Detectability of High Redshift Ellipticals in the Hubble Deep Field

Relatively few intensively star-forming galaxies at redshifts z>2.5 have been found in the Hubble Deep Field (HDF). This has been interpreted to imply a low space density of elliptical galaxies at high z, possibly due to a late (z<2.5) epoch of formation, or to dust obscuration of the ellipticals that are forming at z~3. I use HST UV (2300 Ang) images of 25 local early-type galaxies to investigate a third option, that ellipticals formed at z>4.5, and were fading passively by 2<z<4.5. Present-day early-types are faint and centrally concentrated in the UV. If ellipticals formed their stars in a short burst at z>4.5, and have faded passively to their present brightnesses at UV wavelengths, they would generally be below the HDF detection limits in any of its bands at z>2.5. Quiescent z ~ 3 ellipticals, if they exist, should turn up in sufficiently deep IR images.Comment: AAS LaTex, 11 pages, 1 table, 1 figure, some corrections and clarifications, accepted for publication in ApJ

Minisuperspace Quantization of "Bubbling AdS" and Free Fermion Droplets

We quantize the space of 1/2 BPS configurations of Type IIB SUGRA found by Lin, Lunin and Maldacena (hep-th/0409174), directly in supergravity. We use the Crnkovic-Witten-Zuckerman covariant quantization method to write down the expression for the symplectic structure on this entire space of solutions. We find the symplectic form explicitly around AdS_5 x S^5 and obtain a U(1) Kac-Moody algebra, in precise agreement with the quantization of a system of N free fermions in a harmonic oscillator potential, as expected from AdS/CFT. As a cross check, we also perform the quantization around AdS_5 x S^5 by another method, using the known spectrum of physical perturbations around this background and find precise agreement with our previous calculation.Comment: 22 Pages + 2 Appendices, JHEP3; v3: explanation of factor 2 mismatch added, references reordered, published versio

The Correlation Between Galaxy HI Linewidths and K' Luminosities

The relationship between galaxy luminosities and rotation rates is studied with total luminosities in the K' band. Extinction problems are essentially eliminated at this band centered at 2.1 micron. A template luminosity-linewidth relation is derived based on 65 galaxies drawn from two magnitude-limited cluster samples. The zero-point is determined using 4 galaxies with accurately known distances. The calibration is applied to give the distance to the Pisces Cluster (60 Mpc) at a redshift in the CMB frame of 4771 km/s. The resultant value of the Hubble Constant is 81 km/s/Mpc. The largest sources of uncertainty arises from the small number of zero-point calibrators at this time at K' and present application to only one cluster.Comment: 13 pages including 5 figures and 2 tables. Accepted for publication in Astrophysical Journa

Approaching the event horizon: 1.3mm VLBI of SgrA*

Advances in VLBI instrumentation now allow wideband recording that significantly increases the sensitivity of short wavelength VLBI observations. Observations of the super-massive black hole candidate at the center of the Milky Way, SgrA*, with short wavelength VLBI reduces the scattering effects of the intervening interstellar medium, allowing observations with angular resolution comparable to the apparent size of the event horizon of the putative black hole. Observations in April 2007 at a wavelength of 1.3mm on a three station VLBI array have now confirmed structure in SgrA* on scales of just a few Schwarzschild radii. When modeled as a circular Gaussian, the fitted diameter of SgrA* is 37 micro arcsec (+16,-10; 3-sigma), which is smaller than the expected apparent size of the event horizon of the Galactic Center black hole. These observations demonstrate that mm/sub-mm VLBI is poised to open a new window onto the study of black hole physics via high angular resolution observations of the Galactic Center.Comment: 6 pages, 4 figures, Proceedings for "The Universe under the Microscope" (AHAR 2008), held in Bad Honnef (Germany) in April 2008, to be published in Journal of Physics: Conference Series by Institute of Physics Publishing, R. Schoedel, A. Eckart, S. Pfalzner, and E. Ros (eds.

Rapid X-ray Variability of the BL Lacertae Object PKS 2155-304

(Abridged) We present a detailed power density spectrum and cross-correlation analysis of the X-ray light curves of the BL Lac object PKS 2155-304, observed with BeppoSAX in 1997 and 1996, aimed at exploring the rapid variability properties and the inter-band cross correlations in the X-rays. We also perform the same analysis on the (archival) X-ray light curve obtained with ASCA in 1994.Comment: 47 pages, 11 figures, AAS Latex macros V4.0, accepted for publication in the Astrophysical Journa

The Type Ia Supernova Rate in Redshift 0.5--0.9 Galaxy Clusters

Supernova (SN) rates are potentially powerful diagnostics of metal enrichment and SN physics, particularly in galaxy clusters with their deep, metal-retaining potentials and relatively simple star-formation histories. We have carried out a survey for supernovae (SNe) in galaxy clusters, at a redshift range 0.5<z<0.9, using the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. We reimaged a sample of 15 clusters that were previously imaged by ACS, thus obtaining two to three epochs per cluster, in which we discovered five likely cluster SNe, six possible cluster SNe Ia, two hostless SN candidates, and several background and foreground events. Keck spectra of the host galaxies were obtained to establish cluster membership. We conducted detailed efficiency simulations, and measured the stellar luminosities of the clusters using Subaru images. We derive a cluster SN rate of 0.35 SNuB +0.17/-0.12 (statistical) \pm0.13 (classification) \pm0.01 (systematic) [where SNuB = SNe (100 yr 10^10 L_B_sun)^-1] and 0.112 SNuM +0.055/-0.039 (statistical) \pm0.042 (classification) \pm0.005 (systematic) [where SNuM = SNe (100 yr 10^10 M_sun)^-1]. As in previous measurements of cluster SN rates, the uncertainties are dominated by small-number statistics. The SN rate in this redshift bin is consistent with the SN rate in clusters at lower redshifts (to within the uncertainties), and shows that there is, at most, only a slight increase of cluster SN rate with increasing redshift. The low and fairly constant SN Ia rate out to z~1 implies that the bulk of the iron mass in clusters was already in place by z~1. The recently observed doubling of iron abundances in the intracluster medium between z=1 and 0, if real, is likely the result of redistribution of existing iron, rather than new production of iron.Comment: Accepted to ApJ. Full resolution version available at http://kicp.uchicago.edu/~kerens/HSTclusterSNe

