M. A. Hughes

The origin of the UV excess in powerful radio galaxies: spectroscopy and polarimetry of a complete sample of intermediate-redshift radio galaxies

We present spectroscopic and polarimetric observations of a complete, optically unbiased sample of 2-Jy radio galaxies at intermediate redshifts (0.15 10 per cent level. Careful measurement and modelling of our spectra have allowed us to quantify the contributions of other components to the UV excess. We show that nebular continuum (present in all objects at the 3-40 per cent level), direct active galactic nucleus (AGN) light (significant in 40 per cent of objects) and young stellar populations (significant in 15 - 50 per cent of objects) all make important contributions to the UV continuum in the population of powerful radio galaxies. These results serve to emphasize the multicomponent nature of the UV continuum in radio galaxies. The results also point to an interesting link between the optical/UV and far-IR properties of our sample objects, in the sense that the objects with the clearest evidence for optical/UV starburst activity are also the most luminous at far-IR wavelengths. This supports the idea that the cooler dust components in radio galaxies are heated by starbursts rather than by AGN.

Is There Really a Black Hole at the Center of NGC 4041? Constraints from Gas Kinematics

We present Space Telescope Imaging Spectrograph spectra of the Sbc spiral galaxy NGC 4041, which were used to map the velocity field of the gas in its nuclear region. We detect the presence of a compact (r 04 40 pc), high surface brightness, rotating nuclear disk cospatial with a nuclear star cluster. The disk is characterized by a rotation curve with a peak-to-peak amplitude of ~40 km s-1 and is systematically blueshifted by ~10-20 km s-1 with respect to the galaxy systemic velocity. With the standard assumption of constant mass-to-light ratio and with the nuclear disk inclination taken from the outer disk, we find that a dark point mass of (1) × 107 M☉ is needed to reproduce the observed rotation curve. However, the observed blueshift suggests the possibility that the nuclear disk could be dynamically decoupled. Following this line of reasoning, we relax the standard assumptions and find that the kinematical data can be accounted for by the stellar mass provided that either the central mass-to-light ratio is increased by a factor of ~2 or the inclination is allowed to vary. This model results in a 3 σ upper limit of 6 × 106 M☉ on the mass of any nuclear black hole (BH). Overall, our analysis only allows us to set an upper limit of 2 × 107 M☉ on the mass of the nuclear BH. If this upper limit is taken in conjunction with an estimated bulge B magnitude of -17.7 and with a central stellar velocity dispersion of 95 km s-1, then these results are not inconsistent with both the MBH-Lsph and the MBH-σ* correlations. Constraints on BH masses in spiral galaxies of types as late as Sbc are still very scarce; therefore, the present result adds an important new data point to our understanding of BH demography.

Spectroscopy of the γ‐ray burst GRB 021004: a structured jet ploughing through a massive stellar wind

We present spectra of the afterglow of the γ-ray burst GRB 021004 taken with the ISIS spectrograph on the William Herschel Telescope (WHT) and with the Focal Reducer/Low Dispersion Spectrograph 1 (FORS1) on the Very Large Telescope (VLT) at three epochs spanning 0.49-6.62 d after the burst. We observe strong absorption probably coming from the host galaxy, alongside absorption in H i, Si iv and C iv with blueshifts of up to 2900 km s -1 from the explosion centre, which we assume originates close to the progenitor. We find no significant variability of these spectral features. We investigate the origin of the outflowing material and evaluate various possible progenitor models. The most plausible explanation is that these result in the fossil stellar wind of a highly evolved Wolf-Rayet (WR) star. However, ionization from the burst itself prevents the existence of H I, Si iv and C iv close to the afterglow surface where the fast stellar wind should dominate, and large amounts of blueshifted hydrogen are not expected in a WR star wind. We propose that the WR star wind is enriched by a hydrogen-rich companion, and that the GRB has a structured jet geometry in which the γ-rays emerge in a small opening angle within the wider opening angle of the cone of the afterglow. This scenario is able to explain both the spectral-line features and the irregular light curve of this afterglow.

Supermassive black hole mass measurements for NGC 1300 and 2748 based on Hubble Space Telescope emission-line gas kinematics

We present Space Telescope Imaging Spectrograph emission-line spectra of the central regions of the spiral galaxies NGC 1300 and 2748. From the derived kinematics of the nuclear gas we have found evidence for central supermassive black holes in both galaxies. The estimated masses of the black holes in NGC 1300 and 2748 are (6.6 +6.3) × 10 7 and (4.4 +3.5) × 10 7 M� , respectively (both at the 95 per cent confidence level). These two black hole mass estimates contribute to the poorly sampled low-mass end of the nuclear black hole mass spectrum. Ke yw ords: black hole physics ‐ galaxies: individual: NGC 1300 ‐ galaxies: individual: NGC 2748 ‐ galaxies: kinematics and dynamics ‐ galaxies: nuclei ‐ galaxies: spiral.

