Nuclear properties of a sample of nearby spirals from STIS imaging (original) (raw)
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Nuclear Properties of a Sample of Nearby Spiral Galaxies from Hubble Space Telescope STIS Imaging
The Astronomical Journal, 2004
We present surface photometry for the central regions of a sample of 48 spiral galaxies (mostly unbarred and barred of type Sbc or Sc) observed with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. Surface brightness profiles (SBPs) were derived and modeled with a Nuker law. We also analyzed archival Wide Field Planetary Camera 2 images with a larger field of view, which are available for 18 galaxies in our sample. We modeled the extracted bulge SBPs with an exponential, an r 1/4 , or an r n 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 r 1/4 profile. Only one galaxy requires the use of a more general Sérsic 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 on the basis of 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.
The Astronomical Journal, 2005
We investigate the central regions of 23 spiral galaxies using archival NICMOS imaging and STIS spectroscopy. The sample is taken from our program to determine the masses of central massive black holes (MBH) 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 3 of the 23 galaxies studied (13 per cent). 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 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 -2total nuclear stellar population they form. Also, 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 AGN in NGC 1300 and NGC 4536.
The Astronomical …, 2006
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. At a spatial resolution of ∼ 0. ′′ 2 the spectra provide a better separation of cluster light from underlying galaxy light than is possible with ground-based spectra. Approximately half of the spectra have a sufficiently high signal-to-noise ratio for detailed stellar population analysis. For the other half we only measure the continuum slope, as quantified by the B − V color. To infer the star formation history, metallicity and dust extinction, we fit weighted superpositions of singleage stellar population templates to the high signal-to-noise spectra. We use the results to determine the luminosity-weighted age, mass-to-light ratio, and masses 1 Based on observations made with the NASA/ESA Hubble Space Telescope, obtained [from the Data Archive] at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with proposals #9070 and #9783.
An Atlas of Hubble Space Telescope Spectra and Images of Nearby Spiral Galaxies
The Astronomical Journal, 2003
We have observed 54 nearby spiral galaxies with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope to obtain optical long-slit spectra of nuclear gas disks and STIS optical ($R band) images of the central 5 00 Â 5 00 of the galaxies. These spectra are being used to determine the velocity field of nuclear disks and hence to detect the presence of central massive black holes. Here we present the spectra for the successful observations. Dust obscuration can be significant at optical wavelengths, and so we also combine the STIS images with archival Near-Infrared Camera and Multi-Object Spectrometer H-band images to produce color maps to investigate the morphology of gas and dust in the central regions. We find a great variety in the different morphologies, from smooth distributions to well-defined nuclear spirals and dust lanes.
BVRI Surface Photometry of Isolated Spiral Galaxies
The Astronomical Journal, 2007
A release of multicolor broad band (BV RI) photometry for a subsample of 44 isolated spirals drawn from the Catalogue of Isolated Galaxies (CIG) is presented. Total magnitudes and colors at various circular apertures, as well as some global structural/morphological parameters are estimated. Morphology is reevaluated through optical and sharp/filtered R band images, (B − I) color index maps, and archive near-IR JHK images from the Two-Micron Survey. The CAS structural parameters (Concentration, Asymmetry, and Clumpiness) were calculated from the images in each one of the bands. The fraction of galaxies with well identified optical/near-IR bars (SB) is 63%, while a 17% more shows evidence of weak or suspected bars (SAB). The sample average value of the maximum bar ellipticity is ǫ max ≈ 0.4. Half of the galaxies in the sample shows rings. We identify two candidates for isolated galaxies with disturbed morphology. The structural CAS parameters change with the observed band, and the tendencies they follow with the morphological type and global color are more evident in the redder bands. In any band, the major difference between our isolated spirals and a sample of interacting spirals is revealed in the A − S plane. A deep and uniformly observed sample of isolated galaxies is intended for various purposes including (i) comparative studies of environmental effects, (ii) confronting model predictions of galaxy evolution and (iii) evaluating the change of galaxy properties with redshift.
Monthly Notices of the Royal Astronomical Society, 2009
We analyse V and H-band surface photometry of a sample of 18 Sb-Sd galaxies. Combining high resolution HST images with ground-based NIR observations, we extract photometric profiles, which cover the whole disk and provide the highest possible resolution. This is the first photometric study of late-type spirals for which the stellar kinematics have been measured. For 10 out of the 18 galaxies, HST data in both F160W (H) and F606W (V ) are available, and, for those, we present colour maps and radial colour profiles at the resolution of the Hubble Space Telescope.
