant in that the AGN is coincident with a compact star cluster known to reside in the nucleus, thus providing an example where the two types of central mass concentration coexist. The existence of a central black hole is additionally remarkable in that NGC 1042 lacks a stellar bulge. Objects such as NGC 1042 may have an important role in testing theories for the genesis of massive black holes in galaxy nuclei, and the extent to which they are in symbiosis with the larger stellar host.Comment: 15 pages, 6 figures, accepted for publication in Ap

Chandra Observations of the Nuclear Star Cluster and Ultraluminous X-ray Sources in NGC 2139

We report Chandra observations of the Scd galaxy NGC 2139, which is known to host a recently formed (10^7.6 yrs) nuclear star cluster. The star cluster is undetected in X-rays, with an upper bound on 0.5-7 keV luminosity of L_X < 7.1 x 10^37 erg/s. This bound implies a bolometric accretion luminosity <0.3 percent of the Eddington luminosity for a black hole with the mass (approximately 3400 M_sun) expected from extrapolation of the M-sigma relation. The lack of X-ray emission indicates that a black hole, if present, is not undergoing significant accretion at the current time. While the central cluster is undetected, the data reveal a substantial population of bright X-ray point sources elsewhere in this galaxy, with eight qualifying as ultraluminous X-ray sources with L_X > 10^39 erg/s. We use archival Hubble Space Telescope images to identify candidate optical counterparts for seven Chandra sources, which in most cases have optical luminosities and spatial profiles consistent with star clusters. Compared with other galaxies, the number of luminous X-ray sources in NGC 2139 is larger by a factor of 4 - 10 than expected based on its present star formation rate and stellar mass. This finding can be understood if NGC 2139 has concluded a burst of star formation in the recent past, and suggests that this galaxy could be important for testing the use of X-ray source populations as a chronometer of star formation history.Comment: 17 pages, 3 figures, accepted for publication in A

HST/STIS Spectra of Nuclear Star Clusters in Spiral Galaxies: Dependence of Age and Mass On Hubble Type

(Abridged) We study the nuclear star clusters in spiral galaxies of various Hubble types using spectra obtained with STIS on-board HST. We observed the nuclear clusters in 40 galaxies, selected from two previous HST/WFPC2 imaging surveys. The spectra provide a better separation of cluster light from underlying galaxy light than is possible with ground-based spectra. To infer the star formation history, metallicity and dust extinction, we fit weighted superpositions of single-age stellar population templates to the spectra. The luminosity-weighted age ranges from 10 Myrs to 10 Gyrs. The stellar populations of NCs are generally best fit as a mixture of populations of different ages. This indicates that NCs did not form in a single event, but instead they had additional star formation long after the oldest stars formed. On average, the sample clusters in late-type spirals have a younger luminosity-weighted mean age than those in early-type spirals (log(age/yr) = 8.37+/-0.25 vs. 9.23+/-0.21). The average cluster masses are smaller in late-type spirals than in early-type spirals (log(M/Msun) = 6.25+/-0.21 vs. 7.63+/-0.24), and exceed the masses typical of globular clusters. The cluster mass correlates strongly with both the Hubble type of the host galaxy and the luminosity of its bulge. The latter correlation has the same slope as the well-known correlation between supermassive black hole mass and bulge luminosity. The properties of both nuclear clusters and black holes are therefore intimately connected to the properties of the host galaxy.Comment: AJ submitted (original submission Nov 30, 2005, present version includes changes based on referee recommendations). 69 pages, 16 figures, 7 table