Supermassive black holes in the Sbc spiral galaxies NGC 3310, NGC 4303 and NGC 4258 ,

We have undertaken an HST Space Telescope Imaging Spectrograph survey of 54 late type spiral galaxies to study the scalin g relations between black holes and their host spheroids at the low mass end. Our aim is to measure black hole masses or to set upper limits for a sizeable sample of spiral galaxies. In this paper we present new Space Telescope Imaging Spectrograph (STIS) observations of three spiral galaxies, NGC 4303, NGC 3310 and NGC 4258. The bright optical emission lines Hα λ 6564A, [NII]λλ 6549, 6585A and [SII]λλ 6718, 6732A were used to study the kinematics of the ionized gas in the nuclear region of each galaxy with a∼ 0.07 ′′ spatial resolution. Our STIS data for NGC 4258 were analyzed in conjunction with archival ones to compare the gas kinematical estimate of the black hole mass with the accurate value from H20-maser observations. In NGC 3310, the observed gas kinematics is well matched by a circularly rotating disk model but we are only able to set an upper limit to the BH mass which, taking into account the allowed disk inclinations, varies in the range 5.0× 10 6 − 4.2× 10 7 M⊙ at the 95% confidence level. In NGC 4303 the kinematical data require the presence of a BH with mass MBH = (5.0) +0.87

Integral Field Spectroscopy of 23 Spiral Bulges

We have obtained integral-field spectroscopy for 23 spiral bulges using INTEGRAL on the William Herschel Telescope and SPIRAL on the Anglo-Australian Telescope. This is the first two-dimensional survey directed solely at the bulges of spiral galaxies. Eleven galaxies of the sample do not have previous measurements of the stellar velocity dispersion (σ*). These data are designed to complement our Space Telescope Imaging Spectrograph program for estimating black hole masses in the range 106-108 M☉ using gas kinematics from nucleated disks. These observations will serve to derive the stellar dynamical bulge properties using the traditional Mg b and Ca II triplets. We use both cross-correlation and maximum penalized likelihood to determine projected σ* in these systems and present radial velocity fields, major axis rotation curves, curves of growth, and σ* fields. Using cross-correlation to extract the low-order two-dimensional stellar dynamics we generally see coherent radial rotation and irregular velocity dispersion fields suggesting that σ* is a nontrivial parameter to estimate.

The GRB 060218/SN 2006aj Event in the Context of other Gamma-Ray Burst Supernovae

The supernova SN 2006aj associated with GRB 060218 is the second-closest GRB-SN observed to date (z = 0.033). We present Very Large Telescope, Liverpool Telescope, and Katzman Automatic Imaging Telescope multi-color photometry of SN 2006aj. This supernova is found to be subluminous and rapidly evolving. Its early light curve includes an additional wavelength-dependent component, which can be interpreted as shock break-out. We compare the photometric evolution of multi-band light curves with the corresponding properties of the present sample of more than 10 GRB-SNe with precisely known redshifts. Using host-galaxy extinction measurements, we derive extinction-corrected GRB-SN luminosities and place SN 2006aj in the context of this GRB-selected supernova sample as well as in the context of local stripped-envelope supernovae.

Nuclear Properties of a Sample of Nearby Spiral Galaxies from Hubble Space Telescope STIS Imaging