Optical Spectroscopy of Active Galactic Nuclei in SA57

The cosmological evolution of X-ray-selected and optically selected Active Galactic Nuclei (AGNs) show different behaviours interpreted in terms of two different populations. The difference is evident mainly for low luminosity AGNs (LLAGNs), many of which are lost by optical photometric surveys. We are conducting a spectroscopical study of a composite sample of AGN candidates selected in SA57 following different searching techniques, to identify low luminosity AGNs and break down the sample into different classes of objects. AGN candidates were obtained through optical variability and/or X-ray emission. Of special interest are the extended variable objects, which are expected to be galaxies hosting LLAGNs. Among the 26 classified objects a fair number (9) show typical AGN spectra. 10 objects show Narrow Emission Line Galaxy spectra, and in most of them (8/10) optical variability suggests the presence of LLAGNs.Comment: 7 pages, 8 figures, to appear in A&

A NWB-based dataset and processing pipeline of human single-neuron activity during a declarative memory task

A challenge for data sharing in systems neuroscience is the multitude of different data formats used. Neurodata Without Borders: Neurophysiology 2.0 (NWB:N) has emerged as a standardized data format for the storage of cellular-level data together with meta-data, stimulus information, and behavior. A key next step to facilitate NWB:N adoption is to provide easy to use processing pipelines to import/export data from/to NWB:N. Here, we present a NWB-formatted dataset of 1863 single neurons recorded from the medial temporal lobes of 59 human subjects undergoing intracranial monitoring while they performed a recognition memory task. We provide code to analyze and export/import stimuli, behavior, and electrophysiological recordings to/from NWB in both MATLAB and Python. The data files are NWB:N compliant, which affords interoperability between programming languages and operating systems. This combined data and code release is a case study for how to utilize NWB:N for human single-neuron recordings and enables easy re-use of this hard-to-obtain data for both teaching and research on the mechanisms of human memory

The Narrow-Line Regions of LINERs as Resolved with the Hubble Space Telescope

LINERs exist in the nuclei of a large fraction of luminous galaxies, but their connection with the AGN phenomenon has remained elusive. We present Hubble Space Telescope narrowband [O III]5007 and H-alpha+[N II] emission-line images of the central regions of 14 galaxies with LINER nuclei. The compact, ~1 arcsec-scale, unresolved emission that dominates the line flux in ground-based observations is mostly resolved by HST. The bulk of this emission comes from regions with sizes of tens to hundreds of parsecs that are resolved into knots, filaments, and diffuse gas whose morphology differs from galaxy to galaxy. Most of the galaxies do not show clear linear structures or ionization cones analogous to those often seen in Seyfert galaxies. An exception is NGC 1052, the prototypical LINER, in which we find a 3 arcsec-long (~ 250 pc) biconical structure that is oriented on the sky along the galaxy's radio jet axis. Seven of the galaxies have been shown in previously published HST images to have a bright compact ultraviolet nuclear source, while the other seven do not have a central UV source. Our images find evidence of dust in the nuclear regions of all 14 galaxies, with clear indications of nuclear obscuration in most of the "UV-dark" cases. The data suggest that the line-emitting gas in most LINERs is photoionized by a central source (which may be stellar, nonstellar, or a combination thereof) but that this source is often hidden from direct view. We find no obvious morphological differences between LINERs with detected weak broad H-alpha wings in their spectra and those with only narrow lines. Likewise, there is no clear morphological distinction between objects whose UV spectra are dominated by hot stars (e.g., NGC 4569) and those that are AGN-like (e.g., NGC 4579).Comment: Accepted for publication in the ApJ. 25 pages, 3 tables, 9 JPEG Figure

Optical Versus Mid-Infrared Spectroscopic Classification of Ultraluminous Infrared Galaxies

The origin of huge infrared luminosities of ultraluminous infrared galaxies (ULIGs) is still in question. Recently, Genzel et al. made mid-infrared (MIR) spectroscopy of a large number of ULIGs and found that the major energy source in them is massive stars formed in the recent starburst activity; i.e., $\sim$ 70% -- 80% of the sample are predominantly powered by the starburst. However, it is known that previous optical spectroscopic observations showed that the majority of ULIGs are classified as Seyferts or LINERs (low-ionization nuclear emission-line regions). In order to reconcile this difference, we compare types of emission-line activity for a sample of ULIGs which have been observed in both optical and MIR. We confirm the results of previous studies that the majority of ULIGs classified as LINERs based on the optical emission-line diagnostics turn to be starburst-dominated galaxies based on the MIR ones. Since the MIR spectroscopy can probe more heavily-reddened, inner parts of the ULIGs, it is quite unlikely that the inner parts are powered by the starburst while the outer parts are powered by non-stellar ionization sources. The most probable resolution of this dilemma is that the optical emission-line nebulae with the LINER properties are powered predominantly by shock heating driven by the superwind activity; i.e., a blast wave driven by a collective effect of a large number of supernovae in the central region of galaxy mergers.Comment: 15 pages, 2 tables, and 3 eps figures. The Astrophysical Journal (Part 1), in pres