J. Atkinson

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.

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

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

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.

Nuclear clusters, bulges and massive black holes in spiral galaxies

We report on some of the recent work that has come from our Hubble Space Telescope programme to find massive black holes in nearby spiral galaxies. Determining black hole masses from gas kinematics in spiral galaxies is difficult, but results have been reported for NGC 4041 and new results are soon to be reported for NGC 1300 and NGC 2748. Complementary programmes are also looking for the presence of nuclear star clusters in our Space Telescope Imaging Spectrograph (STIS) and archival Near-infrared Camera and Multi-Object Spectrometer (NICMOS) images. We are also currently analysing United Kingdom Infrared Telescope (UKIRT) Fast Track Imager (UFTI) near-infrared images to determine the surface brightness profiles for 37 of the galaxies in the sample. 1. Massive Black Holes in Nearby Spirals Massive black holes seem to be a common component of galactic nuclei. Attempts by the community to establish a demography for massive black holes has lead to various correlations between the mass of the black hole and other host galaxy properties (e.g. Ferrarese & Merritt 2000, Gebhardt et al. 2000, Marconi & Hunt 2003). However, for all these correlations spiral galaxies are relatively under-represented with respect to elliptical galaxies. To address this problem, and in an attempt to quantify the demography of massive black holes in nearby spiral galaxies, we had an HST/STIS programme (GO:8228, PI:Axon) to determine black hole masses using gas dynamics of the nuclear discs in 54 spirals. Marconi et al. (2003) reported the first black hole mass determination from this programme for NGC 4041, while an atlas of the spectra with reasonable signal to noise are presented in Hughes et al. (2003). Examples of some of the spectra and images, plus colour maps made using archival NICMOS images are shown in figure 1. The next paper to report black hole masses from the programme is now near completion (Atkinson et al., in prep) and will present results for NGC 1300 and NGC 2748. 2. Complimentary Work While the main emphasis of the program was to find black hole masses, other complimentary work is underway to understand the environments of the centres of these galaxies. One of the principle host-galaxy properties that has been shown to be correlated with black hole mass is stellar velocity dispersion (Ferrarese & Merritt 2000, Gebhardt 181 182 M. Hughes et al.

The black hole mass vs bulge mass relationship in spiral galaxies

We describe an on-going HST program aimed at determining the relationship between the nuclear black hole mass and bulge mass in spiral galaxies. We have selected a volume limited sample of 54 nearby spiral galaxies for which we already have ground based emission line rotation curves, CCD surface photometry and radio maps. We are now obtaining HST/STIS longslit observations of each of the galaxies in the sample in order to determine the nuclear Hα rotation curve at high (∼ 0. 1) spatial resolution. We will use these data to measure the unresolved dark mass concentration at the nucleus of each object. Here we show the first results from observations of objects in the sample.