ABSTRACTWe present surface photometry for the central regions of a sample of 48 spiral galaxies (mostly unbarred andbarred of type Sbc or Sc) observed with the Space Telescope Imaging Spectrograph on board theHubble SpaceTelescope. Surface brightness profiles (SBPs) were derived and modeled with a Nuker law. We also analyzedarchival Wide Field Planetary Camera 2 images with a larger field of view, which are available for 18 galaxies inour sample. We modeled the extracted bulge SBPs with an exponential, anr 1/4 ,oranr n profile. In agreementwith previous studies, we find that bulges of Sbc galaxies fall into two categories: bulges well described by anexponential profile and those well described by anr 1/4 profile. Only one galaxy requires the use of a more generalSe´rsic profile to properly describe the bulge. Nuclear photometrically distinct components are found in 55% ofthe galaxies. For those that we classify as star clusters on the basis of their resolved extent, we find absolutemagnitudes that are brighter on average than those previously identified in spiral galaxies. This might be due to abias in our sample toward star-forming galaxies, combined with a trend for star-forming galaxies to host brightercentral clusters.Key words: galaxies: bulges — galaxies: nuclei — galaxies: spiral — galaxies: structure1. INTRODUCTIONThis article is part of a series of papers presenting the resultsof our Hubble Space Telescope(HST) program GO-8228 (PI:D. Axon), executed with the Space Telescope Imaging Spec-trograph (STIS). The goal of the program is to study the blackhole (BH) mass distribution in spiral galaxies.Studies of the centers of nearby early-type galaxies (ellip-tical and lenticular galaxies) have revealed that most containsupermassive black holes (see Kormendy & Gebhardt 2001 fora recent review). These studies also revealed a strong corre-lation between the mass of the BH (MWe present surface photometry for the central regions of a sample of 48 spiral galaxies (mostly unbarred and barred of types Sbc or Sc) observed with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. Surface brightness profiles were derived and modeled with a Nuker law. We also analyzed archival Wide Field Planetary Camera 2 images with a larger field of view, available for 18 galaxies in our sample. We modeled the extracted bulge surface brightness profiles with an exponential, an r1/4, or an rn profile. In agreement with previous studies, we find that bulges of Sbc galaxies fall into two categories: bulges well described by an exponential profile and those well described by an r1/4 profile. Only one galaxy requires the use of a more general Sersic profile to properly describe the bulge. Nuclear photometrically distinct components are found in ∼ 55% of the galaxies. For those that we classify as star clusters based on their resolved extent we find absolute magnitudes that are brighter on average than those previously identified in spiral galaxies. This might be due to a bias in our sample toward star forming galaxies, combined with a trend for star forming galaxies to host brighter central clusters. Department of Astronomy, Univeristà degli Studi di Padova, Padova, Italy Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 Department of Physics, Astronomy and Mathematics, University of Hertfordshire, Hatfield, Hertfordshire, AL10 9AB, UK Department of Physics, RIT, 84 Lomb Memorial Dr., Rochester, NY 14623-5603 Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 Oxford University, Theoretical Physics, Keble Road, Oxford, OX1 3NP, UK INAF-Osservatorio Astronomico di Torino, I-10025 Pino Torinese, Italy Physics Department, ETH, Hoenggerberg HPF G4.3, CH–8092 Zurich, Switzerland INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy School of Physics and Astronomy, University of Nottingham, NG7 2RD, UK Center for Astrophysical Sciences, Johns Hopkins University, 239 Bloomberg Center for Physics & Astronomy, 3400 North Charles Street, Baltimore, MD 21218

The First Swift X-Ray Flash: The Faint Afterglow of XRF 050215B

We present the discovery of XRF 050215B and its afterglow. The burst was detected by the Swift BAT during the check-out phase, and observations with the X-Ray Telescope began approximately 30 minutes after the burst. These observations found a faint, slowly fading X-ray afterglow near the center of the error box as reported by the BAT. Infrared data obtained at UKIRT after 10 hr also revealed a very faint K-band afterglow. The afterglow appears unusual since it is very faint, especially in the infrared, with K > 20 only 9 hr postburst. The X-ray and infrared light curves exhibit a slow, monotonic decay with α ~ 0.8 and no evidence for a steepening associated with the jet break to 10 days postburst. We discuss possible explanations for the faintness and slow decay in the context of present models for the production of X-ray flashes.

Nuclear Properties of Nearby Spiral Galaxies from Hubble Space Telescope NICMOS Imaging and STIS Spectroscopy

We investigate the central regions of 23 spiral galaxies using Space Telescope Imaging Spectrograph (STIS) spectroscopy and archival Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) imaging. The sample is taken from our program to determine the masses of central massive black holes (MBHs) in 54 nearby spiral galaxies. Stars are likely to contribute significantly to any dynamical central mass concentration that we find in our MBH program, and this paper is part of a series to investigate the nuclear properties of these galaxies. We use the Nuker law to fit surface brightness profiles, derived from the NICMOS images, to look for nuclear star clusters and find possible extended sources in three of the 23 galaxies studied (13%). The fact that this fraction is lower than that inferred from optical Hubble Space Telescope studies is probably due to the greater spatial resolution of those studies. Using R - H and J - H colors and equivalent widths of Hα emission (from the STIS spectra), we investigate the nature of the stellar population with evolutionary models. Under the assumption of hot stars ionizing the gas, as opposed to a weak active galactic nucleus (AGN), we find that there are young stellar populations (~10–20 Myr); however, these data do not allow us to determine what percentage of the total nuclear stellar population they form. In addition, in an attempt to find any unknown AGN, we use [N II] and [S II] line flux ratios (relative to Hα) and find tentative evidence for weak AGNs in NGC 1300 and NGC 4536.