Nuclear Stellar Disks in Spiral Galaxies
The Astrophysical Journal, 2002
We report evidence for nuclear stellar disks in three early-type spirals, namely, NGC 1425, NGC 3898, and NGC 4698, revealed by Wide Field Planetary Camera 2 F606W images out of a sample of 38 spiral galaxies, selected from the Hubble Space Telescope data archive. Adopting the photometric method introduced by Scorza & Bender, we derived their central surface brightness and scale length by assuming them to be infinitesimally thin exponential disks. No nuclear disk was found in barred galaxies or galaxies of Hubble type later than Sb. The external origin of the disk in NGC 4698 is strongly suggested by its orthogonal geometrical decoupling with respect to the host galaxy.
The Astronomical Journal, 2002
This is the first of two papers where we present the analysis of an HST NICMOS-Cam2 near-infared (NIR) snapshot survey in the F160W (H) filter for a sample of 78 spiral galaxies selected from the UGC and ESOLV catalogs. For 69 of these objects we provide nuclear color information derived by combining the H data either with additional NICMOS F110W (J) images or with V WFPC2/HST data.
Near‐Infrared and Optical Morphology of Spiral Galaxies
The Astrophysical Journal Supplement Series, 2002
We announce the initial release of data from the Ohio State University Bright Spiral Galaxy Survey, a BV RJHK imaging survey of a well-defined sample of 205 bright, nearby spiral galaxies. We present H-band morphological classification on the Hubble sequence for the OSU Survey sample. We compare the H-band classification to B-band classification from our own images and from standard galaxy catalogs. Our B-band classifications match well with those of the standard catalogs. On average, galaxies with optical classifications -2from Sa through Scd appear about one T-type earlier in the H-band than in the B-band, but with large scatter. This result does not support recent claims made in the literature that the optical and near-IR morphologies of spiral galaxies are uncorrelated. We present detailed descriptions of the H-band morphologies of our entire sample, as well as B-and H-band images for a set of 17 galaxies chosen as type examples, and BRH color-composite images of six galaxies chosen to demonstrate the range in morphological variation as a function of wavelength. Data from the survey are accessible at A common property, and, therefore, a common weakness of all these schemes has been the nearly exclusive use of B-band plate material for galaxy classification (although see Zwicky 1955 and Schweizer 1976 for early work on multiwavelength morphology). This constrains existing classification schemes in two major ways. First, as classification has been done primarily in the B-band, it is very sensitive to the distribution of blue stars and dust. This is particularly unfortunate for the study of late-type galaxies, as the distribution of the young, blue stars and the dust can be very different from the distribution of the total baryonic mass. Second, although well-exposed plates, taken under good seeing conditions, can offer excellent spatial resolution, plates are poor photometric detectors, and have a very limited dynamic range. Thus, for instance, it is possible to miss features such as nuclear bars in classification plates that are deeply exposed in order to reveal the structure of spiral arms in the outer disk (see for a discussion of this effect).
Probing nuclear starburst activity in a sample of nearby spiral galaxies
Astronomy and Astrophysics
As part of a systematic study of the UV properties of galaxies in the IUE library, we present in this paper an analysis of nuclear stellar populations in spiral galaxies with radial velocity ≤ 5 000 km s −1 . In this sample of 60 galaxies the IUE aperture probes a mean 1.0 kpc × 2.1 kpc area. Prior to any comparison of galaxy spectra in the range covered by IUE (1200-3200Å), we have formed subsets according to the absolute magnitude and morphological type of the studied galaxies. In a second step, and within each subset, we have co-added the spectra, and hence the objects into groups of similar spectral properties in the UV, also taking into account their spectral properties in the visible/nearinfrared ranges. As a result, high signal-to-noise ratio templates have been obtained, and information on spectral features can now be extracted and interpreted. We distinguish 4 groups for Sa, 8 for Sb, and 4 for Sc galaxies. We have carried out population syntheses using as base elements: H ii regions, integrated star clusters, and far-UV weak elliptical galaxies as representative of bulge stellar population. The variety of UV spectral types found in the central regions of spiral galaxies can be readily explained by different mixtures of bulge, circumnuclear burst and disc populations. Across different morphological types, similar templates can also be found. This is due to compensation effects of bulge contribution with the disc and circumnuclear burst ones. Flux fractions derived from the population synthesis have been converted into mass contributions and inferences have been made on the star-formation histories. In the central kpc of the galaxies with strong UV flux, we find that the mass stored in the young components (t < 500 Myr) is typically ≈ 10 7 M . We confirm that such star-formation enhancements occur preferentially in barred spirals. Internal reddening in the templates has been studied and inferences have been made on the corresponding reddening laws. We find cases where an SMC-like law applies and others where a faint λ2200Å absorption feature occurs resembling the reddening law of the LMC. The interest of the IUE data set resides in its rather large entrance aperture which samples a large portion of nearby galaxies, and is therefore quite suitable for the interpretation of large redshift galaxies.