Dissipation and Extra Light in Galactic Nuclei: II. 'Cusp' Ellipticals

We study the origin and properties of 'extra' or 'excess' central light in the surface brightness profiles of cusp or power-law ellipticals. Dissipational mergers give rise to two-component profiles: an outer profile established by violent relaxation acting on stars present in the progenitors prior to the final merger, and an inner stellar population comprising the extra light, formed in a compact starburst. Combining a large set of hydrodynamical simulations with data that span a broad range of profiles and masses, we show that this picture is borne out -- cusp ellipticals are indeed 'extra light' ellipticals -- and examine how the properties of this component scale with global galaxy properties. We show how to robustly separate the 'extra' light, and demonstrate that observed cusps are reliable tracers of the degree of dissipation in the spheroid-forming merger. We show that the typical degree of dissipation is a strong function of stellar mass, tracing observed disk gas fractions at each mass. We demonstrate a correlation between extra light content and effective radius at fixed mass: systems with more dissipation are more compact. The outer shape of the light profile does not depend on mass, with a mean outer Sersic index ~2.5. We explore how this relates to shapes, kinematics, and stellar population gradients. Simulations with the gas content needed to match observed profiles also reproduce observed age, metallicity, and color gradients, and we show how these can be used as tracers of the degree of dissipation in spheroid formation.Comment: 40 pages, 32 figures, accepted to ApJ (revised to match accepted version

Immune or genetic-mediated disruption of CASPR2 causes pain hypersensitivity due to enhanced primary afferent excitability

Human autoantibodies to contactin-associated protein-like 2 (CASPR2) are often associated with neuropathic pain, and CASPR2 mutations have been linked to autism spectrum disorders, in which sensory dysfunction is increasingly recognized. Human CASPR2 autoantibodies, when injected into mice, were peripherally restricted and resulted in mechanical pain-related hypersensitivity in the absence of neural injury. We therefore investigated the mechanism by which CASPR2 modulates nociceptive function. Mice lacking CASPR2 (Cntnap2 ) demonstrated enhanced pain-related hypersensitivity to noxious mechanical stimuli, heat, and algogens. Both primary afferent excitability and subsequent nociceptive transmission within the dorsal horn were increased in Cntnap2 mice. Either immune or genetic-mediated ablation of CASPR2 enhanced the excitability of DRG neurons in a cell-autonomous fashion through regulation of Kv1 channel expression at the soma membrane. This is the first example of passive transfer of an autoimmune peripheral neuropathic pain disorder and demonstrates that CASPR2 has a key role in regulating cell-intrinsic dorsal root ganglion (DRG) neuron excitability

On the buildup of massive early-type galaxies at z<~1. I- Reconciling their hierarchical assembly with mass-downsizing

Several studies have tried to ascertain whether or not the increase in abundance of the early-type galaxies (E-S0a's) with time is mainly due to major mergers, reaching opposite conclusions. We have tested it directly through semi-analytical modelling, by studying how the massive early-type galaxies with log(M_*/Msun)>11 at z~0 (mETGs) would have evolved backwards-in-time, under the hypothesis that each major merger gives place to an early-type galaxy. The study was carried out just considering the major mergers strictly reported by observations at each redshift, and assuming that gas-rich major mergers experience transitory phases of dust-reddened, star-forming galaxies (DSFs). The model is able to reproduce the observed evolution of the galaxy LFs at z<~1, simultaneously for different rest-frame bands (B, I, and K) and for different selection criteria on color and morphology. It also provides a framework in which apparently-contradictory results on the recent evolution of the luminosity function (LF) of massive, red galaxies can be reconciled, just considering that observational samples of red galaxies can be significantly contaminated by DSFs. The model proves that it is feasible to build up ~50-60% of the present-day mETG population at z<~1 and to reproduce the observational excess by a factor of ~4-5 of late-type galaxies at 0.8<z<1 through the coordinated action of wet, mixed, and dry major mergers, fulfilling global trends that are in general agreement with mass-downsizing. The bulk of this assembly takes place during ~1 Gyr elapsed at 0.8<z<1. The model suggests that major mergers have been the main driver for the observational migration of mass from the massive-end of the blue galaxy cloud to that of the red sequence in the last ~8 Gyr.(Abridged)Comment: Accepted for publication in Astronomy & Astrophysics; 21 pages, 8 figures. Minor corrections included, shortened title. Results and conclusions unchange

Anleitung zur Mechanick oder Bewegungskunst : zum Gebrauche der deutschen Schulen in den kaiserl. königl. Staaten

[Joseph Walcher]Verfasser bibliographisch ermittel